WO2020189971A1

WO2020189971A1 - Image decoding method and device using transform skip flag in image coding system

Info

Publication number: WO2020189971A1
Application number: PCT/KR2020/003515
Authority: WO
Inventors: 유선미; 남정학
Original assignee: 엘지전자 주식회사
Priority date: 2019-03-15
Filing date: 2020-03-13
Publication date: 2020-09-24

Abstract

An image decoding method performed by a decoding device according the present document comprises the steps of: receiving image information including a transform skip flag; deriving a context model for the transform skip flag indicating whether a transform skip is applied to a current block; decoding the transform skip flag on the basis of the context model; deriving a residual sample on the basis of the decoded transform skip flag; and generating a reconstruction picture on the basis of the residual sample.

Description

Video decoding method and apparatus using transform skip flag in video coding system

This document relates to an image coding technique, and relates to an image decoding method and apparatus for deriving a context model of a transform skip flag in an image coding system and coding the transform skip flag based on the derived context model.

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 the 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.

Another technical problem of this document is to provide a method and an apparatus for deriving and coding a context model of a transform skip flag in coding residual information based on prediction mode information of a current block or at least one of neighboring blocks of the current block. Is in.

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 a transform skip flag; Deriving a context model for the transform skip flag indicating whether transform skip has been applied to the current block;

Decoding the transform skip flag based on the context model; Deriving a residual sample based on the decoded transform skip flag; And generating a reconstructed picture based on the residual sample, wherein the context model for the transform skip flag is determined based on a context index increment for the transform skip flag, and the transform The context index increment for the skip flag is derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.

According to another embodiment of the present document, a video encoding method performed by an encoding device is provided. The method includes the steps of deriving a context model for a transform skip flag indicating whether transform skip is applied to the current block; Encoding the transform skip flag based on the context model; And outputting encoded image information including the encoded transform skip flag, wherein the context model for the transform skip flag is determined based on a context index increment for the transform skip flag. The context index increment for the transform skip flag is derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.

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 a transform skip flag; Deriving a context model for the transform skip flag indicating whether transform skip has been applied to the current block; Decoding the transform skip flag based on the context model; Deriving a residual sample based on the decoded transform skip flag; And generating a reconstructed picture based on the residual sample, wherein the context model for the transform skip flag is determined based on a context index increment for the transform skip flag, and the transform The context index increment for the skip flag is derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.

According to this document, overall video/video compression efficiency can be improved.

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

According to this document, a transform skip flag is coded based on a context model, thereby saving the amount of bits allocated to the transform skip flag and improving overall residual coding efficiency.

According to this document, the context model of the transform skip flag is derived based on prediction mode information of the current block or at least one of neighboring blocks of the current block to save the amount of bits allocated to the transform skip flag, and overall residual coding efficiency. Can improve.

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 the present disclosure, 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 present disclosure 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 the present disclosure. 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 disclosure is independently illustrated for convenience of description of different characteristic functions, and does not mean that each component is 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 present disclosure unless departing from the essence of the disclosure.

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)” refers to “only A”, “only B”, “only C”, or “A, B, and any combination of C ( It can mean any combination of A, B and C)”.

A forward slash (/) or comma used in the present specification may mean "and/or". For example, “A/B” may 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 this specification, the expression “at least one of A or B” or “at least one of A and/or B” means “at least one It can be interpreted the same as "at least one of A and B".

In addition, in the present specification, “at least one of A, B and C” means “only A”, “only B”, “only C”, or “A, B and C Can mean any combination of A, B and C”. In addition, "at least one of A, B or C" or "at least one of A, B and/or C" means 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.

Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same constituent elements in the drawings, and duplicate descriptions for the same constituent elements may be omitted.

1 schematically shows an example of a video/video coding system to which the present disclosure can be applied.

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 slice/tile is a unit constituting a part of a picture in coding. A slice/tile may include one or more coding tree units (CTU). One picture may be composed of one or more slices/tiles.

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 multiple complete tiles or multiple consecutive CTU rows in one tile of a picture that may be included in one NAL unit. 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.

Meanwhile, one picture may be divided into two or more subpictures. The subpicture may be an rectangular region of one or more slices within a picture.

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.

2 is a diagram schematically illustrating a configuration of a video/video encoding apparatus to which the present disclosure 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 the present disclosure 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 encoding apparatus 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 C 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 the form of blocks 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 155 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 100 and the decoding device, and may 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.

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

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 intra prediction unit 331 and an inter prediction unit 332. The residual processing unit 320 may include a dequantizer 321 and an inverse transformer 321. 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 device of FIG. 3. 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. 3 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 decoding information on a block to be decoded and a neighbor or a 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 the information about the prediction output from the entropy decoding unit 310, and may determine a specific intra/inter prediction mode.

The prediction unit 330 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 332 in order to be used as motion information of spatial neighboring blocks or motion information of temporal neighboring blocks. 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 100 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.

