WO2021045491A1 - Procédé et appareil de codage/décodage vidéo pour effectuer une prédiction intra d'une composante de chroma, et procédé de transmission de flux binaire - Google Patents

Procédé et appareil de codage/décodage vidéo pour effectuer une prédiction intra d'une composante de chroma, et procédé de transmission de flux binaire Download PDF

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Publication number
WO2021045491A1
WO2021045491A1 PCT/KR2020/011722 KR2020011722W WO2021045491A1 WO 2021045491 A1 WO2021045491 A1 WO 2021045491A1 KR 2020011722 W KR2020011722 W KR 2020011722W WO 2021045491 A1 WO2021045491 A1 WO 2021045491A1
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intra prediction
block
chroma
prediction mode
mode
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PCT/KR2020/011722
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English (en)
Korean (ko)
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허진
최장원
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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
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
    • 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
    • H04N19/169—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
    • H04N19/597—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding specially adapted for multi-view video sequence encoding
    • 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
    • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards

Definitions

  • the present disclosure relates to an image encoding/decoding method, an apparatus, and a method of transmitting a bitstream, and more particularly, an image encoding/decoding method, an apparatus and a method for performing an intra prediction process based on an MPM list for a current chroma block, and It relates to a method of transmitting a bitstream generated by an image encoding method/apparatus of the present disclosure.
  • An object of the present disclosure is to provide a video encoding/decoding method and apparatus with improved encoding/decoding efficiency.
  • an object of the present disclosure is to provide an image encoding/decoding method and apparatus for performing improved intra prediction on a chroma component.
  • an object of the present disclosure is to provide an image encoding/decoding method and apparatus for performing a unified intra prediction process based on an MPM list for a luma component and a chroma component.
  • an object of the present disclosure is to provide a method for transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure.
  • an object of the present disclosure is to provide a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure.
  • an object of the present disclosure is to provide a recording medium storing a bitstream that is received and decoded by an image decoding apparatus according to the present disclosure and used for restoring an image.
  • An image decoding method includes decoding intra prediction mode information of a current chroma block from a bitstream, based on the intra prediction mode information and an intra prediction mode of a neighboring chroma block adjacent to the current chroma block. , Constructing a candidate list including intra prediction mode candidates of the current chroma block, determining an intra prediction mode of the current chroma block based on the intra prediction mode information and the candidate list, and the current chroma It may include generating a prediction block for the current chroma block by performing intra prediction based on the intra prediction mode of the block.
  • An image decoding apparatus includes a memory and at least one processor, wherein the at least one processor decodes intra prediction mode information of a current chroma block from a bitstream, and includes the intra prediction mode information and A candidate list including intra prediction mode candidates of the current chroma block is constructed based on an intra prediction mode of a neighboring chroma block adjacent to the current chroma block, and the current chroma is based on the intra prediction mode information and the candidate list.
  • a prediction block for the current chroma block may be generated by determining an intra prediction mode of a block and performing intra prediction based on the intra prediction mode of the current chroma block.
  • An image encoding method includes determining an intra prediction mode of a current chroma block, and performing intra prediction based on the intra prediction mode of the current chroma block, thereby providing a prediction block for the current chroma block.
  • a transmission method may transmit a bitstream generated by the image encoding apparatus or image encoding method of the present disclosure.
  • a computer-readable recording medium may store a bitstream generated by the image encoding method or image encoding apparatus of the present disclosure.
  • an image encoding/decoding method and apparatus with improved encoding/decoding efficiency may be provided.
  • an image encoding/decoding method and apparatus for performing improved intra prediction on a chroma component may be provided.
  • an image encoding/decoding method and apparatus for performing unified intra prediction based on an MPM list on a luma component and a chroma component may be provided.
  • a method for transmitting a bitstream generated by an image encoding method or an apparatus according to the present disclosure may be provided.
  • a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure may be provided.
  • a recording medium may be provided that stores a bitstream that is received and decoded by the image decoding apparatus according to the present disclosure and used for image restoration.
  • FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.
  • FIG. 2 is a schematic diagram of an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
  • FIG. 3 is a schematic diagram of an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
  • FIG. 4 is a flowchart illustrating a video/video encoding method based on intra prediction.
  • FIG. 5 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • FIG. 6 is a flowchart illustrating a video/video decoding method based on intra prediction.
  • FIG. 7 is a diagram illustrating an exemplary configuration of an intra prediction unit according to the present disclosure.
  • FIG. 8A is a diagram illustrating an intra prediction direction according to an embodiment of the present disclosure.
  • 8B is a diagram illustrating an intra prediction direction according to another embodiment of the present disclosure.
  • 9A to 9C are diagrams for explaining a relationship between a luma component block (a luma component array) and a chroma component block (a chroma component array) according to a chroma format.
  • FIG. 10 is a diagram illustrating an example of an SPS syntax including signaling information in a chroma format.
  • FIG. 11 is a diagram illustrating a predetermined position for deriving an intra prediction mode of a current chroma block in the case of a DM.
  • FIG. 12 is a diagram illustrating a size of a current chroma block according to a chroma format.
  • FIG. 13 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to an embodiment of the present disclosure.
  • FIG. 14 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to an embodiment of the present disclosure.
  • 15 is a flowchart for describing a procedure for deriving an intra prediction mode in more detail.
  • 16 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • 17 is a diagram showing syntax of a slice header including slice type information.
  • FIG. 18 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • 19 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • 20 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • 21 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • 22 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • FIG. 23 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • 24 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • 25 is a diagram illustrating a content streaming system to which an embodiment according to the present disclosure can be applied.
  • a component when a component is said to be “connected”, “coupled” or “connected” with another component, it is not only a direct connection relationship, but also an indirect connection relationship in which another component exists in the middle. It can also include.
  • a certain component when a certain component “includes” or “have” another component, it means that other components may be further included rather than excluding other components unless otherwise stated. .
  • first and second are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise noted. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment is referred to as a first component in another embodiment. It can also be called.
  • components that are distinguished from each other are intended to clearly describe each feature, and do not necessarily mean that the components are separated. That is, a plurality of components may be integrated into one hardware or software unit, or one component may be distributed to form a plurality of hardware or software units. Therefore, even if not stated otherwise, such integrated or distributed embodiments are also included in the scope of the present disclosure.
  • components described in various embodiments do not necessarily mean essential components, and some may be optional components. Accordingly, an embodiment consisting of a subset of components described in an embodiment is also included in the scope of the present disclosure. In addition, embodiments including other elements in addition to the elements described in the various embodiments are included in the scope of the present disclosure.
  • the present disclosure relates to encoding and decoding of an image, and terms used in the present disclosure may have a common meaning commonly used in the technical field to which the present disclosure belongs unless newly defined in the present disclosure.
  • a “picture” generally refers to a unit representing one image in a specific time period
  • a slice/tile is a coding unit constituting a part of a picture
  • one picture is one It may be composed of more than one slice/tile.
  • a slice/tile may include one or more coding tree units (CTU).
  • pixel or “pel” may mean a minimum unit constituting one picture (or image).
  • sample may be used as a term corresponding to a pixel.
  • a sample may generally represent a pixel or a value of a pixel, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.
  • unit may represent a basic unit of image processing.
  • the unit may include at least one of a specific area of a picture and information related to the corresponding area.
  • the unit may be used interchangeably with terms such as “sample array”, “block”, or “area” depending on the case.
  • the MxN block may include samples (or sample arrays) consisting of M columns and N rows, or a set (or array) of transform coefficients.
  • current block may mean one of “current coding block”, “current coding unit”, “coding object block”, “decoding object block”, or “processing object block”.
  • current block may mean “current prediction block” or “prediction target block”.
  • transformation inverse transformation
  • quantization inverse quantization
  • current block may mean “current transform block” or “transform target block”.
  • filtering is performed, “current block” may mean “block to be filtered”.
  • current block may mean a block including both a luma component block and a chroma component block or "a luma block of the current block” unless explicitly stated as a chroma block.
  • the luma component block of the current block may be explicitly expressed by including an explicit description of a luma component block, such as a "luma block” or a "current luma block”.
  • the chroma component block of the current block may be explicitly expressed by including an explicit description of a chroma component block such as a "chroma block” or a "current chroma block”.
  • FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.
  • a video coding system may include an encoding device 10 and a decoding device 20.
  • the encoding device 10 may transmit the encoded video and/or image information or data in a file or streaming format to the decoding device 20 through a digital storage medium or a network.
  • the encoding apparatus 10 may include a video source generator 11, an encoding unit 12, and a transmission unit 13.
  • the decoding apparatus 20 may include a receiving unit 21, a decoding unit 22, and a rendering unit 23.
  • the encoder 12 may be referred to as a video/image encoder, and the decoder 22 may be referred to as a video/image decoder.
  • the transmission unit 13 may be included in the encoding unit 12.
  • the receiving unit 21 may be included in the decoding unit 22.
  • the rendering unit 23 may include a display unit, and the display unit may be configured as a separate device or an external component.
  • the video source generator 11 may acquire a video/image through a process of capturing, synthesizing, or generating a video/image.
  • the video source generator 11 may include a video/image capturing device and/or a video/image generating device.
  • the video/image capture device may include, for example, one or more cameras, a video/image archive including previously captured video/images, and the like.
  • the video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate a video/image.
  • a virtual video/image may be generated through a computer or the like, and in this case, a video/image capturing process may be substituted as a process of generating related data.
  • the encoder 12 may encode an input video/image.
  • the encoder 12 may perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency.
  • the encoder 12 may output encoded data (coded video/image information) in the form of a bitstream.
  • the transmission unit 13 may transmit the encoded video/image information or data output in the form of a bitstream to the reception unit 21 of the decoding apparatus 20 through a digital storage medium or a network in a file or streaming form.
  • Digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD.
  • the transmission unit 13 may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast/communication network.
  • the receiving unit 21 may extract/receive the bitstream from the storage medium or network and transmit it to the decoding unit 22.
  • the decoder 22 may decode the video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoder 12.
  • the rendering unit 23 may render the decoded video/image.
  • the rendered video/image may be displayed through the display unit.
  • FIG. 2 is a schematic diagram of an image encoding apparatus to which an embodiment according to the present disclosure can be applied.
  • the image encoding apparatus 100 includes an image segmentation unit 110, a subtraction unit 115, a transformation unit 120, a quantization unit 130, an inverse quantization unit 140, and an inverse transformation unit ( 150), an addition unit 155, a filtering unit 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoding unit 190.
  • the inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as a “prediction unit”.
  • the transform unit 120, the quantization unit 130, the inverse quantization unit 140, and the inverse transform unit 150 may be included in a residual processing unit.
  • the residual processing unit may further include a subtraction unit 115.
  • All or at least some of the plurality of constituent units constituting the image encoding apparatus 100 may be implemented as one hardware component (eg, an encoder or a processor) according to embodiments.
  • the memory 170 may include a decoded picture buffer (DPB), and may be implemented by a digital storage medium.
  • DPB decoded picture buffer
  • the image segmentation unit 110 may divide an input image (or picture, frame) input to the image encoding apparatus 100 into one or more processing units.
  • the processing unit may be referred to as a coding unit (CU).
  • the coding unit is a coding tree unit (CTU) or a largest coding unit (LCU) recursively according to a QT/BT/TT (Quad-tree/binary-tree/ternary-tree) structure ( It can be obtained by dividing recursively.
  • 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 tree structure.
  • a quad tree structure may be applied first and a binary tree structure and/or a ternary tree structure may be applied later.
  • the coding procedure according to the present disclosure may be performed based on the final coding unit that is no longer divided.
  • the largest coding unit may be directly used as the final coding unit, or a coding unit of a lower depth obtained by dividing the largest coding unit may be used as the final cornet unit.
  • the coding procedure may include a procedure such as prediction, transformation, and/or restoration, which will be described later.
  • the processing unit of the coding procedure may be a prediction unit (PU) or a transform unit (TU).
  • the prediction unit and the transform unit may be divided or partitioned from the final coding unit, respectively.
  • the prediction unit may be a unit of sample prediction
  • the transform unit may be a unit for inducing a transform coefficient and/or a unit for inducing a residual signal from the transform coefficient.
  • the prediction unit (inter prediction unit 180 or intra prediction unit 185) performs prediction on a block to be processed (current block), and generates a predicted block including prediction samples for the current block. Can be generated.
