WO2018026028A1

WO2018026028A1 - Method and apparatus for encoding/decoding residual signal by using sub-coefficient group

Info

Publication number: WO2018026028A1
Application number: PCT/KR2016/008522
Authority: WO
Inventors: 이재호
Original assignee: 엘지전자(주)
Priority date: 2016-08-02
Filing date: 2016-08-02
Publication date: 2018-02-08

Abstract

The present invention provides a method for encoding a video signal, the method comprising the steps of: determining whether a coefficient group including a non-zero coefficient exists among multiple coefficient groups within a conversion block; when it is determined that the coefficient group including the non-zero coefficient exists, dividing the coefficient group into multiple sub-coefficient groups; determining, for each of the multiple sub-coefficient groups, whether the non-zero coefficient exists in the corresponding sub-coefficient group; and when it is determined that a sub-coefficient group including the non-zero coefficient exists, encoding the non-zero coefficient only for the sub-coefficient group.

Description

Method and apparatus for encoding and decoding residual signal using sub coefficient group

The present invention relates to a method and apparatus for encoding / decoding a video signal, and more particularly, to a technique for encoding and decoding a residual signal using a sub coefficient group.

Compression coding refers to a series of signal processing techniques for transmitting digitized information through a communication line or for storing in a form suitable for a storage medium. Media such as an image, an image, an audio, and the like may be a target of compression encoding. In particular, a technique of performing compression encoding on an image is called video image compression.

Next-generation video content will be characterized by high spatial resolution, high frame rate and high dimensionality of scene representation. Processing such content would result in a tremendous increase in terms of memory storage, memory access rate, and processing power.

Accordingly, there is a need to design coding tools for more efficiently processing next generation video content.

The present invention proposes a method for more efficiently processing a complex image.

The present invention intends to propose a new residual signal encoding and decoding method in consideration of the characteristics of the residual signal.

The present invention proposes a method of dividing and coding one coefficient group (CG) into sub coefficient groups (sub-CG).

The present invention proposes a method for implicitly performing coding of a sub coefficient group (sub-CG).

In order to solve the above technical problem,

The present invention provides a method of designing a coding tool for high efficiency compression.

The present invention provides a method for more efficiently processing a complex image.

The present invention provides a novel residual signal encoding and decoding method in consideration of the characteristics of the residual signal.

The present invention provides a method of dividing and coding one coefficient group (CG) into sub coefficient groups (sub-CG).

The present invention provides a method for implicitly performing coding of a sub coefficient group (sub-CG).

The present invention provides a method of coding the presence or absence of nonzero coefficients in sub-block units in a transform unit (TU).

According to the present invention, a new residual signal encoding and decoding method is proposed in consideration of the characteristics of the residual signal, so that a complex image can be processed more efficiently.

In addition, according to the present invention, unnecessary coding bits can be reduced and coding can be performed with fewer bits by dividing one coefficient group (CG) into sub coefficient groups (sub-CG).

According to the present invention, coding bits can be saved by implicitly performing coding of a sub coefficient group (sub-CG).

1 is a schematic block diagram of an encoder in which encoding of a video signal is performed as an embodiment to which the present invention is applied.

2 is a schematic block diagram of a decoder in which decoding of a video signal is performed as an embodiment to which the present invention is applied.

3 is a diagram for describing a division structure of a coding unit according to an embodiment to which the present invention is applied.

FIG. 4 is an embodiment to which the present invention is applied and shows syntax definition of a flag indicating whether a nonzero coefficient exists in a coefficient group and a flag indicating whether a coefficient value is zero.

FIG. 5 is a diagram for describing an encoding method when all coefficients in a coefficient group are 0 according to an embodiment to which the present invention is applied.

FIG. 6 is a diagram for describing an encoding method when a non-zero coefficient exists among all coefficients in a coefficient group according to an embodiment to which the present invention is applied.

FIG. 7 illustrates a syntax definition of a flag indicating whether a non-zero coefficient exists in a sub coefficient group (sub-CG) according to an embodiment to which the present invention is applied.

8 to 11 illustrate embodiments to which the present invention may be applied, and show examples of a sub coefficient group (sub-CG) in which a non-zero coefficient exists among four sub coefficient groups (sub-CG). A diagram for describing a method of encoding according to the number.

FIG. 12 is a diagram for describing the number of coded bits according to the number of sub coefficient groups (sub-CGs) in which a non-zero coefficient exists as an embodiment to which the present invention is applied.

FIG. 13 is a diagram for describing a method of implicitly performing coding of a sub coefficient group (sub-CG) as an embodiment to which the present invention is applied.

14 is a diagram for describing a method of deriving a flag indicating whether a non-zero coefficient exists in a sub coefficient group (sub-CG) according to an embodiment to which the present invention is applied.

