Patent Description:
AOMedia Video <NUM> (AV1) is an open video coding format designed for video transmissions over the Internet and was developed as a successor to VP9 by the Alliance for Open Media (AOMedia), a consortium founded in <NUM> that includes semiconductor firms, video on demand providers, video content producers, software development companies and web browser vendors. Many of the components of the AV1 project were sourced from previous research efforts by Alliance members. Individual contributors started experimental technology platforms years before: Xiph's/Mozilla's Daala already published code in <NUM>, Google's experimental VP9 evolution project VP10 was announced on September <NUM>, <NUM>, and Cisco's Thor was published on August <NUM>, <NUM>. Building on the codebase of VP9, AV1 incorporates additional techniques, several of which were developed in these experimental formats. The first version <NUM>. <NUM> of the AV1 reference codec was published on April <NUM>, <NUM>. The Alliance announced the release of the AV1 bitstream specification on March <NUM>, <NUM>, along with a reference, software-based encoder and decoder. On June <NUM>, <NUM>, a validated version <NUM>. <NUM> of the specification was released, and on January <NUM>, <NUM> a validated version <NUM>. <NUM> with Errata <NUM> of the specification was released. The AV1 bitstream specification includes a reference video codec.

<FIG> represents a simplified block diagram <NUM> of aspects of block partitioning with VP9 which uses a <NUM>-way partition tree starting from the 64x64 level at block <NUM> of block <NUM> down to a 4x4 level, with some additional restrictions for blocks 8x8 and below at level <NUM>. Note that partitions designated as R may be referred to as recursive in that a same partition tree may be repeated at a lower scale until reaching a lowest 4x4 level according to exemplary embodiments.

<FIG> represents a simplified block diagram <NUM> of aspects of block partitioning with AV1 which not only expands such partition-tree to a <NUM>-way structure as shown in <FIG> at level <NUM>, but also increases a largest size (referred to as superblock in VP9/AV1 parlance) to start from 128x128 at block <NUM> of block <NUM>. Note that levels <NUM> include <NUM>:<NUM>/<NUM>:<NUM> rectangular partitions that did not exist in VP9 as described above, and none of the rectangular partitions can be further subdivided according to exemplary embodiments. In addition, AV1 adds more flexibility to the use of partitions below an 8x8 level, as, for example, in a sense that 2x2 chroma inter prediction becomes possible thereby on certain cases.

According to embodiments with HEVC, a coding tree unit (CTU) is split into coding units (CUs) by using a quadtree structure denoted as coding tree to adapt to various local characteristics. The decision on whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four prediction units (PUs) according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure like the coding tree for the CU. One of key features of the HEVC structure is that it has the multiple partition conceptions including CU, PU, and TU. In HEVC, a CU or a TU can only be square shape, while a PU may be square or rectangular shape for an inter predicted block. In HEVC, one coding block may be further split into four square sub-blocks, and transform is performed on each sub-block, i.e., TU. Each TU can be further split recursively (using quadtree split) into smaller TUs, which is called Residual Quad-Tree (RQT).

At picture boundary, HEVC employs implicit quad-tree split so that a block will keep quad-tree splitting until the size fits the picture boundary.

<FIG> represents a simplified block diagram <NUM> VVC with respect to a Multi-type-tree (MTT) structure <NUM> that is included, which is a combination of the illustrated a quadtree (QT) with nested binary trees (BT) and triple- / ternary trees (TT). A CTU or CU is first partitioned recursively by a QT into square shaped blocks. Each QT leaf may then be further partitioned by a BT or TT, where BT and TT splits can be applied recursively and interleaved but no further QT partitioning can be applied. In all relevant proposals, the TT splits a rectangular block vertically or horizontally into three blocks using a <NUM>:<NUM>:<NUM> ratio (thus avoiding non-power-of-two widths and heights). For partition emulation prevention, additional split constraints are typically imposed on the MTT, as shown in the simplified diagram <NUM> of <FIG>, QT-BT-TT block partitioning in VVC, with respect to blocks <NUM> (quad), <NUM> (binary, JEM), and <NUM> (ternary) to avoid duplicated partitions (e.g. prohibiting a vertical/horizontal binary split on the middle partition resulting from a vertical/horizontal ternary split). Further limitations may be set to the maximum depth of the BT and TT.

VP9 supports <NUM> directional modes corresponding to angles from <NUM> to <NUM> degrees. To exploit more varieties of spatial redundancy in directional textures, in AV1, directional intra modes are extended to an angle set with finer granularity. The original <NUM> angles are slightly changed and made as nominal angles, and these <NUM> nominal angles are named as V_PRED <NUM>, H_PRED <NUM>, D45_PRED <NUM>, D135_PRED <NUM>, D113_PRED <NUM>, D157_PRED <NUM>, D203_PRED <NUM>, and D67_PRED <NUM>, which is illustrated in the simplified diagram <NUM> in <FIG> with respect to intra prediction modes in AVI and more specifically to direction intra prediction in AVI. For each nominal angle, there may be <NUM> finer angles according to embodiments, so AV1 has <NUM> directional angles in total. The prediction angle is presented by a nominal intra angle plus an angle delta, which is -<NUM> ~ <NUM> multiplies the step size of <NUM> degrees. In AV1, <NUM> nominal modes together with <NUM> non-angular smooth modes are firstly signaled, then if current mode is angular mode, an index is further signaled to indicate the angle delta to the corresponding nominal angle. To implement directional prediction modes in AV1 via a generic way, all the <NUM> directional intra prediction mode in AV1 are implemented with a unified directional predictor that projects each pixel to a reference sub-pixel location and interpolates the reference pixel by a <NUM>-tap bilinear filter.

