Image decoding method and apparatus therefor

Abstract

The invention relates to an image decoding method and an apparatus therefor. A method for decoding an image according to a decoding device of the document comprises the following steps: acquiring image information; and generating a reconstructed picture based on the image information.

Description

[0001] This application is a divisional application of a patent application with application number 202080058222.2 (PCT / KR2020 / 011086), which was submitted to the China Patent Office on February 17, 2022, with an international application date of August 20, 2020, and the invention name is “Image decoding method and device thereof”. Technical Field

[0002] The present document relates to image coding technology, and more particularly, to an image decoding method for coding CU-level chroma quantization parameter offset related information in an image coding system, and a device used for the image decoding method. 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 sent 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 increasing data coding efficiency for deriving quantization parameters of chrominance components.

[0008] Technical Solution

[0009] According to an embodiment of this document, an image decoding method performed by a decoding device is provided. The method includes: obtaining image information, and generating a reconstructed picture based on the image information, wherein the process of obtaining the image information includes obtaining prediction information and residual information for a current chroma block, and obtaining coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on the size and tree type of the current chroma block, wherein the CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current chroma block.

[0010] According to another embodiment of this document, a decoding device for performing image decoding is provided. The decoding device includes: an entropy decoder configured to obtain image information; and a residual processor configured to generate a reconstructed picture based on the image information, wherein the entropy decoder obtains prediction information and residual information for a current chroma block, and obtains coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on a tree type and size of the current chroma block, wherein the CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current chroma block.

[0011] According to another embodiment of this document, a video encoding method performed by an encoding device is provided. The method includes: deriving prediction samples and residual samples for a current chroma block, generating a reconstructed picture based on the prediction samples and the residual samples, and encoding image information, wherein the process of encoding the image information includes generating prediction information for the current chroma block, generating coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on the tree type and size of the current chroma block, deriving chroma QP for the current chroma block based on CU chroma QP offset related information, deriving transform coefficients for the current chroma block by quantizing the residual samples based on the chroma QP, generating residual information for the transform coefficients, and encoding image information including CU chroma QP offset related information, prediction information, and residual information, wherein the CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current chroma block.

[0012] According to another embodiment of this document, a video encoding device is provided. The encoding device includes: a residual processor configured to derive prediction samples and residual samples for a current chroma block; an adder configured to generate a reconstructed picture based on the prediction samples and the residual samples; and an entropy encoder configured to encode image information, wherein the entropy encoder generates prediction information for the current chroma block, generates coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on a tree type and a size of the current chroma block, derives a chroma QP for the current chroma block based on the CU chroma QP offset related information, derives a transform coefficient for the current chroma block by quantizing the residual samples based on the chroma QP, generates residual information for the transform coefficient, and encodes image information including CU chroma QP offset related information, prediction information, and residual information, wherein the CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current chroma block.

[0013] According to another embodiment of this document, a computer-readable digital storage medium is provided, which stores a bit stream including image information for causing a decoding device to perform an image decoding method. In the computer-readable storage medium, the image decoding method includes: obtaining image information, and generating a reconstructed picture based on the image information, wherein the process of obtaining the image information includes obtaining prediction information and residual information for a current chroma block, and obtaining coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on a tree type and size of the current chroma block, wherein the CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current chroma block.

[0014] Beneficial Effects

[0015] According to this document, even if the first transform block in the current chroma block does not include a non-zero transform coefficient level, and when at least one of the width and height of the current chroma block is greater than a specific size, information about the CU chroma QP offset can be sent by a signal, thereby reducing the cost of configuring the decoding device.

[0016] According to this document, even if the first transform block in the current chroma block does not include a non-zero transform coefficient level, information about the CU chroma QP offset can be signaled in the transform unit syntax of the first transform block based on the size and tree type of the current chroma block, and therefore, the cache requirements of the decoding device can be reduced and the cost of configuring the decoding device can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 An example of a video / image coding device to which embodiments of the present disclosure can be applied is briefly illustrated.

[0018] 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.

[0019] 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.

[0020] Figure 4 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0021] Figure 5 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0022] Figure 6 The intra prediction process is schematically shown.

[0023] Figure 7 An example of a video / image encoding method based on inter-frame prediction is illustrated.

[0024] Figure 8 An example of a video / image decoding method based on inter-frame prediction is illustrated.

[0025] Fig. 9 The inter-frame prediction process is schematically illustrated.

[0026] Fig.10 An example of transmitting cu_qp_delta for a TU within a CU having a size of 128×128 is shown.

[0027] Fig.11 Shows an example of a QP map for luma blocks and chroma blocks when a single tree is used.

[0028] Fig.12 Shows an example of a QP map for a chroma block when dual trees are used.

[0029] Fig.13 The sample positions used for deblocking filtering are exemplarily indicated.

[0030] Fig.14 The image encoding method of the encoding device according to this document is schematically shown.

[0031] Fig.15 A coding device for performing an image coding method according to the present document is schematically shown.

[0032] Fig.16 The image decoding method of the decoding device according to this document is schematically shown.

[0033] Fig.17 A decoding device for performing an image decoding method according to the present document is schematically shown.

[0034] Fig.18 The present invention is a structural diagram of a content streaming system to which the present invention is applied. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Figure 1 An example of a video / image coding device to which embodiments of the present disclosure can be applied is briefly illustrated.

[0039] refer to 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.

[0040] 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.

[0041] The video source may acquire 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.

[0042] 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 bit stream.

[0043] The transmitter may transmit the encoded image / image information or data output in the form of a bit stream to a receiver of a receiving device in the form of a file or stream via 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 via a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0044] 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.

[0045] The renderer may render the decoded video / image. The rendered video / image may be displayed by a display.

[0046] 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.).

[0047] The present disclosure presents various embodiments of video / image coding, and unless otherwise mentioned, the embodiments may be performed in combination with each other.

[0048] 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.

[0049] A pixel or a picture element (pel) may represent the smallest unit constituting a picture (or image). In addition, "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.

[0050] 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.

[0051] 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".

[0052] A slash ( / ) or a comma used in this specification may mean "and / or". For example, "A / B" may mean "A and / or B". Therefore, "A / B" may mean "only A", "only B", or "A and B". For example, "A, B, C" may mean "A, B, or C".

[0053] 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".

[0054] 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".

[0055] 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 (ie, intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction".

[0056] In this specification, technical features described separately in one figure may be implemented separately or may be implemented simultaneously.

[0057] 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.

[0058] 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.

[0059] refer to 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 the memory 270 as an internal / external component.

[0060] The image divider 210 may divide the input image (or picture or frame) input to the encoding device 200 into one or more processors. For example, the processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, a coding unit may be divided into a plurality of coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, a quadtree structure may be applied first, and then a binary tree structure and / or a ternary structure may be applied. Alternatively, a binary tree structure may be applied first. The coding process according to the present disclosure may be performed based on a final coding unit that is no longer divided. In this case, the maximum coding unit may be used as the final coding unit based on coding efficiency according to image characteristics, or if necessary, the coding unit may be recursively divided into coding units with a deeper depth and a coding unit with an optimal size may be used as the final coding unit. Here, the coding 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 split or partitioned from the above-mentioned final coding unit. The prediction unit may be a unit of 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 a transform coefficient.

[0061] 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 luma component, or a pixel / pixel value of only a chroma component. A sample may be used as a term corresponding to a picture (or image) of a pixel or a pixel element.

[0062] In the encoding device 200, a 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 200 can be called a subtractor 231. The predictor can perform prediction on a block to be processed (hereinafter referred to as a current block) and generate a prediction block including prediction samples 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. Information about the prediction can be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0063] 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 neighboring blocks.

[0064] 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 the motion information between the neighboring 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 neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a co-located CU (colCU), etc., and the reference picture including the temporal neighboring 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 neighboring 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.

[0065] 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 coding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but IBC 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.

[0066] 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 other than square.

[0067] 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. Encoding 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 the encoding device to the decoding device may be included in the video / picture information. The video / image information may be encoded and included in the 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) that sends a signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores 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.

[0068] 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.

[0069] Furthermore, during picture encoding and / or reconstruction, luma mapping and chroma scaling (LMCS) may be applied.

[0070] 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.

[0071] 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 coding efficiency may be improved.

[0072] 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 spatially adjacent block or motion information of a temporally adjacent 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.

[0073] 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.

[0074] refer to 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 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 the memory 360 as an internal / external component.

[0075] When a bit stream including video / image information is input, the decoding apparatus 300 can be used with Figure 2 The image is reconstructed corresponding 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 divided 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.

[0076] The decoding device 300 may receive the bit stream from Figure 2The received signal may be decoded by the entropy decoder 310. For example, the entropy decoder 310 may 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 syntax elements required for image reconstruction and quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method may receive a bin (binary bit) corresponding to each syntax element in the bitstream, determine a context model using information of a decoding target syntax element, information of a decoding target block, or information of a symbol / bin decoded in a previous stage, 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 may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin. Information related to prediction among the information decoded by the entropy decoder 310 may be provided to the predictor (inter-frame predictor 332 and intra-frame predictor 331), and the residual value (that is, quantized transform coefficient and related parameter information) on which entropy decoding is performed in the entropy decoder 310 may be input to the residual processor 320. The residual processor 320 may 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 may 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.

[0077] 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 dequantize the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0078] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0079] 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.

[0080] The predictor 320 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 intra prediction and inter prediction at the same time. This may be referred to as combined inter and intra 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 coding of games, etc., such as screen content coding (SCC). IBC basically performs prediction in the current picture, but IBC may be performed similarly to inter prediction because a 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 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.

[0081] 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.

[0082] 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 neighboring 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 neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter-frame predictor 332 may configure a motion information candidate list based on neighboring blocks, and derive a motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-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.

[0083] 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.

[0084] 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.

[0085] Additionally, luminance mapping and chroma scaling (LMCS) can be applied during picture decoding.

[0086] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 360 (specifically, the DPB of the memory 360). The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0087] 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 260 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.

[0088] 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.

[0089] 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.

