Image decoding and encoding method and method for transmitting bit stream

Abstract

Disclosed are an image decoding and encoding method and a method for transmitting a bitstream. An image decoding method performed by a decoding apparatus according to the present document comprises the steps of: acquiring a block-based incremental pulse code modulation (BDPCM) flag indicating whether BDPCM is applied to a current block; acquiring residual information and a BDPCM direction flag indicating a prediction direction of the current block based on the BDPCM flag; deriving a prediction direction based on the BDPCM direction sign; and 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.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080048822.0 (International application number: PCT / KR2020 / 006700, application date: May 22, 2020, invention name: Method and device for decoding images using BDPCM in an image coding system). Technical Field

[0002] The present disclosure relates to an image encoding technology, and more particularly, to an image decoding method and device for encoding a current block performing BDPCM in an image encoding 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 coding efficiency.

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

[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 includes: obtaining a BDPCM flag indicating whether block-based incremental pulse code modulation (BDPCM) is applied to a current block; obtaining residual information and a BDPCM direction flag indicating a prediction direction of the current block based on the BDPCM flag; deriving a prediction direction based on the BDPCM direction flag; deriving a prediction sample of the current block by performing intra-frame prediction according to the derived prediction direction; deriving a residual sample of the current block based on the residual information; deriving a reconstructed sample of the current block based on the prediction sample and the residual sample; and storing an intra-frame prediction mode of the 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, which is configured to obtain a BDPCM flag indicating whether block-based incremental pulse code modulation (BDPCM) is applied to a current block, so as to obtain residual information and a BDPCM direction flag indicating a prediction direction of the current block based on the BDPCM flag; a predictor, which is configured to derive a prediction direction based on the BDPCM direction flag, so as to derive a prediction sample of the current block by performing intra-frame prediction according to the derived prediction direction; a residual processor, which is configured to derive a residual sample of the current block based on the residual information; an adder, which is configured to derive a reconstructed sample of the current block based on the prediction sample and the residual sample; and a memory, which is configured to store an intra-frame prediction mode of the 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: deriving a prediction sample of a current block based on block-based incremental pulse code modulation (BDPCM); deriving a residual sample of the current block based on the prediction sample; encoding residual information of the residual sample based on 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 a prediction direction derived based on the BDPCM direction flag 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 based on block-based incremental pulse code modulation (BDPCM); a subtractor configured to derive a residual sample of the current block based on the prediction sample; an entropy encoder configured to encode residual information of the residual sample based on BDPCM 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 a prediction direction derived based on the BDPCM direction flag as an intra-frame prediction mode of the current block.

[0013] Technical 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 can be improved.

[0015] According to the present disclosure, by storing the intra prediction mode according to the BDPCM prediction direction as the intra prediction mode of the current block, an accurate intra prediction mode can be referenced in the prediction of adjacent blocks, and the 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 The embodiment 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.

[0023] Figure 8 An image encoding method of an encoding device according to this document is schematically shown.

[0024] Fig. 9 A coding device for performing an image coding method according to the present document is schematically shown.

[0025] Fig.10 An image decoding method of a decoding device according to the present document is schematically illustrated.

[0026] Fig.11 A decoding device for performing an image decoding method according to the present document is schematically shown.

[0027] Fig.12 A structural diagram of a content streaming system to which the present disclosure is applied is illustrated. DETAILED DESCRIPTION

[0028] 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, numbers, steps, operations, elements, components, or combinations thereof used in the following description, and therefore it should be understood that the possibility of the presence or addition of one or more different features, numbers, steps, operations, elements, components, or combinations thereof is not excluded.

[0029] 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 embodied 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 embodiments of combining elements and / or dividing elements belong to the present disclosure without departing from the concept of the present disclosure.

[0030] 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.

[0031] Figure 1 An example of a video / image encoding device to which an embodiment of the present disclosure can be applied is briefly illustrated.

[0032] 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 send 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The transmitter may transmit the encoded image / 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.

[0037] The decoding device may decode the video / image by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0038] The renderer may render the decoded video / image. The rendered video / image may be displayed by a display.

[0039] 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.).

[0040] The present disclosure presents various embodiments of video / image encoding, and unless otherwise mentioned, the embodiments may be performed in combination with each other.