In AV1, there are <NUM> non-directional smooth intra prediction modes, which are DC, PAETH, SMOOTH, SMOOTH_V, and SMOOTH_H. For DC prediction, the average of left and above neighboring samples is used as the predictor of the block to be predicted. For PAETH predictor, top, left and top-left reference samples are firstly fetched, and then the value which is closest to (top + left - topleft) is set as the predictor for the pixel to be predicted. With the simplified block diagram <NUM> in <FIG> with respect to non-directional smooth intra predictors in AVI there is illustrated positions of top, left, and top-left samples for one pixel in a current block. For SMOOTH, SMOOTH_V, and SMOOTH_H modes, there is prediction of the block using quadratic interpolation in vertical or horizontal directions, or by the average both directions.

To capture decaying spatial correlation with references on the edges, FILTER INTRA modes are designed for luma blocks. Five filter intra modes are defined for AV1, each represented by a set of eight <NUM>-tap filters reflecting correlation between pixels in a 4x2 patch and <NUM> neighbors adjacent to it. In other words, the weighting factors for <NUM>-tap filter are position dependent. Take an 8x8 block for example, it is split into <NUM>4x2 patches, which is shown with respect to simplified block diagram <NUM> of <FIG> with respect to recursive-filtering-based intra predictor features. These patches are indicated by B0, B1, B2, B3, B4, B5, B6, and B7 in <FIG>. For each patch, its <NUM> neighbors, indicated by R0 ~ R7, are used to predict the pixels in current patch. For patch B0, all the neighbors are already reconstructed. But for other patches, not all the neighbors are reconstructed, then the predicted values of immediate neighbors are used as the reference. For example, all the neighbors of patch B7 are not reconstructed, so the prediction samples of neighbors (i.e., B5 and B6) are used instead according to embodiments.

Chroma from Luma (CfL) is a chroma-only intra predictor that models chroma pixels as a linear function of coincident reconstructed luma pixels. The CfL prediction is expressed as follows: <MAT> Wherein LAC denotes the AC contribution of luma component, α denotes the parameter of the linear model, and DC denotes the DC contribution of the chroma component. To be specific, the reconstructed luma pixels are subsampled into the chroma resolution, and then the average value is substracted to form the AC contribution. To approximate chroma AC component from the AC contribution, instead of requiring the decoder to calculate the scaling parameters as in some prior art, AV1 CfL determines the parameter α based on the original chroma pixels and signals them in the bitstream. This reduces decoder complexity and yields more precise predictions. As for the DC contribution of the chroma component, it is computed using intra DC mode, which is sufficient for most chroma content and has mature fast implementations.

Multi-line intra prediction was proposed to use more reference lines for intra prediction, and encoder decides and signals which reference line is used to generate the intra predictor. The reference line index is signaled before intra prediction modes, and only the most probable modes are allowed in case a nonzero reference line index is signaled. As shown in the simplified diagram <NUM> with respect to multiline intra prediction modes shown in <FIG>, an example of <NUM> reference lines (reference line <NUM> (<NUM>), reference line <NUM> (<NUM>), reference line <NUM> (<NUM>), and reference line <NUM> (<NUM>)) is depicted, where each reference line is composed of four segments, i.e., Segment A (<NUM>), Segment B (<NUM>), Segment C (<NUM>), Segment D (<NUM>). In addition, the reconstructed samples in different reference lines are filled with different patterns in <FIG> for ease of understanding, and multiline intra prediction mode may be also called Multiple Reference Line Prediction (MRLP) mode.

With L-type partitions, more fully described herein (for example with <FIG> among other Figures herein), one or more neighboring reconstructed samples may be also available from any of a right side and/or a bottom side, which may not be fully compatible with intra prediction schemes using top and left reference samples for performing prediction. Further, with L-type partitions, the neighboring reference samples may no longer form a straight line, such that harmonization between Multiple Reference Line Prediction (MRLP) and L-type partitions may need to be addressed to make both MRLP and L-type partition functioning at a same time.

<CIT> discloses a method of video decoding according to the present invention, the method may include determining an intra prediction mode of a current block, determining a DC value based on at least one of top reference samples or left reference samples of the current block when the intra prediction mode of the current block is a DC mode, and deriving a prediction sample of the current block based on the DC value.

<CIT> discloses a video intra-frame encoding method combining direction prediction and block copy prediction. In the method, a coding block is partitioned into two sub-blocks using a flexible block partitioning approach, which allows the prediction content of the same block to simultaneously include both local and non-local information. Subsequently, Rate-Distortion Optimization (RDO) is used to determine the prediction with the lowest cost for each block. Additionally, a fast RDO and a full RDO are combined, which reduces coding complexity without influencing coding performance. The overall effect is to achieve higher compression efficiency without significantly increasing the complexity at the decoder side.

<CIT> discloses an object-based intra-prediction encoding, including generating, by a processor in response to instructions stored on a non-transitory computer readable medium, an encoded block of a current frame of a video stream by encoding a current block from the current frame, including the encoded block in an output bitstream, and outputting or storing the output bitstream. Encoding the current block may include identifying a first spatial portion of the current block, wherein the first spatial portion includes a first pixel from the current block and omits a second pixel from the current block, encoding the first pixel using a first intra-prediction mode, and encoding the second pixel using a second intra-prediction mode, wherein the second intra-prediction mode differs from the first intra-prediction mode.

Therefore, there is a desire for a technical solution to such problems.

Enabling disclosure for the invention is found in the embodiments of <FIG>, <FIG>, <FIG>, <FIG> and <FIG>. The remaining embodiments are to be understood as examples which do not describe parts of the present invention.

Further features, nature, and various advantages of the disclosed subject matter will be more apparent from the following detailed description and the accompanying drawings in which:.

The proposed features discussed below may be used separately or combined in any order. Further, the embodiments may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program that is stored in a non-transitory computer-readable medium.

<FIG> illustrates a simplified block diagram of a communication system <NUM> according to an embodiment of the present disclosure. The communication system <NUM> may include at least two terminals <NUM> and <NUM> interconnected via a network <NUM>. For unidirectional transmission of data, a first terminal <NUM> may code video data at a local location for transmission to the other terminal <NUM> via the network <NUM>. The second terminal <NUM> may receive the coded video data of the other terminal from the network <NUM>, decode the coded data and display the recovered video data.