[0090] 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 the 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.

[0091] At the same time, as described above, when performing video coding, 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 coded (ie, a coding 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 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.

[0092] The residual information may be generated through 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 residual samples (or residual blocks). The decoding device may generate a reconstructed picture based on the prediction block and the residual block. In addition, for reference for 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.

[0093] 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.

[0094] 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.

[0095] When deriving neighboring reference samples, (i) the prediction sample may be derived based on an average or interpolation of neighboring reference samples of the current block, or (ii) the prediction sample may be derived based on a reference sample existing in a specific (prediction) direction relative to the prediction sample 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.

[0096] In addition, the prediction sample can be generated by interpolating the first neighboring sample located in the prediction direction of the intra prediction mode of the current block based on the prediction sample of the current block among the adjacent reference samples and the second neighboring sample located in the direction opposite to the prediction direction. The above situation can be called linear interpolation intra prediction (LIP). In addition, a linear model (LM) can be used to generate chroma prediction samples based on luma samples. This situation can be called LM mode or chroma component LM (CCLM) mode.

[0097] In addition, a 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 weighting and 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).

[0098] 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 encoding 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.

[0099] 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).

[0100] 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.

[0101] 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.

[0102] Figure 4 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0103] refer to 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 may be performed simultaneously, or one process may be performed before the other. The encoding device may determine a mode / type to be applied to the current block from a plurality of intra prediction modes / types. The encoding device may compare the RD costs of the intra prediction modes / types and determine the optimal intra prediction mode / type for the current block.

[0104] At the same time, 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.

[0105] The encoding apparatus generates residual samples of the current block based on the (filtered) prediction samples (S410). The encoding apparatus may compare the prediction samples among the original samples of the current block based on a phase and derive the residual samples.

[0106] 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.

[0107] The residual information may include a residual coding 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.

[0108] At the same time, 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.

[0109] Figure 5 An example of a video / image encoding method based on intra-frame prediction is illustrated.

[0110] The decoding device may perform operations corresponding to those performed by the encoding device.

[0111] 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.

[0112] 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.

[0113] The decoding device generates residual samples for the current block based on the received residual information (S530). The decoding device may generate reconstructed samples of the current block based on the prediction samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S540). A reconstructed picture of the current picture may be generated based on the reconstructed block. As described above, the in-loop filtering process may be further applied to the reconstructed picture.

[0114] 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 remaining 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 remaining 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-frame prediction type information can be implemented in various forms. For example, the intra-frame prediction type information may include intra-frame prediction type index information indicating one of the intra-frame prediction types. As another example, the intra-frame prediction type information may include at least one of the following: reference sample line information (e.g., intra_luma_ref_idx), which indicates whether MRL is applied to the current block, and, if applied, which reference sample line is used; ISP flag information, indicating whether ISP is applied to the current block (example: intra_subpartitions_mode_flag); or ISP type information, indicating the partition type of the sub-partition when ISP is applied (example: intra_subpartitions_split_flag). In addition, the intra-frame prediction type information may include a MIP flag indicating whether matrix-based intra-frame prediction (MIP) is applied to the current block.

[0116] The intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by the coding 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 (eg, CABAC, CAVLC).

[0117] Figure 6 The intra prediction process is schematically shown.

[0118] refer to Figure 6 As 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 coding device may include an encoding device and / or a decoding device.

[0119] refer to Figure 6 , the coding device determines the intra-frame prediction mode / type S600.

[0120] The encoding device may determine the intra-prediction mode / type applied to the current block from the various intra-prediction modes / types described above, and may generate prediction related information. The prediction related information may include intra-prediction mode information indicating the intra-prediction mode applied to the current block and / or intra-prediction type information indicating the intra-prediction type applied to the current block. The decoding device may determine the intra-prediction mode / type applied to the current block based on the prediction related information.

[0121] 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.

[0122] In addition, the intra-frame prediction type information can be implemented in various forms. For example, the intra-frame prediction type information may include intra-frame prediction type index information indicating one of the intra-frame prediction types. As another example, the intra-frame prediction type information may include at least one of the following: reference sample line information (e.g., intra_luma_ref_idx), which indicates whether MRL is applied to the current block, and, if applied, which reference sample line is used; ISP flag information, indicating whether ISP is applied to the current block (example: intra_subpartitions_mode_flag); or ISP type information, indicating the partition type of the sub-partition when ISP is applied (example: intra_subpartitions_split_flag). In addition, the intra-frame prediction type information may include a MIP flag indicating whether matrix-based intra-frame prediction (MIP) is applied to the current block.

[0123] For example, when intra prediction is applied, the intra prediction mode of the neighboring block may be used to determine the intra prediction mode applied to the current block. For example, the coding device may select one of the most likely mode (MPM) candidates in the MPM list derived based on the intra prediction mode of the neighboring blocks (e.g., left and / or upper neighboring blocks) of the additional candidate mode and / or the current block, or select one of the remaining intra prediction modes not included in the MPM candidate (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-plane flag may be signaled. Furthermore, when the value of the non-plane flag is 1, the MPM index may be signaled. Here, the fact that the MPM list is configured not to include the plane mode as a candidate is that the plane mode is always considered as the MPM rather than considering that the plane mode is not the MPM, and therefore, the flag (non-plane flag) is signaled first to check whether it is the plane mode.

[0124] 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.

[0125] When a MIP is applied to a 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.

[0126] In other words, in general, when performing block segmentation of an image, the current block to be coded and the neighboring blocks have similar image features. Therefore, the possibility that the current block and the neighboring blocks have the same or similar intra-frame prediction mode is high. Therefore, the encoder can use the intra-frame prediction mode of the neighboring block to encode the intra-frame prediction mode of the current block.

[0127] The coding device may construct a most probable mode (MPM) list for the current block. The MPM list may be referred to as an MPM candidate list. Here, MPM may refer to a mode for improving coding efficiency by considering the similarity between the current block and the neighboring blocks during intra-frame prediction mode coding. As described above, the MPM list may be constructed to include a planar mode, or may be constructed to exclude a planar mode. For example, when the MPM list includes a planar mode, the number of candidates in the MPM list may be 6. And when the MPM list does not include a planar mode, the number of candidates in the MPM list may be 5.

[0128] The encoding device may perform prediction based on various intra prediction modes, and may determine the best intra prediction mode based on rate distortion optimization (RDO) therefrom. In this case, the encoding device may determine the best intra prediction mode by using only the MPM candidates and plane mode configured in the MPM list, or by further using the remaining intra prediction modes and the MPM candidates and 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 best intra prediction mode by considering only the MPM candidates and 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 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.

[0129] Meanwhile, generally, when the intra prediction mode of the current block is not the planar 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 planar mode). The MPM residual information may include, for example, an intra_luma_mpm_remainder syntax element.

[0130] 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 neighboring blocks, or may further include a specific intra-frame prediction mode according to a predetermined method.

[0131] 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 (based on the non-planar flag) derive the plane mode as the intra prediction mode of the current block, 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 represent only 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.

[0132] For another example, when the value of the MPM flag is 0, the decoding device can derive the intra prediction mode indicated by the remaining intra prediction mode information (which can be referred to as mpm residual 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 can 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.

[0133] The coding device derives neighboring reference samples of the current block (S610). When intra prediction is applied to the current block, neighboring reference samples to be used for intra prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block of size 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 neighboring samples and multiple rows of left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size 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.

[0134] 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.

[0135] The coding device derives a prediction sample by performing intra prediction on the current block (S620). The coding device may derive the prediction sample based on the intra prediction mode / type and the neighboring samples. The coding 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.

[0136] Meanwhile, when inter-frame prediction is applied, the predictor of the encoding device / decoding device may derive prediction samples by performing inter-frame prediction in units of blocks. When prediction is performed on the current block, inter-frame prediction may be applied. That is, the predictor of the encoding / decoding device (more specifically, the inter-frame predictor) may derive prediction samples by performing inter-frame prediction in units of blocks. Inter-frame prediction may represent a prediction derived by a method depending on data elements (e.g., sample values ​​or motion information) of (one or more) pictures other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of applying inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same as or different from each other. The temporal neighboring block may be referred to as a name such as a collocated reference block, a collocated CU (ColCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (ColPic). For example, a motion information candidate list may be configured based on the neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) may be signaled to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes, and, for example, in the case of a skip mode and a merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block. In the case of the skip mode, unlike the merge mode, a residual signal may not be sent. In the case of the motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived by using the sum of the motion vector predictor and the motion vector difference.

[0137] According to the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may further include L0 motion information and / or L1 motion information. The L0 direction motion vector may be referred to as the L0 motion vector or MVL0, and the L1 direction motion vector may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bi-prediction. Here, the L0 motion vector may indicate a motion vector associated with the reference picture list L0, and the L1 motion vector may indicate a motion vector associated with the reference picture list L1. The reference picture list L0 may include pictures before the current picture in output order, and the reference picture list L1 may include pictures after the current picture in output order as reference pictures. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may further include pictures after the current picture in output order as reference pictures. In this case, the previous picture may be indexed first in the reference picture list L0, and then the subsequent picture may be indexed. The reference picture list L1 may further include a picture before the current picture in the output order as a reference picture. In this case, the subsequent picture may be indexed first in the reference picture list L1, and then the previous picture may be indexed. Here, the output order may correspond to a picture sequence count (POC) order.

[0138] The video / image encoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0139] Figure 7 An example of a video / image encoding method based on inter-frame prediction is illustrated.

