Image decoding and encoding method, method for transmitting bitstream, and medium

Abstract

Disclosed are an image decoding and encoding method, a method for transmitting a bitstream, and a medium. An image decoding method performed by a decoding device according to the present document comprises the steps of: acquiring a block-based delta pulse code modulation (BDPCM) flag of a current block; acquiring a BDPCM direction flag of the current block based on a BDPCM flag indicating that BDPCM is applied to the current block; and storing, as an intra prediction mode of the current block, an intra prediction mode of a prediction direction derived on the basis of the BDPCM direction flag.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080053031.7 (International application number: PCT / KR2020 / 006703, application date: May 22, 2020, invention name: Image decoding method and device thereof). Technical Field

[0002] The present disclosure relates to an image coding technology, and more particularly, to an image decoding method and device using BDPCM in an image coding system. Background Art

[0003] Recently, in various fields, the demand for high-resolution, high-quality images such as HD (high definition) images and UHD (ultra high definition) images is growing. Because image data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired / wireless broadband line or stored using an existing storage medium, its transmission cost and storage cost increase.

[0004] Therefore, there is a need for efficient image compression technology for effectively transmitting, storing and reproducing information of high-resolution and high-quality images. Summary of the invention

[0005] Technical issues

[0006] The technical purpose of the present disclosure is to provide a method and device for improving image encoding efficiency.

[0007] Another technical objective of the present disclosure is to provide a method and apparatus for increasing the efficiency of BDPCM.

[0008] Technical Solution

[0009] According to an embodiment of the present disclosure, an image decoding method performed by a decoding device is provided. The method comprises the following steps: obtaining a block-based incremental pulse code modulation (BDPCM) flag of a current block; obtaining a BDPCM direction flag of the current block based on a BDPCM flag indicating that BDPCM is applied to the current block; and storing an intra-frame prediction mode of a prediction direction derived based on the BDPCM direction flag as an intra-frame prediction mode of the current block.

[0010] According to another embodiment of the present disclosure, a decoding device for performing image decoding is provided. The decoding device includes: an entropy decoder configured to obtain a block-based incremental pulse code modulation (BDPCM) flag of a current block, and obtain a BDPCM direction flag of the current block based on a BDPCM flag indicating that BDPCM is applied to the current block; and a memory configured to store an intra-frame prediction mode of a prediction direction derived based on the BDPCM direction flag as an intra-frame prediction mode of the current block.

[0011] According to another embodiment of the present disclosure, an image encoding method performed by an encoding device is provided. The method includes the following steps: deriving a prediction sample of a current block according to block-based incremental pulse code modulation (BDPCM); encoding a BDPCM flag indicating that BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction of the current block; and storing an intra-frame prediction mode of the prediction direction as an intra-frame prediction mode of the current block.

[0012] According to another embodiment of the present disclosure, an image encoding device is provided. The encoding device includes: a predictor configured to derive a prediction sample of a current block according to block-based incremental pulse code modulation (BDPCM); an entropy encoder configured to encode a BDPCM flag indicating that BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction of the current block; and a memory configured to store an intra-frame prediction mode of the prediction direction as an intra-frame prediction mode of the current block.

[0013] Beneficial Effects

[0014] According to the present disclosure, by storing an intra prediction mode according to a BDPCM prediction direction as an intra prediction mode of a current block, intra prediction accuracy and encoding efficiency may be improved.

[0015] According to the present disclosure, by storing an intra prediction mode according to a BDPCM prediction direction as an intra prediction mode of a current block, an accurate intra prediction mode can be referred to in prediction of neighboring blocks, and overall residual encoding efficiency can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 An example of a video / image encoding device to which an embodiment of the present disclosure can be applied is briefly illustrated.

[0017] Figure 2 is a schematic diagram illustrating a configuration of a video / image encoding device to which an embodiment of the present disclosure can be applied.

[0018] Figure 3 is a schematic diagram illustrating a configuration of a video / image decoding device to which an embodiment of the present disclosure can be applied.

[0019] Figure 4 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0020] Figure 5 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0021] Figure 6 The intra prediction process is schematically shown.

[0022] Figure 7 An example of a video / image encoding method based on inter-frame prediction is illustrated.

[0023] Figure 8 An example of a video / image decoding method based on inter-frame prediction is illustrated.

[0024] Fig. 9 The inter-frame prediction process is schematically illustrated.

[0025] Fig.10 An implementation manner proposed in the present disclosure of determining the intra prediction mode of the current block to be stored based on the BDPCM direction flag is illustrated.

[0026] Fig.11 The image encoding method of the encoding device according to this document is schematically shown.

[0027] Fig.12 A coding device for performing the image coding method according to the present document is schematically shown.

[0028] Fig.13 The image decoding method of the decoding device according to the present document is schematically shown.

[0029] Fig.14 A decoding device for performing the image decoding method according to the present document is schematically shown.

[0030] Fig.15 A structural diagram of a content streaming system to which the present disclosure is applied is illustrated. DETAILED DESCRIPTION

[0031] The present disclosure can be modified in various forms, and its specific embodiments will be described and illustrated in the accompanying drawings. However, the embodiments are not intended to limit the present disclosure. The terms used in the following description are only used to describe specific embodiments and are not intended to limit the present disclosure. As long as it is clearly understood in different ways, the expression of the singular includes the expression of the plural. Terms such as "including" and "having" are intended to indicate the presence of features, quantities, steps, operations, elements, components, or combinations thereof used in the following description, so it should be understood that the possibility of the presence or addition of one or more different features, quantities, steps, operations, elements, components, or combinations thereof is not excluded.

[0032] In addition, the elements in the drawings described in the present disclosure are drawn independently for the convenience of explaining different specific functions, and do not mean that these elements are specifically implemented by independent hardware or independent software. For example, two or more elements in the elements can be combined to form a single element, or an element can be divided into multiple elements. The implementation of combining and / or dividing elements belongs to the present disclosure without departing from the concept of the present disclosure.

[0033] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, throughout the accompanying drawings, like reference numerals are used to indicate like elements, and the same description of the like elements will be omitted.

[0034] Figure 1 An example of a video / image encoding device to which an embodiment of the present disclosure can be applied is briefly illustrated.

[0035] Reference Figure 1 The video / image coding system may include a first device (source device) and a second device (receiving device). The source device may transmit coded video / image information or data to the receiving device in the form of a file or stream via a digital storage medium or a network.

[0036] The source device may include a video source, an encoding device, and a transmitter. The receiving device may include a receiver, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display, and the display may be configured as a separate device or an external component.

[0037] The video source can obtain the video / image by capturing, synthesizing or generating the video / image process. The video source may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generation device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capture process may be replaced by a process that generates relevant data.

[0038] The encoding device can encode the input video / image. The encoding device can perform a series of processes such as prediction, transformation and quantization to achieve compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0039] The transmitter may transmit the encoded video / image information or data output in the form of a bit stream to the receiver of the receiving device in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include an element for generating a media file in a predetermined file format, and may include an element for transmitting through a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0040] The decoding device may decode a video / image by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0041] The renderer may render the decoded video / image. The rendered video / image may be displayed by a display.

[0042] The present disclosure relates to video / image coding. For example, the methods / implementations disclosed in the present disclosure may be applied to methods disclosed in Versatile Video Coding (VVC), EVC (Basic Video Coding) standard, AOMedia Video 1 (AV1) standard, 2nd generation Audio Video Coding standard (AVS2) or next generation video / image coding standard (e.g., H.267, or H.268, etc.).

[0043] The present disclosure presents various embodiments of video / image encoding, and unless otherwise mentioned, the embodiments may be performed in combination with each other.

[0044] In the present disclosure, video may refer to a series of images over time. Generally, a picture refers to a unit representing an image in a specific time region, and a sub-picture / slice / tile is a unit that constitutes a part of a picture in coding. A sub-picture / slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more sub-pictures / slices / tiles. A picture may be composed of one or more tile groups. A tile group may include one or more tiles. A tile may represent a rectangular area of ​​a CTU row within a tile in a picture. A tile may be partitioned into a plurality of tiles, each tile consisting of one or more CTU rows within a tile. Tiles that are not partitioned into a plurality of tiles may also be referred to as tiles. Tile scanning is a specific sequential ordering of CTUs that partition a picture, wherein CTUs are continuously ordered in tiles by CTU raster scanning, tiles within tiles are continuously ordered by raster scanning of tiles of tiles, and tiles in a picture are continuously ordered by raster scanning of tiles of tiles of a picture. In addition, a sub-picture may represent a rectangular area of ​​one or more slices within a picture. That is, a sub-picture contains one or more slices that cover a rectangular area of ​​the picture together. A patch is a rectangular area of ​​a CTU within a specific patch column and a specific patch row in a picture. A patch column is a rectangular area of ​​a CTU whose height is equal to the height of the picture and whose width is specified by a syntax element in a picture parameter set. A patch row is a rectangular area of ​​a CTU whose height is specified by a syntax element in a picture parameter set and whose width is equal to the width of the picture. Patch scanning is a specific sequential ordering of CTUs that partition a picture, wherein CTUs may be continuously ordered in a patch by a CTU raster scan, and patches in a picture may be continuously ordered by a raster scan of patches of a picture. A slice includes an integer number of tiles of a picture that may be exclusively contained in a single NAL unit. A slice may consist of a plurality of complete tiles or only of a continuous sequence of complete tiles of a patch. In the present disclosure, patch groups and slices may be used interchangeably. For example, in this disclosure, a tile group / tile group header may be referred to as a slice / slice header.

[0045] A pixel or a picture element (pel) may represent the smallest unit constituting a picture (or image). In addition, a "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0046] A unit may represent a basic unit of image processing. A unit may include at least one of a specific area of ​​a picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit may be used interchangeably with terms such as a block or an area. In general, an M×N block may include a set (or array) of samples (or sample arrays) or transform coefficients of M columns and N rows.

[0047] In this specification, "A or B" may mean "only A", "only B", or "A and B". In other words, in this specification, "A or B" may be interpreted as "A and / or B". For example, "A, B or C" herein means "only A", "only B", "only C", or "any one and any combination of A, B, and C".

[0048] A slash ( / ) or a comma used in this specification may mean "and / or". For example, "A / B" may mean "A and / or B". Thus, "A / B" may mean "only A", "only B", or "A and B". For example, "A,B,C" may mean "A, B, or C".

[0049] In the present specification, "at least one of A and B" may mean "only A", "only B", or "both A and B". In addition, in the present specification, the expression "at least one of A or B" or "at least one of A and / or B" may be interpreted as being the same as "at least one of A and B".

[0050] In addition, in the present specification, "at least one of A, B, and C" means "only A", "only B", "only C", or "any combination of A, B, and C". In addition, "at least one of A, B, or C" or "at least one of A, B and / or C" may mean "at least one of A, B, and C".

[0051] In addition, brackets used in this specification may refer to "for example". Specifically, when "prediction (intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction". In other words, "prediction" in this specification is not limited to "intra-frame prediction", and "intra-frame prediction" may be proposed as an example of "prediction". In addition, even when "prediction (i.e., intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction".

[0052] In this specification, technical features described separately in one figure may be implemented separately or may be implemented simultaneously.

[0053] The following figures are created to explain specific examples of this specification. Since the names of specific devices or the names of specific signals / messages / fields described in the figures are presented by way of example, the technical features of this specification are not limited to the specific names used in the following figures.

[0054] Figure 2 is a schematic diagram illustrating a configuration of a video / image encoding device to which an embodiment of the present disclosure can be applied. Hereinafter, a video encoding device may include an image encoding device.

[0055] Reference Figure 2 , the encoding device 200 includes an image segmenter 210, a predictor 220, a residual processor 230 and an entropy encoder 240, an adder 250, a filter 260 and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234 and an inverse transformer 235. The residual processor 230 may also include a subtractor 231. The adder 250 may be called a reconstructor or a reconstructed block generator. According to an embodiment, the image segmenter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250 and the filter 260 may be composed of at least one hardware component (e.g., an encoder chipset or processor). In addition, the memory 270 may include a decoded picture buffer (DPB) or may be composed of a digital storage medium. The hardware component may also include a memory 270 as an internal / external component.

[0056] The image divider 210 may divide the input image (or picture or frame) input to the encoding device 200 into one or more processors. For example, a processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, a coding unit may be divided into a plurality of coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, a quadtree structure may be applied first, and then a binary tree structure and / or a ternary structure may be applied. Alternatively, a binary tree structure may be applied first. The encoding process according to the present disclosure may be performed based on a final coding unit that is no longer divided. In this case, the maximum coding unit may be used as the final coding unit based on coding efficiency according to image characteristics, or if necessary, the coding unit may be recursively divided into coding units with a deeper depth and a coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include a process of prediction, transformation, and reconstruction, which will be described later. As another example, the processor may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be separated or partitioned from the above-mentioned final coding unit. The prediction unit may be a unit for sample prediction, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0057] In some cases, a unit may be used interchangeably with terms such as a block or region. In general, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, may represent a pixel / pixel value of a luminance component only, or may represent a pixel / pixel value of a chrominance component only. A sample may be used as a term corresponding to a picture (or image) of a pixel or a picture element.

