WO2021034100A1

WO2021034100A1 - Image decoding method employing lossless coding in image coding system, and apparatus therefor

Info

Publication number: WO2021034100A1
Application number: PCT/KR2020/011034
Authority: WO
Inventors: 최정아; 허진; 유선미; 최장원; 임재현; 김승환; 장형문
Original assignee: 엘지전자 주식회사
Priority date: 2019-08-19
Filing date: 2020-08-19
Publication date: 2021-02-25

Abstract

According to the disclosure of the present document, whether lossless coding is used or not is determined, and when, on the basis of the result of the determination, lossless coding is used, syntax elements according to a transform skip residual coding (TSRC) syntax structure are parsed for a current block, whereby the coding efficiency and complexity of residual coding can be reduced.

Description

Video decoding method and apparatus for applying lossless coding in video coding system

The present technology relates to a video decoding method and apparatus for applying lossless coding in a video coding system.

Recently, demand for high-resolution and high-quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields. As the image data becomes high-resolution and high-quality, the amount of information or bits to be transmitted is relatively increased compared to the existing image data. Therefore, the image data is transmitted using a medium such as an existing wired or wireless broadband line, or image data is stored using an existing storage medium In the case of storage, the transmission cost and storage cost increase.

Accordingly, high-efficiency image compression technology is required to effectively transmit, store, and reproduce information of high-resolution and high-quality images.

The technical problem of this document is to provide a method and apparatus for increasing image coding efficiency.

Another technical problem of this document is to provide a method and apparatus for increasing the efficiency of residual coding.

According to an embodiment of the present document, an image decoding method performed by a decoding apparatus is provided. The method includes the steps of: receiving image information including residual information through a bitstream; Determining whether lossless coding is used from the image information; Generating residual samples for a current block based on the determination result and the residual information; And generating reconstructed samples for the current block based on the residual samples, and if the lossless coding is used based on the determination result, transform skip residual coding for the current block Syntax elements according to the Skip Residual Coding (TSRC) syntax structure are parsed.

According to another embodiment of the present document, a video encoding method performed by an encoding device is provided. The method includes deriving a residual sample of a current block; Determining whether lossless coding is used for the current block; Encoding residual information on the residual sample of the current block based on the determination result; And generating a bitstream including the residual information, and a Transform Skip Residual Coding (TSRC) syntax for the current block based on a determination that the lossless coding is used. Syntax elements according to the structure are encoded.

According to yet another embodiment of the present document, a computer-readable digital storage medium is provided in which a bitstream including image information causing a decoding apparatus to perform an image decoding method is stored. The video decoding method includes: receiving video information including residual information through a bitstream; Determining whether lossless coding is used from the image information; Generating residual samples for a current block based on the determination result and the residual information; And generating reconstructed samples for the current block based on the residual samples, and if the lossless coding is used based on the determination result, transform skip residual coding for the current block Syntax elements according to the Skip Residual Coding (TSRC) syntax structure are parsed.

According to this document, the efficiency of residual coding can be improved.

According to this document, it is possible to determine a residual coding method of residual information based on whether lossless coding is used, and through this, a residual coding method with better efficiency can be selected while reducing coding efficiency and complexity to obtain a residual sample. And improve the overall residual coding efficiency.

1 schematically shows an example of a video/video coding system to which embodiments of this document can be applied.

2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which embodiments of the present document can be applied.

3 is a diagram schematically illustrating a configuration of a video/image decoding apparatus to which embodiments of the present document can be applied.

FIG. 4 exemplarily shows context-adaptive binary arithmetic coding (CABAC) for encoding a syntax element.

5 is a diagram illustrating an example of transform coefficients in a 4x4 block.

6 schematically shows an image encoding method by an encoding apparatus according to this document.

7 schematically shows an encoding apparatus that performs an image encoding method according to this document.

8 schematically shows an image decoding method by a decoding apparatus according to this document.

9 schematically shows a decoding apparatus that performs an image decoding method according to this document.

10 exemplarily shows a structural diagram of a content streaming system to which embodiments of the present document are applied.

In this document, various changes may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the embodiments of this document to specific embodiments. Terms commonly used in the present specification are used only to describe specific embodiments, and are not intended to limit the technical idea of this document. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features or It is to be understood that the presence or addition of numbers, steps, actions, components, parts or combinations thereof does not preclude the possibility of preliminary exclusion.

Meanwhile, each of the components in the drawings described in the present document is independently illustrated for convenience of description of different characteristic functions, and does not mean that the components are implemented as separate hardware or separate software. For example, two or more of the configurations may be combined to form one configuration, or one configuration may be divided into a plurality of configurations. Embodiments in which each configuration is integrated and/or separated are also included in the scope of the rights of this document, unless departing from the essence of this document.

Hereinafter, exemplary embodiments of the present document will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant descriptions for the same components may be omitted.

Referring to FIG. 1, a video/image coding system may include a first device (a source device) and a second device (a receiving device). The source device may transmit the encoded video/image information or data in a file or streaming form to the receiving device through a digital storage medium or a network.

The source device may include a video source, an encoding device, and a transmission unit. The receiving device may include a receiving unit, 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 unit, and the display unit may be configured as a separate device or an external component.

The video source may acquire a video/image through a process of capturing, synthesizing, or generating a video/image. The video source may include a video/image capturing device and/or a video/image generating device. The video/image capture device may include, for example, one or more cameras, a video/image archive including previously captured video/images, and the like. The video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate a video/image. For example, a virtual video/image may be generated through a computer or the like, and in this case, a video/image capturing process may be substituted as a process of generating related data.

The encoding device may encode the input video/video. The encoding apparatus may perform a series of procedures such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video/video information) may be output in the form of a bitstream.

The transmission unit may transmit the encoded video/video information or data output in the form of a bitstream to the reception unit of the receiving device through a digital storage medium or a network in a file or streaming form. Digital storage media may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD. The transmission unit may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast/communication network. The receiver may receive/extract the bitstream and transmit it to the decoding device.

The decoding device may decode the video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding device.

The renderer can render the decoded video/video. The rendered video/image may be displayed through the display unit.

This document is about video/image coding. For example, the method/embodiment disclosed in this document is a versatile video coding (VVC) standard, an essential video coding (EVC) standard, an AOMedia Video 1 (AV1) standard, a 2nd generation of audio video coding standard (AVS2), or a next-generation video/ It can be applied to a method disclosed in an image coding standard (ex. H.267 or H.268, etc.).

In this document, various embodiments related to video/image coding are presented, and the embodiments may be performed in combination with each other unless otherwise stated.

In this document, video may mean a set of images over time. A picture generally refers to a unit representing one image in a specific time period, and a subpicture/slice/tile is a unit constituting a part of a picture in coding. The subpicture/slice/tile may include one or more coding tree units (CTU). One picture may consist of one or more subpictures/slices/tiles. One picture may consist of one or more tile groups. One tile group may include one or more tiles. A brick may represent a rectangular region of CTU rows within a tile in a picture. A tile may be partitioned into multiple bricks, each of which consisting of one or more CTU rows within the tile. ). A tile that is not partitioned into multiple bricks may be also referred to as a brick. A brick scan may represent a specific sequential ordering of CTUs partitioning a picture, the CTUs may be arranged in a CTU raster scan within a brick, and bricks in a tile may be sequentially arranged in a raster scan of the bricks of the tile. And, tiles in a picture may be sequentially aligned by raster scan of the tiles of the picture (A brick scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a brick. , bricks within a tile are ordered consecutively in a raster scan of the bricks of the tile, and tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture). In addition, a subpicture may represent a rectangular region of one or more slices within a picture. That is, a subpicture may include one or more slices that collectively cover a rectangular region of a picture. A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. The tile column is a rectangular region of CTUs, the rectangular region has a height equal to the height of the picture, and the width may be specified by syntax elements in a picture parameter set (The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set). The tile row is a rectangular region of CTUs, the rectangular region has a width specified by syntax elements in a picture parameter set, and a height may be the same as the height of the picture (The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the width of the picture). A tile scan may represent a specific sequential ordering of CTUs that partition a picture, the CTUs may be sequentially arranged in a CTU raster scan in a tile, and tiles in a picture may be sequentially arranged in a raster scan of the tiles of the picture. (A tile scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture). A slice may include an integer number of bricks of a picture, and the integer number of bricks may be included in one NAL unit (A slice includes an integer number of bricks of a picture that may be exclusively contained in a single NAL unit). A slice may consist of either a number of complete tiles or only a consecutive sequence of complete bricks of one tile. ). Tile groups and slices can be used interchangeably in this document. For example, in this document, the tile group/tile group header may be referred to as a slice/slice header.

A pixel or pel may mean a minimum unit constituting one 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 value of a pixel, may represent only a pixel/pixel value of a luma component, or may represent only a pixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit may include at least one of a specific area of a picture and information related to the corresponding area. One unit may include one luma block and two chroma (ex. cb, cr) blocks. The unit may be used interchangeably with terms such as a block or an area depending on the case. In general, the MxN block may include samples (or sample arrays) consisting of M columns and N rows, or a set (or array) of transform coefficients.

In the present specification, "A or B (A or B)" may mean "only A", "only B", or "both A and B". In other words, in the present specification, "A or B (A or B)" may be interpreted as "A and/or B (A and/or B)". For example, in the present specification, "A, B or C (A, B or C)" means "only A", "only B", "only C", or "any and all combinations of A, B and C ( It can mean any combination of A, B and C)".

A slash (/) or comma used in the present specification may mean "and/or". For example, "A/B" can mean "A and/or B". Accordingly, "A/B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B or C".

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" means "at least one A and B (at least one of A and B)" can be interpreted the same.

In addition, in the present specification, "at least one of A, B and C (at least one of A, B and C)" means "only A", "only B", "only C", or "A, B and C May mean any combination of A, B and C". In addition, "at least one of A, B or C (at least one of A, B or C)" or "at least one of A, B and/or C (at least one of A, B and/or C)" It can mean "at least one of A, B and C".

