WO2020149616A1 - Procédé et dispositif de décodage d'image sur la base d'une prédiction cclm dans un système de codage d'image - Google Patents

Procédé et dispositif de décodage d'image sur la base d'une prédiction cclm dans un système de codage d'image Download PDF

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WO2020149616A1
WO2020149616A1 PCT/KR2020/000685 KR2020000685W WO2020149616A1 WO 2020149616 A1 WO2020149616 A1 WO 2020149616A1 KR 2020000685 W KR2020000685 W KR 2020000685W WO 2020149616 A1 WO2020149616 A1 WO 2020149616A1
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samples
chroma
mode
block
current
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PCT/KR2020/000685
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English (en)
Korean (ko)
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최장원
허진
유선미
이령
최정아
김승환
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엘지전자 주식회사
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/11—Selection of coding mode or of prediction mode among a plurality of spatial predictive coding modes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/132—Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/593—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial prediction techniques

Definitions

  • This document relates to an image decoding method and apparatus using CCLM prediction in an image coding system.
  • VR Virtual Reality
  • AR Artificial Realtiy
  • holograms video/video having a video characteristic different from a real video such as a game video
  • video/video having a video characteristic different from a real video such as a game video
  • the broadcast for is increasing.
  • a high-efficiency video/video compression technology is required to effectively compress, transmit, store, and reproduce information of a high-resolution, high-quality video/video having various characteristics as described above.
  • the technical problem of this document is to provide a method and apparatus for improving image coding efficiency.
  • Another technical task of this document is to provide a method and apparatus for improving intra prediction efficiency.
  • Another technical task of this document is to provide a method and apparatus for improving the efficiency of intra prediction based on a cross-component linear model (CCLM).
  • CCLM cross-component linear model
  • Another technical problem of the present document is to provide an efficient encoding and decoding method of CCLM prediction including a plurality of CCLM prediction modes, and an apparatus for performing the encoding and decoding method.
  • Another technical task of this document is to provide a method and apparatus for selecting a peripheral sample for deriving a linear model parameter for a number of CCLM prediction modes.
  • an image decoding method performed by a decoding apparatus includes obtaining image information including prediction mode information for a current chroma block, and deriving one of a plurality of CCLM prediction modes as a CCLM prediction mode of the current chroma block based on the prediction mode information, Deriving the number of samples of neighboring chroma samples of the current chroma block based on the CCLM prediction mode of the current chroma block, and the width and height of the current chroma block, deriving neighboring chroma samples of the sample number, down of the current luma block Deriving sampled peripheral luma samples and down sampled luma samples, deriving CCLM parameters based on peripheral chroma samples and down sampled peripheral luma samples, based on CCLM parameters and down sampled luma samples And deriving prediction samples for the current chroma block, and generating reconstruction samples for the current chroma block
  • a decoding apparatus for performing image decoding.
  • the decoding apparatus derives one of a plurality of CCLM prediction modes as a CCLM prediction mode of the current chroma block based on the prediction mode information, the entropy decoding unit obtaining image information including prediction mode information for the current chroma block, Based on the CCLM prediction mode of the current chroma block and the width and height of the current chroma block, the number of samples of neighboring chroma samples of the current chroma block is derived, the number of neighboring chroma samples is derived, and the downsampling of the current luma block is sampled.
  • Derive luma samples and down-sampled luma samples derive CCLM parameters based on periphery chroma samples and down-sampled luma samples, and derive the current chroma block based on CCLM parameters and down-sampled luma samples. It includes a prediction unit for deriving the prediction samples for, and an adder for generating reconstruction samples for the current chroma block based on the prediction samples.
  • an image encoding method performed by an encoding device includes deriving one of a plurality of CCLM prediction modes as a CCLM prediction mode of the current chroma block, a CCLM prediction mode of the current chroma block, and a periphery of the current chroma block based on the width and height of the current chroma block.
  • Deriving the number of samples of the chroma samples deriving the neighboring chroma samples of the number of samples, deriving the down sampled neighboring luma samples and the down sampled luma samples of the current luma block, the surrounding chroma samples and down sampling Deriving CCLM parameters based on the extracted peripheral luma samples, deriving prediction samples for the current chroma block based on the CCLM parameters and down-sampled luma samples, and deriving residual samples based on the prediction samples , Generating residual information based on the residual samples, and encoding image information including the residual information.
  • an encoding apparatus for performing image encoding derives one of a plurality of CCLM prediction modes as a CCLM prediction mode of the current chroma block, and a CCLM prediction mode of the current chroma block and a neighboring chroma sample of the current chroma block based on the width and height of the current chroma block. Derive the number of samples of the samples, derive the number of neighboring chroma samples, and derive the down-sampled and down-sampled luma samples of the current luma block, the surrounding chroma samples, and the down-sampled neighboring luma samples.
  • a prediction unit Based on CCLM parameters, CCLM parameters and down-sampled luma samples, a prediction unit to derive prediction samples for a current chroma block, residual samples based on prediction samples, and residual samples It characterized in that it comprises a residual processing unit for generating residual information, and an entropy encoding unit for encoding image information including residual information.
  • a computer-readable storage medium storing image information (or indication information) that causes the image decoding method performed by the decoding apparatus according to the above-described embodiment to be performed.
  • a computer-readable storage medium in which a bitstream (or encoded image information) generated according to an image encoding method performed by the encoding apparatus according to the above-described embodiment is stored is provided.
  • the efficiency of intra prediction can be improved.
  • CCLM including a multi-directional linear model (MDLM).
  • MDLM multi-directional linear model
  • complexity of intra prediction can be reduced by limiting the number of neighboring samples selected to derive a linear model parameter for MDLM to a specific number.
  • FIG. 1 schematically shows an example of a video/image coding system to which embodiments of the present document can be applied.
  • FIG. 2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which embodiments of the present document can be applied.
  • FIG. 3 is a diagram schematically illustrating a configuration of a video/video decoding apparatus to which embodiments of the present document can be applied.
  • 4 exemplarily shows intra directional modes of 65 prediction directions.
  • FIG. 5 is a diagram for explaining a process of deriving an intra prediction mode of a current chroma block according to an embodiment.
  • 6 shows 2N reference samples for parameter calculation for CCLM prediction.
  • LM mode 7 and 8 exemplarily show a top linear model (LM) mode and a left LM mode, respectively, according to an embodiment of the present document.
  • 9 and 10 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • FIG. 11 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • FIG. 13 and 14 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • 15 and 16 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • 17 and 18 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • 19 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • 20 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • FIG. 21 schematically shows a video encoding method by an encoding device according to the present document.
  • FIG. 22 schematically shows an encoding apparatus that performs a video encoding method according to the present document.
  • FIG. 24 schematically shows a decoding apparatus performing an image decoding method according to the present document.
  • 25 exemplarily shows a structure diagram of a content streaming system to which embodiments of the present document are applied.
  • each component in the drawings described in this specification is independently shown for convenience of description of different characteristic functions, and does not mean that each component is implemented with separate hardware or separate software.
  • two or more components of each component may be combined to form one component, or one component may be divided into a plurality of components.
  • Embodiments in which each component is integrated and/or separated are also included in the scope of the present specification without departing from the essence of the present specification.
  • a or B (A or B) may mean “only A”, “only B”, or “both A and B”.
  • a or B (A or B)” in this specification may be interpreted as “A and/or B (A and/or B)”.
  • “A, B or C (A, B or C)” means “only A”, “only B”, “only C”, or any combination of “A, B and C” ( any combination of A, B and C).
  • slash (/) or comma (comma) used in this specification may mean “and/or” (and/or).
  • A/B may mean “A and/or B”. Accordingly, “A/B” can mean “only A”, “only B”, or “both A and B”.
  • A, B, C may mean “A, B, or C”.
  • At least one of A and B may mean “only A”, “only B”, or “both A and B”. Also, in this specification, the expression “at least one A or B (at least one of A and B)” or “at least one A and/or B (at least one of A and/or B)” means “at least one. A and B (at least one of A and B).
  • “at least one of A, B and C” means “only A”, “only B”, “only C”, or “A, B and C”. Any combination of (A, B and C). Also, “at least one of A, B and/or C” or “at least one of A, B and/or C” It may mean “at least one of A, B and C”.
  • control information when indicated as “control information (PDCCH)”, “PDCCH” may be proposed as an example of “control information”.
  • control information in this specification is not limited to “PDCCH”, and “PDDCH” may be proposed as an example of “control information”.
  • PDCCH control information
  • PDCCH control information
  • VVC Versatile Video Coding
  • EVC essential video coding
  • AV1 AOMedia Video 1
  • AVS2 Next-generation video/image coding standard
  • next-generation video/image coding standard ex. H.267 or H.268, etc.
  • VVC and later video/image coding standards or standards before VVC (e.g., HEVC (High Efficiency Video Coding) standard (ITU-T Rec. H.265, etc.) may be related to the disclosure.
  • HEVC High Efficiency Video Coding
  • video may mean a set of images over time.
  • a picture generally refers to a unit representing one image in a specific time period, and a slice is a unit constituting a part of a picture in coding.
  • One picture may be composed of a plurality of slices, and if necessary, a picture and a slice may be used interchangeably.
  • image may mean a concept including a still image and a video, which is a set of a series of still images over time.
  • video does not necessarily mean a set of a series of still images over time, and in some embodiments, a still image may be interpreted as a concept included in a video.
  • a pixel or pel may mean a minimum unit constituting one picture (or image). Also, as a term corresponding to a pixel,'sample' may be used.
  • a sample can generally represent a pixel or pixel value. Specifically, the sample may represent a pixel/pixel value of a luma component and/or a pixel/pixel value of a chroma component.
  • the unit represents a basic unit of image processing.
  • the unit may include at least one of a specific region of a picture and information related to the region.
  • One unit may include one luma block and two chroma (ex. cb, cr) blocks.
  • the unit may be used interchangeably with terms such as a block or area in some cases.
  • the MxN block may represent samples (or sample arrays) of M columns and N rows or a set of transform coefficients.
  • FIG. 1 is a block diagram illustrating a video/image coding system to which the present specification can be applied.
  • a video/image coding system may include a first device (source device) and a second device (receiving device).
  • the source device may transmit the encoded video/image information or data to a receiving device through a digital storage medium or network in the form of a file or streaming.
