RU2785816C2 - Position-dependent intra-prediction combination expanded with angular modes - Google Patents

Abstract

FIELD: video encoding/decoding.

SUBSTANCE: method for using a position-dependent intra-prediction combination (PDPC) in cases, where the current block is predicted in an intra-mode, using an angular intra-prediction mode, is proposed.

EFFECT: improvement of the encoding efficiency.

55 cl, 14 dwg

Description

[0001] This application claims priority of U.S. Application No. 16/371,638, filed April 1, 2019, which claims priority of U.S. Provisional Application No. 62/651,424, filed April 2, 2018, the entire contents of both of which are incorporated herein by reference.

Technical field

[0002] This disclosure relates to video coding and video decoding.

PRIOR ART

[0003] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recorders, digital media players, video game devices, video game consoles, cellular or satellite radio telephones, so-called smartphones, teleconferencing devices, video streaming devices and the like. Digital video devices implement video coding techniques such as those described in the standards defined by MPEG-2, MPEG-4, ITEG-T H.263, ITEG-T H.264/MPEG-4 Part 10, Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC) standard and extensions of such standards. Video devices can transmit, receive, encode, decode and/or store digital video information more efficiently by implementing such video coding techniques.

[0004] Video coding techniques include spatial (intra-frame) prediction and/or temporal (inter-frame) prediction to reduce or remove redundancy inherent in video sequences. For block video coding, a video slice (eg, a video frame or part of a video frame) may be divided into video blocks, which may also be referred to as tree blocks, CUs, and/or coding nodes. Images (pictures) may be referred to as frames. Reference pictures may be referred to as reference frames.

[0005] Spatial or temporal prediction results in a prediction block for the block to be coded. The residual data represents the pixel differences between the original block to be encoded and the prediction block. For additional compression, the residual data may be converted from the pixel domain to the transform domain, resulting in residual transform coefficients, which may then be quantized. Entropy encoding can be used to achieve even greater compression.

Brief description of the essence of the invention

[0006] This disclosure describes methods for encoding a block of video data using intra-frame (intra-) prediction. For example, the techniques of the present disclosure include encoding a block of video data using a position-dependent intra prediction combination (PDPC) extended for use with an intra prediction angular mode (e.g., diagonal intra prediction modes or intra prediction angular modes adjacent to diagonal modes of intra-prediction). In intra-prediction, a prediction block is generated for the current block based on pixels adjacent to the current block. In PDPC, the prediction samples in a prediction block are modified, and the modified prediction samples are used to encode or decode the current block. For encoding, the video encoder uses the modified prediction samples to determine the residuals that are signaled to the video decoder, and for decoding, the video decoder adds the modified prediction samples to the received residuals to reconstruct the current block.

[0007] PDPC methods have been limited to certain intra-prediction modes, such as DC, planar, vertical, and horizontal intra-prediction modes. This disclosure describes exemplary methods for how to extend PDPC techniques to intra-prediction angular modes. For example, in PDPC techniques, reference samples external to the current block are used to modify the prediction samples. There may be difficulties in determining which reference samples should be used when PDPC methods are extended to intra-prediction angular modes. This disclosure describes exemplary methods of how to determine the reference samples to use, and the manner in which the reference samples and prediction samples are weighted to perform PDPC methods for intra-prediction angular modes, such as determining reference samples based on intra-prediction angular modes (e.g., based on the angles of the intra-prediction angular modes).

[0008] In one example, the disclosure describes a method for decoding video data, the method comprising determining a prediction block, which includes a plurality of prediction samples, for the current block based on an intra-prediction angular mode that is not DC, planar, horizontal, or vertical mode. intra-prediction, modifying a prediction sample from a plurality of prediction samples of a prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein the modification of the prediction sample comprises determining one or more reference samples that are external to to the current block, based on the intra-prediction angular mode, and modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, and re-sampling the current block based on the modified prediction sample niya and residual value.

[0009] In one example, the disclosure describes a method for encoding video data, the method comprising determining a prediction block, which includes a plurality of prediction samples, for the current block based on an intra-prediction angular mode that is not DC, planar, horizontal, or vertical mode. intra-prediction, modifying a prediction sample from a plurality of prediction samples of a prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein the modification of the prediction sample comprises determining one or more reference samples that are external to to the current block, based on the intra-prediction angular mode, and modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, determining a residual value for the residual block based on the modified sample prediction orks and sample values in the current block, and signaling information indicating the residual value.

[0010] In one example, the disclosure describes an apparatus for decoding video data, the apparatus comprising a memory configured to store a prediction block and a video decoder comprising at least one of a fixed function circuit and a programmable circuit. The video decoder is configured to determine a prediction block that includes a plurality of prediction samples for the current block to be stored in memory, based on an intra-prediction angular mode that is not a DC, planar, horizontal, or vertical intra-prediction mode, modify the sample multiple prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein to modify the prediction sample, the video decoder is configured to determine one or more reference samples that are external to the current block, based on the intra-prediction angular mode, and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, and resample the current block based on the modified prediction sample and the residual th value.

[0011] In one example, the disclosure describes an apparatus for encoding video data, the apparatus comprising a memory configured to store a prediction block and a video encoder comprising at least one of a fixed function circuit and a programmable circuit. The video encoder is configured to determine a prediction block, which includes a plurality of prediction samples, for the current block, for storage in memory, based on an intra-prediction angular mode that is not DC, planar, horizontal, or vertical intra-prediction mode, modify the sample multiple prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein to modify the prediction sample, the video encoder is configured to determine one or more reference samples that are external to the current block, based on the intra-prediction angle mode, and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, determine a residual value for the residual block based on the modified prediction sample, and sample values in the current block and signal information indicating the residual value.

[0012] In one example, the disclosure describes a computer-readable storage medium that stores instructions that, when executed, cause one or more processors of a device to decode video data:

[0013] In one example, the disclosure describes a computer-readable storage medium storing instructions that, when executed, causes one or more processors of a video decoding device to determine a prediction block, which includes a plurality of prediction samples, for the current block based on the angle mode of the intra- prediction that is not DC, planar, horizontal, or vertical intra-prediction mode, modify a prediction sample from a plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, wherein the instructions that cause one or more processors modify prediction samples contain instructions that cause one or more processors to determine one or more reference samples that are external to the current block based on the intra-prediction angular mode and modify a prediction sample to generate a modified prediction sample based on the determined one or more reference samples; and to resample the current block based on the modified prediction sample and the residual.

[0014] In one example, the disclosure describes a computer-readable storage medium storing instructions that, when executed, causes one or more processors of a video encoding device to determine a prediction block, which includes a plurality of prediction samples, for the current block, based on the angle mode of the intra -prediction that is not DC, planar, horizontal, or vertical intra-prediction mode, to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein the instructions that cause one or more processors to modify the prediction sample comprise instructions that cause one or more processors to determine one or more reference samples that are external to the current block based on the intra-prediction angular mode and modify the prediction sample to generate a modified prediction sample based on o determined by one or more reference samples, determine a residual value for the residual block based on the modified prediction sample and the sample value in the current block, and signal information indicating the residual value.

[0015] In one example, the disclosure describes an apparatus for decoding video data, the apparatus comprising means for determining a prediction block, which includes a plurality of prediction samples, for a current block based on an intra-prediction angular mode that is not DC, planar, horizontal. or vertical intra-prediction mode, means for modifying a prediction sample from a plurality of prediction samples in the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein the means for modifying the prediction sample comprises means for determining one or more reference samples that are external to the current block based on the intra-prediction angular mode and means for modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, and cf. A tool for restoring the sample of the current block based on the modified prediction sample and the residual.

[0016] In one example, the disclosure describes an apparatus for encoding video data, the apparatus comprising means for determining a prediction block, which includes a plurality of prediction samples, for a current block based on an intra-prediction angular mode that is not DC, planar, horizontal. or vertical intra-prediction mode, means for modifying a prediction sample from a plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein the means for modifying the prediction sample comprises means for determining one or more reference samples that are external to the current block based on the intra-prediction angular mode and means for modifying the prediction sample for generating a modified prediction sample based on the determined one or more reference samples, means for determining a residual value for the residual block based on the modified prediction sample and the sample value in the current block; and means for signaling information indicating the residual value.

[0017] Details of one or more examples are set forth in the accompanying drawings and in the description below. Other features, objectives and advantages will be apparent from the description, drawings and claims.

Brief description of the drawings

[0018] FIG. 1 is a block diagram illustrating an exemplary video encoding and decoding system configured to implement disclosure techniques.

[0019] FIG. 2A and 2B are conceptual diagrams illustrating examples of DC mode PDPC weights for sample positions within a 4×4 block.

[0020] FIG. 3 is a conceptual diagram illustrating examples of intra prediction angular modes.

[0021] FIG. 4A is a conceptual diagram illustrating an example of diagonal up-right mode.

[0022] FIG. 4B is a conceptual diagram illustrating an example of a diagonal down-left mode.

[0023] FIG. 4C is a conceptual diagram illustrating an example of an adjacent up-right diagonal mode.

[0024] FIG. 4D is a conceptual diagram illustrating an example of an adjacent diagonal down-left mode.

[0025] FIG. 5A is a conceptual diagram illustrating an example of Table 1 containing "BD-Rates" full intra-test conditions for a PDPC extension eliminating diagonal and adjacent mode edge filtering.

[0026] FIG. 5B is a conceptual diagram illustrating an example of Table 2 containing "BD-Rates" full intra-test conditions for a PDPC extension including diagonal and adjacent mode edge filtering.

[0027] FIG. 6 is a block diagram illustrating an example of a video encoder.

[0028] FIG. 7 is a block diagram illustrating an example of a video decoder.

[0029] FIG. 8 is a flowchart illustrating an exemplary method for encoding video data.

[0030] FIG. 9 is a flowchart illustrating an exemplary method for decoding video data.

Detailed description

[0031] The present disclosure describes methods for encoding a block of video data using intra-prediction, and more specifically, the present disclosure describes methods related to using intra-prediction in such a way as to use a position-dependent intra-prediction (PDPC) combination approach and, more specifically, use a PDPC approach that extends such a PDPC approach to intra-prediction angular modes (eg, diagonal intra modes and angular modes that are adjacent to diagonal intra modes). The techniques described herein introduce compression efficiency in general for encoding a block of video data, and in particular introduce compression efficiency into the PDPC approach by using such methods for intra-prediction angle modes (e.g., intra-prediction diagonal modes or intra-angle angle modes). prediction adjacent to diagonal intra-prediction modes), where compression efficiency is generally a desirable goal for improving the state of existing video coding techniques and improving the performance of video coding processors and video codecs.

[0032] As used herein, the term "video coding" refers to either video coding or video decoding. Likewise, the term "video encoder" may refer generally to a video encoder or video decoder. In addition, certain techniques described in this disclosure with respect to video decoding may also apply to video coding and vice versa. For example, often video encoders and video decoders are configured to perform the same process or reciprocal processes. In addition, video encoders typically perform video decoding as part of the processes of determining how to encode video data. Thus, unless otherwise indicated, it should not be assumed that the method described with respect to video decoding cannot also be performed as part of video coding, or vice versa.

[0033] The present disclosure may also use terms such as current layer, current block, current picture (frame), current slice, and so on. In the context of this disclosure, the term "current" is intended to identify a block, picture, slice, etc. that is currently being encoded, as opposed to, for example, previously or already encoded blocks, pictures, and slices or not yet encoded blocks, pictures. and slices.

[0034] FIG. 1 is a block diagram illustrating an exemplary video encoding and decoding system 10 that may use the techniques of this disclosure to encode a block of video data using a PDPC approach, and more specifically, using a PDPC approach that extends such a PDPC approach to intra-prediction angular mode. (for example, diagonal intra-modes and angled modes adjacent to diagonal intra-modes). As shown in FIG. 1, system 10 includes source device 12 that provides encoded video data to be decoded later by destination device 14. In particular, source device 12 provides video data to destination device 14 via computer-readable media 16. Source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, laptops (i.e., laptops), tablet computers, set-top boxes, handsets such as so-called smartphones, tablet computers, televisions, cameras, display devices, digital media players, video game consoles, video streaming device or the like. In some cases, source device 12 and destination device 14 may be equipped for wireless communication. Thus, source device 12 and destination device 14 may be wireless communication devices. The source device 12 is an exemplary video encoding device (ie, a device for encoding video data). Destination device 14 is an exemplary video decoding device (eg, a device or apparatus for decoding video data).

[0035] In the example shown in FIG. 1, source device 12 includes a video source 18, storage media 20 configured to store video data, a video encoder 22, and an output interface 24. The destination device 14 includes an input interface 26, storage media 28 configured to store encoded video data, a video decoder 30, and a display device 32. In other examples, source device 12 and destination device 14 include other components or arrangements. For example, source device 12 may receive video data from an external video source such as an external camera. Likewise, destination device 14 may communicate with an external display device, instead of including an integrated display device.