In addition, parentheses used in the present specification may mean "for example". Specifically, when indicated as "prediction (intra prediction)", "intra prediction" may be proposed as an example of "prediction". In other words, "prediction" in the present specification is not limited to "intra prediction", and "intra prediction" may be suggested as an example of "prediction". In addition, even when displayed as "prediction (ie, intra prediction)", "intra prediction" may be proposed as an example of "prediction".

In the present specification, technical features that are individually described in one drawing may be implemented individually or simultaneously.

The following drawings are prepared to explain a specific example of the present specification. Since the names of specific devices or names of specific signals/messages/fields described in the drawings are provided by way of example, technical features of the present specification are not limited to specific names used in the following drawings.

2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which embodiments of the present document can be applied. Hereinafter, the video encoding device may include an image encoding device.

2, the encoding device 200 includes an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, and It may be configured to include an adder 250, a filter 260, and a memory 270. The prediction unit 220 may include an inter prediction unit 221 and an intra prediction unit 222. The residual processing unit 230 may include a transform unit 232, a quantizer 233, an inverse quantizer 234, and an inverse transformer 235. The residual processing unit 230 may further include a subtractor 231. The addition unit 250 may be referred to as a reconstructor or a recontructged block generator. The image segmentation unit 210, the prediction unit 220, the residual processing unit 230, the entropy encoding unit 240, the addition unit 250, and the filtering unit 260 described above may include one or more hardware components ( For example, it may be configured by an encoder chipset or a processor). In addition, the memory 270 may include a decoded picture buffer (DPB), and may be configured by a digital storage medium. The hardware component may further include the memory 270 as an internal/external component.

The image segmentation unit 210 may divide an input image (or picture, frame) input to the encoding apparatus 200 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). In this case, the coding unit is recursively divided according to the QTBTTT (Quad-tree binary-tree ternary-tree) structure from a coding tree unit (CTU) or a largest coding unit (LCU). I can. For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and/or a ternary structure. In this case, for example, a quad tree structure may be applied first, and a binary tree structure and/or a ternary structure may be applied later. Alternatively, the binary tree structure may be applied first. The coding procedure according to this document may be performed based on the final coding unit that is no longer divided. In this case, based on the coding efficiency according to the image characteristics, the maximum coding unit can be directly used as the final coding unit, or if necessary, the coding unit is recursively divided into coding units of lower depth to be optimal. A coding unit of the size of may be used as the final coding unit. Here, the coding procedure may include a procedure such as prediction, transformation, and restoration described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be divided or partitioned from the above-described final coding unit, respectively. The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for inducing a transform coefficient and/or a unit for inducing a residual signal from the transform coefficient.

The unit may be used interchangeably with terms such as a block or an area depending on the case. In general, the MxN block may represent a set of samples or transform coefficients consisting of M columns and N rows. In general, a sample may represent a pixel or a value of a pixel, may represent only a pixel/pixel value of a luminance component, or may represent only a pixel/pixel value of a saturation component. A sample may be used as a term corresponding to one picture (or image) as a pixel or pel.

The encoding apparatus 200 subtracts the prediction signal (predicted block, prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from the input video signal (original block, original sample array) to make a residual. A signal (residual signal, residual block, residual sample array) may be generated, and the generated residual signal is transmitted to the converter 232. In this case, as illustrated, a unit that subtracts the prediction signal (prediction block, prediction sample array) from the input image signal (original block, original sample array) in the encoder 200 may be referred to as a subtraction unit 231. The prediction unit may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit may generate various information related to prediction, such as prediction mode information, as described later in the description of each prediction mode, and transmit it to the entropy encoding unit 240. The information on prediction may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the vicinity of the current block or may be located apart according to the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional mode may include, for example, a DC mode and a planar mode (Planar mode). The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes according to a detailed degree of the prediction direction. However, this is an example, and more or less directional prediction modes may be used depending on the setting. The intra prediction unit 222 may determine a prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

The inter prediction unit 221 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on correlation between 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 prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a co-located CU (colCU), and the like, and a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). May be. For example, the inter prediction unit 221 constructs a motion information candidate list based on neighboring blocks, and provides information indicating which candidate is used to derive a motion vector and/or a reference picture index of the current block. Can be generated. Inter prediction may be performed based on various prediction modes. For example, in the case of a skip mode and a merge mode, the inter prediction unit 221 may use motion information of a neighboring block as motion information of a current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the current block is calculated by using the motion vector of the neighboring block as a motion vector predictor and signaling a motion vector difference. I can instruct.

The prediction unit 220 may generate a prediction signal based on various prediction methods to be described later. For example, the prediction unit may apply intra prediction or inter prediction for prediction of one block, as well as simultaneously apply intra prediction and inter prediction. This can be called combined inter and intra prediction (CIIP). In addition, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode to predict a block. The IBC prediction mode or the palette mode may be used for content image/video coding such as a game, for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction in that it derives a reference block in the current picture. That is, the IBC may use at least one of the inter prediction techniques described in this document. The palette mode can be viewed as an example of intra coding or intra prediction. When the palette mode is applied, a sample value in a picture may be signaled based on information about a palette table and a palette index.

The prediction signal generated through the prediction unit (including the inter prediction unit 221 and/or the intra prediction unit 222) may be used to generate a reconstructed signal or may be used to generate a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transformation technique uses at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen-Loeve Transform), GBT (Graph-Based Transform), or CNT (Conditionally Non-linear Transform). Can include. Here, GBT refers to the transformation obtained from this graph when the relationship information between pixels is expressed in a graph. CNT refers to a transformation obtained based on generating a prediction signal using all previously reconstructed pixels. In addition, the conversion process may be applied to a pixel block having the same size of a square, or may be applied to a block having a variable size other than a square.

The quantization unit 233 quantizes the transform coefficients and transmits it to the entropy encoding unit 240, and the entropy encoding unit 240 encodes the quantized signal (information on quantized transform coefficients) and outputs it as a bitstream. have. The information on the quantized transform coefficients may be called residual information. The quantization unit 233 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and the quantized transform coefficients in the form of the one-dimensional vector It is also possible to generate information about transform coefficients. The entropy encoding unit 240 may perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoding unit 240 may encode together or separately information necessary for video/image reconstruction (eg, values of syntax elements) in addition to quantized transform coefficients. The encoded information (eg, encoded video/video information) may be transmitted or stored in a bitstream format in units of network abstraction layer (NAL) units. The video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/video information may further include general constraint information. In this document, information and/or syntax elements transmitted/signaled from the encoding device to the decoding device may be included in the video/video information. The video/video information may be encoded through the above-described encoding procedure and included in the bitstream. The bitstream may be transmitted through a network or may be stored in a digital storage medium. Here, the network may include a broadcasting 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, and SSD. For the signal output from the entropy encoding unit 240, a transmission unit (not shown) for transmitting and/or a storage unit (not shown) for storing may be configured as an internal/external element of the encoding apparatus 200, or the transmission unit It may be included in the entropy encoding unit 240.

The quantized transform coefficients output from the quantization unit 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual samples) may be restored by applying inverse quantization and inverse transform to the quantized transform coefficients through the inverse quantization unit 234 and the inverse transform unit 235. The addition unit 250 adds the reconstructed residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222 to obtain a reconstructed signal (restored picture, reconstructed block, reconstructed sample array). Can be created. When there is no residual for a block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block. The addition unit 250 may be referred to as a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, and may be used for inter prediction of the next picture through filtering as described later.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied during picture encoding and/or reconstruction.

The filtering unit 260 may improve subjective/objective image quality by applying filtering to the reconstructed signal. For example, the filtering unit 260 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and the modified reconstructed picture may be converted to the memory 270, specifically, the DPB of the memory 270. Can be saved on. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like. The filtering unit 260 may generate a variety of filtering information and transmit it to the entropy encoding unit 240 as described later in the description of each filtering method. The filtering information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter prediction unit 221. When inter prediction is applied through this, the encoding device may avoid prediction mismatch between the encoding device 200 and the decoding device 300 and improve encoding efficiency.

The memory 270 DPB may store the modified reconstructed picture for use as a reference picture in the inter prediction unit 221. The memory 270 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of blocks in a picture that have already been reconstructed. The stored motion information may be transferred to the inter prediction unit 221 in order to be used as motion information of spatial neighboring blocks or motion information of temporal neighboring blocks. The memory 270 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 222.

Referring to FIG. 3, the decoding apparatus 300 includes an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, and a filtering unit. It may be configured to include (filter, 350) and memory (memory, 360). The prediction unit 330 may include an inter prediction unit 331 and an intra prediction unit 332. The residual processing unit 320 may include a dequantizer 321 and an inverse transformer 322. The entropy decoding unit 310, the residual processing unit 320, the prediction unit 330, the addition unit 340, and the filtering unit 350 described above are one hardware component (for example, a decoder chipset or a processor). ) Can be configured. In addition, the memory 360 may include a decoded picture buffer (DPB), and may be configured by a digital storage medium. The hardware component may further include the memory 360 as an internal/external component.

When a bitstream including video/image information is input, the decoding apparatus 300 may reconstruct an image in response to a process in which the video/image information is processed by the encoding apparatus of FIG. 2. For example, the decoding apparatus 300 may derive units/blocks based on block division related information obtained from the bitstream. The decoding device 300 may perform decoding using a processing unit applied in the encoding device. Thus, the processing unit of decoding may be, for example, a coding unit, and the coding unit may be divided from a coding tree unit or a maximum coding unit along a quad tree structure, a binary tree structure and/or a ternary tree structure. One or more transform units may be derived from the coding unit. In addition, the reconstructed image signal decoded and output through the decoding device 300 may be reproduced through the playback device.