FIG. 15 is a diagram for describing a method of implicitly performing coding of a coefficient group including a last coefficient as another embodiment to which the present invention is applied.

FIG. 16 is a flowchart illustrating a method of encoding one coefficient group into a plurality of sub coefficient groups by encoding according to an embodiment to which the present invention is applied.

17 is a flowchart illustrating a method of decoding a video signal encoded using a plurality of sub coefficient groups as an embodiment to which the present invention is applied.

The present invention provides a method of encoding a video signal, the method comprising: checking whether a non-zero coefficient exists in a coefficient group for a plurality of coefficient groups in a transform block; Dividing the coefficient group into a plurality of sub coefficient groups when there is a coefficient group including the nonzero coefficient as a result of the checking; Checking whether a non-zero coefficient exists for each of the plurality of sub coefficient groups; And encoding the non-zero coefficient only for the sub coefficient group when the sub coefficient group including the non-zero coefficient exists as a result of the checking. To provide.

In the present invention, the method may further include setting a non-zero coefficient flag indicating whether a non-zero coefficient exists in the coefficient group according to the first check result.

In the present invention, the method may further include setting a sub non-zero coefficient flag indicating whether a non-zero coefficient exists in the sub coefficient group according to the second check result. .

In the present invention, non-zero coefficients for the sub coefficient group are encoded using a coefficient value flag.

In the present invention, coding bits are different according to the number of sub coefficient groups in which a non-zero coefficient exists among the plurality of sub coefficient groups.

In the present invention, in the case of the coefficient block including the last non-zero coefficient, a sub non-zero coefficient flag is derived with a value of 1, and the sub non-zero coefficient The flag (sub non-zero coefficient flag) is characterized by indicating whether there is a non-zero coefficient in the sub coefficient group.

In the present invention, a non-zero coefficient exists in the coefficient group, and a non-zero coefficient in the first three sub coefficient groups in the scanning order. If no coefficient exists, a sub non-zero coefficient flag for the last sub coefficient group is derived with a value of 1, and the sub non-zero coefficient flag is derived. zero coefficient flag) is characterized by indicating whether a non-zero coefficient exists in the sub coefficient group.

In the present invention, the method may further include encoding position information of a last non-zero coefficient in the transform block.

The present invention provides a method of decoding a video signal, the method comprising: receiving a sub non-zero coefficient flag for each sub coefficient group in a transform block from the video signal, wherein the sub non-zero coefficient The flag indicates whether a nonzero coefficient exists in the sub coefficient group; Obtaining a nonzero coefficient present in a sub coefficient group based on the sub nonzero coefficient flag; And performing an inverse transform on the non-zero coefficients.

In the present invention, the video signal is characterized by being encoded with a different number of bits according to the number of sub coefficient groups in which the non-zero coefficient exists.

In the present invention, the non-zero coefficient is identified by a coefficient value flag.

The present invention relates to a device for encoding a video signal, to determine whether a non-zero coefficient exists in a coefficient group for a plurality of coefficient groups in a transform block, and If there is a coefficient group including the nonzero coefficient as a result of the checking, the coefficient group is divided into a plurality of sub coefficient groups, and whether the nonzero coefficient exists for each of the plurality of sub coefficient groups. And a residual signal encoding unit for encoding the non-zero coefficient only for the sub coefficient group when the sub coefficient group including the non-zero coefficient exists as a result of the checking. It provides a device characterized in that.

An apparatus for decoding a video signal, the apparatus comprising: an entropy decoding unit for receiving a sub non-zero coefficient flag for each sub coefficient group in a transform block from the video signal; And an inverse transform unit for obtaining a nonzero coefficient existing in the sub coefficient group based on the sub nonzero coefficient flag and performing an inverse transform on the nonzero coefficient, wherein the sub nonzero coefficient flag is a sub coefficient group. An apparatus is provided that indicates whether a nonzero coefficient is present in a channel.

Hereinafter, the configuration and operation of the embodiments of the present invention with reference to the accompanying drawings, the configuration and operation of the present invention described by the drawings will be described as one embodiment, whereby the technical spirit of the present invention And its core composition and operation are not limited.

In addition, the terminology used in the present invention was selected as a general term widely used as possible now, in a specific case will be described using terms arbitrarily selected by the applicant. In such a case, since the meaning is clearly described in the detailed description of the part, it should not be interpreted simply by the name of the term used in the description of the present invention, and it should be understood that the meaning of the term should be interpreted. .

In addition, terms used in the present invention may be replaced for more appropriate interpretation when there are general terms selected to describe the invention or other terms having similar meanings. For example, signals, data, samples, pictures, frames, blocks, etc. may be appropriately replaced and interpreted in each coding process. In addition, partitioning, decomposition, splitting, and division may be appropriately replaced and interpreted in each coding process.