  • the prediction unit may determine whether intra prediction or inter prediction is applied in units of a current block or CU.
  • the prediction unit may generate various information on prediction of the current block and transmit it to the entropy encoding unit 190.
  • the information on prediction may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
  • the intra prediction unit 185 may predict the current block by referring to samples in the current picture.
  • the referenced samples may be located in a neighborhood of the current block or may be located away from each other according to an intra prediction mode and/or an intra prediction technique.
  • the intra 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 planar mode and a DC 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 185 may determine a prediction mode applied to the current block by using the prediction mode applied to the neighboring block.
  • the inter prediction unit 180 may derive a 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 a correlation between 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 existing in the current picture and a temporal neighboring block existing 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 from each other.
  • the temporal neighboring block may be referred to by a name such as a collocated reference block and a collocated CU (colCU).
  • a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic).
  • the inter prediction unit 180 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive a motion vector and/or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes.
  • the inter prediction unit 180 may use motion information of a neighboring block as motion information of a current block.
  • a residual signal may not be transmitted.
  • MVP motion vector prediction
  • a motion vector of a neighboring block is used as a motion vector predictor, and an indicator for a motion vector difference and a motion vector predictor ( indicator) to signal the motion vector of the current block.
  • the motion vector difference may mean a difference between a motion vector of a current block and a motion vector predictor.
  • the prediction unit may generate a prediction signal based on various prediction methods and/or prediction techniques to be described later.
  • the prediction unit may apply intra prediction or inter prediction for prediction of the current block, and may simultaneously apply intra prediction and inter prediction.
  • a prediction method in which intra prediction and inter prediction are applied simultaneously for prediction of the current block may be referred to as combined inter and intra prediction (CIIP).
  • the prediction unit may perform intra block copy (IBC) for prediction of the current block.
  • the intra block copy may be used for content image/movie coding such as games, such as, for example, screen content coding (SCC).
  • IBC is a method of predicting a current block by using a reference block in a current picture at a distance from the current block by a predetermined distance. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to the predetermined distance.
  • the prediction signal generated through the prediction unit may be used to generate a reconstructed signal or may be used to generate a residual signal.
  • the subtraction unit 115 subtracts the prediction signal (predicted block, prediction sample array) output from the prediction unit from the input image signal (original block, original sample array), and subtracts a residual signal (remaining block, residual sample array). ) Can be created.
  • the generated residual signal may be transmitted to the converter 120.
  • the transform unit 120 may generate transform coefficients by applying a transform technique to the residual signal.
  • the transformation technique uses at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform).
  • DCT Discrete Cosine Transform
  • DST Discrete Sine Transform
  • KLT Kerhunen-Loeve Transform
  • GBT Graph-Based Transform
  • CNT Conditionally Non-linear Transform
  • GBT refers to the transformation obtained from this graph when the relationship information between pixels is expressed in a graph.
  • CNT refers to a transformation obtained based on generating a prediction signal using all previously reconstructed pixels.
  • the conversion process may be applied to a block of pixels having the same size of a square, or may be applied to a block of a variable size other than a square.
  • the quantization unit 130 may quantize the transform coefficients and transmit the quantization to the entropy encoding unit 190.
  • the entropy encoding unit 190 may encode a quantized signal (information on quantized transform coefficients) and output it as a bitstream. Information about the quantized transform coefficients may be called residual information.
  • the quantization unit 130 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and the quantized transform coefficients in the form of the one-dimensional vector It is also possible to generate information about transform coefficients.
  • the entropy encoding unit 190 may perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC).
  • the entropy encoding unit 190 may encode together or separately information necessary for video/image restoration (eg, values of syntax elements) in addition to quantized transform coefficients.
  • the encoded information (e.g. encoded video/video information) may be transmitted or stored in a bitstream format in units of network abstraction layer (NAL) units.
  • the video/video information may further include information on 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 signaling information, transmitted information, and/or syntax elements mentioned in the present disclosure may be encoded through the above-described encoding procedure and included in the bitstream.
  • the bitstream may be transmitted through a network or may be stored in 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, and SSD.
  • a transmission unit (not shown) for transmitting the signal output from the entropy encoding unit 190 and/or a storage unit (not shown) for storing may be provided as an internal/external element of the image encoding apparatus 100, or transmission The unit may be provided as a component of the entropy encoding unit 190.
  • the quantized transform coefficients output from the quantization unit 130 may be used to generate a residual signal.
  • a residual signal residual block or residual samples
  • inverse quantization and inverse transform residual transforms
  • the addition unit 155 adds the reconstructed residual signal to the prediction signal output from the inter prediction unit 180 or the intra prediction unit 185 to obtain a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array). Can be generated.
  • a reconstructed signal (a reconstructed picture, a reconstructed block, and a reconstructed sample array).
  • the predicted block may be used as a reconstructed block.
  • the addition unit 155 may be referred to as a restoration unit or a restoration block generation unit.
  • the generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, and may be used for inter prediction of the next picture through filtering as described later.
  • LMCS luma mapping with chroma scaling
  • the filtering unit 160 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 160 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 170, specifically, the DPB of the memory 170. Can be saved on.
  • the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
  • the filtering unit 160 may generate various information about filtering and transmit it to the entropy encoding unit 190 as described later in the description of each filtering method. Information about filtering may be encoded by the entropy encoding unit 190 and output in the form of a bitstream.
  • the modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180.
  • the image encoding apparatus 100 may avoid prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus, and may improve encoding efficiency.
  • the DPB in the memory 170 may store a reconstructed picture modified to be used as a reference picture in the inter prediction unit 180.
  • the memory 170 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 have already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 180 in order to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 170 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 185.
  • FIG. 3 is a schematic diagram of an image decoding apparatus to which an embodiment according to the present disclosure can be applied.
  • the image decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, and a memory 250. ), an inter prediction unit 260 and an intra prediction unit 265.
  • the inter prediction unit 260 and the intra prediction unit 265 may be collectively referred to as a “prediction unit”.
  • the inverse quantization unit 220 and the inverse transform unit 230 may be included in the residual processing unit.
  • All or at least some of the plurality of constituent units constituting the image decoding apparatus 200 may be implemented as one hardware component (eg, a decoder or a processor) according to embodiments.
  • the memory 170 may include a DPB, and may be implemented by a digital storage medium.
  • the image decoding apparatus 200 receiving a bitstream including video/image information may reconstruct an image by performing a process corresponding to the process performed by the image encoding apparatus 100 of FIG. 2.
  • the image decoding apparatus 200 may perform decoding using a processing unit applied by the image encoding apparatus.
  • the processing unit of decoding may be, for example, a coding unit.
  • the coding unit may be a coding tree unit or may be obtained by dividing the largest coding unit.
  • the reconstructed image signal decoded and output through the image decoding apparatus 200 may be reproduced through a reproducing apparatus (not shown).
  • the image decoding apparatus 200 may receive a signal output from the image encoding apparatus of FIG. 2 in the form of a bitstream.
  • the received signal may be decoded through the entropy decoding unit 210.
  • the entropy decoding unit 210 may parse the bitstream to derive information (eg, video/video information) necessary for image restoration (or picture restoration).
  • the video/video information may further include information on 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 image decoding apparatus may additionally use information on the parameter set and/or the general restriction information to decode an image.
  • the signaling information, received information, and/or syntax elements mentioned in the present disclosure may be obtained from the bitstream by decoding through the decoding procedure.
  • the entropy decoding unit 210 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and a value of a syntax element required for image restoration, a quantized value of a transform coefficient related to a residual Can be printed.
  • the CABAC entropy decoding method a bin corresponding to each syntax element is received in a bitstream, and information on the syntax element to be decoded, decoding information of a neighboring block and a block to be decoded, or information of a symbol/bin decoded in a previous step
  • the context model is determined by using and, according to the determined context model, the probability of occurrence of bins is predicted to perform arithmetic decoding of the bins to generate a symbol corresponding to the value of each syntax element.
  • the CABAC entropy decoding method may update the context model using information of the decoded symbol/bin for the context model of the next symbol/bin after the context model is determined.
  • information about prediction is provided to the prediction unit (inter prediction unit 260 and intra prediction unit 265), and the register on which entropy decoding is performed by the entropy decoding unit 210
  • the dual value that is, quantized transform coefficients and related parameter information may be input to the inverse quantization unit 220.
  • information about filtering among information decoded by the entropy decoding unit 210 may be provided to the filtering unit 240.
  • a receiving unit for receiving a signal output from the image encoding device may be additionally provided as an inner/outer element of the image decoding device 200, or the receiving unit is provided as a component of the entropy decoding unit 210 It could be.
  • the video decoding apparatus may include an information decoder (video/video/picture information decoder) and/or a sample decoder (video/video/picture sample decoder).
  • the information decoder may include an entropy decoding unit 210, and the sample decoder includes an inverse quantization unit 220, an inverse transform unit 230, an addition unit 235, a filtering unit 240, a memory 250, It may include at least one of the inter prediction unit 260 and the intra prediction unit 265.
  • the inverse quantization unit 220 may inverse quantize the quantized transform coefficients and output transform coefficients.
  • the inverse quantization unit 220 may rearrange the quantized transform coefficients in a two-dimensional block shape. In this case, the rearrangement may be performed based on a coefficient scan order performed by the image encoding apparatus.
  • the inverse quantization unit 220 may perform inverse quantization on quantized transform coefficients using a quantization parameter (eg, quantization step size information) and obtain transform coefficients.
  • a quantization parameter eg, quantization step size information
  • the inverse transform unit 230 may inverse transform 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 or inter prediction is applied to the current block based on the prediction information output from the entropy decoding unit 210, and determine a specific intra/inter prediction mode (prediction technique). I can.
  • the prediction unit can generate the prediction signal based on various prediction methods (techniques) to be described later.
  • the intra prediction unit 265 may predict the current block by referring to samples in the current picture.
  • the description of the intra prediction unit 185 may be equally applied to the intra prediction unit 265.
  • the inter prediction unit 260 may derive a 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 a correlation between 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 existing in the current picture and a temporal neighboring block existing in the reference picture.
  • the inter prediction unit 260 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or a reference picture index of the current block based on the received candidate selection information.
  • Inter prediction may be performed based on various prediction modes (techniques), and the information on prediction may include information indicating a mode (technique) of inter prediction for the current block.
  • the addition unit 235 is reconstructed by adding the obtained residual signal to the prediction signal (predicted block, prediction sample array) output from the prediction unit (including the inter prediction unit 260 and/or the intra prediction unit 265).
  • a signal (restored picture, reconstructed block, reconstructed sample array) can be generated.
  • the description of the addition unit 155 may be equally applied to the addition unit 235.
  • LMCS luma mapping with chroma scaling
  • the filtering unit 240 may improve subjective/objective image quality by applying filtering to the reconstructed signal.
  • the filtering unit 240 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 250, specifically, the DPB of the memory 250. Can be saved on.
  • the various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.
  • the reconstructed picture (modified) stored in the DPB of the memory 250 may be used as a reference picture in the inter prediction unit 260.
  • the memory 250 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 have already been reconstructed.
  • the stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block.
  • the memory 250 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 265.
  • embodiments described in the filtering unit 160, the inter prediction unit 180, and the intra prediction unit 185 of the image encoding apparatus 100 are respectively the filtering unit 240 of the image decoding apparatus 200, The same or corresponding to the inter prediction unit 260 and the intra prediction unit 265 may be applied.
  • Intra prediction may represent prediction of generating prediction samples for a current block based on reference samples in a picture (hereinafter, referred to as a current picture) to which the current block belongs.
  • a current picture a picture to which the current block belongs.
  • neighboring reference samples to be used for intra prediction of the current block may be derived.
  • the neighboring reference samples of the current block are a sample adjacent to the left boundary of the current block of size nWxnH, a total of 2xnH samples adjacent to the bottom-left, and a sample adjacent to the top boundary of the current block. And a total of 2xnW samples adjacent to the top-right side and one sample adjacent to the top-left side of the current block.
  • the peripheral reference samples of the current block may include a plurality of columns of upper peripheral samples and a plurality of rows of left peripheral samples.
  • the neighboring reference samples of the current block are a total of nH samples adjacent to the right boundary of the current block of size nWxnH, a total of nW samples adjacent to the bottom boundary of the current block, and the lower right side of the current block. It may include one sample adjacent to (bottom-right).
  • the decoder may construct neighboring reference samples to be used for prediction by substituting samples that are not available with available samples.