[0041] In the present disclosure, a video may refer to a series of images over time. Generally, a picture refers to a unit representing an image in a specific time zone, 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 brick 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. A tile scan may sort the CTUs partitioned in a picture in a specific order, wherein the CTUs are sorted continuously in the tile by a CTU raster scan, the tiles within the tile are sorted continuously by a raster scan of the tile, and the tiles in the picture are sorted continuously by a raster scan of the tile of the 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 ​​a picture together. A tile is a rectangular area of ​​a CTU within a specific tile column and a specific tile row in a picture. A tile 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 tile 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. Tile scanning is a specific order sorting of CTUs that partition a picture, wherein CTUs may be sorted continuously in a tile by a CTU raster scan, and tiles in a picture may be sorted continuously by a raster scan of tiles 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 multiple complete tiles or only of a complete sequence of tiles of a continuous sequence. In the present disclosure, tile groups and slices may be used interchangeably. For example, in the present disclosure, a tile group / tile group header may be referred to as a slice / slice header.

[0042] 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.

[0043] 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.

[0044] 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".

[0045] 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".

[0046] 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".

[0047] 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".

[0048] 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".

[0049] In this specification, technical features described separately in one figure may be implemented separately or may be implemented simultaneously.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The image segmenter 210 may segment 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 segmented 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 segmented into multiple 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 segmented. 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 segmented 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.

[0054] 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, and may represent a pixel / pixel value of only a luminance component, or a pixel / pixel value of only a chrominance component. A sample may be used as a term corresponding to a picture (or image) of a pixel or a pixel element.

[0055] In the encoding device 200, the prediction signal (prediction block, prediction sample array) output from the inter predictor 221 or the intra 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 encoder (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 prediction or inter 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.

[0056] The intra-frame predictor 222 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 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 block.

[0057] 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 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. 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 the 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.

[0058] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply both intra prediction and inter prediction at the same time. This may be referred to as intra-frame combined prediction (CIIP). In addition, the predictor may predict a block based on an intra-block copy (IBC) prediction mode or a palette mode. The IBC prediction mode or the palette mode may 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 may be performed similarly to inter prediction because the reference block is derived in the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. The palette mode may be considered as an example of intra coding or intra prediction. When the palette mode is applied, the sample values ​​within the picture may be signaled based on information about the palette table and the palette index.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Furthermore, during picture encoding and / or reconstruction, luma mapping and chroma scaling (LMCS) may be applied.

[0063] 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.

[0064] The modified reconstructed picture sent to the memory 270 may be used as a reference picture in the inter-frame predictor 221. When inter-frame prediction is applied by the encoding device, prediction mismatch between the encoding device 200 and the decoding device may be avoided, and encoding efficiency may be improved.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The decoding device 300 may receive the bit stream from Figure 2The received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive 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.

[0070] 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.

[0071] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0072] 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.

[0073] The predictor 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 and intra-frame combined prediction (CIIP). In addition, the predictor can predict blocks based on intra-frame block copy (IBC) prediction mode or palette mode. IBC prediction mode or 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 similar 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 this 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.

[0074] 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.

[0075] 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 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.

[0076] 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.

[0077] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra 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 prediction of the next picture.

[0078] In addition, luma mapping and chroma scaling (LMCS) may be applied in the picture decoding process.

[0079] 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). Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0080] 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 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In addition, as described above, when performing video encoding, prediction is performed to improve compression efficiency. In this way, a prediction block including prediction samples of the 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 the spatial domain (or 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 the decoding device with information about the residual between the original block and the prediction block (residual information) instead of the original sample value of the original block, thereby improving the 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.

[0085] 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 a transformation coefficient, may perform a quantization process on the transformation coefficient to derive a quantized transformation coefficient, 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 coefficient. The decoding device may perform a dequantization / inverse transformation process based on the residual information and derive a residual sample (or residual block). 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 coefficient to derive a residual block, and generate a reconstructed picture based on this.

[0086] 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 nWxnH and a total of 2xnH samples adjacent to the lower left of the current block, samples adjacent to the upper boundary of the current block and a total of 2xnW 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 adjacent samples and multiple rows of left adjacent 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 nWxnH, 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.

[0087] 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.

[0088] 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.

[0089] 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 chrominance prediction samples based on luma samples. This situation can be called LM mode or chrominance component LM (CCLM) mode.

[0090] 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).

[0091] 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.

