BR122023023402A2 - IMAGE CODING METHOD BASED ON A TRANSFORM, AND APPARATUS THEREOF - Google Patents

Abstract

An image decoding method according to the present document comprising a step of applying an inverse primary transform together with a transform coefficient in order to derive residual samples for a current block, wherein: the inverse primary transform is performed based on in an MTS index received from a bit stream; the MTS index is parsed based on a non-existing effective coefficient in a second area that excludes the first left-top area of the current block; and the first area consists of a top 16x16 area to the left of the current block.

Description

FIELD OF TECHNIQUE

[001] The present disclosure relates to an image coding technique and, more particularly, to a method and apparatus for coding an image based on the transform in an image coding system.

RELATED TECHNIQUE

[002] Currently, the demand for high-resolution and high-quality images/videos, such as 4K, 8K or more ultra-high definition (UHD) images/videos, is increasing in various fields. As image/video data becomes of higher resolution and quality, the amount of information transmitted or the number of bits increases compared to conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or image/video data is stored using an existing storage medium, the transmission cost and storage cost are increased.

[003] Furthermore, nowadays, the interest and demand for immersive media such as virtual reality (VR), artificial reality (AR) content or hologram, or the like, is increasing, and the transmission of images/videos with image characteristics different from those of real images such as a game image is increasing.

[004] Consequently, there is a need for a highly efficient image/video compression technique to effectively compress and transmit or store and reproduce high-resolution, high-quality image/video information with various features, as described above.

SUMMARY

[005] A technical aspect of the present disclosure is to provide a method and apparatus for increasing image coding efficiency.

[006] Another technical aspect of the present disclosure is to provide a method and apparatus for increasing efficiency in coding a transform index.

[007] Yet another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus using an MTS.

[008] Yet another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus for signaling an MTS index.

[009] According to an embodiment of the present disclosure, an image decoding method performed by a decoding apparatus is provided. The method may include deriving residual samples for the current block by applying an inverse primary transform to the transform coefficients, wherein the inverse primary transform is performed based on an MTS index received from the bit stream, wherein the MTS index is analyzed based on a significant coefficient not being in a second region other than a first top region to the left of the current block and that the first region is a 16 x 16 top region to the left of the current block.

[010] The MTS index is analyzed based on the flag information indicating whether the significant coefficient exists in the second region and in which the flag information is derived by determining whether the significant coefficient exists in the second region by one unit of a sub-block of scanning the significant coefficient.

[011] When a value of a flag indicating whether the significant coefficient exists in the scanning sub-block is 1 and the significant coefficient existing in the scanning sub-block is positioned in the second region, the flag information indicates that the significant coefficient exists in the second region.

[012] When a value of a flag indicating whether the significant coefficient exists in the scanning sub-block is 1 and the scanning sub-block is positioned in the second region, the flag information indicates that the significant coefficient exists in the second region.

[013] The flag information is initially set to 1, and when the significant coefficient is positioned in the second region, the flag information is changed to 0.

[014] The scanning sub-block is a 4 x 4 block, and the scanning sub-block is scanned according to an inverse diagonal scanning direction from the position of the last significant coefficient in the current block.

[015] According to another embodiment of the present disclosure, an image coding method performed by a coding apparatus is provided. The method may include deriving transform coefficients for the current block by applying an MTS to the residual samples; zeroing a second region different from a first top region to the left of the current block; derive residual information based on the transform coefficient of the first region; and constructing image information to analyze an MTS index indicating that an MTS transform kernel based on a significant coefficient exists in the second region; where the first region is a top 16 x 16 region to the left of the current block.

[016] According to yet another embodiment of the present disclosure, a digital storage medium may be provided that stores image data including encoded image information and a bit stream generated in accordance with an image coding method performed by a coding device.

[017] According to yet another embodiment of the present disclosure, a digital storage medium may be provided that stores image data including encoded image information and a bit stream to cause a decoding apparatus to perform the decoding method of image.

[018] According to the present disclosure, it is possible to increase the overall efficiency of image/video compression.

[019] According to the present disclosure, it is possible to increase efficiency in coding an MTS index.

[020] According to the present disclosure, it is possible to increase the efficiency of an image coding method using an MTS.

[021] The effects that can be obtained through specific examples of the present disclosure are not limited to the effects listed above. For example, there may be various technical effects that a person skilled in the related art can understand or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described in the present disclosure and may include various effects that can be understood or derived from the technical features of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[022] Figure 1 schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.

[023] Figure 2 is a diagram that schematically illustrates a configuration of a video/image coding apparatus to which the present disclosure is applicable.

[024] Figure 3 is a diagram that schematically illustrates a configuration of a video/image decoding apparatus to which the present disclosure is applicable.

[025] Figure 4 schematically illustrates a multiple transform scheme according to an embodiment of the present document.

[026] Figure 5 exemplifies intradirectional modes of 65 prediction directions.

[027] Figure 6 is a diagram to explain RST according to one embodiment of the present.

[028] Figure 7 is a diagram illustrating an output data arrangement sequence of a direct primary transform into a one-dimensional vector according to an example.

[029] Figure 8 is a diagram illustrating an output data arrangement sequence of a direct secondary transform in a two-dimensional block according to an example.

[030] Figure 9 is a diagram illustrating wide-angle intra prediction modes according to an embodiment of the present document.

[031] Figure 10 is a diagram illustrating a block format to which LFNST is applied.

[032] Figure 11 is a diagram illustrating an output data arrangement of a direct LFNST according to an example.

[033] Figure 12 is a diagram illustrating that the number of output data for a direct LFNST is limited to a maximum of 16 according to an example.

[034] Figure 13 is a diagram illustrating zero-out in a block to which LFNST 4 x 4 is applied according to an example.

[035] Figure 14 is a diagram illustrating zero-out in a block to which LFNST 8 x 8 is applied according to an example.

[036] Figure 15 illustrates a scan of a 32 x 32 transform block according to an embodiment of the present disclosure.

[037] Figure 16 is a flowchart for explaining an image decoding method according to an example.

[038] Figure 17 is a flowchart for explaining an image coding method according to an example.

[039] Figure 18 illustrates the structure of a content streaming system to which the present disclosure is applied.

DESCRIPTION OF EXAMPLE MODALITIES

[040] Although the present disclosure may be susceptible to various modifications and includes various embodiments, specific embodiments thereof have been shown in the drawings by way of example and will now be described in detail. However, this is not intended to limit the present disclosure to the specific embodiments disclosed herein. The terminology used herein is intended to describe only specific embodiments and is not intended to limit the technical idea of the present disclosure. Singular forms may include plural forms, except where the context clearly indicates otherwise. Terms such as "include" and "have" are intended to indicate that there are features, numbers, steps, operations, elements, components or combinations thereof used in the following description and therefore it should not be understood that the possibility of existence or addition of one or more different characteristics, numbers, steps, operations, elements, components or combinations thereof is not excluded in advance.

[041] However, each component in the drawings described herein is illustrated independently for convenience of description regarding characteristic functions different from each other and, however, does not mean that each component is realized by separate hardware or software. For example, any two or more of these components can be combined to form a single component, and any single component can be divided into multiple components. The embodiments in which the components are combined and/or divided will fall within the scope of the patent right of the present disclosure, as long as they do not depart from the essence of the present disclosure.

[042] Later in this document, preferred embodiments of the present disclosure will be explained in more detail while referring to the attached drawings. Furthermore, the same reference signs are used for the same components in the drawings, and repeated descriptions for the same components will be omitted.

[043] This document refers to video/image coding. For example, the method/example disclosed in this document may refer to a VVC (Versatile Video Coding) standard (ITU-T Rec. H.266), a next-generation video/image coding standard after VVC, or others standards related to video coding (e.g. HEVC (High Efficiency Video Coding) standard (ITU-T Rec. H.265), EVC (Essential Video Coding) standard, AVS2 standard, etc.).

[044] In this document, a variety of modalities related to video/image coding may be provided and, except where otherwise specified, the modalities may be combined with each other and executed.

[045] In this document, a video can mean a set of a series of images over time. Generally an image means a unit that represents an image in a specific time zone, and a slice/block is a unit that constitutes a part of the image. The slice/block may include one or more coding tree units (CTUs). An image can be made up of one or more slices/tiles. An image can be made up of one or more groups of blocks. A block group can include one or more blocks.

[046] A pixel or a pel can mean the smallest unit that constitutes an image (or image). Also, ‘sample’ can be used as a term corresponding to a pixel. A swatch may, in general, represent a pixel or a value of a pixel, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chroma component. Alternatively, the sample may refer to a pixel value in the spatial domain, or when that pixel value is converted to the frequency domain, it may refer to a transform coefficient in the frequency domain.

[047] A unit may represent the basic image processing unit. The unit can include at least one of a specific region and information related to the region. A unit may include one luma block and two chroma blocks (e.g. cb, cr). The unit and a term such as a block, an area, or the like may be used in place of each other according to circumstances. In a general case, an M x N block may include a set (or a matrix) of samples (or sample matrices) or transform coefficients consisting of M columns and N rows.

[048] In this document, the term “/” “and“, must be interpreted to indicate “and/or”. For example, the expression “A/B” can mean “A and/or B”. Furthermore, “A, B” can mean “A and/or B”. Furthermore, “A/B/C” can mean “at least one of A, B and/or C”. Also, “A/B/C” can mean “at least one of A, B and/or C”.

[049] Furthermore, in the document, the term “or” must be interpreted to indicate “and/or”. For example, the expression “A or B” may include 1) A only, 2) B only, and/or 3) both A and B. In other words, the term “or” in this document should be interpreted to indicate “additional or alternatively".

[050] In the present disclosure, "at least one of A and B" may mean “A only”, “B only” or “both A and B”. Furthermore, in the present disclosure, the expression “at least one of A or B” or “at least one of A and/or B” may be interpreted as “at least one of A and B”.

[051] Furthermore, in the present disclosure, “at least one of A, B and C” may mean “A only”, “B only”, “C only”, or “any combination of A, B and C”. Furthermore, “at least one of A, B or C” or “at least one of A, B and/or C” can mean “at least one of A, B and C”.

[052] Furthermore, a parenthesis used in the present disclosure may mean “for example”. Specifically, when indicated as “prediction (intraprediction)”, it may mean that “intraprediction” is proposed as an example of “prediction”. That is, “prediction” in the present disclosure is not limited to “intraprediction”, and “intraprediction” may be proposed as an example of “prediction”. Furthermore, when indicated as “prediction (i.e., intraprediction)”, it can also mean that “intraprediction” is proposed as an example of “prediction”.

[053] The technical features described individually in a figure in the present disclosure can be implemented individually or can be implemented simultaneously.

[054] Figure 1 schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.

[055] Referring to Figure 1, the video/image coding system may include a first device (source device) and a second device (receiving device). The source device may provide information or encoded video/image data in the form of a file or stream to the receiving device via a digital storage medium or network.

[056] The source device may include a video source, an encoding apparatus and a transmitter. The receiving device may include a receiver, a decoding apparatus, and a renderer. The encoding apparatus may be called a video/image encoding apparatus, and the decoding apparatus may be called a video/image decoding apparatus. The transmitter may be included in the coding apparatus. The receiver may be included in the decoding apparatus. The renderer can include a canvas, and the canvas can be configured as a separate device or an external component.

[057] The video source can obtain a video/image through a process to capture, synthesize or generate a video/image. The video source may include a video/image capture device and/or a video/image generating device. The video/image capture device may include, for example, one or more cameras, video/image files including previously captured video/images, or the like. The video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate video/image. For example, a virtual video/image can be generated using a computer or the like. In this case, the video/image capture process can be replaced by a related data generation process.

[058] The encoding apparatus can encode an input video/image. The coding apparatus can perform a series of procedures such as prediction, transform and quantization for compression and coding efficiency. The encoded data (encoded video/image information) can be output in the form of a bit stream.

[059] The transmitter may transmit the encoded video/image information or data in the form of a bit stream to the receiver of the receiving device via a digital storage medium or a network in the form of a file or stream. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. The transmitter may include an element for generating a media file via a predetermined file format and may include an element for transmission over a broadcast/communication network. The receiver can receive/extract the bit stream and transmit the received/extracted bit stream to the decoding apparatus.

[060] The decoding apparatus can decode a video/image by performing a series of procedures such as dequantization, inverse transform, prediction, and the like corresponding to the operation of the coding apparatus.

[061] The renderer can render the decoded video/image. The rendered video/image can be displayed across the screen.

[062] Figure 2 is a diagram that schematically illustrates a configuration of a video/image coding apparatus to which the present disclosure is applicable. Later in this document, what is referred to as the video coding apparatus may include an image coding apparatus.

[063] Referring to Figure 2, the coding apparatus 200 may include an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. predictor 220 may include an interpredictor 221 and an intrapredictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, an inverse transformer 235. The residual processor 230 may additionally include a subtractor 231. The adder 250 may be called a rebuilder or rebuilt block generator. The image partitioner 210, predictor 220, residual processor 230, entropy encoder 240, adder 250, and filter 260 that have been described above may be comprised of one or more hardware components (e.g., encoder chipsets or processors) according to an embodiment. Furthermore, memory 270 may include a decoded picture buffer (DPB), and may be comprised of a digital storage medium. The hardware component may additionally include memory 270 as an internal/external component.

[064] Image partitioner 210 may partition an input image (or an image or a frame) inserted into the encoding apparatus 200 into one or more processing units. As an example, the processing unit may be called a coding unit (CU). In this case, starting with a coding tree unit (CTU) or the largest coding unit (LCU), the coding unit can be recursively partitioned according to the Quad-tree binary tree ternary tree (QTBTTT) structure. For example, a coding unit can be divided into a plurality of coding units of greater depth based on the quaternary tree structure, a binary tree structure, and/or the ternary structure. In this case, for example, the quaternary tree structure can be applied first and the binary tree structure and/or ternary structure can be applied later. Alternatively, the binary tree structure can be applied first. The coding procedure according to the present disclosure can be performed based on the final coding unit that is not additionally partitioned. In this case, the maximum coding unit can be directly used as a final coding unit based on the coding efficiency according to the image characteristic. Alternatively, the coding unit can be recursively partitioned into coding units of even greater depth as needed, so that the coding unit of an optimal size can be used as a final coding unit. Here, the coding procedure may include procedures such as prediction, transformation and reconstruction, which will be described later. As another example, the processing unit may additionally include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit can be divided or partitioned from the final coding unit described above. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and/or a unit for deriving a residual signal from a transform coefficient.

[065] The unit and a term such as a block, an area, or the like can be used in place of each other according to the circumstances. In a general case, an M x N block can represent a set of samples or transform coefficients consisting of M columns and N rows. The sample may, in general, represent a pixel or a value of a pixel, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chroma component. Sample can be used as a term corresponding to a pixel or a pel of an image (or image).

[066] Subtractor 231 subtracts an output prediction signal (predicted block, prediction sample matrix) of predictor 220 from an input image signal (original block, original sample matrix) to generate a residual signal (residual block , residual sample matrix), and the generated residual signal is transmitted to the transformer 232. The predictor 220 may perform prediction on a target processing block (hereinafter referred to as 'current block') and may generate a predicted block including samples of prediction for the current block. The predictor 220 can determine whether the intra prediction or inter prediction is applied on a current block or CU basis. As discussed further in the description of each prediction mode, the predictor may generate various information related to the prediction, such as prediction mode information, and transmit the generated information to the entropy encoder 240. The prediction information may be encoded in the entropy encoder 240 and output in the form of a bit stream.

[067] The intrapredictor 222 can predict the current block by referring to samples in the current image. Said samples can be located close to or far from the current block according to the prediction mode. In intraprediction, the prediction modes may include a plurality of non-directional modes and a plurality of directional modes. Non-directional modes may include, for example, a DC mode and a flat mode. The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes according to the degree of detail of the prediction direction. However, this is merely an example, and more or less directional prediction modes can be used depending on a configuration. The intrapredictor 222 may determine the prediction mode applied to the current block using the prediction mode applied to the neighboring block.