<FIG> illustrates a second pair of terminals <NUM> and <NUM> provided to support bidirectional transmission of coded video that may occur, for example, during videoconferencing. For bidirectional transmission of data, each terminal <NUM> and <NUM> may code video data captured at a local location for transmission to the other terminal via the network <NUM>. Each terminal <NUM> and <NUM> also may receive the coded video data transmitted by the other terminal, may decode the coded data and may display the recovered video data at a local display device.

In <FIG>, the terminals <NUM>, <NUM>, <NUM> and <NUM> may be illustrated as servers, personal computers and smart phones but the principles of the present disclosure are not so limited. The network <NUM> represents any number of networks that convey coded video data among the terminals <NUM>, <NUM>, <NUM> and <NUM>, including for example wireline and/or wireless communication networks. The communication network <NUM> may exchange data in circuit-switched and/or packet-switched channels. For the purposes of the present discussion, the architecture and topology of the network <NUM> may be immaterial to the operation of the present disclosure unless explained herein below.

<FIG> illustrates, as an example for an application for the disclosed subject matter, the placement of a video encoder and decoder in a streaming environment.

A streaming system may include a capture subsystem <NUM>, that can include a video source <NUM>, for example a digital camera, creating, for example, an uncompressed video sample stream <NUM>. That sample stream <NUM> may be emphasized as a high data volume when compared to encoded video bitstreams and can be processed by an encoder <NUM> coupled to the camera <NUM>. The encoder <NUM> can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter as described in more detail below. The encoded video bitstream <NUM>, which may be emphasized as a lower data volume when compared to the sample stream, can be stored on a streaming server <NUM> for future use. One or more streaming clients <NUM> and <NUM> can access the streaming server <NUM> to retrieve copies <NUM> and <NUM> of the encoded video bitstream <NUM>. A client <NUM> can include a video decoder <NUM> which decodes the incoming copy of the encoded video bitstream <NUM> and creates an outgoing video sample stream <NUM> that can be rendered on a display <NUM> or other rendering device (not depicted). In some streaming systems, the video bitstreams <NUM>, <NUM> and <NUM> can be encoded according to certain video coding/compression standards. Examples of those standards are noted above and described further herein.

<FIG> may be a functional block diagram of a video decoder <NUM> according to an embodiment of the present invention.

A receiver <NUM> may receive one or more codec video sequences to be decoded by the decoder <NUM>; in the same or another embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent from other coded video sequences. The coded video sequence may be received from a channel <NUM>, which may be a hardware/software link to a storage device which stores the encoded video data. The receiver <NUM> may receive the encoded video data with other data, for example, coded audio data and/or ancillary data streams, that may be forwarded to their respective using entities (not depicted). The receiver <NUM> may separate the coded video sequence from the other data. To combat network jitter, a buffer memory <NUM> may be coupled in between receiver <NUM> and entropy decoder / parser <NUM> ("parser" henceforth). When receiver <NUM> is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosychronous network, the buffer <NUM> may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer <NUM> may be required, can be comparatively large and can advantageously of adaptive size.

The video decoder <NUM> may include a parser <NUM> to reconstruct symbols <NUM> from the entropy coded video sequence. Categories of those symbols include information used to manage operation of the decoder <NUM>, and potentially information to control a rendering device such as a display <NUM> that is not an integral part of the decoder but can be coupled to it. The control information for the rendering device(s) may be in the form of Supplementary Enhancement Information (SEI messages) or Video Usability Information (VUI) parameter set fragments (not depicted). The parser <NUM> may parse / entropy-decode the coded video sequence received. The coding of the coded video sequence can be in accordance with a video coding technology or standard, and can follow principles well known to a person skilled in the art, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, and so forth. The parser <NUM> may extract from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based upon at least one parameters corresponding to the group. The entropy decoder / parser may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, motion vectors, and so forth.

The parser <NUM> may perform entropy decoding / parsing operation on the video sequence received from the buffer <NUM>, so to create symbols <NUM>. The parser <NUM> may receive encoded data, and selectively decode particular symbols <NUM>. Further, the parser <NUM> may determine whether the particular symbols <NUM> are to be provided to a Motion Compensation Prediction unit <NUM>, a scaler / inverse transform unit <NUM>, an Intra Prediction Unit <NUM>, or a loop filter <NUM>.

Reconstruction of the symbols <NUM> can involve multiple different units depending on the type of the coded video picture or parts thereof (such as: inter and intra picture, inter and intra block), and other factors. Which units are involved, and how, can be controlled by the subgroup control information that was parsed from the coded video sequence by the parser <NUM>. The flow of such subgroup control information between the parser <NUM> and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder <NUM> can be conceptually subdivided into a number of functional units as described below.

A first unit is the scaler / inverse transform unit <NUM>. The scaler / inverse transform unit <NUM> receives quantized transform coefficient as well as control information, including which transform to use, block size, quantization factor, quantization scaling matrices, etc. as symbol(s) <NUM> from the parser <NUM>. It can output blocks comprising sample values, that can be input into aggregator <NUM>.

In some cases, the output samples of the scaler / inverse transform <NUM> can pertain to an intra coded block; that is: a block that is not using predictive information from previously reconstructed pictures, but can use predictive information from previously reconstructed parts of the current picture. Such predictive information can be provided by an intra picture prediction unit <NUM>. In some cases, the intra picture prediction unit <NUM> generates a block of the same size and shape of the block under reconstruction, using surrounding already reconstructed information fetched from the current (partly reconstructed) picture <NUM>. The aggregator <NUM>, in some cases, adds, on a per sample basis, the prediction information the intra prediction unit <NUM> has generated to the output sample information as provided by the scaler / inverse transform unit <NUM>.