  • neighboring reference samples to be used for prediction may be configured through interpolation of available samples.
  • a prediction sample can be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) neighboring reference samples of the current block Among them, the prediction sample may be derived based on a reference sample existing in a specific (prediction) direction with respect to the prediction sample.
  • it may be called a non-directional mode or a non-angular mode
  • it may be called a directional mode or an angular mode.
  • LIP linear interpolation intra prediction
  • chroma prediction samples may be generated based on luma samples using a linear model. This case may be called LM (Linear Model) mode.
  • LM Linear Model
  • a temporary prediction sample of the current block is derived based on the filtered surrounding reference samples, and at least one derived according to the intra prediction mode among the existing surrounding reference samples, that is, unfiltered surrounding reference samples.
  • a prediction sample of the current block may be derived by weighted summation of a reference sample and the temporary prediction sample. This case may be called PDPC (Position dependent intra prediction).
  • a reference sample line having the highest prediction accuracy among the neighboring multi-reference sample lines of the current block may be selected, and a prediction sample may be derived using a reference sample positioned in the prediction direction from the corresponding line.
  • information on the used reference sample line eg, intra_luma_ref_idx
  • MRL multi-reference line intra prediction
  • the current block may be divided into vertical or horizontal subpartitions, and intra prediction may be performed for each subpartition based on the same intra prediction mode.
  • neighboring reference samples for intra prediction may be derived for each subpartition. That is, the reconstructed sample of the previous sub-partition in the encoding/decoding order may be used as a neighboring reference sample of the current sub-partition.
  • the intra prediction mode for the current block is equally applied to the subpartitions, but the intra prediction performance may be improved in some cases by deriving and using neighboring reference samples in units of the subpartition.
  • This prediction method may be called intra sub-partitions (ISP) or ISP-based intra prediction.
  • the intra prediction technique may include at least one of the aforementioned LIP, LM, PDPC, MRL, and ISP. Meanwhile, post-processing filtering may be performed on the derived prediction samples as necessary.
  • the intra prediction procedure may include an intra prediction mode/type determination step, a neighbor reference sample derivation step, and an intra prediction mode/type-based prediction sample derivation step. Also, if necessary, a post-filtering step may be performed on the derived prediction samples.
  • FIG. 4 is a flowchart illustrating a video/video encoding method based on intra prediction.
  • the encoding method of FIG. 4 may be performed by the video encoding apparatus of FIG. 2. Specifically, step S410 may be performed by the intra prediction unit 185, and step S420 may be performed by the residual processing unit. Specifically, step S420 may be performed by the subtraction unit 115. Step S430 may be performed by the entropy encoding unit 190.
  • the prediction information of step S430 may be derived by the intra prediction unit 185, and the residual information of step S430 may be derived by the residual processing unit.
  • the residual information is information on the residual samples.
  • the residual information may include information on quantized transform coefficients for the residual samples.
  • the residual samples may be derived as transform coefficients through the transform unit 120 of the image encoding apparatus, and the transform coefficients may be derived as quantized transform coefficients through the quantization unit 130.
  • Information on the quantized transform coefficients may be encoded by the entropy encoding unit 190 through a residual coding procedure.
  • the image encoding apparatus may perform intra prediction on the current block (S410).
  • the video encoding apparatus determines the intra prediction mode/type for the current block, derives neighboring reference samples of the current block, and then generates prediction samples in the current block based on the intra prediction mode/type and the neighboring reference samples. can do.
  • the procedure of determining the intra prediction mode/type, deriving neighboring reference samples, and generating prediction samples may be performed simultaneously, or one procedure may be performed before the other procedure.
  • FIG. 5 is a diagram illustrating a configuration of an intra prediction unit according to the present disclosure.
  • the intra prediction unit 185 of the video encoding apparatus may include an intra prediction mode/type determination unit 186, a reference sample derivation unit 187, and/or a prediction sample derivation unit 188.
  • the intra prediction mode/type determiner 186 may determine an intra prediction mode/type for the current block.
  • the reference sample derivation unit 187 may derive neighboring reference samples of the current block.
  • the prediction sample derivation unit 188 may derive prediction samples of the current block.
  • the intra prediction unit 185 may further include a prediction sample filter unit (not shown).
  • the image encoding apparatus may determine a mode/type applied to the current block from among a plurality of intra prediction modes/types.
  • the video encoding apparatus may compare RD costs for the intra prediction modes/types and determine an optimal intra prediction mode/type for the current block.
  • the image encoding apparatus may perform a prediction sample filtering procedure.
  • Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.
  • the apparatus for encoding an image may generate residual samples for the current block based on prediction samples or filtered prediction samples (S420).
  • the image encoding apparatus may derive the residual samples by subtracting the prediction samples from original samples of the current block. That is, the image encoding apparatus may derive the residual sample value by subtracting the corresponding predicted sample value from the original sample value.
  • the image encoding apparatus may encode image information including information about the intra prediction (prediction information) and residual information about the residual samples (S430).
  • the prediction information may include intra prediction mode information and/or intra prediction technique information.
  • the image encoding apparatus may output the encoded image information in the form of a bitstream.
  • the output bitstream may be delivered to an image decoding apparatus through a storage medium or a network.
  • the residual information may include a residual coding syntax to be described later.
  • the image encoding apparatus may transform/quantize the residual samples to derive quantized transform coefficients.
  • the residual information may include information on the quantized transform coefficients.
  • the image encoding apparatus may generate a reconstructed picture (including reconstructed samples and a reconstructed block). To this end, the image encoding apparatus may perform inverse quantization/inverse transformation on the quantized transform coefficients again to derive (modified) residual samples. The reason why the residual samples are transformed/quantized and then inverse quantized/inverse transformed is performed to derive residual samples that are the same as the residual samples derived from the image decoding apparatus.
  • the image encoding apparatus may generate a reconstructed block including reconstructed samples for the current block based on the prediction samples and the (modified) residual samples. A reconstructed picture for the current picture may be generated based on the reconstructed block. As described above, an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
  • FIG. 6 is a flowchart illustrating a video/video decoding method based on intra prediction.
  • the image decoding apparatus may perform an operation corresponding to an operation performed by the image encoding apparatus.
  • the decoding method of FIG. 6 may be performed by the video decoding apparatus of FIG. 3.
  • Steps S610 to S630 may be performed by the intra prediction unit 265, and the prediction information of step S610 and the residual information of step S640 may be obtained from the bitstream by the entropy decoding unit 210.
  • the residual processing unit of the image decoding apparatus may derive residual samples for the current block based on the residual information (S640).
  • the inverse quantization unit 220 of the residual processing unit derives transform coefficients by performing inverse quantization based on the quantized transform coefficients derived based on the residual information
  • the inverse transform unit of the residual processing unit ( 230) may derive residual samples for the current block by performing inverse transform on the transform coefficients.
  • Step S650 may be performed by the addition unit 235 or the restoration unit.
  • the image decoding apparatus may derive an intra prediction mode/type for the current block based on the received prediction information (intra prediction mode/type information) (S610). Also, the image decoding apparatus may derive neighboring reference samples of the current block (S620). The image decoding apparatus may generate prediction samples in the current block based on the intra prediction mode/type and the neighboring reference samples (S630). In this case, the image decoding apparatus may perform a prediction sample filtering procedure. Predictive sample filtering may be referred to as post filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.
  • the image decoding apparatus may generate residual samples for the current block based on the received residual information (S640).
  • the image decoding apparatus may generate reconstructed samples for the current block based on the prediction samples and the residual samples, and derive a reconstructed block including the reconstructed samples (S650).
  • a reconstructed picture for the current picture may be generated based on the reconstructed block.
  • an in-loop filtering procedure or the like may be further applied to the reconstructed picture.
  • FIG. 7 is a diagram illustrating an exemplary configuration of an intra prediction unit according to the present disclosure.
  • the intra prediction unit 265 of the image decoding apparatus may include an intra prediction mode/type determination unit 266, a reference sample derivation unit 267, and a prediction sample derivation unit 268. .
  • the intra prediction mode/type determiner 266 determines an intra prediction mode/type for the current block based on intra prediction mode/type information generated and signaled by the intra prediction mode/type determiner 186 of the image encoding apparatus.
  • the reference sample deriving unit 266 may derive neighboring reference samples of the current block from the reconstructed reference region in the current picture.
  • the prediction sample derivation unit 268 may derive prediction samples of the current block.
  • the intra prediction unit 265 may further include a prediction sample filter unit (not shown).
  • the intra prediction mode information may include flag information (eg intra_luma_mpm_flag and/or intra_chroma_mpm_flag) indicating whether a most probable mode (MPM) is applied to the current block or a remaining mode is applied, for example. And, when the MPM is applied to the current block, the intra prediction mode information may further include index information (eg intra_luma_mpm_idx and/or intra_chroma_mpm_idx) indicating one of intra prediction mode candidates (MPM candidates).
  • the intra prediction mode candidates (MPM candidates) may be composed of an MPM candidate list or an MPM list.
  • the intra prediction mode information includes remaining mode information (eg intra_luma_mpm_remainder and/or intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes excluding the intra prediction mode candidates (MPM candidates).
  • intra_chroma_mpm_remainder may be further included.
  • the video decoding apparatus may determine an intra prediction mode of the current block based on the intra prediction mode information.
  • the MPM candidate modes may include an intra prediction mode and additional candidate modes of a neighboring block (e.g. a left neighboring block and/or an upper neighboring block) of the current block.
  • FIG. 8A is a diagram illustrating an intra prediction direction according to an embodiment of the present disclosure.
  • the intra prediction mode may include two non-directional intra prediction modes and 33 directional intra prediction modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode, and the directional intra prediction modes may include intra prediction modes 2 to 34.
  • the planar intra prediction mode may be referred to as a planner mode, and the DC intra prediction mode may be referred to as a DC mode.
  • the intra prediction mode includes two non-directional intra prediction modes and 65 extended directional intra prediction. It can include modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode, and the extended directional intra prediction modes may include intra prediction modes 2 to 66.
  • the intra prediction mode can be applied to blocks of all sizes, and can be applied to both a luma component (a luma block) and a chroma component (a chroma block).
  • the intra prediction mode may include two non-directional intra prediction modes and 129 directional intra prediction modes.
  • the non-directional intra prediction modes may include a planar mode and a DC mode, and the directional intra prediction modes may include 2 to 130 intra prediction modes.
  • the intra prediction mode may further include a cross-component linear model (CCLM) mode for chroma samples in addition to the aforementioned intra prediction modes.
  • CCLM cross-component linear model
  • the CCLM mode can be divided into L_CCLM, T_CCLM, and LT_CCLM depending on whether left samples are considered, upper samples are considered, or both are considered to derive LM parameters, and can be applied only to a chroma component.
  • the intra prediction mode may be indexed, for example, as shown in Table 1 below.
  • a mode number of a planner mode may be 0, and a mode number of a DC mode may be 1.
  • mode numbers of the plurality of directional intra prediction modes may be 2 to 66.
  • mode numbers of the LT_CCLM mode, the L_CCLM mode, and the T_CCLM mode may be 81 to 83.
  • an intra prediction mode in order to capture an arbitrary edge direction presented in a natural video, includes 93 directions along with two non-directional intra prediction modes. It may include an intra prediction mode. Non-directional intra prediction modes may include planar mode and DC mode.
  • the directional intra prediction mode may include an intra prediction mode composed of times 2 to 80 and -1 to -14 as indicated by the arrow of FIG. 8B.
  • the planar mode may be indicated as INTRA_PLANAR, and the DC mode may be indicated as INTRA_DC.
  • the directional intra prediction mode may be expressed as INTRA_ANGULAR-14 to INTRA_ANGULAR-1, and INTRA_ANGULAR2 to INTRA_ANGULAR80.
  • the intra prediction technique information may be implemented in various forms.
  • the intra prediction technique information may include intra prediction technique index information indicating one of a plurality of intra prediction techniques.
  • the intra prediction technique information includes reference sample line information (eg intra_luma_ref_idx) indicating whether the MRL is applied to the current block and, if applied, a reference sample line (eg intra_luma_ref_idx), and the ISP is applied to the current block.
  • ISP flag information indicating whether it is applied (eg intra_subpartitions_mode_flag), ISP type information indicating the split type of subpartitions when the ISP is applied (eg intra_subpartitions_split_flag), flag information indicating whether or not PDPC is applied, or indicating whether the LIP is applied. It may include at least one of flag information.