[068] The interpredictor 221 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference image. At this time, to reduce the amount of motion information transmitted in interprediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation of motion information between the neighboring block and the current block. The motion information may include a motion vector and a reference image index. The motion information may additionally include inter-prediction direction information (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of interprediction, the neighboring block may include a spatial neighboring block existing in the current image and a temporal neighboring block existing in the reference image. The reference image including the reference block and the reference image including the temporal neighboring block may be the same or different from each other. The temporal neighbor block can be called a co-located reference block, a co-located CU (colCU), and the like, and the reference image including the temporal neighbor block can be called a co-located image (colPic). For example, the interpredictor 221 may configure a candidate list of motion information in neighboring blocks and generate information indicating which candidate is used to derive a motion vector and/or a reference image index of the current block. Inter prediction can be performed based on various prediction modes. For example, in the case of a jump mode and a merge mode, the interpredictor 221 may use movement information from the neighboring block as movement information from the current block. In skip mode, unlike blending mode, the residual signal cannot be transmitted. In the case of motion information prediction (motion vector prediction, MVP), the motion vector of the neighboring block can be used as a motion vector predictor and the motion vector of the current block can be indicated by signaling a motion vector difference.

[069] The predictor 220 can generate a prediction signal based on various prediction methods. For example, the predictor can apply intraprediction or interprediction to predict a block, as well as apply intraprediction and interprediction at the same time. This can be called combined inter- and intra-prediction (CIIP). Furthermore, the predictor can be based on an intra-block copy (IBC) prediction mode or a palette mode to perform prediction on a block. IBC prediction mode or palette mode can be used for image/video coding of game content or the like, such as screen content coding (SCC). Although IBC basically performs prediction on a current block, it can be performed in a similar way to interprediction in that it derives a reference block on a current block. That is, the IBC may use at least one of the interprediction techniques described in the present disclosure.

[070] The prediction signal generated through the interpredictor 221 and/or the intrapredictor 222 can be used to generate a reconstructed signal or to generate a residual signal. Transformer 232 can generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loève transform (KLT), a graph-based transform (GBT), or a conditionally nonlinear transform (CNT). Here, GBT means transform obtained from a graph when the relationship information between pixels is represented by the graph. CNT refers to the transform obtained based on a prediction signal generated using all previously reconstructed pixels. Furthermore, the transform process can be applied to blocks of square pixels with the same size or can be applied to blocks with variable size instead of square.

[071] The quantizer 233 can quantize the transform coefficients and transmit them to the entropy encoder 240, and the entropy encoder 240 can encode the quantized signal (information about the quantized transform coefficients) and output the encoded signal in a stream of bits. Information about quantized transform coefficients can be called residual information. The quantizer 233 can rearrange the block-like quantized transform coefficients into a one-dimensional vector form based on a coefficient scanning order and generate information about the quantized transform coefficients based on the quantized transform coefficients of the one-dimensional vector form. The entropy encoder 240 can perform various encoding methods, such as exponential Golomb, context-adaptive variable-length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoder 240 may encode information necessary for video/image reconstruction instead of quantized transform coefficients (e.g., values of syntax elements, etc.) together or separately. The encoded information (e.g., encoded video/image information) may be transmitted or stored on a unit basis of a network abstraction layer (NAL) in the form of a bit stream. The video/image information may additionally include information about various parameter sets such as an adaptation parameter set (APS), an image parameter set (PPS), a sequence parameter set (SPS), a (VPS) or similar. Furthermore, the video/image information may additionally include general restriction information. In the present disclosure, information and/or syntax elements that are transmitted/signaled to the decoding apparatus of the encoding apparatus may be included in video/image information. Video/image information can be encoded using the encoding procedure described above and included in the bit stream. The bit stream can be transmitted over a network or stored on a digital storage medium. Here, the network may include a broadcast network, a communication network, and/or the like, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown) that transmits a signal emitted from the entropy encoder 240 and/or a store (not shown) that stores the same may be configured as an internal/external element of the coding apparatus 200, or the transmitter may be included in entropy encoder 240.

[072] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, by applying dequantization and inverse transform to the quantized transform coefficients through the dequantizer 234 and the inverse transformer 235, the residual signal (residual block or residual samples) can be reconstructed. Adder 155 adds the reconstructed residual signal to a prediction signal output from interpredictor 221 or intrapredictor 222, so that a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample matrix) can be generated. When there is no residue for a processing target block such as in a case where skip mode is applied, the predicted block can be used as a reconstructed block. The 250 adder can be called a rebuilder or a rebuilt block generator. The generated reconstructed signal can be used for intraprediction of a next processing target block in the current block, and as described later, it can be used for interprediction of a next image through filtering.

[073] However, in the image coding and/or reconstruction process, chroma scale luma mapping (LMCS) can be applied.

[074] Filter 260 can improve subjective/objective video quality by applying filtering to the reconstructed signal. For example, filter 260 may generate a modified reconstructed image by applying various filtering methods to the reconstructed image and may store the modified reconstructed image in memory 270, specifically, in the DPB of memory 270. The various filtering methods may include, e.g. example, deblocking filtering, a sample-adaptive shift, an adaptive loop filter, a two-sided filter, or the like. As discussed later in the description of each filtering method, the filter 260 may generate various filtering-related information and transmit the generated information to the entropy encoder 240. The information in the filtering may be encoded in the entropy encoder 240 and output in the form of a stream of bits.

[075] The modified reconstructed image that has been transmitted to memory 270 can be used as a reference image in interpredictor 221. Through this, the encoding apparatus can avoid prediction incompatibility in the encoding apparatus 100 and a decoding apparatus when inter prediction is applied and can also improve coding efficiency.

[076] Memory DPB 270 may store the modified reconstructed image for use as a reference image in interpredictor 221. Memory 270 may store motion information of a block in the current image, from which motion information were derived (or encoded) and/or block motion information in an already reconstructed image. The stored motion information can be transmitted to the interpredictor 221 which will be used as motion information of a neighboring block or motion information of a temporal neighboring block. Memory 270 may store the reconstructed samples of reconstructed blocks in the current image and transmit the same to the intrapredictor 222.

[077] Figure 3 is a diagram that schematically illustrates a configuration of a video/image decoding apparatus to which the present disclosure is applicable.

[078] Referring to Figure 3, video decoding apparatus 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an interpredictor 331 and an intrapredictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 321. The entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350, which were described above , may be constituted by one or more hardware components (for example, decoder chipsets or processors) according to one embodiment. Furthermore, the memory 360 may include a decoded picture buffer (DPB), and may consist of a digital storage medium. The hardware component may additionally include memory 360 as an internal/external component.

[079] When a bit stream including video/image information is input, the decoding apparatus 300 can reconstruct an image corresponding to a process by which the video/image information was processed in the encoding apparatus of Figure 2. For example, decoding apparatus 300 may derive units/blocks based on block partition information obtained from the bit stream. The decoding apparatus 300 may perform decoding using a processing unit applied to the encoding apparatus. Therefore, the decoding processing unit may be, for example, an encoding unit, which may be partitioned along the quaternary tree structure, the binary tree structure, and/or the ternary tree structure of a data tree unit. encoding or a larger encoding unit. One or more transform units may be derived from the coding unit. And, the reconstructed image signal decoded and output through the decoding apparatus 300 can be reproduced through a player.

[080] The decoding apparatus 300 can receive a signal emitted from the encoding apparatus of Figure 2 in the form of a bit stream, and the received signal can be decoded through the entropy decoder 310. For example, the entropy decoder 310 may analyze the bit stream to derive information (e.g., video/image information) necessary for image reconstruction (or image reconstruction). The video/image information may additionally include information about various parameter sets such as an adaptation parameter set (APS), an image parameter set (PPS), a sequence parameter set (SPS), a (VPS) or similar. Furthermore, the video/image information may additionally include general restriction information. The decoding apparatus may further decode an image based on information in the parameter set and/or general constraint information. In the present disclosure, the signaled/received information and/or syntax elements, which will be described later, can be decoded through the decoding procedure and obtained from the bit stream. For example, the entropy decoder 310 may decode information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, CABAC, or the like, and may output a value of a syntax element necessary for image reconstruction. and quantized values of a transform coefficient referring to a residual. More specifically, a CABAC entropy decoding method can receive a bin corresponding to each syntax element in a bitstream, determine a context model using decoding target syntax element information and decoding information from neighboring target blocks. and decoding or symbol/bin information decoded in a previous step, predicting the bin generation probability according to the given context model, and performing arithmetic bin decoding to generate a symbol corresponding to each syntax element value. Here, the CABAC entropy decoding method can update the context model using information from a decoded symbol/bin to a context model of the next symbol/bin after determining the context model. Prediction information between the information decoded in the entropy decoder 310 may be provided to the predictor (interpredictor 332 and intrapredictor 331), and residual values, i.e., quantized transform coefficients, where entropy decoding was performed in the entropy decoder 310 and associated parameter information may be input into the residual processor 320. The residual processor 320 may derive the residual signal (residual block, residual samples, residual sample matrix). Furthermore, filtering information between the information decoded in the entropy decoder 310 may be provided to the filter 350. However, a receiver (not shown) that receives a signal emitted from the encoding apparatus may additionally constitute the decoding apparatus 300 as a internal/external element, and the receiver may be a component of the entropy decoder 310. However, the decoding apparatus in accordance with the present disclosure may be called a video/image/image coding apparatus, and the decoding apparatus can be classified into an information decoder (video/image/image information decoder) and a sample decoder (video/image/image sample decoder). The information decoder may include the entropy decoder 310, and the sample decoder may include at least one of the dequantizer 321, the inverse transformer 322, the adder 340, the filter 350, the memory 360, the interpredictor 332, and the intrapredictor. 331.

[081] The dequantizer 321 can output transform coefficients by dequantizing the quantized transform coefficients. The dequantizer 321 can rearrange the quantized transform coefficients in the form of a two-dimensional block. In this case, the rearrangement can be performed based on a coefficient scanning order that was performed on the coding apparatus. The dequantizer 321 can perform dequantization on the quantized transform coefficients using quantization parameter (example, quantization step size information), and obtain transform coefficients.

[082] The dequantizer 322 obtains a residual signal (residual block, residual sample matrix) by inverse transform of transform coefficients.

[083] The predictor can perform the prediction on the current block and generate a predicted block including prediction samples for the current block. The predictor may determine whether intra-prediction or inter-prediction is applied to the current block based on information in the prediction output from entropy decoder 310, and specifically may determine an intra-/inter-prediction mode.

[084] The predictor can generate a prediction signal based on various prediction methods. For example, the predictor can apply intraprediction or interprediction to predict a block, as well as apply intraprediction and interprediction at the same time. This can be called combined inter- and intra-prediction (CIIP). Furthermore, the predictor can perform a block copy (IBC) for prediction on a block. Intrablock copy can be used for image/video encoding of game content or the like, such as screen content coding (SCC). Although IBC basically performs prediction on a current block, it can be performed in a similar way to interprediction in that it derives a reference block on a current block. That is, the IBC may use at least one of the interprediction techniques described in the present disclosure.

[085] The intrapredictor 331 can predict the current block by referring to the samples in the current image. Said samples can be located close to or far from the current block according to the prediction mode. In intra prediction, the prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intrapredictor 331 may determine the prediction mode applied to the current block using the prediction mode applied to the neighboring block.

[086] Interpredictor 332 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector in a reference image. At this time, to reduce the amount of motion information transmitted in interprediction mode, motion information can be predicted in a block, sub-block or sample base based on the correlation of motion information between the neighboring block and the block current. The motion information may include a motion vector and a reference image index. The motion information may additionally include inter-prediction direction information (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of interprediction, the neighboring block may include a spatial neighboring block existing in the current image and a temporal neighboring block existing in the reference image. For example, the interpredictor 332 may configure a candidate list of motion information based on neighboring blocks, and derive a motion vector and/or a reference image index of the current block based on the received candidate selection information. Interprediction may be performed based on various prediction modes, and information about the prediction may include information indicating an interprediction mode for the current block.

[087] The adder 340 can generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample matrix) by adding the residual signal obtained to the prediction signal (predicted block, prediction sample matrix) emitted by the predictor 330. When not If there is residue for a processing target block as in a case where skip mode is applied, the predicted block can be used as a reconstructed block.

[088] Adder 340 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used to intra-predict a next processing target block in the current block, and as described later, can be output through filtering or be used to inter-predict a next image.

[089] However, in the image decoding process, chroma scaled luma mapping (LMCS) can be applied.

[090] Filter 350 can improve subjective/objective video quality by applying filtering to the reconstructed signal. For example, filter 350 may generate a modified reconstructed image by applying various filtering methods to the reconstructed image and may transmit the modified reconstructed image into memory 360, specifically, into the DPB of memory 360. The various filtering methods may include, e.g. example, deblocking filtering, a sample-adaptive shift, an adaptive loop filter, a two-sided filter, or the like.

[091] The reconstructed (modified) image that was stored in the DPB of memory 360 can be used as a reference image in interpredictor 332. Memory 360 can store motion information of a block in the current image, from which information motion information was derived (or decoded) and/or block motion information in an already reconstructed image. The stored motion information can be transmitted to interpredictor 260 which will be used as motion information of a neighboring block or motion information of a temporal neighboring block. The memory 360 may store the reconstructed samples of reconstructed blocks in the current image and transmit the same to the intrapredictor 331.

[092] In this specification, the examples described in the predictor 330, the dequantizer 321, the inverse transformer 322 and the filter 350 of the decoding apparatus 300 can be applied in a similar or corresponding way to the predictor 220, the dequantizer 234, the inverse transformer 235 and filter 260 of coding apparatus 200, respectively.

[093] As described above, prediction is performed to increase compression efficiency to perform video coding. Through this, a predicted block including prediction samples for a current block, which is an encoding target block, can be generated. Here, the predicted block includes prediction samples in a spatial domain (or pixel domain). The predicted block can be identically derived in the encoding apparatus and the decoding apparatus, and the encoding apparatus can increase the image coding efficiency by signaling to the decoding apparatus not the original sample value of an original block itself, but the residual information (residual information) between the original block and the predicted block. The decoding apparatus may derive a residual block including residual samples based on the residual information, generate a reconstructed block including reconstructed samples by summing the residual block to the prediction block, and generate a reconstructed image including reconstructed blocks.

[094] Residual information can be generated through transform and quantization procedures. For example, the coding apparatus may derive a residual block between the original block and the predicted block, derive transform coefficients by performing a transform procedure on residual samples (residual sample matrix) included in the residual block, and derive quantized transform coefficients. carrying out a quantization process on the transform coefficients, so that they can signal the residual information associated with the decoding device (through a stream of bits). Here, the residual information may include value information, position information, a transform technique, transform kernel, a quantization parameter, or the like of quantized transform coefficients. The decoding apparatus may perform a quantization/dequantization procedure and derive the residual samples (or residual sample block) based on the residual information. The decoding apparatus may generate a reconstructed block based on a predicted block and the residual block. The coding apparatus may derive a residual block by dequantization/inverse transform of quantized transform coefficients for reference for interprediction of a next image, and may generate a reconstructed image therefrom.

[095] Figure 4 schematically illustrates a multiple transform technique according to an embodiment of the present disclosure.

[096] With reference to Figure 4, a transformer may correspond to the transformer in the coding apparatus of Figure 2, and an inverse transformer may correspond to the inverse transformer in the coding apparatus of Figure 2 above, or the inverse transformer in the decoding apparatus of Figure 2. Figure 3.