In other cases, the output samples of the scaler / inverse transform unit <NUM> can pertain to an inter coded, and potentially motion compensated block. In such a case, a Motion Compensation Prediction unit <NUM> can access reference picture memory <NUM> to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols <NUM> pertaining to the block, these samples can be added by the aggregator <NUM> to the output of the scaler / inverse transform unit (in this case called the residual samples or residual signal) so to generate output sample information. The addresses within the reference picture memory form where the motion compensation unit fetches prediction samples can be controlled by motion vectors, available to the motion compensation unit in the form of symbols <NUM> that can have, for example X, Y, and reference picture components. Motion compensation also can include interpolation of sample values as fetched from the reference picture memory when subsample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator <NUM> can be subject to various loop filtering techniques in the loop filter unit <NUM>. Video compression technologies can include in-loop filter technologies that are controlled by parameters included in the coded video bitstream and made available to the loop filter unit <NUM> as symbols <NUM> from the parser <NUM>, but can also be responsive to meta-information obtained during the decoding of previous (in decoding order) parts of the coded picture or coded video sequence, as well as responsive to previously reconstructed and loop-filtered sample values.

The output of the loop filter unit <NUM> can be a sample stream that can be output to the render device <NUM> as well as stored in the reference picture memory <NUM> for use in future inter-picture prediction.

Once a coded picture is fully reconstructed and the coded picture has been identified as a reference picture (by, for example, parser <NUM>), the current reference picture <NUM> can become part of the reference picture buffer <NUM>, and a fresh current picture memory can be reallocated before commencing the reconstruction of the following coded picture.

The video decoder <NUM> may perform decoding operations according to a predetermined video compression technology that may be documented in a standard, such as ITU-T Rec. The coded video sequence may conform to a syntax specified by the video compression technology or standard being used, in the sense that it adheres to the syntax of the video compression technology or standard, as specified in the video compression technology document or standard and specifically in the profiles document therein.

In an embodiment, the receiver <NUM> may receive additional (redundant) data with the encoded video. The additional data may be used by the video decoder <NUM> to properly decode the data and/or to more accurately reconstruct the original video data. Additional data can be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, and so on.

<FIG> may be a functional block diagram of a video encoder <NUM> according to an embodiment of the present disclosure.

The encoder <NUM> may receive video samples from a video source <NUM> (that is not part of the encoder) that may capture video image(s) to be coded by the encoder <NUM>.

The video source <NUM> may provide the source video sequence to be coded by the encoder (<NUM>) in the form of a digital video sample stream that can be of any suitable bit depth (for example: <NUM> bit, <NUM> bit, <NUM> bit,. ), any color space (for example, BT. <NUM> Y CrCB, RGB,. ) and any suitable sampling structure (for example Y CrCb <NUM>:<NUM>:<NUM>, Y CrCb <NUM>:<NUM>:<NUM>). In a media serving system, the video source <NUM> may be a storage device storing previously prepared video. In a videoconferencing system, the video source <NUM> may be a camera that captures local image information as a video sequence.

According to an embodiment, the encoder <NUM> may code and compress the pictures of the source video sequence into a coded video sequence <NUM> in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed is one function of Controller <NUM>. Controller controls other functional units as described below and is functionally coupled to these units. Parameters set by controller can include rate control related parameters (picture skip, quantizer, lambda value of rate-distortion optimization techniques,. A person skilled in the art can readily identify other functions of controller <NUM> as they may pertain to video encoder <NUM> optimized for a certain system design.

Some video encoders operate in what a person skilled in the art readily recognizes as a "coding loop. " As an oversimplified description, a coding loop can consist of the encoding part of an encoder <NUM> ("source coder" henceforth) (responsible for creating symbols based on an input picture to be coded, and a reference picture(s)), and a (local) decoder <NUM> embedded in the encoder <NUM> that reconstructs the symbols to create the sample data that a (remote) decoder also would create (as any compression between symbols and coded video bitstream is lossless in the video compression technologies considered in the disclosed subject matter). That reconstructed sample stream is input to the reference picture memory <NUM>. As the decoding of a symbol stream leads to bit-exact results independent of decoder location (local or remote), the reference picture buffer content is also bit exact between local encoder and remote encoder. This fundamental principle of reference picture synchronicity (and resulting drift, if synchronicity cannot be maintained, for example because of channel errors) is well known to a person skilled in the art.

The operation of the "local" decoder <NUM> can be the same as of a "remote" decoder <NUM>, which has already been described in detail above in conjunction with <FIG>. Briefly referring also to <FIG>, however, as symbols are available and en/decoding of symbols to a coded video sequence by entropy coder <NUM> and parser <NUM> can be lossless, the entropy decoding parts of decoder <NUM>, including channel <NUM>, receiver <NUM>, buffer <NUM>, and parser <NUM> may not be fully implemented in local decoder <NUM>.

As part of its operation, the source coder <NUM> may perform motion compensated predictive coding, which codes an input frame predictively with reference to one or more previously-coded frames from the video sequence that were designated as "reference frames. " In this manner, the coding engine <NUM> codes differences between pixel blocks of an input frame and pixel blocks of reference frame(s) that may be selected as prediction reference(s) to the input frame.

The local video decoder <NUM> may decode coded video data of frames that may be designated as reference frames, based on symbols created by the source coder <NUM>. Operations of the coding engine <NUM> may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown in <FIG>), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder <NUM> replicates decoding processes that may be performed by the video decoder on reference frames and may cause reconstructed reference frames to be stored in the reference picture cache <NUM>. In this manner, the encoder <NUM> may store copies of reconstructed reference frames locally that have common content as the reconstructed reference frames that will be obtained by a far-end video decoder (absent transmission errors).