[0036] The illustrated system 10 shown in FIG. 1 is just one example. The video data processing techniques may be performed by any digital device or video encoding and/or decoding apparatus. Although the methods of the present disclosure are generally performed by a video encoder and a video decoder, the methods can also be performed by a combined video encoder/decoder, commonly referred to as a codec. Source device 12 and destination device 14 are merely examples of such encoders, in which source device 12 generates encoded video data for transmission to destination device 14. In some examples, source device 12 and destination device 14 operate in a substantially symmetrical manner such that source device 12 and destination device 14 each include video encoding and decoding components. Therefore, system 10 can support unidirectional or bidirectional video transmission between source device 12 and destination device 14, such as for video streaming, video playback, video broadcasting, or video telephony.

[0037] Video source 18 of source device 12 may include a video capture device such as a video camera, a video archive containing previously captured video, and/or a video input interface for receiving video data from a video content provider. As a further alternative, video source 18 may generate computer graphics based data as source video, or a combination of live video, archived video, and computer generated video. Source device 12 may include one or more storage media (eg, storage media 20) configured to store video data. The techniques described in this disclosure may apply to video coding in general and may apply to wireless and/or wired applications. In each case, captured, pre-captured, or computer-generated video may be encoded by video encoder 22. Output interface 24 may output encoded video information to computer-readable media 1615.

[0038] Destination device 14 may receive encoded video data to be decoded via computer-readable medium 16. Computer-readable medium 16 may comprise any type of media or device capable of transferring encoded video data from source device 12 to destination device 14. In some examples, computer-readable medium 16 includes a communication medium to enable source device 12 to transmit encoded video data directly to destination device 14 in real time. The encoded video data may be modulated according to a communication standard such as a wireless communication protocol and transmitted to the destination device 14 . The communication medium may comprise any wireless or wired communication medium, such as radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet network such as a local area network, a wide area network, or a wide area network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful in facilitating communications from source device 12 to destination device 14. Destination device 14 may include one or more storage media configured to store encoded video data and decoded video data.

[0039] In some examples, encoded data (eg, encoded video data) may be output from the output interface 24 to a storage device. Likewise, the encoded data can be accessed from the storage device via the input interface 26 . The storage device may include any of a variety of distributed or locally available storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In another example, the storage device may correspond to a file server or other intermediate storage device that can store the encoded video generated by source device 12. The destination device 14 can access the stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting this encoded video data to the destination device 14 . Examples of file servers include a web server (eg, for a website), an FTP server, network attached storage (NAS), or a local drive. Destination device 14 can access the encoded video data via any standard data connection, including an Internet connection. This may include a wireless link (eg, a Wi-Fi connection), a wired connection (eg, DSL, cable modem, etc.), or a combination thereof suitable for accessing encoded video data stored on a file server. The transmission of the encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof.

[0040] The techniques of the present disclosure may be applied to video coding supporting any of a variety of multimedia applications, such as broadcast television transmissions, cable television transmissions, satellite television transmissions, video streaming over the Internet, such as adaptive streaming techniques, including dynamic adaptive streaming over HTTP (DASH), digital video that is encoded on a storage medium, decoding of digital video stored on a storage medium, or other applications. In some examples, system 10 may be configured to support unidirectional or bidirectional video to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

[0041] Computer-readable media 16 may include transient media such as wireless broadcast or wired network transmission, or storage media (i.e., non-transient (non-transient) storage media) such as a hard drive, flash drive, compact disc, digital video disc, Blu-ray disc, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from source device 12 and provide encoded video data to destination device 14, such as via a network transmission. ​Similarly, the computing device of media production equipment, such as disc stamping equipment, may receive encoded video data from source device 12 and produce a disc containing encoded video data. Therefore, computer-readable media 16 can be understood to include one or more computer-readable media in various forms, in various examples.

[0042] The input interface 26 of the destination device 14 receives information from the computer-readable medium 16. The information of the computer-readable medium 16 may include syntax information defined by video encoder 22, also used by video decoder 30, which includes syntax elements that describe characteristics and /or processing of blocks and other coded units, such as groups of pictures (pictures) (GOP). The storage media 28 may store the encoded video data received by the input interface 26 . The display device 32 displays the decoded video data to the user. The display device 32 may comprise any of a variety of display devices such as a cathode ray tube (CRT), liquid crystal display (LCD), plasma display, organic light emitting diode (OLED) display, or other type of display device.

[0043] Video encoder 22 and video decoder 30 may be implemented as any of a variety of suitable encoder or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. ​When the methods are implemented in part in software, the device may store the instructions for the software in a suitable non-transitory computer-readable medium and may execute the instructions in hardware using one or more processors to execute the methods of this disclosure. Each of video encoder 22 and video decoder 30 may be included in one or more encoders or decoders, each of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.

[0044] In some examples, video encoder 22 and video decoder 30 may operate in accordance with a video coding standard. Examples of video coding standards include, but are not limited to, ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO /IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multi-View Video Coding (MVC) extensions. The HEVC (High Efficiency Video Coding) or ITU-T H 265 video coding standard, including its range and screen content coding extensions, 3D video coding (3D-HEVC) and multi-view extensions (MV-HEVC) and scalable extension (SHVC), were developed by the Joint Video Coding Group (JCT-VC) of the ITU-T Video Coding Expert Group (VCEG) and the ISO/IEC Moving Picture Expert Group (MPEG). The HEVC project specification, hereinafter referred to as HEVC WD, is available from ttp://phenix.int-evry.fr/jct/doc_end_user/documents/

l4_Vienna/wg11/JCTVC-Nl003-vl.zip.

[0045] Video encoder 22 and video decoder 30 may also operate in accordance with other proprietary or industry standards such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also referred to as Versatile Video Coding (VVC). A recent draft VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 4)”, Joint Video Experts Team (JVET) ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 13th ^Meeting : Marrakech, MA, 9-18 January 2019 , JVET-M1001-v5 (hereinafter referred to as “VVC Draft 4”). However, the techniques of the present disclosure are not limited to any particular coding standard.

[0046] In HEVC and VVC and other video coding specifications, a video sequence typically includes a sequence of images (pictures). Pictures may also be referred to as frames. The picture may include three arrays of samples, denoted as S _L , S _Cb and S _Cr . S _L is a two-dimensional array (ie block) of luminance samples. S _Cb is a two-dimensional array of chroma samples Cb. S _Cr is a two-dimensional array of Cr chromaticity samples. Chroma samples may also be referred to herein as chroma samples. In other cases, the picture may be monochrome and may include only an array of luminance samples.

[0047] In addition, in HEVC and other video coding specifications, to generate an encoded representation of a picture, video encoder 22 may generate a set of coding tree units (CTUs). Each of the CTUs may contain a luminance sample coding tree block, two corresponding chrominance sample coding tree blocks, and syntax structures used to encode the coding tree block samples. In monochrome pictures or pictures having three separate color planes, the CTU may contain one coding tree block and the syntax structures used to encode samples of the coding tree block. The coding tree block may be a block of NxN samples. A CTU may also be referred to as a "tree block" or "largest coding unit" (LCU). CTUs in HEVC may be broadly similar to macroblocks in other standards such as H.264/AVC. ​However, a CTU is not necessarily limited to a specific size and may include one or more coding units (CUs). A slice may include an integer number of CTUs ordered sequentially in raster scan order.

[0048] When operating in accordance with HEVC, to generate an encoded CTU, video encoder 22 may recursively perform quadtree splitting into coding tree blocks from the CTU to split coding tree blocks into coding blocks, hence the name “coding tree units”. The coding block is a block of N×N samples. The CU may comprise a luminance sample coding block and two corresponding chrominance sample coding blocks of a picture that has a luminance sample array, a Cb sample array, and a Cr sample array, and syntax structures used to encode the coding block samples. In monochrome pictures or pictures having three separate color planes, a CU may contain one coding unit and syntax structures used to encode the coding unit samples.

[0049] The syntax data in the bitstream may also determine the size for the CTU. A slice includes a number of consecutive CTUs in coding order. A video frame or picture may be divided into one or more slices. As mentioned above, each tree block can be divided into CUs according to the quadtree. In general, the quadtree data structure includes one node per CU, with the root node corresponding to the tree block. If the CU is split into four sub-CUs, the node corresponding to the CU includes four leaf nodes, each corresponding to one of the sub-CUs.

[0050] Each node of the quadtree data structure may provide syntax data for the corresponding CU. For example, a node in the quadtree may include a split flag indicating whether the CU corresponding to the node is split into sub-CUs. The syntax elements for a CU may be determined recursively and may depend on whether the CU is split into sub-CUs. If the CU is not split further, then it is referred to as a leaf CU. If the CU is split further, then it may generally be referred to as a non-leaf CU. In some examples of this disclosure, four sub-CUs of a leaf-CU may be referred to as leaf-CUs even if there is no explicit separation of the original leaf-CU. For example, if a 16x16 CU is not split further, then four 8x8 sub-CUs may also be referred to as leaf CUs, even though the 16x16 CU has never been split.

[0051] The CU has the same purpose as the H.264 macroblock, except that the CU has no difference in size. For example, a tree block may be divided into four child nodes (also referred to as sub-CUs), and each child node may in turn be a parent node and be divided into another four child nodes. Finally, an unshared child node, referred to as a quadtree leaf node, contains an encoding node, also referred to as a leaf CU. The syntax data associated with the encoded bitstream may define the maximum number of times a tree block is split, referred to as the maximum CU depth, and may also define the minimum size of coding nodes. Accordingly, the bitstream may also define a smallest coding unit (SCU). This disclosure uses the term "block" to refer to any of a CU, PU, or TU, in the context of HEVC, or similar data structures in the context of other standards (eg, macroblocks and their subblocks in H.264/AVC).

[0052] The CU includes an encoding node, as well as prediction units (PUs) and transformation units (TUs) associated with the encoding node. The size of the CU corresponds to the size of the coding unit and may, in some examples, be square. In the HEVC example, the CU size may range from 8x8 pixels up to a tree block size of at most 64x64 pixels or more. Each CU may contain one or more PUs and one or more TUs. The syntax data associated with a CU may describe, for example, the partitioning of the CU into one or more PUs. The partitioning modes may differ between whether the CU is skipped or encoded in direct mode, encoded in intra-prediction mode, or encoded in inter-prediction mode. PUs can be broken so as to have a non-square shape. Syntax data associated with a CU may also describe, for example, partitioning the CU into one or more TUs according to a quadtree. The TU may be square or non-square (eg, rectangular) in shape.

[0053] The HEVC standard allows conversions according to TU. TUs may differ for different CUs. The TU sizes are usually chosen based on the size of the PUs in a given CU as defined for the broken LCU, although this may not always be the case. TUs are usually the same size or smaller than PUs. In some examples, the residual samples corresponding to the CU may be divided into smaller units using a quadtree structure, sometimes referred to as a "residual quadtree" (RQT). Leaf nodes of an RQT may be referred to as TUs. The pixel differences associated with the TU may be transformed to obtain transform coefficients, which may be quantized.

[0054] A leaf CU may include one or more PUs. In general, a PU is a spatial region corresponding to all or part of a corresponding CU and may include data for extracting a reference sample for the PU. In addition, the PU includes prediction-related data. For example, when the PU is intra-mode encoded, data for the PU may be included in the RQT, which may include data describing the intra-prediction mode for the TU corresponding to the PU. As another example, when the PU is inter-mode encoded, the PU may include data specifying one or more motion vectors for the PU. The data defining the motion vector for the PU may describe, for example, the horizontal component of the motion vector, the vertical component of the motion vector, the resolution for the motion vector (e.g., one quarter pixel precision or one eighth pixel precision), the reference picture pointed to by the motion vector motion, and/or a list of reference pictures (eg, list 0, list 1, or list C) for the motion vector.

[0055] A leaf CU having one or more PUs may also include one or more TUs. TUs can be defined using the RQT (also referred to as the TU quadtree structure) as discussed above. For example, the split flag may indicate whether the leaf-CU is divided into four transform units. In some examples, each transformation unit may be further divided into further sub-TUs. If the TU is not further partitioned, then it may be referred to as a leaf TU. In general, for intra coding, all leaf TUs belonging to a leaf CU contain residual data obtained from the same intra prediction mode. That is, the same intra-prediction mode is generally applied to calculate predicted values to be transformed across all TUs of a leaf-CU. For intra coding, video encoder 22 may calculate a residual value for each leaf TU using the intra prediction mode as the difference between the portion of the CU corresponding to the TU and the original block. The TU is not necessarily limited by the size of the PU. Thus, TUs may be larger or smaller than PUs. For intra coding, a PU may be co-located with a corresponding leaf TU for the same CU. In some examples, the maximum leaf TU size may correspond to the corresponding leaf CU size.

[0056] In addition, leaf-CU TUs may also be associated with corresponding RQT structures. That is, the leaf-CU may include a quadtree indicating how the leaf-CU is partitioned into TUs. A TU quadtree root node usually corresponds to a leaf CU, while a CU quadtree root node usually corresponds to a tree block (or LCU).