  • the source device may include a video source, an encoding apparatus, and a transmitter.
  • the receiving device may include a receiver, a decoding apparatus, and a renderer.
  • the encoding device may be referred to as a video/video encoding device, and the decoding device may be referred to as a video/video decoding device.
  • the renderer may include a display unit, and the display unit may be configured as a separate device or an external component.
  • the video source may acquire a video/image through a capture, synthesis, or generation process of the video/image.
  • the video source may include a video/image capture device and/or a video/image generation device.
  • a video/image capture device may include one or more cameras and/or a video/image archive including previously captured video/images and the like.
  • the video/image generating device may include a computer, a tablet, and a smart phone, and the like (electronically) to generate the video/image.
  • a virtual video/image may be generated through a computer, etc. In this case, the video/image capture process may be replaced with a process in which related data is generated.
  • the encoding device can encode the input video/video.
  • the encoding apparatus may perform a series of procedures such as prediction, transformation, and quantization for compression and coding efficiency.
  • the encoded data (encoded video/image information) may be output in the form of a bitstream.
  • the transmitter may transmit the encoded video/video information or data output in the form of a bitstream to a receiver of a receiving device through a digital storage medium or a network in a file or streaming format.
  • the digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD.
  • the transmitter may include an element for generating a media file through a predetermined file format, and may include an element for transmitting the media file generated through a broadcast/communication network.
  • the receiver may receive/extract the bitstream and deliver it to a decoding device.
  • the decoding apparatus may decode a video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding apparatus.
  • the renderer can render the decoded video/image.
  • the rendered video/image may be displayed through the display unit.
  • video may refer to a set of images over time.
  • a picture generally refers to a unit representing one image in a specific time period, and a slice/tile is a unit constituting a part of a picture in coding.
  • the slice/tile may include one or more coding tree units (CTUs).
  • CTUs coding tree units
  • One picture may be composed of one or more slices/tiles.
  • One picture may be composed of one or more tile groups.
  • One tile group may include one or more tiles.
  • the brick may represent a rectangular region of CTU rows within a tile in a picture. Tiles can be partitioned into multiple bricks, and each brick can be composed of one or more CTU rows in the tile (A tile may be partitioned into multiple bricks, each of which consisting of one or more CTU rows within the tile ).
  • a tile that is not partitioned into multiple bricks may be also referred to as a brick.
  • a brick scan can indicate a specific sequential ordering of CTUs partitioning a picture, the CTUs can be aligned with a CTU raster scan within a brick, and the bricks in a tile can be aligned sequentially with a raster scan of the bricks of the tile.
  • A, and tiles in a picture can be sequentially aligned with a raster scan of the tiles of the picture
  • a brick scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a brick , bricks within a tile are ordered consecutively in a raster scan of the bricks of the tile, and tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture).
  • a tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture.
  • the tile column is a rectangular area of CTUs, the rectangular area has a height equal to the height of the picture, and the width can be specified by syntax elements in a picture parameter set (The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set).
  • the tile row is a rectangular region of CTUs, the rectangular region has a width specified by syntax elements in a picture parameter set, and the height can be the same as the height of the picture (The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the width of the picture).
  • a tile scan can indicate a specific sequential ordering of CTUs partitioning a picture, the CTUs can be successively aligned with a CTU raster scan in a tile, and the tiles in a picture can be successively aligned with a raster scan of the tiles of the picture.
  • a tile scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture).
  • a slice may include an integer number of bricks of a picture, and the integer number of bricks may be included in one NAL unit (A slice includes an integer number of bricks of a picture that may be exclusively contained in a single NAL unit). A slice may consist of either a number of complete tiles or only a consecutive sequence of complete bricks of one tile ).
  • Tile groups and slices are used interchangeably in this document. For example, the tile group/tile group header in this document may be referred to as a slice/slice header.
  • the video encoding device may include a video encoding device.
  • the encoding apparatus 200 includes an image partitioner 210, a predictor 220, a residual processor 230, and an entropy encoder 240. It may be configured to include an adder (250), a filtering unit (filter, 260) and a memory (memory, 270).
  • the prediction unit 220 may include an inter prediction unit 221 and an intra prediction unit 222.
  • the residual processing unit 230 may include a transform unit 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235.
  • the residual processing unit 230 may further include a subtractor 231.
  • the adder 250 may be referred to as a reconstructor or a recontructged block generator.
  • the above-described image segmentation unit 210, prediction unit 220, residual processing unit 230, entropy encoding unit 240, adding unit 250, and filtering unit 260 may include one or more hardware components (for example, it may be configured by an encoder chipset or processor).
  • the memory 270 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium.
  • the hardware component may further include a memory 270 as an internal/external component.
  • the image division unit 210 may divide an input image (or picture, frame) input to the encoding apparatus 200 into one or more processing units.
  • the processing unit may be called a coding unit (CU).
  • the coding unit is recursively divided according to a quad-tree binary-tree ternary-tree (QTBTTT) structure from a coding tree unit (CTU) or a largest coding unit (LCU).
  • QTBTTT quad-tree binary-tree ternary-tree
  • CTU coding tree unit
  • LCU largest coding unit
  • one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and/or a ternary structure.
  • a quad tree structure may be applied first, and a binary tree structure and/or ternary structure may be applied later.
  • a binary tree structure may be applied first.
  • a coding procedure according to an embodiment may be performed based on a final coding unit that is no longer split.
  • the maximum coding unit may be directly used as the final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units having a lower depth than optimal if necessary.
  • the coding unit of the size of can be used as the final coding unit.
  • the coding procedure may include procedures such as prediction, transformation, and reconstruction, which will be described later.
  • the processing unit may further include a prediction unit (PU) or a transform unit (TU).
  • the prediction unit and the transform unit may be partitioned or partitioned from the above-described final coding unit, respectively.
  • the prediction unit may be a unit of sample prediction
  • the transformation unit may be a unit for deriving a transform coefficient and/or a unit for deriving a residual signal from the transform coefficient.
  • the unit may be used interchangeably with terms such as a block or area in some cases.
  • the MxN block may represent samples of M columns and N rows or a set of transform coefficients.
  • the sample may generally represent a pixel or a pixel value, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.
  • the sample may be used as a term for one picture (or image) corresponding to a pixel or pel.
  • the encoding device 200 subtracts a prediction signal (a predicted block, a prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from the input image signal (original block, original sample array).
  • a signal residual signal, residual block, residual sample array
  • the prediction unit may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block.
  • the prediction unit may determine whether intra prediction or inter prediction is applied in units of the current block or CU. As described later in the description of each prediction mode, the prediction unit may generate various information about prediction, such as prediction mode information, and transmit it to the entropy encoding unit 240.
  • the prediction information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.
  • the intra prediction unit 222 may predict the current block by referring to samples in the current picture.
  • the referenced samples may be located in the neighborhood of the current block or may be located apart depending on a prediction mode.
  • prediction modes may include a plurality of non-directional modes and a plurality of directional modes.
  • the non-directional mode may include, for example, a DC mode and a planar mode (Planar mode).
  • the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of detail of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting.
  • the intra prediction unit 222 may determine a prediction mode applied to the current block by using a prediction mode applied to neighboring blocks.
  • the inter prediction unit 221 may derive the predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture.
  • motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block.
  • the motion information may include a motion vector and a reference picture index.
  • the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
  • the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture.
  • the reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different.
  • the temporal neighboring block may be called a name such as a collocated reference block or a CUCU, and a reference picture including the temporal neighboring block may be called a collocated picture (colPic). It might be.
  • the inter prediction unit 221 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive the motion vector and/or reference picture index of the current block. Can be created. Inter prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 221 may use motion information of neighboring blocks as motion information of the current block.
  • the residual signal may not be transmitted.
  • the motion vector of the current block is obtained by using the motion vector of the neighboring block as a motion vector predictor and signaling a motion vector difference. I can order.
  • the prediction unit 220 may generate a prediction signal based on various prediction methods described below.
  • the prediction unit may apply intra prediction or inter prediction as well as intra prediction and inter prediction at the same time for prediction for one block. This can be called combined inter and intra prediction (CIIP).
  • the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block.
  • the IBC prediction mode or palette mode may be used for content video/video coding such as a game, such as screen content coding (SCC).
  • SCC screen content coding
  • IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in that a reference block is derived in the current picture. That is, the IBC can use at least one of the inter prediction techniques described in this document.
  • the palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, a sample value in a picture may be signaled based on information on the palette table and palette index.
  • the prediction signal generated by the prediction unit may be used to generate a reconstructed signal or may be used to generate a residual signal.
  • the transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, at least one of a DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform) It can contain.
  • GBT means a transformation obtained from this graph when it is said that the relationship information between pixels is graphically represented.
  • CNT means a transform obtained by generating a prediction signal using all previously reconstructed pixels and based on it.
  • the transform process may be applied to pixel blocks having the same size of a square, or may be applied to blocks of variable sizes other than squares.
  • the quantization unit 233 quantizes the transform coefficients and transmits them to the entropy encoding unit 240, and the entropy encoding unit 240 encodes a quantized signal (information about quantized transform coefficients) and outputs it as a bitstream. have. Information about the quantized transform coefficients may be called residual information.
  • the quantization unit 233 may rearrange block-type quantized transform coefficients into a one-dimensional vector form based on a coefficient scan order, and quantize the quantized transform coefficients based on the one-dimensional vector form. Information regarding transform coefficients may be generated.
  • the entropy encoding unit 240 may perform various encoding methods such as exponential Golomb (CAVLC), context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC).
  • CAVLC exponential Golomb
  • CAVLC context-adaptive variable length coding
  • CABAC context-adaptive binary arithmetic coding
  • the entropy encoding unit 240 may encode information necessary for video/image reconstruction (eg, a value of syntax elements, etc.) together with the quantized transform coefficients together or separately.
  • the encoded information (ex. encoded video/video information) may be transmitted or stored in units of network abstraction layer (NAL) units in the form of a bitstream.
  • NAL network abstraction layer
  • the video/video information may further include information regarding various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
  • the video/video information may further include general constraint information.
  • information and/or syntax elements transmitted/signaled from an encoding device to a decoding device may be included in video/video information.