[0058] In the encoding device 200, the prediction signal (prediction block, prediction sample array) output from the inter-frame predictor 221 or the intra-frame predictor 222 is subtracted from the input image signal (original block, original sample array) to generate a residual signal (residual block, residual sample array) and the generated residual signal is sent to the transformer 232. In this case, as shown in the figure, the unit for subtracting the prediction signal (prediction block, prediction sample array) from the input image signal (original block, original sample array) in the encoding device 200 can be called a subtractor 231. The predictor can perform prediction on the block to be processed (hereinafter referred to as the current block) and generate a prediction block including the prediction sample of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction in units of the current block or CU. As described later in the description of each prediction mode, the predictor can generate various information related to the prediction (such as prediction mode information) and send the generated information to the entropy encoder 240. The information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bit stream.

[0059] The intra-frame predictor 222 can predict the current block by referring to the samples in the current picture. Depending on the prediction mode, the referenced samples can be located near the current block, or can be far away from the current block. In intra-frame prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used depending on the setting. The intra-frame predictor 222 may determine the prediction mode applied to the current block by using the prediction mode applied to the adjacent blocks.

[0060] The inter-frame predictor 221 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. Here, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between adjacent blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the adjacent blocks may include spatial adjacent blocks present in the current picture and temporal adjacent blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal adjacent block may be the same or different. The temporal adjacent block may be referred to as a collocated reference block, a co-located CU (colCU), etc., and the reference picture including the temporal adjacent block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on adjacent blocks, and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 may use the motion information of the neighboring block as the motion information of the current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling a motion vector difference.

[0061] The predictor 220 can generate a prediction signal based on various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply both intra prediction and inter prediction at the same time. This can be called inter-frame intra-frame combined prediction (CIIP). In addition, the predictor can predict the block based on an intra-frame block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or the palette mode can be used for content image / video encoding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but IBC can be performed similarly to inter prediction because the reference block is derived in the current picture. That is, IBC can use at least one of the inter prediction techniques described in the present disclosure. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, the sample value within the picture can be signaled based on information about the palette table and the palette index.

[0062] The prediction signal generated by the predictor (including the inter-frame predictor 221 and / or the intra-frame predictor 222) can be used to generate a reconstruction signal or to generate a residual signal. The transformer 232 can generate a transform coefficient by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT represents a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT refers to a transform generated based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process can be applied to square pixel blocks of the same size, or can be applied to blocks of variable size rather than square.

[0063] The quantizer 233 may quantize the transform coefficients and send them to the entropy encoder 240, and the entropy encoder 240 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. Information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the block type quantized transform coefficients into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. Information about the transform coefficients may be generated. The entropy encoder 240 may perform various encoding methods, such as, for example, exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 may encode information required for video / image reconstruction (e.g., values ​​of syntax elements, etc.) other than the quantized transform coefficients together or separately. Encoded information (e.g., encoded video / image information) may be transmitted or stored in units of NAL (network abstraction layer) in the form of a bitstream. The video / image information may also include information about various parameter sets such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. In the present disclosure, information and / or syntax elements sent / signaled from an encoding device to a decoding device may be included in the video / picture information. The video / image information may be encoded and included in a bitstream through the above-mentioned encoding process. The bitstream may be sent through a network, or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for sending a signal output from the entropy encoder 240 and / or a storage unit (not shown) for storing the signal may be included as an internal / external element of the encoding device 200, alternatively, the transmitter may be included in the entropy encoder 240.

[0064] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients using the dequantizer 234 and the inverse transformer 235. The adder 250 adds the reconstructed residual signal to the prediction signal output from the inter-frame predictor 221 or the intra-frame predictor 222 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual (such as the case where the skip mode is applied), the prediction block can be used as a reconstructed block. The adder 250 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0065] Furthermore, during picture encoding and / or reconstruction, luma mapping and chroma scaling (LMCS) may be applied.

[0066] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 270 (specifically, the DPB of the memory 270). Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 260 can generate various information related to filtering, and send the generated information to the entropy encoder 240, as described later in the description of various filtering methods. The information related to filtering can be encoded by the entropy encoder 240 and output in the form of a bit stream.

[0067] The modified reconstructed picture sent to the memory 270 may be used as a reference picture in the inter predictor 221. When inter prediction is applied by the encoding apparatus, prediction mismatch between the encoding apparatus 200 and the decoding apparatus may be avoided, and encoding efficiency may be improved.

[0068] The DPB of the memory 270 may store a modified reconstructed picture used as a reference picture in the inter-frame predictor 221. The memory 270 may store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of a reconstructed block in the picture. The stored motion information may be sent to the inter-frame predictor 221 and used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 270 may store reconstructed samples of a reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame predictor 222.

[0069] Figure 3 is a schematic diagram illustrating a configuration of a video / image decoding device to which an embodiment of the present disclosure can be applied.

[0070] Reference Figure 3 , the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 332 and an intra-frame predictor 331. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be composed of hardware components (e.g., a decoder chipset or a processor). In addition, the memory 360 may include a decoded picture buffer (DPB), or may be composed of a digital storage medium. The hardware component may also include a memory 360 as an internal / external component.

[0071] When a bit stream including video / image information is input, the decoding device 300 can be used with Figure 2 The image is reconstructed correspondingly to the processing of the video / image information in the encoding device. For example, the decoding device 300 can derive the unit / block based on the block segmentation related information obtained from the bit stream. The decoding device 300 can perform decoding using a processor applied in the encoding device. Therefore, the decoding processor can be, for example, a coding unit, and the coding unit can be segmented from the coding tree unit or the maximum coding unit according to a quadtree structure, a binary tree structure and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0072] The decoding device 300 may receive the bit stream from Figure 2The signal output by the encoding device of the present invention can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive the information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The signaled / received information and / or syntax elements described later in this disclosure may be decoded by a decoding process and obtained from the bitstream. For example, the entropy decoder 310 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, and arithmetically decode the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, after determining the context model, the CABAC entropy decoding method can update the context model by using the decoded symbol / bin information for the context model of the next symbol / bin. Information related to prediction among the information decoded by the entropy decoder 310 can be provided to the predictor (inter-frame predictor 332 and intra-frame predictor 331), and the residual value (that is, quantized transform coefficients and related parameter information) for which entropy decoding is performed in the entropy decoder 310 can be input to the residual processor 320. The residual processor 320 can derive a residual signal (residual block, residual sample, residual sample array). In addition, information about filtering among the information decoded by the entropy decoder 310 can be provided to the filter 350. In addition, a receiver (not shown) for receiving a signal output from the encoding device may be further configured as an internal / external element of the decoding device 300, or the receiver may be a component of the entropy decoder 310. In addition, the decoding device according to the present disclosure may be referred to as a video / image / picture decoding device, and the decoding device may be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include the entropy decoder 310, and the sample decoder may include at least one of the dequantizer 321, the inverse transformer 322, the adder 340, the filter 350, the memory 360, the inter-frame predictor 332, and the intra-frame predictor 331.

[0073] The dequantizer 321 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 321 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The dequantizer 321 may perform dequantization on the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0074] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0075] The predictor may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on information on prediction output from the entropy decoder 310, and may determine a specific intra / inter prediction mode.

[0076] The predictor 330 can generate a prediction signal based on various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply intra prediction and inter prediction at the same time. This can be called inter-frame intra combined prediction (CIIP). In addition, the predictor can predict the block based on the intra block copy (IBC) prediction mode or the palette mode. The IBC prediction mode or the palette mode can be used for content image / video encoding of games, etc., for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but IBC can be performed similarly to inter prediction because the reference block is derived in the current picture. That is, IBC can use at least one of the inter prediction techniques described in the present disclosure. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, the sample value within the picture can be signaled based on information about the palette table and the palette index.

[0077] The intra-frame predictor 331 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the referenced sample can be located near the current block, or can be far away from the current block. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The intra-frame predictor 331 can determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

[0078] The inter-frame predictor 332 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the adjacent blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the adjacent blocks may include spatial adjacent blocks present in the current picture and temporal adjacent blocks present in the reference picture. For example, the inter-frame predictor 332 may configure a motion information candidate list based on the adjacent blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating a mode of inter-frame prediction for the current block.

[0079] The adder 340 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (including the inter-frame predictor 332 and / or the intra-frame predictor 331). If the block to be processed has no residual (for example, when the skip mode is applied), the prediction block can be used as the reconstructed block.

[0080] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra-frame prediction of the next block to be processed in the current picture, may be output through filtering as described below, or may be used for inter-frame prediction of the next picture.

[0081] In addition, luma mapping and chroma scaling (LMCS) can be applied during picture decoding.

[0082] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 360 (specifically, the DPB of the memory 360). The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0083] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter-frame predictor 332. The memory 360 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information can be sent to the inter-frame predictor 332 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 360 can store the reconstructed samples of the reconstructed block in the current picture, and can transmit the reconstructed samples to the intra-frame predictor 331.

[0084] In the present disclosure, the embodiments described in the filter 260, the inter-frame predictor 221, and the intra-frame predictor 222 of the encoding device 200 may be the same as the filter 350, the inter-frame predictor 332, and the intra-frame predictor 331 of the decoding device 300 or may be respectively applied to correspond to the filter 350, the inter-frame predictor 332, and the intra-frame predictor 331 of the decoding device 300. The same contents may also be applied to the inter-frame predictor 332 and the intra-frame predictor 331.

[0085] In the present disclosure, at least one of quantization / inverse quantization and / or transform / inverse transform may be omitted. When quantization / inverse quantization is omitted, the quantized transform coefficient may be referred to as a transform coefficient. When transform / inverse transform is omitted, the transform coefficient may be referred to as a coefficient or a residual coefficient, or may still be referred to as a transform coefficient for the sake of uniformity of expression.

[0086] In the present disclosure, the quantized transform coefficient and the transform coefficient may be referred to as a transform coefficient and a scaled transform coefficient, respectively. In this case, the residual information may include information about the transform coefficient, and the information about the transform coefficient may be signaled by a residual coding syntax. The transform coefficient may be derived based on the residual information (or information about the transform coefficient), and the scaled transform coefficient may be derived by inversely transforming (scaling) the transform coefficient. The residual sample may be derived based on inversely transforming (transforming) the scaled transform coefficient. This may also be applied / expressed in other parts of the present disclosure.

[0087] In addition, as described above, when performing video encoding, prediction is performed to improve compression efficiency. In this way, a prediction block including a prediction sample of a current block can be generated as a block to be encoded (i.e., an encoding target block). Here, the prediction block includes prediction samples in a spatial domain (or a pixel domain). The prediction block is derived in the same manner in the encoding device and the decoding device, and the encoding device can signal information about the residual between the original block and the prediction block (residual information) to the decoding device instead of the original sample value of the original block, thereby improving image coding efficiency. The decoding device can derive a residual block including residual samples based on the residual information, add the residual block and the prediction block to generate a reconstructed block including reconstructed samples, and generate a reconstructed picture including the reconstructed block.

[0088] The residual information may be generated by a transformation and quantization process. For example, the encoding device may derive a residual block between the original block and the prediction block, may perform a transformation process on the residual samples (residual sample array) included in the residual block to derive the transformation coefficients, may perform a quantization process on the transformation coefficients to derive the quantized transformation coefficients, and may signal the relevant residual information (through a bitstream) to the decoding device. Here, the residual information may include value information, position information, transformation technology, transformation core, and value information of quantization parameters, etc. of the quantized transformation coefficients. The decoding device may perform a dequantization / inverse transformation process based on the residual information and derive residual samples (or residual blocks). The decoding device may generate a reconstructed picture based on the prediction block and the residual block. In addition, for reference to inter-frame prediction of a reference picture later, the encoding device may dequantize / inverse transform the quantized transformation coefficients to derive the residual block, and generate a reconstructed picture based on this.

[0089] Intra-frame prediction may refer to generating a prediction of a prediction sample for a current block based on a reference sample in a picture to which the current block belongs (hereinafter referred to as the current picture). When intra-frame prediction is applied to the current block, the neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size nW×nH and a total of 2×nH samples adjacent to the lower left of the current block, samples adjacent to the upper boundary of the current block and a total of 2×nW samples adjacent to the upper right, and samples adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nW samples adjacent to the lower boundary of the current block, and samples adjacent to the lower right of the current block.

[0090] However, some neighboring reference samples of the current block have not been decoded or may not be available. In this case, the decoder can construct neighboring reference samples to be used for prediction by replacing unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction can be configured by interpolation of available samples.

[0091] When deriving the neighboring reference samples, (i) the prediction samples may be derived based on an average or interpolation of the neighboring reference samples of the current block, or (ii) the prediction samples may be derived based on reference samples present in a specific (prediction) direction relative to the prediction samples in the neighboring reference samples of the current block. Case (i) may be referred to as a non-directional mode or a non-angular mode, and case (ii) may be referred to as a directional mode or an angular mode.