[0057] As discussed above, video encoder 22 may partition a CU coding block into one or more prediction blocks. A prediction block is a rectangular (ie, square or non-square) block of samples over which the same prediction is applied. The PUs in the CU may contain a luminance sample predictor, two corresponding chrominance sample predictors, and syntax structures used to predict the prediction blocks. In monochrome pictures or images having three separate color planes, the PU may contain one prediction block and syntax structures used to predict the prediction block. Video encoder 22 may generate prediction blocks (eg, luminance prediction blocks, Cb and Cr) for prediction blocks (eg, luminance prediction blocks, Cb and Cr) of each PU in the CU.

[0058] Video encoder 22 and video decoder 30 may be configured to operate in accordance with VVC. According to VVC, a video encoder (such as video encoder 22) partitions a picture into multiple coding tree units (CTUs). Video encoder 22 may partition the CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or a multiple tree type (MTT) structure. The QTBT structure removes the concepts of multiple partition types, such as the partition between CUs, PUs, and TUs in HEVC. The QTBT structure includes two levels: a first level split according to a quadtree split and a second level split according to a binary tree split. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of binary trees correspond to coding units (CUs).

[0059] In an MTT split structure, blocks may be split using a quadtree split (QT), a binary tree split (BT), and one or more types of ternary tree split (TT). A ternary tree split is a split in which a block is divided into three subblocks. In some examples, splitting a ternary tree divides a block into three subblocks without splitting the original block through the center. Partition types in MTT (for example, QT, BT and TT) can be symmetrical or asymmetric.

[0060] In some examples, video encoder 22 and video decoder 30 may use one QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder 22 and video decoder 30 may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luminance component and another QTBT/MTT structure for both chrominance components (or two QTBT/MTT structures for the respective chrominance components).

[0061] Video encoder 22 and video decoder 30 may be configured to use HEVC quadtree partitioning, QTBT partitioning, MTT partitioning, or other partitioning structures. For the purposes of explanation, the description of the methods of the present disclosure is presented in relation to partitioning QTBT. However, it should be understood that the techniques of the present disclosure may also apply to video encoders configured to use quadtree splitting or other types of splitting.

[0062] Video encoder 22 may use intra-prediction or inter-prediction to generate prediction blocks for the PU. If video encoder 22 uses intra prediction to generate PU prediction blocks, video encoder 22 may generate PU prediction blocks based on decoded samples of a picture that includes the PU.

[0063] After video encoder 22 generates prediction blocks (eg, luminance, Cb, and Cr prediction blocks) for one or more PUs in a CU, video encoder 22 may generate one or more residual blocks for the CU. For example, video encoder 22 may generate a residual luminance block for the CU. Each sample in the CU's residual luminance block indicates the difference between a luminance sample in one of the CU's luminance prediction blocks and a corresponding sample in the original CU's luminance coding block. In addition, video encoder 22 may generate a residual block Cb for the CU. Each sample in the residual Cb CU may indicate a difference between a sample Cb in one of the prediction blocks Cb CU and a corresponding sample in the original coding block Cb CU. Video encoder 22 may also generate a residual Cr for the CU. Each sample in the CU residual Cr may indicate a difference between a Cr sample in one of the CU prediction Crs and a corresponding sample in the original CU Cr coding block.

[0064] In addition, as discussed above, video encoder 22 may use quadtree partitioning to decompose residual blocks (eg, luminance residual blocks, Cb and Cr) of the CU into one or more transform blocks (eg, luma transform blocks, Cb and Cr). A transform block is a rectangular (eg, square or non-square) block of samples to which the same transform is applied. A transform unit (TU) in the CU may contain a luminance sample transform unit, two corresponding chrominance sample transform units, and syntax structures used to transform the transform block samples. Thus, each TU in a CU may have a luminance transform block, a Cb transform block, and a Cr transform block. The luminance transform block TU may be a sub-block of the residual luminance block CU. The transform block Cb may be a subblock of the residual block Cb of the CU. The Cr transform block may be a sub-block of the CU residual block Cr. In monochrome pictures or pictures having three separate color planes, a TU may contain one transform block and syntax structures used to transform the transform block samples.

[0065] Video encoder 22 may apply one or more TU transform block transforms to generate a coefficient block for the TU. For example, video encoder 22 may apply one or more transforms to the TU luminance transform block to generate a luminance coefficient block for the TU. The coefficient block may be a two-dimensional array of transform coefficients. The conversion factor can be a scalar value. Video encoder 22 may apply one or more transforms to the transform block Cb of the TU to generate a block of Cb coefficients for the TU. Video encoder 22 may apply one or more transforms to the TU Cr transform block to generate a TU Cr coefficient block.

[0066] In some examples, video encoder 22 skips applying transforms to the transform block. In such examples, video encoder 22 may process sample residuals in the same manner as transform coefficients. Thus, in examples where video encoder 22 skips applying transforms, the following discussion of transform coefficients and coefficient blocks may apply to transform blocks of the residual samples.

[0067] After generating a coefficient block (eg, a luma coefficient block, a Cb coefficient block, or a Cr coefficient block), video encoder 22 may quantize the coefficient block to possibly reduce the amount of data used to represent the coefficient block, potentially providing additional compression. Quantization generally refers to a process in which a range of values is compressed into a single value. For example, quantization may be performed by dividing a value by a constant and then rounding to the nearest whole number. To quantize the coefficient block, video encoder 22 may quantize the transform coefficients of the coefficient block. After video encoder 22 quantizes the block of coefficients, video encoder 22 may entropy encode syntax elements indicating the quantized transform coefficients. For example, video encoder 22 may perform context adaptive binary arithmetic coding (CABAC) or other entropy coding techniques on syntax elements indicating quantized transform coefficients.

[0068] Video encoder 22 may output a bit stream that includes a bit sequence that forms a representation of encoded pictures and associated data. Thus, the bitstream contains an encoded representation of the video data. The bitstream may contain a sequence of Network Abstraction Layer (NAL) units. The NAL unit is a syntactic structure containing an indication of the type of data in the NAL unit, and bytes containing this data in the form of a payload (RBSP) of the original sequence of bytes, distributed as necessary with emulation prevention bits. Each of the NAL units may include a NAL unit header and may encapsulate an RBSP. The NAL unit header may include a syntax element indicating a NAL unit type code. The NAL unit type code given by the NAL unit header in the NAL unit indicates the type of the NAL unit. An RBSP may be a syntax structure containing an integer number of bytes that is encapsulated in a NAL unit. In some cases, RBSP includes zero bits.

[0069] Video decoder 30 may receive a bitstream generated by video encoder 22. Video decoder 30 may decode the bitstream to recover pictures of the video data. As part of bitstream decoding, video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct pictures of video data based at least in part on syntax elements obtained from the bitstream. The video data recovery process may be generally the reverse of the process performed by video encoder 22. For example, video decoder 30 may use PU motion vectors to determine prediction blocks for PUs of the current CU. In addition, video decoder 30 may perform inverse quantization of the TU coefficient blocks of the current CU. Video decoder 30 may perform inverse transforms on the coefficient blocks to recover the TU transform blocks of the current CU. Video decoder 30 may recover the coding blocks of the current CU by summing the prediction block samples for the PUs of the current CU with the corresponding transform block samples of the TUs of the current CU. By recovering the coding blocks for each picture CU, video decoder 30 can recover the picture.

[0070] The methods disclosed herein are based on block intra-prediction, which is part of the video standards, including AVC, HEVC, and VVC. In block intra-prediction, typically reference sample lines from adjacent reconstructed blocks are used to predict samples in the current block. One or more sample lines may be used for prediction. Reference samples are used by typical intra-prediction modes such as DC, planar, and angle/directional modes.

[0071] Intra-prediction performs prediction of image blocks using spatially adjacent reconstructed block image samples. In intra-prediction, an N×M (eg, 4×4) block is predicted by the top and left adjacent reconstructed samples (reference samples) along the selected prediction direction. As one example, the block is predicted by top and left adjacent recovered samples (ie, pivot samples) along the selected prediction direction. Reference samples are external to the predicted block. With the reference samples, video encoder 22 generates a prediction block having prediction samples based on the reference samples.

[0072] In general, in intra-prediction techniques, video encoder 22 determines a residual block indicating differences between a prediction block and the current block (e.g., residuals indicating differences between prediction samples and current block samples), and signals information indicating residual values in the rest block. Video decoder 30 similarly determines the reference samples and generates a prediction block. ​Video decoder 30 determines the residual block residuals based on the received information, and sums the residual block residuals with the prediction block prediction samples to reconstruct the current block.

[0073] As described in more detail, the exemplary methods described in this disclosure modify one or more (eg, all) of the prediction samples of a prediction block. Video encoder 22 may determine residuals based on the modified prediction samples. Video decoder 30 may add the residuals with the modified prediction samples to reconstruct the current block. As also described in more detail, the methods are applicable to the intra-prediction angle modes, and the manner in which the prediction samples are modified may be based on the intra-angle mode used to encode or decode the current block.

[0074] There are many intra-prediction modes. In some examples, luma block intra prediction includes 35 modes including planar mode, DC mode, and 33 angle modes (eg, diagonal intra prediction modes and angle modes adjacent to diagonal intra prediction modes). The 35 intra-prediction modes are indexed as shown in the table below. In other examples, more intra modes may be defined, including prediction angles, which may not be represented by the 33 angle modes. In other examples, the prediction angles associated with the angle modes may be different from the angles used in HEVC.

Table 1. Intra prediction mode specification and associated names

Intra prediction mode Associated name 0 INTRA_PLANAR one INTRA_DC 2…34 INTRA_ANGULAR2…INTRA_ANGULAR34

[0075] To perform planar prediction for an N×N block, for each sample p _xy located at (x, y), a prediction value may be computed by applying a bilinear filter to four specific adjacent reconstructed samples, i.e. base samples. The four pivot samples include a top-right reconstruction sample TR, a bottom-left reconstruction sample BL, and two reconstruction samples located in the same column (r _x,-1 ) and row (r _-1,y ) of the current sample. The planar regime can be formulated as follows:

p _xy =((N-x1)∙L+(N-y1)∙T+x1∙R+y1∙B)/(2*N)

where x1=x+1, y1=y+1, R=TR and B=BL

[0076] For the DC mode, the prediction block is filled with the average of adjacent recovered samples. As a rule, both planar and DC modes are used to simulate smoothly changing and constant areas of the image.

[0077] For the intra-prediction angular modes in HEVC, which include 33 different prediction directions, the intra-prediction process can be described as follows. For each given intra-prediction angular mode, the intra-prediction direction can be identified appropriately; for example, intra mode 18 corresponds to a purely horizontal prediction direction, and intra mode 26 corresponds to a purely vertical prediction direction.

[0078] Considering a specific intra-prediction direction, for each prediction block sample, its (x, y) coordinate is first projected onto a row/column of adjacent reconstructed samples along the prediction direction. Assume that (x, y) is projected onto the fractional position α between two adjacent reconstructed samples L and R; then the prediction value for (x, y) can be computed using a two-tap bilinear interpolation filter, formulated as follows:

p _xy \u003d (1-a) ∙ L + a ∙ R

For example, the (x, y) coordinates of a prediction block sample are projected along a particular intra-prediction direction (eg, one of the intra-prediction angular modes). To avoid floating point operations, in HEVC, the above calculation is actually approximated using integer arithmetic as:

p _xy =((32-a')∙L+a'∙R+16>>5,

where a' is an integer equal to 32*a.

[0079] In some examples, prior to intra-prediction, adjacent reference samples are filtered using a 2-tap bilinear or 3-tap (1,2,1)/4 filter, known as intra-reference smoothing or mode-dependent intra-smoothing (MDIS). ). When intra-prediction is performed, considering the intra-prediction mode index (predModelntra) and the block size (nTbS), it is decided whether a reference smoothing process is performed and which anti-aliasing filter is used. The intra prediction mode index is an index indicating the intra prediction mode.

[0080] Prediction block prediction samples are generated using the exemplary methods above. After generating the prediction samples, one or more of the prediction samples may be modified using a position-dependent intra-prediction (PDPC) combination. PDPC forms are described in ITU-T SG16/Q6 Doc. COM16-C1046, “Position Dependent intra Prediction Combination (PDPC), and X. Zhao, V. Seregin, A. Said, M. Karczewicz, “EE1 related: Simplification and extension of PDPC”, 8th JVET Meeting, Macau, Oct. 2018, JVET-H0057. This document discloses the introduction of PDPC as applied to planar, DC, horizontal and vertical modes without signaling, as summarized below.