[0140] The encoding device performs inter prediction on the current block (S700). The encoding device may derive the inter prediction mode and motion information of the current block, and generate a prediction sample of the current block. Here, the inter prediction mode determination process, the motion information derivation process, and the prediction sample generation process may be performed simultaneously, and any one process may be performed earlier than the other processes. For example, the inter prediction unit of the encoding device may include a prediction mode determination unit, a motion information derivation unit, and a prediction sample derivation unit, and the prediction mode determination unit may determine the prediction mode of the current block, the motion information derivation unit may derive the motion information of the current block, and the prediction sample derivation unit may derive the prediction sample of the current block. For example, the inter prediction unit of the encoding device may search for a block similar to the current block in a predetermined area (search area) of the reference picture through motion estimation, and derive a reference block with the smallest difference from the current block or equal to or less than a predetermined criterion. A reference picture index indicating the reference picture where the reference block is located may be derived based on this, and a motion vector may be derived based on the position difference between the reference block and the current block. The encoding device may determine a mode applied to the current block among various prediction modes. The encoding apparatus may compare the RD costs of various prediction modes and determine an optimal prediction mode for the current block.

[0141] For example, when the skip mode or merge mode is applied to the current block, the encoding device may configure a merge candidate list to be described below, and derive a reference block having the smallest difference with the current block or being equal to or less than a predetermined criterion among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the current block may be derived by using the motion information of the selected merge candidate.

[0142] As another example, when the (A) MVP mode is applied to the current block, the encoding device may configure the (A) MVP candidate list to be described below, and use the motion vector of the selected MVP candidate among the motion vector predictor (MVP) candidates included in the (A) MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by motion estimation may be used as the motion vector of the current block, and the MVP candidate having the motion vector with the minimum difference from the motion vector of the current block among the MVP candidates may become the selected MVP candidate. A motion vector difference (MVD) may be derived, which is the difference obtained by subtracting the MVP from the motion vector of the current block. In this case, information about the MVD may be signaled to the decoding device. In addition, when the (A) MVP mode is applied, the value of the reference picture index may be configured as reference picture index information and signaled to the decoding device separately.

[0143] The encoding apparatus may derive residual samples based on the prediction samples (S710). The encoding apparatus may derive residual samples by comparing original samples and prediction samples of the current block.

[0144] The encoding device encodes the image information including prediction information and residual information (S720). The encoding device can output the encoded image information in the form of a bitstream. The prediction information may include information about prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information as information related to the prediction process. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index), which is information for deriving a motion vector. In addition, the information about the motion information may include information about the MVD and / or reference picture index information. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or dual prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0145] The output bitstream may be stored in a (digital) storage medium and transmitted to a decoding device, or transmitted to a decoding device via a network.

[0146] At the same time, as described above, the encoding device can generate a reconstructed picture (including a reconstructed sample and a reconstructed block) based on the reference sample and the residual sample. This is to derive the same prediction result as the prediction result performed by the decoding device, and as a result, the coding efficiency can be improved. Therefore, the encoding device can store the reconstructed picture (or the reconstructed sample or the reconstructed block) in a memory and use the reconstructed picture as a reference picture. As described above, the in-loop filtering process can be further applied to the reconstructed picture.

[0147] The video / image decoding process based on inter-frame prediction may schematically include, for example, the following contents.

[0148] Figure 8 An example of a video / image decoding method based on inter-frame prediction is illustrated.

[0149] refer to Figure 8 The decoding device may perform an operation corresponding to the operation performed by the encoding device. The decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0150] Specifically, the decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S800). The decoding apparatus may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

[0151] For example, it may be determined whether to apply the merge mode or (A) MVP mode to the current block based on the merge flag. Alternatively, one of various inter prediction mode candidates may be selected based on the mode index. The inter prediction mode candidate may include a skip mode, a merge mode, and / or a (A) MVP mode, or may include various inter prediction modes described below.

[0152] The decoding device derives motion information of the current block based on the determined inter prediction mode (S810). For example, when the skip mode or the merge mode is applied to the current block, the decoding device may configure a merge candidate list to be described below, and select a merge candidate from among the merge candidates included in the merge candidate list. Here, the selection may be performed based on the selection information (merge index). The motion information of the current block may be derived by using the motion information of the selected merge candidate. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0153] As another example, when the (A) MVP mode is applied to the current block, the decoding device may configure the (A) MVP candidate list to be described below, and use the motion vector of the selected MVP candidate among the motion vector predictor (MVP) candidates included in the (A) MVP candidate list as the MVP of the current block. Here, the selection may be performed based on the selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list of the current block may be derived as the reference picture referenced by the inter-frame prediction of the current block.

[0154] Meanwhile, as described below, the motion information of the current block may be derived without the candidate list configuration, and in this case, the motion information of the current block may be derived according to the process disclosed in the prediction mode. In this case, the candidate list configuration may be omitted.

[0155] The decoding device may generate a prediction sample for the current block based on the motion information of the current block (S820). In this case, a reference picture may be derived based on a reference picture index of the current block, and a prediction sample of the current block may be derived by using a sample of the reference block indicated by a motion vector of the current block on the reference picture. In this case, in some cases, a prediction sample filtering process for all or some prediction samples of the current block may be further performed.

[0156] For example, the inter-frame prediction unit of the decoding device may include a prediction mode determination unit, a motion information export unit and a prediction sample export unit, and the prediction mode determination unit can determine the prediction mode of the current block based on the received prediction mode information, the motion information export unit can export the motion information (motion vector and / or reference picture index) of the current block based on the information about the received motion information, and the prediction sample export unit can export the prediction sample of the current block.

[0157] The decoding device generates residual samples of the current block based on the received residual information (S830). The decoding device may generate reconstructed samples of the current block based on the predicted samples and the residual samples, and generate a reconstructed picture based on the generated reconstructed samples (S840). Thereafter, as described above, the in-loop filtering process may be further applied to the reconstructed picture.

[0158] Fig. 9 The inter-frame prediction process is schematically illustrated.

[0159] refer to Fig. 9 As described above, the inter-frame prediction process may include an inter-frame prediction mode determination step, a motion information derivation step according to the determined prediction mode, and a prediction processing (prediction sample generation) step based on the derived motion information. The inter-frame prediction process may be performed by the encoding device and the decoding device as described above. In this article, the coding device may include an encoding device and / or a decoding device.

[0160] refer to Fig. 9 , the coding device determines the inter prediction mode of the current block (S900). Various inter prediction modes may be used for the prediction of the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, merge with MVD (MMVD) mode, and historical motion vector prediction (HMVP) mode may be used. Decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, dual prediction with CU-level weights (BCW), and bidirectional optical flow (BDOF) may be further used as additional modes. Affine mode may also be referred to as affine motion prediction mode. MVP mode may also be referred to as advanced motion vector prediction (AMVP) mode. In this article, some modes and / or motion information candidates derived from some modes may also be included in one of the motion information-related candidates in other modes. For example, an HMVP candidate may be added to a merge candidate of a merge / skip mode, or to an MVP candidate of an MVP mode. If the HMVP candidate is used as a motion information candidate for a merge mode or a skip mode, the HMVP candidate may be referred to as an HMVP merge candidate.

[0161] Prediction mode information indicating the inter-frame prediction mode of the current block can be signaled from the encoding device to the decoding device. In this case, the prediction mode information can be included in the bitstream and received by the decoding device. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter-frame prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, whether the skip mode is applied can be indicated by signaling a skip flag, when the skip mode is not applied, whether the merge mode is applied can be indicated by signaling a merge flag, and when the merge mode is not applied, the MVP mode is indicated to be applied or a flag for additional distinction can be further signaled. The affine mode can be signaled as an independent mode, or signaled as a subordinate mode with respect to the merge mode or the MVP mode. For example, the affine mode may include an affine merge mode and an affine MVP mode.

[0162] The coding apparatus derives motion information of a current block (S910). The motion information may be derived based on an inter prediction mode.

[0163] The coding device may perform inter-frame prediction using the motion information of the current block. The coding device may derive the best motion information of the current block through a motion estimation process. For example, the coding device may search for a similar reference block with high correlation in units of fractional pixels within a predetermined search range in a reference picture by using an original block in an original picture of the current block, and derive motion information through the searched reference block. The similarity of the blocks may be derived based on the difference in sample values ​​based on the phase. For example, the similarity of the blocks may be calculated based on the sum of absolute differences (SAD) between the current block (or the template of the current block) and the reference block (or the template of the reference block). In this case, the motion information may be derived based on the reference block with the smallest SAD in the search area. The derived motion information may be signaled to the decoding device according to various methods based on the inter-frame prediction mode.

[0164] The coding apparatus performs inter prediction based on the motion information of the current block (S920). The coding apparatus may derive (one or more) prediction samples of the current block based on the motion information. The current block including the prediction samples may be referred to as a prediction block.

[0165] Meanwhile, as described above, the quantizer of the encoding device may derive quantized transform coefficients by applying quantization to the transform coefficients. The dequantizer of the encoding device or the dequantizer of the decoding device may derive transform coefficients by applying dequantization to the quantized transform coefficients.

[0166] Generally, in video / image coding, the quantization ratio can be changed, and the compression rate can be adjusted using the changed quantization ratio. In terms of implementation, a quantization parameter (QP) can be used by considering complexity instead of directly using the quantization ratio. For example, a quantization parameter having an integer value of 0 to 63 can be used, and each quantization parameter value can correspond to an actual quantization ratio. In addition, for example, the quantization parameter QP for the luminance component Y and the quantization parameter QP for the chroma components C Can be configured differently.

[0167] In the quantization process, the transform coefficients C can be input, and the quantization ratio (Q step ) can be divided, and the quantized transform coefficient C' can be obtained based on the quantization ratio. In this case, by multiplying the quantization ratio by the scale in consideration of computational complexity, the quantization ratio can be generated in an integer form, and the shift operation can be performed by a value corresponding to the scale value. The quantization scale can be derived based on the product of the quantization ratio and the scale value. That is, the quantization scale can be derived based on the QP. For example, the quantization scale can be applied to the transform coefficient C', and the quantized transform coefficient C' can be derived based on the result of the application.

[0168] The dequantization process is the inverse process of the quantization process. In this process, the quantized transform coefficient C' can be multiplied by the quantization ratio (Q step ), and the reconstructed transform coefficient C'' can be obtained based on the result of the multiplication. In this case, the level scale can be derived based on the quantization parameter, the level scale can be applied to the quantized transform coefficient C', and the reconstructed transform coefficient C'' can be derived. Due to losses in the transformation and / or quantization process, the reconstructed transform coefficient C'' may be slightly different from the first transform coefficient C. Therefore, dequantization is performed in the encoding device as in the decoding device.