The decoding apparatus 300 may receive a signal output from the encoding apparatus of FIG. 2 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (eg, video/video information) necessary for image restoration (or picture restoration). The video/video information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video/video information may further include general constraint information. The decoding apparatus may further decode the picture based on the information on the parameter set and/or the general restriction information. Signaled/received information and/or syntax elements described later in this document may be decoded through the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 decodes information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and a value of a syntax element required for image restoration, a quantized value of a transform coefficient related to a residual. Can be printed. In more detail, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and includes information on a syntax element to be decoded and information on a neighboring and decoding target block or symbol/bin decoded in a previous step. A context model is determined using the context model, and a symbol corresponding to the value of each syntax element can be generated by performing arithmetic decoding of the bin by predicting the probability of occurrence of a bin according to the determined context model. have. In this case, the CABAC entropy decoding method may update the context model using information of the decoded symbol/bin for the context model of the next symbol/bin after the context model is determined. Among the information decoded by the entropy decoding unit 310, information about prediction is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and entropy decoding is performed by the entropy decoding unit 310. The dual value, that is, quantized transform coefficients and related parameter information may be input to the residual processing unit 320. The residual processing unit 320 may derive a residual signal (a residual block, residual samples, and a residual sample array). In addition, information about filtering among information decoded by the entropy decoding unit 310 may be provided to the filtering unit 350. Meanwhile, a receiver (not shown) for receiving a signal output from the encoding device may be further configured as an inner/outer element of the decoding device 300, or the receiver may be a component of the entropy decoding unit 310. Meanwhile, the decoding apparatus according to this document may be called a video/video/picture decoding apparatus, and the decoding apparatus can be divided into an information decoder (video/video/picture information decoder) and a sample decoder (video/video/picture sample decoder). May be. The information decoder may include the entropy decoding unit 310, and the sample decoder includes the inverse quantization unit 321, an inverse transform unit 322, an addition unit 340, a filtering unit 350, and a memory 360. ), an inter prediction unit 332 and an intra prediction unit 331 may be included.

The inverse quantization unit 321 may inverse quantize the quantized transform coefficients and output transform coefficients. The inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block shape. In this case, the rearrangement may be performed based on the coefficient scan order performed by the encoding device. The inverse quantization unit 321 may perform inverse quantization on quantized transform coefficients by using a quantization parameter (for example, quantization step size information) and obtain transform coefficients.

The inverse transform unit 322 obtains a residual signal (residual block, residual sample array) by inverse transforming the transform coefficients.

The prediction unit may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information on the prediction output from the entropy decoding unit 310, and may determine a specific intra/inter prediction mode.

The prediction unit 320 may generate a prediction signal based on various prediction methods to be described later. For example, the prediction unit may apply intra prediction or inter prediction for prediction of one block, as well as simultaneously apply intra prediction and inter prediction. This can be called combined inter and intra prediction (CIIP). In addition, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode to predict a block. The IBC prediction mode or the palette mode may be used for content image/video coding such as a game, for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction in that it derives a reference block in the current picture. That is, the IBC may use at least one of the inter prediction techniques described in this document. The palette mode can be viewed as an example of intra coding or intra prediction. When the palette mode is applied, information about a palette table and a palette index may be included in the video/video information and signaled.

The intra prediction unit 331 may predict the current block by referring to samples in the current picture. The referenced samples may be located in the vicinity of the current block or may be located apart according to the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 may determine a prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

The inter prediction unit 332 may derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, motion information may be predicted in units of blocks, subblocks, or samples based on correlation between 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 prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture. For example, the inter prediction unit 332 may construct a motion information candidate list based on neighboring blocks, and derive a motion vector and/or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and the information about the prediction may include information indicating a mode of inter prediction for the current block.

The addition unit 340 is reconstructed by adding the obtained residual signal to the prediction signal (predicted block, prediction sample array) output from the prediction unit (including the inter prediction unit 332 and/or the intra prediction unit 331). Signals (restored pictures, reconstructed blocks, reconstructed sample arrays) can be generated. When there is no residual for a block to be processed, such as when the skip mode is applied, the predicted block may be used as a reconstructed block.

The addition unit 340 may be referred to as a restoration unit or a restoration block generation unit. The generated reconstructed signal may be used for intra prediction of the next processing target block in the current picture, may be output through filtering as described later, or may be used for inter prediction of the next picture.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied in the picture decoding process.

The filtering unit 350 may improve subjective/objective image quality by applying filtering to the reconstructed signal. For example, the filtering unit 350 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and the modified reconstructed picture may be converted to the memory 360, specifically, the DPB of the memory 360. Can be transferred to. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360 may be used as a reference picture in the inter prediction unit 332. The memory 360 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of blocks in a picture that have already been reconstructed. The stored motion information may be transmitted to the inter prediction unit 260 to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 360 may store reconstructed samples of reconstructed blocks in the current picture, and may be transmitted to the intra prediction unit 331.

In this specification, the embodiments described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding apparatus 200 are respectively the filtering unit 350 and the inter prediction of the decoding apparatus 300. The same or corresponding to the unit 332 and the intra prediction unit 331 may be applied.

In this document, at least one of quantization/inverse quantization and/or transform/inverse transformation may be omitted. When the quantization/inverse quantization is omitted, the quantized transform coefficient may be referred to as a transform coefficient. When the transform/inverse transform is omitted, the transform coefficient may be called a coefficient or a residual coefficient, or may still be called a transform coefficient for uniformity of expression.

In this document, 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(s), and the information about the transform coefficient(s) may be signaled through a residual coding syntax. Transform coefficients may be derived based on the residual information (or information about the transform coefficient(s)), and scaled transform coefficients may be derived through an inverse transform (scaling) of the transform coefficients. Residual samples may be derived based on the inverse transform (transform) of the scaled transform coefficients. This may be applied/expressed in other parts of this document as well.

As described above, the encoding apparatus may perform various encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). In addition, the decoding apparatus may decode information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output a value of a syntax element required for image restoration and quantized values of a transform coefficient for a residual. have.

For example, the above-described coding methods may be performed as described below.

FIG. 4 exemplarily shows context-adaptive binary arithmetic coding (CABAC) for encoding a syntax element. For example, in the encoding process of CABAC, when the input signal is a syntax element other than a binary value, the encoding apparatus may convert the input signal into a binary value by binarizing the value of the input signal. In addition, when the input signal is already a binary value (that is, when the value of the input signal is a binary value), the binarization may not be performed and may be bypassed. Here, each

binary number

0 or 1 constituting the binary value may be referred to as a bin. For example, if the binary string after binarization is 110, each of 1, 1, and 0 is referred to as one bin. The bin(s) for one syntax element may represent a value of the syntax element.

Thereafter, the binarized bins of the syntax element may be input to a regular encoding engine or a bypass encoding engine. The regular encoding engine of the encoding device may allocate a context model that reflects a probability value to the corresponding bin, and encode the corresponding bin based on the allocated context model. The regular encoding engine of the encoding device may update the context model for the corresponding bin after encoding each bin. Bins encoded as described above may be referred to as context-coded bins.

Meanwhile, when binarized bins of the syntax element are input to the bypass encoding engine, they may be coded as follows. For example, the bypass encoding engine of the encoding device omits a procedure for estimating a probability for an input bin and a procedure for updating a probability model applied to the bin after encoding. When bypass encoding is applied, the encoding apparatus may encode an input bin by applying a uniform probability distribution instead of allocating a context model, thereby improving an encoding speed. The bin encoded as described above may be referred to as a bypass bin.

Entropy decoding may refer to a process of performing the same process as the above-described entropy encoding in reverse order.

For example, when a syntax element is decoded based on a context model, the decoding apparatus may receive a bin corresponding to the syntax element through a bitstream, and decoding information of the syntax element and the decoding target block or neighboring block or A context model can be determined using information of symbols/bins decoded in the previous step, and arithmetic decoding of bins by predicting the probability of occurrence of the received bin according to the determined context model The value of the syntax element can be derived by performing. Thereafter, the context model of the next decoded bin may be updated with the determined context model.

In addition, for example, when the syntax element is bypass decoded, the decoding apparatus may receive a bin corresponding to the syntax element through a bitstream, and may decode the input bin by applying a uniform probability distribution. . In this case, the decoding apparatus may omit the procedure of deriving the context model of the syntax element and the procedure of updating the context model applied to the bin after decoding.

As described above, residual samples may be derived into quantized transform coefficients through a transform and quantization process. Quantized transform coefficients may also be called transform coefficients. In this case, the transform coefficients within the block may be signaled in the form of residual information. The residual information may include residual coding syntax. That is, the encoding device may construct a residual coding syntax with residual information, encode it, and output it in the form of a bitstream, and the decoding device decodes the residual coding syntax from the bitstream to obtain residual (quantized) transform coefficients. Can be derived. As will be described later, the residual coding syntax is whether transform is applied to the corresponding block, where the position of the last effective transform coefficient in the block is, whether there is an effective transform coefficient in the subblock, and the size/code of the effective transform coefficient. It may include syntax elements representing the like.

For example, the (quantified) transform coefficient (i.e., the residual information) is last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag elements, sig_coeff_flag_flag elements, sig_coeff_flag_flag, elements of pars, sig_coeff_flag, syntax, abs_level_flag_flag It can be encoded and/or decoded on a basis. Syntax elements related to residual data encoding/decoding may be represented as in Table 1 or Table 2 below.

Meanwhile, transform_skip_flag indicates whether transformation is omitted in an associated block. The transform_skip_flag may be a syntax element of a transform skip flag. The associated block may be a coding block (CB) or a transform block (TB). Regarding the transform (and quantization) and residual coding procedure, CB and TB may be used interchangeably. For example, it is as described above that residual samples are derived for CB, and (quantized) transform coefficients can be derived through transform and quantization of the residual samples, and through a residual coding procedure. Information (eg, syntax elements) efficiently representing the position, size, sign, etc. of the (quantized) transform coefficients may be generated and signaled. Quantized transform coefficients can simply be called transform coefficients. In general, when the CB is not larger than the maximum TB, the size of the CB may be the same as the size of the TB, and in this case, the target block to be transformed (and quantized) and residual coded may be referred to as CB or TB. On the other hand, when CB is larger than the maximum TB, the target block to be transformed (and quantized) and residual coded may be referred to as TB. Hereinafter, syntax elements related to residual coding are described as being signaled in units of a transform block (TB), but this is an example, as described above, that the TB can be mixed with a coding block (CB).