[0081] The prediction sample pred(x, y) located at (x, y) is predicted using the intra-prediction mode (DC, Planar, Angular), and its value is modified using the reference sample single line PDPC expression:

pred(x, y)=(wL×R-1,y+wT×Rx,-1-wTL×R-1,-1+(64-wL-wT+wTL)×pred' (x, y)+ 32)>>6, (Equation 1)

[0082] In Equation 1, pred'(x, y) is a prediction sample value as determined using the above exemplary methods for generating prediction samples, and pred(x, y) is a modified value of pred'(x, y) . In Equation 1, Rx,-l, R-1,y represent the reference samples located above and to the left of the current sample (x, y) and external to the current block, respectively, and R-1,-l represents the reference sample located in the upper left corner and outer for the current block. In other words, Rx,-1 represents the sample that is one row above the current block with the same x-coordinate as the x-coordinate of the prediction sample being modified, and R-1,y represents the sample that is one column to the left of the current block with the same y-coordinate as the y-coordinate of the modified prediction sample.

[0083] The samples (eg, reference samples) that are used to modify the prediction sample are in-picture samples (eg, luma and chrominance samples) and optionally other prediction samples (although possible). For example, let's say that the current intra-predict block has a size of N×M. For this current block, video encoder 22 and video decoder 30 may generate an N×M prediction block. The reference samples used to modify the prediction samples are the current picture samples (eg, luma and/or chroma samples) that includes the current block and are external to the current block.

[0084] The coordinate system is for identifying samples external to the current block that are related to the current block. For example, the selection located in the upper-left corner of the current block has a coordinate of (0,0). Video encoder 22 may determine the residual between the prediction sample located at the upper-left corner of the prediction block (eg, having coordinate (0,0)), and the sample in the current block having coordinate (0,0). To recover the sample located at (0,0) in the current block, video decoder 30 may sum the prediction sample located at (0,0) in the prediction block with the residual value corresponding to the sample located at (0,0). Accordingly, for each sample in the current block, there is a corresponding sample in the prediction block (eg, having the same coordinate).

[0085] Accordingly, Rx,-1 means that the y-coordinate is -1 and therefore refers to the sample in the line that is above the current block. the x-coordinate may be the same as the x-coordinate of the modified prediction sample. For R-1,y, the x-coordinate is -1 and therefore refers to the column to the left of the current box. The y-coordinate may be the same as the y-coordinate of the modified prediction sample.

[0086] It may be possible to use another coordinate system as well, such as a coordinate system where coordinate (0,0) refers to the top-left sample of the picture. The exemplary methods are described with respect to a coordinate system, where the coordinate (0,0) refers to the top-left sample of the block.

[0087] For DC mode, the weights are calculated as follows for a block with width (width) and height (height) measurements:

wT=32>>((y<<1)>>shift), wL=32>>((x<<1)>>shift), wTL=(wL>>4)+(wT>>4),

[0088] In the equation above, the shift is defined as: shift=(log2(width)+log2(height)+2)>>2 while for planar mode wTL=0, for horizontal mode wTL=wT, and for vertical mode wTL=wL. PDPC weights can only be calculated using sums and shifts. The value of pred(x, y) can be calculated in one step using Equation 1.

[0089] FIG. 2A illustrates the DC mode PDPC weights (wL, wT, wTL) for position (0,0) within one 4x4 block. Fig. 2B illustrates the DC mode PDPC weights (wL, wT, wTL) for position (1,0) within one 4x4 block. If PDPC is applied to DC, planar, horizontal, and vertical intra modes, no additional edge filters are applied, such as the DC mode edge filter or horizontal/vertical mode edge filters. Equation 1 can be generalized to include additional reference sample lines (eg, not limited to samples one line above or one line to the left of the current block). In this case, multiple reference samples are possible in the neighborhood of Rx,-1, R-1,y, R-1,-1 and each may have an assigned weight, which may be optimized, for example, by training.

[0090] As disclosed here, PDPC can now extend to corner modes in general (eg, diagonal intra modes and corner modes that are adjacent to diagonal modes). The estimated diagonal intra modes are modes that predict according to the down-left and up-right directions, as well as some adjacent angular modes, for example, N adjacent modes between the diagonal down-left mode and the vertical mode, and N or M adjacent modes between diagonal up-right mode and horizontal mode. Fig. 3 illustrates the identification of angular modes as disclosed here. In general, adjacent modes may be a selected subset of the available angle modes. The spacing between angular modes may, for example, be non-uniform, and some angular modes may, for example, be skipped.

[0091] In the exemplary techniques described in this disclosure, video encoder 22 and video decoder 30 may be configured to perform PDPC where the current block is intra-predicted in an angle mode that excludes DC, planar, vertical, or horizontal modes. However, there may be technical difficulties in extending PDPC to intra-prediction angular modes. For example, reference samples, when positioned externally to the current block, need not have the same x- and/or y-coordinates as the prediction sample being modified. Therefore, it may not be clear which reference samples should be used to modify the prediction sample so as to gain video coding efficiency.

[0092] For example, if the information needed to signal the residuals is reduced, then there is an increase in bandwidth efficiency. Accordingly, the reference samples used to modify the prediction block should be such that the residuals generated from the modified prediction block require less signaling information compared to other methods. However, if the determination of which reference samples to use is excessive, then there may be a lag in the time required for video decoder 30 to recover the current block.

[0093] The present disclosure describes exemplary methods that provide practical application for video coding methods, such as methods for PDPC, used with intra-prediction angular modes. For example, the exemplary methods provide a technical solution for using PDPC with intra-prediction angular modes. Exemplary ways in which video encoder 22 and video decoder 30 can perform PDPC with intra-angle modes are described in more detail below.

[0094] As one example, video encoder 22 may be configured to determine a prediction block that includes a plurality of prediction samples for the current block based on an intra prediction angle mode that is not DC, planar, horizontal, or vertical intra. -prediction, and modify the prediction sample of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC). It should be understood that although the methods are described with respect to a single prediction sample, the exemplary methods are not limited to this. In some examples, video encoder 22 may modify other prediction samples of the prediction block using PDPC.

[0095] To modify the prediction sample, video encoder 22 may determine one or more reference samples that are external to the current block based on the intra-prediction angular mode and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples. . Video encoder 22 may determine the residual value for the residual block based on the modified prediction sample and the sample value in the current block, and signal information indicating the residual value.

[0096] As one example, video decoder 30 may be configured to determine a prediction block that includes a plurality of prediction samples for the current block based on an intra prediction angle mode that is not DC, planar, horizontal, or vertical intra. -prediction, and modify the prediction sample of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC). Similar to the above, although the methods are described with respect to a single prediction sample, the exemplary methods are not limited to this. In some examples, video decoder 30 may modify other prediction samples of the prediction block using PDPC.

[0097] To modify the prediction sample, video decoder 30 may be configured to determine one or more reference samples that are external to the current block based on the intra prediction angular mode and modify the prediction sample to generate a modified prediction sample based on the determined one. or more reference samples. Video decoder 30 may also be configured to resample the current block based on the modified prediction sample and the residual.

[0098] FIG. 4A-4D illustrate the definition of samples used by propagating PDPC to diagonal and adjacent angular intra modes. Fig. 4A illustrates the determination of the reference samples Rx,-1, R-1,y, and R-1,-1 for PDPC propagation in the up-right diagonal mode. The prediction sample pred(x',y') is located at (x',y') in the prediction block. The x-coordinate of the reference sample Rx,-1 is given by: x=x'+y'+1, and the y-coordinate of the reference sample R-1,y is similarly given by: y=x'+y'+1. The PDPC weights for diagonal up-right mode are, for example: wT=16>>((y'<<1)>>shift), wL=16>>((x'<<1)>>shift), wTL= 0.

[0099] Similarly, FIG. 4B illustrates the definition of the reference samples Rx,-1, R-1,y, and R-1,-1 for PDPC propagation to the diagonal down-left mode. The x-coordinate of the reference sample Rx,-1 is given by: x=x'+y'+1, and the y-coordinate of the reference sample R-1,y is: y=x'+y'+1. The PDPC weights for diagonal up-right mode are, for example: wT=16>>((y'<<1)>>shift), wL=16>>((x'<<1)>>shift), wTL= 0.

[0100] In FIG. 4A and 4B, video encoder 22 and video decoder 30 may each determine the line that is above the current block (eg, immediately above, but methods are not limited to this) and determine the x-coordinate in the determined line. The x-coordinate in a certain row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video encoder 22 and video decoder 30 may determine a reference sample from one or more reference samples based on the determined row and the determined x-coordinate.

[0101] Similarly, in FIG. 4A and 4B, video encoder 22 and video decoder 30 may determine the column that is to the left of the current block (eg, immediately to the left, but methods are not limited to this) and determine the y-coordinate in the determined column. The y-coordinate in a certain column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video encoder 22 and video decoder 30 may determine a reference sample from one or more reference samples based on the determined column and the determined y-coordinate.

[0102] Based on the determined x and y coordinates, video encoder 22 and video decoder 30 may determine reference samples (e.g., a first reference sample based on a certain row and a certain x coordinate and a second reference sample based on a certain column and a certain y coordinate) . Also, video encoder 22 and video decoder 30 may determine weights in accordance with the exemplary methods set forth above for diagonal modes (eg, diagonal up-right mode and diagonal down-left mode, as two examples). Then, based on Equation 1 (as one non-limiting example), video encoder 22 and video decoder 30 may determine a modified prediction sample (eg, pred(x, y)).

[0103] The case of the adjacent up-right diagonal mode is illustrated in FIG. 4C. In general, for the angle α defined in FIG. 3, the y-coordinate of the reference sample R-1,y is defined as: y=y'+tan(α)×(x'+1), and the x-coordinate of Rx,-1 is defined by: x=x'+cotan (α)×(y'+1), where tan(α) and cotan(α) are the tangent and cotangent of the angle α. The PDPC weights for the adjacent up-right diagonal mode are, for example: wT=32>>((y'<<1)>>shift), wL=32>>((x'<<1)>>shift), wTL =0 or wT=32>>((y'<<1)>>shift), wL=0, wTL=0.

[0104] Similarly, the case of adjacent diagonal down-left mode is illustrated in FIG. 4D. In general, for the angle β defined in FIG. 3, the x-coordinate of the reference sample Rx,-1 is defined as follows: x=x'+tan(β)×(y'+1), and the y-coordinate of R-1,y is defined by: y=y'+cotan (β)×(x'+1), where tan(β) and cotan(β) are the tangent and cotangent of the angle β. The PDPC weights for the adjacent diagonal down-left mode are, for example: wL=32>>((x'<<1)>>shift), wT=32>>((y'<<1)>>shift), wTL =0 or wL=32>>((x'<<1)>>shift), wT=0, wTL=0.

[0105] In FIG. 4C and 4D, video encoder 22 and video decoder 30 may each determine the line that is above the current block (eg, immediately above, but methods are not limited to this) and determine the x-coordinate in the determined line. The x-coordinate in a certain row is based on the intra-prediction angular mode angle. Video encoder 22 and video decoder 30 may determine a reference sample from one or more reference samples based on a specific row and a specific x-coordinate.

[0106] In order to determine the x-coordinate in a particular line, video encoder 22 and video decoder 30 may determine one of the cotangent (eg, for an adjacent diagonal up-right mode) or the tangent (eg, for an adjacent diagonal down-left mode) of the angular mode angle of the intra -predictions. Video encoder 22 and video decoder 30 may determine an x-coordinate in a certain row based on one of the cotangent or tangent of an intra-prediction angular mode angle, a prediction sample x-coordinate, and a prediction sample y-coordinate. For example, for an adjacent diagonal up-right angle intra-prediction mode, the x-coordinate at a particular row is x'+cotan(α)×(y'+1), and for an adjacent diagonal down-left mode, the x-coordinate at a particular row row is x'+tan(β)×(y'+1), where x' and y' are the x and y coordinates of the modified prediction sample.

[0107] Similarly, in FIG. 4C and 4D, video encoder 22 and video decoder 30 may each determine the column that is to the left of the current block (eg, immediately to the left, but methods are not limited to this) and determine the y-coordinate at the determined column. The y-coordinate in a particular column is based on the intra-prediction angular mode angle. Video encoder 22 and video decoder 30 may determine a reference sample from one or more reference samples based on the determined column and the determined y-coordinate.

[0108] To determine the y-coordinate in a particular column, video encoder 22 and video decoder 30 may determine one of the cotangent (eg, for an adjacent diagonal down-left mode) or tangent (eg, for an adjacent diagonal up-right mode) of the angle mode angle of the intra -predictions. Video encoder 22 and video decoder 30 may determine the y-coordinate in a particular column based on one of the cotangent or tangent of the intra-prediction angular mode angle, the x-coordinate of the prediction sample, and the y-coordinate of the prediction sample. For example, for an adjacent diagonal up-right angle intra-prediction mode, the y-coordinate at a particular column is y'+tan(α)×(x'+1), and for an adjacent diagonal down-left mode, the y-coordinate at a particular column is column is y'+cotan(β)×(x'+1), where x' and y' are the x and y coordinates of the modified prediction sample.