[0092] In addition, the prediction sample can be generated by interpolating the first neighboring sample located in the prediction direction of the intra prediction mode of the current block based on the prediction sample of the current block among the adjacent reference samples and the second neighboring sample located in the direction opposite to the prediction direction. The above situation can be called linear interpolation intra prediction (LIP). In addition, a linear model (LM) can be used to generate chroma prediction samples based on luma samples. This situation can be called LM mode or chroma component LM (CCLM) mode.

[0093] In addition, the temporary prediction sample of the current block is derived based on the filtered adjacent reference sample, and the prediction sample of the current block can also be derived by weighted summing the temporary prediction sample with at least one reference sample derived according to the intra prediction mode in the existing adjacent reference sample (i.e., the unfiltered adjacent reference sample). The above situation can be called position-dependent intra prediction (PDPC).

[0094] In addition, a reference sample line with the highest prediction accuracy among multiple adjacent reference sample lines of the current block is selected, and a prediction sample is derived using a reference sample located in the prediction direction in the selected line. In this case, intra-frame prediction coding can be performed by indicating (signaling) the reference sample line used to the decoding device. The above situation can be referred to as multi-reference line intra-frame prediction or MRL-based intra-frame prediction.

[0095] In addition, the current block is divided into vertical sub-partitions or horizontal sub-partitions and performs intra prediction based on the same intra prediction mode, but adjacent reference samples can be derived and used in units of sub-partitions. That is, in this case, the intra prediction mode of the current block is also applicable to the sub-partitions, but in some cases, the intra prediction performance can be improved by deriving and using adjacent reference samples in units of sub-partitions. This prediction method can be called intra prediction based on intra sub-partition (ISP).

[0096] The above-mentioned intra-frame prediction method may be referred to as an intra-frame prediction type to distinguish it from an intra-frame prediction mode. The intra-frame prediction type may be referred to by various terms, such as an intra-frame prediction technique or an additional intra-frame prediction mode. For example, the intra-frame prediction type (or additional intra-frame prediction mode, etc.) may include at least one of the above-mentioned LIP, PDPC, MRL, and ISP. A general intra-frame prediction method excluding specific intra-frame prediction types such as LIP, PDPC, MRL, and ISP may be referred to as a normal intra-frame prediction type. When the above-mentioned specific intra-frame prediction type is not applied, a normal intra-frame prediction type may generally be applied, and prediction may be performed based on the above-mentioned intra-frame prediction mode. In addition, if necessary, post-processing filtering may be performed on the derived prediction samples.

[0097] Specifically, the intra prediction process may include an intra prediction mode / type determination step, an adjacent reference sample derivation step, and a prediction sample derivation step based on the intra prediction mode / type. In addition, if necessary, a post-filtering step may be performed on the derived prediction samples.

[0098] Figure 4 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0099] Reference Figure 4 , the encoding device performs intra prediction on the current block (S400). The encoding device derives the intra prediction mode / type of the current block, derives the adjacent reference samples of the current block, and generates prediction samples in the current block based on the intra prediction mode / type and the adjacent reference samples. Here, the intra prediction mode / type determination process, the adjacent reference sample derivation process, and the prediction sample generation process can be performed simultaneously, or one process can be performed before the other. The encoding device can determine the mode / type applied to the current block from multiple intra prediction modes / types. The encoding device can compare the RD costs of the intra prediction modes / types and determine the optimal intra prediction mode / type for the current block.

[0100] In addition, the encoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all prediction samples may be filtered by the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0101] The encoding apparatus generates residual samples of the current block based on the (filtered) prediction samples (S410). The encoding apparatus may compare the prediction samples among the original samples of the current block based on the phase and derive the residual samples.

[0102] The encoding device may encode image information including information about intra prediction (prediction information) and residual information about residual samples (S420). The prediction information may include intra prediction mode information and intra prediction type information. The encoding device may output the encoded image information in the form of a bit stream. The output bit stream may be sent to a decoding device via a storage medium or a network.

[0103] The residual information may include a residual encoding syntax described later. The encoding device may transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information about the quantized transform coefficients.

[0104] In addition, as described above, the encoding device can generate a reconstructed picture (including reconstructed samples and reconstructed blocks). To this end, the encoding device can derive (modified) residual samples by performing inverse quantization / inverse transformation on the quantized transform coefficients again. The reason for performing inverse quantization / inverse transformation again after transforming / quantizing the residual samples in this way is to derive the same residual samples as the residual samples derived in the above-mentioned decoding device. The encoding device can generate a reconstructed block including reconstructed samples for the current block based on the predicted samples and the (modified) residual samples. A reconstructed picture for the current picture can be generated based on the reconstructed block. As described above, the in-loop filtering process can be further applied to the reconstructed picture.

[0105] Figure 5 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0106] The decoding device may perform operations corresponding to those performed by the encoding device.

[0107] Prediction information and residual information may be obtained from a bitstream. Residual samples of a current block may be derived based on the residual information. Specifically, transform coefficients may be derived by performing inverse quantization based on quantized transform coefficients derived from the residual information, and residual samples of the current block may be derived by performing inverse transformation on the transform coefficients.

[0108] Specifically, the decoding device may derive the intra prediction mode / type of the current block based on the received prediction information (intra prediction mode / type information) (S500). The decoding device may derive the adjacent reference samples of the current block (S510). The decoding device generates the prediction samples in the current block based on the intra prediction mode / type and the adjacent reference samples (S520). In this case, the decoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post filtering. Some or all prediction samples may be filtered by the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0109] The decoding device generates residual samples for the current block based on the received residual information (S530). The decoding device can generate reconstructed samples of the current block based on the predicted samples and the residual samples, and can derive a reconstructed block including the reconstructed samples (S540). A reconstructed picture of the current picture can be generated based on the reconstructed block. As described above, the in-loop filtering process can be further applied to the reconstructed picture.

[0110] The intra-frame prediction mode information may include, for example, flag information (e.g., intra_luma_mpm_flag) indicating whether MPM (most probable mode) is applied to the current block or whether the residual mode is applied, and when MPM is applied to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra-frame prediction mode candidates (MPM candidates). The intra-frame prediction mode candidates (MPM candidates) may be composed of an MPM candidate list or an MPM list. In addition, when MPM is not applied to the current block, the intra-frame prediction mode information includes residual mode information (e.g., intra_luma_mpm_remainder) indicating one of the remaining intra-frame prediction modes other than the intra-frame prediction mode candidates (MPM candidates). The decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction mode information.

[0111] In addition, the intra prediction type information may be implemented in various forms. For example, the intra prediction type information may include intra prediction type index information indicating one of the intra prediction types. As another example, the intra prediction type information may include reference sample line information (e.g., intra_luma_ref_idx) indicating whether MRL is applied to the current block and, if applied, which reference sample line is used, ISP flag information (e.g., intra_subpartitions_mode_flag) indicating whether ISP is applied to the current block, ISP type information (e.g., intra_subpartitions_split_flag) indicating the split type of the sub-partition when ISP is applied, flag information indicating whether PDPC is applied, or flag information indicating whether LIP is applied. In addition, the intra prediction type information may include a MIP flag indicating whether matrix-based intra prediction (MIP) is applied to the current block.

[0112] The intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by the encoding method described in the present disclosure. For example, the intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by entropy coding (e.g., CABAC, CAVLC).

[0113] Figure 6 The intra prediction process is schematically shown.

[0114] Reference Figure 6As described above, the intra prediction process may include a step of determining an intra prediction mode / type, a step of deriving adjacent reference samples, and a step of performing intra prediction (generating prediction samples). The intra prediction process may be performed by the encoding device and the decoding device as described above. In the present disclosure, the encoding device may include an encoding device and / or a decoding device.

[0115] Reference Figure 6 , the encoding device determines the intra-frame prediction mode / type S600.

[0116] The encoding device may determine the intra-frame prediction mode / type applied to the current block from the above-mentioned various intra-frame prediction modes / types, and may generate prediction related information. The prediction related information may include intra-frame prediction mode information indicating the intra-frame prediction mode applied to the current block and / or intra-frame prediction type information indicating the intra-frame prediction type applied to the current block. The decoding device may determine the intra-frame prediction mode / type applied to the current block based on the prediction related information.

[0117] The intra-frame prediction mode information may include, for example, flag information (e.g., intra_luma_mpm_flag) indicating whether the most probable mode (MPM) is applied to the current block or the residual mode is applied, and when the MPM is applied to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra-frame prediction mode candidates (MPM candidates). The intra-frame prediction mode candidates (MPM candidates) may be composed of an MPM candidate list or an MPM list. In addition, when the MPM is not applied to the current block, the intra-frame prediction mode information may further include residual mode information (e.g., intra_luma_mpm_remainder) indicating one of the remaining intra-frame prediction modes other than the intra-frame prediction mode candidates (MPM candidates). The decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction mode information.

[0118] In addition, the intra prediction type information may be implemented in various forms. For example, the intra prediction type information may include intra prediction type index information indicating one of the intra prediction types. As another example, the intra prediction type information may include reference sample line information indicating whether MRL is applied to the current block and, if applied, which reference sample line is used (e.g., intra_luma_ref_idx), ISP flag information indicating whether ISP is applied to the current block (e.g., intra_subpartitions_mode_flag), ISP type information indicating the split type of the sub-partition when ISP is applied (e.g., intra_subpartitions_split_flag), flag information indicating whether PDPC is applied, or flag information indicating whether LIP is applied. In addition, the intra prediction type information may include a MIP flag indicating whether matrix-based intra prediction (MIP) is applied to the current block.

[0119] For example, when intra prediction is applied, the intra prediction mode of the neighboring blocks may be used to determine the intra prediction mode applied to the current block. For example, the encoding device may select one of the most likely mode (MPM) candidates in the MPM list derived based on the intra prediction mode of the additional candidate mode and / or the neighboring blocks (e.g., left and / or upper neighboring blocks) of the current block or select one of the remaining intra prediction modes not included in the MPM candidates (and the plane mode) based on the MPM residual information (remaining intra prediction mode information). The MPM list may be configured to include or exclude the plane mode as a candidate. For example, when the MPM list includes the plane mode as a candidate, the MPM list may have 6 candidates, and when the MPM list does not include the plane mode as a candidate, the MPM list may have 5 candidates. When the MPM list does not include the plane mode as a candidate, a non-planar flag (e.g., intra_luma_not_planar_flag) indicating whether the intra prediction mode of the current block is not a plane mode may be signaled. For example, the MPM flag may be signaled first, and when the value of the MPM flag is 1, the MPM index and the non-planar flag may be signaled. In addition, when the value of the non-planar flag is 1, the MPM index may be signaled. Here, the fact that the MPM list is configured not to include the planar mode as a candidate is that the planar mode is always considered to be the MPM rather than considering that the planar mode is not the MPM, and therefore, the flag (non-planar flag) is signaled first to check whether it is the planar mode.

[0120] For example, it can be indicated based on an MPM flag (e.g., intra_luma_mpm_flag) whether the intra prediction mode applied to the current block is among the MPM candidates (and planar mode) or among the remaining modes. An MPM flag with a value of 1 can indicate that the intra prediction mode of the current block is within the MPM candidates (and planar mode), while an MPM flag with a value of 0 can indicate that the intra prediction mode of the current block is not within the MPM candidates (and planar mode). A non-planar flag with a value of 0 (e.g., intra_luma_not_planar_flag) can indicate that the intra prediction mode of the current block is a planar mode, and a non-planar flag with a value of 1 can indicate that the intra prediction mode of the current block is not a planar mode. The MPM index can be signaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element, and the remaining intra prediction mode information can be signaled in the form of a rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element. For example, the remaining intra prediction mode information may indicate one of the remaining intra prediction modes that is not included in the MPM candidates (and planar mode) among all intra prediction modes by indexing in order of the prediction mode number. The intra prediction mode may be an intra prediction mode of a luminance component (sample). Hereinafter, the intra prediction mode information may include at least one of an MPM flag (e.g., intra_luma_mpm_flag), a non-planar flag (e.g., intra_luma_not_planar_flag), an MPM index (e.g., mpm_idx or intra_luma_mpm_idx), or the remaining intra prediction mode information (rem_intra_luma_luma_mpm_mode or intra_luma_mpminder). In the present disclosure, the MPM list may be referred to by a variety of terms, such as an MPM candidate list and candModeList.

[0121] When a MIP is applied to the current block, a separate MPM flag (eg, intra_mip_mpm_flag), an MPM index (eg, intra_mip_mpm_idx), and remaining intra prediction mode information (eg, intra_mip_mpm_remainder) for the MIP may be signaled, and a non-planar flag may not be signaled.

[0122] In other words, in general, when performing block segmentation of an image, the current block to be encoded and the adjacent blocks have similar image characteristics. Therefore, there is a high probability that the current block and the adjacent blocks have the same or similar intra-frame prediction mode. Therefore, the encoder can use the intra-frame prediction mode of the adjacent block to encode the intra-frame prediction mode of the current block.