The predictor <NUM> may perform prediction searches for the coding engine <NUM>. That is, for a new frame to be coded, the predictor <NUM> may search the reference picture memory <NUM> for sample data (as candidate reference pixel blocks) or certain metadata such as reference picture motion vectors, block shapes, and so on, that may serve as an appropriate prediction reference for the new pictures. The predictor <NUM> may operate on a sample block-by-pixel block basis to find appropriate prediction references. In some cases, as determined by search results obtained by the predictor <NUM>, an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory <NUM>.

The controller <NUM> may manage coding operations of the video coder <NUM>, including, for example, setting of parameters and subgroup parameters used for encoding the video data.

Output of all aforementioned functional units may be subjected to entropy coding in the entropy coder <NUM>. The entropy coder translates the symbols as generated by the various functional units into a coded video sequence, by loss-less compressing the symbols according to technologies known to a person skilled in the art as, for example Huffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter <NUM> may buffer the coded video sequence(s) as created by the entropy coder <NUM> to prepare it for transmission via a communication channel <NUM>, which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter <NUM> may merge coded video data from the video coder <NUM> with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

The controller <NUM> may manage operation of the encoder <NUM>. During coding, the controller <NUM> may assign to each coded picture a certain coded picture type, which may affect the coding techniques that may be applied to the respective picture. For example, pictures often may be assigned as one of the following frame types:.

Source pictures commonly may be subdivided spatially into a plurality of sample blocks (for example, blocks of <NUM> x <NUM>, <NUM> x <NUM>, <NUM> x <NUM>, or <NUM> x <NUM> samples each) and coded on a block-by-block basis. Pixel blocks of P pictures may be coded non-predictively, via spatial prediction or via temporal prediction with reference to one previously coded reference pictures. Blocks of B pictures may be coded non-predictively, via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures.

The video coder <NUM> may perform coding operations according to a predetermined video coding technology or standard, such as ITU-T Rec. In its operation, the video coder <NUM> may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence.

In an embodiment, the transmitter <NUM> may transmit additional data with the encoded video. The source coder <NUM> may include such data as part of the coded video sequence. Additional data may comprise temporal/spatial/SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, Supplementary Enhancement Information (SEI) messages, Visual Usability Information (VUI) parameter set fragments, and so on.

<FIG> illustrates intra prediction modes used in High Efficiency Video Coding (HEVC) and Joint Exploration Model (JEM). To capture the arbitrary edge directions presented in natural video, the number of directional intra modes is extended from <NUM>, as used in HEVC, to <NUM>. The additional directional modes in JEM on top of HEVC are depicted as dotted arrows in Figure <NUM> (b), and the planar and DC modes remain the same. These denser directional intra prediction modes apply for all block sizes and for both luma and chroma intra predictions. As shown in <FIG>, the directional intra prediction modes as identified by dotted arrows, which is associated with an odd intra prediction mode index, are called odd intra prediction modes. The directional intra prediction modes as identified by solid arrows, which are associated with an even intra prediction mode index, are called even intra prediction modes. In this document, the directional intra prediction modes, as indicated by solid or dotted arrows in <FIG> are also referred as angular modes.

In JEM, a total of <NUM> intra prediction modes are used for luma intra prediction. To code an intra mode, an most probable mode (MPM) list of size <NUM> is built based on the intra modes of the neighboring blocks. If intra mode is not from the MPM list, a flag is signaled to indicate whether intra mode belongs to the selected modes. In JEM-<NUM>, there are <NUM> selected modes, which are chosen uniformly as every fourth angular mode. In JVET-D0114 and JVET-G0060, <NUM> secondary MPMs are derived to replace the uniformly selected modes.

<FIG> illustrates N reference tiers exploited for intra directional modes. There is a block unit <NUM>, a segment A <NUM>, a segment B <NUM>, a segment C <NUM>, a segment D <NUM>, a segment E <NUM>, a segment F <NUM>, a first reference tier <NUM>, a second reference tier <NUM>, a third reference tier <NUM> and a fourth reference tier <NUM>.

In both HEVC and JEM, as well as some other standards such as H. <NUM>/AVC, the reference samples used for predicting the current block are restricted to a nearest reference line (row or column). In the method of multiple reference line intra prediction, the number of candidate reference lines (row or columns) are increased from one (i.e. the nearest) to N for the intra directional modes, where N is an integer greater than or equal to one. <FIG> takes 4x4 prediction unit (PU) as an example to show the concept of the multiple line intra directional prediction method. An intra-directional mode could arbitrarily choose one of N reference tiers to generate the predictors. In other words, the predictor p(x,y) is generated from one of the reference samples S1, S2,. A flag is signaled to indicate which reference tier is chosen for an intra-directional mode. If N is set as <NUM>, the intra directional prediction method is the same as the traditional method in JEM <NUM>. In <FIG>, the reference lines <NUM>, <NUM>, <NUM> and <NUM> are composed of six segments <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> together with the top-left reference sample. In this document, a reference tier is also called a reference line. The coordinate of the top-left pixel within current block unit is (<NUM>,<NUM>) and the top left pixel in the 1st reference line is (-<NUM>,-<NUM>).

In JEM, for the luma component, the neighboring samples used for intra prediction sample generations are filtered before the generation process. The filtering is controlled by the given intra prediction mode and transform block size. If the intra prediction mode is DC or the transform block size is equal to 4x4, neighboring samples are not filtered. If the distance between the given intra prediction mode and vertical mode (or horizontal mode) is larger than predefined threshold, the filtering process is enabled. For neighboring sample filtering, [<NUM>, <NUM>, <NUM>] filter and bi-linear filters are used.

A position dependent intra prediction combination (PDPC) method is an intra prediction method which invokes a combination of the un-filtered boundary reference samples and HEVC style intra prediction with filtered boundary reference samples. Each prediction sample pred[x][y] located at (x, y) is calculated as follows: <MAT> where Rx,-<NUM>,R-<NUM>,y represent the unfiltered reference samples located at top and left of current sample (x, y), respectively, and R-<NUM>,-<NUM> represents the unfiltered reference sample located at the top-left corner of the current block. The weightings are calculated as below, <MAT> <MAT> <MAT> <MAT>.