[0092] In addition, the current block is divided into vertical or horizontal sub-partitions and intra prediction is performed 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).

[0093] 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. At the same time, if necessary, post-processing filtering may be performed on the derived prediction samples.

[0094] 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.

[0095] Figure 4 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0096] 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, adjacent reference sample derivation and prediction sample generation processes 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.

[0097] 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.

[0098] 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 in the original samples of the current block based on phase and derive the residual samples.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] Figure 5 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0103] The decoding device may perform operations corresponding to those performed by the encoding device.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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 at least one of the following: reference sample row information indicating whether MRL is applied to the current block and which reference sample row is used if applied (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. Moreover, the intra prediction type information may include a MIP flag indicating whether matrix-based intra prediction (MIP) is applied to the current block.

[0109] 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).

[0110] Figure 6 The intra prediction process is schematically shown.

[0111] 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.

[0112] Reference Figure 6 , the encoding device determines the intra-frame prediction mode / type S600.

[0113] 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.

[0114] 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.

[0115] 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 at least one of the following: reference sample row information (e.g., intra_luma_ref_idx) indicating whether MRL is applied to the current block and which reference sample row is used if applied; 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. Moreover, the intra prediction type information may include a MIP flag indicating whether matrix-based intra prediction (MIP) is applied to the current block.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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 features. Therefore, there is a high probability that the current block and the adjacent blocks have the same or similar intra-frame prediction modes. 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.

[0120] 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 encoding efficiency by considering the similarity between the current block and 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.

[0121] 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.

[0122] 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 (mpm idx) 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.

[0123] 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.

[0124] 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.

[0125] 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. At the same time, 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.

[0126] The encoding device derives neighboring reference samples of the current block (S610). When intra prediction is applied to the current block, the neighboring reference samples to be used for intra prediction of the current block can be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size nWxnH and a total of 2xnH samples adjacent to the lower left of the current block, samples adjacent to the upper boundary of the current block and a total of 2xnW 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 adjacent samples and multiple rows of left adjacent 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 nWxnH, 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.

[0127] 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. Meanwhile, when ISP is applied, the neighboring reference sample can be derived in units of sub-partitions.

[0128] 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 neighboring samples. The encoding device may derive the reference sample according to the intra prediction mode of the current block among the neighboring reference samples of the current block, and may derive the prediction sample of the current block based on the reference sample.

[0129] 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).

[0130] 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 predicted 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.

[0131] 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 row by row) using the unfiltered samples in the left or upper boundary samples (i.e., the left adjacent samples or the upper adjacent samples) or by performing intra-frame prediction in the vertical direction (copying the upper adjacent sample line to the prediction block row by row) 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.

[0132] Then, if BDPCM is applied to the quantized residual samples, we can derive As an M x N modified array of configurations

[0133] For example, when vertical BDPCM is signaled (ie, when vertical BDPCM is applied), it can be derived as in the following formula:

[0134]

[0135] 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).

[0136] 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 formula.

[0137]

[0138] 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).

[0139] Quantized residual samples can be sent to a decoding device.

[0140] 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).

[0141] The following formula can be applied to vertical prediction.

[0142]

[0143] In addition, the following formula can be applied to horizontal prediction.

[0144]

[0145] The quantized residual (Q -1 (Q(r i，j ))) is added to the intra-block prediction value to derive the reconstructed sample value.

[0146] 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.

[0147] 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 whether BDPCM is available can be signaled in a sequence parameter set (SPS), and the flag can 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.

[0148] When BDPCM is applied, intra prediction 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, i.e., the difference between the original block and the predicted block, is quantized by skipping the transform, and the 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).

[0149] 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 unfiltered reference samples by conventional horizontal or vertical intra prediction processing. In addition, the residual may be quantized, and the difference between each quantized residual and its predictor (e.g., a residual that has been quantized in the horizontal or vertical direction according to the BDPCM prediction direction) may be encoded.

[0150] Furthermore, as will be described later, the above-mentioned BDPCM is described in a standard document format.

[0151] 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.

[0152] [Table 1]

[0153]

[0154] [Table 2]

[0155]

[0156] 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.

[0157] 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.

[0158] [Table 3]

[0159]

[0160] [Table 4]

[0161]

[0162] 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.

[0163] 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.

[0164] [Table 5]

[0165]

[0166] [Table 6]

[0167]

[0168] 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.