  • the ISP flag information may be referred to as an ISP application indicator.
  • the intra prediction mode information and/or the intra prediction technique information may be encoded/decoded using the coding method described in the present disclosure.
  • the intra prediction mode information and/or the intra prediction method information may be encoded/decoded through entropy coding (e.g. CABAC, CAVLC) based on a truncated (rice) binary code.
  • entropy coding e.g. CABAC, CAVLC
  • 9A to 9C are diagrams for explaining a relationship between a luma component block (a luma component array) and a chroma component block (a chroma component array) according to a chroma format.
  • the source or coded picture/video may include a luma component (Y) block and two chroma component (cb, cr) blocks. That is, one pixel of a picture/image may include a luma sample and two chroma samples cb and cr.
  • the chroma format may represent a configuration format of a luma sample and a chroma sample (cb, cr), and may also be called a color format.
  • the chroma format may be predetermined or may be signaled adaptively. For example, the chroma format may be signaled based on at least one of chroma_format_idc and separate_colour_plane_flag as shown in Table 2.
  • chroma_format_idc is information indicating a format of a luma sample and a chroma sample corresponding thereto
  • separate_colour_plane_flag indicates whether three color components (Y, cb, cr) are separately encoded in a 4:4:4 chroma format.
  • chroma_format_idc when chroma_format_idc is 0, the chroma format corresponds to monochrome, and the current block does not include a chroma component block and includes only a luma component block.
  • chroma_format_idc when chroma_format_idc is 1, the chroma format corresponds to a 4:2:0 chroma format, and the width and height of the chroma component block correspond to half of the width and height of the luma component block, respectively.
  • 9A is a diagram showing a positional relationship between a luma sample and a chroma sample in a 4:2:0 chroma format.
  • the chroma format corresponds to the 4:2:2 chroma format
  • the width of the chroma component block is half the width of the luma component block
  • the height of the chroma component block is the luma component block. Is equal to the height of 9B is a diagram showing a positional relationship between a luma sample and a chroma sample in a 4:2:2 chroma format.
  • chroma_format_idc 3
  • the chroma format corresponds to a 4:4:4 chroma format
  • the width and height of the chroma component block are the same as the width and height of the luma component block, respectively.
  • 9C is a diagram showing a positional relationship between a luma sample and a chroma sample in a 4:4:4 chroma format.
  • SubWidthC and SubHeightC represent the ratio between the luma sample and the chroma sample.
  • the width and height of the luma component block are CbWidth and CbHeight, respectively
  • the width and height of the corresponding chroma component block may be derived as (CbWidth/SubwidthC) and (CbHeight/SubHeightC), respectively.
  • FIG. 10 is a diagram illustrating an example of an SPS syntax including signaling information in a chroma format. As shown in FIG. 10, chroma_format_idc and separate_colour_plane_flag may be signaled through SPS, which is a high-level syntax.
  • intra prediction When intra prediction is performed on the current block, prediction on a luma component block (luma block) of the current block and prediction on a chroma component block (chroma block) may be performed.
  • the intra prediction mode for the chroma block is It can be set separately from the intra prediction mode for the luma block.
  • an intra prediction mode for a chroma block may be indicated based on intra chroma prediction mode information, and the intra chroma prediction mode information may be signaled in the form of an intra_chroma_pred_mode syntax element.
  • the intra-chroma prediction mode information includes one of a planar mode, a DC mode, a vertical mode, a horizontal mode, a derived mode (DM), and a cross-component linear model (CCLM) mode.
  • the planar mode may indicate a 0th intra prediction mode
  • the DC mode may indicate a 1st intra prediction mode
  • the vertical mode may indicate a 26th intra prediction mode
  • the horizontal mode may indicate a 10th intra prediction mode.
  • DM can also be called direct mode.
  • CCLM may be referred to as a linear model (LM).
  • DM and CCLM are dependent intra prediction modes for predicting a chroma block using information of a luma block.
  • the DM may represent a mode in which an intra prediction mode identical to an intra prediction mode for the luma component is applied as an intra prediction mode for the chroma component.
  • the CCLM subsamples the reconstructed samples of the luma block in the process of generating the prediction block for the chroma block, and then applies CCLM parameters ⁇ and ⁇ to the subsampled samples to be derived as shown in Equation 1. It may represent an intra prediction mode in which samples are used as prediction samples of the chroma block.
  • pred c (i,j) may represent a predicted sample of (i,j) coordinates of the current chroma block in the current CU.
  • rec L '(i,j) may represent a reconstructed sample of the (i,j) coordinate of the current luma block in the CU.
  • rec L '(i,j) may represent a down-sampled reconstructed sample of the current luma block.
  • the linear model coefficients ⁇ and ⁇ may be signaled, but may also be derived from surrounding samples.
  • the intra prediction mode of the current chroma block may be derived as the intra prediction mode of the corresponding luma block.
  • the intra prediction mode at a predetermined position of the corresponding luma block may be used as the intra prediction mode of the current chroma block.
  • DM may be referred to as a chroma DM.
  • FIG. 11 is a diagram illustrating a predetermined position for deriving an intra prediction mode of a current chroma block in the case of a DM.
  • a chroma block is divided into vertical binaries, and a current chroma block may be a block of a hatched area.
  • the luma block corresponding to the current chroma block may be a block of a shaded area within the luma block.
  • the intra prediction mode (intra chroma prediction mode) of the current chroma block predicted by the DM may be derived to an intra prediction mode (intra luma prediction mode) at a predetermined position in the corresponding luma block.
  • the intra prediction mode of the block covering the lower right center sample (center position) CR in the corresponding luma block may be determined as the intra prediction mode of the current chroma block.
  • the predetermined position is not limited to the center position, and may be another position in the corresponding luma block, such as, for example, the upper left position TL.
  • MDM Direct Modes
  • the multiple DM is a mode in which the single DM is extended to a plurality of modes, and a DM candidate list including a plurality of DM candidates is constructed to induce an intra prediction mode of the current chroma block, and included in the DM candidate list.
  • One of the candidates may be derived as an intra prediction mode of the current chroma block.
  • the DM candidate list may include at least one of a plurality of DM candidates below.
  • -Directional mode derived by adding or subtracting a predetermined offset (e.g. 1) to the already included directional mode
  • -Default DM candidate mode vertical mode, horizontal mode, 2, 34, 66, 10, 26 modes (in case of 65 directional modes)
  • the intra prediction modes of the chroma block may be encoded using a total of eight intra prediction modes.
  • the eight intra prediction modes may include conventional five intra prediction modes and a cross-component linear model mode (CCLM) mode(s).
  • CCLM cross-component linear model mode
  • Whether the CCLM is available may be determined based on information signaled at a higher level (e.g. sps_cclm_enabled_flag transmitted at the sequence level).
  • the intra prediction mode of the chroma block may be derived based on the intra chroma prediction mode information (intra_chroma_pred_mode) and/or the intra prediction mode (IntraPredModeY) of the corresponding luma block.
  • the intra prediction mode of the corresponding luma block may be determined as an intra prediction mode of the luma block that covers the current block or the lower right center sample (center position) of the chroma block.
  • the center of the lower right sample position is derived as (xCb + cbWidth / 2, yCb + cbHeight / 2), where (xCb, yCb) means the coordinates of the top-left sample of the corresponding luma block.
  • cbWidth and cbHeight mean the width and height of the corresponding luma block, respectively.
  • the intra prediction mode of the chroma block is determined as 0 (planner mode), and if the intra_chroma_pred_mode is 1, the intra prediction mode of the chroma block is determined as mode 50 (vertical mode). I can.
  • the intra_chroma_pred_mode is 2
  • the intra prediction mode of the chroma block is determined as mode 18 (horizontal mode)
  • the intra_chroma_pred_mode is 3, the intra prediction mode of the chroma block may be determined as mode 1 (DC mode).
  • the intra prediction mode of the chroma block may be determined to be the same value as the intra prediction mode of the corresponding luma block. That is, when the intra_chroma_pred_mode is 4, it indicates that the intra prediction mode of the chroma block is derived as DM.
  • the indexes of the intra prediction mode (IntraPredModeC[ xCb ][ yCb ]) of the chroma block derived based on Table 3 may correspond to the indexes of the intra prediction mode shown in Table 1 above.
  • the intra prediction mode of the chroma block is determined to be mode 66 instead of the aforementioned intra prediction mode (planner mode, vertical mode, horizontal mode, DC mode) according to the IntraPredModeY value.
  • an intra_chroma_pred_mode value of 0 indicates a planar mode.
  • IntraPredModeY is 0 (planar mode)
  • the intra prediction mode of the chroma block is determined as mode 66.
  • the intra_chroma_pred_mode value is determined to be 4 indicating DM, not 0. Therefore, when the intra_chroma_pred_mode value is 0 to 3, the case where the intra prediction mode of the chroma block is determined to be 66 does not substantially occur. That is, when the intra_chroma_pred_mode is 0 to 3, the intra prediction mode of the chroma block may be derived as one of the planar mode, the vertical mode, the horizontal mode, and the DC mode based on the intra_chroma_pred_mode value. When the intra_chroma_pred_mode is 4, the intra prediction mode of the chroma block The prediction mode may be derived based on an intra_chroma_pred_mode value and an intra prediction mode of a corresponding luma block.
  • Table 4 is a case in which the CCLM is available, and may include modes for signaling the CCLM mode in addition to the modes of Table 3.
  • intra_chroma_pred_mode when intra_chroma_pred_mode is 4 to 6, INTRA_LT_CCLM, INTRA_L_CCLM, and INTRA_T_CCLM may be indicated, respectively.
  • the cases where intra_chroma_pred_mode is 0 to 3 and 7 may correspond to cases where the intra_chroma_pred_mode is 0 to 4 in Table 3, respectively. That is, when the intra_chroma_pred_mode is 7, it indicates that the intra prediction mode of the chroma block is derived as DM.
  • an intra prediction mode of a chroma block may be derived based on intra-chroma prediction mode information (intra_chroma_pred_mode) and/or an intra prediction mode of a corresponding luma block.
  • intra-chroma prediction mode information indicates DM
  • the intra prediction mode of the chroma block may be determined to be the same as the intra prediction mode of the corresponding luma block.
  • intra prediction for a current luma block is performed based on an MPM list, and intra prediction for a current chroma block may be performed based on a predetermined default mode and/or DM (chroma DM).
  • the default intra prediction mode may include a planar mode, a DC mode, a vertical mode, and a horizontal mode.
  • the chroma DM may indicate that the intra prediction mode of the current chroma block is derived to an intra prediction mode at a predetermined position in the luma block corresponding to the current chroma block.
  • the size of the current chroma block may vary according to the chroma format, as described above with reference to FIGS. 9A to 9C.
  • FIG. 12 is a diagram illustrating a size of a current chroma block according to a chroma format.
  • the size of a current chroma block corresponding to a 64x128 luma block is 32x64 in a 4:2:0 chroma format, 32x128 in a 4:2:2 chroma format, and 64x128 in a 4:4:4 chroma format.
  • the size of the current chroma block may increase, which may mean that the amount of information on the chroma component also increases.
  • the chroma format is 4:2:0, since the information amount of the chroma component is relatively small, performance deterioration of intra prediction for the current chroma block does not occur even if the above-described method is followed. However, when the chroma format is 4:2:2 or 4:4:4, since the amount of information on the chroma component is relatively large, performance deterioration of intra prediction for the current chroma block may occur when the above-described method is followed.
  • the complexity of the image encoding/decoding process may increase.
  • the intra prediction process for the current luma block may be performed in the same or similar manner to the current chroma block.
  • the image encoding/decoding apparatus may use an intra prediction mode and additional candidate modes of a neighboring luma block (eg, a left neighboring block and/or an upper neighboring block) adjacent to the current luma block with respect to the current luma block. You can configure an MPM list for luma blocks.
  • the image encoding/decoding apparatus uses intra prediction modes and additional candidate modes of a neighboring chroma block (eg, a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block with respect to the current chroma block. You can configure the MPM list for.
  • the neighboring chroma block may exist at the same position (or corresponding position) as the neighboring luma blocks used to induce the intra prediction mode of the luma block (corresponding luma block) corresponding to the current chroma block. have.
  • at least some of the surrounding chroma blocks may exist in different positions from the surrounding luma blocks.