  • the video/video information may be encoded through the above-described encoding procedure and included in the bitstream.
  • the bitstream can be transmitted over a network or stored on a digital storage medium.
  • the network may include a broadcasting network and/or a communication network
  • the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD.
  • the signal output from the entropy encoding unit 240 may be configured as an internal/external element of the encoding device 200 by a transmitting unit (not shown) and/or a storing unit (not shown) for storing, or the transmitting unit It may be included in the entropy encoding unit 240.
  • the quantized transform coefficients output from the quantization unit 233 may be used to generate a prediction signal.
  • a residual signal residual block or residual samples
  • the adder 155 adds the reconstructed residual signal to the predicted signal output from the inter predictor 221 or the intra predictor 222, so that the reconstructed signal (restored picture, reconstructed block, reconstructed sample array) Can be generated. If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block.
  • the adder 250 may be called a restoration unit or a restoration block generation unit.
  • the generated reconstructed signal may be used for intra prediction of a next processing target block in a current picture, or may be used for inter prediction of a next picture through filtering as described below.
  • LMCS luma mapping with chroma scaling
  • the filtering unit 260 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 260 may generate a modified restoration picture by applying various filtering methods to the restoration picture, and the modified restoration picture may be a DPB of the memory 270, specifically, the memory 270. Can be stored in.
  • the various filtering methods include, for example, deblocking filtering, sample adaptive offset (SAO), adaptive loop filtering (ALF), bilateral filtering, and the like. can do.
  • the filtering unit 260 may generate various pieces of information regarding filtering as described later in the description of each filtering method, and transmit them to the entropy encoding unit 240.
  • the filtering information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.
  • the modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter prediction unit 221.
  • inter prediction When the inter prediction is applied through the encoding apparatus, prediction mismatch between the encoding apparatus 200 and the decoding apparatus can be avoided, and encoding efficiency can be improved.
  • the memory 270 DPB may store the modified reconstructed picture for use as a reference picture in the inter prediction unit 221.
  • the memory 270 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of blocks in a picture that has already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 221 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 270 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 222.
  • FIG. 3 is a block diagram illustrating a video/video decoding apparatus to which the present specification can be applied.
  • the decoding apparatus 300 includes an entropy decoder (310), a residual processor (320), a prediction unit (predictor, 330), an adder (340), and a filtering unit (filter, 350) and memory (memoery, 360).
  • the prediction unit 330 may include an inter prediction unit 331 and an intra prediction unit 332.
  • the residual processing unit 320 may include a dequantizer (321) and an inverse transformer (321).
  • the entropy decoding unit 310, the residual processing unit 320, the prediction unit 330, the adding unit 340, and the filtering unit 350 described above may include one hardware component (eg, a decoder chipset or processor) according to an embodiment. ).
  • the memory 360 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium.
  • the hardware component may further include a memory 360 as an internal/external component.
  • the decoding apparatus 300 may restore an image corresponding to a process in which the video/image information is processed in the encoding apparatus of FIG. 2.
  • the decoding apparatus 300 may derive units/blocks based on block partitioning related information obtained from the bitstream.
  • the decoding apparatus 300 may perform decoding using a processing unit applied in the encoding apparatus.
  • the processing unit of decoding may be, for example, a coding unit, and the coding unit may be divided along a quad tree structure, a binary tree structure and/or a ternary tree structure from a coding tree unit or a largest coding unit.
  • One or more transform units can be derived from the coding unit. Then, the decoded video signal decoded and output through the decoding device 300 may be reproduced through the reproduction device.
  • the decoding apparatus 300 may receive the signal output from the encoding apparatus of FIG. 2 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 310.
  • the entropy decoding unit 310 may parse the bitstream to derive information (eg, video/image information) necessary for image reconstruction (or picture reconstruction).
  • the video/video information may further include information regarding various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS).
  • the video/video information may further include general constraint information.
  • the decoding apparatus may decode a picture further based on the information on the parameter set and/or the general restriction information.
  • Signaling/receiving information and/or syntax elements described later in this document may be decoded through the decoding procedure and obtained from the bitstream.
  • the entropy decoding unit 310 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and quantizes a value of a syntax element required for image reconstruction and a transform coefficient for residual.
  • a coding method such as exponential Golomb coding, CAVLC, or CABAC
  • the CABAC entropy decoding method receives bins corresponding to each syntax element in a bitstream, and decodes syntax element information to be decoded and decoding information of neighboring and decoding target blocks or symbol/bin information decoded in the previous step.
  • the context model is determined by using, and the probability of occurrence of the bin is predicted according to the determined context model, and arithmetic decoding of the bin is performed to generate a symbol corresponding to the value of each syntax element. have.
  • the CABAC entropy decoding method may update the context model using the decoded symbol/bin information for the next symbol/bin context model after determining the context model.
  • prediction information is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and the entropy decoding unit 310 performs entropy decoding.
  • the dual value, that is, quantized transform coefficients and related parameter information may be input to the residual processing unit 320.
  • the residual processor 320 may derive a residual signal (residual block, residual samples, residual sample array). Also, information related to filtering among information decoded by the entropy decoding unit 310 may be provided to the filtering unit 350. Meanwhile, a receiving unit (not shown) receiving a signal output from the encoding device may be further configured as an internal/external element of the decoding device 300, or the receiving unit may be a component of the entropy decoding unit 310.
  • the decoding device may be called a video/picture/picture decoding device, and the decoding device may be classified into an information decoder (video/picture/picture information decoder) and a sample decoder (video/picture/picture sample decoder). It might be.
  • the information decoder may include the entropy decoding unit 310, and the sample decoder may include the inverse quantization unit 321, an inverse transformation unit 322, an addition unit 340, a filtering unit 350, and a memory 360 ), at least one of an inter prediction unit 332 and an intra prediction unit 331.
  • the inverse quantization unit 321 may inverse quantize the quantized transform coefficients to output transform coefficients.
  • the inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block form. In this case, the reordering may be performed based on the coefficient scan order performed by the encoding device.
  • the inverse quantization unit 321 may perform inverse quantization on the quantized transform coefficients by using a quantization parameter (for example, quantization step size information), and obtain transform coefficients.
  • a quantization parameter for example, quantization step size information
  • the inverse transform unit 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).
  • the prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block.
  • the prediction unit may determine whether intra prediction is applied to the current block or inter prediction is applied based on the information on the prediction output from the entropy decoding unit 310, and may determine a specific intra/inter prediction mode.
  • the prediction unit 320 may generate a prediction signal based on various prediction methods described below.
  • the prediction unit may apply intra prediction or inter prediction as well as intra prediction and inter prediction at the same time for prediction for one block. This can be called combined inter and intra prediction (CIIP).
  • the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode for prediction of a block.
  • the IBC prediction mode or palette mode may be used for content video/video coding such as a game, such as screen content coding (SCC).
  • SCC screen content coding
  • IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction in that a reference block is derived in the current picture. That is, the IBC can use at least one of the inter prediction techniques described in this document.
  • the palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, information on the palette table and palette index may be signaled by being included in the video/image information.
  • the intra prediction unit 331 may predict the current block by referring to samples in the current picture.
  • the referenced samples may be located in the neighbor of the current block or may be located apart depending on the intra prediction mode.
  • intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes.
  • the intra prediction unit 331 may determine the intra prediction mode applied to the current block by using the intra prediction mode applied to the neighboring blocks.
  • the inter prediction unit 332 may derive the predicted block for the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture.
  • motion information may be predicted in units of blocks, subblocks, or samples based on the correlation of motion information between a neighboring block and a current block.
  • the motion information may include a motion vector and a reference picture index.
  • the motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information.
  • the neighboring block may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture.
  • the inter prediction unit 332 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or reference picture index of the current block based on the received candidate selection information. Inter-prediction may be performed based on various prediction modes, and information on the prediction may include information indicating an inter-prediction mode for the current block.
  • the adder 340 reconstructs the obtained residual signal by adding it to the predicted signal (predicted block, predicted sample array) output from the predictor (including the inter predictor 332 and/or the intra predictor 331) A signal (restored picture, reconstructed block, reconstructed sample array) can be generated. If there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block.
  • the adding unit 340 may be called a restoration unit or a restoration block generation unit.
  • the generated reconstructed signal may be used for intra prediction of a next processing target block in a current picture, may be output through filtering as described below, or may be used for inter prediction of a next picture.
  • LMCS luma mapping with chroma scaling
  • the filtering unit 350 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 350 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be a DPB of the memory 360, specifically, the memory 360 Can be transferred to.
  • the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
  • the (corrected) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter prediction unit 332.
  • the memory 360 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of blocks in a picture that has already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 260 for use as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 360 may store reconstructed samples of blocks reconstructed in the current picture, and may transmit the reconstructed samples to the intra prediction unit 331.
  • the embodiments described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding device 200 are respectively the filtering unit 350 and the inter prediction of the decoding device 300.
  • the unit 332 and the intra prediction unit 331 may be applied to the same or corresponding.
  • a predicted block including prediction samples for a current block which is a block to be coded
  • the predicted block includes prediction samples in a spatial domain (or pixel domain).
  • the predicted block is derived equally from an encoding device and a decoding device, and the encoding device decodes information (residual information) about the residual between the original block and the predicted block, not the original sample value itself of the original block. Signaling to the device can improve video coding efficiency.
  • the decoding apparatus may derive a residual block including residual samples based on the residual information, generate a reconstruction block including reconstruction samples by combining the residual block and the predicted block, and generate reconstruction blocks. It is possible to generate a reconstructed picture that includes.
  • the residual information may be generated through a transform and quantization procedure.
  • the encoding apparatus derives a residual block between the original block and the predicted block, and performs transformation procedures on residual samples (residual sample array) included in the residual block to derive transformation coefficients. And, by performing a quantization procedure on the transform coefficients, the quantized transform coefficients are derived to signal related residual information (via a bitstream) to a decoding apparatus.
  • the residual information may include information such as value information of the quantized transform coefficients, position information, a transform technique, a transform kernel, and quantization parameters.
  • the decoding apparatus may perform an inverse quantization/inverse transformation procedure based on the residual information and derive residual samples (or residual blocks).
  • the decoding apparatus may generate a reconstructed picture based on the predicted block and the residual block.