[0169] For another 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.

[0170] Furthermore, an example of the inverse quantization process when BDPCM is applied is shown in the following table.

[0171] [Table 7]

[0172]

[0173]

[0174] Alternatively, an example of the inverse quantization process when BDPCM is applied is shown in the following table.

[0175] [Table 8]

[0176]

[0177]

[0178]

[0179]

[0180] 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).

[0181] 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.

[0182] 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] can be derived based on the residual information for the sample signaled.

[0183] 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 the 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 the residual information.

[0184] Furthermore, the present disclosure proposes the following method for a method of applying BDPCM between residual signals in a process of encoding a transform-skipped residual signal.

[0185] 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 row-by-row residual inter prediction in the row or column direction, the size of the generated level can be reduced and the generation of the context-encoded bit (bin) 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-wise prediction or column-wise prediction can be sequentially parsed. In addition, according to the existing BDPCM, if the 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 may refer to MPM candidate 0 of the block to which BDPCM is applied as the 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 an MPM list is stored as a prediction mode of a current block, a difference may occur between an intra prediction mode performed by actual prediction and the stored intra prediction mode.

[0186] Therefore, the present disclosure proposes a method for storing the intra prediction mode of the current block according to the bdpcm_dir_flag (i.e., BDPCM direction flag) which is a syntax element of the current block predicted by BDPCM. Therefore, the stored intra prediction mode of the current block can be stored in the actual prediction direction, and by this, when the MPM list is constructed by referring to the BDPCM block (i.e., the current block) in the adjacent block or the DM mode is constructed 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.

[0187] Figure 7 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.

[0188] Reference Figure 7, the decoding device may parse the bdpcm_flag of the current block (S700). The bdpcm_flag may represent a syntax element of a BDPCM flag indicating 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 a prediction direction of the current block to which BDPCM is applied.

[0189] When the value of bdpcm_flag is 1, the decoding apparatus may parse bdpcm_dir_flag of the current block (S710). bdpcm_dir_flag may represent a syntax element of a BDPCM direction flag indicating a prediction direction of the current block.

[0190] The decoding device may determine whether the value of bdpcm_dir_flag indicates a horizontal direction (S720). 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.

[0191] 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 (S730). 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. 9 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.

[0192] 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 (S740). 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.

[0193] Figure 8 An image encoding method of an encoding device according to this document is schematically shown. Figure 8 The method disclosed in can be Figure 2 Specifically, for example, Figure 8 S800 may be performed by a predictor of an encoding device, Figure 8 S810 to S820 of the encoding device may be performed by a residual processor, S830 may be performed by an entropy encoder of the encoding device, and S840 may be performed by a memory of the encoding device. In addition, although not shown in the figure, the processing for generating a reconstructed sample and a reconstructed picture of the current block based on the predicted sample and the residual sample of the current block may be performed by an adder of the encoding device.

[0194] The encoding apparatus derives prediction samples of a current block based on block-based delta pulse code modulation (BDPCM) S800.

[0195] The encoding device may determine whether BDPCM is applied to the current block, and may determine the 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 the prediction direction in which BDPCM is performed. For example, the prediction direction may be a vertical direction or a horizontal direction, and the prediction sample of the current block may be generated according to an intra-frame prediction mode based on the prediction direction.

[0196] 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 top 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 top 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 top adjacent sample of the same column as the prediction sample as the sample value of the prediction sample.

[0197] 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 separate 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 alone.

[0198] When the tree structure of the current block is a dual tree, BDPCM can 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.

[0199] Alternatively, according to an example, BDPCM can 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 can be 32, or can be set to the maximum height or maximum width of the transform block for which the transform is skipped.

[0200] The encoding apparatus derives residual samples of the current block based on the prediction samples S810. For example, the encoding apparatus may derive residual samples by subtracting original samples and prediction samples of the current block.

[0201] The encoding device encodes the residual information about the residual sample based on BDPCM S820. The image information may include the 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 that the transform is not applied 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 the 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.

[0202] 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.

[0203] 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 top 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 top 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 top adjacent residual sample of the target residual sample. In addition, when the target residual sample is located in the first row or the first 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 the first column of the current block, the syntax element of the target residual sample can represent the residual coefficient value of the target residual sample.

[0204] 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.

[0205] 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.