  • the MPM list for the current chroma block may include a chroma DM indicating that an intra prediction mode of the current chroma block is derived to an intra prediction mode of a corresponding luma block corresponding to the current chroma block.
  • the intra prediction mode of the current chroma block determined as the chroma DM may be derived as an intra prediction mode at a predetermined position in the corresponding luma block. For example, as described above with reference to FIG.
  • the intra prediction mode of a block covering the lower right center sample (center position) in the corresponding luma block may be determined as the intra prediction mode of the current chroma block.
  • the intra prediction mode of the block covering the upper left sample in the corresponding luma block may be determined as the intra prediction mode of the current chroma block.
  • the MPM list may be referred to in various terms such as a candidate list and candModeList.
  • the MPM list for the current luma block may be referred to as a luma MPM list
  • the MPM list for the current chroma block may be referred to as a chroma MPM list.
  • the image decoding apparatus may select one of the MPM candidates in the MPM list as the intra prediction mode based on the MPM index received from the image encoding apparatus.
  • the video decoding apparatus may select one of the remaining intra prediction modes that are not included in the MPM list as the intra prediction mode based on the remaining mode information received from the video encoding apparatus.
  • Whether the intra prediction mode currently applied to the chroma block is among MPM candidates (i.e., is included in the chroma MPM list) or in the remaining mode may be indicated based on the MPM flag (eg intra_chroma_mpm_flag) for the current chroma block.
  • a first value (eg 1) of the MPM flag may indicate that an intra prediction mode of the current chroma block is among MPM candidates, and a second value (eg 0) of the MPM flag is an intra prediction mode of the current chroma block. May indicate that is not among the MPM candidates.
  • the MPM index may be signaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element for the current luma block, and may be signaled in the form of an mpm_idx or intra_chroma_mpm_idx syntax element for the current chroma block.
  • the remaining mode information may be signaled in the form of rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element for the current luma block, and may be signaled in the form of rem_intra_chroma_pred_mode or intra_chroma_mpm_remainder syntax element for the current chroma block.
  • the remaining mode information includes indexing the remaining intra prediction modes that are not included in the MPM candidates (candidates included in the luma MPM list or chroma MPM list) among all intra prediction modes in order of prediction mode number. You can direct one.
  • the intra prediction mode information may include the MPM flag (eg intra_luma_mpm_flag or intra_chroma_mpm_flag), the MPM index (eg mpm_idx, intra_luma_mpm_idx or intra_chroma_mpm_idx), and the remapping mode information (rem_intra_luma_pred_mode, intra_chroma_pred_mode, intra_chroma_pred_mode, intra_chroma_mainder_, or at least one of). , May be signaled through a bitstream.
  • the MPM flag eg intra_luma_mpm_flag or intra_chroma_mpm_flag
  • the MPM index eg mpm_idx, intra_luma_mpm_idx or intra_chroma_mpm_idx
  • remapping mode information rem_intra_luma_pred_mode, intra_chroma_
  • an intra prediction process for a luma block may be applied equally or similarly to a chroma block. Accordingly, since the intra prediction process for the luma block and the intra prediction process for the chroma block can be unified, the complexity of the image encoding/decoding process can be reduced.
  • accuracy of intra prediction may be improved by performing intra prediction on a chroma block based on an MPM list.
  • Embodiment #1 of the present disclosure may configure a chroma MPM list for the current chroma block in an intra prediction process for the current chroma block.
  • FIG. 13 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to an embodiment of the present disclosure.
  • the apparatus for encoding an image may configure a chroma MPM list (candidate list) for a current chroma block (S1310).
  • the chroma MPM list may include one or more intra prediction mode candidates (MPM candidates) that are highly likely to be applied to the current chroma block.
  • MPM candidates intra prediction mode candidates
  • N is an integer greater than or equal to 1
  • M is an integer greater than or equal to 1
  • N ⁇ M is an integer greater than or equal to 1
  • N ⁇ M is an integer greater than or equal to 1
  • N1 is an integer greater than or equal to 1
  • the chroma format is 4:2:2
  • the number of MPM candidates is N2.
  • N2 is an integer greater than or equal to 1
  • N3 is an integer greater than or equal to 1
  • the number of MPM candidates (N, N1, N2 or N3) may be predefined or adaptively determined. For example, when the number of MPM candidates for the current luma block is 6, the number of MPM candidates for the current chroma block (N, N1, N2, or N3) may be determined as one of 3 to 6.
  • K K ⁇ L
  • L L is an integer greater than or equal to 1
  • K K is an integer greater than or equal to 1
  • K ⁇ L K
  • L is 67 (two non-directional modes and 65 directional modes)
  • K may be 35 (two non-directional modes and 33 directional modes).
  • the 33 directional modes for the current chroma block may be modes having an even number (or odd number) among 65 directional modes for the current luma block.
  • the number K of intra prediction modes applicable to the current chroma block may be adaptively determined based on a chroma format.
  • the number K of intra prediction modes applicable to the current chroma block may increase. have.
  • K is 35
  • the chroma format of the current chroma block is 4:2:2 or 4:4:4
  • K is 67.
  • the number of intra prediction modes applicable to the chroma block may increase. Accordingly, the intra prediction accuracy for the current chroma block having an increased amount of information may be further improved.
  • the chroma MPM list may be constructed using at least one neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position (or corresponding position) as the neighboring luma blocks used to induce the intra prediction mode of the luma block (corresponding luma block) corresponding to the current chroma block. have.
  • at least some of the surrounding chroma blocks may exist in different positions from the surrounding luma blocks.
  • the image encoding apparatus uses at least one of the remaining intra prediction modes not included in the chroma MPM list to determine the chroma MPM. You can fill the list further.
  • the image encoding apparatus may further fill the chroma MPM list by using at least one of a plurality of non-directional modes and a plurality of directional modes that are not included in the MPM list.
  • the image encoding apparatus may further fill the chroma MPM list by using at least one of a +1 mode, a +2 mode, a -1 mode, and a -2 mode of a directional mode included in the chroma MPM list.
  • One or more MPM candidates may have a predetermined priority and be included in the chroma MPM list for the current chroma block.
  • the MPM candidate having the highest occurrence frequency may have the highest priority and may be included as a first candidate in the chroma MPM list.
  • the MPM candidate with the least occurrence frequency has the lowest priority and may be included as an Nth candidate in the chroma MPM list.
  • the MPM candidates may be indexed in the order of the highest priority in the chroma MPM list.
  • the MPM index of the first candidate may have a first value (e.g. 0)
  • the MPM index of the N-th candidate may have an Nth value (e.g. N-1).
  • the chroma MPM list may further include specific intra prediction modes according to a predetermined method.
  • the chroma MPM list may further include a chroma DM indicating that an intra prediction mode of the current chroma block is derived to an intra prediction mode of a corresponding luma block.
  • the chroma DM may be included as a first candidate in the chroma MPM list.
  • the image encoding apparatus may perform a redundancy check on the chroma MPM list so that duplicate MPM candidates are not included in the chroma MPM list.
  • the video encoding apparatus may remove the remainder except for one of the duplicate MPM candidates from the chroma MPM list.
  • the redundancy check may be performed whenever a new MPM candidate is inserted into the chroma MPM list. That is, when the same MPM candidate is already included in the chroma MPM list, the new MPM candidate may not be included in the chroma MPM candidate list. Accordingly, when the chroma MPM list is not completely filled, the image encoding apparatus may further fill the chroma MPM list by using at least one of a plurality of non-directional modes and a plurality of directional modes as described above. . Meanwhile, as an example, the image encoding apparatus may skip the redundancy check in order to reduce computational complexity.
  • Cases 1 to 3 show a method of constructing a chroma MPM list including a total of 5 MPM candidates.
  • an MPM list (candModeList[x]) is configured as follows.
  • an MPM list (candModeList[x]) is configured as follows.
  • MinAB Min( candIntraPredModeA, candIntraPredModeB)
  • the first candidate (candModeList[0]) and the second candidate (candModeList[1]) of the MPM list are configured as follows.
  • the third to fifth candidates (candModeList[2] to candModeList[4]) of the MPM list are configured as follows.
  • the first to fifth candidates (candModeList[0] to candModeList[4]) of the MPM list are configured as follows.
  • the first MPM candidate (candIntraPredModeA) and the second MPM candidate (candIntraPredModeB) are, as described above, blocks located around the current chroma block (eg, the left neighboring block and/or the upper peripheral Block).
  • the MPM list (chroma MPM list) for the current chroma block is an intra prediction mode of the current chroma block as an MPM candidate.
  • a chroma DM indicating that the prediction mode is derived to the intra prediction mode of the corresponding luma block may be further included.
  • the apparatus for encoding an image may determine an intra prediction mode of a current chroma block (S1320).
  • the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) on a plurality of intra prediction modes.
  • RDO rate-distortion optimization
  • the plurality of intra prediction modes may include at least one of a plurality of non-directional modes and a plurality of directional modes.
  • the video encoding apparatus may determine the optimal intra prediction mode using only MPM candidates included in the chroma MPM list, or all MPM candidates included in the chroma MPM list as well as all applicable to intra prediction of the chroma block.
  • the optimal intra prediction mode may be determined using intra prediction modes. For example, when the intra prediction type of the current chroma block is a specific type (eg LIP, MRL, or ISP) other than a normal intra prediction type, the video encoding apparatus determines the optimal intra prediction mode using only the MPM candidates. I can. In this case, the intra prediction mode for the current chroma block may be determined only among the MPM candidates, and the MPM flag may not be encoded/signaled. In the case of the specific type, the video decoding apparatus may estimate that the MPM flag has a first value (e.g. 1) without separately signaling the MPM flag.
  • a first value e.g. 1
  • the intra prediction mode of the current chroma block determined in step S1320 is one of the MPM candidates included in the chroma MPM list (when the MPM flag has a first value (eg 1))
  • the video encoding apparatus is selected from among the MPM candidates.
  • An MPM index indicating one eg mpm_idx or intra_chroma_mpm_idx
  • the intra prediction mode of the current chroma block is not in the chroma MPM list (when the MPM flag has a second value (eg 0)
  • the image encoding apparatus is selected from among the remaining intra prediction modes not included in the chroma MPM list. Remaining mode information indicating the same mode as the intra prediction mode of the current chroma block may be generated.
  • the image encoding apparatus may encode the intra prediction mode information and output it in the form of a bitstream (S1330).
  • the intra prediction mode information may include the aforementioned MPM flag, MPM index, and/or remaining mode information.
  • the MPM index and the remaining mode information have an alternate relationship, and may not be signaled at the same time when indicating an intra prediction mode for a current chroma block. That is, when the MPM flag has a first value, the MPM index may be signaled, and when the MPM flag has a second value, the remaining mode information may be signaled.
  • the intra prediction mode information may include only the MPM index.
  • the intra prediction mode information may be encoded using various coding methods described in this disclosure.
  • the intra prediction mode information and/or the intra prediction type information may be encoded through entropy coding (e.g. CABAC, CAVLC) based on truncated (rice) binary code.
  • step S1320 may be performed before step S1310 or may be performed simultaneously with step S1310.
  • step S1310 may be performed prior to step S1320.
  • step S1320 may be performed before step S1310. Or, it may be performed simultaneously with step S1310.
  • FIG. 14 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to an embodiment of the present disclosure.
  • the image decoding apparatus may determine an intra prediction mode of the current chroma block based on intra prediction mode information determined and signaled by the image encoding apparatus.
  • the apparatus for decoding an image may obtain intra prediction mode information for a current chroma block from a bitstream (S1410).
  • the intra prediction mode information may include an MPM flag, an MPM index, and/or a remaining intra prediction mode.
  • the video decoding apparatus may configure a chroma MPM list (S1420).
  • the chroma MPM list may have the same configuration as the chroma MPM list configured in the video encoding apparatus.
  • the chroma MPM list may include an intra prediction mode of a neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list may further include predetermined intra prediction modes according to a predetermined method.
  • step S1420 may be performed prior to step S1410, or may be performed simultaneously with step S1410.
  • the video decoding apparatus may determine an intra prediction mode of the current chroma block based on the intra prediction mode information and the chroma MPM list (S1430). Step S1430 will be described in more detail with reference to FIG. 15.
  • 15 is a flowchart for describing a procedure for deriving an intra prediction mode in more detail.