  • the encoding apparatus can also dequantize/inverse transform quantized transform coefficients for reference for inter prediction of a picture, to derive a residual block, and generate a reconstructed picture based on the quantized/inverse transform.
  • the intra prediction may represent prediction for generating prediction samples for the current block based on reference samples in a picture to which the current block belongs (hereinafter, the current picture).
  • peripheral reference samples to be used for intra prediction of the current block may be derived.
  • the neighboring reference samples of the current block are samples adjacent to the left boundary of the current block of nWxnH size and a total of 2xnH samples neighboring the bottom-left, samples adjacent to the top boundary of the current block. And a total of 2xnW samples neighboring the top-right and one sample neighboring the top-left of the current block.
  • the peripheral reference samples of the current block may include multiple columns of upper peripheral samples and multiple rows of left peripheral samples.
  • the neighboring reference samples of the current block have a total nH samples adjacent to the right boundary of the current block of size nWxnH, a total nW samples adjacent to the bottom boundary of the current block, and the lower right side of the current block. (bottom-right) may include one neighboring sample.
  • the decoder may construct surrounding reference samples to be used for prediction by substituting samples that are not available with available samples.
  • peripheral reference samples to be used for prediction may be configured through interpolation of available samples.
  • a prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) a neighboring reference sample of the current block
  • the prediction sample may be derived based on a reference sample existing in a specific (predictive) direction with respect to the prediction sample. In the case of (i), it may be called a non-directional mode or a non-angular mode, and in the case of (ii) a directional mode or an angular mode.
  • the prediction sample may be generated through interpolation.
  • LIP linear interpolation intra prediction
  • chroma prediction samples may be generated based on luma samples using a linear model. In this case, it can be called LM mode.
  • the temporary prediction sample of the current block is derived based on the filtered neighbor reference samples, and at least one of the existing neighbor reference samples, ie, the unfiltered neighbor reference samples, derived according to the intra prediction mode
  • a prediction sample of the current block may be derived by weighting a sum of a reference sample and the temporary prediction sample.
  • PDPC Porition dependent intra prediction
  • the reference sample line having the highest prediction accuracy among the neighboring multiple reference sample lines of the current block is selected to derive the prediction sample using the reference sample located in the prediction direction on the line, and at this time, the used reference sample line is decoded.
  • Intra prediction encoding may be performed by instructing (signaling) the device.
  • the above-described case may be referred to as multi-reference line (MRL) intra prediction or MRL-based intra prediction.
  • MRL multi-reference line
  • intra prediction is performed based on the same intra prediction mode by dividing the current block into vertical or horizontal sub-partitions, but it is possible to derive and use neighboring reference samples in the sub-partition unit. That is, in this case, the intra prediction mode for the current block is equally applied to the sub-partitions, but the intra-prediction performance may be improved in some cases by deriving and using surrounding reference samples in the sub-partition unit.
  • Such a prediction method may be called intra sub-partitions (ISP) or ISP based intra prediction.
  • the above-described intra prediction methods may be called an intra prediction type separately from the intra prediction mode.
  • the intra prediction type may be called various terms such as an intra prediction technique or an additional intra prediction mode.
  • the intra prediction type (or an additional intra prediction mode, etc.) may include at least one of the aforementioned LIP, PDPC, MRL, ISP.
  • the general intra prediction method except for the specific intra prediction type such as the LIP, PDPC, MRL, ISP, etc. may be referred to as a normal intra prediction type.
  • the normal intra prediction type may be generally applied when the specific intra prediction type as described above is not applied, and prediction may be performed based on the intra prediction mode described above. On the other hand, post-process filtering may be performed on the predicted samples derived as necessary.
  • the intra prediction procedure may include an intra prediction mode/type determination step, a peripheral reference sample derivation step, and an intra prediction mode/type based prediction sample derivation step. Also, a post-filtering step may be performed on the predicted sample derived as necessary.
  • an intra prediction mode applied to a current block may be determined using an intra prediction mode of neighboring blocks.
  • the decoding apparatus receives one of the MPM candidates in the most probable mode (MPM) list derived based on the intra prediction mode and additional candidate modes of the neighboring block of the current block (eg, left and/or upper neighboring blocks)
  • the selected MPM index may be selected, or one of the remaining intra prediction modes not included in the MPM candidates (and the planner mode) may be selected based on the remodeling intra prediction mode information.
  • the MPM list may be configured to include or not include a planner mode as a candidate.
  • the MPM list may have 6 candidates, and if the MPM list does not include a planner mode as the candidate, the MPM list may have 5 candidates. Can.
  • a not planner flag eg, intra_luma_not_planar_flag
  • the MPM flag is signaled first, and the MPM index and the not planner flag can be signaled when the value of the MPM flag is 1.
  • the MPM index may be signaled when the value of the not planner flag is 1.
  • the MPM list is configured not to include the planner mode as a candidate, rather than the planner mode is not the MPM, the planner mode is signaled by signaling a not planar flag first because the planner mode is always considered as the MPM. This is to check whether it is recognized first.
  • whether the intra prediction mode applied to the current block is among the MPM candidates (and the planner mode) or the re-maining mode may be indicated based on the MPM flag (ex. intra_luma_mpm_flag).
  • the value 1 of the MPM flag may indicate that the intra prediction mode for the current block is within MPM candidates (and planner mode), and the value 0 of the MPM flag indicates that the intra prediction mode for the current block is MPM candidates (and planner mode). ).
  • the not planar flag (ex. intra_luma_not_planar_flag) value 0 may indicate that the intra prediction mode for the current block is a planner mode, and the not planar flag value 1 indicates that the intra prediction mode for the current block is not a planar mode. Can.
  • the MPM index may be signaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element
  • the re-maining intra prediction mode information may be signaled in the form of a rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element.
  • the re-maining intra prediction mode information may indicate one of them by indexing the remaining intra prediction modes not included in the MPM candidates (and the planner mode) among the entire intra prediction modes in the order of prediction mode numbers.
  • the intra prediction mode may be an intra prediction mode for luma components (samples).
  • the intra prediction mode information includes the MPM flag (ex.
  • intra_luma_mpm_flag the not planar flag
  • the MPM index (ex. mpm_idx or intra_luma_mpm_idx)
  • remodeling intra prediction mode information rem_intra_luma_prma_prma_m It may include at least one.
  • the MPM list may be referred to as various terms such as the MPM candidate list and candModeList.
  • the encoder can use the intra prediction mode of the neighboring block to encode the intra prediction mode of the current block.
  • the encoder/decoder may construct a list of most probable modes (MPM) for the current block.
  • the MPM list may also be referred to as an MPM candidate list.
  • MPM may refer to a mode used to improve coding efficiency in consideration of the similarity between a current block and a neighboring block when coding an intra prediction mode.
  • the MPM list may be configured including a planner mode, or may be configured excluding a planner mode. For example, if the MPM list includes a planner mode, the number of candidates in the MPM list may be six. And, if the MPM list does not include a planner mode, the number of candidates in the MPM list may be five.
  • the encoder/decoder can construct an MPM list including six MPMs.
  • three types of modes may be considered: default intra modes, neighbor intra modes, and derived intra modes.
  • two peripheral blocks may be considered, a left peripheral block and an upper peripheral block.
  • the MPM list is configured not to include a planner mode, a planar mode is excluded from the list, and the number of MPM list candidates may be set to five.
  • 4 exemplarily shows intra directional modes of 65 prediction directions.
  • the directional mode (or angular mode) is an intra prediction mode having a vertical directionality and a vertical directionality centering on an intra prediction mode No. 34 having a diagonal upward prediction direction. ).
  • H and V in FIG. 4 refer to horizontal and vertical directions, respectively, and numbers from -32 to 32 indicate displacements of 1/32 units on a sample grid position.
  • the intra prediction modes 2 to 33 have horizontal directionality, and the intra prediction modes 34 to 66 have vertical directionality.
  • the intra prediction mode No. 18 and the intra prediction mode No. 50 represent a horizontal intra prediction mode and a vertical intra prediction mode, respectively, and the intra prediction mode No.
  • the 34th intra prediction mode may be called a left upward diagonal intra prediction mode
  • the 66th intra prediction mode may be called a right upward diagonal intra prediction mode.
  • the numbers of each intra prediction modes may be referred to as values of each intra prediction modes.
  • the value of the horizontal intra prediction mode may be 18 and the value of the vertical intra prediction mode may be 50.
  • the non-directional mode may include an average-based DC mode or interpolation-based planar mode of neighboring reference samples of the current block. have.
  • FIG. 5 is a diagram for explaining a process of deriving an intra prediction mode of a current chroma block according to an embodiment.
  • chroma (chroma) block may represent the same meaning as a color difference block, a color difference image, and the like, and chroma and color differences may be used interchangeably.
  • luma block may represent the same meaning as a luminance block, a luminance image, and the like, and luma and luminance may be used interchangeably.
  • current chroma block may mean a chroma component block of a current block that is a current coding unit
  • current luma block may mean a luma component block of a current block that is a current coding unit. Therefore, the current luma block and the current chroma block correspond to each other. However, the block shape and the number of blocks of the current luma block and the current chroma block are not always the same, and may be different in some cases. In some cases, the current chroma block may correspond to the current luma area, and the current luma area may consist of at least one luma block.
  • the “reference sample template” may mean a set of reference samples around the current chroma block to predict the current chroma block.
  • the reference sample template may be predefined, and information about the reference sample template may be signaled from the encoding device 200 to the decoding device 300.
  • a set of samples shaded by one line around a 4x4 block, which is a current chroma block, represents a reference sample template. It can be seen from FIG. 5 that the reference sample template is composed of one line of reference samples, while the reference sample region in the luma region corresponding to the reference sample template is composed of two lines.
  • CCLM cross component linear model
  • CCLM is a method of predicting a pixel value of a chroma image from a pixel value of a reconstructed luma image, and is based on a characteristic of high correlation between a luma image and a chroma image.
  • CCLM prediction of Cb and Cr chroma images may be based on the following Equation 1.
  • Pred c (x,y) is a Cb or Cr chroma image to be predicted
  • Rec L '(x,y) is a reconstructed luma image adjusted to a chroma block size
  • (x,y) is a pixel coordinate. it means.
  • the chroma image Pred c (x) The pixels of the luma image to be used in ,y) can be used in consideration of all the surrounding pixels in addition to Rec L (2x,2y).