Meanwhile, Table 3 to be described later shows an example of a conversion unit syntax in which the conversion skip flag is signaled. In addition, the syntax for residual coding according to the transform skip flag may be as shown in Table 4 or Table 5.

According to the present embodiment, as shown in Table 3, residual coding may be branched according to the value of the transform_skip_flag syntax element of the transform skip flag. That is, a different syntax element may be used for residual coding based on the value of the transform skip flag (based on whether or not to skip transform). The residual coding used when the transform skip is not applied (i.e., when the transform is applied) may be called regular residual coding (RRC), and when the transform skip is not applied (ie, the transform is If not applied), the residual coding may be referred to as Transform Skip Residual Coding (TSRC). In addition, the regular residual coding may be referred to as general residual coding. In addition, the regular residual coding may be referred to as a regular residual coding syntax structure, and the transform skip residual coding may be referred to as a transform skip residual coding syntax structure. Table 4 above can indicate the syntax element of residual coding when the value of transform_skip_flag is 0, that is, when transform is applied, and Table 5 shows the register when the value of transform_skip_flag is 1, that is, when the transform is not applied. It may represent a syntax element of dual coding.

Specifically, for example, a transform skip flag indicating whether to skip transform of a transform block may be parsed, and whether the transform skip flag is 1 may be determined. When the value of the transform skip flag is 0, as shown in Table 4, syntax elements for the residual coefficients of the transform block last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, last_sig_coeff_y_suffix, last_sig_coeff_y_suffix, flag, parg, pars_level_flag, and sublevel_flag_code_level_flag Alternatively, coeff_sign_flag may be parsed, and the residual coefficient may be derived based on the syntax elements. In this case, the syntax elements may be sequentially parsed, or the parsing order may be changed. In addition, the abs_level_gtx_flag may represent abs_level_gt1_flag and/or abs_level_gt3_flag. For example, abs_level_gtx_flag[n][0] may be an example of a first transform coefficient level flag (abs_level_gt1_flag), and the abs_level_gtx_flag[n][1] is an example of a second transform coefficient level flag (abs_level_gt3_flag) I can.

Referring to Table 4 above, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, sb_coded_flag, sig_coeff_flag, abs_level_gt1_flag, coeff_flag, abs_level_gt1_flag, par_level_flag, code_flag, or par_level_flag, may be encoded. Meanwhile, the sb_coded_flag may be expressed as coded_sub_block_flag.

In an embodiment, the encoding device may encode (x, y) position information of the last non-zero transform coefficient in the transform block based on the syntax elements last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. More specifically, the last_sig_coeff_x_prefix represents the prefix of the column position of the last significant coefficient in the scanning order in the transform block, and the last_sig_coeff_y_prefix is within the transform block. Represents a prefix of the row position of the last significant coefficient in the scanning order, and the last_sig_coeff_x_suffix is in the scanning order in the transform block. Represents the suffix of the column position of the last significant coefficient, and the last_sig_coeff_y_suffix is the last significant coefficient in the scanning order in the transform block. coefficient) represents the suffix of the row position. Here, the effective coefficient may represent the non-zero coefficient. In addition, the scan order may be an upward-right diagonal scan order. Alternatively, the scan order may be a horizontal scan order or a vertical scan order. The scan order may be determined based on whether intra/inter prediction is applied to a target block (CB or CB including TB) and/or a specific intra/inter prediction mode.

Next, the encoding apparatus divides the transform block into 4x4 sub-blocks, and then determines whether a non-zero coefficient exists in the current sub-block using a 1-bit syntax element coded_sub_block_flag for each 4x4 sub-block. Can be indicated.

If the value of coded_sub_block_flag is 0, since there is no more information to be transmitted, the encoding apparatus may end the encoding process for the current subblock. Conversely, if the value of coded_sub_block_flag is 1, the encoding device may continue to perform the encoding process for sig_coeff_flag. The coded_sub_block_flag is not coded because the subblock containing the last non-zero coefficient does not require coding of the coded_sub_block_flag, and the subblock containing the DC information of the transform block has a high probability of containing the non-zero coefficient. This can be assumed to be 1.

If it is determined that a non-zero coefficient exists in the current sub-block because the value of coded_sub_block_flag is 1, the encoding apparatus may encode sig_coeff_flag having a binary value according to the reverse scan order. The encoding apparatus may encode a 1-bit syntax element sig_coeff_flag for each transform coefficient according to a scan order. If the value of the transform coefficient at the current scan position is not 0, the value of sig_coeff_flag may be 1. Here, in the case of a subblock including the last non-zero coefficient, since sig_coeff_flag does not need to be encoded for the last non-zero coefficient, the encoding process for the sub-block may be omitted. Level information encoding may be performed only when sig_coeff_flag is 1, and four syntax elements may be used in the level information encoding process. More specifically, each sig_coeff_flag[xC][yC] may indicate whether the level (value) of the corresponding transform coefficient at each transform coefficient position (xC, yC) in the current TB is non-zero (non-zero). In an embodiment, the sig_coeff_flag may correspond to an example of a syntax element of a significant coefficient flag indicating whether a quantized transform coefficient is a non-zero effective coefficient.

The level value remaining after encoding for sig_coeff_flag may be derived as shown in the following equation. That is, the syntax element remAbsLevel representing the level value to be encoded can be derived with the following equation.

Here, coeff means an actual transform coefficient value.

Also, abs_level_gt1_flag may indicate whether the remAbsLevel at the corresponding scanning position n is greater than 1. For example, if the value of abs_level_gt1_flag is 0, the absolute value of the transform coefficient at the corresponding location may be 1. In addition, when the value of abs_level_gt1_flag is 1, the remAbsLevel indicating a level value to be encoded later may be updated as shown in the following equation.

In addition, the least significant coefficient (LSB) value of remAbsLevel described in Equation 2 may be encoded as Equation 3 below through par_level_flag.

Here, par_level_flag[n] may represent parity of the transform coefficient level (value) at the scanning position n.

After encoding par_leve_flag, the transform coefficient level value remAbsLevel to be encoded may be updated as shown in the following equation.

abs_level_gt3_flag may indicate whether remAbsLevel at the corresponding scanning position n is greater than 3. Encoding for abs_remainder may be performed only when abs_level_gt3_flag is 1. The relationship between the actual transform coefficient value coeff and each syntax element may be as follows.

In addition, the following table shows examples related to Equation 5 above.

Where, | coeff| represents a transform coefficient level (value), and may be expressed as AbsLevel for the transform coefficient. In addition, the sign of each coefficient may be encoded using a 1-bit symbol coeff_sign_flag.

In addition, for example, when the value of the transform skip flag is 1, as shown in Table 6, syntax elements sb_coded_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag, par_level_flag and/or abs_remainder for the residual coefficients of the transform block are parsed as shown in Table 6. And the residual coefficient may be derived based on the syntax elements. In this case, the syntax elements may be sequentially parsed, or the parsing order may be changed. In addition, the abs_level_gtx_flag may represent abs_level_gt1_flag, abs_level_gt3_flag, abs_level_gt5_flag, abs_level_gt7_flag and/or abs_level_gt9_flag. For example, abs_level_gtx_flag[n][j] may be a flag indicating whether the absolute value or level (value) of the transform coefficient is greater than (j<<1)+1 at the scanning position n. The (j<<1)+1 may be replaced by a predetermined threshold value, such as a first threshold value and a second threshold value, in some cases.

On the other hand, CABAC provides high performance, but has a disadvantage of poor throughput performance. This is due to CABAC's regular encoding engine, and regular encoding (that is, encoding through CABAC's regular encoding engine) shows high data dependence because it uses the updated probability state and range through encoding of the previous bin. It can take a lot of time to read the probability interval and determine the current state. The throughput problem of CABAC can be solved by limiting the number of context-coded bins. For example, the sum of bins used to express sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag as shown in Table 1 or 3 described above may be limited to the number according to the size of the corresponding block. In addition, for example, as shown in Table 4 above, sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag abs_level_gt5_flag, abs_level_gt7_flag, and abs_level_gt9_flag may be used to express the sum of bin sizes according to the number of bins according to the size of the corresponding block. For example, if the corresponding block is a 4x4 size block, the sum of sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag or sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_flag_flag, for example, the sum of abs_level_gt1_flag, par_level_flag, abs_flag_flag, or abs_level_flag is 32 for ab Number), and when the corresponding block is a 2x2 size block, the sum of bins for the sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag may be limited to 8 (or, for example, 7). The limited number of bins can be represented by remBinsPass1 or RemCcbs. Or, for example, for higher CABAC throughput, the number of context coded bins may be limited for a block (CB or TB) including a CG to be coded. In other words, the number of context encoding bins may be limited in units of blocks (CB or TB). For example, if the size of the current block is 16x16, the number of context encoding bins for the current block may be limited to 1.75 times the number of pixels of the current block, that is, 448, regardless of the current CG.

In this case, if all of the limited number of context encoding bins are used to encode the context element, the encoding device binarizes the remaining coefficients through a binarization method for the coefficients described later without using context coding, and performs bypass coding. can do. In other words, for example, the number of context coded bins coded for 4x4 CG is 32 (or, for example, 28), or the number of context coded bins coded for 2x2 CG is 8 (or for example For example, in the case of 7), sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag, which are no longer coded as context coding bins, may not be coded, and may be directly coded as dec_abs_level as shown in Table 13 below. Alternatively, for example, when the number of context coded bins coded for a 4x4 block is limited to 1.75 times the number of pixels of the entire block, that is, 28, sig_coeff_flag, abs_level_gt1_flag that are no longer coded as context coded bins , par_level_flag, and abs_level_gt3_flag may not be coded, and may be directly coded as dec_abs_level as shown in Table 7 described later.

Based on dec_abs_level |coeff| Values can be derived. In this case, the transform coefficient value, |coeff| Can be derived as the following equation.