  • Steps S1510 and S1520 of FIG. 15 may correspond to steps S1410 and S1420 of FIG. 14, respectively. Therefore, detailed descriptions of steps S1510 and S1520 will be omitted.
  • the image decoding apparatus may obtain intra prediction mode information for the current chroma block from the bitstream, construct a chroma MPM list (S1510 and S1520), and then determine a predetermined condition (S1530).
  • the video decoding apparatus selects a candidate indicated by an MPM index among MPM candidates in the chroma MPM list.
  • the intra prediction mode of the current chroma block may be determined (S1540).
  • the MPM flag has a second value (eg 0) (No in S1530)
  • the video decoding apparatus performs intra prediction indicated by remaining mode information among the remaining intra prediction modes not included in the chroma MPM list.
  • a mode may be determined as an intra prediction mode of the current chroma block (S1550).
  • the video decoding apparatus does not check the value of the MPM flag, and the chroma MPM A candidate indicated by the MPM index among MPM candidates in the list may be determined as an intra prediction mode of the current chroma block (S1540).
  • the MPM flag is not signaled and may be inferred as a first value.
  • the video decoding apparatus is the remaining mode among the remaining intra prediction modes not included in the MPM list.
  • An intra prediction mode indicated by information may be determined as an intra prediction mode of the current chroma block (S1550).
  • the apparatus for encoding/decoding an image configures a chroma MPM list for a current chroma block.
  • the intra prediction process for intra prediction can be unified.
  • intra prediction accuracy for a chroma block may be improved.
  • Embodiment #2 of the present disclosure may configure a chroma MPM list for the current chroma block based on a slice type of a current slice including the current chroma block.
  • 16 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • Steps S1620, S1630, and S1650 of FIG. 16 may correspond to steps S1310 to S1330 of FIG. 13, respectively. Therefore, descriptions of steps S1620, S1630, and S1650 will be briefly described.
  • the apparatus for encoding an image may determine whether a current slice including a current chroma block satisfies a predetermined slice type condition (S1610).
  • the slice type condition may be when the current slice is an intra slice.
  • the intra slice may mean an I slice.
  • inter prediction may not be performed, but only intra prediction may be performed.
  • the intra slice may have a single tree structure or a dual tree structure. In the single tree structure, a luma block and a chroma block may be divided into the same block tree structure. In contrast, in the dual tree structure, a luma block and a chroma block may be divided into different block tree structures.
  • the block tree structure for the luma block may be referred to as a dual tree luma (DUAL_TREE_LUMA), and the block tree structure for the chroma block may be referred to as a dual tree chroma (DUAL_TREE_CHROMA).
  • DUAL_TREE_LUMA dual tree luma
  • DUAL_TREE_CHROMA dual tree chroma
  • the slice type condition may be a case in which the current slice is an inter slice.
  • the inter slice may mean a P slice and/or a B slice.
  • intra prediction or inter prediction may be performed.
  • the inter-slice may have only the single tree structure described above.
  • the slice type information (e.g. slice_type) of the current slice may be signaled in the form of a syntax element of a slice header.
  • a specific example of the slice header is as shown in FIG. 17.
  • 17 is a diagram showing syntax of a slice header including slice type information.
  • a slice header may include information and parameters commonly applicable to all blocks in a current slice including a current chroma block (e.g. sh_picture_header_in_slice_header_flag, sh_subpic_id, etc.).
  • the slice header may include a syntax element (sh_slice_type) indicating type information of the current slice.
  • a chroma MPM list for the current chroma block may be configured regardless of the slice type of the current slice. That is, when the current slice is an intra slice as well as when the current slice is an inter slice, the chroma MPM list may be configured. In this case, Embodiment #1 of the present disclosure described above with reference to FIGS. 13 to 15 may be applied.
  • the image encoding apparatus may configure a chroma MPM list for the current chroma block (S1620).
  • the chroma MPM list may include a chroma DM indicating that an intra prediction mode of the current chroma block is derived to an intra prediction mode of a corresponding luma block.
  • the video encoding apparatus may perform a redundancy check on the chroma MPM list to remove the redundancy of the intra prediction mode indicated by the chroma DM in the chroma MPM list.
  • the image encoding apparatus may determine an intra prediction mode of the current chroma block (S1630). For example, the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) only on MPM candidates included in the chroma MPM list. In this case, as shown in FIG. 16, step S1620 may precede step S1630. Alternatively, the apparatus for encoding an image may determine an optimal intra prediction mode by performing RDO on all intra prediction modes applicable to the current chroma block. In this case, unlike shown in FIG. 16, step S1630 may precede step S1620 or may be performed simultaneously.
  • RDO rate-distortion optimization
  • the intra prediction mode of the current chroma block is one of the MPM candidates in the chroma MPM list (when the MPM flag has a first value (eg 1))
  • an MPM index indicating one of the MPM candidates eg mpm_idx or intra_chroma_mpm_idx
  • the video encoding apparatus includes the remaining intra prediction modes not included in the chroma MPM list. Among them, remaining mode information indicating the same mode as the intra prediction mode of the current chroma block may be generated.
  • the image encoding apparatus may determine and/or encode an intra prediction mode of the current chroma block without configuring a chroma MPM list for the current chroma block. For example, the image encoding apparatus may determine an intra prediction mode of the current chroma block based on a predetermined default mode and chroma DM (S1640). For example, the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) on the default mode and the chroma DM.
  • RDO rate-distortion optimization
  • the default mode may include a planar mode, a DM mode, a vertical mode, and a horizontal mode.
  • the present invention is not limited thereto, and the default mode may include a predetermined intra prediction mode that is preset based on the frequency of occurrence.
  • the apparatus for encoding an image may determine an optimal intra prediction mode by performing an additional RDO for a cross-component linear model (CCLM) mode.
  • CCLM cross-component linear model
  • the CCLM mode may be divided into L_CCLM, T_CCLM, and LT_CCLM according to whether left samples of the current chroma block are considered, upper samples are considered, or both are considered.
  • An intra prediction mode for the current chroma block may be determined separately from an intra prediction mode for a luma block (corresponding luma block) corresponding to the current chroma block, and may be indicated based on intra prediction mode information.
  • the intra prediction mode information may indicate an intra prediction mode of the current chroma block, and may be signaled in the form of an intra_chroma_pred_mode syntax element as described above with reference to Tables 3 and 4, for example.
  • the image encoding apparatus may encode intra prediction mode information for the current chroma block and output it in the form of a bitstream (S1650).
  • the intra prediction mode information may include an MPM flag, an MPM index, and/or remaining mode information.
  • the intra prediction mode information may include information indicating an intra prediction mode of the current chroma block determined in step S1640 (eg intra_chroma_pred_mode). I can.
  • FIG. 18 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • the video decoding apparatus may configure a chroma MPM list for the current chroma block only when the current chroma block is included in a predetermined type of slice. Conversely, when the current chroma block is not included in the predetermined type of slice, the video decoding apparatus may not configure the chroma MPM list.
  • the image decoding apparatus may determine whether a current slice including the current chroma block satisfies a predetermined slice type condition (S1810).
  • the slice type condition may be when the current slice is an intra slice.
  • the intra slice may mean an I slice in which only intra prediction can be performed on blocks included in the intra slice.
  • the slice type condition may be a case in which the current slice is an inter slice.
  • the inter slice may mean a P slice and/or a B slice in which intra prediction or inter prediction may be performed on blocks included in the inter slice.
  • the slice type information of the current slice may be obtained, for example, by decoding the slice_type syntax of the slice header (slice_header) described above with reference to FIG. 17.
  • a chroma MPM list for the current chroma block may be configured regardless of the slice type of the current slice. That is, when the current slice is an intra slice, as well as when the current slice is an inter slice, the chroma MPM list may be configured. In this case, Embodiment #1 of the present disclosure described above with reference to FIGS. 13 to 15 may be applied.
  • the image decoding apparatus may obtain intra prediction mode information for the current chroma block from the bitstream (S1820).
  • the intra prediction mode information may include an MPM flag, an MPM index, and/or a remaining intra prediction mode, as described above with reference to FIG. 16.
  • the video decoding apparatus may configure a chroma MPM list for the current chroma block (S1830).
  • the chroma MPM list may be configured in the same way as the chroma MPM list configured in the video encoding apparatus.
  • the chroma MPM list may be configured using a neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list may further include specific intra prediction modes according to a predetermined method.
  • the chroma MPM list may further include a chroma DM indicating that an intra prediction mode of the current chroma block is derived to an intra prediction mode of a corresponding luma block.
  • the video decoding apparatus may remove duplicate MPM candidates included in the chroma MPM list by performing a redundancy check on the chroma MPM list.
  • step S1830 may be performed prior to step S1820, or may be performed simultaneously with step S1820.
  • the image decoding apparatus may obtain intra prediction mode information for the current chroma block from the bitstream (S1840).
  • the intra prediction mode information may include information (e.g. intra_chroma_pred_mode) indicating an intra prediction mode of the current chroma block determined by the image encoding apparatus, as described above with reference to FIG. 16.
  • the video decoding apparatus may not configure a chroma MPM list for the current chroma block.
  • the image decoding apparatus may determine an intra prediction mode of the current chroma block (S1850).
  • the video decoding apparatus may determine the intra prediction mode of the current chroma block based on the intra prediction mode information acquired in step S1820 and the chroma MPM list configured in step S1830. Specifically, when the MPM flag has a first value (e.g. 1), the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block. In contrast, when the MPM flag has a second value (eg 0), the video decoding apparatus selects an intra prediction mode indicated by remaining mode information among the remaining intra prediction modes not included in the MPM list as the current chroma block. It can be determined as the intra prediction mode of.
  • the MPM flag has a first value (e.g. 1)
  • the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block.
  • the MPM flag has a second value (
  • the video decoding apparatus does not check the value of the MPM flag, and the MPM index among MPM candidates in the chroma MPM list A candidate indicated by may be derived as an intra prediction mode of the current chroma block.
  • a specific type eg LIP, MRL, ISP, etc.
  • the video decoding apparatus does not configure a chroma MPM list, and may determine an intra prediction mode of the current chroma block based on the intra prediction mode information obtained in step S1840.
  • the image decoding apparatus may determine an intra prediction mode of the current chroma block based on intra prediction mode information (e.g. intra_chroma_pred_mode) obtained from a bitstream.
  • intra prediction mode information e.g. intra_chroma_pred_mode
  • the intra prediction mode of the current chroma block may be determined as one of a predetermined default mode and a chroma DM.
  • the default mode may include a planar mode, a DC mode, a vertical mode, and a horizontal mode.
  • the intra prediction mode of the current chroma block may be determined as a cross-component linear model (CCLM) mode.
  • CCLM cross-component linear model
  • the image encoding/decoding apparatus generates a chroma MPM list for the current chroma block only when the current chroma block is included in a slice of a predetermined type.
  • an intra prediction process for a luma block and an intra prediction process for a chroma block can be unified based on a block division structure.
  • a division structure of the current chroma block may be the same as a division structure of a luma block (corresponding luma block) corresponding to the current chroma block.
  • a division structure of the current chroma block may be different from the division structure of the corresponding luma block. Therefore, when the current chroma block has the dual tree structure (that is, when the current chroma block is included in an intra slice), the unification effect of the intra prediction process according to Embodiment #2 of the present disclosure can be more maximized. have.
  • Embodiment #3 of the present disclosure may configure a chroma MPM list for the current chroma block based on whether the intra prediction mode of the current chroma block is the same as the predetermined first mode.
  • 19 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • the apparatus for encoding an image may determine an intra prediction mode of a current chroma block (S1910).
  • the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) on a plurality of intra prediction modes.
  • the plurality of intra prediction modes may include at least one of a plurality of non-directional modes (e.g. a planar mode, a DC mode) and a plurality of directional modes.
  • the apparatus for encoding an image may determine the intra prediction mode of the current chroma block as a chroma DM indicating an intra prediction mode at a predetermined position in a luma block (corresponding luma block) corresponding to the current chroma block.
  • the image encoding apparatus may determine whether the intra prediction mode of the current chroma block is the same as a predetermined first mode (S1920).
  • the first mode may be preset based on the frequency of occurrence.
  • the first mode may be preset as an intra prediction mode having the largest occurrence frequency among the plurality of intra prediction modes.
  • the first mode may be chroma DM.
  • the first mode may be a planner mode.