[097] The transformer can derive transform (primary) coefficients by performing a primary transform based on residual samples (residual sample matrix) in a residual block (S410). This primary transform can be called the kernel transform. Here, the primary transform can be based on multiple transform selection (MTS) and when a multiple transform is applied as the primary transform, it can be termed as a multi-core transform.

[098] The multi-core transform can represent an additional transform method using the discrete cosine transform (DCT) type 2 and the discrete sine transform (DST) type 7, DCT type 8 and/or DST type 1. That is , the multi-core transform The transform can represent a transform method for transforming a residual signal (or residual block) of a space domain into transform coefficients (or primary transform coefficients) of a frequency domain based on a plurality of transform cores selected from DCT type 2, DST type 7, DCT type 8 and DST type 1. Here, the primary transform coefficients can be called temporary transform coefficients from the transformer's point of view.

[099] In other words, when the conventional transform method is applied, the transform coefficients can be generated by applying the transform from a space domain to a frequency domain to a residual signal (or residual block) based on DCT type 2 Contrary to this, when the multi-core transform is applied, the transform coefficients (or primary transform coefficients) can be generated by applying the transform from a space domain to a frequency domain for a residual signal (or residual block). based on DCT type 2, DCT type 7, DCT type 8 and/or DCT type 1. Here, DCT type 2, DST type 7, DCT type 8 and DST type 1 can be called the type of transform, transform core or transform core. These types of DCT/DST transforms can be defined based on basic functions.

[0100] When multi-core transform is performed, a vertical transform core and a horizontal transform core for a target block can be selected from among the transform cores, a vertical transform can be performed on the target block based on the vertical transform core, and a horizontal transform can be performed on the target block based on the horizontal transform core. Here, the horizontal transform may indicate a transform in the horizontal components of the target block and the vertical transform may indicate a transform in the vertical components of the target block. The vertical transform core/horizontal transform core may be adaptively determined based on a prediction mode and/or a transform index for the target block (CU or sub-block) including a residual block.

[0101] Furthermore, according to an example, if the primary transform is performed by applying the MTS, a mapping relationship for transform cores can be defined by setting specific basis functions to predetermined values and combining basis functions to be applied in the vertical transform or horizontal transform. For example, when the horizontal transform kernel is expressed as trTypeHor and the vertical direction transform kernel is expressed as trTypeVer, a trTypeHor or trTypeVer value of 0 can be set to DCT2, a trTypeHor or trTypeVer value of 1 can be set to DST7 and a trTypeHor or trTypeVer value of 2 can be set to DCT8.

[0102] In this case, the MTS index information may be encoded and signaled to the decoding apparatus to indicate any one of a plurality of transform core sets. For example, an MTS index of 0 might indicate that the trTypeHor and trTypeVer values are 0, an MTS index of 1 might indicate that the trTypeHor and trTypeVer values are 1, an MTS index of 2 might indicate that the trTypeHor value is 2 and the value trTypeVer. is 1, an MTS index of 3 might indicate that the trTypeHor value is 1 and the trTypeVer value is 2, and an MTS index of 4 might indicate that both the trTypeHor and trTypeVer values are 2.

[0103] In an example, the transform kernel sets according to the MTS index information are illustrated in the following table. Table 1

[0104] The transformer can derive modified (secondary) transform coefficients by performing the secondary transform based on the (primary) transform coefficients (S420). The primary transform is a transform from a spatial domain to a frequency domain, and the secondary transform refers to transforming into a more compressive expression using an existing correlation between the (primary) transform coefficients. The secondary transform may include a non-separable transform. In this case, the secondary transform can be called the non-separable secondary transform (NSST) or the mode-dependent non-separable secondary transform (MDNSST). The non-separable secondary transform may represent a transform that generates modified transform coefficients (or secondary transform coefficients) for a residual signal by secondary transform, based on a non-separable transform matrix, (primary) transform coefficients derived through the transform primary. At this time, the vertical transform and the horizontal transform cannot be applied separately (or the horizontal and vertical transforms may not be applied independently) to the transform (primary) coefficients, but the transforms can be applied at once based on no separable transformed matrix. In other words, the non-separable secondary transform can represent a transform method in which the vertical direction and the horizontal direction are not applied separately to the (primary) transform coefficients and, for example, two-dimensional signals (transform coefficients) are rearranged for a one-dimensional signal through a certain determined direction (e.g., first row direction or first column direction), and then the modified transform coefficients (or secondary transform coefficients) are generated based on the non-separable transform matrix. For example, according to a first row order, the M x N blocks are arranged in a row in the order of a first row, a second row, ... and an nth row. According to a first column order, the M x N blocks are arranged in a row in the order of a first column, a second column, . and an nth column. The non-separable secondary transform can be applied to a left-top region of a block configured with (primary) transform coefficients (hereafter it can be referred to as a transform coefficient block). For example, if the width (W) and height (H) of the transform coefficient block are all equal to or greater than 8, an 8 x 8 non-separable secondary transform can be applied to a left-top 8 x 8 region of the block transform coefficient. Furthermore, if the width (W) and height (H) of the transform coefficient block are all equal to or greater than 4, and the width (W) or height (H) of the transform coefficient block is less than 8, then a 4 x 4 non-separable secondary transform can be applied to a top-left min(8,W) x min(8,H) region of the transform coefficient block. However, the embodiment is not limited to this and, for example, even if only the condition that the width (W) or height (H) of the transform coefficient block is equal to or greater than 4 is satisfied, the secondary transform non-separable 4 x 4 can be applied to the top left min(8,W)xmin(8,H) region of the transform coefficient block.

[0105] Specifically, for example, if a 4 x 4 input block is used, the non-separable secondary transform can be performed as follows.

[0106] The 4 x 4 X input block can be represented as follows.

[0107] If X is represented in the form of a vector, vector X can be represented as below. Equation 2

[0108] In Equation 2, the vector X is a one-dimensional vector obtained by rearranging the two-dimensional block X of Equation 1 according to first-line order.

[0109] In this case, the secondary non-separable transform can be calculated as below. Equation 3

[0110] In this equation, F represents a transform coefficient vector and T represents a 16 x 16 transform matrix (non-separable).

[0111] Through Equation 3 above, a 16 x 1 transform coefficient vector F can be derived, and the F can be derived and can be rearranged into a 4 x 4 block through a scanning order (horizontal, vertical, diagonal and the like). However, the calculation described above is an example, and the hypercube-Givens transform (HyGT) or similar can be used for the calculation of the non-separable secondary transform in order to reduce the computational complexity of the non-separable secondary transform.

[0112] Meanwhile, in the non-separable secondary transform, a transform core (or transform core, transform type) can be selected to be mode dependent. In this case, the mode may include intra prediction mode and/or inter prediction mode.

[0113] As described above, the non-separable secondary transform can be performed based on an 8 x 8 transform or a 4 x 4 transform determined based on the width (W) and height (H) of the transform coefficient block. The 8 x 8 transform refers to a transform that is applicable to an 8 x 8 region included in the transform coefficient block when W and H are equal to or greater than 8, and the 8 x 8 region can be an 8 x region 8 top left in transform coefficient block. Similarly, the 4 x 4 transform refers to a transform that is applicable to a 4 x 4 region included in the transform coefficient block when W and H are equal to or greater than 4, and the 4 x 4 region can be a top-left 4 x 4 region in the transformed coefficient block. For example, an 8 x 8 transform kernel matrix can be a 64 x 64/16 x 64 transform kernel matrix and a 4 x 4 transform kernel matrix can be a 16 x 16/8 x 16 matrix.

[0114] Here, to select a mode-dependent transform core, two transform non-separable secondary transform cores defined for a non-separable secondary transform can be configured for the 8 x 8 transform and the 4 x 4 transform, and cannot be four transform sets. That is, four transform sets can be configured for the 8 x 8 transform and four transform sets can be configured for the 4 x 4 transform. In this case, each of the four transform sets for the 8 x 8 transform can include two 8 x 8 transform cores and each of the four transform sets for the 4 x 4 transform may include two 4 x 4 transform cores.

[0115] However, as the size of the transform, that is, the size of a region to which the transform is applied, may be, for example, a size other than 8 x 8 or 4 x 4, the number of sets may be n, and the number of transform kernels in each set can be k.

[0116] The transform set can be referred to as an NSST set or an LFNST set. A specific set among the transform sets can be selected, for example, based on the intra prediction mode of the current block (CU or sub-block). A low-frequency non-separable transform (LFNST) can be an example of a reduced non-separable transform, which will be described later and represents a non-separable transform for a low-frequency component.

[0117] For reference, for example, the intra prediction mode may include two non-directional (or non-angular) intra prediction modes and 65 directional (or angular) intra prediction modes. The non-directional intra prediction modes may include a planar intra prediction mode of No. 0 and a DC intra prediction mode of No. 1, and the directional intra prediction modes may include 65 intra prediction modes of No. 2 to 66. However, this is an example, and this document can be applied even when the number of intra prediction modes is different. Meanwhile, in some cases, intra prediction mode No. 67 can be used additionally, and intra prediction mode No. 67 can represent a linear model (LM) mode.

[0118] Figure 5 exemplarily shows intradirectional modes of 65 prediction directions.

[0119] Referring to Figure 5, based on the intra prediction mode 34 with a left-up diagonal prediction direction, the intra prediction modes can be divided into intra prediction modes with horizontal directionality and intra prediction modes with horizontal directionality. vertical. In Figure 5, H and V denote horizontal directionality and vertical directionality, respectively, and the numbers -32 to 32 indicate displacements by 1/32 units in a sample grid position. These numerals can represent an offset to a mode index value. Intra prediction modes 2 to 33 have horizontal directionality and intra prediction modes 34 to 66 have vertical directionality. Strictly speaking, the intra prediction mode 34 can be considered as neither horizontal nor vertical, but can be classified as belonging to horizontal directionality in determining a transform set of a secondary transform. This is because the input data is transposed to be used for a symmetric vertical direction mode based on the intra prediction mode 34, and an input data alignment method for a horizontal mode is used for the intra prediction mode 34 Transposing input data means that rows and columns of two-dimensional M x N block data are switched into N x M data. The intra prediction mode 18 and the intra prediction mode 50 may represent a horizontal intra prediction mode and a horizontal intra prediction mode. vertical intra prediction mode, respectively, and intra prediction mode 2 can be termed as a right-up diagonal intra prediction mode because intra prediction mode 2 has a reference pixel and performs prediction in the right upward direction. Likewise, the intra prediction mode 34 can be termed as a right descending diagonal intra prediction mode and the intra prediction mode 66 can be termed as a left descending diagonal intra prediction mode.

[0120] According to an example, the four transform sets according to the intra prediction mode can be mapped, for example, as shown in the following table. Table 2

[0121] As shown in Table 2, any of the four sets of transforms, that is, lfnstTrSetIdx, can be mapped to any of the four indices, that is, from 0 to 3, according to the intra prediction mode.

[0122] When it is determined that a specific set is used for the non-separable transform, one of the k transform cores in the specific set may be selected by means of a secondary non-separable transform index. An encoding apparatus may derive a non-separable secondary transform index indicating a specific transform core based on a rate distortion (RD) check and may signal the non-separable secondary transform index to a decoding apparatus. The decoding apparatus may select one of the k transform cores in the specific set based on the non-separable secondary transform index. For example, the index value of LFNST 0 may refer to a first non-separable secondary transform kernel, the index value of LFNST 1 may refer to a second non-separable secondary transform kernel, and the index value of LFNST 2 may refer to a third non-separable secondary transform kernel. Alternatively, the LFNST index value 0 may indicate that the first non-separable secondary transform is not applied to the target block, and the LFNST index values 1 to 3 may indicate the three transform cores.

[0123] The transformer can perform the non-separable secondary transform based on the selected transform cores and can obtain modified (secondary) transform coefficients. As described above, the modified transform coefficients can be derived as quantized transform coefficients via the quantizer and can be encoded and signaled to the decoding apparatus and transferred to the dequantizer/inverse transformer in the encoding apparatus.

[0124] Meanwhile, as described above, if the secondary transform is omitted, the (primary) transform coefficients, which are an output of the primary (separable) transform, can be derived as quantized transform coefficients through the quantizer as described above , and can be encoded and signaled to the decoding apparatus and transferred to the dequantizer/inverse transformer in the encoding apparatus.

[0125] The inverse transformer can perform a series of procedures in the reverse order to that in which they were performed in the transformer described above. The inverse transformer can receive transformer coefficients (dequantized) and derive transform coefficients (primary) by performing a secondary (inverse) transform (S450), and can obtain a residual block (residual samples) by performing a primary (inverse) transform on the transformer coefficients. transformed (primaries) (S460). In this context, the primary transform coefficients can be called modified transform coefficients from the point of view of the inverse transformer. As described above, the encoding apparatus and the decoding apparatus can generate the reconstructed block based on the residual block and the predicted block, and can generate the reconstructed image based on the reconstructed block.

[0126] The decoding apparatus may further include a secondary inverse transform determinant (or an element for determining whether to apply a secondary inverse transform) and a secondary inverse transform determinant (or an element for determining a secondary inverse transform). . The secondary inverse transform application determinant can determine whether to apply a secondary inverse transform. For example, the secondary inverse transform may be an NSST, an RST, or an LFNST, and the secondary inverse transform apply determinant may determine whether to apply the secondary inverse transform based on a secondary transform flag obtained by analyzing the bit stream. In another example, the secondary inverse transform application determinant may determine whether to apply the secondary inverse transform based on a transform coefficient of a residual block.

[0127] The secondary inverse transform determinant can determine a secondary inverse transform. In this case, the secondary inverse transform determinant can determine the secondary inverse transform applied to the current block based on a set of LFNST transform (NSST or RST) specified according to an intra prediction mode. In one embodiment, a secondary transform determination method may be determined depending on a primary transform determination method. Various combinations of primary transforms and secondary transforms can be determined according to the intra prediction mode. Furthermore, in one example, the secondary inverse transform determinant may determine a region to which a secondary inverse transform is applied based on the current block size.

[0128] Meanwhile, as described above, if the secondary (inverse) transform is omitted, the (dequantized) transform coefficients can be received, the primary (separable) inverse transform can be performed, and the residual block (residual samples) can be obtained. As described above, the encoding apparatus and the decoding apparatus may generate the reconstructed block based on the residual block and the predicted block, and may generate the reconstructed image based on the reconstructed block.

[0129] Meanwhile, in the present disclosure, a reduced secondary transform (RST) in which the size of a transform matrix (kernel) is reduced can be applied in the NSST concept to reduce the amount of computation and memory required for the transform non-separable secondary.

[0130] Meanwhile, the transform kernel, the transform matrix and the coefficient constituting the transform kernel matrix, that is, the kernel coefficient or the matrix coefficient, described in the present disclosure, can be expressed in 8 bits. This may be a condition for implementation in both the decoding apparatus and the encoding apparatus and may reduce the amount of memory required to store the transform core with a performance degradation that can be reasonably accommodated compared to the existing 9-bit or 10-bit . Additionally, expressing the core matrix in 8 bits can allow a small multiplier to be used and may be more suitable for single instruction multiple data (SIMD) instructions used for optimal software implementation.

[0131] In the present specification, the term “RST” may mean a transform that is performed on residual samples for a target block based on a transform matrix whose size is reduced according to a reduced factor. In the case of performing the reduced transform, the amount of computation required for the transform can be reduced due to a reduction in the size of the transform matrix. In other words, RST can be used to solve the problem of computational complexity that occurs in the non-separable transform or in the transform of a large block.

[0132] RST may be termed as various terms, such as reduced transform, reduced secondary transform, reduction transform, simplified transform, simple transform and the like, and the name that RST may be termed as is not limited to the listed examples. Alternatively, since RST is mainly performed in a low-frequency region by including a non-zero coefficient in a transform block, it can be termed as a Low-Frequency Non-Separable Transform (LFNST). The transform index can be termed as an LFNST index.