[0169] At the same time, an adaptive frequency weighted quantization technique for adjusting the quantization strength according to the frequency may be applied. The adaptive frequency weighted quantization technique is a method of applying the quantization strength differently to each frequency. In the adaptive frequency weighted quantization, the quantization strength for each frequency may be applied differently using a predefined quantization scaling matrix. That is, the above-mentioned quantization / dequantization process may be performed based on the quantization scaling matrix. For example, in order to generate the size of the current block and / or the residual signal of the current block, different quantization scaling matrices may be used depending on whether the prediction mode applied to the current block is inter-frame prediction or intra-frame prediction. The quantization scaling matrix may be referred to as a quantization matrix or a scaling matrix. The quantization scaling matrix may be predefined. In addition, for frequency adaptive scaling, quantization scale information for each frequency of the quantization scaling matrix may be constructed / encoded in the encoding device and signaled to the decoding device. The quantization scale information for each frequency may be referred to as quantization scaling information. The quantization scale information for each frequency may include scaling list data (scaling_list_data). The (modified) quantization scaling matrix may be derived based on the scaling list data. In addition, the quantization scale information for each frequency may include presence flag information indicating whether the scaling list data exists. Alternatively, if the scaling list data is signaled in a higher level (eg, SPS), information indicating whether the scaling list data is modified in a lower level in the higher level (eg, PPS or tile group header, etc.) may also be included.

[0170] As in the foregoing, quantization / dequantization may be applied to luma components and chroma components based on quantization parameters.

[0171] Meanwhile, for quantization groups in current video / image coding standards, information about luma QP may be signaled as delta Qp relative to the previous QP, and transmission of the information may be delayed until the first transform unit has coded coefficients. Specifically, the syntax element cu_qp_delta indicating delta QP may be transmitted in the first transform unit (ie, tu_cbf=1) of the quantization group having coded coefficients.

[0172] Fig.10 An example of sending cu_qp_delta for TUs within a CU having a size of 128×128 is shown. Fig.10 As shown in , in the case of a large-sized CU, the delta QP may not be sent until the last TU in the coding order. However, the delta QP value sent for the last TU may apply to the entire CU.

[0173] In addition, the concept of a 64x64 virtual decoder pipeline unit (VDPU) can be used in current video / image coding standards. In particular, in current video / image coding standards, structures and syntax elements for maximum transform size, luma / chroma syntax interleaving, etc. can be designed so that the decoding device can process 64x64-sized blocks (i.e., VDPU) at a time, even in a large CU with a maximum size of 128x128. Considering the buffering requirements of a 128x128 pipeline, using a 64x64 pipeline can significantly reduce the cost of the decoding device.

[0174] However, the incremental QP design in VVC standard draft 5 and earlier standards is not applicable to the 64x64 pipeline concept. Because the in-loop filtering requires a QP value, the absence of a QP value may mean that the processing of the previous TU of the CU cannot be completed.

[0175] Specifically, the deblocking filter may need QP to determine the filtering threshold. Therefore, in the VVC standard draft 6, conditions are added to the incremental QP signaling. Specifically, in the case of a CU with cbWidth[chType]>64 or cbHeight[chType]>64, a condition for signaling the incremental QP can be added, regardless of whether the first TU has non-zero coefficients (ie, coded coefficients).

[0176] For example, the luma delta QP in VVC standard draft 6 may be signaled as shown in the following table.

[0177] [Table 1]

[0178]

[0179] In addition, for example, in VVC standard draft 5, chroma QP control is only available at picture and slice levels. For example, chroma QP can be derived as follows.

[0180] [Equation 1]

[0181]

[0182] where Qp Y Can represent brightness QP; QpBdOffset C pps_cb_qp_offset, pps_cr_qp_offset, and pps_joint_cbcr_qp_offset may represent the PPS level QP offset of the corresponding chroma component; and slice_cb_qp_offset, slice_cr_qp_offset, and slice_joint_cbcr_qp_offset may represent the slice level QP offset of the corresponding chroma component.Cb It can represent the chromaticity quantization parameter for the chromaticity Cb component; Qp′ Cr It can represent the chromaticity quantization parameter for the chromaticity Cr component; and Qp′ CbCr It can represent the chrominance quantization parameters for joint Cb-Cr coding.

[0183] In addition, for example, in VVC standard draft 6, CU level chroma QP control is also applied. For example, chroma QP can be derived as follows.

[0184] [Equation 2]

[0185]

[0186] Among them, CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr It can represent the CU-level QP offset of the corresponding chrominance component. In addition, Qp′ Cb It can represent the chromaticity quantization parameter for the chromaticity Cb component; Qp′ Cr It can represent the chromaticity quantization parameter for the chromaticity Cr component; and Qp′ CbCr It can represent the chrominance quantization parameters for joint Cb-Cr coding.

[0187] Fig.11 An example of a QP map for luma and chroma blocks when a single tree is used. The CU chroma QP can be derived as the sum of the luma QP and the signaled chroma QP offset. Fig.11 , a rectangle indicated by a solid line may indicate a quantization group, and a rectangle indicated by a dotted line may indicate a CU. In addition, for example, referring to Fig.11 ,CuQpOffset chroma It can be 2. At the same time, the tree type of the current block can be divided into a single tree (SINGLE_TREE) or a dual tree (DUAL_TREE) according to whether the current luminance block and the corresponding current chrominance block have their separate partition structures. For example, if the current chrominance block has the same partition structure as the current luminance block, it can be represented as a single tree, and if the current chrominance block has a different partition structure from the current luminance block, it can be represented as a dual tree. The current block can be a CU or a TU.

[0188] Fig.12 An example of a QP map for a chroma block when a dual tree is used is shown. Fig.12 (a), CuQpOffset chroma Can be -9, and refer to Fig.12 (b), CuQpOffset chromaPossibly 2. When dual-tree is used, luma CU boundaries and chroma CU boundaries may not align. That is, chroma blocks may have a different partition structure than corresponding luma blocks. Therefore, for each chroma CU, the chroma QP may be derived as the sum of the co-located luma QP (corresponding to the center of the chroma CU) and the signaled chroma QP offset. The correlation between luma QP and chroma QP is maintained to some extent, but control of chroma QP may be difficult to predict.

[0189] In addition, in VVC standard draft 6, the joint CbCr residual coding mode is integrated therein by extending the offset table from 2 QPoffsets per entry to 3 QPoffsets per entry.

[0190] In addition, for example, the TU syntax of VVC standard draft 6 may be as shown in the following table.

[0191] [Table 2]

[0192]

[0193]

[0194]

[0195] The transform coefficient level may be represented as an array TransCoeffLevel[x0][y0][cIdx][xC][yC]. Here, the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block of the upper left luma sample of the picture. That is, when the position of the upper left luma sample of the picture is (0, 0), the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block. In addition, the array index cIdx may represent the index of the color component. For example, the array index value of the luma component (Y component) may be equal to 0; the array index value of the chroma Cb component may be equal to 1; and the value of the array index of the chroma Cr component may be equal to 2. In addition, the array indexes xC and yC may represent the position (xC, yC) of the transform coefficient in the current transform block. Meanwhile, if the value of TransCoeffLevel[x0][y0][cIdx][xC][yC] is not specified, the value may be inferred to be equal to 0.

[0196] In addition, for example, if the syntax element tu_cbf_cb[x0][y0] is 1, it may indicate that one or more non-zero transform coefficient levels are included in the Cb transform block. Here, the array indexes x0 and y0 may represent the upper left position (x0, y0) of the transform block under consideration. When the syntax element tu_cbf_cb[x0][y0] does not exist in the current TU, the value of the syntax element tu_cbf_cb[x0][y0] may be inferred to be 0. In addition, tu_cbf_cb[x0][y0] may be expressed as tu_cb_coded_flag[x0][y0].

[0197] In addition, for example, if the syntax element tu_cbf_cr[x0][y0] is 1, it can indicate that one or more non-zero transform coefficient levels are included in the Cr transform block. Here, the array index x0 and y0 can represent the upper left position (x0, y0) of the transform block under consideration. When the syntax element tu_cbf_cr[x0][y0] does not exist in the current TU, the value of the syntax element tu_cbf_cr[x0][y0] can be inferred to be 0. In addition, tu_cbf_cr[x0][y0] can be expressed as tu_cr_coded_flag[x0][y0].

[0198] In addition, for example, if the syntax element tu_cbf_luma[x0][y0] is 1, it may indicate that one or more non-zero transform coefficient levels are included in the luma transform block. Here, the array indexes x0 and y0 may indicate the position (x0, y0) of the upper left luma sample of the corresponding transform block of the upper left luma sample of the picture. That is, when the position of the upper left luma sample of the picture is (0,0), the array indexes x0 and y0 may indicate the position (x0, y0) of the upper left luma sample of the corresponding transform block. When the syntax element tu_cbf_luma[x0][y0] does not exist in the current TU, the value of the syntax element tu_cbf_luma[x0][y0] may be inferred as follows.

[0199] For example, when the value of cu_sbt_flag is 1 and one of the conditions to be described later is true, the value of the syntax element tu_cbf_luma[x0][y0] may be inferred to be 0.

[0200] - When subTuIndex is 0 and cu_sbt_pos_flag is 1

[0201] - When subTuIndex is 1 and cu_sbt_pos_flag is 0

[0202] Meanwhile, in other cases, the value of the syntax element tu_cbf_luma[x0][y0] may be inferred to be 1. In addition, tu_cbf_luma[x0][y0] may be expressed as tu_y_coded_flag[x0][y0].

[0203] In addition, for example, the syntax element tu_joint_cbcr_residual_flag[x0][y0] may indicate whether the residual samples of the chroma component Cb and the chroma component Cr are coded with a single transform block. Here, the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block of the upper left luma sample of the picture. That is, when the position of the upper left luma sample of the picture is (0, 0), the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block.