[0123] The encoding device may construct a most probable mode (MPM) list for the current block. The MPM list may be referred to as an MPM candidate list. Here, MPM may refer to a mode for improving coding efficiency by considering the similarity between the current block and the adjacent blocks during intra-frame prediction mode encoding. As described above, the MPM list may be constructed to include a plane mode, or may be constructed to exclude a plane mode. For example, when the MPM list includes a plane mode, the number of candidates in the MPM list may be 6. And when the MPM list does not include a plane mode, the number of candidates in the MPM list may be 5.

[0124] The encoding device may perform prediction based on various intra prediction modes, and may determine the optimal intra prediction mode based on rate distortion optimization (RDO) therefrom. In this case, the encoding device may determine the optimal intra prediction mode by using only the MPM candidates and the plane mode configured in the MPM list, or by further using the remaining intra prediction modes and the MPM candidates and the plane mode configured in the MPM list. Specifically, for example, if the intra prediction type of the current block is a specific type other than the normal intra prediction type (e.g., LIP, MRL, or ISP), the encoding device may determine the optimal intra prediction mode by considering only the MPM candidates and the plane mode as intra prediction mode candidates for the current block. That is, in this case, the intra prediction mode of the current block may be determined only from the MPM candidates and the plane mode, and in this case, encoding / signaling of the MPM flag may not be performed. In this case, the decoding device may infer that the MPM flag is 1 without separately signaling the MPM flag.

[0125] In addition, generally, when the intra prediction mode of the current block is not a plane mode but one of the MPM candidates in the MPM list, the encoding device generates an MPM index (mpmidx) indicating one of the MPM candidates. When the intra prediction mode of the current block is not included in the MPM list, the encoding device generates MPM residual information (remaining intra prediction mode information) indicating the same mode as the intra prediction mode of the current block among the remaining intra prediction modes not included in the MPM list (and the plane mode). The MPM residual information may include, for example, an intra_luma_mpm_remainder syntax element.

[0126] The decoding device obtains intra-frame prediction mode information from the bitstream. As described above, the intra-frame prediction mode information may include at least one of an MPM flag, a non-plane flag, an MPM index, and MPM residual information (residual intra-frame prediction mode information). The decoding device may construct an MPM list. The construction of the MPM list is the same as the MPM list constructed in the encoding device. That is, the MPM list may include intra-frame prediction modes of adjacent blocks, or may further include a specific intra-frame prediction mode according to a predetermined method.

[0127] The decoding device can determine the intra prediction mode of the current block based on the MPM list and the intra prediction mode information. For example, when the value of the MPM flag is 1, the decoding device can derive the plane mode as the intra prediction mode of the current block (based on the non-plane flag), or derive the candidate indicated by the MPM index among the MPM candidates in the MPM list as the intra prediction mode of the current block. Here, the MPM candidate may only represent the candidates included in the MPM list, or may include not only the candidates included in the MPM list, but also the plane mode applicable when the value of the MPM flag is 1.

[0128] For another example, when the value of the MPM flag is 0, the decoding device may derive the intra prediction mode indicated by the remaining intra prediction mode information (which may be referred to as mpm remaining information) among the remaining intra prediction modes not included in the MPM list and the plane mode as the intra prediction mode of the current block. In addition, as another example, when the intra prediction type of the current block is a specific type (such as LIP, MRL, or ISP, etc.), the decoding device may derive the candidate indicated by the MPM flag in the plane mode or the MPM list as the intra prediction mode of the current block without parsing / decoding / checking the MPM flag.

[0129] The encoding device derives neighboring reference samples of the current block (S610). When intra prediction is applied to the current block, neighboring reference samples to be used for intra prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size nW×nH and a total of 2×nH samples adjacent to the lower left of the current block, samples adjacent to the upper boundary of the current block and a total of 2×nW samples adjacent to the upper right, and samples adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nW samples adjacent to the lower boundary of the current block, and samples adjacent to the lower right of the current block.

[0130] On the other hand, when MRL is applied (ie, when the value of the MRL index is greater than 0), the neighboring reference sample may be located on line 1 to 2 instead of line 0 adjacent to the current block on the left / upper side, and in this case, the number of neighboring reference samples can be further increased. In addition, when ISP is applied, the neighboring reference sample can be derived in units of sub-partitions.

[0131] The encoding device derives a prediction sample by performing intra prediction on the current block (S620). The encoding device may derive the prediction sample based on the intra prediction mode / type and the adjacent samples. The encoding device may derive the reference sample according to the intra prediction mode of the current block among the adjacent reference samples of the current block, and may derive the prediction sample of the current block based on the reference sample.

[0132] In addition, when inter-frame prediction is applied, the predictor of the encoding device / decoding device can derive prediction samples by performing inter-frame prediction in units of blocks. When prediction is performed on the current block, inter-frame prediction can be applied. That is, the predictor of the encoding / decoding device (more specifically, the inter-frame predictor) can derive prediction samples by performing inter-frame prediction in units of blocks. Inter-frame prediction can represent a prediction derived by a method that depends on data elements (e.g., sample values ​​or motion information) of (one or more) pictures other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block can be predicted in units of blocks, sub-blocks or samples based on the correlation of motion information between adjacent blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of applying inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same as or different from each other. The temporal neighboring block may be referred to as a name such as a collocated reference block, a collocated CU (ColCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (ColPic). For example, a motion information candidate list may be configured based on the neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) may be signaled to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes, and for example, in the case of a skip mode and a merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In the case of the skip mode, unlike the merge mode, a residual signal may not be sent. In the case of a motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived by using the sum of the motion vector predictor and the motion vector difference.

[0133] According to the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may further include L0 motion information and / or L1 motion information. The L0 direction motion vector may be referred to as the L0 motion vector or MVL0, and the L1 direction motion vector may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bi-prediction. Here, the L0 motion vector may indicate a motion vector associated with the reference picture list L0, and the L1 motion vector may indicate a motion vector associated with the reference picture list L1. The reference picture list L0 may include a picture before the current picture in output order, and the reference picture list L1 may include a picture after the current picture in output order as a reference picture. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may further include a picture after the current picture in output order as a reference picture. In this case, the previous picture may be indexed first in the reference picture list L0, and then the subsequent picture may be indexed. The reference picture list L1 may further include a picture preceding the current picture in the output order as a reference picture. In this case, the subsequent picture may be indexed first in the reference picture list L1, and then the previous picture may be indexed. Here, the output order may correspond to a picture sequence count (POC) order.

[0134] The video / image encoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0135] Figure 7 An example of a video / image encoding method based on inter-frame prediction is illustrated.

[0136] The encoding device performs inter prediction on the current block (S700). The encoding device may derive the inter prediction mode and motion information of the current block, and generate a prediction sample of the current block. Here, the inter prediction mode determination process, the motion information derivation process, and the prediction sample generation process may be performed simultaneously, and any one process may be performed earlier than the other processes. For example, the inter prediction unit of the encoding device may include a prediction mode determination unit, a motion information derivation unit, and a prediction sample derivation unit, and the prediction mode determination unit may determine the prediction mode of the current block, the motion information derivation unit may derive the motion information of the current block, and the prediction sample derivation unit may derive the prediction sample of the current block. For example, the inter prediction unit of the encoding device may search for a block similar to the current block in a predetermined area (search area) of the reference picture through motion estimation, and derive a reference block with the smallest difference from the current block or equal to or less than a predetermined standard. A reference picture index indicating the reference picture where the reference block is located may be derived based on this, and a motion vector may be derived based on the position difference between the reference block and the current block. The encoding device may determine the mode applied to the current block among various prediction modes. The encoding apparatus may compare RD costs of various prediction modes and determine an optimal prediction mode for the current block.

[0137] For example, when the skip mode or merge mode is applied to the current block, the encoding device may configure a merge candidate list to be described below, and derive a reference block whose difference with the current block is the smallest or equal to or less than a predetermined standard among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the current block may be derived by using the motion information of the selected merge candidate.

[0138] As another example, when the (A)MVP mode is applied to the current block, the encoding device may configure the (A)MVP candidate list to be described below, and use the motion vector of the selected MVP candidate among the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by motion estimation may be used as the motion vector of the current block, and the MVP candidate having the motion vector with the minimum difference from the motion vector of the current block among the MVP candidates may become the selected MVP candidate. A motion vector difference (MVD) may be derived, which is the difference obtained by subtracting the MVP from the motion vector of the current block. In this case, information about the MVD may be signaled to the decoding device. In addition, when the (A)MVP mode is applied, the value of the reference picture index may be configured as reference picture index information and signaled to the decoding device separately.

[0139] The encoding apparatus may induce residual samples based on the prediction samples (S710). The encoding apparatus may induce residual samples by comparing original samples and prediction samples of the current block.

[0140] The encoding device encodes the image information including prediction information and residual information (S720). The encoding device can output the encoded image information in the form of a bitstream. The prediction information may include information about prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information as information related to the prediction process. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index), which is information for deriving a motion vector. In addition, the information about the motion information may include information about the MVD and / or reference picture index information. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or dual prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0141] The output bitstream may be stored in a (digital) storage medium and transmitted to a decoding device, or transmitted to a decoding device via a network.

[0142] In addition, as described above, the encoding device can generate a reconstructed picture (including a reconstructed sample and a reconstructed block) based on the reference sample and the residual sample. This is to derive a prediction result that is the same as the prediction result performed by the decoding device, and as a result, the coding efficiency can be increased. Therefore, the encoding device can store the reconstructed picture (or reconstructed sample or reconstructed block) in a memory and use the reconstructed picture as a reference picture. As described above, the in-loop filtering process can be further applied to the reconstructed picture.

[0143] The video / image decoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0144] Figure 8 An example of a video / image decoding method based on inter-frame prediction is illustrated.

[0145] Reference Figure 8 The decoding device may perform an operation corresponding to the operation performed by the encoding device. The decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0146] Specifically, the decoding device may determine a prediction mode of the current block based on the received prediction information (S800). The decoding device may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

[0147] For example, it may be determined whether to apply the merge mode or (A)MVP mode to the current block based on the merge flag. Alternatively, one of various inter-prediction mode candidates may be selected based on the mode index. The inter-prediction mode candidate may include a skip mode, a merge mode, and / or an (A)MVP mode, or may include various inter-prediction modes described below.

[0148] The decoding device derives motion information of the current block based on the determined inter-frame prediction mode (S810). For example, when the skip mode or merge mode is applied to the current block, the decoding device may configure a merge candidate list to be described below, and select a merge candidate from among the merge candidates included in the merge candidate list. Here, the selection may be performed based on the selection information (merge index). The motion information of the current block may be derived by using the motion information of the selected merge candidate. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0149] As another example, when the (A)MVP mode is applied to the current block, the decoding device may configure the (A)MVP candidate list to be described below, and use the motion vector of the selected MVP candidate among the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. Here, the selection may be performed based on the selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list of the current block may be derived as the reference picture referenced by the inter-frame prediction of the current block.

[0150] In addition, as described below, the motion information of the current block can be derived without the candidate list configuration, and in this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode. In this case, the candidate list configuration can be omitted.

[0151] The decoding device may generate a prediction sample for the current block based on the motion information of the current block (S820). In this case, a reference picture may be derived based on a reference picture index of the current block, and a prediction sample of the current block may be derived by using a sample of the reference block indicated by a motion vector of the current block on the reference picture. In this case, in some cases, a prediction sample filtering process for all or some prediction samples of the current block may be further performed.

[0152] For example, the inter-frame prediction unit of the decoding device may include a prediction mode determination unit, a motion information derivation unit and a prediction sample derivation unit, and the prediction mode determination unit may determine the prediction mode of the current block based on the received prediction mode information, the motion information derivation unit may derive the motion information (motion vector and / or reference picture index) of the current block based on the information about the received motion information, and the prediction sample derivation unit may derive the prediction sample of the current block.

[0153] The decoding device generates a residual sample of the current block based on the received residual information (S830). The decoding device can generate a reconstructed sample of the current block based on the predicted sample and the residual sample, and generate a reconstructed picture based on the generated reconstructed sample (S840). Thereafter, as described above, the in-loop filtering process can be further applied to the reconstructed picture.

[0154] Fig. 9 The inter-frame prediction process is schematically illustrated.

[0155] Reference Fig. 9 As described above, the inter-frame prediction process may include an inter-frame prediction mode determination step, a motion information derivation step according to the determined prediction mode, and a prediction processing (prediction sample generation) step based on the derived motion information. The inter-frame prediction process may be performed by the encoding device and the decoding device as described above. In this article, the encoding device may include an encoding device and / or a decoding device.