  • Rec L '(x,y) may be represented as a downsampled luma sample.
  • ⁇ and ⁇ can be referred to as linear models or CCLM parameters.
  • the ⁇ may be called a scaling factor, and the ⁇ may be called an offset.
  • Prediction mode information indicating whether CCLM prediction is applied to the current block may be generated by an encoding device and transmitted to a decoding device. The same can be calculated.
  • Rec L '(x,y) may be derived using six peripheral pixels as in Equation 2 below.
  • the CCLM parameter when calculating the CCLM parameters ⁇ and ⁇ , the CCLM parameter may be calculated using a gradient of change of two luma and chroma sample pairs to reduce operations of multiplication and addition.
  • the CCLM parameters may be calculated as in Equation 3 and Equation 4 below.
  • (x A , y A ) is a sample value of a luma sample (y A ) having the smallest luma value among the neighboring reference samples of the current block for CCLM parameter calculation and a chroma sample (y A ) that is a pair of the luma sample.
  • (X B , y B ) is the luma sample (y B ) having the largest luma value among the neighboring reference samples of the current block for CCLM parameter calculation and the chroma sample (y B ) that is a pair of the luma sample. Sample values can be represented.
  • y A may represent a luma sample having the smallest luma value among neighboring reference samples of the current block
  • x A may represent a chroma sample that is a pair of the luma sample y A
  • y B is currently A luma sample having the largest luma value among the neighboring reference samples of the block may be represented
  • x B may represent a chroma sample that is a pair of the luma sample y B.
  • Table 1 above exemplarily shows CCLM parameters derived by a simplified calculation method.
  • multi-directional LM may be performed, which will be described in FIGS. 7 and 8.
  • 2N reference sample pairs derived for parameter calculation for CCLM prediction described above may be represented.
  • the 2N reference sample pairs may include 2N reference samples adjacent to the current chroma block and 2N reference samples adjacent to the current luma block.
  • the parameters ⁇ and ⁇ of the linear model may be derived based on neighboring samples used for intra prediction of the current luma block and neighboring samples used for intra prediction of the current chroma block.
  • the parameter ⁇ and the parameter ⁇ may be derived based on the following equation.
  • L(n) may represent upper peripheral samples and/or left peripheral samples of the current luma block
  • C(n) may indicate upper peripheral samples and/or left peripheral samples of the current chroma block.
  • L(n) may represent down-sampled upper peripheral samples and/or left peripheral samples of the current luma block.
  • N may represent a value that is twice the smaller of the width and height of the current chroma block.
  • the intra chroma prediction mode is based on the values of the intra luma prediction mode and the signaled intra chroma prediction mode (intra_chroma_pred_mode) information for the luma block (ex. DUAL_TREE is applied) that covers the center lower right sample of the current block or the chroma block. It can be determined by.
  • L(n) may represent upper peripheral samples and/or left peripheral samples of the current luma block
  • C(n) may indicate upper peripheral samples and/or left peripheral samples of the current chroma block.
  • L(n) may represent down-sampled upper peripheral samples and/or left peripheral samples of the current luma block.
  • N may represent a value that is twice the smaller of the width and height of the current chroma block.
  • the intra chroma prediction mode is based on the values of the intra luma prediction mode and the signaled intra chroma prediction mode (intra_chroma_pred_mode) information for the luma block (ex. DUAL_TREE is applied) that covers the center lower right sample of the current block or the chroma block. It can be determined by.
  • LM mode 7 and 8 exemplarily show a top linear model (LM) mode and a left LM mode, respectively, according to an embodiment of the present document.
  • the CCLM prediction in which the modes included in these drawings are added may be referred to as a multi-directional linear model (MDLM).
  • MDLM multi-directional linear model
  • the encoding device and the decoding device may perform CCLM prediction in which the top LM mode and the left LM mode are added.
  • the top LM mode may indicate a CCLM mode in which CCLM is performed using only the upper reference samples (samples located at the upper side) of the current (luma or chroma) block.
  • CCLM prediction may be performed based on upper reference samples that are doubled to the right in the upper reference samples in the existing CCLM prediction.
  • the top LM mode may be referred to as LM_A mode, LM_T (Linear Model_Top, LM_T) mode, A_LM mode, T_LM mode, A_CCLM mode, or T_CCLM mode.
  • the left LM mode may indicate a CCLM mode in which CCLM is performed using only the left reference samples (samples located on the left) of the current (luma or chroma) block.
  • the left LM mode may be referred to as LM_L mode, L_LM mode, or L_CCLM mode.
  • CCLM prediction may be performed based on left reference samples that are doubled downward to the left reference samples in the existing CCLM prediction.
  • a common CCLM prediction that is, a mode for performing CCLM prediction based on upper reference samples (samples located at the top) and left reference samples (samples located at the left) of the current (luma or chroma) block May be referred to as a left-top LM mode, LM_LA mode, LM_LT mode, LA_LM mode, LT_LM mode, or LT_CCLM mode.
  • samples for parameter calculation may be selected as follows.
  • a top LM mode may be applied to the current chroma block, and a total of 2N upper peripheral reference samples may be selected as shown in FIG. 7.
  • a left LM mode may be applied to the current chroma block, and a total of 2N left peripheral reference samples may be selected as shown in FIG. 8.
  • the parameters ⁇ and ⁇ in MDLM including a plurality of CCLM modes can be calculated using the gradients of change of the two luma and chroma sample pairs described above, and thus a lot of comparison operations are required when calculating parameters for MDLM.
  • the addition of the comparison operation may cause a delay in hardware implementation.
  • prediction may be performed through linear modeling using pixel values of a co-located luma block that has already been encoded. Therefore, a dependency between the luma block and the chroma block may occur. That is, in the conventional technology, the decoding of the luma block and the corresponding chroma block may be simultaneously performed in the hardware implementation of the decoder, but when the intra-prediction of the present embodiment is implemented in hardware, after the decoding of the luma block is completed (prediction and pixel reconstruction) (Complete all until reconstruction)) Decoding of the chroma block may be possible. Therefore, a pipeline delay in hardware implementation may occur.
  • luma and chroma blocks of the I-slice are performed in independent intra prediction in units of 64x64 luma blocks (32x32 chroma blocks), and dual with CCLM mode.
  • decoding of the 64x64 luma block and 32x32 chroma blocks at positions corresponding to the 64x64 luma block may be performed after all decoding of the 64x64 luma block is completed, which causes pipeline delay in hardware implementation. Can occur.
  • CCLM prediction when CCLM prediction is performed in the decoder, an additional operation for calculating CCLM parameters is required, and thus, the complexity of the decoder may be increased, and when all of the chroma blocks perform 2x2 CCLM prediction, the complexity of the decoder is further increased. Can be.
  • luma samples and chroma samples for calculation of CCLM (or MDLM) parameters to reduce delay in hardware implementation of a decoding device (or encoding device) and to reduce computational complexity of a decoder due to CCLM prediction A method for efficiently selecting them will be proposed. According to the proposed method, the hardware cost of the decoding device (or encoding device) and the complexity and time of the coding process will be minimized.
  • 9 and 10 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • a method of performing LM prediction using only reference samples having the same number of samples as the width or height of the current chroma block is proposed. That is, when the current chroma block is N x M, in the LM_A mode, the number of N samples equal to the width of the current chroma block may be selected in the LM_A mode, and in the LM_L mode, the current chroma block for the calculation of the LM parameters. The number of M samples equal to the height of can be selected.
  • the existing LM prediction performs the calculation of LM parameters in the decoder, there is a problem of increasing complexity in hardware implementation, and in the case of MDLM, a step of determining whether there are surrounding reference samples of the current chroma block is added. Higher complexity is required than the existing CCLM.
  • the step of determining whether there are neighboring reference samples may be eliminated.
  • the number of samples of the reference samples for MDLM prediction is reduced by half, a comparison computation amount for calculation of LM parameters can be reduced by half.
  • the capacity of the buffer storing the down-sampled luma sample may be reduced by half.
  • the promised method can be used in both the encoder and decoder without transmitting additional information about whether the method proposed in this embodiment is used, or information about whether the proposed method is used is tile, picture, or sequence units. Can be transmitted to the decoder.
  • sending or signaling the proposed method may mean “sending or signaling information on whether or not the proposed method is used from the encoder to the decoder.” If the proposed method is not used, it means that the same method as the existing MDLM is used.
  • the encoder determines whether the proposed method is used through high level syntax (HLS) as shown in Tables 2 to 4 below.
  • HLS high level syntax
  • Information about can be signaled (or transmitted) to the decoder.
  • information on whether the proposed method is used may be included in a bitstream (high-level syntax among syntaxes included in the bitstream) after being encoded by the encoder and transmitted in the form of a bitstream to the decoder.
  • mdlm_reduced_sample_num may be signaled through a tile group header, picture parameter set (PSP), or sequence parameter set (SPS).
  • the tile group header may be replaced with a slice header. Whether the proposed method is used as shown in Table 5 below may be determined through the value of mdlm_reduced_sample_num.
  • mdlm_reduced_sample_num when the value of mdlm_reduced_sample_num is 0, the proposed method may not be used, and when the value of mdlm_reduced_sample_num is 1, the proposed method may be used.
  • mdlm_reduced_sample_num may be referred to as information indicating whether to use the corrected surrounding sample.
  • mdlm_reduced_sample_num may be referred to as information indicating whether to use the reduced number of samples.
  • MDLM mode is a prediction mode within a chroma screen
  • chroma blocks predicted through MDLM mode are used to obtain a residual image through a difference from an original image in an encoder, or register in a decoder. It can be used to obtain a reconstructed image through summing with dual signals.
  • FIG. 11 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • a method of MDLM chroma intra prediction which is one of CCLM, is exemplarily illustrated. 11 will be described with reference to FIGS. 9 and 10.
  • the decoding device may determine that the MDLM chroma intra prediction mode is applied to the current chroma block.
  • the decoding apparatus may determine that the MDLM chroma intra prediction mode is applied to the current chroma block based on the prediction mode information (chroma intra prediction mode information) received from the encoding apparatus.
  • the decoding device may calculate the MDLM parameter (or CCLM parameter) according to the methods described above.