[0204] For example, if the syntax element tu_joint_cbcr_residual_flag[x0][y0] is 1, it may indicate that the transform unit syntax includes transform coefficient levels for a single transform block from which residual samples for the chroma component Cb and the chroma component Cr are derived. In addition, for example, if the syntax element tu_joint_cbcr_residual_flag[x0][y0] is 0, it may indicate that the transform coefficient levels of the chroma components are coded, as represented by the syntax elements tu_cbf_cb[x0][y0] and tu_cbf_cr[x0][y0]. When the syntax element tu_joint_cbcr_residual_flag[x0][y0] does not exist, the value of the syntax element tu_joint_cbcr_residual_flag[x0][y0] may be inferred to be 0.

[0205] For example, from tu_joint_cbcr_residual_flag[x0][y0], tu_cbf_cb[x0][y0], and tu_cbf_cr[x0][y0], the variable TuCResMode[x0][y0] may be derived as follows.

[0206] - For example, when the value of tu_joint_cbcr_residual_flag[x0][y0] is 0, the variable TuCResMode[x0][y0] can be set to 0.

[0207] - If it does not correspond to the above situation and tu_cbf_cb[x0][y0] is 1 and tu_cbf_cr[x0][y0] is 0, the variable TuCResMode[x0][y0] can be set to 1.

[0208] - If it does not correspond to the above situation and tu_cbf_cb[x0][y0] is 1, the variable TuCResMode[x0][y0] can be set to 2.

[0209] - If it does not correspond to the above situation, the variable TuCResMode[x0][y0] can be set to 3.

[0210] In addition, for example, the syntax element cu_qp_delta_abs may represent the absolute value of the difference CuQpDeltaVal between the quantization parameter of the current coding unit and its prediction.

[0211] Furthermore, for example, the syntax element cu_qp_delta_sign_flag may indicate the sign of CuQpDeltaVal as follows.

[0212] - For example, when cu_qp_delta_sign_flag is 0, the corresponding CuQpDeltaVal may have a positive value.

[0213] - If it does not correspond to the above case (ie, when cu_qp_delta_sign_flag is 1), the corresponding CuQpDeltaVal may have a negative value.

[0214] Meanwhile, when the syntax element cu_qp_delta_sign_flag does not exist, the value of the syntax element cu_qp_delta_sign_flag may be inferred to be 0.

[0215] Furthermore, for example, when cu_qp_delta_abs exists, the variable IsCuQpDeltaCoded and the variable CuQpDeltaVal can be derived as the following equation.

[0216] [Equation 3]

[0217]

[0218] The value of CuQpDeltaVal can be in the range of -(32 + QpBdOffsetY / 2) to +(31 + QpBdOffsetY / 2).

[0219] In addition, for example, if the syntax element cu_chroma_qp_offset_flag is present and equal to 1, the syntax element cu_chroma_qp_offset_flag may indicate that the entry of cb_qp_offset_list[] is used to determine CuQpOffset CbThe corresponding entry of cr_qp_offset_list[] is used to determine CuQpOffset Cr The value of , and the corresponding entry in joint_cbcr_qp_offset_list[] is used to determine CuQpOffset CbCr In addition, for example, if the syntax element cu_chroma_qp_offset_flag is 0, the syntax element cu_chroma_qp_offset_flag may indicate that cb_qp_offset_list[], cr_qp_offset_list[], and joint_cbcr_qp_offset_list[] are not used to determine CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr The value of .

[0220] In addition, for example, when the syntax element cu_chroma_qp_offset_idx exists, the syntax element cu_chroma_qp_offset_idx may indicate the number of bits used to determine CuQpOffset Cb 、CuQpOffset Cr and CuQpOffsetCb CbCr _chroma_qp_offset_list_len_minus1. When the syntax element cu_chroma_qp_offset_idx is present, the value of the syntax element cu_chroma_qp_offset_idx may be in the range from 0 to chroma_qp_offset_list_len_minus1. When the syntax element cu_chroma_qp_offset_idx is not present, the syntax element cu_chroma_qp_offset_idx may be inferred to be 0.

[0221] Furthermore, for example, when the syntax element cu_chroma_qp_offset_flag is present, the following description may apply.

[0222] - If cu_chroma_qp_offset_flag is 1, CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr The value of can be derived as shown in the following equation.

[0223] [Equation 4]

[0224]

[0225] - If it does not correspond to the above case (i.e., when cu_chroma_qp_offset_flag is 0), CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr Set to 0.

[0226] In addition, for example, the syntax element transform_skip_flag[x0][y0] may indicate whether a transform is applied to a luma transform block. Here, the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block of the upper left luma sample of the picture. That is, when the position of the upper left luma sample of the picture is (0, 0), the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block. For example, if transform_skip_flag[x0][y0] is 1, it may indicate that no transform is applied to the luma transform block. In addition, for example, if transform_skip_flag[x0][y0] is 0, it may indicate that whether a transform is applied to the luma transform block may be determined based on another syntax element.

[0227] In addition, for example, when transform_skip_flag[x0][y0] does not exist, the value of transform_skip_flag[x0][y0] can be inferred as follows.

[0228] - For example, if BdpcmFlag[x0][y0] is 1, then transform_skip_flag[x0][y0] can be inferred to be 1.

[0229] - If it does not correspond to the above situation (ie, for example, when BdpcmFlag[x0][y0] is 0), transform_skip_flag[x0][y0] can be inferred to be 0.

[0230] In addition, for example, the syntax element tu_mts_idx[x0][y0] may represent a transform kernel applied to the residual sample in the horizontal and vertical directions of the associated luma transform block. Here, the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block of the upper left luma sample of the picture. That is, when the position of the upper left luma sample of the picture is (0, 0), the array indexes x0 and y0 may represent the position (x0, y0) of the upper left luma sample of the corresponding transform block. In addition, for example, when the syntax element tu_mts_idx[x0][y0] does not exist, the syntax element tu_mts_idx[x0][y0] may be inferred to be 0.

[0231] Fig.13 The sample positions used for deblocking filtering are exemplarily indicated.

[0232] At the same time, chroma QP can be used for deblocking filtering of chroma components. However, for example, for chroma QP for deblocking filtering, slice level and CU level QP adjustment may not be considered. For example, the chroma QP for deblocking filtering can be derived based on the corresponding luma QP and the picture level chroma QP offset cQpPicOffset. Here, for example, if cIdx is 1, cQpPicOffset representing the picture level chroma QP offset can be derived as pps_cb_qp_offset, and if cIdx is not 1, it can be derived as pps_cr_qp_offset.

[0233] In addition, for example, the variable Qp Q can be set equal to the Qp of the coding unit that includes the coding block Y Value, the compilation block includes Figure 6 The sample q0,0 shown in , and the variable Qp P can be set equal to the Qp of the coding unit that includes the coding block Y Value, the compilation block includes Figure 6 The sample p0,0 is shown in .

[0234] After that, the chroma QP Qp used for deblocking filtering C It can be derived as the following equation.

[0235] [Equation 5]

[0236]

[0237] At the same time, there may be some shortcomings in the chroma QP-related design of the deblocking filter of the existing VVC standard. Because VVC supports dual trees, there may be a large difference between the luma QP and chroma QP of the CU due to the different partitions of the luma block and the chroma block. In addition, the VVC standard supports the YUV 4:2:2 format and the YUV 4:4:4 format as well as the YUV 4:2:0 format. Here, in the case of the YUV 4:4:4 format, if an inaccurate chroma QP is used for deblocking filtering, it may have a greater effect and visual artifacts may occur.

[0238] Therefore, this document proposes an efficient chroma QP signaling scheme, as in the embodiments described later.

[0239] In one embodiment, chroma QP offset signaling supporting VDPU level processing is proposed. In this embodiment, for a chroma CU having a cbWidth or cbHeight greater than 64, the CU chroma QP offset can be signaled (when there is a chroma QP offset for the chroma CU), regardless of whether a non-zero chroma CBF is included in the first TU. That is, according to this embodiment, when the cbWidth or cbHeight of the current chroma CU is greater than 64, the CU chroma QP offset can be signaled (when there is a chroma QP offset for the chroma CU), regardless of whether the first TU has a non-zero coefficient. Here, cbWidth and cbHeight may represent the CU width and CU height of a luminance element or a chroma element according to a channel type or a tree type. For example, in the case of an image in YUV 4:4:4 format, since a chroma CU with a width or height greater than 64 may be generated, VDPU level processing may be performed by the method proposed in this embodiment, and QP may be enabled when parsing the VDPU.

[0240] For example, the transformation unit syntax according to this embodiment may be as shown in the following table.

[0241] [Table 3]

[0242]

[0243] Referring to Table 3, "CbWidth[chType][x0][y0] > 64 || CbHeight[chType][x0][y0] > 64 ||" may be added to the signaling condition of the CU chroma QP offset related information. That is, referring to Table 3, when CbWidth[chType][x0][y0] is greater than 64 or CbHeight[chType][x0][y0] is greater than 64, the CU chroma QP offset related information may be signaled. The CU chroma QP offset related information may include a syntax element cu_chroma_qp_offset_flag and / or a syntax element cu_chroma_qp_offset_idx.

[0244] For example, if the syntax element cu_chroma_qp_offset_flag is present and equal to 1, the syntax element cu_chroma_qp_offset_flag may indicate that the entry of cb_qp_offset_list[] is used to determine CuQpOffset Cb The corresponding entry of cr_qp_offset_list[] is used to determine CuQpOffset Cr The value of , and the corresponding entry in joint_cbcr_qp_offset_list[] is used to determine CuQpOffset CbCr In addition, for example, if the syntax element cu_chroma_qp_offset_flag is 0, the syntax element cu_chroma_qp_offset_flag may indicate that cb_qp_offset_list[], cr_qp_offset_list[], and joint_cbcr_qp_offset_list[] are not used to determine CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr The value of .