[0156] Reference Fig. 9 , the encoding device determines the inter prediction mode of the current block (S900). Various inter prediction modes can be used for the prediction of the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, merge with MVD (MMVD) mode and historical motion vector prediction (HMVP) mode can be used. Decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, dual prediction with CU-level weights (BCW) and bidirectional optical flow (BDOF) can be further used as additional modes. Affine mode can also be referred to as affine motion prediction mode. MVP mode can also be referred to as advanced motion vector prediction (AMVP) mode. In this article, some modes and / or motion information candidates derived from some modes can also be included in one of the motion information related candidates in other modes. For example, HMVP candidates can be added to the merge candidates of merge / skip mode, or to the MVP candidates of MVP mode. If the HMVP candidate is used as a motion information candidate for a merge mode or a skip mode, the HMVP candidate may be referred to as an HMVP merge candidate.

[0157] Prediction mode information indicating the inter prediction mode of the current block may be signaled from the encoding device to the decoding device. In this case, the prediction mode information may be included in the bitstream and received by the decoding device. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, whether the skip mode is applied may be indicated by signaling a skip flag, and when the skip mode is not applied, whether the merge mode is applied may be indicated by signaling a merge flag, and when the merge mode is not applied, the MVP mode may be indicated to be applied or a flag for additional distinction may be further signaled. The affine mode may be signaled as an independent mode, or signaled as a subordinate mode with respect to the merge mode or the MVP mode. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0158] The encoding apparatus derives motion information of a current block (S910). The motion information may be derived based on an inter prediction mode.

[0159] The encoding device may use the motion information of the current block to perform inter-frame prediction. The encoding device may derive the optimal motion information of the current block through a motion estimation process. For example, the encoding device may search for a similar reference block with high correlation in units of fractional pixels within a predetermined search range in a reference picture by using the original block in the original picture of the current block, and derive motion information through the searched reference block. The similarity of the blocks may be derived based on the difference in sample values ​​based on the phase. For example, the similarity of the blocks may be calculated based on the sum of absolute differences (SAD) between the current block (or the template of the current block) and the reference block (or the template of the reference block). In this case, the motion information may be derived based on the reference block with the minimum SAD in the search area. The derived motion information may be signaled to the decoding device according to various methods based on the inter-frame prediction mode.

[0160] The encoding device performs inter prediction based on the motion information of the current block (S920). The encoding device may derive (one or more) prediction samples of the current block based on the motion information. The current block including the prediction samples may be referred to as a prediction block.

[0161] In addition, according to an embodiment, a block differential pulse code modulation (BDPCM) technique may be used. BDPCM may also be referred to as RDPCM (block-based delta pulse code modulation).

[0162] When a block is predicted by applying BDPCM, the reconstructed samples can be used to predict the rows or columns of the block line by line. In this case, the reference samples used can be unfiltered samples. The BDPCM direction can indicate whether the vertical or horizontal direction prediction is used. That is, when BDPCM is applied, the vertical direction or the horizontal direction can be selected as the BDPCM direction, and the prediction can be performed in the BDPCM direction. The prediction error can be quantized in the spatial domain, and the sample can be reconstructed by adding the inverse quantized prediction error to the prediction (ie, the prediction sample). The prediction error may refer to the residual. As an alternative to this BDPCM, a quantized residual domain BDPCM can be proposed, and the prediction direction or signaling can be the same as the BDPCM applied to the spatial domain. That is, the quantized coefficients themselves can be accumulated by quantizing the residual domain BDPCM like DPCM (Delta Pulse Code Modulation), and then the residual can be reconstructed by inverse quantization. Therefore, in the sense of applying DPCM in the residual coding state, a quantized residual domain BDPCM can be used. The quantized residual domain used below is based on the residual derived from the prediction being quantized without being transformed, meaning a domain for quantizing residual samples. For example, the quantized residual domain may include quantized residuals (or quantized residual coefficients) to which a transform is skipped, i.e., the transform is skipped but quantization is applied to the residual samples. Or, for example, the quantized residual domain may include quantized transform coefficients.

[0163] For a block of size M×N, it can be assumed that the residual derived from the prediction value obtained by performing intra-frame prediction in the horizontal direction (copying the left adjacent sample line to the prediction block line by line) or by performing intra-frame prediction in the vertical direction (copying the upper adjacent sample line by line) using the unfiltered samples in the left or upper boundary samples (i.e., the left adjacent samples or the upper adjacent samples) is r(i,j)(0≤i≤M-1,0≤j≤N-1). Here, M can represent a row or height, and N can represent a column or width. And, it can be assumed that the quantization value of the residual r(i,j) is Q(r(i,j))(0≤i≤M-1,0≤j≤N-1). Here, the residual refers to the difference between the original block and the predicted block value.

[0164] Then, if BDPCM is applied to the quantized residual samples, we can derive As an M x N modified array of configurations

[0165] For example, when vertical BDPCM is signaled (ie, when vertical BDPCM is applied), it can be derived as in the following equation:

[0166] [Formula 1]

[0167]

[0168] That is, for example, when vertical BDPCM is applied, the encoding device may perform vertical intra prediction based on the upper adjacent sample, and may derive the quantized residual sample of the current block as in the above formula 1. Referring to the above formula 1, the quantized residual sample of the row other than the first row of the current block may be derived as the difference between the quantized value of the corresponding position and the quantized value of the position of the previous row of the corresponding position (i.e., the upper adjacent position of the corresponding position).

[0169] Furthermore, when similarly applied to horizontal prediction (ie, when BDPCM in the horizontal direction is applied), the residual quantized sample can be derived as in the following equation.

[0170] [Formula 2]

[0171]

[0172] That is, for example, when horizontal BDPCM is applied, the encoding device may perform horizontal intra prediction based on the left adjacent sample, and may derive the quantized residual sample of the current block as in the above formula 2. Referring to the above formula 2, the quantized residual sample of the column other than the first column of the current block may be derived as the difference between the quantized value of the corresponding position and the quantized value of the position of the previous column of the corresponding position (i.e., the left adjacent position of the corresponding position).

[0173] Quantized residual samples can be sent to a decoding device.

[0174] In the decoding device, the above operation can be performed in reverse to derive Q(r(i,j))(0≤i≤M-1,0≤j≤N-1).

[0175] The following formula can be applied to vertical prediction.

[0176] [Formula 3]

[0177]

[0178] In addition, the following formula can be applied to horizontal prediction.

[0179] [Formula 4]

[0180]

[0181] The quantized residual (Q -1 (Q(r i ,j))) is added to the intra-block prediction value to derive the reconstructed sample value.

[0182] The main advantage of this technique is that inverse BDPCM can be performed by simply adding the predictor while parsing the coefficients or even after parsing.

[0183] As described above, BDPCM can be applied to a quantized residual domain, and the quantized residual domain may include a quantized residual (or a quantized residual coefficient), in which case transform skipping is applied to the residual. That is, when BDPCM is applied, the transform can be skipped and quantization can be applied to the residual sample. Alternatively, the quantized residual domain may include quantized transform coefficients. A flag indicating whether BDPCM is available may be signaled in a sequence parameter set (SPS), and the flag may be signaled only when the transform skip mode is enabled in the SPS. The flag may be referred to as a BDPCM enable flag or an SPS BDPCM enable flag.

[0184] When BDPCM is applied, intra prediction in the quantized residual domain can be performed on the entire block by sample replication according to a prediction direction similar to the intra prediction direction (e.g. vertical prediction or horizontal prediction). The residual is quantized and a delta value, i.e. the difference between the quantized residual and the predictor in the horizontal or vertical direction, can be encoded. (ie, the quantized residual in the horizontal or vertical direction).

[0185] If BDPCM is applicable, when the CU size is less than or equal to the MaxTsSize (maximum transform skip block size) of the luminance sample and the CU is encoded using intra prediction, flag information may be sent at the CU level. The flag information may be referred to as a BDPCM flag. Here, MaxTsSize may refer to the maximum block size for which the transform skip mode is allowed. The flag information may indicate whether traditional intra coding or BDPCM is applied. When BDPCM is applied, a BDPCM prediction direction flag may be sent indicating whether the prediction direction is horizontal or vertical. The BDPCM prediction direction flag may be referred to as a BDPCM direction flag. Thereafter, the block may be predicted using a traditional horizontal or vertical intra prediction process using unfiltered reference samples. In addition, the residual may be quantized, and the difference between each quantized residual and its predictor (e.g., between residuals that have been quantized in the horizontal or vertical direction according to the BDPCM prediction direction) may be encoded.

[0186] Furthermore, as described later, the above-mentioned BDPCM is described in a standard document format.

[0187] For example, as shown in the following table, syntax elements for the above-mentioned BDPCM enable flag and semantics for the syntax elements are represented.

[0188] [Table 1]

[0189]

[0190] [Table 2]

[0191]

[0192] Table 1 shows sps_bdpcm_enabled_flag signaled in a sequence parameter set (SPS), and when the syntax element sps_bdpcm_enabled_flag is 1, the syntax element sps_bdpcm_enabled_flag may indicate that there is flag information indicating whether BDPCM is applied to a coding unit for performing intra prediction, i.e., "intra_bdpcm_luma_flag" and "intra_bdpcm_chroma_flag" in the coding unit. The syntax element sps_bdpcm_enabled_flag may be a syntax element for the above-mentioned BDPCM enabling flag. In addition, if the syntax element "sps_bdpcm_enabled_flag" is not present, its value may be inferred to be equal to 0.

[0193] In addition, for example, syntax elements for the BDPCM flag and the BDPCM direction flag and the semantics of the syntax elements may be as shown in the following table.

[0194] [Table 3]

[0195]

[0196] [Table 4]

[0197]

[0198] The syntax element bdpcm_flag of Table 3 may indicate whether BDPCM is applied to the current block. The syntax element bdpcm_flag may be a syntax element of a BDPCM flag. For example, when the value of bdpcm_flag is 1, BDPCM may be applied to the current block, the transformation of the current block may be skipped, and bdpcm_dir_flag indicating the prediction direction of the current block may be present. In addition, for example, when the value of bdpcm_flag is 0, BDPCM may not be applied to the current block. In addition, for example, when bdpcm_flag does not exist, the value of bdpcm_flag may be inferred to be equal to 0. The current block may be a coding block. bdpcm_dir_flag may indicate the prediction direction of the current block. For example, referring to Table 4, when the value of bdpcm_dir_flag is 1, the prediction direction of the current block may be a vertical direction. When the value of bdpcm_dir_flag is 0, the prediction direction of the current block may be a horizontal direction. The syntax element bdpcm_flag may be a syntax element for the above-mentioned BDPCM flag, and the syntax element bdpcm_dir_flag may be a syntax element for the above-mentioned BDPCM direction flag.

[0199] In addition, for example, the above syntax elements for the BDPCM flag and the BDPCM direction flag may be signaled for the luma component and the chroma component, respectively. For example, the semantics of the syntax elements may be as shown in the following table.

[0200] [Table 5]

[0201]

[0202] [Table 6]

[0203]

[0204]

[0205] As described above, the syntax element intra_bdpcm_luma_flag of Table 5 may indicate whether BDPCM is applied to the current luma block, and intra_bdpcm_chroma_flag may indicate whether BDPCM is applied to the current luma block or the current chroma block. For example, when the value of intra_bdpcm_luma_flag or intra_bdpcm_chroma_flag is 1, the transformation of the corresponding coding block may be skipped, and the prediction mode for the coding block may be set in the horizontal or vertical direction by intra_bdpcm_luma_dir_flag or intra_bdpcm_chroma_dir_flag indicating the prediction direction. When intra_bdpcm_luma_flag or intra_bdpcm_chroma_flag does not exist, the value of intra_bdpcm_luma_flag or intra_bdpcm_chroma_flag may be inferred to be equal to 0.

[0206] In addition, for example, when the value of intra_bdpcm_luma_dir_flag or intra_bdpcm_chroma_dir_flag indicating the prediction direction is 0, intra_bdpcm_luma_dir_flag or intra_bdpcm_chroma_dir_flag may indicate that the BDPCM prediction direction is the horizontal direction, and when the value of intra_bdpcm_chroma_dir_flag or intra_bdpcm_chroma_dir_flag is 1, intra_bdpcm_luma_dir_flag or intra_bdpcm_chroma_dir_flag may indicate that the BDPCM prediction direction is the vertical direction.

[0207] Furthermore, an example of the inverse quantization process when BDPCM is applied is shown in the following table.

[0208] [Table 7]

[0209]

[0210]

[0211] Alternatively, an example of an inverse quantization process when BDPCM is applied is shown in the following table.

[0212] [Table 8]

[0213]

[0214]

[0215]

[0216] Referring to Table 7 or Table 8, when the value of bdpcm_flag is 1, the inverse quantization residual value d[x][y] may be derived based on the intermediate variable dz[x][y]. Here, x is a horizontal coordinate increasing from left to right, y is a vertical coordinate increasing from top to bottom, and the position in the two-dimensional block may be represented as (x, y). In addition, the position in the two-dimensional block indicates the (x, y) position when the upper left position of the block is set to (0, 0).