<FIG> illustrates a diagram <NUM> in which DC mode PDPC weights (wL, wT, wTL) for (<NUM>, <NUM>) and (<NUM>, <NUM>) positions inside one 4x4 block. If PDPC is applied to DC, planar, horizontal, and vertical intra modes, additional boundary filters are not needed, such as the HEVC DC mode boundary filter or horizontal/vertical mode edge filters. <FIG> illustrates the definition of reference samples Rx,-<NUM>, R-<NUM>,y and R-<NUM>,-<NUM> for PDPC applied to the top-right diagonal mode. The prediction sample pred(x', y') is located at (x', y') within the prediction block. The coordinate x of the reference sample Rx,-<NUM> is given by: x = x' + y' + <NUM>, and the coordinate y of the reference sample R-<NUM>,y is similarly given by: y = x' + y' + <NUM>.

<FIG> illustrates a Local Illumination Compensation (LIC) diagram <NUM> and is based on a linear model for illumination changes, using a scaling factor a and an offset b. And it is enabled or disabled adaptively for each inter-mode coded coding unit (CU).

When LIC applies for a CU, a least square error method is employed to derive the parameters a and b by using the neighboring samples of the current CU and their corresponding reference samples. More specifically, as illustrated in <FIG>, the subsampled (<NUM>:<NUM> subsampling) neighboring samples of the CU and the corresponding samples (identified by motion information of the current CU or sub-CU) in the reference picture are used. The IC parameters are derived and applied for each prediction direction separately.

When a CU is coded with merge mode, the LIC flag is copied from neighboring blocks, in a way similar to motion information copy in merge mode; otherwise, an LIC flag is signaled for the CU to indicate whether LIC applies or not.

<FIG> illustrates intra prediction modes <NUM> used in HEVC. In HEVC, there are total <NUM> intra prediction modes, among which mode <NUM> is horizontal mode, mode <NUM> is vertical mode, and mode <NUM>, mode <NUM> and mode <NUM> are diagonal modes. The intra prediction modes are signaled by three most probable modes (MPMs) and <NUM> remaining modes.

<FIG> illustrates, in embodiments of Versatile Video Coding (VVC), there are total <NUM> intra prediction modes where mode <NUM> is horizontal mode, mode <NUM> is vertical mode, and mode <NUM>, mode <NUM> and mode <NUM> are diagonal modes. Modes -<NUM> ~ -<NUM> and Modes <NUM> ~ <NUM> are called Wide-Angle Intra Prediction (WAIP) modes.

The prediction sample pred(x,y) located at position (x, y) is predicted using an intra prediction mode (DC, planar, angular) and a linear combination of reference samples according to the PDPC expression: <MAT> where Rx,-<NUM>, R-<NUM>,y represent the reference samples located at the top and left of current sample (x, y), respectively, and R-<NUM>,-<NUM> represents the reference sample located at the top-left corner of the current block.

For the DC mode the weights are calculated as follows for a block with dimensions width and height: <MAT> with nScale = ( log2( width ) - <NUM> + log2( height ) - <NUM> + <NUM> ) >> <NUM>, where wT denotes the weighting factor for the reference sample located in the above reference line with the same horizontal coordinate, wL denotes the weighting factor for the reference sample located in the left reference line with the same vertical coordinate, and wTL denotes the weighting factor for the top-left reference sample of the current block, nScale specifies how fast weighting factors decrease along the axis (wL decreasing from left to right or wT decreasing from top to bottom), namely weighting factor decrement rate, and it is the same along x-axis (from left to right) and y-axis (from top to bottom) in current design. And <NUM> denotes the initial weighting factors for the neighboring samples, and the initial weighting factor is also the top (left or top-left) weightings assigned to top-left sample in current CB, and the weighting factors of neighboring samples in PDPC process should be equal to or less than this initial weighting factor.

For planar mode wTL = <NUM>, while for horizontal mode wTL = wT and for vertical mode wTL = wL. The PDPC weights can be calculated with adds and shifts only. The value of pred(x,y) can be computed in a single step using Eq. <NUM>.

<FIG> illustrates a simplified block diagram <NUM> of an L-type partition. As will be understood from the illustration of <FIG>, an L-type partitioning can split a block into one or more L-shape partition and one or more rectangular partitions and/or one or more L-shaped partitions, and an L-shaped (or L-Type) partition is defined as the following shape, shown in <FIG> having a height <NUM>, a width <NUM>, a shorter width <NUM>, and a shorter height <NUM>, and a rotated L-shaped partition is also regarded as an L-shaped partition herein.

Several terms are associated with an L-shaped partition, including width, height, shorter width and shorter height, as indicated in the above discussion with respect to <FIG>.

In the present invention, an L-type partitioning tree is described with respect to an arrangement <NUM> in the simplified block diagram <NUM> of <FIG>, in which one block is split into two partitions, including one L-shape partition (partition <NUM>) and one rectangular partition (partition <NUM>) located in a left-top direction of the L-shaped partition. Examples of the L-type partitioning tree are further described as follows with respect to the simplified block diagram <NUM> of <FIG>, in which one block is split into two partitions, including one L-shape partition (partition <NUM>) and one rectangular partition (<NUM>) in, for example, any of the arrangements <NUM>, <NUM>, and <NUM> shown in <FIG>, according to exemplary embodiments.

Similarly, <FIG> shows a diagram 1300B that in which block <NUM> and block <NUM> can be split into an L-shaped partition (partition <NUM>) and another L-shaped partition (partition <NUM>).

Exemplary embodiment herein with respect to one or more L-shaped partitions may be used separately or combined in any order. In this document, an L-shaped (or L-Type) partition is defined as the shape illustrated in <FIG>, and a rotated L-shaped partition will also be understood as regarded as an L-shaped partition.