In addition, the coeff_sign_flag may represent a sign of a transform coefficient level at a corresponding scanning position n. That is, the coeff_sign_flag may represent the sign of the transform coefficient at the corresponding scanning position n.

The 4x4 block of FIG. 5 shows an example of quantized coefficients. The block shown in FIG. 5 may be a 4x4 transform block or a 4x4 sub-block of an 8x8, 16x16, 32x32, or 64x64 transform block. The 4x4 block of FIG. 5 may represent a luma block or a chroma block.

Meanwhile, as described above, when the input signal is a syntax element other than a binary value, the encoding apparatus may convert the input signal into a binary value by binarizing the value of the input signal. In addition, the decoding apparatus may decode the syntax element to derive a binarized value (ie, binarized bin) of the syntax element, and inverse binarize the binarized value to derive the value of the syntax element. The binarization process is a Truncated Rice (TR) binarization process, a k-th order Exp-Golomb (EGk) binarization process, a k-order Limited Exp. -Golomb (Limited k-th order Exp-Golomb, Limited EGk), or a fixed-length (FL) binarization process, etc. may be performed. In addition, the inverse binarization process may be performed based on the TR binarization process, the EGk binarization process, or the FL binarization process to derive a value of the syntax element.

For example, the TR binarization process may be performed as follows.

The input of the TR binarization process may be a request for TR binarization and cMax and cRiceParam for a syntax element. Further, the output of the TR binarization process may be TR binarization for a value symbolVal corresponding to an empty string.

Specifically, as an example, when there is a suffix empty string for a syntax element, the TR empty string for the syntax element may be a concatenation of a prefix empty string and a suffix empty string, and the When the suffix bin string does not exist, the TR bin string for the syntax element may be the prefix bin string. For example, the prefix empty string may be derived as described later.

The prefix value of the symbolVal for the syntax element may be derived as the following equation.

Here, prefixVal may represent the prefix value of the symbolVal. A prefix of the TR bin string of the syntax element (that is, a prefix bin string) may be derived as described later.

For example, when the prefixVal is smaller than cMax >> cRiceParam, the prefix bin string may be a bit string of length prefixVal + 1 indexed by binIdx. That is, when the prefixVal is smaller than cMax >> cRiceParam, the prefix empty string may be a bitstring of prefixVal + 1 bit number indicated by binIdx. The bin for binIdx less than prefixVal can be equal to 1. Also, a bin for binIdx that is identical to prefixVal may be equal to 0.

For example, an empty string derived by unary binarization for the prefixVal may be as shown in the following table.

Meanwhile, when the prefixVal is not smaller than cMax >> cRiceParam, the prefix bean string may be a bit string having a length of cMax >> cRiceParam and all bins being 1.

In addition, when cMax is greater than symbolVal and cRiceParam is greater than 0, a suffix of the TR bin string may exist. For example, the suffix bin string may be derived as described later.

The suffix value of the symbolVal for the syntax element may be derived as follows.

Here, suffixVal may represent a suffix value of symbolVal.

The suffix of the TR bean string (ie, the suffix bean string) may be derived based on the FL binarization process for suffixVal whose cMax value is (1 << cRiceParam)-1.

On the other hand, if the value of the input parameter cRiceParam is 0, the TR binarization may be exactly truncated unary binarization, and a cMax value equal to the maximum possible value of the syntax element to be always decoded may be used.

Also, for example, the EGk binarization process may be performed as follows. The syntax element coded with ue(v) may be an Exp-Golomb coded syntax element.

For example, a 0-th order Exp-Golomb (EG0) binarization process may be performed as follows.

The parsing process for the syntax element may be started by reading a bit including the first non-zero bit starting from the current position of the bitstream and counting the number of preceding bits equal to 0. have. The process can be expressed as shown in the following table.

In addition, the variable codeNum can be derived as the following equation.

Here, the value returned from read_bits(leadingZeroBits), that is, the value indicated by read_bits(leadingZeroBits), is a binary representation of an unsigned integer for the most significant bit recorded first. Can be interpreted.

The structure of the Exp-Golomb code in which the bit string is divided into "prefix" bits and "suffix" bits can be expressed as shown in the following table.

The "prefix" bit may be a bit parsed as described above for calculating leadingZeroBits, and may be represented as 0 or 1 of the bit string in Table 10. That is, the bit string disclosed by 0 or 1 in Table 10 described above may represent a prefix bit string. The "suffix" bit may be a bit parsed in the calculation of codeNum, and may be indicated by xi in Table 10 described above. That is, the bit string disclosed by xi in Table 10 may represent a suffix bit string. Here, i may be a value in the range of 0 to LeadingZeroBits-1. In addition, each xi may be equal to 0 or 1.

The bit string allocated to the codeNum may be as shown in the following table.

When the descriptor of the syntax element is ue(v), that is, when the syntax element is coded as ue(v), the value of the syntax element may be the same as codeNum.

Also, for example, the EGk binarization process may be performed as follows.

An input of the EGk binarization process may be a request for EGk binarization. In addition, an output of the EGk binarization process may be EGk binarization for a value symbolVal corresponding to an empty string.

The bit string of the EGk binarization process for symbolVal can be derived as follows.

Referring to Table 12 above, a binary value X may be added to the end of an empty string through each call of put(X). Here, X may be 0 or 1.

Further, for example, the Limited EGk binarization process may be performed as follows.

The input of the Limited EGk binarization process may be a request for Limited EGk binarization and a Rice parameter riceParam, log2TransformRange, a variable representing the maximum binary logarithm, and maxPreExtLen, a variable representing the maximum prefix extension length. Also, the output of the Limited EGk binarization process may be Limited EGk binarization for a value symbolVal corresponding to an empty string.

The bit string of the Limited EGk binarization process for symbolVal can be derived as follows.

Also, for example, the FL binarization process may be performed as follows.

An input of the FL binarization process may be a request for FL binarization and cMax for the syntax element. Also, an output of the FL binarization process may be FL binarization for a value symbolVal corresponding to an empty string.

FL binarization can be constructed using a bit string having a fixed number of bits of the symbol value symbolVal. Here, the fixed length bit may be an unsigned integer bit string. That is, a bit string for the symbol value symbolVal may be derived through FL binarization, and the bit length (ie, the number of bits) of the bitstring may be a fixed length.

For example, the fixed length may be derived as follows.

The indexing of bins for FL binarization may be a method of using a value increasing from the most significant bit to the least significant bit. For example, the bin index related to the most significant bit may be binIdx = 0.

Meanwhile, for example, the binarization process for the syntax element abs_remainder among the residual information may be performed as follows.

The input of the binarization process for abs_remainder may be a request for binarization of the syntax element abs_remainder[n], a color component cIdx, and a luma position (x0, y0). The luma position (x0, y0) may indicate an upper left sample of the current luma transform block based on the upper left luma sample of the picture.

The output of the binarization process for the abs_remainder may be the binarization of the abs_remainder (ie, the binarized bin string of the abs_remainder). Usable bin strings for the abs_remainder may be derived through the binarization process.

Rice parameter cRiceParam for the abs_remainder[n] is the color component cIdx and luma position (x0, y0), the current coefficient scan position (xC, yC), log2TbWidth which is the binary logarithm of the width of the transform block, and the binary of the height of the transform block. It can be derived through a rice parameter derivation process performed by inputting log2TbHeight, which is an algebraic number. A detailed description of the process of deriving the rice parameter will be described later.

In addition, for example, cMax for abs_remainder[n] currently coded may be derived based on the Rice parameter cRiceParam. The cMax can be derived as the following equation.

On the other hand, the binarization for abs_remainder, that is, the empty string for abs_remainder may be a concatenation of a prefix empty string and a suffix empty string when a suffix empty string exists. In addition, when the suffix empty string does not exist, the empty string for abs_remainder may be the prefix empty string.

For example, the prefix empty string may be derived as described later.

The prefixVal of the abs_remainder[n] may be derived as the following equation.

The prefix of the empty string of abs_remainder[n] (that is, the prefix empty string) may be derived through the TR binarization process for the prefixVal using the cMax and cRiceParam as inputs.

If the prefix bin string is equal to a bit string in which all bits are 1 and a bit length is 6, a suffix bin string of the bin string of abs_remainder[n] may exist and may be derived as described later.

A process of deriving a Rice parameter for abs_remainder[n] may be as follows.

The input of the Rice parameter derivation process includes a color component index cIdx, a luma position (x0, y0), a current count scan position (xC, yC), a binary logarithm of the transform block width, log2TbWidth, and It may be log2TbHeight, which is the binary logarithm of the height of the transform block. The luma position (x0, y0) may indicate an upper left sample of the current luma transform block based on the upper left luma sample of the picture. In addition, the output of the rice parameter derivation process may be the rice parameter cRiceParam.

For example, based on the given component index cIdx, the array AbsLevel[x][y] for the transform block having the upper left luma position (x0, y0), the variable locSumAbs is the pseudo code disclosed in the following table and Can be derived together.

Thereafter, based on the given variable locSumAbs, the Rice parameter cRiceParam may be derived as shown in the following table.

In addition, for example, in the process of deriving a rice parameter for abs_remainder[n], the baseLevel may be set to 4.

Or, for example, the Rice parameter cRiceParam may be determined based on whether the current block is skipped. That is, when transformation is not applied to the current TB including the current CG, that is, when transform skip is applied to the current TB including the current CG, the Rice parameter cRiceParam is 1 Can be derived.

In addition, the suffix value suffixVal of the abs_remainder may be derived by the following equation.

The empty string suffix of the empty string of abs_remainder is k is set to cRiceParam+1, riceParam is set to cRiceParam, log2TransformRange is set to 15, and maxPreExtLen is set to 11 through the Limited EGk binarization process for the suffixVal. Can be derived.

Meanwhile, for example, the binarization process for the syntax element dec_abs_level among the residual information may be performed as follows.

The input of the binarization process for the dec_abs_level is a request for binarization of the syntax element dec_abs_level[n], a color component cIdx, a luma position (x0, y0), a current coefficient scan position (xC, yC), and a transform block. It may be log2TbWidth, which is the binary logarithm of the width, and log2TbHeight, which is the binary logarithm of the height of the transform block. The luma position (x0, y0) may indicate an upper left sample of the current luma transform block based on the upper left luma sample of the picture.