[0217] For example, when the value of bdpcm_dir_flag is 0, that is, when horizontal BDPCM is applied, when x is 0, the variable dz[x][y] may be TransCoeffLevel[xTbY][yTbY][cIdx][x][y], and when x is not 0, dz[x][y] may be derived based on dz[x-1][y]+dz[x][y]. That is, when horizontal BDPCM is applied (the value of bdpcm_dir_flag is 0), the variable dz[x][y] of the sample located in the first column where x is 0 is derived as TransCoeffLevel[xTbY][yTbY][cIdx][x][y] derived based on the residual information of the sample, and the variable dz[x][y] of the sample located in the column other than the first column where x is not 0 is derived as the sum of dz[x-1][y] of the left adjacent sample of the sample and dz[x][y] of the sample. Here, dz[x][y] of the sample added to dz[x-1][y] may be derived based on the signaled residual information for that sample.

[0218] In addition, for example, when the value of bdpcm_dir_flag is 1, that is, when vertical BDPCM is applied, the variable dz[x][y] is derived based on dz[x][y-1]+dz[x][y]. That is, when vertical BDPCM is applied (the value of bdpcm_dir_flag is 1), the variable dz[x][y] of the sample located in the first row where y is 0 is derived as TransCoeffLevel[xTbY][yTbY][cIdx][x][y] derived based on the residual information of the sample, and the variable dz[x][y] of the sample located in the other rows except the first row where y is not 0 is derived as the sum of dz[x][y-1] of the upper adjacent sample of the sample and dz[x][y] of the sample. Here, dz[x][y] of the sample added to dz[x][y-1] may be derived based on the residual information for the sample signaled.

[0219] As described above, the residual of a specific position can be derived based on the sum of the residual of the previous position (ie, left or top) in the horizontal or vertical direction and the value received as the residual information of the specific position. This is because, when BDPCM is applied, the difference between the residual sample value of a specific position (x, y) in the horizontal or vertical direction and the residual sample value of the previous position (ie, (x-1, y) or (x, y-1)) is signaled as residual information.

[0220] In addition, the present disclosure proposes the following method for a method of applying BDPCM between residual signals in a process in which the residual signals are skipped during transformation encoding.

[0221] First, as described above, BDPCM can be applied only when the prediction mode of the current block is an intra prediction mode, and intra prediction can be performed in the same direction as the direction in which BDPCM is applied. That is, by performing inter-frame residual prediction line by line in the row or column direction, the size of the generated level can be reduced and the generation of context coding bins required to encode the level can be reduced, which can help improve the throughput of the decoding device. In addition, as described above, the BDPCM syntax can be parsed at the CU level, and the bdpcm_flag indicating whether BDPCM is applied or the bdpcm_dir_flag indicating whether the prediction is row-direction prediction or column-direction prediction can be parsed in sequence. In addition, according to the existing BDPCM, if a block to which BDPCM is applied is referenced for decoding of adjacent blocks or is referenced by other chrominance components (Cb, Cr, etc.), the block to which BDPCM is applied can be identified as an intra prediction block, and the intra prediction mode of the block to which BDPCM is applied can be derived as the intra prediction mode corresponding to index 0 of the most probable mode (MPM) list of the block to which BDPCM is applied. That is, a neighboring block or a corresponding block of another chroma component can refer to MPM candidate 0 of the block to which BDPCM is applied as an intra prediction mode of the block to which BDPCM is applied. However, according to BDPCM, even if vertical intra prediction or horizontal intra prediction is performed by determining a prediction direction based on a BDPCM direction flag, if an intra prediction mode corresponding to index 0 of the MPM list is stored as a prediction mode of the current block, a difference may occur between the intra prediction mode performed for actual prediction and the stored intra prediction mode.

[0222] Therefore, the present disclosure proposes a method for storing the intra prediction mode of the current block according to the syntax element bdpcm_dir_flag (i.e., BDPCM direction flag) of the BDPCM prediction of the current block. Therefore, the stored intra prediction mode of the current block can be stored in the actual prediction direction, and thus, when constructing the MPM list with reference to the BDPCM block (i.e., the current block) in the adjacent block or constructing the DM mode in the corresponding block of the chrominance component, since encoding can be performed using accurate adjacent information, the prediction accuracy can be improved and the encoding efficiency can be improved.

[0223] Fig.10 An implementation of determining the intra prediction mode of the current block to be stored based on the BDPCM direction flag proposed in the present disclosure is shown.

[0224] Reference Fig.10, the decoding device may parse the bdpcm_flag of the current block (S1000). The bdpcm_flag may represent a syntax element of a BDPCM flag, which indicates whether BDPCM is applied to the current block. For example, when the value of bdpcm_flag is 0, BDPCM may not be applied to the current block. When the value of bdpcm_flag is 1, BDPCM may be applied to the current block, and there may be a bdpcm_dir_flag indicating the prediction direction of the current block to which BDPCM is applied.

[0225] When the value of bdpcm_flag is 1, the decoding apparatus may parse bdpcm_dir_flag of the current block (S1010). bdpcm_dir_flag may represent a syntax element of a BDPCM direction flag, which indicates a prediction direction of the current block.

[0226] The decoding device may determine whether the value of bdpcm_dir_flag indicates a horizontal direction (S1020). The decoding device may derive a prediction direction of the current block based on the parsed value of bdpcm_dir_flag. For example, when the value of bdpcm_dir_flag is 0, bdpcm_dir_flag may indicate that the prediction direction is a horizontal direction, and when the value of bdpcm_dir_flag is 1, bdpcm_dir_flag may indicate that the prediction direction is a vertical direction.

[0227] When bdpcm_dir_flag indicates a horizontal direction, the decoding device may store the intra prediction mode of the current block as a horizontal intra prediction mode (S1030). For example, when bdpcm_dir_flag indicates a horizontal direction, that is, when the value of bdpcm_dir_flag is 0, the decoding device may set or store the intra prediction mode of the current block as a horizontal intra prediction mode. Here, Fig.10 The IntraPredModeY shown may represent the intra prediction mode of the luminance component of the current block, HOR_IDX may represent the horizontal intra prediction mode, and VER_IDX may represent the vertical intra prediction mode.

[0228] In addition, when bdpcm_dir_flag does not indicate the horizontal direction, the decoding device may store the intra prediction mode of the current block as the vertical intra prediction mode (S1040). For example, when bdpcm_dir_flag indicates the vertical direction, that is, when the value of bdpcm_dir_flag is 1, the decoding device may set or store the intra prediction mode of the current block as the vertical intra prediction mode.

[0229] Fig.11 The image encoding method of the encoding device according to this document is schematically shown. Fig.11 The method disclosed in can be Figure 2 Specifically, for example, Fig.11 S1100 may be performed by a predictor of the encoding device, S1110 may be performed by an entropy encoder of the encoding device, and S1120 may be performed by a memory of the encoding device. In addition, although not shown in the figure, the process of deriving the residual sample of the current block based on the prediction sample may be performed by a subtractor of the encoding device, the process of encoding the residual information of the residual sample based on BDPCM may be performed by an entropy encoder of the encoding device, and the process of generating the reconstructed sample and the reconstructed picture of the current block based on the prediction sample and the residual sample of the current block may be performed by an adder of the encoding device.

[0230] The encoding apparatus derives prediction samples of a current block according to block-based delta pulse code modulation (BDPCM) S1100.

[0231] The encoding device may determine whether to apply BDPCM to the current block and may determine a direction in which BDPCM is performed. For example, the encoding device may derive a prediction sample by performing intra-frame prediction on the current block based on a prediction direction in which BDPCM is performed. For example, the prediction direction may be a vertical direction or a horizontal direction, and a prediction sample of the current block may be generated based on an intra-frame prediction mode according to the prediction direction.

[0232] For example, when the prediction direction of the current block is derived as a horizontal direction, the encoding device may derive the prediction sample of the current block by performing intra-frame prediction based on the left adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a horizontal direction, the encoding device may derive the prediction sample of the current block based on the left adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a horizontal direction, the encoding device may derive the sample value of the left adjacent sample of the same row as the prediction sample as the sample value of the prediction sample. In addition, for example, when the prediction direction of the current block is derived as a vertical direction, the encoding device may derive the prediction sample of the current block based on the upper adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a vertical direction, the encoding device may derive the prediction sample of the current block based on the upper adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a vertical direction, the encoding device may derive the sample value of the upper adjacent sample of the same column as the prediction sample as the sample value of the prediction sample.

[0233] In addition, the tree type of the current block can be divided into a single tree (SINGLE_TREE) or a dual tree (DUAL_TREE) based on whether the luminance block and the corresponding chrominance block have respective partition structures. When the chrominance block has the same partition structure as the luminance block, it can be represented as a single tree, and when the chrominance component block has a partition structure different from that of the luminance block, it can be represented as a dual tree. According to an example, BDPCM can be applied to the luminance block or the chrominance block of the current block separately.

[0234] When the tree structure of the current block is a dual tree, BDPCM may be applied to only one component block, and even when the tree structure of the current block is a single tree structure, BDPCM may be applied to only one component block.

[0235] Alternatively, according to an example, BDPCM may be applied only when the width of the current block is less than or equal to the first threshold and the height of the current block is less than or equal to the second threshold. The first threshold and the second threshold may be 32, or may be set to the maximum height or maximum width of the transform block for which transform skipping is performed.

[0236] The encoding device encodes a BDPCM flag indicating whether BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction of the current block S1110. For example, the encoding device may generate and encode a BDPCM flag indicating whether BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction of the current block. The image information may include the BDPCM flag and the BDPCM direction flag.

[0237] For example, the BDPCM flag may indicate whether BDPCM is applied to the current block. For example, when the value of the BDPCM flag is 0, the BDPCM flag may indicate that BDPCM is not applied to the current block. When the value of the BDPCM flag is 1, the BDPCM flag may indicate that BDPCM is applied to the current block and there is a BDPCM direction flag for the current block. That is, for example, when the value of the BDPCM flag is 0, the BDPCM flag may indicate that BDPCM is not applied to the current block, and general intra-frame prediction is performed. When the value of the BDPCM flag is 1, the BDPCM flag may indicate that BDPCM is applied to the current block and there is a BDPCM direction flag for the current block. For example, the syntax element of the BDPCM flag may be bdpcm_flag, intra_bdpcm_luma_flag, or intra_bdpcm_chroma_flag. In addition, for example, the BDPCM flag may be signaled in units of coding units (CUs).

[0238] In addition, for example, the BDPCM direction flag may indicate the prediction direction of the current block. For example, when the value of the BDPCM flag is 1, the encoding device may generate and encode the BDPCM direction flag. For example, the BDPCM direction flag may indicate the vertical direction or the horizontal direction as the prediction direction of the current block. For example, when the value of the BDPCM direction flag is 0, the BDPCM direction flag may indicate that the prediction direction of the current block is the horizontal direction, and when the value of the BDPCM direction flag is 1, the BDPCM direction flag may indicate that the prediction direction of the current block is the vertical direction. For example, the syntax element of the BDPCM direction flag may be bdpcm_dir_flag, intra_bdpcm_luma_dir_flag, or intra_bdpcm_chroma_dir_flag.

[0239] The encoding device stores the intra prediction mode of the prediction direction as the intra prediction mode of the current block S1120. The encoding device may store the intra prediction mode (vertical intra prediction mode or horizontal intra prediction mode) of the prediction direction as the intra prediction mode of the current block. For example, when the prediction direction is a horizontal direction, the horizontal intra prediction mode may be stored as the intra prediction mode of the current block, and when the prediction direction is a vertical direction, the vertical intra prediction mode may be stored as the intra prediction mode of the current block. For example, the stored intra prediction mode may be used for prediction of the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components. For example, the stored intra prediction mode may be used to derive the intra prediction mode of the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components. For example, the stored intra prediction mode may be used as an intra prediction mode candidate for the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components.

[0240] In addition, for example, the encoding device may derive residual samples of the current block based on the prediction samples. For example, the encoding device may derive residual samples by subtracting original samples and prediction samples of the current block.

[0241] In addition, for example, the encoding device may encode residual information about the residual sample based on BDPCM. The image information may include residual information. For example, the encoding device may derive the residual coefficient of the current block based on the residual sample. For example, when BDPCM is applied to the current block, the encoding device may determine not to apply the transform to the current block. In this case, for example, the encoding device may derive the residual coefficient by performing quantization on the residual sample. Here, for example, a block to which a transform is not applied may be referred to as a transform skip block. That is, for example, the current block may be a transform skip block.

[0242] Then, for example, the encoding device may encode the residual information of the residual coefficient. For example, the residual information may include the residual information of the residual coefficient of the residual sample.

[0243] For example, the residual information may include a syntax element of a residual sample of the current block, and the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the left adjacent residual sample or the upper adjacent residual sample of the target residual sample may be derived based on the syntax element of the target residual sample. For example, when the prediction direction of the current block is the horizontal direction, the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the left adjacent residual sample of the target sample is derived based on the syntax element of the target residual sample. That is, for example, when the prediction direction of the current block is the horizontal direction, the syntax element of the target residual sample may represent the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the left adjacent residual sample of the target residual sample. In addition, for example, when the prediction direction of the current block is the vertical direction, the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the upper adjacent residual sample of the target residual sample is derived based on the syntax element of the target residual sample. That is, for example, when the prediction direction of the current block is the vertical direction, the syntax element of the target residual sample can represent the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the upper adjacent residual sample of the target residual sample. In addition, when the target residual sample is located in the first row or column of the current block, the residual coefficient value of the target residual sample can be derived based on the syntax element of the target residual sample. That is, when the target residual sample is located in the first row or column of the current block, the syntax element of the target residual sample can represent the residual coefficient value of the target residual sample.