According to exemplary embodiments discussed below and illustrated with <FIG> for example, when a block is partitioned into multiple L-shape partitions (LP) and rectangular partitions (RP), the reference samples used for performing intra prediction of the L-shape partitions comes from the neighboring reconstructed samples of another LP or RP, while the neighboring reconstructed samples form an group of consecutive samples that form a chain in arbitrary shape instead of one horizontal and one vertical straight line. It will be understood that such reference samples together are called a reference sample chain (RSC).

In the present invention, according to the simplified block diagram <NUM> of <FIG>, a block A is partitioned as two partitions, one LP (noted as "<NUM>") and one RP (noted as "<NUM>") as shown in <FIG>. To perform intra prediction of partition <NUM>, the samples in the reconstructed samples chain (indicated in shaded blocks in <FIG>) are used as reference samples.

In the present invention, when doing the directional (or angular) intra prediction for a sample (c0 and c1 in <FIG>) in LP (partition <NUM>), the sample coordinates are projected to the RSC. If a sample coordinate is projected to a vertical side of the RSC, samples along the vertical like directions (e.g., r0 and r1) are used to generate a prediction sample value. If a sample coordinate is projected to a horizontal side of the RSC, samples along the horizontal like directions (e.g., r2 and r3) are used to generate the prediction sample value.

Further, according to embodiments, when doing the MRLP, multiple RSCs are used instead of multiple reference lines, as shown in an example in the simplified diagram <NUM> of <FIG> which is using four RSCs and samples within each RSC is marked with a same respective texture for ease of understanding at sides of the LP <NUM>.

In embodiments, when doing the MRLP, non-adjacent reconstructed samples may be used and only top and left reconstructed samples that form straight lines can be used for intra prediction in MRLP, and for example, see the simplified diagram <NUM> of <FIG> in which the top samples and left samples may include one or more samples that are not direct neighbor(s) of a current block. It will be understood from <FIG> that one or more of the textured samples are used for performing MRLP of the LP (partition <NUM>).

Further, for exemplary embodiments with respect to the simplified diagram <NUM> of <FIG> not being part of the invention, In another embodiment, when the right or bottom side neighboring samples from a different partition (either LP or RP) are reconstructed prior to the reconstruction of samples in a current block, the right and bottom side neighboring samples may form an RSC and are used for performing intra prediction. An example is shown in the <FIG>, where LP (partition <NUM>) is reconstructed before RP (partition <NUM>), and therefore the samples (as indicated by shaded blocks) form an RSC and may be used for intra prediction of RP (partition <NUM>).

According to exemplary embodiments, when doing the Planar mode (defined in HEVC and VVC) or SMOOTH, SMOOTH-H, SMOOTH-V modes (defined in AV1), if the right or bottom samples are reconstructed, these reconstructed samples can be used directly in the <NUM>-tap interpolation in Planar (or SMOOTH, SMOOTH-H, SMOOTH-V) mode instead of extrapolating the right and bottom samples by the top and left reconstructed samples, and when doing a DC mode, not only the above and left neighboring reconstructed samples, all the samples available in an RSC, which may include right and bottom reconstructed samples, can be used for generating the DC predictor.

Further, with the DC mode, not only the above and left neighboring reconstructed samples, all the samples except bottom-left and top-right available in the RSC, which may include right and bottom reconstructed samples, can be used for generating the DC predictor. When doing the boundary filtering (defined in HEVC) or PDPC (defined in VVC), not only the above and left neighboring reconstructed samples, all the samples available in the RSC which may include right and bottom reconstructed samples can be used to apply boundary filtering and PDPC predictions.

With respect to examples such as the diagram <NUM> of <FIG> not being part of the invention, bi-directional intra prediction can be applied when reconstructed samples are available on both opposite sides as indicated by the lines drawn to the shaded areas from the partition <NUM> in <FIG>.

For example, when both left and right samples are reconstructed before the current block, the bi-directional prediction modes can be enabled which utilize a weighted sum of left and right samples along a horizontal-like prediction direction to generate the predictor as for example shown with respect to the diagram <NUM> of <FIG>. In one embodiment, when both left and right samples are reconstructed before the current block, the bi-directional prediction modes, which utilize weighted sum of left and right samples along a horizontal-like prediction direction to generate the predictor, are employed to replace the horizontal-like prediction. Thereby, in a bidirectional prediction mode, there may be generated a predictor for a current block in the rectangular shaped partition <NUM> of <FIG> by utilizing a weighted sum of first and second portions of the shaded reference sample chain where the first and second portions are respectively from the right and left of, and are non-neighboring sides to, the current block and the reference sample chain, as shown in <FIG>, surrounds the current block at at least three sides: a left side, a top side, and a right side as understood from the orientations illustrated by the <FIG>. As shown in <FIG> and <FIG>, the first portion of the reference sample chain is both to the right and to the top of the current block, and the second portion of the reference sample chain is both to the left and to the bottom of the current block as indicated by the respective arrows to the reference sample chains in those Figures.

Further, as shown with the diagram <NUM> of <FIG> not being part of the invention, when both top and bottom samples are reconstructed before a current block, bi-directional prediction modes can be enabled which utilize a weighted sum of left and right samples along a vertical-like prediction direction to generate the predictor, and when both top and bottom samples are reconstructed before the current block, the bi-directional prediction modes, which utilize weighted sum of left and right samples along a vertical-like prediction direction to generate the predictor, is employed to replace the vertical-like prediction.

When a block is partitioned into several L-shape partitions (LP) and rectangular partitions (RP), if the neighboring reconstructed samples form an arbitrary chain (RSC) instead of one horizontal and one vertical straight line, the samples in the RSC are first mapped to a top row and left column, such that the reference samples in these top row and left column can be used for intra prediction of current block as illustrated by such mapping in the diagram <NUM> of <FIG>. According to exemplary embodiments, such mapping of samples from RSC to the top and left column is done along the intra prediction direction. Alternatively, such mapping of samples from RSC to the top and left column is done using a <NUM>-tap bi-linear filter or a <NUM>-tap cubic filter or the nearest integer sample. Further alternatively, all the samples in the RSC may mapped to a top row, an example is shown in the diagram <NUM> of <FIG>.