Referring to FIG. 1, the encoder 100 may include an image splitter 110, a transformer 120, a quantizer 130, an inverse quantizer 140, an inverse transformer 150, a filter 160, and a decoder. It may include a decoded picture buffer (DPB) 170, an inter predictor 180, an intra predictor 185, and an entropy encoder 190.

The image divider 110 may divide an input image (or a picture or a frame) input to the encoder 100 into one or more processing units. For example, the processing unit may be a Coding Tree Unit (CTU), a Coding Unit (CU), a Prediction Unit (PU), or a Transform Unit (TU).

However, the terms are only used for the convenience of description of the present invention, the present invention is not limited to the definition of the terms. In addition, in the present specification, for convenience of description, the term coding unit is used as a unit used in encoding or decoding a video signal, but the present invention is not limited thereto and may be appropriately interpreted according to the present invention.

The encoder 100 may generate a residual signal by subtracting a prediction signal output from the inter predictor 180 or the intra predictor 185 from the input image signal and generate the residual signal. The dual signal is transmitted to the converter 120.

The transform unit 120 may generate a transform coefficient by applying a transform technique to the residual signal. The conversion process may be applied to pixel blocks having the same size as the square, or may be applied to blocks of variable size rather than square.

The quantization unit 130 may quantize the transform coefficients and transmit the quantized coefficients to the entropy encoding unit 190, and the entropy encoding unit 190 may entropy code the quantized signal and output the bitstream.

The quantized signal output from the quantization unit 130 may be used to generate a prediction signal. For example, the quantized signal may restore the residual signal by applying inverse quantization and inverse transformation through an inverse quantization unit 140 and an inverse transformation unit 150 in a loop. A reconstructed signal may be generated by adding the reconstructed residual signal to a prediction signal output from the inter predictor 180 or the intra predictor 185.

Meanwhile, in the compression process as described above, adjacent blocks are quantized by different quantization parameters, thereby causing deterioration of the block boundary. This phenomenon is called blocking artifacts, which is one of the important factors in evaluating image quality. In order to reduce such deterioration, a filtering process may be performed. Through this filtering process, the image quality can be improved by removing the blocking degradation and reducing the error of the current picture.

The filtering unit 160 applies filtering to the reconstruction signal and outputs it to the reproduction apparatus or transmits the decoded picture buffer to the decoding picture buffer 170. The filtered signal transmitted to the decoded picture buffer 170 may be used as the reference picture in the inter predictor 180. As such, by using the filtered picture as a reference picture in the inter prediction mode, not only image quality but also encoding efficiency may be improved.

The decoded picture buffer 170 may store the filtered picture for use as a reference picture in the inter prediction unit 180.

The inter prediction unit 180 performs temporal prediction and / or spatial prediction to remove temporal redundancy and / or spatial redundancy with reference to a reconstructed picture. Here, since the reference picture used to perform the prediction is a transformed signal that has been quantized and dequantized in units of blocks at the time of encoding / decoding, a blocking artifact or a ringing artifact may exist. have.

Accordingly, the inter prediction unit 180 may interpolate the signals between pixels in sub-pixel units by applying a lowpass filter in order to solve performance degradation due to discontinuity or quantization of such signals. Herein, the subpixels mean virtual pixels generated by applying an interpolation filter, and the integer pixels mean actual pixels existing in the reconstructed picture. As the interpolation method, linear interpolation, bi-linear interpolation, wiener filter, or the like may be applied.

The interpolation filter may be applied to a reconstructed picture to improve the precision of prediction. For example, the inter prediction unit 180 generates an interpolation pixel by applying an interpolation filter to integer pixels, and uses an interpolated block composed of interpolated pixels as a prediction block. You can make predictions.

The intra predictor 185 may predict the current block by referring to samples around the block to which current encoding is to be performed. The intra prediction unit 185 may perform the following process to perform intra prediction. First, reference samples necessary for generating a prediction signal may be prepared. The prediction signal may be generated using the prepared reference sample. Then, the prediction mode is encoded. In this case, the reference sample may be prepared through reference sample padding and / or reference sample filtering. Since the reference sample has been predicted and reconstructed, there may be a quantization error. Accordingly, the reference sample filtering process may be performed for each prediction mode used for intra prediction to reduce such an error.

An embodiment of the present invention provides a method of predicting a residual signal generated during intra prediction from an image which is already reconstructed from a surrounding.