[0245] In addition, for example, when the syntax element cu_chroma_qp_offset_idx exists, the syntax element cu_chroma_qp_offset_idx may indicate the number of bits used to determine CuQpOffset Cb 、CuQpOffset Cr and CuQpOffset CbCr_chroma_qp_offset_list_len_minus1. When the syntax element cu_chroma_qp_offset_idx is present, the value of the syntax element cu_chroma_qp_offset_idx may be in the range from 0 to chroma_qp_offset_list_len_minus1. When the syntax element cu_chroma_qp_offset_idx is not present, the syntax element cu_chroma_qp_offset_idx may be inferred to be 0.

[0246] In addition, as an embodiment, this document proposes a method for adding conditions to CU-level chroma QP offset signaling for dual trees. This embodiment proposes a method for modifying the availability conditions of the existing syntax of the CU chroma QP offset flag in order to avoid unnecessary signaling. For example, according to this embodiment, when the coding tree is dual-tree luminance (DUAL_TREE_LUMA), that is, when the coding tree is neither a single tree (SINGLE_TREE) nor a dual-tree chroma (DUAL_TREE_CHROMA), CU chroma QP offset related information may not be signaled.

[0247] For example, the transformation unit syntax according to this embodiment may be as shown in the following table.

[0248] [Table 4]

[0249]

[0250] Referring to Table 4, "&& treeType!= DUAL_TREE_LUMA" may be added to the signaling condition of the CU chroma QP offset related information. That is, referring to Table 4, only when the coding tree is not DUAL_TREE_LUMA, the CU chroma QP offset related information may be signaled. The CU chroma QP offset related information may include a syntax element cu_chroma_qp_offset_flag and / or a syntax element cu_chroma_qp_offset_idx.

[0251] In addition, as an embodiment, this document proposes another method of adding conditions to CU-level chroma QP offset signaling. This embodiment proposes a method of modifying the availability conditions of the existing syntax of the CU chroma QP offset flag in order to avoid unnecessary signaling. For example, this embodiment proposes a method of modifying the availability conditions of the existing syntax by combining the signaling conditions of the above-mentioned embodiment.

[0252] For example, the transformation unit syntax according to this embodiment may be as shown in the following table.

[0253] [Table 5]

[0254]

[0255] Referring to Table 5, "CbWidth[chType][x0][y0] > 64 || CbHeight[chType][x0][y0] > 64 ||" and "&& treeType != DUAL_TREE_LUMA" may be added to the signaling conditions of the CU chroma QP offset related information. That is, referring to Table 5, if the coding tree is not DUAL_TREE_LUMA and CbWidth[chType][x0][y0] is greater than 64, or CbHeight[chType][x0][y0] is greater than 64, the CU chroma QP offset related information may be signaled. Therefore, when the coding tree is DUAL_TREE_LUMA, the CU chroma QP offset related information may not be signaled. The CU chroma QP offset related information may include the syntax element cu_chroma_qp_offset_flag and / or the syntax element cu_chroma_qp_offset_idx.

[0256] In addition, this document proposes a method for deblocking filtering using CU-level chroma QP. This embodiment proposes a method for integrating slice-level chroma QP and / or CU-level chroma QP into a chroma QP expressed as a QpC and used for chroma deblocking processing. Deblocking parameters can be determined based on the derived QpC.

[0257] For example, the variable QpC may be derived based on the Qp of the neighboring CU as shown in the following equation.

[0258] [Equation 6]

[0259]

[0260] Here, Qp Q 'cIdx can represent the chroma QP of the CU P adjacent to the block boundary to be deblocked, and Qp P 'cIdx may represent the chroma QP of the CU Q adjacent to the block boundary to be deblocked. In addition, cIdx may be an index representing a chroma component. For example, cIdx may represent a chroma Cb component, a chroma Cr component, or a chroma CbCr component. Qp Q 'cIdx and Qp P 'cIdx may be a value that has taken slice level QP adjustment and CU level QP adjustment into consideration.

[0261] Alternatively, for example, the variable QpC may be first derived based on the luma QP of the neighboring CU P and the neighboring CU Q, and then the slice level QP adjustment and the CU level QP adjustment may be added. For example, the variable QpC may be derived as follows.

[0262] [Equation 7]

[0263]

[0264] Here, CuQpOffset PcIdx It can represent the CuQPOffset of the element cIdx of the adjacent CU P, and CuQpOffset QcIdx The CuQPOffset of the element cIdx of the adjacent CU Q can be represented.

[0265] Fig.14 The image encoding method of the encoding device according to this document is schematically shown. Fig.14 The method disclosed in can be Figure 2 Specifically, for example, Fig.14 S1400 may be performed by a predictor and a residual processor of the encoding device, S1410 may be performed by an adder of the encoding device, and S1420 may be performed by an entropy encoder of the encoding device.

[0266] The encoding apparatus derives a prediction sample and a residual sample of the current chroma block (S1400). The encoding apparatus may derive a prediction sample and a residual sample of the current chroma block.

[0267] For example, the encoding device may derive a prediction sample of the current chrominance block based on the prediction mode. In this case, various prediction methods disclosed in this document, such as inter-frame prediction or intra-frame prediction, may be applied.

[0268] For example, the encoding device may determine whether to perform inter prediction or intra prediction on the current chroma block, and may determine a specific inter prediction mode or a specific intra prediction mode based on the RD cost. According to the determined mode, the encoding device may derive a prediction sample of the current chroma block.

[0269] Then, for example, the encoding device may derive residual samples by subtracting the predicted samples of the current chroma block from the original samples.

[0270] The encoding apparatus generates a reconstructed picture based on the prediction sample and the residual sample (S1410). For example, the encoding apparatus may generate a reconstructed sample and / or a reconstructed picture by adding the prediction sample and the residual sample.

[0271] Thereafter, as described above, an in-loop filtering process, such as an ALF process, SAO and / or deblocking filtering, may be applied to the reconstructed samples as needed in order to improve the subjective / objective video quality.

[0272] At the same time, for example, deblocking filtering can be performed on the edge of the current chroma block. For example, a specific value can be derived based on the chroma QP of the current chroma block and the chroma QP of the neighboring block of the current chroma block adjacent to the edge, and the deblocking parameters for deblocking filtering can be derived based on the specific value. For example, the specific value can be derived as in Equation 6 above. The chroma QP of the current chroma block can be derived based on the CU chroma QP offset of the current chroma block as described above, and the chroma QP of the neighboring block can be derived based on the CU chroma QP offset of the neighboring block. Here, for example, the edge can represent the area of ​​the current chroma block to which deblocking filtering is applied.

[0273] Alternatively, for example, a specific value may be derived based on the chroma QP of the current chroma block, the chroma QP of the neighboring block of the current chroma block adjacent to the edge, and the CU chroma QP offset, and a deblocking parameter for deblocking filtering may be derived based on the specific value. For example, the specific value may be derived as in the above equation 7. Here, for example, the edge may represent an area of ​​the current chroma block to which the deblocking filter is applied.

[0274] The encoding device encodes the image information (S1420). The encoding device may encode the image information. The image information may include prediction information, residual information, and / or chroma quantization parameter (QP) offset related information of the current chroma block.

[0275] For example, the encoding device may generate and encode prediction information for the current chroma block. In this case, various prediction methods disclosed in this document, such as inter-frame prediction or intra-frame prediction, may be applied. For example, the encoding device may determine whether to perform inter-frame prediction or intra-frame prediction on the current chroma block, and may determine a specific inter-frame prediction mode or a specific intra-frame prediction mode based on the RD cost. According to the determined mode, the encoding device may derive a prediction sample for the current chroma block. The prediction information may include prediction mode information for the current chroma block. The image information may include prediction information.

[0276] In addition, for example, the encoding device may generate and encode the coding unit (CU) chroma quantization parameter (QP) offset related information for the current chroma block based on the size and tree type of the current chroma block. The CU chroma QP offset related information may be referred to as CU-level chroma QP offset related information. Here, the tree type may be one of a single tree, a dual-tree luminance, and a dual-tree chroma. In addition, for example, the CU chroma QP offset related information may be signaled as a transform unit syntax for the first transform block among the transform blocks for the current chroma block. That is, for example, the transform unit syntax for the first transform block may include the CU chroma QP offset related information. The first transform block may be a transform block that is first coded in the decoding order among the transform blocks of the current chroma block. For example, the first transform block may be the upper left transform block among the transform blocks of the current chroma block.

[0277] Specifically, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be sent by a signal. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be generated. In this regard, for example, the specific value may be 64. In addition, for example, the transform unit syntax for the first transform block may include the CU chroma QP offset related information of the current chroma block. For example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be sent by a signal in the transform unit syntax of the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0278] Alternatively, for example, when the tree type is dual-tree luma, the CU chroma QP offset related information of the current chroma block may not be signaled. That is, for example, when the tree type is dual-tree luma, the CU chroma QP offset related information of the current chroma block may not be generated. Therefore, for example, when the tree type is not dual-tree luma (that is, when the tree type is one of single tree and dual-tree chroma), the CU chroma QP offset related information of the current chroma block may be signaled. That is, for example, when the tree type is not dual-tree luma (that is, when the tree type is one of single tree and dual tree chroma), the CU chroma QP offset related information of the current chroma block may be generated. At this point, for example, the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block. For example, when the tree type is not dual-tree luma (that is, when the tree type is one of single tree and dual tree chroma), the CU chroma QP offset related information of the current chroma block may be signaled through the transform unit syntax for the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when the tree type is not dual-tree luminance (i.e., when the tree type is one of single-tree and dual-tree chroma), the transform unit syntax for the first transform block may include CU chroma QP offset related information of the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0279] Alternatively, for example, when at least one of the width and height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luminance (i.e., when the tree type is one of single-tree and dual-tree chroma), CU chroma QP offset related information of the current chroma block may be sent by a signal. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luminance (i.e., when the tree type is one of single-tree and dual-tree chroma), CU chroma QP offset related information of the current chroma block may be generated. At this point, for example, the specific value may be 64. Therefore, for example, when the tree type is dual-tree luminance, CU chroma QP offset related information of the current chroma block may not be sent by a signal. In addition, for example, the transform unit syntax of the first transform block may include CU chroma QP offset related information of the current chroma block. For example, when at least one of the width and the height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luma (i.e., when the tree type is one of single-tree and dual-tree chroma), the CU chroma QP offset related information of the current chroma block may be signaled through the transform unit syntax of the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when at least one of the width and the height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luma (i.e., when the tree type is one of single-tree and dual-tree chroma), the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0280] Meanwhile, for example, the CU chroma QP offset related information may include a CU chroma QP offset index and / or a CU chroma QP offset flag for the current chroma block. The CU chroma QP offset flag may also be referred to as a CU-level chroma QP offset flag, and the CU chroma QP offset index may also be referred to as a CU-level chroma QP offset index.