[0206] 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. At the same time, 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] The encoding device encodes 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 S830. The encoding device may generate and 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. The image information may include the BDPCM flag and the BDPCM direction flag.

[0211] 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 the BDPCM direction flag of the current block exists. 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 prediction, IBC prediction, palette prediction, or inter 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 the BDPCM direction flag of the current block exists. For example, the syntax element of the BDPCM flag may be bdpcm_flag, intra_bdpcm_luma_dir_flag, or intra_bdpcm_chroma_dir_flag. In addition, for example, the BDPCM flag may be signaled in units of coding units (CUs).

[0212] 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 the BDPCM direction flag and encode it. 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.

[0213] The encoding device stores the intra-frame prediction mode of the prediction direction as the intra-frame prediction mode of the current block S840. The encoding device may store the intra-frame prediction mode (vertical intra-frame prediction mode or horizontal intra-frame prediction mode) of the prediction direction as the intra-frame prediction mode of the current block. For example, when the prediction direction is the horizontal direction, the horizontal intra-frame prediction mode may be stored as the intra-frame prediction mode of the current block, and when the prediction direction is the vertical direction, the vertical intra-frame prediction mode may be stored as the intra-frame prediction mode of the current block. For example, the stored intra-frame 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-frame prediction mode may be used to derive the intra-frame prediction mode of the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components. For example, the stored intra-frame prediction mode may be used as an intra-frame prediction mode candidate for the neighboring blocks of the current block and / or the corresponding blocks of the chrominance components.

[0214] In addition, the bit stream including the image information can be transmitted 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.

[0215] Fig. 9 A coding device for performing an image coding method according to the present document is schematically shown. Figure 8 The method disclosed in can be Fig. 9 Specifically, for example, Fig. 9 The predictor of the encoding device in can perform Figure 8 S800 in Fig. 9 The residual processor of the encoding device can perform Figure 8 S810 to S820, Fig. 9 The entropy encoder of the encoding device can perform Figure 8 S830, Fig. 9 The memory of the encoding device can perform Figure 8 In addition, although not shown in the figure, 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 the adder of the encoding device.

[0216] Fig.10 An image decoding method of a decoding device according to the present document is schematically illustrated. Fig.10 The method disclosed in can be Figure 3 Specifically, for example, Fig.10 S1000 to S1010 may be performed by an entropy decoder of a decoding device, Fig.10 S1020 to S1030 may be performed by a predictor of a decoding device, Fig.10 S1040 may be executed by a residual processor of a decoding device, Fig.10 S1050 may be executed by an adder of a decoding device, Fig.10 S1060 may be executed by a memory of the decoding device.

[0217] The decoding apparatus obtains a block-based delta pulse code modulation (BDPCM) flag indicating whether BDPCM is applied to a current block S1000.

[0218] 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 the BDPCM direction flag of the current block exists. 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, IBC prediction, inter-frame prediction, or palette 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 the BDPCM direction flag of the current block exists. For example, the syntax element of the BDPCM flag may be bdpcm_flag, intra_bdpcm_luma_idr_flag, or intra_bdpcm_chroma_dir_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.

[0219] The decoding apparatus obtains residual information and a BDPCM direction flag indicating a prediction direction of the current block based on the BDPCM flag S1010.

[0220] The decoding device can obtain a BDPCM direction flag indicating the prediction direction of the current block and residual information based on the BDPCM flag. 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 a vertical direction or a 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 can indicate that the prediction direction of the current block is a horizontal direction, and when the value of the BDPCM direction flag is 1, the BDPCM direction flag can indicate that the prediction direction of the current block is a 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.

[0221] In addition, for example, the decoding device can obtain 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 syntax elements of the residual samples 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 top adjacent residual sample of the target residual sample can be derived based on the syntax elements of the target residual 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 residual sample and the residual coefficient value of the left adjacent residual sample of the target residual sample can be derived based on the syntax elements of the target residual sample. In addition, for example, when the prediction direction of the current block is derived as 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 residual sample and the residual coefficient value of the top adjacent residual sample of the target residual sample can be derived based on the syntax element of the target residual sample. In addition, when the target residual sample is located in the first row or the first 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.

[0222] 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.