[0133] Meanwhile, when the secondary inverse transform is performed based on RST, the inverse transformer 235 of the coding apparatus 200 and the inverse transformer 322 of the decoding apparatus 300 may include a reduced secondary inverse transformer that derives modified transform coefficients. based on the inverse RST of the transform coefficients and an inverse primary transformer that derives residual samples for the target block based on the inverse primary transform of the modified transform coefficients. The inverse primary transform refers to the inverse transform of the primary transform applied to the residue. In the present disclosure, deriving a transform coefficient based on a transform may refer to deriving a transform coefficient by applying the transform.

[0134] Figure 6 is a diagram illustrating an RST in accordance with an embodiment of the present disclosure.

[0135] In the present disclosure, a “target block” may refer to a current block to be encoded, a residual block, or a transform block.

[0136] In RST according to an example, an N-dimensional vector can be mapped to an R-dimensional vector located in another space, so that the reduced transform matrix can be determined, where R is less than N. may mean the square of the length of a side of a block to which the transform is applied, or the total number of transform coefficients corresponding to a block to which the transform is applied, and the reduced factor may mean an R/N value. The reduced factor can be termed as a reduced factor, reduction factor, simplified factor, simple factor or other various terms. Meanwhile, R can be termed as a reduced coefficient, but according to the circumstances, the reduced factor can mean R. Also, according to the circumstances, the reduced factor can mean the N/R value.

[0137] In an example, the reduced factor or reduced coefficient may be signaled via a bit stream, but the example is not limited to this. For example, a predefined value for the reduced factor or the reduced coefficient may be stored in each encoding apparatus 200 and decoding apparatus 300, and in this case the reduced factor or the reduced coefficient may not be signaled separately.

[0138] The size of the reduced transform matrix according to an example may be R x N less than N x N, the size of a conventional transform matrix and may be defined as in Equation 4 below. Equation 4

[0139] The matrix T in the Reduced Transform block shown in Figure 5(a) may mean the TRxN matrix of Equation 4. As shown in Figure 5(a), when the reduced transform matrix TRxN is multiplied by residual samples for the block target, the transform coefficients for the target block can be derived.

[0140] In an example, if the size of the block to which the transform is applied is 8 x 8 and R = 16 (i.e., R/N = 16/64 = 1/4), then the RST according to Figure 5(a) can be expressed as a matrix operation as shown in Equation 5 below. In this case, the memory and multiplication calculation can be reduced to approximately 1/4 by the reduced factor.

[0141] In the present disclosure, a matrix operation can be understood as an operation of multiplying a column vector by a matrix, arranged to the left of the column vector, to obtain a column vector. Equation 5

[0142] In Equation 5, r1 to r64 may represent residual samples for the target block and may specifically be transform coefficients generated by applying a primary transform. As a result of calculating Equation 5, the ci transform coefficients for the target block can be derived and a ci derivation process can be as in Equation 6. Equation 6

[0143] As a result of calculating Equation 6, the transform coefficients c1 to cR for the target block can be derived. That is, when R = 16, the transform coefficients c1 to c16 for the target block can be derived. If, instead of RST, a regular transform is applied and a transform matrix of size 64 x 64 (N x N) is multiplied to residual samples of size 64 x 1 (N x 1), only 16 (R) coefficients of transform will be derived for the target block because RST was applied, although 64 (N) transform coefficients will be derived for the target block. Once the total number of transform coefficients for the target block is reduced from N to R, the amount of data transmitted by the encoding apparatus 200 to the decoding apparatus 300 decreases, so that the transmission efficiency between the encoding apparatus 200 and the decoding apparatus encoding 200 and decoding apparatus 300 may be improved.

[0144] When considered from the point of view of the transform matrix size, the size of the regular transform matrix is 64 x 64 (N x N), but the size of the reduced transform matrix is reduced to 16 x 64 (R x N), then the memory usage in the case of performing the RST can be reduced by an R/N ratio when compared to the case of performing the regular transform. Furthermore, when compared to the number of N x N multiplication calculations in the case of using the regular transformed matrix, the use of the reduced transformed matrix can reduce the number of multiplication calculations by the ratio R/N (R x N).

[0145] In one example, transformer 132 of coding apparatus 200 may derive transform coefficients for the target block by performing the primary transform and the RST-based secondary transform on residual samples for the target block. These transform coefficients may be transferred to the inverse transformer of the decoding apparatus 300 and the inverse transformer 322 of the decoding apparatus 300 may derive the modified transform coefficients based on the reduced inverse secondary transform (RST) for the transform coefficients and may derive residual samples for the target block based on the inverse primary transform for the modified transform coefficients.

[0146] The size of the TRxN inverse RST matrix according to an example is N x R smaller than the N x N size of the regular inverse transform matrix and is in a transpose relationship with the TRxN reduced transform matrix shown in Eq. 4.

[0147] The Tt matrix in the Reduced Inv Transform Block shown in Figure 5(b) can mean the inverse RST matrix TRxNT (the superscript T means transpose). When the inverse RST matrix TRxNT is multiplied by the transform coefficients for the target block as shown in Figure 5(b), the modified transform coefficients for the target block or the residual samples for the current block can be derived. The inverse RST matrix TRxNT can be expressed as (TRxNT)NxR.

[0148] More specifically, when the inverse RST is applied as the secondary inverse transform, the modified transform coefficients for the target block can be derived when the inverse RST matrix TRxNT multiplied by the transform coefficients for the target block. Meanwhile, the inverse RST can be applied as the inverse primary transform, and in this case, the residual samples for the target block can be derived when the inverse RST matrix TRxNT is multiplied by the transform coefficients for the target block.

[0149] In an example, if the size of the block to which the inverse transform is applied is 8 x 8 and R = 16 (i.e., R/N = 16/64 = 1/4), then the RST according to Figure 5(b) can be expressed as a matrix operation as shown in Equation 7 below. Equation 7

[0150] In Equation 7, c1 to c16 can represent the transform coefficients for the target block. As a result of calculating Equation 7, ri representing the modified transform coefficients for the target block or the residual samples for the target block can be derived and the derivation process of ri can be as in Equation 8. Equation 8

[0151] As a result of calculating Equation 8, r1 to rN representing the modified transform coefficients for the target block or the residual samples for the target block can be derived. When considered from the point of view of the size of the inverse transform matrix, the size of the regular inverse transform matrix is 64 x 64 (N x N), but the size of the reduced inverse transform matrix is reduced to 64 x 16 (R x N), then the memory usage in a case of performing the inverse RST can be reduced by an R/N ratio when compared to a case of performing the regular inverse transform. Furthermore, when compared to the number of N x N multiplication calculations in a regular inverse transform matrix use case, the use of the reduced inverse transform matrix can reduce the number of multiplication calculations by the ratio R/N (N x R).

[0152] A transform set configuration shown in Table 2 can also be applied to an 8 x 8 RST. That is, the 8 x 8 RST can be applied according to a set of transforms in Table 2. As a set of transform includes two or three transforms (kernels) according to an intra prediction mode, it can be configured to select one of up to four transforms including the one in a case where no secondary transform is applied. In a transform where no secondary transform is applied, one can consider applying an identity matrix. Assuming that the indices 0, 1, 2 and 3 are respectively assigned to the four transforms (for example, the index 0 can be allocated to a case where an identity matrix is applied, i.e., a case where no secondary transform is applied), a transform index or an LFNST index as a syntax element can be signaled for each transform coefficient block, thus designating a transform to be applied. That is, for a top left 8 x 8 block, through the transform index, it is possible to designate an 8 x 8 RST in an RST configuration, or designate an 8 x 8 lfnst when LFNST is applied. lfnst 8 x 8 and RST 8 x 8 refer to transforms applicable to an 8 x 8 region included in the transform coefficient block when W and H of the target block to be transformed are equal to or greater than 8, and the region 8x8 can be a left-top 8x8 region in the transform coefficient block. Likewise, a 4 x 4 lfnst and a 4 x 4 RST refer to transforms applicable to a 4 x 4 region included in the transform coefficient block when W and H of the target block are equal to or greater than 4, and the 4x4 region can be a left-top 4x4 region in the transform coefficient block.

[0153] According to one embodiment of the present disclosure, for a transform in an encoding process, only 48 pieces of data can be selected and a maximum transform kernel matrix of 16 x 48 can be applied thereto, instead of apply a 16 x 64 transform kernel matrix to 64 pieces of data forming an 8 x 8 region. Here, “maximum” means that m has a maximum value of 16 in an m x 48 transform kernel matrix to generate m coefficients . That is, when an RST is performed by applying an m x 48 transform kernel matrix (m < 16) to an 8 x 8 region, 48 data are entered and m coefficients are generated. When m is 16, 48 data are entered and 16 coefficients are generated. That is, assuming that 48 data pieces form a 48 x 1 vector, a 16 x 48 matrix and a 48 x 1 vector are multiplied sequentially, thus generating a 16 x 1 vector. Here, the 48 pieces of data that form the 8 x region 8 can be arranged accordingly, thus forming the 48 x 1 vector. For example, a 48 x 1 vector can be constructed based on 48 pieces of data that constitute a region excluding the lower right 4 x 4 region between the 8 x 8 regions Here, when a matrix operation is performed by applying a maximum transform kernel matrix of 16 x 48, 16 modified transform coefficients are generated and the 16 modified transform coefficients can be arranged in a top-left 4 x 4 region. according to a scanning order, and a top right 4 x 4 region and a bottom left 4 x 4 region can be filled with zeros.

[0154] For an inverse transform in a decoding process, the transposed matrix of the previous transform kernel matrix can be used. That is, when an inverse RST or LFNST is performed in the inverse transform process performed by the decoding apparatus, the input coefficient data to which the inverse RST is applied is configured into a one-dimensional vector according to a predetermined arrangement order and a modified coefficient vector obtained by multiplying the one-dimensional vector and a corresponding inverse RST matrix to the left of the one-dimensional vector can be arranged in a two-dimensional block according to a predetermined arrangement order.

[0155] In summary, in the transform process, when an RST or LFNST is applied to an 8 x 8 region, a matrix operation of 48 transform coefficients on the top left, top right and bottom left regions of the 8 x regions 8 by deleting the lower right region between the transform coefficients in the 8 x 8 region and a 16 x 48 transform kernel matrix. For the matrix operation, the 48 transform coefficients are inserted into a one-dimensional matrix. When the matrix operation is performed, 16 modified transform coefficients are derived, and the modified transform coefficients can be arranged in the top left region of the 8 x 8 region.

[0156] On the contrary, in the inverse transform process, when an inverse RST or LFNST is applied to an 8 x 8 region, 16 transform coefficients corresponding to a top region to the left of the 8 x 8 region between the transform coefficients transformed in the 8 x 8 region can be inserted into a one-dimensional matrix according to a scan order and can be subjected to a matrix operation with a 48 x 16 transform kernel matrix. That is, the matrix operation can be expressed as (48 x 16 matrix) * (16 x 1 transform coefficient vector) = (48 x 1 modified transform coefficient vector). Here, an n x 1 vector can be interpreted as having the same meaning as an n x 1 matrix and can therefore be expressed as an n x 1 column vector. Furthermore, *denotes matrix multiplication. When the matrix operation is performed, 48 modified transform coefficients can be derived and the 48 modified transform coefficients can be arranged in the top left, top right and bottom left regions of the 8 x 8 region excluding a bottom right region.

[0157] When a secondary inverse transform is based on an RST, the inverse transformer 235 of the coding apparatus 200 and the inverse transformer 322 of the decoding apparatus 300 may include a stepped-down secondary inverse transformer for deriving modified transform coefficients based on a Inverse RST on transform coefficients and an inverse primary transformer to derive residual samples for the target block based on an inverse primary transform on the modified transform coefficients. The inverse primary transform refers to the inverse transform of a primary transform applied to a residue. In the present disclosure, deriving a transform coefficient based on a transform may refer to deriving the transform coefficient by applying the transform.

[0158] The non-separated transform described above, the LFNST, will be described in detail below. The LFNST may include a forward transform by the encoding apparatus and an inverse transform by the decoding apparatus.

[0159] The coding apparatus receives a result (or part of a result) derived after applying a primary transform (core) as input and applies a direct secondary transform (secondary transform). Equation 9

[0160] In Equation 9, x and y are inputs and outputs of the secondary transform, respectively, and G is a matrix representing the secondary transform, and the base vectors of the transform are composed of column vectors. In the case of an inverse LFNST, when the dimension of the transform matrix G is expressed as [number of rows x number of columns], in the case of a direct LFNST, the transpose of the matrix G becomes the dimension of GT.

[0161] For the inverse LFNST, the dimensions of the matrix G are [48 x 16], [48 x 8], [16 x 16], [16 x 8], and the matrix [48 x 8] and the [16 ]x8] are partial matrices that sampled 8 transform basis vectors from the left of the [48 x 16] matrix and the [16 x 16] matrix, respectively.

[0162] On the other hand, for direct LFNST, the dimensions of the GT matrix are [16 x 48], [8 x 48], [16 x 16], [8 x 16], and the [8 x 48] matrix and matrix [8 x 16] are partial matrices obtained by sampling 8 transform basis vectors from the top of matrix [16 x 48] and matrix [16 x 16], respectively.

[0163] Therefore, in the case of direct LFNST, a vector [48 x 1] or [16 x 1] is possible as an input x, and a vector [16 x 1] or a vector [8 x 1] is possible as a y output. In video encoding and decoding, the output of the direct primary transform is two-dimensional (2D) data, so to construct vector [48 x 1] or vector [16 x 1] as the input x, a one-dimensional vector must be constructed by arranging appropriately the 2D data that is the output of the direct transform.

[0164] Figure 7 is a diagram illustrating an output data arrangement sequence of a direct primary transform into a one-dimensional vector according to an example. The left diagrams of (a) and (b) of Figure 7 show the sequence for constructing a [48 x 1] vector and the right diagrams of (a) and (b) of Figure 7 show the sequence for constructing a vector [16 x 1]. In the case of LFNST, a one-dimensional vector x can be obtained by sequentially arranging the 2D data in the same order as in (a) and (b) of Figure 7.

[0165] The arrangement direction of the direct primary transform output data can be determined according to an intra prediction mode of the current block. For example, when the intra prediction mode of the current block is in the horizontal direction with respect to the diagonal direction, the output data of the direct primary transform can be arranged in the order of (a) in Figure 7, and when the intra prediction mode of the current block is in the vertical direction with respect to the diagonal direction, the output data of the direct primary transform can be arranged in the order of (b) in Figure 7.

[0166] According to an example, an arrangement order different from the arrangement orders of (a) and (b) Figure 7 can be applied, and to derive the same result (y vector) as when the arrangement orders of ( a) and (b) Figure 7 is applied, the column vectors of the matrix G can be rearranged according to the arrangement order. In other words, it is possible to rearrange the column vectors of G so that each element that constitutes the vector x is always multiplied by the same base vector of the transform.

[0167] Since the output y derived through Equation 9 is a one-dimensional vector, when two-dimensional data is required as input data in the process of using the result of the direct secondary transform as input, for example, in the process of performing quantization or residual encoding, the output vector y of Equation 9 must be properly organized as 2D data again.

[0168] Figure 8 is a diagram illustrating an output data arrangement sequence of a direct secondary transform in a two-dimensional block according to an example.

[0169] In the case of LFNST, the output values can be arranged in a 2D block according to a predetermined scanning order. (a) of Figure 8 shows that when the output y is a vector [16 x 1], the output values are arranged in 16 positions of the 2D block according to a diagonal scanning order. (b) of Figure 8 shows that when the output y is a vector [8 x 1], the output values are arranged in 8 positions of the 2D block according to the diagonal scanning order, and the remaining 8 positions are filled with zeros. X in (b) of Figure 7 indicates that it is zero-filled.