In an embodiment, the region most similar to the surrounding region of the region to be coded is searched in the reconstructed image, and when the region most similar to the region is searched, the prediction residual signal of the region to which the residual signal of the region is currently coded. Can be utilized as

In addition, another embodiment of the present invention may receive the position information most similar to the peripheral region of the region to be coded from the encoder, and utilize the residual signal of the region as a predictive residual signal of the region to be currently coded.

A prediction signal generated by the inter predictor 180 or the intra predictor 185 may be used to generate a reconstruction signal or to generate a residual signal.

2, the decoder 200 includes an entropy decoding unit 210, an inverse quantizer 220, an inverse transform unit 230, a filtering unit 240, and a decoded picture buffer unit (DPB) 250. ), An inter predictor 260, and an intra predictor 265.

The reconstructed video signal output through the decoder 200 may be reproduced through the reproducing apparatus.

The decoder 200 may receive a signal output from the encoder 100 of FIG. 1, and the received signal may be entropy decoded through the entropy decoding unit 210.

The inverse quantization unit 220 obtains a transform coefficient from the entropy decoded signal using the quantization step size information.

The inverse transformer 230 inversely transforms a transform coefficient to obtain a residual signal.

A reconstructed signal is generated by adding the obtained residual signal to a prediction signal output from the inter predictor 260 or the intra predictor 265.

The filtering unit 240 applies filtering to the reconstructed signal and outputs the filtering to the reproducing apparatus or transmits it to the decoded picture buffer unit 250. The filtered signal transmitted to the decoded picture buffer unit 250 may be used as the reference picture in the inter predictor 260.

In the present specification, the embodiments described by the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the encoder 100 are respectively the filtering unit 240, the inter prediction unit 260, and the decoder. The same may be applied to the intra predictor 265.

The encoder may split one image (or picture) in units of a rectangular Coding Tree Unit (CTU). In addition, one CTU is sequentially encoded according to a raster scan order.

For example, the size of the CTU may be set to any one of 64x64, 32x32, and 16x16, but the present invention is not limited thereto. The encoder may select and use the size of the CTU according to the resolution of the input video or the characteristics of the input video. The CTU may include a coding tree block (CTB) for a luma component and a coding tree block (CTB) for two chroma components corresponding thereto.

One CTU may be decomposed into a quadtree (QT) structure. For example, one CTU may be divided into four units having a square shape and each side is reduced by half in length. The decomposition of this QT structure can be done recursively.

Referring to FIG. 3, a root node of a QT may be associated with a CTU. The QT may be split until it reaches a leaf node, where the leaf node may be referred to as a coding unit (CU).

A CU may mean a basic unit of coding in which an input image is processed, for example, intra / inter prediction is performed. The CU may include a coding block (CB) for a luma component and a CB for two chroma components corresponding thereto. For example, the size of the CU may be determined as any one of 64x64, 32x32, 16x16, and 8x8. However, the present invention is not limited thereto, and in the case of a high resolution image, the size of the CU may be larger or more diverse.

Referring to FIG. 3, the CTU corresponds to a root node and has the smallest depth (ie, level 0) value. The CTU may not be divided according to the characteristics of the input image. In this case, the CTU corresponds to a CU.

The CTU may be decomposed in QT form, and as a result, lower nodes having a depth of level 1 may be generated. And, a node that is no longer partitioned (ie, a leaf node) in a lower node having a depth of level 1 corresponds to a CU. For example, in FIG. 3 (b), CU (a), CU (b) and CU (j) corresponding to nodes a, b and j are divided once in the CTU and have a depth of level 1. FIG.

At least one of the nodes having a depth of level 1 may be split into QT again. And, a node that is no longer partitioned (ie, a leaf node) in a lower node having a level 2 depth corresponds to a CU. For example, in FIG. 3 (b), CU (c), CU (h), and CU (i) corresponding to nodes c, h and i are divided twice in the CTU and have a depth of level 2. FIG.

In addition, at least one of the nodes having a depth of 2 may be divided into QTs. And, a node that is no longer partitioned (ie, a leaf node) in a lower node having a depth of level 3 corresponds to a CU. For example, in FIG. 3 (b), CU (d), CU (e), CU (f), and CU (g) corresponding to nodes d, e, f, and g are divided three times in the CTU, and level 3 Has a depth of

In the encoder, the maximum size or the minimum size of the CU may be determined according to characteristics (eg, resolution) of the video image or in consideration of encoding efficiency. Information about this or information capable of deriving the information may be included in the bitstream. A CU having a maximum size may be referred to as a largest coding unit (LCU), and a CU having a minimum size may be referred to as a smallest coding unit (SCU).

In addition, a CU having a tree structure may be hierarchically divided with predetermined maximum depth information (or maximum level information). Each partitioned CU may have depth information. Since the depth information indicates the number and / or degree of division of the CU, the depth information may include information about the size of the CU.