  • the decoding device (or encoding device) may generate an MDLM predictor for the current chroma block based on the MDLM parameters. In this case, as described above, reconstructed samples of the luma block may be used as reference samples.
  • the MDLM predictor may represent prediction sample(s) derived based on MDLM.
  • the decoding device may determine whether the top LM mode (LM_A mode) is derived as the CCLM prediction mode based on the prediction mode information.
  • the decoding device sets the number of samples of the upper peripheral (reference) chroma samples (pixels) equal to the width of the current chroma block as shown in FIG. 9. You can choose.
  • the decoding device determines the number of samples of the left peripheral (reference) chroma samples as shown in FIG. 10. You can select the same height as the current chroma block.
  • the calculation method of MDLM parameters ⁇ and ⁇ may follow the method described with Equations 3 to 6.
  • LM prediction may be performed using reference samples that do not overlap with each other. That is, each of the plurality of CCLM/MDLM prediction modes may use different peripheral chroma samples.
  • the width and height of the current chroma block are N and M, respectively.
  • the number of samples of the upper peripheral chroma samples may be half (N/2) of the width of the current chroma block, and the number of samples of the left peripheral chroma samples may be the height of the current chroma block. It may be half (M/2). Specifically, the N/2 upper peripheral chroma samples may be located between the left and the center (N/2 position) of the upper boundary of the current chroma block, and the M/2 left peripheral chroma samples may be left of the current chroma block. It can be located between the top of the border and the center (M/2 position).
  • N/2 upper peripheral chroma samples may be the left half of samples adjacent to the upper boundary of the current chroma block
  • M/2 left peripheral chroma samples may be the upper half adjacent to the left boundary of the current chroma block.
  • 13 and 14 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document. 13 and 14, the width and height of the current chroma block are N and M, respectively. 13 and 14 may be described with reference to FIG. 12.
  • the number of samples of the upper peripheral chroma samples may be the same as the width N of the current chroma block.
  • the N upper peripheral chroma samples may be selected in order in the right direction from the center (N/2 position) of the upper boundary of the current chroma block. That is, the N upper peripheral chroma samples in FIG. 13 may be different from the N/2 upper peripheral chroma samples in FIG. 12. In other words, the N upper peripheral chroma samples in FIG. 13 may not include the N/2 upper peripheral chroma samples in FIG. 12.
  • the number of samples of left peripheral chroma samples may be the same as the height M of the current chroma block.
  • the M left peripheral chroma samples may be sequentially selected from the center (M/2 position) of the left border of the current chroma block in the downward direction. That is, the M left peripheral chroma samples in FIG. 13 may be different from the M/2 left peripheral chroma samples in FIG. 12. In other words, the M left peripheral chroma samples in FIG. 13 may not include the M/2 left peripheral chroma samples in FIG. 12.
  • different peripheral chroma samples may be used in respective MDLM prediction modes, and thus the encoding efficiency of the decoding device (or encoding device) may be increased.
  • 15 and 16 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document.
  • the width and height of the current chroma block are N and M, respectively. 15 and 16 can be described with reference to FIG. 12.
  • the number of samples of the upper peripheral chroma samples may be equal to half (N/2) of the width of the current chroma block.
  • N/2 upper peripheral chroma samples may be located between the center (N/2 position) and the right side of the upper boundary of the current chroma block.
  • the N/2 upper peripheral chroma samples may be the right half of samples adjacent to the upper boundary of the current chroma block. That is, the N/2 upper peripheral chroma samples in FIG. 15 may be different from the N/2 upper peripheral chroma samples in FIG. 12. In other words, the N/2 upper peripheral chroma samples in FIG. 15 may not include the N/2 upper peripheral chroma samples in FIG. 12.
  • the number of samples of the left peripheral chroma samples may be equal to half (M/2) of the height of the current chroma block.
  • M/2 left peripheral chroma samples may be located between the center (M/2 position) and the bottom side of the left border of the current chroma block.
  • the M/2 left peripheral chroma samples may be the lower half adjacent to the left border of the current chroma block. That is, the M/2 left peripheral chroma samples in FIG. 16 may be different from the M/2 left peripheral chroma samples in FIG. 12. In other words, the M/2 left peripheral chroma samples in FIG. 16 may not include the M/2 left peripheral chroma samples in FIG. 12.
  • fewer peripheral reference samples can be used compared to the existing CCLM, so that the calculation amount of LM parameters of the decoding device (or encoding device) can be reduced.
  • 17 and 18 exemplarily show a top LM mode and a left LM mode, respectively, according to another embodiment of the present document. 17 and 18, the width and height of the current chroma block are N and M, respectively. 17 and 18 can be described with reference to FIG. 12.
  • the number of samples of the upper peripheral chroma samples may be equal to 1.5 times the width of the current chroma block (1.5N).
  • 1.5N upper peripheral chroma samples may be selected in order in the right direction from the center (N/2 position) of the upper boundary of the current chroma block. That is, the 1.5N upper peripheral chroma samples in FIG. 17 may be different from the N/2 upper peripheral chroma samples in FIG. 12. In other words, the 1.5N upper peripheral chroma samples in FIG. 17 may not include N/2 upper peripheral chroma samples in FIG. 12.
  • the number of samples of the left peripheral chroma samples may be equal to 1.5 times the height of the current chroma block (1.5M).
  • 1.5M left peripheral chroma samples may be selected in order from the center (M/2 position) of the left border of the current chroma block in the downward direction. That is, the 1.5M left peripheral chroma samples in FIG. 18 may be different from the M/2 left peripheral chroma samples in FIG. 12. In other words, the 1.5M left peripheral chroma samples in FIG. 18 may not include the M/2 left peripheral chroma samples in FIG. 12.
  • different peripheral chroma samples may be used in respective MDLM prediction modes, and thus the encoding efficiency of the decoding device (or encoding device) may be increased.
  • FIG. 19 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • a method of MDLM chroma intra prediction which is one of CCLM, is exemplarily illustrated. 19 will be described with reference to FIGS. 12 to 18.
  • the decoding device may determine that the MDLM chroma intra prediction mode is applied to the current chroma block. For example, the decoding apparatus may determine that the MDLM chroma intra prediction mode is applied to the current chroma block based on the prediction mode information (chroma intra prediction mode information) received from the encoding apparatus.
  • the decoding device may calculate the MDLM parameter (or CCLM parameter) according to the methods described above.
  • the decoding device (or encoding device) may generate an MDLM predictor for the current chroma block based on the MDLM parameters. In this case, as described above, reconstructed samples of the luma block may be used as reference samples.
  • the MDLM predictor may represent prediction sample(s) derived based on MDLM.
  • the decoding device may determine whether the left-top LM mode (LM mode) is derived as the CCLM prediction mode based on the prediction mode information.
  • LM_A mode left top LM mode
  • the decoding device sets the number of samples of the upper peripheral (reference) chroma samples (pixels) as shown in FIG. 12 to half the width of the current chroma block. And the number of samples of the left peripheral (reference) chroma samples equal to half the height of the current chroma block.
  • the decoding device determines whether the top LM mode (LM_A mode) is derived as the CCLM prediction mode based on the prediction mode information. Can.
  • the decoding device may select the number of samples of the upper peripheral (reference) chroma samples as shown in FIGS. 13, 15, or 17.
  • the decoding device when the top LM mode (LM_A mode) is derived as the CCLM prediction mode, the decoding device (or encoding device) sets the number of upper peripheral (reference) chroma samples equal to the width of the current chroma block as shown in FIG. 13. You can choose. In another example, when the top LM mode (LM_A mode) is derived as the CCLM prediction mode, the decoding device (or encoding device) sets the number of samples of the upper peripheral (reference) chroma samples to half of the width of the current chroma block as shown in FIG. 15. You can choose the same as.
  • the decoding device determines the number of samples of the upper peripheral (reference) chroma samples as shown in FIG. 17 of the width of the current chroma block. It can be selected equal to 1.5 times.
  • the decoding device As a CCLM prediction mode, when the left LM mode (LM_L mode), which is not the top LM mode (LM_A mode) is derived, the decoding device (or encoding device) is left peripheral (refer to FIG. 14, 16, or 18). ) You can select the number of samples of chroma samples. In one example, when the left LM mode (LM_L mode) is derived as the CCLM prediction mode, the decoding device (or encoding device) equals the number of samples of the left peripheral (reference) chroma samples to the width of the current chroma block, as shown in FIG. 14. You can choose.
  • the decoding device when the left LM mode (LM_L mode) is derived as the CCLM prediction mode, the decoding device (or encoding device) sets the number of samples of the left peripheral (reference) chroma samples to half of the width of the current chroma block, as shown in FIG. 16. You can choose the same as.
  • the decoding device when the left LM mode (LM_L mode) is derived as the CCLM prediction mode, the decoding device (or encoding device) determines the number of samples of the left peripheral (reference) chroma samples as shown in FIG. 18 of the width of the current chroma block. It can be selected equal to 1.5 times.
  • the calculation method of MDLM parameters ⁇ and ⁇ may follow the method described with Equations 3 to 6.
  • the promised method can be used in both the encoder and decoder without transmitting additional information about whether the method proposed in this embodiment is used, or information about whether the proposed method is used is tile, picture, or sequence units. Can be transmitted to the decoder.
  • sending or signaling the proposed method may mean “sending or signaling information on whether or not the proposed method is used from the encoder to the decoder.” If the proposed method is not used, it means that the same method as the existing MDLM is used.
  • the encoder determines whether the proposed method is used through high level syntax (HLS) as shown in Tables 2 to 4 below.
  • HLS high level syntax
  • Information about can be signaled (or transmitted) to the decoder.
  • information on whether the proposed method is used may be included in a bitstream (high-level syntax among syntaxes included in the bitstream) after being encoded by the encoder and transmitted in the form of a bitstream to the decoder.
  • lm_modified_sample_group may be signaled through a tile group header (PPS), a picture parameter set (PSP), or a sequence parameter set (SPS).
  • PPS tile group header
  • PSP picture parameter set
  • SPS sequence parameter set
  • the tile group header may be replaced with a slice header.