[0244] For example, the residual information may include syntax elements such as transform_skip_flag, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag, par_level_flag, abs_level_gt1_flag, abs_level_gtX_flag, abs_remainder, coeff_sign_flag, dec_abs_level, and / or mts_idx.

[0245] Specifically, for example, the residual information may include a transform skip flag of the current block. The transform skip flag may indicate whether a transform is applied to the current block. That is, the transform skip flag may indicate whether a transform is applied to the residual coefficients of the current block. In addition, for example, when BDPCM is applied to the current block, the transform skip flag of the current block may not be signaled, and the value of the transform skip flag may be inferred to be equal to 1. That is, when BDPCM is applied to the current block, the residual information may not include the transform skip flag of the current block, the value of the transform skip flag may be inferred to be equal to 1, and the current block may be a transform skip block. The syntax element representing the transform skip flag may be transform_skip_flag.

[0246] In addition, for example, the residual information may include position information indicating the position of the last non-zero residual coefficient in the residual coefficient array of the current block. That is, the residual information may include position information indicating the position of the last non-zero residual coefficient in the scanning order of the current block. The position information may include information indicating the prefix of the column position of the last non-zero residual coefficient, information indicating the prefix of the row position of the last non-zero residual coefficient, information indicating the suffix of the column position of the last non-zero residual coefficient, and information indicating the suffix of the row position of the last non-zero residual coefficient. The syntax elements of the position information may be last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. In addition, the non-zero residual coefficient may be referred to as a valid coefficient. In addition, for example, when the current block is a transform skip block, the residual information may not include position information indicating the position of the last non-zero residual coefficient in the residual coefficient array of the current block.

[0247] In addition, for example, the residual information may include a significant coefficient flag indicating whether a residual coefficient of a residual sample of the current block is a non-zero residual coefficient, a parity level flag for the parity of a coefficient level of the residual coefficient, a first coefficient level flag indicating whether the coefficient level is greater than a first threshold, and a second coefficient level flag indicating whether the coefficient level is greater than a second threshold. Here, the significant coefficient flag may be sig_coeff_flag, the parity level flag may be par_level_flag, the first coefficient level flag may be abs_level_gt1_flag, and the second coefficient level flag may be abs_level_gt3_flag or abs_level_gtx_flag.

[0248] In addition, for example, the residual information may include a sign flag indicating a sign of a residual coefficient of a residual sample of the current block. The sign flag may be coeff_sign_flag.

[0249] In addition, for example, the residual information may include coefficient value related information of the value of the residual coefficient of the residual sample of the current block. The coefficient value related information may be abs_remainder and / or dec_abs_level.

[0250] In addition, the bit stream including the image information can be sent to the decoding device via a network or a (digital) storage medium. Here, the network can include a broadcast network and / or a communication network, and the digital storage medium can include various types of storage media, such as USB disk, SD, CD, DVD, Blu-ray disc, HDD and SSD.

[0251] Fig.12 A coding device that performs the image coding method according to the present document is schematically shown. Fig.11 The method disclosed in can be Fig.12 Specifically, for example, Fig.12 The predictor of the encoding device can perform Fig.11 S1100, Fig.12 The entropy encoder of the encoding device can perform Fig.11 S1110, Fig.12 The memory of the encoding device can perform Fig.11 In addition, although not shown in the figure, the process of deriving the residual samples of the current block based on the prediction samples can be performed by the subtractor of the encoding device, the process of encoding the residual information of the residual samples based on BDPCM can be performed by the entropy encoder of the encoding device, and the process of generating the reconstructed samples and reconstructed pictures of the current block based on the prediction samples and residual samples of the current block can be performed by the adder of the encoding device.

[0252] Fig.13 The image decoding method of the decoding device according to this document is schematically shown. Fig.13 The method disclosed in Figure 3 Specifically, for example, Fig.13 S1300 to S1310 may be performed by an entropy decoder of a decoding device, Fig.13S1320 may be executed by a memory of the decoding device. In addition, although not shown in the figure, the process of deriving the prediction sample of the current block based on BDPCM may be executed by a predictor of the decoding device, the process of deriving the residual sample of the current block based on the residual information may be executed by a residual processor of the decoding device, and the process of generating a reconstructed picture based on the prediction sample and the residual sample may be executed by an adder of the decoding device.

[0253] The decoding apparatus obtains a block-based delta pulse code modulation (BDPCM) flag of a current block S1300.

[0254] The decoding device may obtain image information through a bitstream. For example, the image information may include a BDPCM flag indicating whether BDPCM is applied to the current block. For example, the decoding device may obtain a BDPCM flag indicating whether BDPCM is applied to the current block through a bitstream. For example, when the value of the BDPCM flag is 0, the BDPCM flag may indicate that BDPCM is not applied to the current block. When the value of the BDPCM flag is 1, the BDPCM flag may indicate that BDPCM is applied to the current block and there is a BDPCM direction flag for the current block. That is, for example, when the value of the BDPCM flag is 0, the BDPCM flag may indicate that BDPCM is not applied to the current block and general intra-frame prediction is performed. When the value of the BDPCM flag is 1, the BDPCM flag may indicate that BDPCM is applied to the current block and there is a BDPCM direction flag for the current block. For example, the syntax element of the BDPCM flag may be bdpcm_flag, intra_bdpcm_luma_flag, or intra_bdpcm_chroma_flag. In addition, for example, the BDPCM flag may be signaled in units of coding units (CUs).For example, the current block may be a coding block.

[0255] The decoding apparatus obtains a BDPCM direction flag of the current block based on the BDPCM flag indicating that BDPCM is applied to the current block S1310. For example, the decoding apparatus may obtain a BDPCM direction flag indicating a prediction direction of the current block and residual information based on the BDPCM flag indicating that BDPCM is applied to the current block.

[0256] For example, when the BDPCM flag indicates that BDPCM is applied to the current block, the decoding device can obtain the BDPCM direction flag. That is, for example, when the value of the BDPCM flag is 1, the decoding device can obtain the BDPCM direction flag. For example, the BDPCM direction flag can indicate the vertical direction or the horizontal direction as the prediction direction for the current block. For example, when the value of the BDPCM direction flag is 0, the BDPCM direction flag can indicate that the prediction direction for the current block is the horizontal direction, and when the value of the BDPCM direction flag is 1, the BDPCM direction flag can indicate that the prediction direction for the current block is the vertical direction. For example, the syntax element of the BDPCM direction flag can be bdpcm_dir_flag, intra_bdpcm_luma_dir_flag, or intra_bdpcm_chroma_dir_flag.

[0257] In addition, for example, the decoding device may obtain the residual information of the current block based on the BDPCM flag. For example, when the BDPCM flag indicates that BDPCM is applied to the current block, that is, when BDPCM is applied to the current block, the residual information may include a syntax element of a residual sample of the current block, and the difference between the residual coefficient value of the target sample and the left or upper residual coefficient value of the target residual sample may be derived based on the syntax element of the residual sample of the target sample. For example, when the prediction direction of the current block is a horizontal direction, that is, when the prediction direction of the current block is derived as a horizontal direction based on the BDPCM direction flag, the difference between the residual coefficient value of the target sample and the left residual coefficient value may be derived based on the syntax element of the residual sample of the target sample. In addition, for example, when the prediction direction of the current block is a vertical direction, that is, when the prediction direction of the current block is derived as a vertical direction based on the BDPCM direction flag, the difference between the residual coefficient value of the target sample and the upper residual coefficient value may be derived based on the syntax element of the target sample. In addition, when the target sample is located in the first row or column of the current block, the residual coefficient value of the target sample may be derived based on the syntax element of the target sample.

[0258] For example, the residual information may include syntax elements such as transform_skip_flag, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag, par_level_flag, abs_level_gt1_flag, abs_level_gtX_flag, abs_remainder, coeff_sign_flag, dec_abs_level, and / or mts_idx.

[0259] Specifically, for example, the residual information may include a transform skip flag of the current block. The transform skip flag may indicate whether a transform is applied to the current block. That is, the transform skip flag may indicate whether a transform is applied to the residual coefficients of the current block. In addition, for example, when the value of the BDPCM flag is 1, that is, when BDPCM is applied to the current block, the transform skip flag of the current block may not be signaled, and the value of the transform skip flag may be inferred to be equal to 1. That is, when the value of the BDPCM flag is 1, that is, when BDPCM is applied to the current block, the image information may not include the transform skip flag of the current block, the value of the transform skip flag may be inferred to be equal to 1, and the current block may be a transform skip block.

[0260] In addition, for example, the residual information may include position information indicating the position of the last non-zero residual coefficient in the residual coefficient array of the current block. That is, the residual information may include position information indicating the position of the last non-zero residual coefficient in the scanning order of the current block. The position information may include information indicating the prefix of the column position of the last non-zero residual coefficient and information indicating the prefix of the row position of the last non-zero residual coefficient, information indicating the suffix of the column position of the last non-zero residual coefficient and information indicating the suffix of the row position of the last non-zero residual coefficient. The syntax elements of the position information may be last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. In addition, the non-zero residual coefficient may be referred to as a valid coefficient. In addition, for example, when the current block is a transform skip block, the residual information may not include position information indicating the position of the last non-zero residual coefficient in the residual coefficient array of the current block.

[0261] In addition, for example, the residual information may include a significant coefficient flag indicating whether the residual coefficient of the residual sample of the current block is a non-zero residual coefficient, a parity level flag of the parity of the coefficient level of the residual coefficient, a first coefficient level flag indicating whether the coefficient level is greater than a first threshold, and a second coefficient level flag indicating whether the coefficient level is greater than a second threshold. Here, the significant coefficient flag may be sig_coeff_flag, the parity level flag may be par_level_flag, the first coefficient level flag may be abs_level_gt1_flag, and the second coefficient level flag may be abs_level_gt3_flag or abs_level_gtx_flag.

[0262] In addition, for example, the residual information may include a sign flag indicating the sign of the residual coefficient of the residual sample of the current block. The sign flag may be coeff_sign_flag.

[0263] In addition, for example, the residual information may include coefficient value related information of the value of the residual coefficient of the residual sample of the current block. The coefficient value related information may be abs_remainder and / or dec_abs_level.

[0264] The decoding device stores the intra prediction mode of the prediction direction derived based on the BDPCM direction flag as the intra prediction mode of the current block S1320. The decoding device may store the intra prediction mode (vertical intra prediction mode or horizontal intra prediction mode) of the prediction direction derived based on the BDPCM direction flag as the intra prediction mode of the current block. For example, when the prediction direction is a horizontal direction, the horizontal intra prediction mode may be stored as the intra prediction mode of the current block, and when the prediction direction is a vertical direction, the vertical intra prediction mode may be stored as the intra prediction mode of the current block. For example, the stored intra prediction mode may be used for the prediction of the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components. For example, the stored intra prediction mode may be used to derive the intra prediction mode of the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components. For example, the stored intra prediction mode may be used as an intra prediction mode candidate for the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components.

[0265] In addition, for example, the decoding device may derive the prediction direction based on the BDPCM direction flag. For example, the decoding device may derive the prediction direction indicated by the BDPCM direction flag as the prediction direction for the current block. For example, when the value of the BDPCM direction flag is 0, the BDPCM direction flag may indicate that the prediction direction for the current block is a horizontal direction, and when the value of the BDPCM direction flag is 1, the BDPCM direction flag may indicate that the prediction direction for the current block is a vertical direction. For example, when the value of the BDPCM direction flag is 0, the prediction direction for the current block is derived in the horizontal direction, and when the value of the BDPCM direction flag is 1, the prediction direction for the current block is derived in the vertical direction.

[0266] The decoding device may derive a prediction sample of the current block by performing intra prediction according to the derived prediction direction.

[0267] For example, when the prediction direction is a horizontal direction, the decoding device may derive a prediction sample of a target sample of the current block based on a left adjacent sample of the current block, derive a residual coefficient of the target sample based on the residual information, derive a modified residual coefficient based on the sum of a left residual coefficient of the residual coefficient and the residual coefficient, derive a residual sample of the target sample based on the modified residual coefficient, and derive a reconstructed sample of the target sample based on the prediction sample and the residual sample.

[0268] That is, for example, when the prediction direction of the current block is derived as the horizontal direction, the decoding device may derive the prediction sample of the current block by performing intra-frame prediction based on the left adjacent sample of the current block. For example, when the prediction direction of the current block is derived as the horizontal direction, the decoding device may derive the prediction sample of the current block based on the left adjacent sample of the current block. For example, when the prediction direction of the current block is derived as the horizontal direction, the decoding device may derive the sample value of the left adjacent sample in the same row as the prediction sample as the sample value of the prediction sample.