The output of the binarization process for the dec_abs_level may be the binarization of the dec_abs_level (ie, the binarized bin string of the dec_abs_level). Usable bin strings for the dec_abs_level may be derived through the binarization process.

Rice parameter cRiceParam for the dec_abs_level[n] is the color component cIdx and luma position (x0, y0), the current coefficient scan position (xC, yC), log2TbWidth, which is the binary logarithm of the width of the transform block, and the binary of the height of the transform block. It can be derived through a rice parameter derivation process performed by inputting log2TbHeight, which is an algebraic number. A detailed description of the process of deriving the rice parameter will be described later.

Also, for example, cMax for the dec_abs_level[n] may be derived based on the Rice parameter cRiceParam. The cMax can be derived as the following equation.

On the other hand, binarization of the dec_abs_level[n], that is, the empty string for the dec_abs_level[n] is a concatenation of a prefix empty string and a suffix empty string if there is a suffix empty string. I can. In addition, when the suffix bin string does not exist, the bin string for dec_abs_level[n] may be the prefix bin string.

For example, the prefix empty string may be derived as described later.

The prefixVal of the dec_abs_level[n] may be derived as the following equation.

The prefix of the empty string of dec_abs_level[n] (that is, the prefix empty string) may be derived through a TR binarization process for the prefixVal using the cMax and cRiceParam as inputs.

If the prefix bin string is the same as a bit string in which all bits are 1 and a bit length is 6, a suffix bin string of the bin string of dec_abs_level[n] may exist and may be derived as described later.

A process of deriving a Rice parameter for dec_abs_level[n] may be as follows.

In addition, for example, in the process of deriving a Rice parameter for dec_abs_level[n], baseLevel may be set to 0, and ZeroPos[n] may be derived as follows.

In addition, the suffix value suffixVal of the dec_abs_level[n] may be derived as the following equation.

The suffix bin string of the empty string of dec_abs_level[n] can be derived through the Limited EGk binarization process for the suffixVal in which k is set to cRiceParam+1, truncSuffixLen is set to 15, and maxPreExtLen is set to 11. .

Meanwhile, the above-described Regular Residual Coding (RRC) and Transform Skip Residual Coding (TSRC) may have the following differences.

For example, in transform skip residual coding, the Rice parameter for the syntax element abs_remainder[] may be derived as 1. The rice parameter cRiceParam of the syntax element abs_remainder[] in regular residual coding can be derived based on the lastAbsRemainder and the lastRiceParam as described above, but the rice parameter cRiceParam of the syntax element abs_remainder[] in transform skip residual coding Can be derived as 1. That is, for example, when transform skip is applied to the current block (eg, the current TB), the Rice parameter cRiceParam for abs_remainder[] of the transform skip residual coding for the current block is 1 Can be derived as

In addition, for example, referring to Tables 4 and 5, abs_level_gtx_flag[n][0] and/or abs_level_gtx_flag[n][1] may be signaled in regular residual coding, but abs_level_gtx_flag[] in transform skip residual coding. n][0], abs_level_gtx_flag[n][1], abs_level_gtx_flag[n][2], abs_level_gtx_flag[n][3], and abs_level_gtx_flag[n][4] may be signaled. Here, the abs_level_gtx_flag[n][0] can be expressed as abs_level_gt1_flag or a first coefficient level flag, and the abs_level_gtx_flag[n][1] can be expressed as abs_level_gt3_flag or a second coefficient level flag, and the abs_level_gtx_flag[n][ 2] may be expressed as abs_level_gt5_flag or a third coefficient level flag, and abs_level_gtx_flag[n][3] may be expressed as abs_level_gt7_flag or a fourth coefficient level flag, and abs_level_gtx_flag[n][4] is abs_level_gt9_flag or a fifth coefficient It can be expressed as a level flag. Specifically, the first count level flag is a flag indicating whether the count level is greater than a first threshold (eg, 1), and the second count level flag is a count level is a second threshold value (eg, 3). A flag indicating whether the coefficient level is greater than or not, the third coefficient level flag is a flag indicating whether the coefficient level is greater than a third threshold value (eg, 5), and the fourth coefficient level flag indicates whether the coefficient level is a fourth threshold value (eg For example, a flag indicating whether the coefficient is greater than 7), and the fifth coefficient level flag may be a flag indicating whether the coefficient level is greater than a fifth threshold (eg, 9). As described above, the transform skip residual coding is compared with the regular residual coding, along with abs_level_gtx_flag[n][0], abs_level_gtx_flag[n][1], abs_level_gtx_flag[n][2], abs_level_gtx_flag[n][3] and It may further include abs_level_gtx_flag[n][4].

In addition, for example, in regular residual coding, the syntax element coeff_sign_flag may be bypass coded, but in transform skip residual coding, the syntax element coeff_sign_flag may be bypass coded or context coded.

Meanwhile, in lossless coding, processing that may cause information loss in an image coding system such as transform and quantization may be modified and/or bypassed. For example, lossless coding is a coding technique that causes information loss in coding residual information, such as high frequency zero-out, joint Cb Cr (joint Cb Cr), and sine data hiding ( sign data hiding), LMCS, and/or at least one of (inverse) transformation, (inverse) quantization, etc. may not be applied. Alternatively, when the lossless coding is applied, the decoded image may be the same as the original image, and therefore, in-loop filtering may not be necessary to introduce unwanted distortion.

Alternatively, lossless coding may mean coding in which at least one of (inverse) transformation and/or (inverse) quantization is not applied in coding residual information. Alternatively, lossless coding may mean coding to which (inverse) transformation and (inverse) quantization are not applied in coding residual information.

Whether the lossless coding is applied may be determined in units of CU, slice, tile, subpicture, picture, or sequence.

For example, whether the lossless coding is applied may be signaled/determined based on flag information on whether the lossless coding is applied. However, this is an example, and it may be determined or indicated whether the lossless coding is applied by another method.

For example, whether the lossless coding is used may be determined based on a quantization parameter (QP) value. For example, the video/video information may include information related to the QP, and when lossless coding is used, the information related to the QP may indicate that the QP is 4. As another example, when lossless coding is used, the QP may be derived as 4 without signaling the information related to the QP. A quantization/dequantization procedure may be performed based on the QP. For example, when the QP is 4, quantization/inverse quantization may be omitted for the current block. In this case, for example, the value of the transform coefficient in the current block and the value of the quantized transform coefficient may be the same. For example, (quantized) transform coefficients may be derived based on a transform skip residual coding syntax or a regular residual coding syntax, and a transform coefficient of the current block based on the (quantized) transform coefficients and the QP Can be derived. As described above, the residual samples of the current block can be derived through an inverse transform procedure for the transform coefficients of the current block.

Alternatively, as another example, whether the lossless coding is applied may be signaled in units of high level syntax (HLS) or blocks. For example, when the HLS indicates that the image relates to defense or medical care, the lossless coding may be applied.

According to an embodiment of the present document, when lossless coding is used for the current block, syntax elements according to a transform skip residual coding (TSRC) syntax structure may be parsed to perform residual coding. The transform skip residual coding syntax according to the above-described embodiment may be shown in Table 16 or Table 17 below. Alternatively, the transform skip residual coding syntax may be as shown in Table 4 above. Alternatively, when lossless coding is not used in the current block, syntax elements according to a regular residual coding syntax structure may be parsed to perform residual coding.

Alternatively, as another example, whether lossless coding is used may be determined based on a flag indicating whether lossless coding is used. For example, a syntax element cu_transquant_bypass_flag indicating whether lossless coding is used in a CU (coding unit) unit may be signaled. That is, the syntax element cu_transquant_bypass_flag may indicate whether lossless coding is used for the current block. For example, when the value of cu_transquant_bypass_flag is 1, it may indicate that lossless coding is used for the current block.

Meanwhile, the above-described scheme is an example, and HLS such as a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, etc. not the CU syntax. A flag indicating whether lossless coding is used may be signaled in (High Level Syntax).

Meanwhile, as described above in Table 3, the syntax element transform_skip_flag of the transform skip flag may indicate whether or not transform is omitted in the current block. Meanwhile, the semantics and CU syntax for the existing transform skip flag may be as shown in the following tables.

Referring to the above tables, if the value of the syntax element BdcpmFlag indicating whether or not BDPCM (Block-based Delta Pulse Code Modulation) is applied to the current block is 1, then the Transform Skip Residual Coding (TSRC) syntax The syntax elements according to the structure are parsed to perform residual coding, and when the value of BdcpmFlag is 0, the syntax elements according to the regular residual coding syntax structure are parsed and residual coding may be performed. That is, even when lossless coding is used, if the current block is not a BDPCM block, syntax elements according to a regular residual coding syntax structure may be parsed to perform residual coding.

According to an embodiment of the present document, when lossless coding is used in the current block, the syntax according to the syntax structure of regular residual coding is inferred as the value of the transform_skip_flag syntax element of the transform skip flag as 1 Elements can be parsed. For example, when a flag indicating whether lossless coding is used is 1, the value of transform_skip_flag may be inferred as 1. Semantics for the transform skip flag according to an embodiment of the present document may be as follows.

According to Table 22 above, when the transform_skip_flag syntax element for the current block does not exist, the value of transform_skip_flag may be inferred or derived. For example, when the transform_skip_flag syntax element for the corresponding block does not exist, the value of transform_skip_flag may be inferred based on the value of cu_transquant_bypass_flag. For example, when the transform_skip_flag syntax element for the current block does not exist and the cu_transquant_bypass_flag value is 1, the value of transform_skip_flag may be deduced as 1. That is, when lossless coding is used, the transform_skip_flag syntax element does not exist, and the value of transform_skip_flag may be inferred as 1. Meanwhile, when lossless coding is not used, transform_skip_flag may be determined based on the syntax element BdcpmFlag indicating whether BDPCM is applied to the current block.