  • the proposed method when the lm_modified_sample_group value is 0, the proposed method may not be used, and when the lm_modified_sample_group value is 1, 2, or 3, the proposed method may be used. Specifically, when the lm_modified_sample_group value is 1, a method proposed from the embodiments according to FIGS. 13 and 14 may be used. When the value of lm_modified_sample_group is 2, a method proposed from the embodiments according to FIGS. 15 and 16 may be used. When the lm_modified_sample_group value is 3, a method proposed from the embodiments according to FIGS. 17 and 18 may be used.
  • lm_modified_sample_group may be referred to as information indicating whether to use a modified neighboring sample.
  • FIG. 20 is a flowchart illustrating a method of applying CCLM prediction according to another embodiment of the present document.
  • the method described with reference to FIG. 20 may include a method of performing downsampling using adaptively selected luma samples.
  • downsampling of luma samples that are not used for CCLM parameter calculation may be skipped during downsampling of the luma block. According to this embodiment, the amount of computation generated in the downsampling process may be reduced.
  • a linear model (LM) chroma intra prediction method includes downsampling a luma block (samples), calculating LM parameters, and multi-model linear model (CCLM/MDLM/MMLM)/MM And generating a multi-model multi-directional linear model (MDLM) predictor.
  • MMLM may refer to chroma intra prediction based on a plurality of linear models.
  • two linear models can be used for prediction of chroma samples.
  • luma samples of the luma block and neighboring luma samples may be classified into two groups.
  • chroma samples of the chroma block and neighboring chroma samples may be classified into two groups.
  • the first LM parameter may be derived based on the first surrounding luma samples and the first surrounding chroma samples
  • the second LM parameter may be derived based on the second surrounding luma samples and the second surrounding chroma samples.
  • First predictive samples in the chroma block may be derived based on the first LM parameter and first luma samples
  • second predictive samples in the chroma block based on the second LM parameter and second luma samples.
  • (Chroma) prediction samples in the chroma block may be derived based on the first prediction samples and the second prediction samples.
  • MM-MDLM may refer to the combination of MMLM and MDLM. From a broad perspective, MDLM, MMLM, MM-MDLM can be included in CCLM.
  • the predictor can represent the prediction sample(s) derived from each prediction mode.
  • a reference region used for LM prediction may be set, and a down-sampling filter may be selected. Down-sampling may be performed on luma samples included in the reference region set based on the selected down-sampling filter.
  • down-sampling filters having a smaller amount of computation than the 6-tap down-sampling described with reference to FIGS. 5 and 2 above can be used for CCLM/MDLM prediction.
  • the following equations (Equations 7 to 12) may represent respective exemplary down-sampling filters according to this embodiment.
  • Rec L '(x,y) means a down-sampling result value, in other words, may mean the value of a down-sampled neighboring luma sample located at (x,y).
  • Rec L (2x,2y) means the value of the surrounding luma sample (before downsampling) at (2x,2y)
  • Rec L (2x-1,2y) is (down) at (2x-1,2y)
  • Rec L (2x+1,2y) means the value of the surrounding luma sample (before downsampling) at the position (2x+1,2y)
  • Rec L (2x, 2y+1) means the value of the surrounding luma sample at the (2x,2y+1) position (before downsampling)
  • Rec L (2x-1,2y+1) is the position (2x-1,2y+1)
  • Rec L (2x+1,2y+1) means the value of the surrounding luma sample (before downsampling)
  • Rec L (2x+1,2y+1) means the value of the surrounding lum
  • the method according to the embodiment of FIG. 20 may reduce the complexity of calculating parameters through the existing CCLM/MDLM prediction through the downsampling filters described above.
  • FIG. 21 schematically shows a video encoding method by an encoding device according to the present document.
  • the method disclosed in FIG. 21 may be performed by the encoding device disclosed in FIG. 2.
  • S2110 to S2160 of FIG. 21 may be performed by the prediction unit of the encoding device
  • S2170 of FIG. 21 may be performed by the entropy encoding unit of the encoding device.
  • a process of deriving reconstructed samples for the current chroma block based on prediction samples and residual samples for the current chroma block may be performed by an adder of the encoding device.
  • the encoding apparatus may derive one of a plurality of CCLM prediction modes as a CCLM prediction mode of the current chroma block (S2110).
  • the plurality of CCLM prediction modes as described above, may include a left top LM mode, a top LM mode, and a left LM mode.
  • the encoding device may derive the number of samples of neighboring chroma samples of the current chroma block based on the CCLM prediction mode of the current chroma block and the width and height of the current chroma block (S2120).
  • the peripheral chroma samples may include upper peripheral chroma samples located above the current chroma block, and/or left peripheral chroma samples located to the left of the current chroma block.
  • the number of samples of the upper peripheral chroma samples and the number of samples of the left peripheral chroma samples can be derived individually.
  • the number of samples of the peripheral chroma samples may be the sum of the number of samples of the upper peripheral chroma samples and the number of samples of the left peripheral chroma samples.
  • the encoding device may derive the peripheral chroma samples of the number of samples (S2130).
  • the upper peripheral chroma samples may be adjacent to the upper boundary of the current chroma block
  • the left peripheral chroma samples may be adjacent to the left boundary of the current chroma block.
  • the peripheral chroma samples when the CCLM prediction mode of the current chroma block is a top LM mode, the peripheral chroma samples include upper peripheral chroma samples, and the upper peripheral chroma samples are the current chroma block
  • the number of samples adjacent to the upper boundary of and the upper peripheral chroma samples may be equal to the width of the current chroma block.
  • the peripheral chroma samples include left peripheral chroma samples, and the left peripheral chroma samples are the current chroma block
  • the number of samples adjacent to the left boundary of and the left peripheral chroma samples may be the same as the height of the current chroma block.
  • the peripheral chroma samples when the CCLM mode is a left-top LM mode, include first upper peripheral chroma samples and first left peripheral chroma samples, and the first upper peripheral The number of samples of chroma samples may be half the width of the current chroma block, and the number of samples of the first left peripheral chroma samples may be half the height of the current chroma block.
  • the peripheral chroma samples include second upper peripheral chroma samples, and the number of samples of the second upper peripheral chroma samples is the current chroma block And the second upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include second left peripheral chroma samples, and the number of samples of the second left peripheral chroma samples is the current chroma block And the second left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the peripheral chroma samples include third upper peripheral chroma samples, and the number of samples of the third upper peripheral chroma samples is the current chroma block , And the third upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include third left peripheral chroma samples, and the number of samples of the third left peripheral chroma samples is the current chroma block And half of the height, and the third left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the peripheral chroma samples include fourth upper peripheral chroma samples, and the number of samples of the fourth upper peripheral chroma samples is the current chroma block 1.5 times the width, and the fourth upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include fourth left peripheral chroma samples, and the number of samples of the fourth left peripheral chroma samples is the current chroma. It is 1.5 times the height of the block, and the fourth left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the encoding apparatus may derive down-sampled neighboring luma samples and down-sampled luma samples of the current luma block (S2140).
  • the down sampling procedure may be performed based on at least one of Equation 2 and Equation 7 to Equation 12 described above.
  • the down-sampled neighboring luma samples may be derived based on Equation 7 or Equation 8.
  • the encoding apparatus may derive CCLM parameters based on the peripheral chroma samples and the down-sampled peripheral luma samples (S2150).
  • the CCLM parameters may include ⁇ and ⁇ described above.
  • the encoding apparatus may derive prediction samples for the current chroma block based on CCLM parameters and down-sampled luma samples (S2160).
  • the procedure for deriving prediction samples may be performed based on Equation 1 described above.
  • the encoding device may generate information indicating whether to use the modified surrounding samples.
  • the information indicating whether to use the corrected surrounding sample may correspond to mdlm_reduced_sample_num included in Tables 2 to 4 described above or lm_modified_sample_group included in Tables 6 to 8.
  • the number of samples of the upper peripheral chroma samples among the peripheral chroma samples is the current chroma block. It may be equal to the width or half of the width.
  • the number of samples of the upper peripheral chroma samples among the peripheral chroma samples is the current chroma block. It may be equal to twice the width of the.
  • the encoding apparatus may encode image information based on the predicted samples (S2170). For example, the encoding apparatus may derive residual samples based on prediction samples. Residual samples may be derived based on a comparison of the original samples of the current chroma block and the predicted samples. The encoding device may generate residual information based on residual samples. As described above, a transform and/or quantization procedure may be performed on the residual samples, and the residual information may include information about (quantized) transform coefficients. The encoding device may encode video information including residual information. The image information may include prediction mode information for the current chroma block and information indicating whether to use the corrected neighboring sample.
  • the encoding device may output the video information in the form of a bitstream. Meanwhile, the bitstream may be transmitted to a decoding device through a network or (digital) storage medium.
  • the network may include a broadcasting network and/or a communication network
  • the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD.
  • FIG. 22 schematically shows an encoding apparatus that performs a video encoding method according to the present document.
  • the method disclosed in FIG. 21 may be performed by the encoding apparatus disclosed in FIG. 22.
  • the prediction unit of the encoding device of FIG. 22 may perform S2110 to S2160 of FIG. 21, and the entropy encoding unit of the encoding device of FIG. 22 may perform S2170 of FIG. 21.
  • the adder of the encoding apparatus of FIG. 22 may perform a process of deriving reconstruction samples for the current chroma block based on prediction samples and residual samples for the current chroma block.
  • FIG. 23 schematically shows a video decoding method by a decoding apparatus according to the present document.
  • the method disclosed in FIG. 23 may be performed by the decoding apparatus disclosed in FIG. 3.
  • S2310 to S2350 of FIG. 23 may be performed by the prediction unit of the decoding apparatus
  • S2360 of FIG. 23 may be performed by the addition unit of the decoding apparatus.
  • the process of obtaining image information including information on the residual of the current block through the bitstream may be performed by the entropy decoding unit of the decoding apparatus, and the information on the residual
  • the process of deriving the residual samples for the current block may be performed by a residual processing unit (specifically, an inverse transform unit of the residual processing unit) of the decoding apparatus.
  • a residual processing unit specifically, an inverse transform unit of the residual processing unit
  • the decoding apparatus may derive one of the plurality of CCLM prediction modes as the CCLM prediction mode of the current chroma block (S2310).
  • the plurality of CCLM prediction modes as described above, may include a left top LM mode, a top LM mode, and a left LM mode.
  • the decoding apparatus may derive the number of samples of neighboring chroma samples of the current chroma block based on the CCLM prediction mode of the current chroma block and the width and height of the current chroma block (S2320).