[0109] Based on the determined x and y coordinates, video encoder 22 and video decoder 30 may determine reference samples (e.g., a first reference sample based on a certain row and a certain x-coordinate and a second reference sample based on a certain column and a certain y-coordinate) . Also, video encoder 22 and video decoder 30 may determine weights in accordance with the exemplary methods set forth above for adjacent diagonal modes (eg, adjacent diagonal up-right mode and adjacent diagonal down-left mode, as two examples). Then, based on Equation 1 (as one non-limiting example), video encoder 22 and video decoder 30 may determine a modified prediction sample (eg, pred(x, y)).

[0110] The above describes exemplary methods for diagonal up-right and down-left modes and adjacent diagonal up-right and adjacent diagonal down-left modes as exemplary angular modes for which PDPC can be applied. The exemplary methods can be extended to other angle modes as well. Also, in some examples, one or more reference samples have both an x- and a y-coordinate that is different from both the x- and y-coordinates of the prediction sample in the prediction block. For example, in the above example equations, to determine the x- and y-coordinates in the respective rows and columns to determine the reference samples, the x-coordinate is different from the x-coordinate of the modified prediction sample, and the y-coordinate is different from the y-coordinate of the modified sample predictions. That is, the reference samples may not be in the same row or the same column as the modified prediction sample.

[0111] As is the case for DC, planar, horizontal, and vertical PDPC modes, there is no additional edge filtering, such as as specified in 'J. Chen, E. Alshina, G. J. Sullivan, J.-R. Ohm, J. Boyce, “Algorithm description of Joint Exploration Test Model 7,” 7th JVET Meeting, Torino, Italy, July 2017, JVET-G1001, for diagonal and adjacent diagonal modes when PDPC extends to these angular modes.

[0112] As described above, the exemplary techniques described in this disclosure can enable the application of PDPC to intra-prediction angular modes with minimal impact on complexity. In practical implementation, the values of tangents and cotangents of angles can be stored in tables so that they are not calculated on the fly (eg, at runtime). Below are sample tables for 129 angle modes in total:

[0113] TanAngTable[33] = {0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34 , 36, 38, 40, 42, 44, 46, 49, 52, 55, 58, 61, 64}.

[0114] CotanAngTable[33] = {0, 65536, 32768, 21845, 16384, 13107, 10923, 8192, 6554, 5461, 4681, 4096, 3641, 3277, 2979, 2731, 2521, 2185 , 1820, 1725, 1638, 1560, 1489, 1425, 1337, 1260, 1192, 1130, 1074, 1024}.

[0115] Moreover, the tables may already be used by angular block intra-prediction and may be reused to propagate PDPC to diagonal and adjacent modes (eg, angular intra-prediction modes). Therefore, no additional tables may be required in a PDPC implementation. In some examples, custom tables may be generated, for example, by training, to further optimize PDPC.

[0116] In some cases, all horizontal angular modes are mapped to vertical modes by mirroring the block about the bottom-right diagonal. Symmetry about vertical mode allows you to further reduce the number of angles to 33 when storing tangent and cotangent values in TanAngTable and CotanAngTable, respectively. Due to the required integer precision, the values in both tables are scaled by a factor of 64 in the case of TanAngTable and a value of 1024 in the case of CotanAngTable. Multiplications in the formulas above to calculate the x and y coordinates are avoided by accumulating table values corresponding to the angular mode as x' and y' increase as the prediction block is passed.

[0117] Interpolation of reference samples, such as by linear or cubic interpolation, or rounding to the nearest neighbor, may be used if fractional values are being calculated. For example, to determine one or more reference samples that are external to the current block based on the intra-angle mode, video encoder 22 and video decoder 30 may be configured to determine a set of one or more samples based on the intra-angle mode and interpolate a set of one or more samples to generate one or more pivot samples. Interpolation is one example. In some examples, video encoder 22 or video decoder 30 may perform at least one of interpolation, round with offset, or round without offset. Video encoder 22 or video decoder 30 may perform such offset or non-offset rounding based on adjacent samples in the set of one or more samples to generate one or more reference samples.

[0118] Clipping may be required to prevent the availability of reference samples outside the boundaries of the reference line buffer, in case large coordinate values are calculated. If clipping is performed, the last available reference sample may be used, or PDPC may only fall back to angular intra-prediction, which is equivalent to applying zero weights for wL, wT, wTL in Equation. 1 for example. For example, to determine one or more reference samples that are external to the current block based on the intra-prediction angle mode, video encoder 22 and video decoder 30 may be configured to determine that one or more samples external to the current block identified on based on the intra-prediction angle mode are not stored in the reference line buffer, and determine one or more reference samples based on the last reference sample stored in the reference line buffer.

[0119] In some examples, instead of using the last sample in the reference line buffer, PDPC may be turned off for the current block, or PDPC may be turned off for certain predicted samples such that normal intra-prediction is used (e.g., no modified prediction samples). As one example, for a prediction sample in a prediction block, video encoder 22 or video decoder 30 may determine that the first reference sample is available in the reference buffer, but that the second reference sample is not available in the reference buffer. In this example, video encoder 22 or video decoder 30 may determine that PDPC is off for the prediction sample. However, in some examples, video encoder 22 or video decoder 30 may use the first reference sample for PDPC and not use the second reference sample (eg, by setting the weight for the second reference sample to zero).

[0120] As described above, in some examples, video encoder 22 and video decoder 30 may perform exemplary PDPC techniques on a plurality of prediction samples in a prediction block. However, there may be cases where PDPC methods are used on some prediction samples but not on other prediction samples in the same prediction block. For example, suppose that for the first prediction sample in a prediction block, video encoder 22 or video decoder 30 performs the PDPC techniques described in this disclosure. However, for the second prediction sample in the same prediction block, assume that the reference samples needed to perform the PDPC methods on the second prediction sample are not stored in the reference line buffer. In this example, for the second prediction sample, video encoder 22 or video decoder 30 may not perform PDPC techniques and normal intra-prediction techniques may be used. In some cases, for the second prediction sample, it may be possible that one of the reference samples is available in the reference line buffer and the other is not. In some examples, video encoder 22 or video decoder 30 may not perform PDPC techniques on the second prediction sample, or may only use a reference sample that is available and assign zero weight to weights applied to a reference sample that is not available.

[0121] The compression efficiency for propagating PDPC to diagonal and adjacent corner modes is illustrated in the following tables. There are a total of 16 modes adjacent to the diagonal up-right mode and 16 modes adjacent to the diagonal down-left mode in this exemplary testing. The exemplary testing condition is 'full intra' and the QP values used are {22, 27, 32, 37}. Table 1 (FIG. 5A) presents the BD-rates full intra-test conditions for PDPC expansion (diagonal and adjacent), without diagonal and adjacent mode boundary filtering. The table in FIG. 5A lists the BD-rates when testing is done with edge filtering turned off for the diagonal and adjacent modes. Additionally, Table 2 (FIG. 5B) presents the BD-rates of the full intra-test conditions for PDPC extension (diagonal and adjacent), including diagonal and adjacent mode boundary filtering. Additionally, Table 2 in FIG. 5B lists the BD-rates when testing is done with edge filtering enabled for the diagonal and adjacent modes.

[0122] Similar to the extension of PDPC to diagonal and adjacent angular modes, PDPC can be extended to angular modes that are adjacent to horizontal and vertical modes. Adjacent angular modes in this case may refer to the angular modes on either side of the horizontal and vertical modes. In the case of adjacent horizontal angle modes, the x-coordinate of Rx,-1 is equal to the x-coordinate of pred(x, y). Approximate PDPC weights are: wT=16>>((y<<1)>>shift), wL=0, wTL=wT. In the case of adjacent vertical angle modes, the y-coordinate of R-1,y is equal to the y-coordinate of pred(x, y). Approximate PDPC weights are: wL=16>>((x<<1)>>shift), wT=0, wTL=wL.

[0123] FIG. 6 is a block diagram illustrating an exemplary video encoder 22 that may implement the techniques of the present disclosure. Fig. 6 is provided for the purpose of explanation and is not to be understood as limiting the methods as broadly explained by way of example and described in this disclosure. The techniques of this disclosure may be applicable to various coding standards (eg, HEVC or VVC) or methods.

[0124] Various modules (blocks) in FIG. 6 are illustrated to aid understanding of the operations performed by video encoder 22. The modules may be implemented as fixed function circuits, programmable circuits, or a combination of both. Fixed function circuits refer to circuits that provide specific functionality and are preconfigured for operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, the programmable circuits may execute software or firmware that causes the programmable circuits to operate in a manner determined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (eg, accept parameters or output parameters), but the types of operations that fixed-function circuits perform are generally unchanged. In some examples, one or more modules may be separate circuit blocks (fixed function or programmable), and in some examples, one or more modules may be integrated circuits.

[0125] In the example of FIG. 6, the video encoder 22 includes a prediction processing unit 100, a video data memory 101, a residual generation unit 102, a transform processing unit 104, a quantization unit 106, an inverse quantization unit 108, an inverse transform processing unit 110, a reconstruction unit 112, a filtering unit 114, a buffer. 116 of the decoded picture and the entropy encoding module 118 . The prediction processing unit 100 includes an inter prediction processing unit 120 and an intra prediction processing unit 126 . The inter prediction processing module 120 may include a motion estimation module and a motion compensation module (not shown).

[0126] The video data memory 101 may be configured to store video data to be encoded by the components of the video encoder 22. The video data stored in the video data memory 101 may be obtained from a video source 18, for example. The decoded picture buffer 116 may be a reference picture memory that stores reference video data for use in encoding video data by video encoder 22, such as in intra- or inter-coding modes. The video data memory 101 and the decoded picture buffer 116 may be formed by any of a variety of memory devices such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of devices. memory. The video data memory 101 and the decoded picture buffer 116 may be provided by the same memory device or by separate memory devices. In various examples, video data memory 101 may be on the same chip as other components of video encoder 22, or off-chip relative to those components. The video data memory 101 may be the same as the storage media 20 in FIG. 1 or part of them.

[0127] Video encoder 22 receives video data. Video encoder 22 may encode each CTU in a video data picture slice. Each of the CTUs may be associated with equal-sized luma CTBs and corresponding picture CTBs. As part of CTU coding, prediction processing unit 100 may perform partitioning to divide the CTB CTU into progressively smaller blocks. Smaller blocks may be CU coding blocks. For example, the prediction processing module 100 may partition the CTB associated with the CTU according to a tree structure. In accordance with one or more methods of the present disclosure, for each respective non-leaf node of the tree structure, at each depth level of the tree structure, there are a plurality of allowed split patterns for the respective non-leaf node, and the video block corresponding to the respective non-leaf node is split into video blocks corresponding to the child nodes of the respective non-leaf node according to one of the plurality of allowed partition patterns. In one example, prediction processing module 100 or another processing module of video encoder 22 may be configured to perform any combination of the techniques described herein.

[0128] Video encoder 22 may encode the CTU CUs to generate encoded CU representations (ie, encoded CUs). As part of CU encoding, prediction processing unit 100 may partition coding blocks associated with a CU among one or more CU PUs. In accordance with the techniques of the present disclosure, a CU may include only one PU. That is, in some examples of the present disclosure, the CU is not divided into separate prediction blocks, but rather, the prediction process is performed on the entire CU. Thus, each CU may be associated with a luminance predictor and corresponding chrominance predictors. Video encoder 22 and video decoder 30 may support CUs having different sizes. As stated above, the CU size may refer to the size of the CU luminance coding block as well as the size of the luminance prediction block. As discussed above, video encoder 22 and video decoder 30 may support CU sizes defined by any combination of the exemplary partitioning methods described herein.

[0129] The inter prediction processing unit 120 may generate prediction data for the PU by performing inter prediction on each PU of the CU. As explained here, in some examples of the present disclosure, a CU may contain only one PU, that is, CU and PU may be synonymous. The prediction data for the PU may include PU prediction blocks and motion information for the PU. The inter-prediction processing unit 120 may perform different operations for a PU or a CU depending on whether the PU is in an I-slice, a P-slice, or a B-slice. In an I-slice, all PUs match the intra-prediction. Thus, if the PU is in an I slice, the inter prediction processing unit 120 does not perform inter prediction on the PU. Thus, for blocks encoded in I-mode, a predicted block is generated using spatial prediction from previously encoded adjacent blocks in the same frame. If the PU is in a P slice, inter prediction processing unit 120 may use unidirectional inter prediction to generate a PU prediction block. If the PU is in a B slice, inter prediction processing unit 120 may use unidirectional or bidirectional inter prediction to generate a PU prediction block.

[0130] The intra prediction processing unit 126 may generate prediction data for the PU by performing intra prediction on the PU. The prediction data for the PU may include PU prediction blocks and various syntax elements. The intra-prediction processing unit 126 may perform intra-prediction on PUs in I-slices, P-slices, and B-slices.