For example, with respect to <FIG>, embodiments may map all samples in the RSC to the top row, as in <FIG>, when it is determined that the intra prediction direction is vertical like, or when it is determined that the intra prediction direction is horizontal like.

Alternatives are also comprised by exemplary embodiments such as that all samples in the RSC may be mapped to a left column, or, for example, all samples in the RSC may be mapped to a left top column only when it is determined that the intra prediction direction is horizontal like. Similarly, an alternative embodiment also includes features that all samples in the RSC may be mapped to the left top column only when the intra prediction direction is determined to be vertical like.

In view of such embodiments, with L-type partitions, one or more neighboring reconstructed samples that may be also available from any of a right side and/or a bottom side, and even if the neighboring reference samples may no longer form a straight line, such samples may still be utilized.

Accordingly, by exemplary embodiments described herein, the technical problems noted above may be advantageously improved upon by one or more of these technical solutions.

The techniques described above, can be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media or by a specifically configured one or more hardware processors. For example, <FIG> shows a computer system <NUM> suitable for implementing certain embodiments of the disclosed subject matter.

The components shown in <FIG> for computer system <NUM> are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the present disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of a computer system <NUM>.

Input human interface devices may include one or more of (only one of each depicted): keyboard <NUM>, mouse <NUM>, trackpad <NUM>, touch screen <NUM>, joystick <NUM>, microphone <NUM>, scanner <NUM>, camera <NUM>.

Computer system <NUM> may also include certain human interface output devices. Such human interface output devices may include tactile output devices (for example tactile feedback by the touch-screen <NUM>, or joystick <NUM>, but there can also be tactile feedback devices that do not serve as input devices), audio output devices (such as: speakers <NUM>, headphones (not depicted)), visual output devices (such as screens <NUM> to include CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch-screen input capability, each with or without tactile feedback capability-some of which may be capable to output two dimensional visual output or more than three dimensional output through means such as stereographic output; virtual-reality glasses (not depicted), holographic displays and smoke tanks (not depicted)), and printers (not depicted).

Computer system <NUM> can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW <NUM> with CD/DVD <NUM> or the like media, thumb-drive <NUM>, removable hard drive or solid state drive <NUM>, legacy magnetic media such as tape and floppy disc (not depicted), specialized ROM/ASIC/PLD based devices such as security dongles (not depicted), and the like.

Computer system <NUM> can also include interface <NUM> to one or more communication networks <NUM>. Networks <NUM> can for example be wireless, wireline, optical. Networks <NUM> can further be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, and so on. Examples of networks <NUM> include local area networks such as Ethernet, wireless LANs, cellular networks to include GSM, <NUM>, <NUM>, <NUM>, LTE and the like, TV wireline or wireless wide area digital networks to include cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial to include CANBus, and so forth. Certain networks <NUM> commonly require external network interface adapters that attached to certain general-purpose data ports or peripheral buses (<NUM> and <NUM>) (such as, for example USB ports of the computer system <NUM>; others are commonly integrated into the core of the computer system <NUM> by attachment to a system bus as described below (for example Ethernet interface into a PC computer system or cellular network interface into a smartphone computer system). Using any of these networks <NUM>, computer system <NUM> can communicate with other entities. Such communication can be uni-directional, receive only (for example, broadcast TV), uni-directional send-only (for example CANbusto certain CANbus devices), or bi-directional, for example to other computer systems using local or wide area digital networks. Certain protocols and protocol stacks can be used on each of those networks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storage devices, and network interfaces can be attached to a core <NUM> of the computer system <NUM>.

The core <NUM> can include one or more Central Processing Units (CPU) <NUM>, Graphics Processing Units (GPU) <NUM>, a graphics adapter <NUM>, specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) <NUM>, hardware accelerators for certain tasks <NUM>, and so forth. These devices, along with Read-only memory (ROM) <NUM>, Random-access memory <NUM>, internal mass storage such as internal non-user accessible hard drives, SSDs, and the like <NUM>, may be connected through a system bus <NUM>. In some computer systems, the system bus <NUM> can be accessible in the form of one or more physical plugs to enable extensions by additional CPUs, GPU, and the like. The peripheral devices can be attached either directly to the core's system bus <NUM>, or through a peripheral bus <NUM>.

CPUs <NUM>, GPUs <NUM>, FPGAs <NUM>, and accelerators <NUM> can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM <NUM> or RAM <NUM>. Transitional data can be also be stored in RAM <NUM>, whereas permanent data can be stored for example, in the internal mass storage <NUM>. Fast storage and retrieval to any of the memory devices can be enabled through the use of cache memory, that can be closely associated with one or more CPU <NUM>, GPU <NUM>, mass storage <NUM>, ROM <NUM>, RAM <NUM>, and the like.

Claim 1:
A method performed by at least one processor, comprising:
obtaining a block of video data;
splitting the block into an L-shaped partition and a second partition, the second partition being a rectangular partition located in a left-top direction of the L-shaped partition; and
performing directional intra prediction of the L-shaped partition by using a reference sample chain for the L-shaped partition, comprising a chain of top and left reconstructed samples neighboring the L-shaped partition, as reference samples,
characterized in that the reference sample chain for the L-shaped partition comprises: two horizontal reference lines and two vertical reference lines, that are directly connected, from the reconstructed samples,
one of the two horizontal reference lines and one of the two vertical reference lines are within the block and are both neighboring the L-shaped partition, and
the other of the two horizontal reference lines and the other of the two vertical reference lines are located outside the block and are at least partly neighboring the L-shaped partition.