Accordingly, when lossless coding is used for the current block, the syntax elements according to the Transform Skip Residual Coding (TSRC) syntax structure are parsed regardless of whether the current block is a BDPCM block, and residual coding is performed. Can be.

Meanwhile, the semantics for the transform skip flag according to an embodiment of the present document may be as shown in the following table.

According to Table 23 above, when lossless coding is used for the current block and the prediction mode of the current block is not the inter prediction mode, syntax elements according to a transform skip residual coding syntax structure are parsed to perform residual coding. have. When the prediction mode of the current block is not the inter prediction mode, it may correspond to a case where the prediction mode of the current block is an intra prediction mode or an intra block copy (IBC) prediction mode. In addition, when lossless coding is used for the current block and the prediction mode of the current block is the inter prediction mode, syntax elements according to a regular residual coding syntax structure may be parsed to perform residual coding. Meanwhile, when lossless coding is not used, transform_skip_flag may be determined based on the syntax element BdcpmFlag indicating whether BDPCM is applied to the current block.

Alternatively, the semantics for the transform skip flag according to an embodiment of the present document may be as shown in the following table.

According to Table 24 above, when lossless coding is used for the current block and the prediction mode of the current block is not an intra prediction mode, syntax elements according to a regular residual coding syntax structure are parsed to perform residual coding. . When the prediction mode of the current block is not the intra prediction mode, it may correspond to a case where the prediction mode of the current block is an inter prediction mode or an intra block copy (IBC) prediction mode. Also, when lossless coding is used for the current block and the prediction mode of the current block is an intra prediction mode, syntax elements according to a transform skip residual coding syntax structure may be parsed to perform residual coding. Meanwhile, when lossless coding is not used, transform_skip_flag may be determined based on the syntax element BdcpmFlag indicating whether BDPCM is applied to the current block.

6 schematically shows an image encoding method by an encoding apparatus according to this document. The method disclosed in FIG. 6 may be performed by the encoding apparatus disclosed in FIG. 2. Specifically, for example, S600 of FIG. 6 may be performed by a subtraction unit of the encoding device, S610 of FIG. 6 may be performed by a residual processing unit of the encoding device, and S620 to S640 are the encoding devices. It can be performed by the entropy encoding unit of. In addition, although not shown, the process of deriving a prediction sample may be performed by the prediction unit of the encoding device, and a reconstructed sample and a reconstructed sample for the current block based on a residual sample and a prediction sample for the current block. A process of generating a picture may be performed by an adding unit of the encoding device, and a process of encoding prediction information for the current block may be performed by an entropy encoding unit of the encoding device.

The encoding apparatus derives a residual sample of the current block (S600). For example, the encoding apparatus may determine whether to perform inter prediction or intra prediction on the current block, and may determine a specific inter prediction mode or a specific intra prediction mode based on RD cost. Depending on the determined mode, the encoding apparatus may derive a prediction sample for the current block, and may derive the residual sample by subtracting the original sample for the current block and the prediction sample.

The encoding device determines whether lossless coding is used for the current block (S610). In lossless coding, processing that may cause information loss in a video coding system can be modified and/or bypassed. For example, at least one of (inverse) transformation and/or (inverse) quantization, which are coding techniques that cause information loss, may not be applied. Alternatively, lossless coding may mean coding in which at least one of (inverse) transformation and/or (inverse) quantization is not applied in coding residual information.

That is, the encoding device may determine whether (inverse) transform and/or (inverse) quantization is applied to the current block. The encoding apparatus may determine whether (inverse) transform and/or (inverse) quantization is applied to the residual sample of the current block.

Also, the encoding device may generate a flag indicating whether lossless coding is used for the current block.

The encoding apparatus encodes residual information for the residual sample of the current block based on the determination result (S620).

For example, the encoding apparatus may encode syntax elements according to a Transform Skip Residual Coding (TSRC) syntax structure for the current block based on a determination that lossless coding is used. That is, based on the determination that lossless coding is used, the residual information on the residual sample of the current block may include syntax elements according to the transform skip residual coding syntax structure.

Alternatively, for example, the encoding apparatus may encode syntax elements according to a regular residual coding syntax structure for the current block based on a determination that lossless coding is not used. That is, based on the determination that lossless coding is not used, the residual information on the residual sample of the current block may include syntax elements according to the regular residual coding syntax structure.

Meanwhile, the syntax elements according to the transform skip residual coding syntax structure are a coded sub-block flag indicating whether the current sub-block of the current block includes a non-zero residual coefficient, and the residual coefficient of the current block is non-zero. (non-zero) a significant coefficient flag indicating whether the residual coefficient is a residual coefficient, a sine flag indicating the sign of the residual coefficient, a parity level flag for the parity of the coefficient level for the residual coefficient, the coefficient level is the first threshold A first coefficient level flag for whether or not greater than, a second coefficient level flag for whether the coefficient level of the residual coefficient is greater than a second threshold, a third coefficient level flag for whether the coefficient level of the residual coefficient is greater than a third threshold The coefficient level flag, the fourth coefficient level flag for whether the coefficient level of the residual coefficient is greater than the fourth threshold, the fifth coefficient level flag for whether the coefficient level of the residual coefficient is greater than the fifth threshold, and the residual coefficient. It may include information related to the coefficient value for the value.

In addition, the syntax elements according to the regular residual coding syntax structure include position information on the position of the last non-zero residual coefficient in the residual coefficient array of the current block, and the current subblock of the current block. Coded sub-block flag for whether to include a non-zero residual coefficient, an effective coefficient flag for whether the residual coefficient of the current block is a non-zero residual coefficient, a coefficient for the residual coefficient A first coefficient level flag for whether the level is greater than a first threshold, a parity level flag for parity of the coefficient level, a second coefficient level flag for whether the coefficient level of the residual coefficient is greater than a second threshold, It may include information related to the coefficient value for the residual coefficient value and a sign flag for the sign of the residual coefficient.

Meanwhile, the encoding device may generate and encode a flag indicating whether lossless coding is used. For example, a flag indicating whether lossless coding is used may be signaled through a coding unit (CU) syntax.

In addition, the encoding device may generate and encode a transform skip flag indicating whether to apply the transform of the current block. In this case, when lossless coding is used, the value of the transform skip flag may be set to 1. Alternatively, when lossless coding is used, a quantization parameter (QP) for the current block may be set to 4.

The encoding device generates a bitstream including residual information (S630).

For example, the encoding device may output image information including residual information as a bitstream. Meanwhile, the bitstream may be transmitted to a decoding device through a network or a (digital) storage medium. Here, the network may include a broadcasting 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, and SSD.

7 schematically shows an encoding apparatus that performs an image encoding method according to this document. The method disclosed in FIG. 6 may be performed by the encoding apparatus disclosed in FIG. 7. Specifically, for example, the subtraction unit of the encoding device of FIG. 6 may perform S600 of FIG. 6, the residual processing unit of the encoding device may perform S610 of FIG. 6, and The entropy encoding unit may perform S620 and S630 of FIG. 6. In addition, although not shown, the process of deriving a prediction sample may be performed by the prediction unit of the encoding device, and a reconstructed sample for the current block is derived based on a residual sample and a prediction sample for the current block. The process may be performed by an adder of the encoding device, and a process of encoding prediction information for the current block may be performed by an entropy encoding unit of the encoding device.

8 schematically shows an image decoding method by a decoding apparatus according to this document. The method disclosed in FIG. 8 may be performed by the decoding apparatus disclosed in FIG. 3. Specifically, for example, S800 and S810 of FIG. 8 may be performed by the entropy decoding unit of the decoding device, S820 of FIG. 8 may be performed by the residual processing unit of the decoding device, and S830 is the decoding This can be done by the addition of the device. In addition, although not shown, the process of receiving prediction information on the current block may be performed by the entropy decoding unit of the decoding device, and the process of deriving the prediction sample of the current block is performed by the prediction unit of the decoding device. Can be done.

The decoding apparatus receives image information including residual information through a bitstream (S800). For example, the image information may be referred to as video information. The image information may include various information according to the above-described embodiment(s) of this document. For example, the image information may include at least some of prediction related information or residual information.

The decoding apparatus determines whether lossless coding is used for the current block (S810). In lossless coding, processing that may cause information loss in a video coding system can be modified and/or bypassed. For example, at least one of (inverse) transformation and/or (inverse) quantization, which are coding techniques that cause information loss, may not be applied. Alternatively, lossless coding may mean coding in which at least one of (inverse) transformation and/or (inverse) quantization is not applied in coding residual information.

For example, the image information includes a flag indicating whether lossless coding is used, and whether lossless coding is used may be determined based on a flag indicating whether lossless coding is used. For example, a flag indicating whether lossless coding is used may be received through a coding unit (CU) syntax.

Also, the image information may include a transform skip flag indicating whether to apply the transform of the current block. For example, when lossless coding is used, the value of the transform skip flag may be set to 1. In addition, when lossless coding is used, a quantization parameter (QP) for the current block may be set to 4.

The decoding apparatus generates residual samples for the current block based on the determination result and residual information (S820).

For example, when lossless coding is used based on a determination result, syntax elements according to a transform skip residual coding (TSRC) syntax structure may be parsed for the current block.

Alternatively, for example, when the lossless coding is not used based on a determination result, syntax elements according to a regular residual coding syntax structure may be parsed for the current block.

The decoding apparatus generates reconstructed samples for the current block based on the residual samples (S830).

The decoding apparatus may generate a reconstructed sample or a reconstructed picture based on the residual sample. For example, the decoding apparatus may derive a prediction sample by performing an inter prediction mode or an intra prediction mode for the current block based on prediction information received through a bitstream, and the prediction sample and the residual sample The reconstructed sample may be generated through addition.

Specifically, for example, the image information may include prediction information on the current block. The prediction information may include information on an inter prediction mode or an intra prediction mode performed on the current block.