[0269] Alternatively, for example, when the prediction direction is a vertical direction, the decoding device may derive a prediction sample of a target sample of the current block based on an upper adjacent sample of the current block, derive a residual coefficient of the target sample based on the residual information, derive a modified residual coefficient based on the sum of an upper residual coefficient of the residual coefficient and the residual coefficient, derive a residual sample of the target sample based on the modified residual coefficient, and derive a reconstructed sample of the target sample based on the prediction sample and the residual sample.

[0270] That is, for example, when the prediction direction of the current block is derived as a vertical direction, the decoding device may derive the prediction sample of the current block based on the upper adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a vertical direction, the decoding device may derive the prediction sample of the current block based on the upper adjacent sample of the current block. For example, when the prediction direction of the current block is derived as a vertical direction, the decoding device may derive the sample value of the upper adjacent sample in the same column as the prediction sample as the sample value of the prediction sample.

[0271] In addition, for example, when BDPCM is applied to the current block, the residual information may include a syntax element of a residual sample of the current block (that is, when BDPCM is applied to the current block, the residual information may include a syntax element of a residual sample of a target sample of the current block), and the syntax element of the target sample may represent the difference between the residual coefficient value of the target sample and the left or upper residual coefficient value. That is, for example, when BDPCM is applied to the current block, the residual information may include a syntax element of a target sample of the current block, and the difference between the residual coefficient value of the target sample and the left or upper residual coefficient value may be derived based on the syntax element of the target sample.

[0272] For example, when BDPCM is applied to the current block and the prediction direction of the current block is the horizontal direction, the syntax element of the target sample may represent the difference between the residual coefficient value of the target sample and the left residual coefficient value. That is, for example, the difference between the residual coefficient value of the target sample and the left residual coefficient value may be derived based on the syntax element of the target sample. Thereafter, the residual coefficient of the target sample may be derived as the sum of the residual coefficient value of the left sample of the target sample and the difference. Here, the target sample may be a sample in a column other than the first column of the current block. For example, the residual coefficient of the target sample may be derived based on Formula 4. In addition, for example, when the target sample is a sample in the first column of the current block, the residual coefficient of the target sample may be derived based on the syntax element of the target sample.

[0273] In addition, for example, when BDPCM is applied to the current block and the prediction direction of the current block is the vertical direction, the syntax element of the target sample may represent the difference between the residual coefficient value of the target sample and the upper residual coefficient value. That is, for example, the difference between the residual coefficient value of the target sample and the upper residual coefficient value may be derived based on the syntax element of the target sample. Thereafter, the residual coefficient of the target sample may be derived as the sum of the residual coefficient value of the upper sample of the target sample and the difference. Here, the target sample may be a sample in a row other than the first row of the current block. For example, the residual coefficient of the target sample may be derived based on Formula 3. In addition, for example, when the target sample is a sample in the first row of the current block, the residual coefficient of the residual sample of the target sample may be derived based on the syntax element of the target sample.

[0274] Then, for example, the decoding device may dequantize the residual coefficient to derive the residual sample of the target sample. That is, for example, the residual sample of the target sample may be derived by dequantizing the residual coefficient.

[0275] In addition, for example, the decoding device may derive a reconstructed sample of the current block based on the prediction sample and the residual sample. For example, the decoding device may derive the reconstructed sample by adding the prediction sample and the residual sample. That is, for example, the decoding device may derive the reconstructed sample of the target sample by adding the prediction sample of the target sample and the residual sample of the target sample.

[0276] Thereafter, depending on need, in order to improve subjective / objective image quality, an in-loop filtering process such as deblocking filtering as well as SAO and / or ALF processes may be applied to the reconstructed samples as described above.

[0277] Fig.14 A decoding device for performing the image decoding method according to the present document is schematically shown. Fig.13 The method disclosed in can be Fig.14 Specifically, for example, Fig.14 The entropy decoder of the decoding device can perform Fig.13 S1300 to S1310, and Fig.14 The memory of the decoding device can perform Fig.13 In addition, although not shown in the figure, the process of deriving the prediction sample of the current block based on BDPCM can be performed by the predictor of the decoding device, the process of deriving the residual sample of the current block based on the residual information can be performed by the residual processor of the decoding device, and the process of generating the reconstructed picture based on the prediction sample and the residual sample can be performed by the adder of the decoding device.

[0278] According to the present disclosure, by storing an intra prediction mode according to a BDPCM prediction direction as an intra prediction mode of a current block, intra prediction accuracy and encoding efficiency may be improved.

[0279] In addition, according to the present disclosure, by storing an intra prediction mode according to a BDPCM prediction direction as an intra prediction mode of a current block, an accurate intra prediction mode can be referred to in prediction of adjacent blocks, and overall residual encoding efficiency can be improved.

[0280] In the above-mentioned embodiment, method is described based on the flow chart with a series of steps or square frames. The present disclosure is not limited to the order of the above steps or square frames. Some steps or square frames can be performed in an order different from other steps or square frames mentioned above or performed simultaneously. In addition, it will be appreciated by those skilled in the art that the steps shown in the flow chart are not exclusive, and other steps may also be included, or one or more steps in the flow chart may be deleted without affecting the scope of the present disclosure.

[0281] The embodiments described in this specification may be implemented on a processor, a microprocessor, a controller or a chip. For example, the functional units shown in each figure may be implemented on a computer, a processor, a microprocessor, a controller or a chip. In this case, information (e.g., information about instructions) or algorithms for implementation may be stored in a digital storage medium.

[0282] In addition, the decoding device and encoding device of the present disclosure can be included in the following devices: multimedia broadcast sending / receiving devices, mobile communication terminals, home theater video devices, digital theater video devices, surveillance cameras, video chat devices, real-time communication devices such as video communication, mobile streaming devices, storage media, portable cameras, VoD service providing devices, over-the-top (OTT) video devices, Internet streaming service providing devices, three-dimensional (3D) video devices, teleconferencing video devices, transportation user devices (e.g., vehicle user devices, aircraft user devices, and ship user devices) and medical video devices; and the decoding device and encoding device of the present disclosure can be used to process video signals or data signals. For example, over-the-top (OTT) video devices can include game consoles, Blu-ray players, Internet access televisions, home theater systems, smart phones, tablet computers, digital video recorders (DVRs), etc.

[0283] In addition, the processing method of the present invention can be generated in the form of a program executed by a computer and can be stored in a computer-readable recording medium. The multimedia data with a data structure according to the present invention can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices in which computer-readable data is stored. The computer-readable recording medium may include, for example, a BD, a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (e.g., transmission via the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium or transmitted via a wired / wireless communication network.

[0284] In addition, the embodiments of the present disclosure may be implemented using a computer program product according to a program code, and the program code may be executed in a computer through the embodiments of the present disclosure. The program code may be stored on a computer readable carrier.

[0285] Fig.15 A structural diagram of a content streaming system to which the present disclosure is applied is illustrated.

[0286] The content streaming system to which the embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a network server, a media storage, a user device, and a multimedia input device.

[0287] The encoding server compresses the content input from a multimedia input device such as a smartphone, a camera, or a camcorder into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, a camera, or a camcorder directly generates a bitstream, the encoding server may be omitted.

[0288] A bitstream may be generated by an encoding method or a bitstream generating method to which an embodiment of the present disclosure is applied, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0289] The streaming server sends multimedia data to the user device through the network server based on the user request, and the network server is used as a medium to notify the user of the service. When the user requests the required service from the network server, the network server transmits the request to the streaming server, and the streaming server sends the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control the command / response between the devices within the content streaming system.

[0290] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from an encoding server, the content can be received in real time. In this case, in order to provide a stable streaming service, the streaming server can store the bitstream for a predetermined time.

[0291] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigators, touch screen PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, and head mounted displays), digital TVs, desktop computers, and digital signage, etc. Each server within the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0292] The claims described in this disclosure may be combined in various ways. For example, the technical features of the method claims of this disclosure may be combined to be implemented as a device, and the technical features of the device claims of this disclosure may be combined to be implemented as a method. In addition, the technical features of the method claims of this disclosure and the technical features of the device claims may be combined to be implemented as a device, and the technical features of the method claims of this disclosure and the technical features of the device claims may be combined to be implemented as a method.

Claims

1. A method for decoding an image performed by a decoding device, the method for decoding an image The following steps are involved: Get the block-based delta pulse code modulation BDPCM flag for the current block; Obtaining a BDPCM direction flag for the current block based on the BDPCM flag indicating that BDPCM is applied to the current block; as well as storing the intra prediction mode of the prediction direction derived based on the BDPCM direction flag as the intra prediction mode of the current block, The BDPCM direction flag indicates the horizontal direction or the vertical direction as the prediction direction.

2. The image decoding method according to claim 1, further comprising: The following steps are involved: When the prediction direction is the horizontal direction, deriving a prediction sample of a target sample of the current block based on a left adjacent sample of the current block; Derivation of residual coefficients for the target sample based on the residual information; deriving a modified residual coefficient based on a sum of a left residual coefficient of the residual coefficient and the residual coefficient; deriving a residual sample for the target sample based on the modified residual coefficient; as well as A reconstructed sample for the target sample is derived based on the prediction sample and the residual sample.

3. The image decoding method according to claim 1, further comprising: The following steps are involved: When the prediction direction is the vertical direction, deriving a prediction sample of a target sample of the current block based on an upper adjacent sample of the current block; Derivation of residual coefficients for the target sample based on the residual information; Derivation of a modified residual coefficient based on a sum of an upper residual coefficient of the residual coefficient and the residual coefficient; deriving a residual sample for the target sample based on the modified residual coefficient; as well as A reconstructed sample for the target sample is derived based on the prediction sample and the residual sample.

4. The image decoding method according to claim 1, in, The prediction direction is the horizontal direction, the horizontal intra prediction mode is stored as the intra prediction mode of the current block, and The prediction direction is the vertical direction, and the vertical intra-frame prediction mode is stored as the intra-frame prediction mode of the current block.

5. The image decoding method according to claim 1, in, When the BDPCM is applied to the current block and the prediction direction for the current block is the vertical direction, the residual information includes a syntax element for a target sample of the current block, and The syntax element for the target sample represents a difference between a residual coefficient value of the target sample and an upper residual coefficient value of the target sample.

6. The image decoding method according to claim 1, in, When the value of the BDPCM direction flag is 0, the BDPCM direction flag indicates the horizontal direction as the prediction direction. When the value of the BDPCM direction flag is 1, the BDPCM direction flag indicates the vertical direction as the prediction direction.

7. The image decoding method according to claim 1, in, When the value of the BDPCM flag is 1, the BDPCM direction flag indicates that the BDPCM is applied to the current block and the BDPCM direction flag exists.

8. The image decoding method according to claim 1, in, The stored intra prediction mode is used for prediction of neighboring blocks of the current block.

9. An image encoding method performed by an encoding device, the image encoding method The following steps are involved: Derives prediction samples of the current block according to block-based delta pulse code modulation BDPCM; encoding a BDPCM flag indicating that the BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction for the current block; as well as The intra prediction mode of the prediction direction is stored as the intra prediction mode of the current block.

10. The image encoding method according to claim 9, in, When the value of the BDPCM flag is 1, the BDPCM direction flag indicates that the BDPCM is applied to the current block and the BDPCM direction flag exists.

11. The image encoding method according to claim 9, in, The BDPCM direction flag indicates the horizontal direction or the vertical direction as the prediction direction.

12. The image encoding method according to claim 11, further comprising: The following steps are involved: Derived residual samples of the current block based on the prediction samples; as well as Encoding the residual information for the residual sample based on the BDPCM, Wherein, when the prediction direction for the current block is the vertical direction, the residual information includes a syntax element of a target residual sample for the current block, and The syntax element for the target residual sample represents a difference between a residual coefficient value of the target residual sample and a residual coefficient value of an upper adjacent residual sample of the target residual sample.

13. The image encoding method according to claim 12, in, When the prediction direction for the current block is the horizontal direction, the residual information includes a syntax element of a target residual sample for the current block, and The syntax element for the target residual sample represents a difference between a residual coefficient value of the target residual sample and a residual coefficient value of a left adjacent residual sample of the target residual sample.

14. A non-transitory computer-readable storage medium storing a bit stream generated by an image encoding method, wherein the image encoding method The following steps are involved: Derives prediction samples of the current block according to block-based delta pulse code modulation BDPCM; encoding a BDPCM flag indicating that the BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction for the current block; as well as The intra prediction mode of the prediction direction is stored as the intra prediction mode of the current block.

15. A method for transmitting a bit stream generated by an image encoding method, the image encoding method The following steps are involved: Derives prediction samples of the current block according to block-based delta pulse code modulation BDPCM; encoding a BDPCM flag indicating that the BDPCM is applied to the current block and a BDPCM direction flag indicating a prediction direction for the current block; as well as The intra prediction mode of the prediction direction is stored as the intra prediction mode of the current block.

Images