Since the LCU is divided into QT forms, the size of the SCU can be obtained by using the size and maximum depth information of the LCU. Or conversely, using the size of the SCU and the maximum depth information of the tree, the size of the LCU can be obtained.

For one CU, information indicating whether the corresponding CU is split may be delivered to the decoder. For example, the information may be defined as a split flag and may be represented by a syntax element "split_cu_flag". The division flag may be included in all CUs except the SCU. For example, if the split flag value is '1', the corresponding CU is divided into four CUs again. If the split flag value is '0', the CU is not divided any more and the coding process for the CU is not divided. Can be performed.

In the embodiment of FIG. 3, the division process of the CU has been described as an example, but the QT structure described above may also be applied to the division process of a transform unit (TU) which is a basic unit for performing transformation.

The TU may be hierarchically divided into a QT structure from a CU to be coded. For example, a CU may correspond to a root node of a tree for a transform unit (TU).

Since the TU is divided into QT structures, the TU divided from the CU may be divided into smaller lower TUs. For example, the size of the TU may be determined by any one of 32x32, 16x16, 8x8, and 4x4. However, the present invention is not limited thereto, and in the case of a high resolution image, the size of the TU may be larger or more diverse.

For one TU, information indicating whether the corresponding TU is divided may be delivered to the decoder. For example, the information may be defined as a split transform flag and may be represented by a syntax element "split_transform_flag".

The division conversion flag may be included in all TUs except the TU of the minimum size. For example, if the value of the division conversion flag is '1', the corresponding TU is divided into four TUs again. If the value of the division conversion flag is '0', the corresponding TU is no longer divided.

As described above, a CU is a basic unit of coding in which intra prediction or inter prediction is performed. In order to code an input image more effectively, a CU may be divided into prediction units (PUs).

The PU is a basic unit for generating a prediction block, and may generate different prediction blocks in PU units within one CU. The PU may be divided differently according to whether an intra prediction mode or an inter prediction mode is used as a coding mode of a CU to which the PU belongs.

The present invention proposes a new residual signal encoding method in consideration of the characteristics of the residual signal. For example, one coefficient group (CG) may be divided into a plurality of sub-coefficient groups (sub-CG) and encoded. As another example, encoding bits may be reduced by implicitly performing encoding of a sub-coefficient group (sub-CG).

The residual signal encoding process of the transform unit may be performed as follows. First, the encoder may encode coordinate information of a non-zero transform coefficient located last in a transform unit.

The encoder divides a transform unit into 4x4 coefficient groups (CGs) and indicates a nonzero coefficient flag indicating whether a nonzero coefficient exists in each coefficient group (CG). -zero coefficient flag) can be encoded. For example, the non-zero coefficient flag may be represented by coded_sub_block_flag. If coded_sub_block_flag = 0, this indicates that there is no non-zero coefficient in the coefficient group (CG), and coded_sub_block_flag = 1 indicates that non-zero coefficients exist in the coefficient group (CG).

The encoder may encode the absolute value and the sign of the coefficient in the coefficient group (CG) when a non-zero coefficient exists in the coefficient group (CG).

One embodiment of the present invention proposes a method for improving the coding of non-zero coefficient flags when non-zero coefficients exist in a coefficient group (CG).

In addition, the present invention may define a coefficient value flag indicating whether a coefficient value in a coefficient group (CG) is zero. For example, referring to FIG. 4, the coefficient value flag may be expressed as sig_coefficient_flag. If sig_coefficient_flag = 0, this may indicate that a coefficient value in a coefficient group (CG) is 0. If sig_coefficient_flag = 1, this may indicate that a coefficient value in a coefficient group (CG) is not zero. This is only an example, and the present invention is not limited thereto, and the count value flag may be set to have a different value.

The present invention proposes a method of improving the coding for at least one of a non-zero coefficient flag or a coefficient value flag.

For example, referring to FIG. 5, when all coefficients in a coefficient group are 0, a non-zero coefficient flag and a coefficient value flag are coded according to the present invention. The method is shown. Referring to FIG. 5, since all coefficients in a coefficient group are 0, the non-zero coefficient flag is set to 0, and the coefficient value flag needs to be coded. There is no. Thus, coding bits can be saved.

The present invention proposes a method for improving the coding of at least one of a non-zero coefficient flag or a coefficient value flag.

For example, referring to FIG. 6, if a non-zero coefficient exists in a coefficient group, a non-zero coefficient flag and a coefficient value flag according to the present invention are determined. It shows how to code.

First, since a non-zero coefficient exists in a coefficient group, the non-zero coefficient flag may be set to one. 6, when the coefficients follow an up-right diagonal scanning order, bits corresponding to the coefficient value flag may be allocated as shown in FIG. 6. .