[0131] In order to perform intra prediction on the PU, the intra prediction processing unit 126 may use a plurality of intra prediction modes to generate a plurality of prediction data sets for the PU. Intra-prediction processing unit 126 may use samples from neighboring PU sample blocks to generate a prediction block for the PU. Neighbor PUs may be above, above and to the right, above and to the left, or to the left of the PU, assuming the encoding order is left to right, top to bottom for PUs, CUs, and CTUs. The intra-prediction processing unit 126 may use various numbers of intra-prediction modes, for example, 35 directional intra-prediction modes. In some examples, the number of intra prediction modes may depend on the size of the region associated with the PU.

[0132] In one example, intra-prediction processing module 126 may be configured to implement disclosure techniques. In other examples, other blocks or modules may be configured to implement all or some of the expansion methods.

[0133] The prediction processing unit 100 may select the prediction data for the CU PU from the prediction data generated by the PU inter prediction processing unit 120 or the prediction data generated by the PU intra prediction processing unit 126 . In some examples, the prediction processing unit 100 selects prediction data for the CU PUs based on the rate/distortion metrics of the prediction data sets. Prediction blocks of selected prediction data may be referred to herein as selected prediction blocks.

[0134] Residual generation unit 102 may generate, based on coding blocks (eg, luminance coding blocks, Cb and Cr) for CUs and selected prediction blocks (eg, luminance prediction blocks, Cb and Cr) for CU PUs, residual blocks (eg , luma residual blocks, Cb and Cr) for CU. For example, residual generation module 102 may generate residual CUs such that each sample in the residual blocks has a value equal to the difference between a sample in the coding block of the CU and a corresponding sample in the corresponding selected prediction block of the CU PU.

[0135] Transform processing unit 104 may perform quadtree splitting or quadtree/binary tree splitting (QTBT) to split residual blocks associated with a CU into transform blocks associated with a TU of the CU. Thus, a TU may be associated with a luma transform block and two chrominance transform blocks. The sizes and positions of the CU TU luma and chrominance transform blocks may or may not be based on the sizes and positions of the CU PU prediction blocks. The quadtree structure, known as a "residual quadtree" (RQT), may include nodes associated with each of the regions. The CU TUs may correspond to RQT leaf nodes. Video encoder 22 cannot further divide CUs into TUs using the RQT structure. For example, in one example, a CU includes one TU.

[0136] Transform processing unit 104 may generate transform coefficient blocks for each TU of the CU by applying one or more transforms to the transform blocks of the TU. Transform processing module 104 may apply various transforms to a transform unit associated with a TU. For example, transform processing module 104 may apply a discrete cosine transform (DCT), a directional transform, or a conceptually similar transform to the transform block. In some examples, the transform processing module 104 does not apply transforms to the transform block. In such examples, a transform block may be interpreted as a transform coefficient block.

[0137] Quantization module 106 may quantize the transform coefficients in the coefficient block. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, an n-bit transform factor may be rounded down to an m-bit transform factor during quantization, where n is greater than m. Quantization unit 106 may quantize the coefficient block associated with the TU of the CU based on the value of a quantization parameter (QP) associated with the CU. Video encoder 22 may adjust the amount of quantization applied to the coefficient blocks associated with the CU by adjusting the QP value associated with the CU. Quantization may introduce loss of information. Thus, the quantized transform coefficients may have lower accuracy than the original ones.

[0138] The inverse quantization unit 108 and the inverse transform processing unit 110 may apply inverse quantization and inverse transforms to the coefficient block, respectively, to recover the residual block from the coefficient block. Recovery unit 112 may add the recovered residual block with corresponding samples from one or more prediction blocks generated by prediction processing unit 100 to form a recovered transform block associated with the TU. By recovering the transform blocks for each TU of the CU in this way, video encoder 22 can recover the coding blocks of the CU.

[0139] Filtering module 114 may perform one or more deblocking filters and/or other filtering operations to reduce blocking artifacts in coding blocks associated with a CU. The decoded picture buffer 116 may store the recovered coding blocks after the filter module 114 performs one or more deblocking operations on the recovered coding blocks. Inter-prediction processing unit 120 may use a reference picture that contains recovered coding blocks to perform inter-prediction on PUs of other pictures. In addition, the intra prediction processing unit 126 may use the recovered coding blocks in the decoded picture buffer 116 to perform intra prediction on other PUs in the same picture as the CU.

[0140] Entropy encoding unit 118 may receive data from other functional components of video encoder 22. For example, entropy encoding unit 118 may receive blocks of coefficients from quantization unit 106 and may receive syntax elements from prediction processing unit 100. Entropy encoding module 118 may perform one or more entropy encoding operations on the data to generate entropy encoded data. For example, entropy encoding unit 118 may perform a CABAC operation, a context adaptive variable length coding (CAVLC) operation, a variable to variable length (V2V) coding operation, a syntactic context adaptive binary arithmetic coding (SBAC) operation, an entropy coding operation with interval partitioning (PIPE), an exponential Golomb encoding operation, or another type of entropy encoding operation on the data. Video encoder 22 may output a bit stream that includes entropy encoded data generated by entropy encoding module 118 . For example, the bitstream may include data that represents a split structure for a CU in accordance with the techniques of the present disclosure.

[0141] FIG. 7 is a block diagram illustrating an exemplary video decoder 30 that is configured to implement the techniques of the present disclosure. Fig. 7 is provided for the purpose of explanation and is not intended to limit the methods as broadly illustrated and described in this disclosure. For the purpose of explanation, the present disclosure describes video decoder 30 in the context of HEVC or VVC coding. However, the methods of this disclosure may be applicable to other standards or encoding methods.

[0142] The various modules shown in FIG. 7 are illustrated to explain the operations performed by video decoder 30. The modules may be implemented as fixed function circuits, programmable circuits, or a combination of both. Similarly to FIG. 6, fixed function circuits refer to circuits that provide specific functionality and are pre-configured for operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, the programmable circuits may execute software or firmware that cause the programmable circuits to operate in a manner determined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (eg, accept parameters or output parameters), but the types of operations that fixed-function circuits perform are generally unchanged. In some examples, one or more modules may be separate circuit blocks (fixed function or programmable), and in some examples, one or more modules may be integrated circuits.

[0143] In the example of FIG. 7, the video decoder 30 includes an entropy decoding unit 150, a video data memory 151, a prediction processing unit 125, an inverse quantization unit 154, an inverse transform processing unit 156, a reconstruction unit 158, a filtering unit 160, and a decoded picture buffer 162. The prediction processing unit 125 includes a motion compensation unit 164 and an intra prediction processing unit 166 . In other examples, video decoder 30 may include more, less, or other functional components.

[0144] The video data memory 151 may store encoded video data, such as an encoded video bitstream, to be decoded by the components of the video decoder 30. The video data stored in the video data memory 151 may be obtained, for example, from a computer-readable medium 16, such as from a local video source such as as a camera, through a wired or wireless video network, or through access to physical storage media. The video data memory 151 may generate a coded picture buffer (CPB) that stores encoded video data from an encoded video bitstream. The decoded picture buffer 162 may be a reference picture memory that stores reference video data for use in video decoding by video decoder 30, such as in intra- or inter-coding modes, or for output. The video data memory 151 and the decoded picture buffer 162 may be formed by any of a variety of memory devices such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of devices. memory. The video data memory 151 and the decoded picture buffer 162 may be provided by the same memory device or by separate memory devices. In various examples, video data memory 151 may be on-chip with other components of video decoder 30, or off-chip relative to those components. The video data memory 151 may be the same as the storage media 28 in FIG. 1, or part of them.

[0145] The video data memory 151 receives and stores encoded video data (eg, NAL units) of the bitstream. Entropy decoding module 150 may receive encoded video data (eg, NAL units) from video data memory 151 and may parse the NAL units to obtain syntax elements. Entropy decoding module 150 may entropy decode entropy encoded syntax elements in NAL units. Prediction processing unit 125, inverse quantization unit 154, inverse transform processing unit 156, reconstruction unit 158, and filter unit 160 may generate decoded video data based on syntax elements extracted from the bitstream. Module 150 entropy decoding may perform a process essentially reverse process module 118 entropy encoding.

[0146] In accordance with some examples of the present disclosure, entropy decoding module 150 or another processing module of video decoder 30 may determine a tree structure as part of deriving syntax elements from a bitstream. The tree structure may specify how a source video block, such as a CTB, is split into smaller video blocks, such as coding units. In accordance with one or more methods of the present disclosure, for each respective non-leaf node of the tree structure at each depth level of the tree structure, there is a plurality of allowed split types for the respective non-leaf node, and the video block corresponding to the respective non-leaf node is partitioned into video blocks corresponding to the child nodes of the respective non-leaf node according to one of the plurality of allowed partition patterns.

[0147] In addition to obtaining syntax elements from a bitstream, video decoder 30 may perform a recovery operation on an unsplit CU. To perform a restore operation on a CU, video decoder 30 may perform a restore operation on each TU of the CU. By performing a restore operation for each CU TU, video decoder 30 can restore the remaining CUs. As discussed above, in one exemplary disclosure, a CU includes one TU.

[0148] As part of performing a recovery operation on the TU CU, inverse quantizer 154 may inverse quantize, i.e. de-quantize, blocks of coefficients associated with the TU. After inverse quantizer 154 has inversely quantized the coefficient block, inverse transform processing module 156 may apply one or more inverse transforms to the coefficient block to generate a residual block associated with the TU. For example, inverse transform processing module 156 may apply an inverse DCT, inverse integer transform, inverse Karhunen-Loeve (KLT), inverse rotation, inverse directional transform, or other inverse transform to the coefficient block.

[0149] If the CU or PU is encoded using intra prediction, intra prediction processing unit 166 may perform intra prediction to generate PU prediction blocks. The intra-prediction processing unit 166 may use the intra-prediction mode to generate PU prediction blocks based on samples of spatially adjacent blocks. The intra-prediction processing unit 166 may determine the intra-prediction mode for the PU based on one or more syntax elements obtained from the bitstream.

[0150] In one example, intra-prediction processing module 166 may be configured to implement disclosure techniques. In other examples, other blocks or modules may be configured to implement all or some of the expansion methods.

[0151] If the PU is encoded using inter-prediction, entropy decoding module 150 may determine motion information for the PU. The motion compensation module 164 may determine, based on the motion information of the PU, one or more reference blocks. Motion compensation module 164 may generate, based on one or more reference blocks, prediction blocks (eg, luma, Cb, and Cr prediction blocks) for the PU. As discussed above, a CU may include only one PU. That is, a CU may not be divided into multiple PUs.

[0152] Recovery module 158 may use transform blocks (eg, luminance transform blocks, Cb and Cr) for CU TUs and prediction blocks (eg, luminance blocks, Cb and Cr) of CU PUs, i.e., either intra-prediction data , or inter-prediction data, as applicable, to recover the coding blocks (eg, luminance, Cb, and Cr coding blocks) for the CU. For example, deconstructor 158 may add samples of transform blocks (eg, luminance transform blocks, Cb and Cr) with corresponding samples of prediction blocks (eg, luminance prediction blocks, Cb and Cr) to recover coding blocks (eg, luminance coding blocks, Cb and Cr) CU.

[0153] Filtering module 160 may perform a deblocking operation to reduce blocking artifacts associated with CU coding blocks. Video decoder 30 may store coding units CU in decoded picture buffer 162 . The decoded picture buffer 162 may provide reference pictures for subsequent motion compensation, intra-prediction, and presentation on a display device, such as display device 32 in FIG. 1. For example, video decoder 30 may perform, based on the blocks in decoded picture buffer 162, intra-prediction or inter-prediction operations for PUs of other CUs.

[0154] The video decoder outputs a decoded version of the current picture, which includes the decoded version of the current block. When the video decoder is a video decoder configured to output displayed decoded video, the video decoder may, for example, output a decoded version of the current picture to a display device. When decoding is performed as part of a decoding cycle of a video encoding process, the video decoder may store a decoded version of the current picture as a reference picture for use in encoding another picture of video data.

[0155] FIG. 8 is a flowchart illustrating an exemplary method for encoding video data. Video encoder 22 (eg, with intra prediction processing unit 126) may be configured to determine a prediction block that includes a plurality of prediction samples for the current block based on an intra prediction angular mode that is not DC, planar, horizontal, or vertical intra-prediction mode (200). The video data memory 101 or DPB 16 may store a prediction block.

[0156] Video encoder 22 (eg, with intra-prediction processing module 126) may be configured to modify the prediction block prediction sample to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC) (202). For example, to modify the prediction sample, video encoder 22 may be configured to determine one or more reference samples that are external to the current block based on the intra-prediction angle mode (204) and modify the prediction sample to generate a modified prediction sample based on a certain one or more reference samples (206). In one example, to determine one or more reference samples that are external to the current block, video encoder 22 may be configured to determine one or more reference samples having an x- and y-coordinate different from the x- and y-coordinate of the sample. predictions in the prediction block.