  • the image encoding apparatus When the intra prediction mode of the current chroma block is the first mode (Yes in S1920), the image encoding apparatus encodes a first mode flag indicating whether the determined intra prediction mode is the first mode, and converts it into a bitstream form. Can be output (S1930).
  • the encoded first mode flag may have a first value (e.g. 1), and the image encoding apparatus may not configure a chroma MPM list for the current chroma block.
  • the image encoding apparatus may encode only the first mode flag as intra prediction mode information of the current chroma block. That is, in this case, the intra prediction mode information of the current chroma block may include only the first mode flag and may not include the above-described MPM flag, MPM index, and remaining mode information.
  • the image encoding apparatus may configure a chroma MPM list for the current chroma block (S1940).
  • the chroma MPM list may include N intra prediction mode candidates (MPM candidates) that are highly likely to be applied to the current chroma block (N is an integer greater than or equal to 1).
  • N is an integer greater than or equal to 1
  • the number (N) of the MPM candidates may be less than or equal to the number (M) of the MPM candidates for the luma block (corresponding luma block) corresponding to the current chroma block (N ⁇ M).
  • the number (N) of the MPM candidates may increase in proportion to the information amount of the chroma component of the current chroma block.
  • the number of MPM candidates (N1) is when the chroma format of the current chroma block is 4:2:2 or 4:4:4 It may be less than or equal to the number of MPM candidates (N2) (N1 ⁇ N2).
  • the number (N) of the MPM candidates may be predefined or may be signaled through a bitstream.
  • the chroma MPM list may be configured using an intra prediction mode of at least one neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list includes a chroma DM indicating that the intra prediction mode of the current chroma block is determined as an intra prediction mode of a predetermined position (eg center position) of the corresponding luma block. can do.
  • the image encoding apparatus may encode the intra prediction mode information of the current chroma block and output it in the form of a bitstream (S1950).
  • the intra prediction mode information may include the aforementioned first mode flag.
  • the encoded first mode flag may have a second value (e.g. 0).
  • the intra prediction mode information may further include the above-described MPM flag, MPM index, and/or remaining mode information. That is, the MPM flag, the MPM index, and/or the remaining mode information may be signaled only when the first mode flag has a second value (e.g. 0).
  • 20 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • the apparatus for decoding an image may obtain intra prediction mode information for a current chroma block from a bitstream (S2010).
  • the intra prediction mode information may include a first mode flag as described above with reference to FIG. 19.
  • the intra prediction mode information may further include an MPM flag, an MPM index, and/or remaining mode information.
  • the image decoding apparatus may determine whether the first mode flag has a first value (e.g. 1) (S2020).
  • the image decoding apparatus may determine the intra prediction mode of the current chroma block as the first mode (S2030).
  • the first mode may be chroma DM.
  • the first mode may be a planner mode.
  • the video decoding apparatus may not configure a chroma MPM list for the current chroma block.
  • the image decoding apparatus uses the current chroma block
  • a chroma MPM list for can be configured (S2040).
  • the chroma MPM list may be configured in the same way as the chroma MPM list configured by the video encoding apparatus.
  • the chroma MPM list may be configured using a neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list may further include specific intra prediction modes according to a predetermined method. For example, if the first mode is not chroma DM, the chroma MPM list indicates that the intra prediction mode of the current chroma block is determined as an intra prediction mode of a predetermined position (eg center position) of the corresponding luma block. DM can be included.
  • the video decoding apparatus may determine an intra prediction mode of the current chroma block based on the intra prediction mode information and a chroma MPM list (S2050). Specifically, when the MPM flag has a first value (e.g. 1), the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block. In contrast, when the MPM flag has a second value (eg 0), the video decoding apparatus selects an intra prediction mode indicated by the remaining mode information among the remaining intra prediction modes not included in the MPM list. It can be determined as the intra prediction mode of the block.
  • a first value e.g. 1
  • the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block.
  • the MPM flag has a second value (eg 0)
  • the video decoding apparatus selects an intra prediction
  • the video decoding apparatus does not decode the value of the MPM flag.
  • a candidate indicated by the MPM index among MPM candidates in the chroma MPM list may be determined as an intra prediction mode of the current chroma block.
  • the image encoding/decoding apparatus configures a chroma MPM list for a current chroma block based on a predetermined first mode flag, thereby encoding an image. /Can improve decryption efficiency.
  • Embodiment #4 of the present disclosure is a modified example of Embodiment #3 of the present disclosure, in which a chroma MPM list for a current chroma block is constructed, and an intra prediction mode of the current chroma block is used by using a predetermined first mode flag. And intra prediction mode information may be adaptively determined.
  • 21 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • Steps S2110 and S2120 of FIG. 21 may correspond to steps S1910 and S1940 of FIG. 19, respectively. Therefore, the description of steps S2110 and S2120 will be briefly described.
  • the apparatus for encoding an image may determine an intra prediction mode of a current chroma block (S2110).
  • the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) on a plurality of intra prediction modes.
  • RDO rate-distortion optimization
  • the image encoding apparatus may configure a chroma MPM list for the current chroma block (S2120).
  • the chroma MPM list may include one or more intra prediction mode candidates (MPM candidates) that are highly likely to be applied to the current chroma block.
  • MPM candidates intra prediction mode candidates
  • the number of MPM candidates may be less than or equal to the number of MPM candidates in a luma MPM list for a luma block corresponding to the current chroma block.
  • the number of MPM candidates may increase in proportion to an information amount of a chroma component of the current chroma block.
  • the number of MPM candidates may be predefined or may be signaled through a bitstream.
  • the chroma MPM list may be configured using an intra prediction mode of at least one neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the image encoding apparatus may determine whether the intra prediction mode of the current chroma block is included in the chroma MPM list or is the same as a predetermined first mode (S2130).
  • the first mode may be preset as one of MPM candidates not included in the chroma MPM list.
  • the first mode may be a chroma DM or a planar mode.
  • the image encoding apparatus determines whether the intra prediction mode of the current chroma block is the same as the first mode. Can be determined (S2140).
  • the video encoding apparatus encodes an MPM flag and a first mode flag as intra prediction mode information of the current chroma block to a bitstream. It can be output in the form (S2150).
  • the MPM flag and the first mode flag may be encoded with a first value (e.g. 1), respectively.
  • the image encoding apparatus may include an MPM flag, a first mode flag, and an MPM index as intra prediction mode information of the current chroma block. May be encoded and output in the form of a bitstream (S2160).
  • the MPM flag may be encoded as a first value (e.g. 1)
  • the first mode flag may be encoded as a second value (e.g. 0).
  • the intra prediction mode of the current chroma block is not included in the chroma MPM list, and is not the same as the first mode (No in S2130), the video encoding apparatus, the intra prediction mode of the current chroma block As information, the MPM flag and the remaining mode information may be encoded and output in the form of a bitstream (S2170).
  • 22 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • Steps S2210 and S2220 of FIG. 22 may correspond to steps S2010 and S2040 of FIG. 20, respectively. Therefore, the description of steps S2210 and S2220 will be briefly described.
  • the image decoding apparatus may obtain intra prediction mode information for a current chroma block from a bitstream (S2210).
  • the intra prediction mode information may include an MPM flag and a first mode flag.
  • the intra prediction mode information may include an MPM flag, a first mode flag, and an MPM index.
  • the intra prediction mode information may include an MPM flag and remaining mode information.
  • the video decoding apparatus may configure a chroma MPM list for the current chroma block (S2220).
  • the chroma MPM list may be configured in the same way as the chroma MPM list configured by the video encoding apparatus.
  • the chroma MPM list may be configured using a neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the chroma MPM list may further include specific intra prediction modes according to a predetermined method. For example, when a predetermined first mode indicated by the first mode flag is not chroma DM, the chroma MPM list may include the chroma DM.
  • the image decoding apparatus may determine whether the MPM flag acquired in step S2210 has a first value (e.g. 1) (S2230).
  • the image decoding apparatus may determine whether the first mode flag obtained in step S2210 has a first value (e.g. 1) (S2240).
  • the image decoding apparatus may determine an intra prediction mode of the current chroma block as the first mode.
  • the first mode may be preset based on the frequency of occurrence or may be signaled through a bitstream.
  • the first mode may be a chroma DM or a planar mode.
  • the video decoding apparatus may determine the intra prediction mode of the current chroma block as an intra prediction mode indicated by the MPM index obtained in step S2210. Yes (S2260).
  • the video decoding apparatus may determine the intra prediction mode of the current chroma block as the intra prediction mode indicated by the remaining mode information obtained in step S2210. Yes (S2270).
  • the image encoding/decoding apparatus uses a predetermined first mode flag to determine the intra prediction mode and intra prediction mode information of the current chroma block. By adaptively determining, video encoding/decoding efficiency can be improved.
  • Embodiment #5 of the present disclosure is a modified example of embodiment #3, wherein the current chroma block is based on whether the intra prediction mode of the current chroma block is the same as a predetermined first intra prediction mode or a second intra prediction mode. You can configure a chroma MPM list for.
  • FIG. 23 is a flowchart illustrating an intra prediction mode signaling procedure in an image encoding apparatus according to another embodiment of the present disclosure.
  • Steps S2310, S2360, and S2370 of FIG. 23 may correspond to steps S1910, S1940, and S1950 of FIG. 19, respectively. Therefore, descriptions of steps S2310, S2360, and S2370 will be briefly described.
  • the apparatus for encoding an image may determine an intra prediction mode of a current chroma block (S2310).
  • the image encoding apparatus may determine an optimal intra prediction mode by performing rate-distortion optimization (RDO) on a plurality of intra prediction modes.
  • RDO rate-distortion optimization
  • the image encoding apparatus may determine whether the intra prediction mode of the current chroma block is the same as a predetermined first mode (S2320).
  • the first mode may be predefined based on the frequency of occurrence or may be signaled through a bitstream.
  • the first mode may be a chroma DM indicating that the intra prediction mode of the current chroma block is determined as an intra prediction mode of a predetermined position (e.g. a center position) in a corresponding luma block.
  • the first mode may be a planar mode. Whether the intra prediction mode of the current chroma block is the same as the first mode may be indicated based on a first mode flag.
  • a first value (eg 1) of the first mode flag may indicate that the intra prediction mode of the current chroma block is the first mode, and a second value (eg 0) of the first mode flag is the current chroma It may indicate that the intra prediction mode of the block is not the first mode.
  • the image encoding apparatus When the intra prediction mode of the current chroma block is the first mode (when the first mode flag has a first value) (Yes in S2320), the image encoding apparatus encodes the first mode flag to form a bitstream. It can be output as (S2330). In this case, the image encoding apparatus may not configure a chroma MPM list for the current chroma block. Also, the image encoding apparatus may encode only the first mode flag as intra prediction mode information of the current chroma block. That is, the intra prediction mode information of the current chroma block may not include the above-described MPM flag, MPM index, and remaining mode information.
  • the video encoding apparatus determines the intra prediction mode of the current chroma block. It may be determined whether it is the same as the second mode of (S2340).
  • the second mode may be predefined based on the frequency of occurrence or may be signaled through a bitstream. In one example, the second mode may be a planar mode. In another example, the second mode may be a chroma DM indicating that an intra prediction mode of the current chroma block is determined as an intra prediction mode of a predetermined position in a corresponding luma block.
  • Whether the intra prediction mode of the current chroma block is the same as the second mode may be indicated based on a second mode flag.
  • a first value (eg 1) of the second mode flag may indicate that the intra prediction mode of the current chroma block is the second mode, and a second value (eg 0) of the second mode flag is the current chroma It may indicate that the intra prediction mode of the block is not the second mode.
  • the image encoding apparatus When the intra prediction mode of the current chroma block is the second mode (when the second mode flag has a first value) (Yes in S2340), the image encoding apparatus includes the first mode flag and the second mode flag May be encoded and output in the form of a bitstream (S2350). In this case, the image encoding apparatus may not configure a chroma MPM list for the current chroma block. Also, the image encoding apparatus may encode only the first mode flag and the second mode flag as intra prediction mode information of the current chroma block. That is, the intra prediction mode information of the current chroma block may not include the above-described MPM flag, MPM index, and remaining mode information.
  • the image encoding apparatus provides a chroma MPM list for the current chroma block. It can be configured (S2360).
  • the chroma MPM list may be configured using an intra prediction mode of at least one neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list may further include specific intra prediction modes according to a predetermined method. For example, if the first mode and the second mode are not chroma DM, the chroma MPM list indicates that the intra prediction mode of the current chroma block is an intra prediction mode of a predetermined position (eg a center position) of the corresponding luma block. It may include a chroma DM indicating that it is determined.