In this case, 17 bits may be coded by adding 16 bits of the coefficient value flag and 1 bit of the non-zero coefficient flag.

The present invention provides a method of dividing one coefficient group (CG) into a plurality of sub-coefficient groups (sub-CG). However, the present invention is not limited thereto, and the sub-coefficient group sub-CG may be divided into sub-sub-cog groups and encoded. The sub-coefficient group may be encoded. -CG) may be divided again and encoded.

In the present specification, the sub-coefficient group sub-CG is referred to as a first sub-coefficient group 1st sub-CG, and the sub-sub-coefficient group sub-sub-CG is referred to as a second sub-coefficient group 2nd. sub-CG), which is generally referred to as an Nth sub-CG. Here, N may be determined based on the block size, for example, the block size may mean the size of the transform unit. However, the present invention is not limited thereto, and the block may correspond to any one of various units corresponding to the block.

In an embodiment of the present invention, when a coefficient group is defined as a 4x4 block size, only 1 bit is included in the coefficient group when the non-zero coefficient flag coded_sub_block_flag = 0. It can be expressed that the coefficients are all 0, and thus, efficient encoding can be performed. However, in the case of non-zero coefficient flag coded_sub_block_flag = 1, coding efficiency may be relatively low because encoding should be performed on each of 16 coefficients. In addition, even if a non-zero coefficient exists in a coefficient group (coded_sub_block_flag = 1), it can be confirmed that most coefficients are zero.

Accordingly, the present invention divides a coefficient group into 2x2 sub-coefficient groups when the non-zero coefficient flag coded_sub_block_flag = 1, and sub-coefficients of each sub-coefficient. A sub non-zero coefficient flag indicating whether a non-zero coefficient exists in a group may be defined.

For example, referring to FIG. 7, the sub non-zero coefficient flag may be represented by coded_sub_sub_block_flag. If coded_sub_sub_block_flag = 0, a non-zero coefficient in the sub coefficient group is 0. That is, there is no coefficient, that is, all coefficients are zero, and if coded_sub_sub_block_flag = 1, it indicates that a non-zero coefficient exists in the sub coefficient group.

If coded_sub_sub_block_flag = 1, the coefficient value flag sig_coefficient_flag is encoded. If coded_sub_sub_block_flag = 0, all coefficients in the sub coefficient group are 0, so encoding of the coefficient value flag sig_coefficient_flag is performed. Can be omitted.

The present invention provides a method of dividing one coefficient group (CG) into a plurality of sub-coefficient groups (sub-CGs), and specifically, a non-zero coefficient flag and a sub nonzero. A method of encoding using at least one of a sub non-zero coefficient flag is provided.

For example, referring to FIGS. 8 to 11, when a coefficient group is divided into four sub coefficient groups, a non-zero coefficient among four sub coefficient groups Represents a method of encoding according to the number of sub coefficient groups present.

FIG. 8 illustrates a case where the number of sub coefficient groups in which non-zero coefficients exist is one, and FIGS. 9 to 11 illustrate two, three, and four cases, respectively.

As shown in FIG. 8 and FIG. 9, in the case where the number of sub coefficient groups having coded_sub_sub_block_flag = 1 is 1 and 2, the bits required for encoding are 9 bits and 13 bits, respectively. Thus, coding with fewer bits is possible.

However, as shown in FIG. 10, when the number of sub coefficient groups having coded_sub_sub_block_flag = 1 is three, 17 bits are required as in the embodiment described with reference to FIG. 6, and thus there is no gain on coding bits.

In addition, as shown in FIG. 11, when the number of sub coefficient groups having coded_sub_sub_block_flag = 1 is 4, 21 bits are required, and thus, more bits may be needed than the embodiment described with reference to FIG. 6. .

For the four cases described with reference to FIG. 8 to FIG. 11, the distribution of the test sequence in the HEVC CTC (Common Test Condition) can be obtained.

Referring to FIG. 12, it can be seen that the occurrence probability of the embodiment of FIG. 11, which is the case where encoding is performed using more bits than the embodiment described with reference to FIG. 6, is low. In addition, when the average predicted bits required based on the probability distribution are obtained, it can be confirmed that encoding is possible using 1.7 bits (17 to 15.3) on average less than the embodiment described with reference to FIG. 6.

An embodiment of the present invention provides coding when the non-zero coefficient flag is 1 and the sub non-zero coefficient flags of the first three sub-coefficient groups in the scanning order are zero. A method is provided to further increase efficiency (ie, further reduce use bits).