[0170] According to another example, since the order in which the output vector y is processed in performing quantization or residual coding can be predefined, the output vector y cannot be arranged in the 2D block as shown in Figure 8. However, in case of residual coding, data coding can be performed in 2D block units (e.g. 4 x 4) as CG (Coefficient Group), and in this case, data is organized according to a specific order as in the diagonal scanning order of Figure 8.

[0171] Meanwhile, the decoding apparatus may configure the one-dimensional input vector y by arranging the two-dimensional data output through a dequantization or similar process according to a predefined scanning order for the inverse transform. The input vector y can be output as the output vector x by the following equation. Equation 10

[0172] In the case of inverse LFNST, an output vector x can be derived by multiplying an input vector y, which is a [16 x 1] vector or an [8 x 1] vector, by a matrix G. For LFNST Inversely, the output vector x can be a [48 x 1] vector or a [16 x 1] vector.

[0173] The output vector x is arranged in a two-dimensional block according to the order shown in Figure 7 and is organized as two-dimensional data, and this two-dimensional data becomes input data (or a part of the input data) of the inverse primary transform.

[0174] Consequently, the inverse secondary transform is the opposite of the direct secondary transform process as a whole, and in the case of the inverse transform, unlike the direct direction, the inverse secondary transform is applied first and then the inverse primary transform is applied.

[0175] In inverse LFNST, one of the 8 [48 x 16] matrices and 8 [16 x 16] matrices can be selected as the transform matrix G. Whether to apply the matrix [48 x 16] or the [16 x 16 ]] depends on the size and shape of the block.

[0176] Furthermore, 8 matrices can be derived from four sets of transforms as shown in Table 2 above, and each set of transforms can consist of two matrices. Which set of transforms to use among the 4 sets of transforms is determined according to the intra prediction mode and, more specifically, the set of transforms is determined based on the value of the extended intra prediction mode considering the intra prediction of wide angle (WAIP). Which matrix to select from the two matrices that constitute the selected transform set is derived through index signaling. More specifically, 0, 1 and 2 are possible as the transmitted index value, 0 can indicate that LFNST is not applied, and 1 and 2 can indicate either of the two transform matrices that constitute a transform set selected based on the mode intra prediction value.

[0177] Figure 9 is a diagram illustrating wide-angle intra prediction modes in accordance with an embodiment of the present document.

[0178] The general intra prediction mode value can have values from 0 to 66 and 81 to 83, and the extended intra prediction mode value due to WAIP can have a value from -14 to 83 as shown. Values from 81 to 83 indicate the CCLM (Crossed Component Linear Model) mode, and values from -14 to -1 and values from 67 to 80 indicate the extended intra prediction mode due to the WAIP application.

[0179] When the width of the current prediction block is greater than the height, the upper reference pixels are generally closer to the positions within the block to be predicted. Therefore, it may be more accurate to predict in the lower left direction than in the upper right direction. On the other hand, when the block height is greater than the width, the reference pixels on the left are usually close to the positions within the block to be predicted. Therefore, it may be more accurate to predict in the upper-right direction than in the lower-left direction. Therefore, it may be advantageous to apply remapping, i.e. mode index modification, to the wide-angle intra prediction mode index.

[0180] When wide-angle intra prediction is applied, information about the existing intra prediction can be flagged, and after the information is analyzed, the information can be remapped to the wide-angle intra prediction mode index. Therefore, the total number of intra prediction modes for a specific block (e.g., a non-square block of a specific size) may not change, that is, the total number of intra prediction modes is 67 and the intra prediction mode the encoding for the specific block cannot be changed.

[0181] Table 3 below shows a process of deriving a modified intra-prediction mode by remapping the intra-prediction mode to the wide-angle intra-prediction mode.

[0182] In Table 3, the value of the extended intra prediction mode is finally stored in the predModeIntra variable, and ISP_NO_SPLIT indicates that the CU block is not divided into subpartitions by the Intra Subpartition (ISP) technique currently adopted in the VVC standard, and Variable cIdx values of 0, 1 and 2 indicate the case of the luma components, Cb and Cr, respectively. The Log2 function shown in Table 3 returns a base-2 log value, and the Abs function returns an absolute value.

[0183] The predModeIntra variable indicating the intra prediction mode and the height and width of the transform block, etc., are used as input values of the wide-angle intra prediction mode mapping process, and the output value is the intra prediction mode modified predModeIntra. The height and width of the transform block or encoding block can be the height and width of the current block for intra prediction mode remapping. At this time, the whRatio variable that reflects the relationship between width and width can be set to Abs(Log2(nW / nH))).

[0184] For a non-square block, the intra prediction mode can be divided into two cases and modified.

[0185] First, if all conditions (1) ~ (3) are satisfied, (1) the width of the current block is greater than the height, (2) the intra prediction mode before modifying is equal to or greater than 2 , (3) the intra prediction mode is less than the value derived from (8 + 2 * whRatio) when the whRatio variable is greater than 1, and is less than 8 when the whRatio variable is less than or equal to 1 [predModeIntra is less than ( whRatio > 1 )? ( 8 + 2 * whRatio ): 8], the intra prediction mode is set to a value 65 greater than the intra prediction mode [predModeIntra is set equal to ( predModeIntra + 65)].

[0186] If different from the above, that is, the following conditions (1) ~ (3) are satisfied, (1) the height of the current block is greater than the width, (2) the intra prediction mode before modifying is less than or equal to 66, (3) the intra prediction mode is greater than the value derived from ( 60 - 2 * whRatio ) when the variable whRatio is greater than 1, and is greater than 60 when the variable whRatio is less than or equal to 1 [predModeIntra is greater than ( whRatio > 1 )? ( 60 - 2 * whRatio ) : 60], the intra prediction mode is set to a value 67 smaller than the intra prediction mode [predModeIntra is set equal to ( predModeIntra - 67)].

[0187] Table 2 above shows how a transform set is selected based on the value of the intra prediction mode extended by the WAIP in the LFNST. As shown in Figure 9, modes 14 to 33 and modes 35 to 80 are symmetric about the prediction direction around mode 34. For example, mode 14 and mode 54 are symmetric about the direction corresponding to mode 34. Therefore, the same set of transform is applied to modes located in mutually symmetric directions, and this symmetry is also reflected in Table 2.

[0188] Meanwhile, it is assumed that the direct LFNST input data for mode 54 is symmetric with the direct LFNST input data for mode 14. For example, for mode 14 and mode 54, the data two-dimensional data are rearranged into one-dimensional data according to the arrangement order shown in (a) of Figure 7 and (b) of Figure 7, respectively. Furthermore, it can be seen that the patterns in the order shown in (a) of Figure 7 and (b) of Figure 7 are symmetric with respect to the direction (diagonal direction) indicated by Mode 34.

[0189] Meanwhile, as described above, which transform matrix of the [48 x 16] matrix and the [16 x 16] matrix is applied to the LFNST is determined by the size and shape of the transform target block.

[0190] Figure 10 is a diagram illustrating a block format to which LFNST is applied. (a) Figure 10 shows 4 x 4 blocks, (b) shows 4 x 8 and 8 x 4 blocks, (c) shows 4 x N or N x 4 blocks where N is 16 or more, (d) shows 8 x 8, (e) shows M x N blocks where M > 8, N > 8, and N > 8 or M > 8.

[0191] In Figure 10, blocks with thick edges indicate regions in which LFNST is applied. For the blocks of Figures 10 (a) and (b), the LFNST is applied to the top left 4 x 4 region and for the block of Figure 10 (c), the LFNST is applied individually to the two 4 x 4 regions. upper left are arranged continuously. In (a), (b) and (c) of Figure 10, since the LFNST is applied in 4 x 4 region units, this LFNST will be referred to as “LFNST 4 x 4” from now on. Based on the matrix dimension for G, a [16 x 16] or [16 x 8] matrix can be applied.

[0192] More specifically, the [16 x 8] matrix is applied to the 4 x 4 block (4 x 4 TU or 4 x 4 CU) of Figure 10 (a) and the [16 x 16] matrix is applied to the blocks in (b) and (c) of Figure 10. This is to adjust the computational complexity for the worst case for 8 multiplications per sample.

[0193] With respect to (d) and (e) of Figure 10, the LFNST is applied to the top left 8 x 8 region and this LFNST is hereinafter referred to as “LFNST 8 x 8”. As the corresponding transform matrix, a [48 x 16] matrix or a [48 x 8] matrix can be applied. In the case of direct LFNST, since the vector [48 x 1] (vector x in Equation 9) is entered as input data, all sample values from the top left 8 x 8 region are not used as output values. direct entry from LFNST. That is, as can be seen from the left order of Figure 7 (a) or the left order of Figure 7 (b), the vector [48 x 1] can be constructed based on samples belonging to the 3 blocks 4 x 4 remaining, leaving the bottom right 4 x 4 block as is.

[0194] The matrix [48 x 8] can be applied to an 8 x 8 block (8 x 8 TU or 8 x 8 CU) in Figure 10 (d), and the matrix [48 x 16] can be applied to the block 8 x 8 in Figure 10 (e). This also serves to adjust the computational complexity for the worst case for 8 multiplications per sample.

[0195] Depending on the shape of the block, when the corresponding direct LFNST (LFNST 4 x 4 or LFNST 8 x 8) is applied, 8 or 16 output data (vector y in Equation 9, vector [8 x 1] or [16 x 1]) is generated. In direct LFNST, the number of output data is equal to or less than the number of input data due to the characteristics of the GT matrix.

[0196] Figure 11 is a diagram illustrating an arrangement of output data from a direct LFNST according to an example, and shows a block in which output data from the direct LFNST is arranged according to a block format.

[0197] The shaded area at the top left of the block shown in Figure 11 corresponds to the area where the direct LFNST output data is located, positions marked with 0 indicate samples filled with 0 values, and the remaining area represents regions which are not changed by direct LFNST. In the area not changed by LFNST, the output data of the direct primary transform remains unchanged.

[0198] As described above, since the dimension of the applied transform matrix varies according to the shape of the block, the number of output data also varies. Like Figure 11, direct LFNST output data may not completely fill the top left 4 x 4 block. In the case of (a) and (d) of Figure 11, a [16 x 8] matrix and a [48 x 8] matrix are applied to the block indicated by a thick line or a partial region within the block, respectively, and a vector [8 x 1] as output of the forward LFNST is generated. That is, according to the scanning order shown in (b) of Figure 8, only 8 output data can be filled as shown in (a) and (d) of Figure 11, and 0 can be filled in the remaining 8 positions. In the case of the block applied to the LFNST in Figure 10 (d), as shown in Figure 11 (d), two upper right and lower left 4 x 4 blocks adjacent to the upper left 4 x 4 block are also filled with 0 values.

[0199] As described above, basically, when signaling the LFNST index, it is specified whether to apply the LFNST and the transform matrix to be applied. As shown in Figure 11, when LFNST is applied, since the number of output data of direct LFNST may be equal to or less than the number of input data, a region filled with a zero value occurs as follows.

[0200] 1) As shown in (a) of Figure 11, samples from the 8th position and later in the scanning order in the upper left 4 x 4 block, that is, samples from the 9th to the 16th.

[0201] 2) As shown in (d) and (e) of Figure 11, when the [48 x 16] matrix or the [48 x 8] matrix is applied, two 4 x 4 blocks adjacent to the upper 4 x 4 block left or the second and third 4 x 4 blocks in the scan order.

[0202] Therefore, if there is non-zero data checking areas 1) and 2), it is certain that LFNST is not applied, so the corresponding LFNST index flag can be omitted.

[0203] According to an example, for example, in the case of LFNST adopted in the VVC standard, since the LFNST index signaling is performed after residual coding, the coding apparatus can know whether non-zero data exists (significant coefficients) for all positions within the TU or CU block through residual coding. Accordingly, the encoding apparatus can determine whether to perform signaling on the LFNST index based on the existence of non-zero data and the decoding apparatus can determine whether the LFNST index is parsed. When non-zero data does not exist in the area designated in 1) and 2) above, LFNST index signaling is performed.

[0204] As a truncated unary code is applied as a binarization method for the LFNST index, the LFNST index consists of up to two bins and 0, 10 and 11 are assigned as binary codes for possible LFNST index values of 0 , 1 , and 2, respectively. According to an example, context-based CABAC coding can be applied to the first compartment (regular coding) and context-based CABAC coding can also be applied to the second compartment. The LFNST index coding is shown in the table below. Table 4

[0205] As shown in Table 4, for the first bin (binIdx = 0), context 0 can be applied to a single tree and context 1 can be applied to a non-single tree. As shown in Table 4, for the second bin (binIdx = 1), context 2 can be applied. That is, two contexts can be allocated to the first compartment, one context can be allocated to the second compartment, and each context can be distinguished by a ctxInc value (0, 1, and 2).

[0206] Here, the single tree indicates that the luma component and the chroma component are encoded with the same encoding structure. When the encoding unit is divided with the same encoding structure and the size of the encoding unit becomes less than or equal to a specific threshold size and therefore the luma component and chroma component are encoded with separate tree structures , context for the first bin can be determined by considering the coding unit as a double tree. That is, as shown in Table 4, context 1 can be allocated.

[0207] Alternatively, when the value of a treeType variable is allocated as SINGLE_TREE to the first bin, context 0 can be used for encoding, and otherwise context 1 can be used for encoding.

[0208] However, for the adopted LFNST, the following simplification methods can be applied.

[0209] (i) According to an example, the number of output data for direct LFNST may be limited to a maximum of 16.

[0210] In the case of (c) of Figure 10, the 4 x 4 LFNST can be applied to two 4 x 4 regions adjacent to the top left part, respectively, and in this case, a maximum of 32 LFNST output data can be generated when the number of output data for direct LFNST is limited to a maximum of 16, in case of 4 x N/N x 4 (N > 16) blocks (TU or CU), 4 x 4 LFNST is applied only to a top left 4 x 4 region, LFNST can be applied only once to all blocks in Figure 10. With this, the implementation of image coding can be simplified.

[0211] Figure 12 shows that the number of output data for direct LFNST is limited to a maximum of 16 according to an example. As Figure 12, when LFNST is applied to the top left 4 x 4 region in a 4 x N or N x 4 block in which N is 16 or more, the direct LFNST output data becomes 16 pieces.

[0212] (ii) According to an example, zero-out can be additionally applied to a region to which LFNST is not applied. In this document, zero-out can mean filling values of all positions belonging to a given region with value 0. That is, zero-out can be applied to a region that is not changed due to LFNST and maintains the result of the direct primary transform. As described above, since the LFNST is divided into LFNST 4 x 4 and LFNST 8 x 8, the zero-out can be divided into two types ((ii)-(A) and (ii)-(B)) as he follows.

[0213] (ii)-( A) When LFNST 4 x 4 is applied, a region to which LFNST 4 x 4 is not applied can be reset. Figure 11 is a diagram illustrating zero-out in a block to which LFNST 4 x 4 is applied according to an example.

[0214] As shown in Figure 13, with respect to a block to which LFNST 4 x 4 is applied, that is, for all blocks in (a), (b) and (c) of Figure 11, the entire region to which LFNST is not applied can be padded with zeros.

[0215] On the other hand, (d) of Figure 13 shows that when the maximum value of the number of direct LFNST output data is limited to 16 as shown in Figure 12, zero-out is performed in the remaining blocks to which the LFNST 4 x 4 is not applied.

[0216] (ii)-(B) When an 8 x 8 LFNST is applied, a region to which the 8 x 8 LFNST is not applied can be reset. Figure 14 illustrates zero-out in a block to which an 8 x 8 LFNST is applied according to an example.

[0217] As shown in Figure 14, with respect to a block to which the LFNST 8 x 8 is applied, that is, for all blocks in (d) and (e) of Figure 11, the entire region to which the LFNST is not applied can be filled with zeros.