For example, the decoding apparatus may perform inter prediction or intra prediction for the current block based on the prediction information received through the bitstream, and may derive a prediction sample of the current block. As an example, the decoding apparatus may derive a prediction mode applied to the current block based on the prediction information. For example, when inter prediction is applied to the current block, the decoding apparatus may derive motion information of the current block based on the prediction information, and calculate the prediction sample of the current block based on the motion information. Can be derived. In addition, for example, when intra prediction is applied to the current block, the decoding apparatus may derive a reference sample based on neighboring samples of the current block, and based on the reference sample and an intra prediction mode of the current block. As a result, the prediction sample of the current block can be derived. The decoding apparatus may generate the reconstructed sample by adding the prediction sample and the residual sample.

Thereafter, as described above, an in-loop filtering procedure such as deblocking filtering, SAO and/or ALF procedure can be applied to the reconstructed sample in order to improve subjective/objective image quality as needed.

9 schematically shows a decoding apparatus that performs an image decoding method according to this document. The method disclosed in FIG. 8 may be performed by the decoding apparatus disclosed in FIG. 9. Specifically, for example, the entropy decoding unit of the decoding apparatus of FIG. 9 may perform S800 to S810 of FIG. 8, and the residual processing unit of the decoding apparatus of FIG. 9 may perform S820 of FIG. 8, and The adder of the decoding apparatus of 9 may perform S830 of FIG. 8. In addition, although not shown, the process of receiving prediction information on the current block may be performed by the entropy decoding unit of the decoding device, and the process of deriving the prediction sample of the current block is performed by the prediction unit of the decoding device. Can be done.

In the above-described embodiment, the methods are described on the basis of a flowchart as a series of steps or blocks, but this document is not limited to the order of the steps, and certain steps may occur in a different order or concurrently with the steps described above. have. Further, those skilled in the art will appreciate that the steps shown in the flowchart are not exclusive, other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of this document.

The embodiments described in this document may be implemented and performed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each drawing may be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, information for implementation (ex. information on instructions) or an algorithm may be stored in a digital storage medium.

In addition, the decoding device and the encoding device to which the embodiments of the present document are applied include a multimedia broadcasting transmission/reception device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, a real-time communication device such as video communication. , Mobile streaming device, storage medium, camcorder, video-on-demand (VoD) service provider, OTT video (Over the top video) device, Internet streaming service provider, three-dimensional (3D) video device, video telephony video device, vehicle It may be included in a terminal (ex. a vehicle terminal, an airplane terminal, a ship terminal, etc.) and a medical video device, and may be used to process a video signal or a data signal. For example, an OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).

In addition, the processing method to which the embodiments of the present document are applied may be produced in the form of a program executed by a computer, and stored in a computer-readable recording medium. Multimedia data having a data structure according to this document can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices in which computer-readable data is stored. The computer-readable recording medium is, for example, Blu-ray disk (BD), universal serial bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical It may include a data storage device. In addition, the computer-readable recording medium includes a media implemented in the form of a carrier wave (for example, transmission through the Internet). In addition, the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.

Further, an embodiment of this document may be implemented as a computer program product using a program code, and the program code may be executed in a computer according to the embodiment of this document. The program code may be stored on a carrier readable by a computer.

The content streaming system to which the embodiments of this document are applied may largely include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.

The encoding server serves to generate a bitstream by compressing content input from multimedia input devices such as smartphones, cameras, camcorders, etc. into digital data, and transmits it to the streaming server. As another example, when multimedia input devices such as smartphones, cameras, camcorders, etc. directly generate bitstreams, the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstream generation method to which the embodiments of the present document are applied, and the streaming server may temporarily store the bitstream while transmitting or receiving the bitstream.

The streaming server transmits multimedia data to a user device based on a user request through a web server, and the web server serves as an intermediary for notifying the user of a service. When a user requests a desired service from the web server, the web server transmits it to the streaming server, and the streaming server transmits multimedia data to the user. In this case, the content streaming system may include a separate control server, and in this case, the control server serves to control commands/responses between devices in the content streaming system.

The streaming server may receive content from a media storage and/or encoding server. For example, when content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate PC, and Tablet PC, ultrabook, wearable device, for example, smartwatch, smart glass, head mounted display (HMD)), digital TV, desktop There may be computers, digital signage, etc. Each server in the content streaming system may be operated as a distributed server, and in this case, data received from each server may be distributedly processed.

The claims set forth herein may be combined in a variety of ways. For example, the technical features of the method claims of the present specification may be combined to be implemented as a device, and the technical features of the device claims of the present specification may be combined to be implemented by a method. In addition, the technical characteristics of the method claim of the present specification and the technical characteristics of the device claim may be combined to be implemented as a device, and the technical characteristics of the method claim of the present specification and the technical characteristics of the device claim may be combined to be implemented by a method.

Claims

In the video decoding method performed by the decoding device,

Receiving image information including residual information through a bitstream;

Determining whether lossless coding is used from the image information;

Generating residual samples for a current block based on the determination result and the residual information; And

Generating reconstructed samples for the current block based on the residual samples,

When the lossless coding is used based on the determination result, syntax elements according to a Transform Skip Residual Coding (TSRC) syntax structure are parsed for the current block.
The method of claim 1,

When the lossless coding is not used based on the determination result, syntax elements according to a regular residual coding syntax structure are parsed for the current block.
The method of claim 1,

The image information includes a flag indicating whether the lossless coding is used,

Whether the lossless coding is used is determined based on a flag indicating whether the lossless coding is used.
The method of claim 3,

A flag indicating whether the lossless coding is used is received through a coding unit (CU) syntax.
The method of claim 1,

The image information includes a transform skip flag indicating whether to apply the transform of the current block,

When the lossless coding is used, the value of the transform skip flag is set to 1.
The method of claim 5,

When the lossless coding is used, a quantization parameter (QP) for the current block is set to 4.
The method of claim 1,

The syntax elements according to the transform skip residual coding syntax structure are a coded sub-block flag indicating whether the current sub-block of the current block includes a non-zero residual coefficient, and the residual coefficient of the current block is non- A significant coefficient flag indicating whether it is a non-zero residual coefficient, a sine flag indicating the sign of the residual coefficient, a parity level flag for parity of the coefficient level for the residual coefficient, the coefficient level A first coefficient level flag indicating whether the coefficient is greater than a first threshold, a second coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a second threshold, and the coefficient level of the residual coefficient is a third threshold A third coefficient level flag indicating whether or not it is greater than, a fourth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fourth threshold value, and whether the coefficient level of the residual coefficient is greater than a fifth threshold value A video decoding method comprising a fifth coefficient level flag for and coefficient value related information for a value of the residual coefficient.
The method of claim 2,

The syntax elements according to the regular residual coding syntax structure include position information on the position of the last non-zero residual coefficient in the residual coefficient array of the current block, and the current sub of the current block. A coded sub-block flag indicating whether a block includes a non-zero residual coefficient, an effective coefficient flag indicating whether the residual coefficient of the current block is a non-zero residual coefficient, the residual A first coefficient level flag for whether a coefficient level for a coefficient is greater than a first threshold, a parity level flag for a parity of the coefficient level, and whether the coefficient level of the residual coefficient is greater than a second threshold. And a second coefficient level flag for, information related to a coefficient value for a value of the residual coefficient, and a sine flag for a sign of the residual coefficient.
In the video encoding method performed by the encoding device,

Deriving a residual sample of the current block;

Determining whether lossless coding is used for the current block;

Encoding residual information on the residual sample of the current block based on the determination result; And

Including the step of generating a bitstream including the residual information,

Syntax elements according to a Transform Skip Residual Coding (TSRC) syntax structure are encoded for the current block based on the determination that the lossless coding is used.
The method of claim 9,

Syntax elements according to a regular residual coding syntax structure are encoded for the current block based on a determination that the lossless coding is not used.
The method of claim 9,

The bitstream includes a flag indicating whether the lossless coding is used.
The method of claim 9,

A flag indicating whether the lossless coding is used is signaled through a coding unit (CU) syntax.
The method of claim 9,

The bitstream includes a transform skip flag indicating whether to apply the transform of the current block,

When the lossless coding is used, the value of the transform skip flag is set to 1.
The method of claim 13,

When the lossless coding is used, a quantization parameter (QP) for the current block is set to 4.
The method of claim 9,

The syntax elements according to the transform skip residual coding syntax structure are a coded sub-block flag indicating whether the current sub-block of the current block includes a non-zero residual coefficient, and the residual coefficient of the current block is non- A significant coefficient flag indicating whether it is a non-zero residual coefficient, a sine flag indicating the sign of the residual coefficient, a parity level flag for parity of the coefficient level for the residual coefficient, the coefficient level A first coefficient level flag indicating whether the coefficient is greater than a first threshold, a second coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a second threshold, and the coefficient level of the residual coefficient is a third threshold A third coefficient level flag indicating whether or not it is greater than, a fourth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fourth threshold value, and whether the coefficient level of the residual coefficient is greater than a fifth threshold value A video encoding method comprising: a fifth coefficient level flag with respect to and coefficient value related information about the value of the residual coefficient.
The method of claim 10,

The syntax elements according to the regular residual coding syntax structure include position information on the position of the last non-zero residual coefficient in the residual coefficient array of the current block, and the current sub of the current block. A coded sub-block flag indicating whether a block includes a non-zero residual coefficient, an effective coefficient flag indicating whether the residual coefficient of the current block is a non-zero residual coefficient, the residual A first coefficient level flag for whether a coefficient level for a coefficient is greater than a first threshold, a parity level flag for a parity of the coefficient level, and whether the coefficient level of the residual coefficient is greater than a second threshold. And a second coefficient level flag for, information related to a coefficient value for a value of the residual coefficient, and a sine flag for a sign of the residual coefficient.
What is claimed is:

Receiving image information including residual information through a bitstream;

Determining whether lossless coding is used from the image information;

Generating residual samples for a current block based on the determination result and the residual information; And

Generating reconstructed samples for the current block based on the residual samples,

When the lossless coding is used based on the determination result, the syntax elements according to the Transform Skip Residual Coding (TSRC) syntax structure are parsed for the current block, computer-readable digital storage media.