[0281] For example, the CU chroma QP offset flag may be a flag regarding whether an entry in a CU QP offset list for a chroma component is used to determine the value of the CU chroma QP offset. That is, for example, the CU chroma QP offset flag may indicate whether an entry in a CU QP offset list for a chroma component is used to determine the value of the CU chroma QP offset. For example, when the CU chroma QP offset flag is present, and when the value of the CU chroma QP offset flag is 1, the CU chroma QP offset flag may indicate that an entry in a CU QP offset list for a chroma component is used to determine the value of the CU chroma QP offset. In addition, for example, when the value of the CU chroma QP offset flag is 0, the CU chroma QP offset flag may indicate that the CU QP offset list for a chroma component is not used to determine the value of the CU chroma QP offset. Here, for example, the chroma component may include a Cb component, a Cr component, and / or a joint CbCr component. In addition, for example, the syntax element of the CU chroma QP offset flag may be the above-mentioned cu_chroma_qp_offset_flag.

[0282] In addition, for example, the CU chroma QP offset index may represent the index of an entry in the CU QP offset list used to determine the value of the CU chroma QP offset. That is, for example, the CU chroma QP offset index may be information about the index of an entry in the CU QP offset list. In addition, for example, the syntax element of the CU chroma QP offset index may be the above-mentioned cu_chroma_qp_offset_idx.

[0283] In addition, for example, the encoding device may derive the chroma QP of the current chroma block based on the CU chroma QP offset related information. For example, the encoding device may derive the CU chroma QP offset of the current chroma block based on the CU chroma QP offset related information, and may derive the chroma QP of the current chroma block based on the CU chroma QP offset. Specifically, for example, the encoding device may derive the chroma QP of the current chroma block by adding the CU chroma QP offset to the first chroma QP of the chroma component.

[0284] Specifically, for example, the encoding device may derive a first chroma QP of a chroma component of a current chroma block based on a luma QP and / or chroma QP mapping table, may derive a CU chroma QP offset of a current chroma block based on CU chroma QP offset related information, and may derive a chroma QP of a current chroma block based on the first chroma QP and the CU chroma QP offset. Here, for example, the first chroma QP may be referred to as a sequence parameter set (SPS) chroma QP or an SPS level chroma QP.

[0285] Then, for example, the encoding device may derive the transform coefficient of the current chroma block based on the chroma QP. The encoding device may derive the transform coefficient of the current chroma block based on the chroma QP. For example, the encoding device may derive the transform coefficient by quantizing the residual samples of the current chroma block based on the chroma QP. Alternatively, for example, the encoding device may derive the transform coefficient that has been transformed by transforming the residual samples of the current chroma block, and may derive the transform coefficient by quantizing the transformed transform coefficient based on the chroma QP.

[0286] In addition, for example, the encoding device may generate and encode residual information for the current chroma block. For example, the encoding device may generate and encode residual information for the transform coefficient. For example, the residual information may include sign flag information and transform coefficient level information for the transform coefficient. For example, the transform coefficient level of the transform coefficient may be derived as a value represented by the transform coefficient level information included in the residual information, and the sign of the transform coefficient may be derived as a sign represented by the sign flag information. For example, the residual information may include syntax elements for the transform coefficient of the current chroma block. For example, the syntax elements may include syntax elements such as coded_sub_block_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder, coeff_sign_flag, etc.

[0287] For example, the encoding device may encode the image information and output it in the form of a bit stream.

[0288] At the same time, the bit stream including the image information can be sent to the decoding device via a network or a (digital) storage medium. In this case, the network can include a broadcast network and / or a communication network. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD and SSD.

[0289] Fig.15 A coding device for performing the image coding method according to this document is schematically shown. Fig.14 The method disclosed in can be Fig.15 Specifically, for example, Fig.15 The predictor and residual processor of the encoding device may perform S1400, Fig.15 The adder of the encoding device may perform S1410, and Fig.15 The entropy encoder of the encoding device may perform S1420.

[0290] Fig.16The image decoding method of the decoding device according to this document is schematically shown. Fig.16 The method disclosed in can be Figure 3 Specifically, for example, Fig.16 S1600 may be performed by an entropy decoder of a decoding device; Fig.16 S1610 may be performed by a residual processor of the decoding device.

[0291] The decoding apparatus obtains image information through a bit stream (S1600). The decoding apparatus may obtain image information through a bit stream.

[0292] For example, the image information may include prediction information and / or residual information of the current chrominance block. For example, the decoding device may obtain prediction information and / or residual information of the current chrominance block.

[0293] For example, the prediction information may include prediction mode information of the current chroma block. The prediction mode information may indicate whether inter prediction or intra prediction is applied to the current block for the chroma component.

[0294] In addition, for example, the residual information may include syntax elements for transform coefficients of the current chrominance block. For example, the syntax elements may include syntax elements such as coded_sub_block_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder, coeff_sign_flag, etc.

[0295] In addition, for example, the image information may be information related to a coding unit (CU) chroma quantization parameter (QP) offset for a current chroma block. For example, the decoding device may obtain information related to a coding unit (CU) chroma quantization parameter (QP) offset for a current chroma block based on the size and tree type of the current chroma block. Information related to the CU chroma QP offset may be referred to as information related to a CU-level chroma QP offset. Here, the tree type may be one of a single tree, a dual-tree luminance, and a dual-tree chroma. In addition, for example, information related to the CU chroma QP offset may be signaled as a transform unit syntax for a first transform block among transform blocks for the current chroma block. That is, for example, the transform unit syntax of the first transform block may include information related to the CU chroma QP offset. The first transform block may be a transform block that is first decoded in a decoding order among the transform blocks of the current chroma block. For example, the first transform block may be an upper left transform block in a transform block of the current chroma block.

[0296] Specifically, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be sent by a signal. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be obtained. In this regard, for example, the specific value may be 64. In addition, for example, the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block. For example, when at least one of the width and height of the current chroma block is greater than a specific value, the CU chroma QP offset related information of the current chroma block may be obtained as the transform unit syntax of the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0297] Alternatively, for example, when the tree type is dual-tree luma, the CU chroma QP offset related information of the current chroma block may not be signaled. That is, for example, when the tree type is dual-tree luma, the CU chroma QP offset related information of the current chroma block may not be obtained. Therefore, for example, when the tree type is not dual-tree luma (that is, when the tree type is one of single-tree and dual-tree chroma), the CU chroma QP offset related information of the current chroma block may be signaled. That is, for example, when the tree type is not dual-tree luma (that is, when the tree type is one of single-tree and dual-tree chroma), the CU chroma QP offset related information of the current chroma block may be obtained. At this point, for example, the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block. For example, when the tree type is not dual-tree luma (that is, when the tree type is one of single-tree and dual-tree chroma), the CU chroma QP offset related information for the current chroma block may be obtained through the transform unit syntax for the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when the tree type is not dual-tree luma (i.e., when the tree type is one of single-tree and dual-tree chroma), the transform unit syntax for the first transform block may include CU chroma QP offset related information for the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0298] Alternatively, for example, when at least one of the width and height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luminance (i.e., when the tree type is one of single-tree and dual-tree chroma), CU chroma QP offset related information of the current chroma block may be sent by a signal. That is, for example, when at least one of the width and height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luminance (i.e., when the tree type is one of single-tree and dual-tree chroma), CU chroma QP offset related information of the current chroma block may be obtained. At this point, for example, the specific value may be 64. Therefore, for example, when the tree type is dual-tree luminance, CU chroma QP offset related information of the current chroma block may not be sent by a signal. In addition, for example, the transform unit syntax of the first transform block may include CU chroma QP offset related information of the current chroma block. For example, when at least one of the width and the height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luma (that is, when the tree type is one of single-tree and dual-tree chroma), the CU chroma QP offset related information of the current chroma block may be obtained through the transform unit syntax of the first transform block, regardless of whether the first transform block includes at least one non-zero transform coefficient level. That is, for example, when at least one of the width and the height of the current chroma block is greater than a specific value, and when the tree type is not dual-tree luma (that is, when the tree type is one of single-tree and dual-tree chroma), the transform unit syntax of the first transform block may include the CU chroma QP offset related information of the current chroma block, regardless of whether the first transform block includes at least one non-zero transform coefficient level.

[0299] Meanwhile, for example, the CU chroma QP offset related information may include the CU chroma QP offset index and / or the CU chroma QP offset flag of the current chroma block. The CU chroma QP offset flag may also be referred to as the CU level chroma QP offset flag, and the CU chroma QP offset index may also be referred to as the CU level chroma QP offset index.

[0300] For example, the CU chroma QP offset flag may be a flag regarding whether an entry in a CU QP offset list for a chroma component is used to determine the value of the CU chroma QP offset. That is, for example, the CU chroma QP offset flag may indicate whether the value of the CU chroma QP offset is determined using an entry in a CU QP offset list for a chroma component. For example, when the CU chroma QP offset flag is present, and when the value of the CU chroma QP offset flag is 1, the CU chroma QP offset flag may indicate that the value of the CU chroma QP offset is determined using an entry in a CU QP offset list for a chroma component. In addition, for example, when the value of the CU chroma QP offset flag is 0, the CU chroma QP offset flag may indicate that the value of the CU chroma QP offset is not determined using a CU QP offset list for a chroma component. Here, for example, the chroma component may include a Cb component, a Cr component, and / or a joint CbCr component. In addition, for example, the syntax element of the CU chroma QP offset flag may be the above-mentioned cu_chroma_qp_offset_flag.