[0157] As one example, to determine one or more reference samples that are external to the current block, video encoder 22 may be configured to determine the line that is above the current block and determine the x-coordinate in the determined line. The x-coordinate in a certain row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video encoder 22 may determine a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. As another example, to determine one or more reference samples that are external to the current block, video encoder 22 may be configured to determine the column that is to the left of the current block and determine the y-coordinate in the determined column. The y-coordinate in a particular column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video encoder 22 may be configured to determine a reference sample from one or more reference samples based on the particular column and the particular y-coordinate.

[0158] As one example, to determine one or more reference samples that are external to the current block, video encoder 22 may be configured to determine the line that is above the current block and determine the x-coordinate in the determined line. The x-coordinate in a specific row is based on the intra-prediction angular mode angle. Video encoder 22 may be configured to determine a reference sample from one or more reference samples based on a specific row and a specific x-coordinate. In order to determine the x-coordinate at a specific row, video encoder 22 may be configured to determine one of the cotangent or tangent of the intra-prediction angular mode angle, and determine the x-coordinate at the specific row based on one of the cotangent or tangent of the intra-prediction angular mode angle, x-coordinates of the prediction sample and y-coordinates of the prediction sample.

[0159] As another example, to determine one or more reference samples that are external to the current block, video encoder 22 may be configured to determine the column that is to the left of the current block and determine the y-coordinate in the determined column. The y-coordinate in a specific column is based on the intra-prediction angular mode angle. Video encoder 22 may be configured to determine a reference sample from one or more reference samples based on a specific column and a specific y-coordinate. To determine the y-coordinate at a specific column, video encoder 22 may be configured to determine one of the cotangent or tangent of the intra-prediction angular mode angle, and determine the y-coordinate at the specific column based on one of the cotangent or tangent of the intra-prediction angular mode angle, x-coordinates of the prediction sample and y-coordinates of the prediction sample.

[0160] As one example, to determine one or more reference samples that are external to the current block based on the intra angle mode, video encoder 22 may be configured to determine a set of one or more samples based on the intra angle mode. -predict and interpolate a set of one or more samples to generate one or more reference samples. In some examples, video encoder 22 may be configured to perform at least one of interpolation, round with a shift, or round without a shift on a set of one or more samples to generate one or more reference samples.

[0161] As one example, to determine one or more reference samples that are external to the current block, based on the intra-prediction angular mode, video encoder 22 may be configured to determine that one or more samples external to the current block identified based on the intra-prediction angle mode are not stored in the reference line buffer, and determine one or more reference samples based on the last reference sample stored in the reference line buffer. In some examples, modifying a prediction block prediction sample may include modifying a first prediction block prediction sample, and the one or more reference samples may be the first set of the one or more reference samples. Video encoder 22 may be configured to determine, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in a reference line buffer, and perform one of the following steps: (a) not apply PDPC to the second prediction sample, or (b) apply PDPC using only the reference samples available in the reference line buffer (eg, by applying zero weight to a reference sample that is not available).

[0162] According to one or more examples, video encoder 22 may be configured to determine a plurality of weights based on the x- and y-coordinates of the prediction sample. To modify the prediction sample, video encoder 22 may be configured to modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample.

[0163] Video encoder 22 may be configured to determine a residual value for the residual block based on the modified prediction sample and the sample value in the current block (208). Video encoder 22 may be configured to signal information indicative of the residual value (210).

[0164] FIG. 9 is a flowchart illustrating an exemplary method for decoding video data. Video decoder 30 (eg, with intra prediction processing module 166) may be configured to determine a prediction block that includes a plurality of prediction samples for the current block based on an intra prediction angular mode that is not DC, planar, horizontal, or vertical intra-prediction mode (212). Video memory 151 or DPB 162 may store a prediction block.

[0165] Video decoder 30 (eg, with intra-prediction processing module 166) may be configured to modify the prediction block prediction sample to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC) (214). For example, to modify the prediction sample, video decoder 30 may be configured to determine one or more reference samples that are external to the current block based on the intra-prediction angle mode (216) and modify the prediction sample to generate a modified prediction sample on based on a defined one or more reference samples (218). In one example, to determine one or more reference samples that are external to the current block, video decoder 30 may be configured to determine one or more reference samples having both an x- and a y-coordinate other than x- and y -coordinates of the prediction sample in the prediction block.

[0166] As one example, to determine one or more reference samples that are external to the current block, video decoder 30 may be configured to determine the line that is above the current block and determine the x-coordinate in the determined line. The x-coordinate in a certain row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video decoder 30 may determine a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. As another example, to determine one or more reference samples that are external to the current block, video decoder 30 may be configured to determine the column that is to the left of the current block and determine the y-coordinate in the determined column. The y-coordinate in a specific column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1. Video decoder 30 may be configured to determine a reference sample from one or more reference samples based on the specific column and the specific y-coordinate.

[0167] As one example, to determine one or more reference samples that are external to the current block, video decoder 30 may be configured to determine the line that is above the current block and determine the x-coordinate in the determined line. The x-coordinate in a certain row is based on the intra-prediction angular mode angle. Video decoder 30 may be configured to determine a reference sample from one or more reference samples based on a specific row and a specific x-coordinate. To determine the x-coordinate in a specific row, video decoder 30 may be configured to determine one of the cotangent or tangent of the intra-prediction angular mode angle, and determine the x-coordinate in the specific row based on one of the cotangent or tangent of the intra-prediction angular mode, x-coordinates of the prediction sample and y-coordinates of the prediction sample.

[0168] As another example, to determine one or more reference samples that are external to the current block, video decoder 30 may be configured to determine the column that is to the left of the current block and determine the y-coordinate in the determined column. The y-coordinate in a particular column is based on the intra-prediction angular mode angle. Video decoder 30 may be configured to determine a reference sample from one or more reference samples based on a specific column and a specific y-coordinate. To determine the y-coordinate at a specific column, video decoder 30 may be configured to determine one of the cotangent or tangent of the intra-prediction angular mode angle, and determine the y-coordinate at the specific column based on one of the cotangent or tangent of the intra-prediction angular mode angle, x-coordinates of the prediction sample and y-coordinates of the prediction sample.

[0169] As one example, to determine one or more reference samples that are external to the current block based on the intra angle mode, video decoder 30 may be configured to determine a set of one or more samples based on the intra angle mode. -predict and interpolate a set of one or more samples to generate one or more reference samples. In some examples, video decoder 30 may be configured to perform at least one of interpolation, round with a shift, or round without a shift on a set of one or more samples to generate one or more reference samples.

[0170] As one example, to determine one or more reference samples that are external to the current block, based on the intra-prediction angular mode, video decoder 30 may be configured to determine that one or more samples external to the current block , identified based on the intra-prediction angle mode, are not stored in the reference line buffer, and determine one or more reference samples based on the last reference sample stored in the reference line buffer. In some examples, modifying a prediction block prediction sample may include modifying a first prediction block prediction sample, and the one or more reference samples may be the first set of the one or more reference samples. Video decoder 30 may be configured to determine, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in a reference line buffer, and perform one of the following steps: (a) not apply PDPC to the second prediction sample, or (b) apply PDPC using only the reference samples available in the reference line buffer (eg, by applying zero weight to a reference sample that is not available).

[0171] According to one or more examples, video decoder 30 may be configured to determine a plurality of weights based on the x- and y-coordinates of the prediction sample. To modify the prediction sample, video decoder 30 may be configured to modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample.

[0172] Video decoder 30 may be configured to resample the current block based on the modified prediction sample and the residual (220). For example, video decoder 30 may receive information for the residual value. Video decoder 30 may add the residual value to the modified prediction sample to reconstruct the sample in the current block.

[0173] Some aspects of the present disclosure have been described with respect to extensions to the HEVC standard for purposes of illustration. However, the techniques described in this disclosure may be used for other video encoding processes, including other standard or proprietary video encoding processes not yet developed.

[0174] A video encoding device as described in this disclosure may refer to a video encoder or video decoder. Likewise, a video coding module may refer to a video encoder or a video decoder. Similarly, video encoding may refer to video encoding or video decoding, as applicable. In the present disclosure, the phrase “based on” may indicate based only, based at least in part, or based in some way. The present disclosure may use the term "video unit" or "video block" or "block" to refer to one or more sample blocks and syntax structures used to encode samples of one or more sample blocks. Exemplary types of video units may include CTUs, CUs, PUs, transform units (TUs), macroblocks, macroblock splits, and so on. In some contexts, the discussion of PUs may be interchangeable with the discussion of macroblocks or macroblock partitions. Exemplary video block types may include coding tree blocks, coding blocks, and other types of video data blocks.

[0175] It should be borne in mind that, depending on the example, certain actions or events of any of the methods described here may be performed in a different sequence, may be summarized, combined, or omitted altogether (for example, not all of the described actions or events are necessary for practical method implementations). Moreover, in some examples, actions or events may be executed simultaneously, such as through multi-threading, interrupt handling, or multiple processors, rather than sequentially.

[0176] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions may be stored or transmitted as one or more instructions or code on a computer-readable medium and executed by a hardware processor. Computer-readable media may include computer-readable storage media that corresponds to a tangible medium, such as storage media, or communication media, including any medium that allows a computer program to be transferred from one place to another, such as in accordance with a communication protocol. Thus, computer-readable media can generally correspond to (1) tangible computer-readable storage media that is non-transient (non-temporal), or (2) a communication medium such as a signal or carrier wave. Storage media can be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code, and/or data structures for implementing the methods described in this disclosure. The computer program product may include a computer-readable medium.

[0177] By way of example, and not limitation, such computer-readable storage media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any another medium that can be used to store the desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection can be properly defined as a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then coaxial cable, fiber optic cable , twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the media definition. It should be understood, however, that computer-readable storage media and storage media do not include connections, carrier waves, signals, or other transient (temporary) media, but instead refer to non-transitory (non-temporal) tangible storage media. The magnetic disc (disk) and the optical disc (disc) as used herein include a compact disc (CD), a laser disc, an optical disc, a digital versatile disc (DVD), a floppy disc, and a Blu-ray disc, where the magnetic discs usually reproduce data magnetically, while optical discs (discs) reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0178] The instructions may be executed by one or more processors, such as one or more DSPs, general purpose digital microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuits. Accordingly, the term "processor", as used here, may refer to any of the structures described above, or any other structure suitable for implementing the methods described here. Also, in some aspects, the functionality described herein may be provided in dedicated hardware and/or software modules configured for encoding and decoding or embedded in a combined codec. Also, the methods may be fully implemented in one or more circuits or logic elements.

[0179] The techniques of the present disclosure may be implemented in a wide variety of devices or devices, including a wireless telephone, an integrated circuit (IC), or a set of ICs (eg, a chipset). Various components, modules, or blocks are described in this disclosure to highlight the functional aspects of devices configured to perform the disclosed methods, but do not necessarily require implementation by different hardware modules. Rather, as described above, various modules may be combined in a codec hardware module, or provided by a combination of cooperating hardware modules, including one or more processors, as described above, in conjunction with suitable software and/or firmware.

[0180] Various examples have been described. These and other examples are within the scope of the following claims.

Claims (199)