[0218] (iii) Due to the zero-out presented in (ii) above, the area filled with zeros may not be the same when LFNST is applied. Thus, it is possible to verify whether non-zero data exist according to the zero-out proposed in (ii) in a wider area than the LFNST case in Figure 11.

[0219] For example, when (ii)-(B) is applied, whether non-zero data exists can be checked in up to a region additionally filled with 0s in Figure 11 in addition to the regions filled with zeros in Figure (d) and ( e) of Figure 14, and then an LFNST index can be signaled only when there is no non-zero data.

[0220] Of course, even if the zero-out proposed in (ii) is applied, it is possible to verify that non-zero data exists in the same way as the existing LFNST index signaling. That is, after checking whether non-zero data exists in the zero-filled block in Figure 11, LFNST index signaling can be applied. In this case, the coding device only performs the zero output and the decoding device does not assume the zero output, that is, checking only whether non-zero data exists only in the area explicitly marked as 0 in Figure 11, it can perform the analysis of the LFNST index.

[0221] Various embodiments in which combinations of the simplification methods ((i), (ii)-(A), (ii)-(B), (iii)) for the LFNST are applied can be derived. Obviously, combinations of the above simplification methods are not limited to the following embodiment and any combination can be applied to LFNST. Modality

[0222] - Limit the number of output data for direct LFNST to a maximum of 16 ^ (i)

[0223] - When LFNST 4 x 4 is applied, all areas in which LFNST 4 x 4 is not applied are zero-out ^ (ii)-(A)

[0224] - When LFNST 8 x 8 is applied, all areas in which LFNST 8 x 8 is not applied are reset to zero ^ (ii)-(B)

[0225] - After checking if the non-zero data there is also the existing area filled with zero value and the area filled with zeros due to additional zero-outs ((ii)-(A), (ii)-(B) ), the LFNST index is signaled only when non-zero data does not exist ^ (iii)

[0226] In the case of the Embodiment, when LFNST is applied, an area in which non-zero output data can exist is limited to the interior of the top left 4 x 4 area. In more detail, in the case of Figure 13 (a) and Figure 14 (a), the 8th position in the scanning order is the last position where non-zero data can exist. In the case of Figure 13 (b) and (c) and Figure 14 (b), the 16th position in the scanning order (i.e. the position of the lower right edge of the upper left 4 x 4 block) is the last position where they can exist data other than 0.

[0227] Therefore, when LFNST is applied, after checking whether non-zero data exists in a position where the residual coding process is not allowed (in a position beyond the last position), it can be determined whether the index of LFNST is flagged.

[0228] In the case of the zero-out method proposed in (ii), since the number of data finally generated when the primary transform and LFNST are applied, the amount of computation required to perform the entire transform process can be reduced . That is, when LFNST is applied, since zero-out is applied to direct primary transform output data existing in a region in which LFNST is not applied, there is no need to generate data for the region that becomes zero-out during performing the direct primary transform. Thus, it is possible to reduce the amount of computation required to generate the corresponding data. The additional effects of the zero-out method proposed in (ii) are summarized below.

[0229] First, as described above, the amount of computation required to perform the entire transform process is reduced.

[0230] In particular, when (ii)-(B) is applied, the amount of calculation for the worst case is reduced, so that the transformation process can be speeded up. In other words, in general, a large amount of computation is required to perform a large primary transform. By applying (ii)-(B), the number of data derived as a result of performing direct LFNST can be reduced to 16 or less. Furthermore, as the size of the entire block (TU or CU) increases, the effect of reducing the amount of transform operation increases further.

[0231] Second, the amount of computation required for the entire transform process can be reduced, thereby reducing the energy consumption required to perform the transform.

[0232] Third, the latency involved in the transform process is reduced.

[0233] The secondary transform, such as the LFNST, adds a computational amount to the existing primary transform, thereby increasing the overall delay time involved in executing the transform. In particular, in the case of intra prediction, since reconstructed data from neighboring blocks are used in the prediction process, during encoding, an increase in latency due to a secondary transform leads to an increase in latency until reconstruction. This can lead to an increase in the overall latency of intra prediction coding.

[0234] However, if the zero-out suggested in (ii) is applied, the delay time for performing the primary transform can be greatly reduced. When LFNST is applied, the delay time for the entire transform is maintained or reduced , so that the coding apparatus can be implemented more simply.

[0235] Meanwhile, in conventional intra prediction, a coding target block is considered as a coding unit, and coding is performed without partitioning it. However, ISP (Intra Sub-Partitions) coding refers to performing intra prediction coding with the coding target block being partitioned in a horizontal or vertical direction. In this case, a reconstructed block can be generated by performing encoding/decoding on partitioned block units, and the reconstructed block can be used as a reference block of the next partitioned block. According to an example, in ISP coding, a coding block can be partitioned into two or four sub-blocks and encoded, and in ISP, intra prediction is performed on a sub-block by referring to the pixel value reconstructed from a sub-block located adjacent to the left or upper side thereof. Hereinafter, the term “encoding” may be used as a concept including both the encoding performed by the encoding apparatus and the decoding performed by the decoding apparatus.

[0236] Next, the signaling of an LFNST index and an MTS index is described.

[0237] A coding unit syntax table, a transform unit syntax table and a residual coding syntax table related to signaling an LFNST index and an MTS index according to an example are shown below. According to Table 5, the MTS index moves from a transform unit-level syntax to a coding unit-level syntax and is signaled after the LFNST index is signaled. Additionally, a restriction of not allowing an LFNST when an ISP is applied to a coding unit is removed. Since the restriction of not allowing LFNST when ISP is applied to the coding unit is removed, LFNST can be applied to all intra prediction blocks. Additionally, both the MTS index and the LFNST index are conditionally signaled at the end at a coding unit level.

[0238] The meanings of the main variables shown in the Table are as follows.

[0239] 1. cbWidth, cbHeight: the width and height of the current coding block

[0240] 2. log2TbWidth, log2TbHeight: The base-2 log value for the width and height of the current transform block may be reduced, reflecting zero-out, to a left-top region in which a different coefficient of zero can exist.

[0241] 3. sps_lfnst_enabled_flag: a flag indicating whether LFNST is enabled or not, if the flag value is 0, it indicates that LFNST is not enabled, and if the flag value is 1, it indicates that LFNST is enabled. It is defined in the Sequence Parameter Set (SPS).

[0242] 4. CuPredMode[chType][x0][y0]: a prediction mode corresponding to the variable chType and position (x0, y0), chType can have values of 0 and 1, where 0 indicates a luma component and 1 indicates a chroma component. The position (x0, y0) indicates a position in the image, and MODE_INTRA (intra prediction) and MODE_INTER (inter prediction) are possible as a value of CuPredMode[chType][x0][y0].

[0243] 5. IntraSubPartitionsSplit[x0][y0]: the contents of position (x0, y0) are the same as No. 4. Indicates which ISP partition at position (x0, y0) is applied, ISP_NO_SPLIT indicates which unit of coding corresponding to position (x0, y0) is not divided into partition blocks.

[0244] 6. intra_mip_flag[x0][y0]: the content of position (x0, y0) is the same as No. 4 above. The intra_mip_flag is a flag that indicates whether a matrix-based intra prediction (MIP) prediction mode is applied or not. If the flag value is 0, it indicates that MIP is not enabled, and if the flag value is 1, it indicates that MIP is enabled.

[0245] 7. cIdx: the value of 0 indicates luma, and the values of 1 and 2 indicate Cb and Cr which are respectively chroma components.

[0246] 8. treeType: indicates single tree and double tree, etc. (SINGLE_TREE: single tree, DUAL_TREE_LUMA: double tree for luma component, DUAL_TREE_CHROMA: double tree for chroma component)

[0247] 9. tu_cbf_cb[x0][y0]: the content of position (x0, y0) is the same as no. 4. Indicates the coded block flag (CBF) for the Cb component. If its value is 0, it means that no non-zero coefficients are present in the corresponding transform unit for the Cb component, and if its value is 1, it indicates that non-zero coefficients are present in the corresponding transform unit for the Cb component. Cb.

[0248] 10. lastSubBlock: Indicates a position in the scanning order of a sub-block (Coefficient Group (CG)) in which the last non-zero coefficient is located. 0 indicates a sub-block in which the DC component is included and, if it is greater than 0, it is not a sub-block in which the DC component is included.

[0249] 11. lastScanPos: Indicates the position where the last significant coefficient is in the scanning order within a sub-block. If a sub-block includes 16 positions, values from 0 to 15 are possible.

[0250] 12. lfnst_idx[ x0 ][ y0 ]: LFNST index syntax element to be parsed. If not parsed, it is inferred as a value of 0. That is, the default value is set to 0, indicating that LFNST is not applied.

[0251] 13. cu_sbt_flag: A flag that indicates whether a sub-block transform (SBT) included in the current VVC standard is applicable. A flag value of 0 indicates that SBT is not applicable and a flag value of 1 indicates that SBT is applied.

[0252] 14. sps_explicit_mts_inter_enabled_flag, sps_explicit_mts_intra_enabled_flag: Flags that indicate whether an explicit MTS is applied to an inter CU and an intra CU, respectively. A flag value of 0 indicates that MTS is not applicable to inter CU or intra CU, and a flag value of 1 indicates that MTS is applicable.

[0253] 15. tu_mts_idx[ x0 ][ y0 ]: An MTS index syntax element to be parsed. When not parsed, this element is inferred as a value of 0. That is, the element is set to a default value of 0, which indicates that DCT-2 is applied horizontally and vertically.

[0254] As shown in Table 4, a plurality of conditions are checked when encoding mts_idx[ x0 ][ y0 ], and tu_mts_idx[ x0 ][ y0 ] is flagged only when lfnst_idx[ x0 ][ y0 ] is equal to 0.

[0255] tu_cbf_luma[ x0 ][ y0 ] is a flag that indicates whether there is a significant coefficient for a luma component.

[0256] According to Table 5, when the width and height of a coding unit for the luma component are 32 or less, mts_idx[ x0 ][ y0 ] is flagged (Max(cbWidth, cbHeight) <= 32 ), that is, whether MTS is applied is determined by the width and height of the encoding unit for the luma component.

[0257] Additionally, according to Table 5, it can be configured to flag lfnst_idx[ x0 ][ y0 ] even in ISP mode (IntraSubPartitionsSplitType != ISP_NO_SPLIT), and the same LFNST index value can be applied to all ISP partition blocks.

[0258] However, mts_idx[ x0 ][ y0 ] can only be signaled in a case other than ISP mode (IntraSubPartitionsSplit[ x0 ][ y0 ] = = ISP_NO_SPLIT).

[0259] As shown in Table 7, checking the value of mts_idx[ x0 ][ y0 ] may be omitted in a process of determining log2ZoTbWidth and log2ZoTbHeight (where log2ZoTbWidth and log2ZoTbHeight respectively denote the base 2 logarithm values of the width and height of a left-top region remaining after performing zero-out).

[0260] According to an example, a sps_mts_enable_flag check condition can be added when determining log2ZoTbWidth and log2ZoTbHeight in the residual encoding.

[0261] A variable LfnstZeroOutSigCoeffFlag in Table 5 is 0 if there is a significant coefficient at a zero-out position when the LFNST is applied, and is 1 otherwise. The LfnstZeroOutSigCoeffFlag variable can be set according to a plurality of conditions shown in Table 7.

[0262] According to an example, a variable LfnstDcOnly in Table 5 is 1 when all last significant coefficients for transform blocks for which a corresponding coded block flag (CBF, which is 1 when there is at least one significant coefficient in a corresponding block, and is 0 otherwise) is 1 are in DC positions (top left positions) and is 0 otherwise. Specifically, the position of the last significant coefficient is checked relative to a luma transform block in a double-tree luma, and the position of the last significant coefficient is checked relative to a transform block for Cb and a transform block to Cr in a double-tree chroma. In a single tree, the position of the last significant coefficient can be checked against the transform blocks for luma, Cb and Cr.

[0263] In Table 5, MtsZeroOutSigCoeffFlag is initially set to 1, and this value can be changed in the residual coding of Table 6. The variable MtsZeroOutSigCoeffFlag is changed from 1 to 0 when there is a significant coefficient in a region to be filled 0s by a zero-out (LastSignificantCoeffX > 15 | | LastSignificantCoeffY > 15 ), in which case the MTS index is not flagged as shown in Table 5.

[0264] As shown in Table 5, when tu_cbf_luma[ x0 ][ y0 ] is 0, the encoding mts_idx[ x0 ][ y0 ] can be omitted. That is, when the CBF value of the luma component is 0, no transform is applied and therefore the MTS index does not need signaling. Therefore, the MTS index encoding can be omitted.

[0265] According to an example, the above technical feature can be implemented in another conditional syntax. For example, after the MTS is performed, a variable indicating whether a significant coefficient exists in a region other than the DC region of the current block can be derived, and when the variable indicates that the significant coefficient exists in the region excluding the DC region, the index from MTS can be flagged. In other words, the existence of the significant coefficient in the region other than the DC region of the current block indicates that the value of tu_cbf_luma[ x0][y0] is 1, and in this case, the MTS index can be signaled.

[0266] The variable may be expressed as MtsDcOnly, and after the variable MtsDcOnly is initially set to 1 at the coding unit level, the value is changed to 0 when it is determined that the significant coefficient is present in the region, except for the region DC of the current block at the residual coding level. When the MtsDcOnly variable is 0, the image information can be configured so that the MTS index is flagged.

[0267] When tu_cbf_luma[ x0 ][ y0 ] is 0, since the residual encoding syntax is not called at the transform unit level of Table 5, the initial value of 1 of the MtsDcOnly variable is maintained. In this case, because the MtsDcOnly variable is not changed to 0, the image information can be configured so that the MTS index is not flagged. In other words, the MTS index is not analyzed and flagged.

[0268] Meanwhile, the decoding apparatus can determine the color index cIdx from the transform coefficient to derive the variable MtsZeroOutSigCoeffFlag from Table 7. The color index cIdx of 0 means a luma component.

[0269] According to an example, since the MTS can be applied only to the luma component of the current block, the decoding apparatus can determine whether the color index is luma by deriving the variable MtsZeroOutSigCoeffFlag to determine whether the color index is luma. MTS must be analyzed.

[0270] The variable MtsZeroOutSigCoeffFlag is a variable that indicates whether zero-out is performed when MTS is applied. Indicates whether the transform coefficient exists in the top left region where the last significant coefficient may exist due to zero-out after performing the MTS, that is, in the region other than the top left region 16 X 16. The variable MtsZeroOutSigCoeffFlag is initially set to 1 at the coding unit level as shown in Table 3 (MtsZeroOutSigCoeffFlag = 1), and when the transform coefficient exists in the region other than the 16 X 16 region, its value can be changed from 1 to 0 at the level region. residual coding as shown in Table 5 (MtsZeroOutSigCoeffFlag = 0). When the value of the MtsZeroOutSigCoeffFlag variable is 0, the MTS index is not flagged.

[0271] As shown in Table 7, at the residual coding level, a non-zero region in which a non-zero transform coefficient may exist may be defined depending on whether the zero-out accompanying the MTS is realized or not, and Even in this case, the color index (cIdx) is 0, the non-zero-out region can be set to the top left 16 X 16 region of the current block.

[0272] Thus, when deriving the variable that determines whether the MTS index is analyzed, it is determined whether the color component is luma or chroma. However, because LFNST can be applied to both the luma component and the chroma component of the current block, the color component is not determined when deriving a variable to determine whether to analyze the LFNST index.