[0301] In addition, for example, the CU chroma QP offset index may represent the index of an entry in the CU QP offset list used to determine the value of the CU chroma QP offset. That is, for example, the CU chroma QP offset index may be information about the index of an entry in the CU QP offset list. In addition, for example, the syntax element of the CU chroma QP offset index may be the above-mentioned cu_chroma_qp_offset_idx.

[0302] The decoding apparatus generates a reconstructed picture based on the image information (S1610). For example, the decoding apparatus may derive prediction samples and residual samples of the current chrominance block, and generate reconstructed samples and / or reconstructed pictures based on the prediction samples and residual samples.

[0303] For example, the decoding apparatus may derive a prediction sample by performing an inter prediction mode or an intra prediction mode on the current chroma block based on the prediction information.

[0304] In addition, for example, the decoding device may derive the transform coefficient of the current chrominance block based on the residual information. The residual information may include transform coefficient level information and sign flag information for the transform coefficient.

[0305] For example, the transform coefficient level of the transform coefficient may be derived as a value represented by the transform coefficient level information included in the residual information, and the sign of the transform coefficient may be derived as a sign represented by the sign flag information.

[0306] Then, for example, the decoding device may derive the chroma QP of the current chroma block based on the CU chroma QP offset related information. For example, the decoding device may derive the CU chroma QP offset of the current chroma block based on the CU chroma QP offset related information, and may derive the chroma QP of the current chroma block based on the CU chroma QP offset. Specifically, for example, the decoding device may derive the chroma QP of the current chroma block by adding the CU chroma QP offset to the first chroma QP of the chroma component.

[0307] Specifically, for example, the decoding device may derive a first chroma QP of a chroma component of a current chroma block based on a luma QP and / or chroma QP mapping table, may derive a CU chroma QP offset of a current chroma block based on CU chroma QP offset related information, and may derive a chroma QP of a current chroma block based on the first chroma QP and the CU chroma QP offset. Here, for example, the first chroma QP may be referred to as a sequence parameter set (SPS) chroma QP or an SPS level chroma QP.

[0308] Then, for example, the decoding device derives the residual samples of the current chroma block by dequantizing the transform coefficients based on the chroma QP. The decoding device may derive the residual samples of the current chroma block based on the chroma QP. For example, the decoding device may derive the residual samples by dequantizing the transform coefficients of the current chroma block based on the chroma QP. Alternatively, for example, the decoding device may derive the inverse transformed transform coefficients by inverse transforming the transform coefficients of the current chroma block, and may derive the residual samples by dequantizing the inverse transformed transform coefficients based on the chroma QP.

[0309] Then, for example, the decoding device may generate a reconstructed picture based on the prediction samples and the residual samples. For example, the decoding device may generate a reconstructed sample and / or a reconstructed picture by adding the prediction samples and the residual samples.

[0310] Thereafter, as described above, an in-loop filtering process such as an ALF process, SAO and / or deblocking filtering may be applied to the reconstructed samples as needed in order to improve the subjective / objective video quality.

[0311] At the same time, for example, deblocking filtering can be performed on the edge of the current chroma block. For example, a specific value can be derived based on the chroma QP of the current chroma block and the chroma QP of the neighboring block of the current chroma block adjacent to the edge, and the deblocking parameters for deblocking filtering can be derived based on the specific value. For example, the specific value can be derived as in Equation 6 above. The chroma QP of the current chroma block can be derived based on the CU chroma QP offset of the current chroma block as described above, and the chroma QP of the neighboring block can be derived based on the CU chroma QP offset of the neighboring block. Here, for example, the edge can represent the area of ​​the current chroma block to which deblocking filtering is applied.

[0312] Alternatively, for example, a specific value may be derived based on the chroma QP of the current chroma block, the chroma QP of the neighboring block of the current chroma block adjacent to the edge, and the CU chroma QP offset, and a deblocking parameter for deblocking filtering may be derived based on the specific value. For example, the specific value may be derived as in the above-mentioned equation 7. Here, for example, the edge may represent an area of ​​the current chroma block to which the deblocking filter is applied.

[0313] Fig.17 A decoding device for executing the image decoding method according to this document is schematically shown. Fig.16 The method disclosed in can be Fig.17 Specifically, Fig.17 The entropy decoder of the decoding device can perform Fig.17 S1600; and Fig.17 The residual processor of the decoding device may perform Fig.16 S1610.

[0314] According to the above document, even if the first transform block in the current chroma block does not include a non-zero transform coefficient level, and when at least one of the width and height of the current chroma block is greater than a specific size, information about the CU chroma QP offset can be sent by a signal, thereby reducing the cost of configuring the decoding device.

[0315] In addition, according to this document, even if the first transform block in the current chroma block does not include a non-zero transform coefficient level, information about the CU chroma QP offset can be signaled in the transform unit syntax of the first transform block based on the size and tree type of the current chroma block, thereby reducing the cache requirements of the decoding device and reducing the cost of configuring the decoding device.

[0316] In the above embodiments, methods are described based on a flow chart with a series of steps or boxes. The present disclosure is not limited to the order of the above steps or boxes. Some steps or boxes can be performed in an order different from other steps or boxes mentioned above or performed simultaneously. In addition, it will be understood 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.

[0317] 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.

[0318] In addition, the decoding device and encoding device to which the present disclosure is applied may 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 equipment; and the decoding device and encoding device to which the present disclosure is applied may be used to process video signals or data signals. For example, over-the-top (OTT) video devices may include game consoles, Blu-ray players, Internet access televisions, home theater systems, smart phones, tablet computers, digital video recorders (DVRs), etc.

[0319] In addition, the processing method of the present disclosure 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 disclosure can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices in which computer-readable data is stored. The computer-readable recording medium may include, for example, a BD, a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (e.g., transmission via the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium or transmitted via a wired / wireless communication network.

[0320] 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.

[0321] Fig.18 A structural diagram of a content streaming system to which the present disclosure is applied is illustrated.

[0322] A content streaming system to which the embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0323] The encoding server compresses the content input from a multimedia input device such as a smartphone, a camera, or a camcorder into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, a camera, or a camcorder directly generates a bitstream, the encoding server can be omitted.

[0324] 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.

[0325] 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.

[0326] 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.

[0327] 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.

[0328] The claims described in this disclosure can be combined in various ways. For example, the technical features of the method claims of this disclosure can be combined to implement as a device, and the technical features of the device claims of this disclosure can be combined to implement as a method. In addition, the technical features of the method claims of this disclosure and the technical features of the device claims can be combined to implement as a device, and the technical features of the method claims of this disclosure and the technical features of the device claims can be combined to implement as a method.

Claims

1. An image decoding method performed by a decoding device, the method comprising: Obtain image information; as well as generating a reconstructed picture based on the image information, The process of obtaining the image information includes: Obtaining prediction information and residual information for a chroma component of a current coding unit; and Based on the tree type and size of the current coding unit, obtain coding unit (CU) chroma quantization parameter (QP) offset related information for the current coding unit, The CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current coding unit. Wherein, based on at least one of the width and the height of the current coding unit being greater than 64 and the tree type being not dual-tree brightness, obtaining the CU chroma QP offset related information, The CU chroma QP offset flag is a flag used to determine whether an entry in the CU QP offset list for the chroma component is used to determine the value of the CU chroma QP offset. The CU chroma QP offset index is the index information of the entry in the CU QP offset list for the chroma component, and Wherein, based on the fact that the tree type is the dual-tree brightness, the CU chroma QP offset related information is not obtained.

2. An image encoding method performed by an encoding device, comprising: deriving prediction samples and residual samples for chroma components of a current coding unit; Generate a reconstructed picture based on the prediction sample and the residual sample; as well as Encode the image information. The process of encoding the image information includes: generating prediction information for the current coding unit; deriving a chroma quantization parameter (QP) for the current coding unit; deriving transform coefficients for the current coding unit by quantizing the residual samples based on the chroma QP; generating residual information for the transform coefficients; generating coding unit (CU) chroma QP offset related information for the chroma QP based on a tree type and a size of the current coding unit; and Encoding the image information including the CU chroma QP offset related information, the prediction information and the residual information, The CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current coding unit. wherein, based on at least one of the width and the height of the current coding unit being greater than 64 and the tree type being not dual-tree brightness, the CU chroma QP offset related information is sent by signaling, The CU chroma QP offset flag is a flag used to determine whether an entry in the CU QP offset list for the chroma component is used to determine the value of the CU chroma QP offset. The CU chroma QP offset index is the index information of the entry in the CU QP offset list for the chroma component, and Wherein, based on the tree type being the dual-tree brightness, no signal is used to send the CU chroma QP offset related information.

3. A method for transmitting image data, the method comprising: Obtaining a bitstream of image information including coding unit (CU) chroma quantization parameter (QP) offset related information, prediction information, and residual information for chroma components of a current coding unit; as well as sending the data of the bitstream including the image information, the image information including the CU chroma QP offset related information, the prediction information and the residual information, wherein a prediction sample for the current coding unit is derived based on the prediction information, wherein a residual sample for the current coding unit is derived based on the residual information, wherein, based on the tree type and size of the current coding unit, the CU chroma QP offset related information for the chroma QP of the current coding unit is generated, The CU chroma QP offset related information includes a CU chroma QP offset flag and a CU chroma QP offset index for the current coding unit. wherein, based on at least one of the width and the height of the current coding unit being greater than 64 and the tree type being not dual-tree brightness, the CU chroma QP offset related information is sent by signaling, The CU chroma QP offset flag is a flag used to determine whether an entry in the CU QP offset list for the chroma component is used to determine the value of the CU chroma QP offset. The CU chroma QP offset index is the index information of the entry in the CU QP offset list for the chroma component, and Wherein, based on the tree type being the dual-tree brightness, no signal is used to send the CU chroma QP offset related information.

Images