  • the image encoding apparatus may encode the intra prediction mode information of the current chroma block and output it in the form of a bitstream (S2370).
  • the intra prediction mode information may include the aforementioned first mode flag and second mode flag.
  • the intra prediction mode information may further include the above-described MPM flag, MPM index, and/or remaining mode information.
  • the first mode flag since the intra prediction mode of the current chroma block is not the first mode, the first mode flag may have a second value (e.g. 0). Also, since the intra prediction mode of the current chroma block is not the second mode, the second mode flag may have a second value (e.g. 0).
  • 24 is a flowchart illustrating a procedure for determining an intra prediction mode in an image decoding apparatus according to another embodiment of the present disclosure.
  • Steps S2410, S2460, and S2470 of FIG. 24 may correspond to steps S2010, S2040, and S2050 of FIG. 20, respectively. Therefore, descriptions of steps S2410, S2460, and S2470 will be briefly described.
  • the apparatus for decoding an image may obtain intra prediction mode information for a current chroma block from a bitstream (S2410).
  • the intra prediction mode information may include only a first mode flag.
  • the intra prediction mode information may include a first mode flag and a second mode flag.
  • the intra prediction mode information may include a first mode flag, a second mode flag, an MPM flag, an MPM index, and/or remaining mode information.
  • the image decoding apparatus may determine whether the first mode flag has a first value (e.g. 1) (S2420).
  • the image decoding apparatus may determine an intra prediction mode of the current chroma block as the first mode (S2430).
  • the first mode may be a chroma DM indicating that an intra prediction mode of the current chroma block is determined as an intra prediction mode of a corresponding luma block.
  • the first mode may be a planar mode.
  • the image decoding apparatus is in the second mode It may be determined whether the flag has a first value (eg 1) (S2440).
  • the image decoding apparatus may determine the intra prediction mode of the current chroma block as the second mode (S2450).
  • the second mode may be a planar mode.
  • the second mode may be chroma DM.
  • the video decoding apparatus may not configure a chroma MPM list for the current chroma block. .
  • the image decoding apparatus uses the current chroma block
  • a chroma MPM list for can be configured (S2460).
  • the chroma MPM list may be configured in the same way as the chroma MPM list configured by the video encoding apparatus.
  • the chroma MPM list may be configured using an intra prediction mode of a neighboring chroma block (e.g. a left neighboring block and/or an upper neighboring block) adjacent to the current chroma block.
  • the neighboring chroma block may exist at the same position as the neighboring luma block used for intra prediction of the luma block (corresponding luma block) corresponding to the current chroma block, or may exist at a different position from the neighboring luma block.
  • the chroma MPM list may include specific intra prediction modes according to a predetermined method. For example, if the first mode and the second mode are not chroma DM, the chroma MPM list indicates that the intra prediction mode of the current chroma block is an intra prediction mode of a predetermined position (eg a center position) of the corresponding luma block. It may include a chroma DM indicating that it is determined.
  • the video decoding apparatus may determine an intra prediction mode of the current chroma block based on the intra prediction mode information and the chroma MPM list (S2470). Specifically, when the MPM flag has a first value (e.g. 1), the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block. In contrast, when the MPM flag has a second value (eg 0), the video decoding apparatus selects an intra prediction mode indicated by the remaining mode information among the remaining intra prediction modes not included in the MPM list. It can be determined as the intra prediction mode of the block.
  • a first value e.g. 1
  • the video decoding apparatus may determine a candidate indicated by an MPM index among MPM candidates in the chroma MPM list as the intra prediction mode of the current chroma block.
  • the MPM flag has a second value (eg 0)
  • the video decoding apparatus selects an intra prediction mode
  • the video decoding apparatus does not decode the value of the MPM flag, and among MPM candidates in the chroma MPM list A candidate indicated by the MPM index may be determined as an intra prediction mode of the current chroma block.
  • a specific type eg LIP, MRL, ISP, etc.
  • the first mode is a chroma DM (or planar mode) and the second mode is a planar mode (or chroma DM).
  • the first mode and the second mode may be configured by a combination of various intra prediction modes.
  • the first mode may be a chroma DM and the second mode may be a DC mode, or the first mode may be a planner mode and the second mode may be a DC mode.
  • the number of intra prediction modes to be compared with the intra prediction mode of the current chroma block may be variously changed.
  • the apparatus for encoding/decoding an image may additionally encode/decode a third mode flag indicating whether the intra prediction mode of the current chroma block is the same as the third mode.
  • the apparatus for encoding/decoding an image may improve image encoding/decoding efficiency by configuring a chroma MPM list for a current chroma block based on a predetermined first mode flag and a second mode flag. I can.
  • the chroma MPM list according to the embodiments #1 to #5 of the present disclosure described with reference to FIGS. 10 to 22 may be configured singly for all chroma components of the current chroma block, or the chroma It may be configured separately for each of the components.
  • the image encoding/decoding apparatus is One commonly applied chroma MPM list can be configured.
  • the image encoding/decoding apparatus may configure a first chroma MPM list for the first chroma component and a second chroma MPM list for the second chroma component.
  • the first chroma MPM list and the second chroma MPM list may be configured in various forms.
  • the first chroma MPM list and the second chroma MPM list may include different numbers of MPM candidates.
  • the first chroma MPM list and the second chroma MPM list may all include the same MPM candidates, or at least some may include different MPM candidates.
  • the chroma DM included in the chroma MPM list according to the embodiments #1 to #5 of the present disclosure may be a multiple direct mode (MDM).
  • the multiple DM is a mode in which a single DM is extended to a plurality of modes, and may indicate that an intra prediction mode indicated by one of a plurality of DM candidates in a DM candidate list is determined as an intra prediction mode of the current chroma block.
  • the DM candidate list may include a plurality of DM candidates below, for example, as described above with reference to FIG. 11.
  • -Directional mode derived by adding or subtracting a predetermined offset (e.g. 1) to the already included directional mode
  • -Default DM candidate mode vertical mode, horizontal mode, 2, 34, 66, 10, 26 modes (in case of 65 directional modes)
  • the exemplary methods of the present disclosure are expressed as a series of operations for clarity of description, this is not intended to limit the order in which steps are performed, and each step may be performed simultaneously or in a different order if necessary.
  • the exemplary steps may include additional steps, other steps may be included excluding some steps, or may include additional other steps excluding some steps.
  • an image encoding apparatus or an image decoding apparatus performing a predetermined operation may perform an operation (step) of confirming an execution condition or situation of a corresponding operation (step). For example, when it is described that a predetermined operation is performed when a predetermined condition is satisfied, the video encoding apparatus or the video decoding apparatus performs an operation to check whether the predetermined condition is satisfied, and then performs the predetermined operation. I can.
  • various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof.
  • one or more ASICs Application Specific Integrated Circuits
  • DSPs Digital Signal Processors
  • DSPDs Digital Signal Processing Devices
  • PLDs Programmable Logic Devices
  • FPGAs Field Programmable Gate Arrays
  • general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, or the like.
  • the image decoding device and the image encoding device to which the embodiment of the present disclosure is applied include a multimedia broadcasting transmission/reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, and a real-time communication device such as video communication , Mobile streaming devices, storage media, camcorders, video-on-demand (VoD) service providers, OTT video (Over the top video) devices, Internet streaming service providers, three-dimensional (3D) video devices, video telephony video devices, and medical use. It may be included in a video device or the like, and may be used to process a video signal or a data signal.
  • an 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).
  • 25 is a diagram illustrating a content streaming system to which an embodiment according to the present disclosure can be applied.
  • the content streaming system to which the embodiment of the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.
  • the encoding server serves to generate a bitstream by compressing content input from multimedia input devices such as a smartphone, a camera, and a camcorder into digital data, and transmits it to the streaming server.
  • multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate bitstreams
  • the encoding server may be omitted.
  • the bitstream may be generated by an image encoding method and/or an image encoding apparatus to which an embodiment of the present disclosure is applied, and the streaming server may temporarily store the bitstream while transmitting or receiving the bitstream.
  • the streaming server may transmit multimedia data to a user device based on a user request through a web server, and the web server may serve as an intermediary for notifying the user of a service.
  • the web server transmits the request to the streaming server, and the streaming server transmits multimedia data to the user.
  • the content streaming system may include a separate control server, and in this case, the control server may play a role of controlling a command/response 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 digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, and Tablet PC (tablet PC), ultrabook (ultrabook), wearable device (e.g., smartwatch, glass terminal (smart glass), HMD (head mounted display)), digital TV, desktop There may be computers, digital signage, etc.
  • PDA personal digital assistant
  • PMP portable multimedia player
  • slate PC slate PC
  • Tablet PC Tablet PC
  • ultrabook ultrabook
  • wearable device e.g., smartwatch, glass terminal (smart glass), HMD (head mounted display)
  • digital TV desktop There may be computers, digital signage, etc.
  • Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be distributedly processed.
  • the scope of the present disclosure is software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause an operation according to the method of various embodiments to be executed on a device or computer, and such software or It includes a non-transitory computer-readable medium (non-transitory computer-readable medium) which stores instructions and the like and is executable on a device or a computer.
  • a non-transitory computer-readable medium non-transitory computer-readable medium
  • An embodiment according to the present disclosure may be used to encode/decode an image.

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  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

L'invention concerne un procédé et un appareil de codage/décodage vidéo. Un procédé de décodage vidéo selon la présente invention peut comporter les étapes consistant à: décoder des informations de mode de prédiction intra d'un bloc de chroma courant à partir d'un flux binaire; construire une liste de candidats comprenant des modes candidats de prédiction intra du bloc de chroma courant sur la base des informations de mode de prédiction intra et d'un mode de prédiction intra d'un bloc de chroma voisin adjacent au bloc de chroma courant; déterminer un mode de prédiction intra du bloc de chroma courant sur la base des informations de mode de prédiction intra et de la liste de candidats; et générer un bloc de prédiction pour le bloc de chroma courant en effectuant une prédiction intra sur la base du mode de prédiction intra du bloc de chroma courant.
PCT/KR2020/011722 2019-09-02 2020-09-01 Procédé et appareil de codage/décodage vidéo pour effectuer une prédiction intra d'une composante de chroma, et procédé de transmission de flux binaire WO2021045491A1 (fr)

Applications Claiming Priority (4)

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US201962894943P 2019-09-02 2019-09-02
US62/894,943 2019-09-02
US201962896512P 2019-09-05 2019-09-05
US62/896,512 2019-09-05

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11563963B2 (en) 2020-05-19 2023-01-24 Qualcomm Incorporated Determining whether to code picture header data of pictures of video data in slice headers

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KR20160009109A (ko) * 2011-06-17 2016-01-25 미디어텍 인크. 인트라 예측 모드의 코딩을 위한 방법 및 장치
KR20180075422A (ko) * 2016-12-26 2018-07-04 에스케이텔레콤 주식회사 인트라 예측을 이용한 영상의 부호화 및 복호화
US20180205946A1 (en) * 2017-01-13 2018-07-19 Qualcomm Incorporated Coding video data using derived chroma mode
KR20190033559A (ko) * 2016-08-15 2019-03-29 퀄컴 인코포레이티드 디커플링된 트리 구조를 이용한 인트라 비디오 코딩
KR20190077298A (ko) * 2010-12-23 2019-07-03 삼성전자주식회사 영상 복호화 방법 및 장치

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KR20190077298A (ko) * 2010-12-23 2019-07-03 삼성전자주식회사 영상 복호화 방법 및 장치
KR20160009109A (ko) * 2011-06-17 2016-01-25 미디어텍 인크. 인트라 예측 모드의 코딩을 위한 방법 및 장치
KR20190033559A (ko) * 2016-08-15 2019-03-29 퀄컴 인코포레이티드 디커플링된 트리 구조를 이용한 인트라 비디오 코딩
KR20180075422A (ko) * 2016-12-26 2018-07-04 에스케이텔레콤 주식회사 인트라 예측을 이용한 영상의 부호화 및 복호화
US20180205946A1 (en) * 2017-01-13 2018-07-19 Qualcomm Incorporated Coding video data using derived chroma mode

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11563963B2 (en) 2020-05-19 2023-01-24 Qualcomm Incorporated Determining whether to code picture header data of pictures of video data in slice headers

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