For example, if the non-zero coefficient flag coded_sub_block_flag = 1 and the sub non-zero coefficient flags coded_sub_sub_block_flag = 0 of the first three sub coefficient group in the scan order, the last The sub non-zero coefficient flag of the fourth sub coefficient group may implicitly infer that the sub non-zero coefficient flag has a value of 1 without assigning an actual value.

Therefore, the present invention can save one bit additionally used for encoding in such a case. Specific embodiments will be described in detail with reference to FIGS. 14 to 15.

As in the embodiment of FIG. 13, the embodiment of FIG. 14 has a non-zero coefficient flag coded_sub_block_flag = 1 and a sub non-zero coefficient flag of the first three sub coefficient groups in the scanning order. When zero coefficient flags) coded_sub_sub_block_flag = 0, this indicates a method of deriving a sub non-zero coefficient flag of the last fourth sub coefficient group.

That is, if the sub non-zero coefficient flag of the last fourth sub coefficient group is coded_sub_sub_block_flag [3], coded_sub_sub_block_flag [3] is coded_sub_block_flag = 1 (S1410), and the first three sub coefficient groups If all of the sub nonzero coefficient flags satisfy coded_sub_sub_block_flag [0] == 0 && coded_sub_sub_block_flag [0] == 0 && coded_sub_sub_block_flag [0] == 0 (S1420, S1430, S1440), lead to coded_sub_sub_block_flag [3] = 1 Can be.

According to the present invention, in the case of a coefficient group including the last coefficient (CG 0 in FIG. 15), the non-zero coefficient flag A does not need to be assigned an actual value. It can be implicitly inferred to have a value of.

Further, the sub non-zero coefficient flag coded_sub_sub_block_flag (B) of the sub coefficient group (sub-CG 4 in FIG. 15) before the last position of the corresponding coefficient group is It can be seen that implicitly 0, and the sub non-zero coefficient flag coded_sub_sub_block_flag (C) value of the sub coefficient group (sub-CG 3 in FIG. 15) at the last position is implicit. It can be seen that 1 is.

Therefore, as shown in FIG. 15, since the bits of the positions A, B, and C described above are not encoded, the number of bits can be saved.

In another embodiment of the present invention, in the case of a coefficient group including a DC coefficient, coded_sub_block_flag may be implicitly assigned a value of 1 regardless of an actual value, assuming that coded_sub_block_flag has a value of 1. The rest of the process may be applied to the embodiments described herein. Alternatively, in the case of a coefficient group including a DC coefficient, embodiments of the present specification may not be applied.

The encoder to which the present invention is applied may check whether a non-zero coefficient exists in a coefficient group with respect to a plurality of coefficient groups in the transform block (S1610).

As a result of the check, when the non-zero coefficient does not exist in the coefficient group, the encoder may set the non-zero coefficient flag to 0 (S1620). Here, the nonzero coefficient flag indicates whether a nonzero coefficient exists in a coefficient group.

On the other hand, if a non-zero coefficient exists in the coefficient group as a result of the check, the encoder may divide the coefficient group into a plurality of sub coefficient groups (S1630).

In addition, the encoder may determine whether a non-zero coefficient exists for each of the plurality of sub coefficient groups (S1640).

As a result of the check, when there is a sub coefficient group including the non-zero coefficient, the encoder may encode the non-zero coefficient only for the sub coefficient group (S1650). In this case, the sub nonzero coefficient flag may be set to one.

On the other hand, if there is no non-zero coefficient in the sub coefficient group, the encoder may set the sub nonzero coefficient flag to 0 (S1660). Here, the sub nonzero coefficient flag indicates whether a nonzero coefficient exists in a sub coefficient group.

In this case, a non-zero coefficient for the sub coefficient group may be encoded using a coefficient value flag.

Also, coding bits may vary according to the number of sub coefficient groups in which a non-zero coefficient exists among the plurality of sub coefficient groups.

In addition, in the case of a coefficient block including a last non-zero coefficient, a sub non-zero coefficient flag may be derived with a value of 1. This can save coding bits.

In addition, a non-zero coefficient exists in a coefficient group, and a non-zero coefficient exists in the first three sub coefficient groups in the scanning order. If not present, the sub non-zero coefficient flag for the last sub coefficient group may be derived with a value of 1.

The encoding process may be performed by a residual signal encoder (not shown).

The decoder may receive a sub non-zero coefficient flag for each sub coefficient group in the transform block from the video signal (S1710). Here, the sub nonzero coefficient flag indicates whether a nonzero coefficient exists in a sub coefficient group.

The decoder may obtain a non-zero coefficient existing in a sub coefficient group based on the sub nonzero coefficient flag (S1720). Herein, the non-zero coefficient may be identified by a coefficient value flag.

In operation S1730, the decoder may perform inverse transform on the non-zero coefficient.