  • the peripheral chroma samples may include upper peripheral chroma samples located above the current chroma block, and left peripheral chroma samples positioned to the left of the current chroma block.
  • the number of samples of the upper peripheral chroma samples and the number of samples of the left peripheral chroma samples can be derived individually.
  • the number of samples of the peripheral chroma samples may be the sum of the number of samples of the upper peripheral chroma samples and the number of samples of the left peripheral chroma samples.
  • the decoding apparatus may derive the neighboring chroma samples of the number of samples (S2330).
  • the upper peripheral chroma samples may be adjacent to the upper boundary of the current chroma block
  • the left peripheral chroma samples may be adjacent to the left boundary of the current chroma block.
  • the peripheral chroma samples when the CCLM prediction mode of the current chroma block is a top LM mode, the peripheral chroma samples include upper peripheral chroma samples, and the upper peripheral chroma samples are the current chroma block
  • the number of samples adjacent to the upper boundary of and the upper peripheral chroma samples may be equal to the width of the current chroma block.
  • the peripheral chroma samples include left peripheral chroma samples, and the left peripheral chroma samples are the current chroma block
  • the number of samples adjacent to the left boundary of and the left peripheral chroma samples may be the same as the height of the current chroma block.
  • the peripheral chroma samples when the CCLM mode is a left-top LM mode, include first upper peripheral chroma samples and first left peripheral chroma samples, and the first upper peripheral The number of samples of chroma samples may be half the width of the current chroma block, and the number of samples of the first left peripheral chroma samples may be half the height of the current chroma block.
  • the peripheral chroma samples include second upper peripheral chroma samples, and the number of samples of the second upper peripheral chroma samples is the current chroma block And the second upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include second left peripheral chroma samples, and the number of samples of the second left peripheral chroma samples is the current chroma block And the second left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the peripheral chroma samples include third upper peripheral chroma samples, and the number of samples of the third upper peripheral chroma samples is the current chroma block , And the third upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include third left peripheral chroma samples, and the number of samples of the third left peripheral chroma samples is the current chroma block And half of the height, and the third left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the peripheral chroma samples include fourth upper peripheral chroma samples, and the number of samples of the fourth upper peripheral chroma samples is the current chroma block 1.5 times the width, and the fourth upper peripheral chroma samples may be different from the first upper peripheral chroma samples.
  • the peripheral chroma samples include fourth left peripheral chroma samples, and the number of samples of the fourth left peripheral chroma samples is the current chroma. It is 1.5 times the height of the block, and the fourth left peripheral chroma samples may be different from the first left peripheral chroma samples.
  • the decoding apparatus may derive down-sampled neighboring luma samples and down-sampled luma samples of the current luma block (S2340).
  • the down sampling procedure may be performed based on at least one of Equation 2 and Equation 7 to Equation 12 described above.
  • the down-sampled neighboring luma samples may be derived based on Equation 7 or Equation 8.
  • the decoding apparatus may derive CCLM parameters based on the peripheral chroma samples and the down-sampled peripheral luma samples (S2350).
  • the CCLM parameters may include ⁇ and ⁇ described above.
  • the decoding apparatus may derive prediction samples for the current chroma block based on CCLM parameters and down-sampled luma samples (S2360).
  • the procedure for deriving prediction samples may be performed based on Equation 1 described above.
  • the decoding apparatus may generate reconstructed samples for the current chroma block based on the predicted samples (S2370). For example, the decoding apparatus may receive information about the residual for the current chroma block from the bitstream output from the encoding apparatus.
  • the residual information may include a transform coefficient for a (chroma) residual sample.
  • the decoding apparatus may derive the residual sample (or residual sample array) for the current chroma block based on the residual information. In this case, the decoding apparatus may generate the reconstructed samples based on the predicted samples and the residual samples.
  • the decoding apparatus may obtain information indicating whether to use the corrected peripheral sample from the bitstream output from the encoding apparatus.
  • the information indicating whether to use the corrected surrounding sample may correspond to mdlm_reduced_sample_num included in Tables 2 to 4 described above or lm_modified_sample_group included in Tables 6 to 8.
  • the number of samples of the upper peripheral chroma samples among the peripheral chroma samples is the current chroma block. It may be equal to the width or half of the width.
  • the number of samples of the upper peripheral chroma samples among the peripheral chroma samples is the current chroma block. It may be equal to twice the width of the.
  • FIG. 24 schematically shows a decoding apparatus performing an image decoding method according to the present document.
  • the method disclosed in FIG. 23 may be performed by the decoding apparatus disclosed in FIG. 24.
  • the prediction unit of the decoding apparatus of FIG. 24 may perform S2310 to S2350 of FIG. 23, and the adder of the decoding apparatus of FIG. 24 may perform S2360 of FIG. 23.
  • the process of obtaining image information including information on the residual of the current block through the bitstream may be performed by the entropy decoding unit of the decoding apparatus of FIG. 24, based on the information on the residual
  • the process of deriving the residual samples for the current block may be performed by the residual processing unit (specifically, the inverse transform unit of the residual processing unit) of the decoding apparatus of FIG. 24.
  • a reconstructed block/picture may be generated based on the reconstructed samples generated by a decoding apparatus.
  • the decoding apparatus can generate the reconstructed samples based on the prediction samples and the residual samples.
  • an in-loop filtering procedure such as deblocking filtering, SAO, ALF, and/or bi-directional filtering can be applied to the reconstructed picture to improve subjective/objective image quality as needed.
  • the complexity of intra prediction can be reduced by limiting the number of neighboring samples selected to derive a linear model parameter for a multi-directional linear model (MDLM) to a specific number.
  • MDLM multi-directional linear model
  • the methods are described based on a flow chart as a series of steps or blocks, but the embodiments are not limited to the order of steps, and some steps may be performed in a different order than the steps described above or simultaneously Can occur.
  • steps shown in the flowchart are not exclusive, other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of the embodiments of the present document.
  • the method according to the above-described embodiments of the present document may be implemented in the form of software, and the encoding device and/or the decoding device according to the present document may be an image of a TV, computer, smartphone, set-top box, display device, etc. It may be included in the apparatus for performing the processing.
  • the above-described method may be implemented as a module (process, function, etc.) performing the above-described function.
  • Modules are stored in memory and can be executed by a processor.
  • the memory may be internal or external to the processor, and may be connected to the processor by various well-known means.
  • the processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and/or data processing devices.
  • the memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media and/or other storage devices. That is, the embodiments described in this document may be implemented and implemented on a processor, microprocessor, controller, or chip.
  • the functional units shown in each figure may be implemented and implemented on a computer, processor, microprocessor, controller, or chip. In this case, information for implementation (ex. information on instructions) or an algorithm may be stored in a digital storage medium.
  • the decoding device and encoding device to which the embodiment(s) of the present document are applied include multimedia broadcast transmission/reception devices, mobile communication terminals, home cinema video devices, digital cinema video devices, surveillance cameras, video communication devices, and video communications.
  • the OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).
  • the processing method to which the embodiment(s) of the present document is applied can be produced in the form of a program executed by a computer, and stored in a computer-readable recording medium.
  • Multimedia data having a data structure according to embodiment(s) of this document may also be stored on a computer-readable recording medium.
  • the computer-readable recording medium includes all kinds of storage devices and distributed storage devices in which computer-readable data is stored.
  • the computer-readable recording medium includes, for example, Blu-ray Disc (BD), Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk and optical. It may include a data storage device.
  • the computer-readable recording medium includes media implemented in the form of a carrier wave (for example, transmission via the Internet).
  • the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.
  • embodiment(s) of this document may be implemented as a computer program product by program code, and the program code may be executed on a computer by the embodiment(s) of this document.
  • the program code can be stored on a computer readable carrier.
  • 25 exemplarily shows a content streaming system according to the present specification.
  • a content streaming system to which embodiments of the present specification are applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.
  • the encoding server serves to compress a content input from multimedia input devices such as a smartphone, a camera, and a camcorder into digital data to generate a bitstream and transmit it to the streaming server.
  • multimedia input devices such as a smart phone, a camera, and a camcorder directly generate a bitstream
  • the encoding server may be omitted.
  • the bitstream may be generated by an encoding method or a bitstream generation method to which embodiments of the present document are applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.
  • the streaming server transmits multimedia data to a user device based on a user request through a web server, and the web server serves as an intermediary to inform the user of the service.
  • the web server delivers it to the streaming server, and the streaming server transmits multimedia data to the user.
  • the content streaming system may include a separate control server, in which case the control server serves to control commands/responses between devices in the content streaming system.
  • the streaming server may receive content from a media storage and/or encoding server. For example, when content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.
  • Examples of the user device include a mobile phone, a smart phone, a laptop computer, a terminal for digital broadcasting, a personal digital assistants (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices, e.g., smartwatches, smart glass, head mounted display (HMD), digital TV, desktop Computers, digital signage, and the like.
  • PDA personal digital assistants
  • PMP portable multimedia player
  • HMD head mounted display
  • Each server in the content streaming system can be operated as a distributed server, and in this case, data received from each server can be distributed.

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Abstract

Le procédé de décodage d'une image effectué par un dispositif de décodage, selon le présent document, comprend les étapes consistant à obtenir, en tant que mode de prédiction de modèle linéaire à composante transversale (CCLM) d'un bloc de chrominance actuel, un mode parmi une pluralité de modes de prédiction CCLM sur la base d'informations de mode de prédiction; obtenir le nombre d'échantillons de chrominance voisins du bloc de chrominance actuel sur la base du mode de prédiction CCLM du bloc de chrominance actuel et d'une largeur et d'une hauteur du bloc de chrominance actuel; obtenir autant d'échantillons de chrominance voisins que le nombre d'échantillons; calculer des paramètres CCLM sur la base des échantillons de chrominance voisins et des échantillons de luminance voisins sous-échantillonnés; et obtenir des échantillons de prédiction pour le bloc de chrominance actuel sur la base des paramètres CCLM et des échantillons de luminance voisins sous-échantillonnés.
PCT/KR2020/000685 2019-01-14 2020-01-14 Procédé et dispositif de décodage d'image sur la base d'une prédiction cclm dans un système de codage d'image WO2020149616A1 (fr)

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