[0223] Specifically, for example, the residual information may include a transform skip flag of the current block. The transform skip flag may indicate whether the transform is applied to the current block. That is, the transform skip flag may indicate whether the 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] The decoding device derives the prediction direction based on the BDPCM direction flag S1020. 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 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 a 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 a vertical direction. For example, when the value of the BDPCM direction flag is 0, the prediction direction of the current block is derived as a horizontal direction, and when the value of the BDPCM direction flag is 1, the prediction direction of the current block is derived as a vertical direction.

[0229] The decoding device derives the prediction sample of the current block by performing intra prediction according to the derived prediction direction S1030. The decoding device may derive the prediction sample of the current block by performing intra prediction according to the derived prediction direction. For example, when the prediction direction of the current block is derived as a horizontal direction, the decoding device may derive the prediction sample of the current block by performing intra 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 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 a horizontal direction, the decoding 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 decoding device may derive the prediction sample of the current block based on the top 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 top 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 top adjacent sample in the same column as the predicted sample as the sample value of the predicted sample.

[0230] The decoding apparatus derives residual samples of the current block based on the residual information S1040. The decoding apparatus may derive residual samples of the current block based on the residual information.

[0231] 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 target residual sample of the current block), and the syntax element of the target residual sample may represent a difference between a residual coefficient value of the target residual sample and a residual coefficient value of a left adjacent residual sample or a top adjacent residual sample of the target residual sample. That is, for example, when BDPCM is applied to the current block, the residual information may include a syntax element of a target residual sample of the current block, and the difference between a residual coefficient value of the target residual sample and a residual coefficient value of a left adjacent residual sample or a top adjacent residual sample of the target residual sample may be derived based on the syntax element of the target residual sample.

[0232] 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 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. That is, for example, 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 may be derived based on the syntax element of the target residual sample. Thereafter, the residual coefficient of the target residual sample may be derived as the sum of the residual coefficient value of the left adjacent residual sample of the target residual sample and the difference. Here, the target residual sample may be a residual sample in a column other than the first column in the current block. For example, the residual coefficient of the target residual sample may be derived based on Formula 4. In addition, for example, when the target residual sample is a residual sample in the first column of the current block, the residual coefficient of the target residual sample may be derived based on the syntax element of the target residual sample.

[0233] 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 residual sample may represent the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the top adjacent residual sample of the target residual sample. That is, for example, the difference between the residual coefficient value of the target residual sample and the residual coefficient value of the top adjacent residual sample of the target residual sample may be derived based on the syntax element of the target residual sample. Thereafter, the residual coefficient of the target residual sample may be derived as the sum of the residual coefficient value of the top adjacent residual sample of the target residual sample and the difference. Here, the target residual sample may be a residual sample in a row other than the first row of the current block. For example, the residual coefficient of the target residual sample may be derived based on Formula 3. In addition, for example, when the target residual sample is a residual sample in the first row of the current block, the residual coefficient of the target residual sample may be derived based on the syntax element of the target residual sample.

[0234] Then, for example, the decoding device may dequantize the residual coefficients to derive the target residual samples. That is, for example, the target residual samples may be derived by dequantizing the residual coefficients.

[0235] The decoding device derives a reconstructed sample of the current block based on the prediction sample and the residual sample S1050. For example, the decoding device can derive the reconstructed sample by adding the prediction sample and the residual sample. Subsequently, as needed, in order to improve the subjective / objective image quality, as described above, an in-loop filtering process such as deblocking filtering and SAO and / or ALF process can be applied to the reconstructed sample.

[0236] 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 S1060. 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 the 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 the 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.

[0237] Fig.11 A decoding device for performing an image decoding method according to the present document is schematically shown. Fig.10 The method disclosed in can be Fig.11 Specifically, for example, Fig.11 The entropy decoder of the decoding device can perform Fig.10 S1000 to S1010, Fig.11 The predictor of the decoding device can perform Fig.10 S1020 to S1030, Fig.11 The residual processor of the decoding device can perform Fig.10 S1040, Fig.11 The decoder device's adder can perform Fig.10 S1050, and Fig.11 The memory of the decoding device can perform Fig.10 S1060.

[0238] 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 can be improved.

[0239] Furthermore, according to the present disclosure, by storing the intra prediction mode according to the BDPCM prediction direction as the intra prediction mode of the current block, an accurate intra prediction mode can be referenced in the prediction of adjacent blocks, and the overall residual encoding efficiency can be improved.