As described above, the embodiments described herein may be implemented and performed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in FIGS. 1 and 2 may be implemented and performed on a computer, a processor, a microprocessor, a controller, or a chip.

In addition, the decoder and encoder to which the present invention is applied include a multimedia broadcasting transmitting and receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, a real time communication device such as video communication, a mobile streaming device, Storage media, camcorders, video on demand (VoD) service providing devices, internet streaming service providing devices, three-dimensional (3D) video devices, video telephony video devices, and medical video devices, and the like, for processing video signals and data signals Can be used for

In addition, the processing method to which the present invention is applied can be produced in the form of a program executed by a computer, and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present invention can also be stored in a computer-readable recording medium. The computer readable recording medium includes all kinds of storage devices for storing computer readable data. The computer-readable recording medium may include, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. Can be. The computer-readable recording medium also includes media embodied in the form of a carrier wave (eg, transmission over the Internet). In addition, the bit stream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.

As mentioned above, preferred embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art can improve and change various other embodiments within the spirit and technical scope of the present invention disclosed in the appended claims below. , Replacement or addition would be possible.

Claims

In a method of encoding a video signal,

Checking, for a plurality of coefficient groups in the transform block, whether a non-zero coefficient exists in the coefficient group;

Dividing the coefficient group into a plurality of sub coefficient groups when there is a coefficient group including the nonzero coefficient as a result of the checking;

Checking whether a non-zero coefficient exists for each of the plurality of sub coefficient groups; And

If the sub coefficient group including the non-zero coefficient exists as a result of the checking, encoding the non-zero coefficient only for the sub coefficient group

Method comprising a.
According to claim 1, According to the first confirmation result,

Setting a non-zero coefficient flag indicating whether a non-zero coefficient exists in the coefficient group

Method further comprising a.
According to claim 2, According to the second confirmation result,

Setting a sub non-zero coefficient flag indicating whether a non-zero coefficient exists in the sub coefficient group

Method further comprising a.
The method of claim 1,

Non-zero coefficients for the sub coefficient group are encoded using a coefficient value flag.
The method of claim 1,

The coding bit is different according to the number of sub coefficient groups in which a non-zero coefficient exists among the plurality of sub coefficient groups.
The method of claim 1,

In the case of the coefficient block including the last non-zero coefficient, the sub non-zero coefficient flag is derived with a value of 1,

And the sub non-zero coefficient flag indicates whether a non-zero coefficient exists in a sub coefficient group.
The method of claim 1,

A non-zero coefficient exists in the coefficient group, and a non-zero coefficient exists in the first three sub coefficient groups in the scanning order. If not, the sub non-zero coefficient flag for the last sub coefficient group is derived with a value of 1,

And the sub non-zero coefficient flag indicates whether a non-zero coefficient exists in a sub coefficient group.
The method of claim 1,

Encoding position information of a last non-zero coefficient in the transform block

Method further comprising a.
In the method for decoding a video signal,

Receiving a sub non-zero coefficient flag for each sub coefficient group in a transform block from the video signal, wherein the sub non-zero coefficient flag indicates whether a non-zero coefficient exists in the sub coefficient group Indicating whether or not;

Obtaining a nonzero coefficient present in a sub coefficient group based on the sub nonzero coefficient flag; And

Performing inverse transform on the nonzero coefficient

Method comprising a.
The method of claim 9,

And the video signal is encoded with a different number of bits according to the number of sub coefficient groups in which the non-zero coefficient exists.
The method of claim 9,

And wherein said nonzero coefficient is identified by a coefficient value flag.
An apparatus for encoding a video signal,

For a plurality of coefficient groups in the transform block, it is determined whether a non-zero coefficient exists in the coefficient group, and as a result of the checking, a coefficient group including the non-zero coefficient is determined. If present, divide the coefficient group into a plurality of sub coefficient groups,

It is determined whether there is a non-zero coefficient for each of the plurality of sub-coefficient groups, and if there is a sub-coefficient group including the non-zero coefficient as a result of the checking, the zero only for the sub-coefficient group Residual signal encoding unit for encoding non-zero coefficients

Apparatus comprising a.
The method of claim 12,

And encoding bits are different according to the number of sub coefficient groups in which non-zero coefficients exist among the plurality of sub coefficient groups.
An apparatus for decoding a video signal,

An entropy decoding unit configured to receive a sub non-zero coefficient flag for each sub coefficient group in a transform block from the video signal; And

An inverse transform unit configured to obtain a nonzero coefficient existing in the subcoefficient group based on the subnonzero coefficient flag and perform an inverse transform on the nonzero coefficient;

And the sub nonzero coefficient flag indicates whether a nonzero coefficient exists in a sub coefficient group.