[0273] For example, Table 5 shows a variable LfnstZeroOutSigCoeffFlag that can indicate that zero-out is performed when LFNST is applied. The variable LfnstZeroOutSigCoeffFlag indicates whether there is a significant coefficient in the second region, except in the first region in the upper left corner of the current block. This value is initially set to 1, and when the significant coefficient is present in the second region, the value can be changed to 0. The LFNST index can be analyzed only when the value of the initially defined variable LfnstZeroOutSigCoeffFlag is kept at 1. When determining and derive whether the value of the LfnstZeroOutSigCoeffFlag variable is 1. Since LFNST can be applied to both the luma component and the chroma component of the current block, the color index of the current block is not determined.

[0274] As shown in Table 5, the MTS index is signaled for each coding unit, and mts_idx (MTS index) is signaled only when MtsZeroOutSigCoeffFlag is equal to 1.

[0275] Furthermore, as shown in Table 7, the value of MtsZeroOutCoeffFlag can be determined according to a specific condition (if( ( LastSignificantCoeffX > 15 | | LastSignificantCoeffY > 15 ) && cIdx = = 0 )) at an encoding level residual.

[0276] The value of MtsZeroOutSigCoeffFlag is set to 0 when the x-coordinate (LastSignificantCoeffX) of the last non-zero coefficient is greater than 15 and the y-coordinate (LastSignificantCoeffY) of the last non-zero coefficient is greater than 15. Here, the coordinates x increases from left to right in the transform block, and y coordinates increase from top to bottom in the transform block. The upper left position of the transform block is (0, 0).

[0277] The value of MtsZeroOutSigCoeffFlag is initialized to 1 in Table 5, and is maintained as 1 if the condition present in Table 7 is not satisfied and, therefore, the value of MtsZeroOutSigCoeffFlag is not set to 0.

[0278] When a primary transform applied in the horizontal direction is A and a primary transform applied in the vertical direction is B, a primary transform can be represented by (A, B). In the current VVC standard, in a case of (DST-7, DST-7), (DST-7, DCT-8), (DCT-8, DST-7), and (DCT-8, DCT-8), a transform coefficient is limited to exist only in an upper left 16 x 16 region of the transform block. Therefore, the condition of (LastSignificantCoeffX > 15 | | LastSignificantCoeffY > 15) in Table 7 indicates that the last non-zero coefficient is positioned outside the upper left 16 x 16 region. In Table 7, a variable cIdx denotes a color component and a variable cIdx value of 0 indicates a luma component.

[0279] In the current VVC standard, the MTS index (mts_idx) is parsed after parsing for residual coding. Specifically, Table 5 is a coding unit that is a parsing function for a coding unit, the MTS index is parsed after a transform tree function, and a residual coding parsing function in the transform tree function is invoked. Therefore, the MTS index is analyzed after residual analysis (a residual analysis function illustrated in Table 6 is responsible for analyzing the residual coding), and since the MTS index information is not known from the decoding perspective during residual coding, it may not be impossible to know which primary transform is applied. However, when MTS is applicable and SBT or ISP is applied or when implicit MTS is applied, MTS is applied implicitly and therefore it is possible to know about the primary transform before analyzing the residual encoding.

[0280] The condition illustrated in Table 7 needs to be verified, because the current VVC standard establishes an output restriction of only 16 transform coefficients when a direct transform is applied to 32-length DST-7 or 32-length DCT-8. For example, when the MTS index value is greater than 0 and therefore indicates that an applied primary transform is one of (DST-7, DST-7), (DST-7, DCT-8), (DCT-8 , DST-7), (DCT-8, DCT-8), a non-zero transform coefficient can exist only in the upper left 16 x 16 region of the transform block.

[0281] Thus, when the position of the last non-zero transform coefficient is outside the upper left 16 x 16 region, which corresponds to a case where the MTS index value is 0, the MTS index flag may be omitted as per shown in Table 5. However, even if the position of the last nonzero transform coefficient is within the upper left 16 x 16 region, a nonzero coefficient may exist outside the upper left 16 x 16 region. MTS index can be flagged as 0 even if the MTS index value is 0, which is described in detail below.

[0282] When the primary transform is (DCT-2, DCT-2), the position of the last non-zero coefficient exists in the upper left region 16 x 16 and a non-zero transform coefficient can also exist outside the upper left region 16 x 16, because in the scan order within the transform block, a region outside the upper left 16 x 16 region, that is, a region other than the upper left 16 x 16 region, can be scanned, and then the region top left 16 x 16 region can be scanned or the top left 16 x 16 region can be scanned and then the region outside the top left 16 x 16 region can be scanned.

[0283] Figure 15 illustrates a scan of a 32 x 32 transform block in accordance with an embodiment of the present disclosure, which specifically shows that the 32 x 32 transform block is divided into 4 x 4 coefficient groups (CGs ) and digitized. In the present disclosure, the CGs divided to be scanned are referred to as “scanning sub-blocks”.

[0284] A number indicated for each CG denotes a forward scanning order, and the CGs can be scanned by the decoding apparatus according to a reverse scanning order starting from the position where the last non-zero transform coefficient exists. In Figure 15, it can be assumed that the last non-zero transform coefficient exists in CG 25 and CG 25 exists in the upper left 16 x 16 region.

[0285] As shown in Figure 15, when the last non-zero transform coefficient exists in CG 25, since the decoding apparatus scans the CGs according to the reverse scanning order of the CG in which the last transform coefficient non-zero exists, the decoding apparatus scans the CGs in an order of 25, 24, 23, ..., 3, 2, 1 based on the numbers indicated in Figure 15. As the CGs 24, 23, 22, 21 , 20, 17, 16, 15 and 11 are positioned outside the top left 16 x 16 region, it is impossible to know if there is a non-zero coefficient just in the top left 16 x 16 region just by checking whether LastSignificantCoeffX and LastSignificantCoeffY correspond to the top left region 16 x 16, as shown in Table 6.

[0286] Therefore, when performing analysis for residual coding, if a corresponding 4 x 4 coefficient group is checked to belong to the upper left 16 x 16 region whenever a non-zero transform coefficient is checked, the value of MtsZeroOutSigCoeffFlag can be set to 0 only in the case where there is a non-zero coefficient outside the upper left 16 x 16 region. In this case, a residual encoding syntax is shown in the following table. Table 8

[0287] As shown in Table 8, whenever a non-zero transform coefficient is found, if the non-zero transform coefficient is positioned in the left-top 16 x 16 region (if( ( xC > 15 | | yC > 15 ) && cIdx = = 0 )) can be checked by thus setting the MtsZeroOutSigCoeffFlag value to 0. Here, this condition is checked when the value of sig_coeff_flag[ xC ][ yC ], which is the flag information that indicates whether the transform coefficient exists, is 1 ( if( sig_coeff_flag[ xC ][ yC ] )), where xC and yC respectively denote an x-coordinate and a y-coordinate in sample units within the transform block. The top left position of the transform block is (0, 0).

[0288] Table 8 includes the condition check presented in Table 7 and an update of MtsZeroOutSigCoeffFlag (if( ( LastSignificantCoeffX > 15 | | LastSignificantCoeffY > 15 ) && cIdx = = 0 ) MtsZeroOutSigCoeffFlag = 0). If the value of sig_coeff_flag[ xC ][ yC ] for the last non-zero transform coefficient is inferred to be 1, the condition check and update of MtsZeroOutSigCoeffFlag can be removed from Table 8.

[0289] In summary, when signaling the MTS index in Table 5 via the syntax configuration shown in Table 8, the MTS index is only signaled when a non-zero transform coefficient exists in a top 16 x 16 region to the left of a block luma transform regardless of which primary transform is applied. When the MTS index is unsigned, the MTS index value is inferred as 0, that is, (DCT-2, DCT-2) is applied.

[0290] As described above, in the following three cases, an applied primary transform may be known before the MTS index is signaled.

[0291] 1) Where the sub-block transform (SBT) is applied

[0292] 2) Where intra sub-partition (ISP) is applied

[0293] 3) Where implicit MTS is applied

[0294] In case (1), since the MTS index is configured to be signaled only when the value of cu_sbt_flag indicating whether SBT is applied in Table 5 is 0, that is, since the MTS index is signaled only when the SBT is not applied, the case of application of the SBT is irrelevant for the modification of Table 7.

[0295] In case (2), since the MTS index is signaled only when the ISP is not applied in Table 4 (a condition if IntraSubPartitionsSplit[ x0 ][ y0 ] = = ISP_NO_SPLIT is checked when signaling the MTS index in Table 5), the case in which the ISP is applied is also irrelevant to the modification of Table 8.

[0296] In case (3), since the MTS index is signaled only when an explicit MTS is enabled in Table 5, the case in which the implicit MTS is applied is also irrelevant for the modification of Table 7. That is , since the MTS index is signaled only when the value of sps_explicit_mts_intra_enabled_flag is 1 in an MTS (intra MTS) applied to a residual block generated by the intra prediction and the value of sps_explicit_mts_inter_enabled_flag is 1 in an MTS (inter MTS) applied to a residual block generated by inter prediction, the modification of Table 8 does not affect the case in which the implicit MTS is applied.

[0297] According to another example, as shown in the following table, it can be checked whether there is a non-zero coefficient outside the left top 16 x 16 region by one unit of a CG. Table 9

[0298] In Table 9, xS and yS denote an x-coordinate position and a y-coordinate position in each CG unit within the current transform block and need to be converted to coordinates in sample units to verify that the transform coefficient is positioned outside the top left 16 x 16 region. That is, xS and yS are converted to coordinates in sample units as in ( xS << log2SbW ) and ( yS << log2SbH ). Here, log2SbW and log2SbH respectively denote the base-2 logarithm values of the width and height of a corresponding CG, the x-coordinates increase from left to right in the transform block and the y-coordinates increase from top to bottom. The coordinates of the top left position of the transform block are (0, 0).

[0299] As shown in Table 9, when scanning a unit of a CG, when there is a non-zero transform coefficient within each CG (when the value of coded_sub_block_flag[ xS ][ yS ] is 1) and the CG is identified to be positioned outside the top left 16 x 16 region of the transform block ( ( xS << log2SbW ) > 15 | | ( yS << log2SbH ) > 15 ) ), the value of MtsZeroOutSigCoeffFlag is set to 0.

[0300] As shown in Table 5, because the value of the MtsZeroOutSigCoeffFlag variable is initialized to 1, the value of MtsZeroOutSigCoeffFlag is kept at 1 unless the value of MtsZeroOutSigCoeffFlag is set to 0. When the value of coded_sub_block_flag[xS][ yS] for a CG to which the last non-zero transform coefficient belongs is inferred as 1, the condition checking part in Table 7 and the update of MtsZeroOutSigCoeffFlag (if ( ( LastSignificantCoeffX > 15 | | LastSignificantCoeffY ) > 15 ) && cIdx = = 0 ) MtsZeroOutSigCoeffFlag = 0) can be removed from Table 9.

[0301] The following drawings are provided to describe specific examples of the present disclosure. Since device-specific terms or specific terms for signals/messages/fields illustrated in the drawings are provided for illustration, the technical features of the present disclosure are not limited to the specific terms used in the following drawings.

[0302] Figure 16 is a flowchart illustrating an operation of a video decoding apparatus in accordance with an embodiment of the present disclosure.

[0303] Each process disclosed in Figure 16 is based on some of the details described with reference to Figure 4 to Figure 15. Therefore, a description of specific details overlapping with those described with reference to Figure 3 to Figure 15 will be omitted or will be done schematically.

[0304] The decoding apparatus 300 in accordance with one embodiment may receive a bit stream including residual information and may derive residual information, e.g., quantized transform coefficients, for a current block, i.e., a transform block to be transformed, double flow (S1610).

[0305] Specifically, the decoding apparatus 300 may decode information about quantized transform coefficients for a current block of the bit stream and may derive quantized transform coefficients for a target block based on information about the quantized transform coefficients for the block. current. Information about the quantized transform coefficients for the target block may be included in a sequence parameter set (SPS) or a slice header and may include at least one information about whether an RST is applied, information about a reduced factor, information about a minimum transform size to apply an RST, information about a maximum transform size to apply an RST, an inverse RST size, and information about a transform index indicating any of the transform kernel matrices included in a set of transformed.

[0306] The decoding apparatus 300 can derive the position of a last significant coefficient in the current block and transform coefficients for the current block based on the residual information (S1620). The decoding apparatus 300 may derive the transform coefficients by dequantizing the quantized transform coefficients of the current block.

[0307] The derived transform coefficients can be arranged two-dimensionally in the current block and the decoding apparatus can derive information about non-zero data, that is, a significant non-zero coefficient, in the current block through this residual encoding. That is, the decoding apparatus can identify the last position information in the non-zero significant coefficient in the current block.

[0308] The transform coefficients derived based on the residual information in S1620 may be the dequantized transform coefficients as described above or may be the quantized transform coefficients. That is, transform coefficients only need to be given to identify non-zero data in the current block and the position of the significant coefficient independently of quantization.

[0309] The decoding apparatus may derive modified transform coefficients by applying an LFNST to the transform coefficients or may not perform the LFNST.

[0310] The decoding apparatus may derive residual samples by performing the inverse primary transform of the transform coefficients or the modified transform coefficients. The decoding apparatus may use general DCT-2 as a transform core or may apply the previous MTS to the inverse primary transform.

[0311] MTS may be executed implicitly or may be performed based on explicit signaling of an MTS index.

[0312] The decoding apparatus may check predetermined conditions to analyze the MTS index. According to one example, the decoding apparatus may analyze an MTS index based on the significant coefficient not being present in a second region other than a first left top region of the current block (S1630).

[0313] The MTS index can be analyzed by deriving flag information indicating whether the significant coefficient exists in the second region, which flag information can be derived by determining whether the significant coefficient exists in the second region by one unit of a sub-block of scanning a significant coefficient.

[0314] The decoding apparatus may perform the inverse primary transform on transform coefficients in the first left top region of the current block to be transformed. That is, the second region different from the first top region to the left of the current block is zeroed and therefore does not include transform coefficient.

[0315] According to an example, when MTS is applied, the first region may be a top 16 x 16 region to the left of the current block, in which case the second region may be a region other than the top 16 x region left 16 region.

[0316] The scanning sub-block may be a 4 x 4 block and may be scanned according to a reverse diagonal scanning direction from the position of the last significant coefficient in the current block, as shown in Figure 15.

[0317] To analyze the MTS index after determining whether there is a significant coefficient in the zero region, the decoding apparatus may derive flag information indicating whether there is a significant coefficient in the second region and may analyze the MTS index based on the MTS index information. flare gun.

[0318] The flag information can be a MtsZeroOutSigCoeffFlag variable, and whether there is a significant coefficient in the second region can be determined by the unit of the significant coefficient scanning sub-block.

[0319] When a flag indicating whether there is a significant coefficient in a scanning sub-block (coded_sub_block_flag or sb_coded_flag) illustrated in Table 9 is equal to a value of 1 and a significant coefficient existing in the scanning sub-block is positioned in the second region ((( xS << log2SbW ) > 15 | | ( yS << log2SbH ) > 15 )), the variable MtsZeroOutSigCoeffFlag can indicate that the significant coefficient exists in the second region.

[0320] Alternatively, the variable MtsZeroOutSigCoeffFlag can be derived by checking whether the 4 x 4 scanning sub-block belongs to the first region whenever scanning the transform coefficients as in Table 8. That is, when a flag indicating whether a significant coefficient exists in a scanning sub-block (sig_coeff_flag) is equal to a value of 1 and a significant coefficient existing in the scanning sub-block is positioned in the second region (if( ( xC > 15 | | yC > 15 )), the variable MtsZeroOutSigCoeffFlag may indicate that the significant coefficient exists in the second region.

[0321] Alternatively, when a flag indicating whether there is a significant coefficient in a scan sub-block is equal to a value of 1 and the scan sub-block is positioned in the second region, the variable MtsZeroOutSigCoeffFlag may indicate that there is a coefficient significant in the second region.