[0240] In the above embodiments, the 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 the above-mentioned other steps or square frames 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.

[0241] 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.

[0242] 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.

[0243] 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, BD, universal serial bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and 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.

[0244] 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.

[0245] Fig.12 A structural diagram of a content streaming system to which the present disclosure is applied is illustrated.

[0246] The content streaming system to which the embodiments of this document 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.

[0247] The encoding server compresses the content input from the multimedia input device such as a smartphone, camera or camcorder into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, when the multimedia input device such as a smartphone, camera or camcorder directly generates the bitstream, the encoding server can be omitted.

[0248] 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.

[0249] 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 delivers 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.

[0250] 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 period of time.

[0251] 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.

[0252] 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: Obtaining a BDPCM flag indicating whether block-based delta pulse code modulation (BDPCM) is applied to a current block from a bit stream; Obtaining residual information and a BDPCM direction flag indicating a prediction direction for the current block from the bitstream based on the BDPCM flag; deriving the prediction direction based on the BDPCM direction flag; deriving a prediction sample of the current block by performing intra prediction according to the derived prediction direction; Deriving residual samples of the current block by performing inverse quantization on the residual information; Derived a reconstructed sample of the current block based on the predicted sample and the residual sample; 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, Wherein, based on the BDPCM being applied to the current block, the transformation of the current block is skipped.

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

3. The image decoding method according to claim 2, in, When the value of the BDPCM direction flag is 0, the BDPCM direction flag indicates that the prediction direction for the current block is a horizontal direction. When the value of the BDPCM direction flag is 1, the BDPCM direction flag indicates that the prediction direction for the current block is a vertical direction.

4. The image decoding method according to claim 3, 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 of a target residual sample for the current block, 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 top neighboring residual sample of the target residual sample.

5. The image decoding method according to claim 4, in, deriving the difference based on the syntax element for the target residual sample, The residual coefficient of the target residual sample is derived as the sum of the residual coefficient values ​​of the top adjacent residual samples and the difference.

6. The image decoding method according to claim 3, in, When the BDPCM is applied to the current block and 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, 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-neighboring residual sample of the target residual sample.

7. The image decoding method according to claim 6, in, The difference is derived based on the syntax element for the target residual sample, The residual coefficient of the target residual sample is derived as the sum of the residual coefficient value of the left adjacent residual sample and the difference.

8. The image decoding method according to claim 3, in, When the prediction direction is the horizontal direction, a horizontal intra prediction mode is stored as the intra prediction mode of the current block, and When the prediction direction is the vertical direction, a vertical intra prediction mode is stored as the intra prediction mode of the current block.

9. 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.

10. 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 based on block-based delta pulse code modulation BDPCM; deriving residual samples of the current block based on the prediction samples; deriving residual information by performing quantization on the residual samples; encoding the residual information for the residual samples into a bitstream based on the BDPCM; encoding into the bitstream a BDPCM flag indicating that the BDPCM applies to the current block and a BDPCM direction flag indicating a prediction direction for the current block; as well as storing an intra prediction mode derived based on the prediction direction for the current block as the intra prediction mode of the current block, Wherein, based on the BDPCM being applied to the current block, the transformation of the current block is skipped.

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

12. The image encoding method according to claim 11, in, When the value of the BDPCM direction flag is 0, the BDPCM direction flag indicates that the prediction direction for the current block is a horizontal direction. When the value of the BDPCM direction flag is 1, the BDPCM direction flag indicates that the prediction direction for the current block is a vertical direction.

13. The image encoding method according to claim 12, 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 of a target residual sample for the current block, 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 top neighboring residual sample of the target residual sample.

14. The image encoding method according to claim 12, in, When the BDPCM is applied to the current block and 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, 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-neighboring residual sample of the target residual sample.

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 based on block-based delta pulse code modulation BDPCM; deriving residual samples of the current block based on the prediction samples; deriving residual information by performing quantization on the residual samples; encoding the residual information for the residual samples into the bitstream based on the BDPCM; encoding into the bitstream a BDPCM flag indicating that the BDPCM applies to the current block and a BDPCM direction flag indicating a prediction direction for the current block; as well as storing an intra prediction mode derived based on the prediction direction for the current block as the intra prediction mode of the current block, Wherein, based on the BDPCM being applied to the current block, the transformation of the current block is skipped.

Images