1. A method for decoding video data, the method comprising: determining a prediction block that includes a plurality of prediction samples for the current block based on an angular intra-prediction mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modifying the prediction sample from the plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, the modification of the prediction sample comprising: determining one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; and restoring a sample of the current block based on the modified prediction sample and the residual. 2. The method of claim 1, wherein determining one or more reference samples that are external to the current block comprises defining one or more reference samples having both an x-coordinate and a y-coordinate that differ from the respective x-coordinates. and y-coordinates of the prediction sample in the prediction block. 3. The method of claim 1, wherein determining one or more reference samples that are external to the current block comprises: determining the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determining a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. 4. The method of claim 1, wherein determining one or more reference samples that are external to the current block comprises: defining the column to the left of the current block; determining a y-coordinate in the determined column, wherein the y-coordinate in the determined column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determining a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 5. The method of claim 1, wherein determining one or more reference samples that are external to the current block comprises: determining the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is based on an angle of the intra-prediction angular mode; and determining a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. 6. The method according to claim 5, wherein the definition of the x-coordinate in a certain line contains: determining one of the cotangent or tangent of the intra-prediction angular mode angle; and determining an x-coordinate in a certain row based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 7. The method of claim 1, wherein determining one or more reference samples that are external to the current block comprises: defining the column to the left of the current block; determining a y-coordinate in the determined column, wherein the y-coordinate in the determined column is based on an intra-prediction angular mode angle; and determining a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 8. The method according to claim 7, wherein the determination of the y-coordinate in a certain column contains: determining one of the cotangent or tangent of the intra-prediction angular mode angle; and determining a y-coordinate in a certain column based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 9. The method of claim 1, wherein determining one or more reference samples that are external to the current block based on the intra-prediction angular mode comprises: determining a set of one or more samples based on the intra-prediction angular mode; and at least one of interpolating, rounding with a bias, or rounding without a bias of a set of one or more samples to generate one or more reference samples. 10. The method of claim 1, wherein determining one or more reference samples that are external to the current block based on the intra-prediction angular mode comprises: determining that one or more samples external to the current block, identified based on the intra-prediction angular mode, are not stored in the reference line buffer; and determining one or more reference samples based on the last reference sample stored in the reference line buffer. 11. The method of claim 1, wherein modifying a prediction block prediction sample comprises modifying a first prediction block prediction sample, and wherein the one or more reference samples comprise a first set of one or more reference samples, the method further comprising: determining, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in the reference line buffer; and either not applying PDPC to the second prediction sample, or applying PDPC using only the reference samples available in the reference line buffer. 12. The method according to p. 1, further comprising determining a set of weights based on the x- and y-coordinates of the prediction sample, wherein modifying the prediction sample comprises modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample. 13. A method for encoding video data, the method comprising: determining a prediction block that includes a plurality of prediction samples for the current block based on an angular intra-prediction mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modifying a prediction sample from the plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, the modification of the prediction sample comprising: determining one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; determining a residual value for the residual block based on the modified prediction sample and the sample value in the current block; and signaling information indicating the residual value. 14. The method of claim 13, wherein determining one or more reference samples that are external to the current block comprises defining one or more reference samples having both an x-coordinate and a y-coordinate that differ from the respective x-coordinates. and y-coordinates of the prediction sample in the prediction block. 15. The method of claim 13, wherein determining one or more reference samples that are external to the current block comprises: determining the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determining a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. 16. The method of claim 13, wherein determining one or more reference samples that are external to the current block comprises: defining the column to the left of the current block; determining a y-coordinate in the determined column, wherein the y-coordinate in the determined column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determining a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 17. The method of claim 13, wherein determining one or more reference samples that are external to the current block comprises: determining the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is based on an intra-prediction angular mode angle; and determining a reference sample from one or more reference samples based on the determined row and the determined x-coordinate. 18. The method according to claim 17, wherein the definition of the x-coordinate in a certain line contains: determining one of the cotangent or tangent of the intra-prediction angular mode angle; and determining an x-coordinate in a certain row based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 19. The method of claim 13, wherein determining one or more reference samples that are external to the current block comprises: defining the column to the left of the current block; determining a y-coordinate in the determined column, wherein the y-coordinate in the determined column is based on an intra-prediction angular mode angle; and determining a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 20. The method according to claim 19, wherein the determination of the y-coordinate in a certain column contains: determining one of the cotangent or tangent of the intra-prediction angular mode angle; and determining a y-coordinate in a certain column based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 21. The method of claim 13, wherein determining one or more reference samples that are external to the current block based on the intra-prediction angular mode comprises: determining a set of one or more samples based on the intra-prediction angular mode; and at least one of interpolating, rounding with a bias, or rounding without a bias of a set of one or more samples to generate one or more reference samples. 22. The method of claim 13, wherein determining one or more reference samples that are external to the current block based on the intra-prediction angular mode comprises: determining that one or more samples external to the current block, identified based on the intra-prediction angular mode, are not stored in the reference line buffer; and determining one or more reference samples based on the last reference sample stored in the reference line buffer. 23. The method of claim 13, wherein modifying the prediction block prediction sample comprises modifying the first prediction block prediction sample, and wherein the one or more reference samples comprise a first set of one or more reference samples, the method further comprising: determining, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in the reference line buffer; and either not applying PDPC to the second prediction sample, or applying PDPC using only the reference samples available in the reference line buffer. 24. The method of claim 13, further comprising determining a set of weights based on the x- and y-coordinates of the prediction sample, wherein modifying the prediction sample comprises modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample. 25. A device for decoding video data, the device comprising: a memory configured to store the prediction block; and a video decoder comprising at least one of a fixed function circuit or a programmable circuit, the video decoder being configured to: determine a prediction block that includes a plurality of prediction samples for the current block to be stored in memory based on an intra-prediction angle mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modify the prediction sample from the plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein, to modify the prediction sample, the video decoder is configured to: determine one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; and resample the current block based on the modified prediction sample and the residual. 26. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block, the video decoder is configured to determine one or more reference samples having both an x-coordinate and a y-coordinate different from the respective x-coordinates and y-coordinates of the prediction sample in the prediction block. 27. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block, the video decoder is configured to: determine the line that is above the current block; determine an x-coordinate in the determined row, wherein the x-coordinate in the determined row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determine a reference sample from one or more reference samples based on the specific row and the specific x-coordinate. 28. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block, the video decoder is configured to: determine the column that is located to the left of the current block; determine a y-coordinate in the determined column, wherein the y-coordinate in the determined column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determine a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 29. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block, the video decoder is configured to: determine the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is based on an intra-prediction angular mode angle; and determine a reference sample from one or more reference samples based on the specific row and the specific x-coordinate. 30. The apparatus of claim 29, wherein, in order to determine the x-coordinate in a particular line, the video decoder is configured to: determine one of the cotangent or tangent of the intra-prediction angular mode angle; and determine an x-coordinate in a certain row based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 31. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block, the video decoder is configured to: determine the column that is located to the left of the current block; determine a y-coordinate in the determined column, wherein the y-coordinate in the determined column is based on the intra-prediction angular mode angle; and determine a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 32. The apparatus of claim 31, wherein in order to determine the y-coordinate in a particular column, the video decoder is configured to: determine one of the cotangent or tangent of the intra-prediction angular mode angle; and determine a y-coordinate in a specific column based on one of the cotangent or tangent of the intra-prediction angular mode angle, the x-coordinate of the prediction sample, and the y-coordinate of the prediction sample. 33. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block based on the intra-prediction angle mode, the video decoder is configured to: determine a set of one or more samples based on the intra-prediction angular mode; and perform at least one of interpolation, round with a shift, or round without a shift on the set of one or more samples to generate one or more reference samples. 34. The apparatus of claim 25, wherein in order to determine one or more reference samples that are external to the current block based on the intra-prediction angle mode, the video decoder is configured to: determine that one or more samples external to the current block, identified based on the intra-prediction angular mode, are not stored in the reference line buffer; and determine one or more reference samples based on the last reference sample stored in the reference line buffer. 35. The apparatus of claim 25, wherein, in order to modify the prediction block prediction sample, the video decoder is configured to modify the first prediction block prediction sample, wherein the one or more reference samples comprise a first set of one or more reference samples, and the video decoder is configured to : determine, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in the reference line buffer; and either not apply PDPC to the second prediction sample, or apply PDPC using only the reference samples available in the reference line buffer. 36. The apparatus of claim 25, wherein the video decoder is configured to determine a set of weights based on the x- and y-coordinates of the prediction sample, wherein, to modify the prediction sample, the video decoder is configured to modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample. 37. The apparatus of claim 25, further comprising a display configured to display the current block. 38. The apparatus of claim 25, wherein the apparatus comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box. 39. Device for encoding video data, and the device contains: a memory configured to store the prediction block; and a video encoder comprising at least one of a fixed function circuit or a programmable circuit, the video encoder configured to: determine a prediction block that includes a plurality of prediction samples for the current block to be stored in memory based on an intra-prediction angle mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modify the prediction sample from the plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction combination (PDPC), wherein, to modify the prediction sample, the video encoder is configured to: determine one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; determine a residual value for the residual block based on the modified prediction sample and the sample value in the current block; and signal information indicating the residual value. 40. The apparatus of claim 39, wherein in order to determine one or more reference samples that are external to the current block, the video encoder is configured to determine one or more reference samples having both x-coordinate and y-coordinate different from the respective x-coordinates and y-coordinates of the prediction sample in the prediction block. 41. The apparatus of claim 39, wherein in order to determine one or more reference samples that are external to the current block, the video encoder is configured to: determine the line that is above the current block; determine an x-coordinate in the determined row, wherein the x-coordinate in the determined row is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determine a reference sample from one or more reference samples based on the specific row and the specific x-coordinate. 42. The apparatus of claim 39, wherein in order to determine one or more reference samples that are external to the current block, the video encoder is configured to: determine the column that is located to the left of the current block; determine a y-coordinate in the determined column, wherein the y-coordinate in the determined column is equal to the x-coordinate of the prediction sample plus the y-coordinate of the prediction sample plus 1; and determine a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 43. The apparatus of claim 39, wherein in order to determine one or more reference samples that are external to the current block, the video encoder is configured to: determine the line that is above the current block; determining an x-coordinate in the determined row, wherein the x-coordinate in the determined row is based on an intra-prediction angular mode angle; and determine a reference sample from one or more reference samples based on the specific row and the specific x-coordinate. 44. The apparatus of claim 43, wherein, in order to determine the x-coordinate in a certain line, the video encoder is configured to: determine one of the cotangent or tangent of the intra-prediction angular mode angle; and determine an x-coordinate in a certain row based on one of the intra-prediction angular mode cotangent or tangent, the prediction sample x-coordinate, and the prediction sample y-coordinate. 45. The apparatus of claim 39, wherein in order to determine one or more reference samples that are external to the current block, the video encoder is configured to: determine the column to the left of the current block; determine a y-coordinate in the determined column, wherein the y-coordinate in the determined column is based on the intra-prediction angular mode angle; and determine a reference sample from one or more reference samples based on the specified column and the specified y-coordinate. 46. The apparatus of claim 45, wherein in order to determine the y-coordinate in a particular column, the video encoder is configured to: determine one of the cotangent or tangent of the intra-prediction angular mode angle; and determine a y-coordinate in a specific column based on one of the cotangent or tangent of the intra-prediction angular mode angle, the x-coordinate of the prediction sample, and the y-coordinate of the prediction sample. 47. The apparatus of claim 39, wherein, in order to determine one or more reference samples that are external to the current block, based on the intra-prediction angle mode, the video encoder is configured to: determine a set of one or more samples based on the intra-prediction angular mode; and perform at least one of interpolation, round with a shift, or round without a shift on the set of one or more samples to generate one or more reference samples. 48. The apparatus of claim 39, wherein, in order to determine one or more reference samples that are external to the current block, based on the intra-prediction angle mode, the video encoder is configured to: determine that one or more samples external to the current block, identified based on the intra-prediction angular mode, are not stored in the reference line buffer; and determine one or more reference samples based on the last reference sample stored in the reference line buffer. 49. The apparatus of claim 39, wherein, in order to modify the prediction block prediction sample, the video encoder is configured to modify the first prediction block prediction sample, wherein the one or more reference samples comprise a first set of one or more reference samples, and the video encoder is configured to : determine, for a second prediction sample of the same prediction block, that at least one reference sample from a second set of one or more reference samples for the second prediction sample is not stored in the reference line buffer; and either not apply PDPC to the second prediction sample, or apply PDPC using only the reference samples available in the reference line buffer. 50. The apparatus of claim 39, wherein the video encoder is configured to determine a set of weights based on the x- and y-coordinates of the prediction sample, wherein, to modify the prediction sample, the video encoder is configured to modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples, the determined weights, and the prediction sample. 51. The apparatus of claim 39, wherein the apparatus comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box. 52. A computer-readable storage medium that stores instructions that, when executed, cause one or more processors of the device to decode video data: determine a prediction block that includes a plurality of prediction samples for the current block based on an angular intra-prediction mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modify a prediction sample from a plurality of prediction samples of a prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, wherein the instructions that cause one or more processors to modify the prediction sample contain instructions that cause one or more processors: determine one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; and resample the current block based on the modified prediction sample and the residual. 53. A computer-readable storage medium that stores instructions that, when executed, cause one or more processors of the device to encode video data: determine a prediction block that includes a plurality of prediction samples for the current block based on an angular intra-prediction mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; modify a prediction sample from a plurality of prediction samples of a prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, wherein the instructions that cause one or more processors to modify the prediction sample contain instructions that cause one or more processors: determine one or more reference samples that are external to the current block based on the intra-prediction angular mode; and modify the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; determine a residual value for the residual block based on the modified prediction sample and the sample value in the current block; and signal information indicating the residual value. 54. Device for decoding video data, and the device contains: means for determining a prediction block that includes a plurality of prediction samples for the current block based on an intra-prediction angular mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; means for modifying a prediction sample from a plurality of prediction samples in the prediction block to generate a modified prediction sample using a position-dependent intra prediction (PDPC) combination, the means for modifying the prediction sample comprising: means for determining one or more reference samples that are external to the current block based on the intra-prediction angular mode; and means for modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; and means for restoring a sample of the current block based on the modified prediction sample and the residual. 55. Device for encoding video data, and the device contains: means for determining a prediction block that includes a plurality of prediction samples for the current block based on an intra-prediction angular mode that is not a DC, planar, horizontal, or vertical intra-prediction mode; means for modifying a prediction sample from a plurality of prediction samples of the prediction block to generate a modified prediction sample using a position-dependent intra-prediction (PDPC) combination, the means for modifying the prediction sample comprising: means for determining one or more reference samples that are external to the current block based on the intra-prediction angular mode; and means for modifying the prediction sample to generate a modified prediction sample based on the determined one or more reference samples; means for determining a residual value for the residual block based on the modified prediction sample and the sample value in the current block; and means for signaling information indicating the residual value.

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