[0322] The variable MtsZeroOutSigCoeffFlag can be initially set to 1, can be kept as 1 when the significant coefficient is not positioned in the second region, and can be changed to 0 when the significant coefficient is positioned in the second region.

[0323] In summary, the decoding apparatus can analyze the MTS index based on the flag information indicating that there is no significant coefficient in the second region and when the value of the MtsZeroOutSigCoeffFlag variable, initially set to 1, is maintained, the decoding index MTS can be analyzed.

[0324] The decoding apparatus may derive residual samples for the current block by applying a transform kernel derived based on the MTS index to transform coefficients in the first region (S1640).

[0325] Subsequently, the decoding apparatus 300 may generate reconstructed samples based on the residual samples for the current block and predication samples for the current block.

[0326] The following drawings are provided to describe specific examples of the present disclosure. Since device-specific terms or specific terms for signals/messages/fields illustrated in the drawings are provided for illustration, the technical features of the present disclosure are not limited to the specific terms used in the following drawings.

[0327] Figure 17 is a flowchart illustrating an operation of a video coding apparatus in accordance with an embodiment of the present disclosure.

[0328] Each process disclosed in Figure 16 is based on some of the details described with reference to Figure 4 to Figure 15. Therefore, a description of specific details overlapping with those described with reference to Figure 2 and Figure 4 to Figure 15 will be omitted or will be done schematically.

[0329] The coding apparatus 100 in accordance with one embodiment may derive prediction samples based on an intra prediction mode applied to a current block (S1710).

[0330] The coding apparatus 100 in accordance with one embodiment may derive residual samples for the current block based on the prediction samples (S1720).

[0331] The coding apparatus 100 in accordance with one embodiment may derive transform coefficients for the current block by applying an MIS to the residual samples (S1730).

[0332] According to an example, the coding apparatus may apply the previous MTS to the primary transform or may use general DCT-2 as a transform core.

[0333] MTS may be executed implicitly or may be performed based on explicit signaling of an MTS index.

[0334] The coding apparatus can determine whether to perform MTS for the primary transform and can derive transform coefficients by applying DCT-8 or DST-7 to the residual samples when MTS is determined to be performed.

[0335] According to one example, when MTS is applied to the primary transform, the coding apparatus may zero out a second region other than a first top region to the left of the current block (S1740).

[0336] According to an example, the first region may be a left-top 16 x 16 region of the current block, in which case the second region may be a region other than the left-top 16 x 16 region.

[0337] Due to this zero-out, it is possible to reduce the amount of computation required to perform the entire transform process and reduce the amount of operation required for the entire transform process, thus reducing the energy consumption required to perform the transform . Furthermore, the latency involved in the transformation process can be reduced, thus increasing the efficiency of image coding.

[0338] The coding apparatus may derive modified transform coefficients by further applying an LFNST to the transform coefficients derived after the primary transform.

[0339] The coding apparatus may derive residual information based on the transform coefficients or modified transform coefficients for the current block (S1750).

[0340] That is, the coding apparatus can generate residual information including information about quantized transform coefficients. The residual information may include an information/syntax element related to the previous transform. The encoding apparatus can encode image/video information including residual information and can output the encoded image/video information in the form of a bit stream.

[0341] Specifically, the coding apparatus 200 can generate information about the quantized transform coefficients and can encode the information generated about the quantized transform coefficients.

[0342] Additionally, the encoding apparatus may configure image information so that an MTS index indicating an MTS transform kernel is analyzed based on the existence of the significant coefficient in the second region (S1760).

[0343] Additionally, the coding apparatus may construct image information to derive flag information indicating whether there is a significant coefficient in the second region per unit of a scan sub-block of a significant coefficient.

[0344] That is, the encoding apparatus can construct the image information so that the image information illustrated in Table 8 or Table 9 can be analyzed in a decoding apparatus.

[0345] According to an example, the scanning sub-block may be a 4 x 4 block and may be scanned according to an inverse diagonal scanning direction from the position of the last significant coefficient in the current block also in the apparatus decoding as shown in Figure 15.

[0346] The flag information can be a MtsZeroOutSigCoeffFlag variable, and whether there is a significant coefficient in the second region can be determined by the unit of the significant coefficient scanning sub-block.

[0347] When a flag indicating whether there is a significant coefficient in a scanning sub-block (coded_sub_block_flag) illustrated in Table 9 is equal to a value of 1 and a significant coefficient existing in the scanning sub-block is positioned in the second region ( ( ( xS << log2SbW ) > 15 | | ( yS << log2SbH ) > 15 )), the variable MtsZeroOutSigCoeffFlag can indicate that the significant coefficient exists in the second region.

[0348] Alternatively, the variable MtsZeroOutSigCoeffFlag can be derived by checking whether the 4 x 4 scanning sub-block belongs to the first region whenever scanning the transform coefficients as in Table 8. That is, when a flag indicating whether a significant coefficient exists in a scanning sub-block (sig_coeff_flag) is equal to a value of 1 and a significant coefficient existing in the scanning sub-block is positioned in the second region (if( ( xC > 15 | | yC > 15 )), the variable MtsZeroOutSigCoeffFlag may indicate that the significant coefficient exists in the second region.

[0349] Alternatively, when a flag indicating whether there is a significant coefficient in a scan sub-block is equal to a value of 1 and the scan sub-block is positioned in the second region, the variable MtsZeroOutSigCoeffFlag may indicate that there is a coefficient significant in the second region.

[0350] The variable MtsZeroOutSigCoeffFlag can be initially set to 1, can be kept as 1 when the significant coefficient is not positioned in the second region, and can be changed to 0 when the significant coefficient is positioned in the second region.

[0351] The encoding apparatus may encode residual information derived based on the transform coefficients and the MTS index based on the signaling information indicating that there is no significant coefficient in the second region, and then may output them.

[0352] In the present disclosure, at least one of quantization/dequantization and/or transform/inverse transform may be omitted. When quantization/dequantization is omitted, a quantified transform coefficient can be termed as a transform coefficient. When the transform/inverse transform is omitted, the transform coefficient may be termed as a coefficient or a residual coefficient, or may be termed as a transform coefficient for consistency of expression.

[0353] Furthermore, in the present disclosure, a quantified transform coefficient and a transform coefficient may be referred to as a transform coefficient and a scaled transform coefficient, respectively. In this case, the residual information may include information about a transform coefficient(s) and the information about the transform coefficient(s) may be signaled using a residual coding syntax. Transform coefficients can be derived based on residual information (or information about the transform coefficient(s), and scaled transform coefficients can be derived by inversely transforming (scaling) the transform coefficients. Residual samples can be derived based on the inverse transform (transform) of the scaled transform coefficients. These details may also be applied/expressed elsewhere in this disclosure.

[0354] In the embodiments described above, the methods are explained based on flowcharts through a series of steps or blocks, but the present disclosure is not limited to the order of the steps and a given step may be performed in a different order or step than described above, or concomitantly with another step. Furthermore, it may be understood by a person skilled in the art that the steps shown in a flowchart are not exclusive and that another step may be incorporated or one or more steps of the flowchart may be removed without affecting the scope of the present disclosure.

[0355] The methods described above in accordance with the present disclosure may be implemented as a form of software and an encoding apparatus and/or decoding apparatus in accordance with the disclosure may be included in a device for image processing, such as a TV, a computer, a smartphone, a set-top box, a display device or the like.

[0356] When embodiments in the present disclosure are incorporated by software, the methods described above may be incorporated as modules (processes, functions, or the like) to perform the functions described above. Modules can be stored in memory and can be executed by a processor. Memory can be inside or outside the processor and can be connected to the processor in several well-known ways. The processor may include an application-specific integrated circuit (ASIC), another chipset, logic circuit, and/or a data processing device. The memory may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium and/or other storage device. That is, the embodiments described in the present disclosure can be incorporated and executed on a processor, a microprocessor, a controller, or a chip. For example, the function units shown in each drawing may be incorporated and executed in a computer, a processor, a microprocessor, a controller, or a chip.

[0357] Furthermore, the decoding apparatus and the encoding apparatus to which the present disclosure is applied may be included in a multimedia transmission transceiver, a mobile communications terminal, a home theater video device, a digital cinema video camera, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile transmission device, a storage medium, a video camera, a video on demand (VoD) service delivery device, an over the top (OTT) video device, an Internet device streaming service delivery device, a three-dimensional (3D) video device, a telephony and a medical video device, and can be used to process a video signal or a data signal. For example, the over the top (OTT) video device may include a game console, a Blu-ray player, an Internet-enabled TV, a home theater system, a smartphone, a Tablet PC, a video recorder digital (DVR) and similar.

[0358] Furthermore, the processing method to which the present disclosure is applied may be produced in the form of a program executed by a computer and stored on a computer-readable recording medium. Multimedia data with a data structure in accordance with the present disclosure may also be stored on a computer-readable recording medium. Computer-readable recording medium includes all types of storage devices and distributed storage devices on which computer-readable data is stored. Computer-readable recording media may include, for example, a Blu-ray Disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk and an optical data storage device. Furthermore, the computer-readable recording medium includes embedded media in the form of a carrier wave (e.g., Internet transmission). Furthermore, a bit stream generated by the encoding method may be stored on a computer-readable recording medium or transmitted over a wired or wireless communication network. Additionally, embodiments of the present disclosure may be embodied as a computer program product by program codes and the program codes may be executed on a computer by embodiments of the present disclosure. Program codes can be stored on a computer-readable medium.

[0359] Figure 18 illustrates the structure of a content streaming system to which the present disclosure is applied.

[0360] Furthermore, the content streaming system to which the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media store, a user equipment, and a device multimedia input.

[0361] The encoding server functions to compress the input content of multimedia input devices, such as the smartphone, camera, camcorder, and the like, into digital data to generate a bit stream and transmit it to the streaming server. As another example, in a case where the multimedia input device such as smart phone, camera, video camera or the like directly outputs a bit stream, the encoding server may be omitted. The bitstream may be generated by a coding method or a bitstream generation method to which the present disclosure is applied. And the streaming server can store the bitstream temporarily during a process to transmit or receive the bitstream.

[0362] The streaming server transmits multimedia data to the user's equipment based on a user's request through the web server, which functions as an instrument that informs the user which service exists. When the user requests a service that the user wants, the web server transfers the request to the streaming server, and the streaming server transmits multimedia data to the user. In this sense, the content streaming system may include a separate control server, and in this case, the control server functions to control commands/responses between respective equipment in the content streaming system.

[0363] The streaming server may receive content from the media store and/or the encoding server. For example, if the content is received from the encoding server, the content can be received in real time. In this case, the streaming server can store the bitstream for a predetermined period of time to provide the streaming service smoothly.

[0364] For example, user equipment may include a cell phone, a smartphone, a laptop, a digital streaming terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation, a PC slate , a tablet PC, an ultrabook, a wearable device (e.g., a watch-type terminal (smart watch), a glass-type terminal (smart glass), a head-mounted display (HMD)), a digital TV, a desktop computer , digital signage or similar. Each of the servers of the content streaming system can be operated as a distributed server, and in this case, the data received by each server can be processed in a distributed manner.

[0365] The claims disclosed herein may be combined in various ways. For example, the technical features of the method claims of the present disclosure may be combined to be implemented or performed in an apparatus and the technical features of the apparatus claims may be combined to be implemented or performed in a method. Furthermore, the technical features of the method claims and apparatus claims may be combined to be implemented or carried out in an apparatus, and the technical features of the method claims and apparatus claims may be combined to be implemented or carried out in a method. .

Claims (10)

1. Image decoding device, CHARACTERIZED by the fact that it comprises: a memory; and at least one processor connected to the memory, the at least one processor configured to: obtain residual information from a bit stream; derive transform coefficients for a current block based on the residual information, and derive residual samples for the current block by applying an inverse primary transform to the transform coefficients based on an MTS index, where if a significant coefficient is present in a sub- scan block is derived by scanning the scan sub-block in a predefined scan sub-block unit according to an inverse diagonal scan order, and wherein the signaling information indicating whether the significant coefficient is present in a second region different from a first region within the current block is derived based on (i) whether the significant coefficient is present in the scan sub-block, (ii) whether the scan sub-block belongs to the second region, and (iii ) if a color index of the current block is 0, the first region being an upper left 16x16 region within the current block, and wherein the MTS index is analyzed based on signaling information indicating that the significant coefficient is not present in the second region. 2. Image decoding apparatus according to claim 1, CHARACTERIZED by the fact that the MTS index is inferred as 0 when the MTS index is not analyzed. 3. Image decoding apparatus according to claim 1, CHARACTERIZED by the fact that if the significant coefficient is present in the scanning sub-block it is derived based on a flag analyzed from the bit stream, the flag indicating whether the significant coefficient is present in the scan sub-block. 4. Image decoding apparatus according to claim 1, CHARACTERIZED by the fact that the flag information is initially set to 1, and wherein, when the significant coefficient is present in the second region, the flag information is changed to 0. 5. Image decoding apparatus according to claim 1, CHARACTERIZED by the fact that the scanning sub-block is a 4x4 block, and wherein the scanning sub-block is scanned according to the diagonal scanning order inverse from a last scanning sub-block including a last significant coefficient in the current block. 6. Image coding device, CHARACTERIZED by the fact that it comprises: a memory; and at least one processor connected to the memory, the at least one processor configured to: derive prediction samples for a current block; derive residual samples for the current block based on the prediction samples; derive transform coefficients for the current block by applying a primary transform to the residual samples; derive residual information based on the transform coefficient of a first region within the current block, the first region being a top left 16x16 region within the current block, and construct image information to signal an MTS index indicating a primary transform kernel based on a significant coefficient that is not present in a second region other than the first region within the current block, wherein a flag indicating whether the significant coefficient is present in a scan sub-block is encoded by the scan of the scan sub-block in a predefined scan sub-block unit according to a reverse diagonal scan order, wherein the signaling information indicating whether the significant coefficient is present in the second region is derived based on (i) whether the significant coefficient is present present in the scan sub-block, (ii) if the scan sub-block belongs to the second region, and (iii) if a color index of the current block is 0, and where the MTS index is encoded based on the information signaling indicating that the significant coefficient is not present in the second region. 7. Image coding apparatus according to claim 6, CHARACTERIZED by the fact that the MTS index is inferred as 0 when the MTS index is not encoded. 8. Image coding apparatus according to claim 6, CHARACTERIZED by the fact that the flag information is initially set to 1, and wherein, when the significant coefficient is present in the second region, the flag information is changed to 0. 9. Image coding apparatus according to claim 6, CHARACTERIZED by the fact that the scanning sub-block is a 4x4 block, and wherein the scanning sub-block is scanned according to the diagonal scanning order inverse from a last scanning sub-block including a last significant coefficient in the current block. 10. Apparatus for transmitting data for image information, CHARACTERIZED by the fact that it comprises: at least one processor configured to obtain a bit stream for the image information, wherein the bit stream is generated based on sample derivation of prediction for a current block, in deriving residual samples for the current block based on the prediction samples, in deriving transform coefficients for the current block by applying a primary transform to the residual samples, deriving residual information based on the coefficient of transform of a first region within the current block, the first region being a top-left 16x16 region within the current block, and construct the image information to signal an MTS index to indicate a primary transform kernel based on a significant coefficient that is not present in a second region different from the first region within the current block; and a transmitter configured to transmit the data comprising the bit stream, wherein a flag indicating whether the significant coefficient is present in a scan sub-block is encoded by scanning the scan sub-block into a sub-block unit predefined scan pattern according to an inverse diagonal scan order, wherein the signaling information indicating whether the significant coefficient is present in the second region is derived based on (i) whether the significant coefficient is present in the scan sub-block , (ii) whether the scanning sub-block belongs to the second region, and (iii) whether a color index of the current block is 0, and wherein the MTS index is encoded based on signaling information indicating that the significant coefficient is not present in the second region.