As described above, prediction is performed to increase compression efficiency in performing video coding. Through this, a predicted block including prediction samples for a current block as a coding target block may be generated. Here, the predicted block includes prediction samples in the spatial domain (or pixel domain). The predicted block is derived equally from the encoding device and the decoding device, and the encoding device decodes information (residual information) about the residual between the original block and the predicted block, not the original sample value of the original block itself. Video coding efficiency can be improved by signaling to the device. The decoding apparatus may derive a residual block including residual samples based on the residual information, and generate a reconstructed block including reconstructed samples by summing the residual block and the predicted block. A reconstructed picture to be included can be generated.

The residual information may be generated through transformation and quantization procedures. For example, the encoding apparatus derives a residual block between the original block and the predicted block, and derives transform coefficients by performing a transformation procedure on residual samples (residual sample array) included in the residual block. And, by performing a quantization procedure on the transform coefficients, quantized transform coefficients may be derived, and related residual information may be signaled to a decoding apparatus (via a bitstream). Here, the residual information may include information such as value information of the quantized transform coefficients, position information, a transform technique, a transform kernel, and a quantization parameter. The decoding apparatus may perform an inverse quantization/inverse transform procedure based on the residual information and derive residual samples (or residual blocks). The decoding apparatus may generate a reconstructed picture based on the predicted block and the residual block. The encoding apparatus may also inverse quantize/inverse transform quantized transform coefficients for reference for inter prediction of a picture to derive a residual block, and generate a reconstructed picture based on this.

For example, in the CABAC encoding process, 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.

The context model may be allocated and updated for each context-coded (normally coded) bin, and the context model may be indicated based on ctxIdx or ctxInc. ctxIdx may be derived based on ctxInc. For example, a context index (ctxIdx) indicating a context model for each of the regularly coded bins may be derived as a sum of a context index increment (ctxInc) and a context index offset (ctxIdxOffset). Here, the ctxInc may be derived differently for each bin. The ctxIdxOffset may be expressed as the lowest value of the ctxIdx. The minimum value of ctxIdx may be referred to as an initial value (initValue) of ctxIdx. The ctxIdxOffset may generally be a value used to distinguish context models for other syntax elements, and a context model for one syntax element may be classified or derived based on ctxInc.

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.

In the entropy encoding procedure, it is possible to determine whether to perform encoding through a regular coding engine or a bypass coding engine, and switch a coding path. Entropy decoding may perform the same process as 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 a block to be decoded or a 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 may 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 an 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 a 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. In the residual coding syntax, as described later, whether transformation 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 (quantized) transformation coefficients of the syntax elements such as (i.e., the residual information) last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag, par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder, coeff_sign_flag, dec_abs_level, mts_idx ( syntax elements) can be encoded and/or decoded. Syntax elements related to residual data encoding/decoding can be represented as shown in the following table.

Referring to Table 1 described above, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag, abs_level_gt1_flag, coeff_flag, abs_level_gt1_flag, par_level_flag, coded_flag, or par_level_flag can be encoded.

Regarding the transform (and quantization) and residual coding procedure, a coding block (CB) and a transform block (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. 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, it is described that the syntax elements related to residual coding are signaled in units of transform blocks (TB), but this is an example, as described above, that the TB can be mixed with the coding block (CB).

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 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 derived 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_level_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 rem_abs_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.

Meanwhile, the above-described residual information may further include transform_skip_flag. 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.

Meanwhile, as an example different from the embodiment in which the above-described syntax elements are transmitted, different residual syntax elements are different depending on whether or not transform skip is applied for residual coding, that is, different residual syntax elements according to whether or not transform skip is applied. An embodiment may be proposed for transmitting the data.

Syntax elements for residual coding according to the above-described example may be represented as in the following tables.

According to the present embodiment, as shown in Table 3, residual coding may be branched according to the value of the syntax element transform_skip_flag 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). Table 4 above may 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.

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 1, as shown in Table 5, syntax elements sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag, and/or abs_remainder for the residual coefficient of the transform block may be parsed, and based on the syntax elements. The residual coefficient may be derived. 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] indicates whether the absolute value of the transform coefficient level (or the transform coefficient level shifted by 1 to the right) at the scanning position n is greater than (j<<1)+1. It can be a flag. 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.

In addition, when the value of the transform skip flag is 0, as shown in Table 4, syntax elements sig_coeff_flag, abs_level_gtx_flag, par_level_flag, abs_remainder, dec_abs_level, coeff_sign_flag can be parsed, as shown in Table 4, and the syntax The residual coefficient may be derived based on the 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.

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, and abs_level_gt3_flag may be limited to the number according to the size of the corresponding block. For example, when the block is a 4x4 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 32. When the corresponding block is a 2x2 size block, the sig_coeff_flag, abs_level_flag, par_level_flag, and par_level_flag , The sum of bins for abs_level_gt3_flag may be limited to 8. The limited number of bins can be represented by remBinsPass1. 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 (CBs or TBs). 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 apparatus binarizes the remaining coefficients through a binarization method for the coefficients described later without using CABAC, and performs bypass encoding. I can. In other words, for example, if the number of context coded bins coded for 4x4 CG is 32, or the number of context coded bins coded for 2x2 CG is 8, then the context coded bins are no longer coded. sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag may not be encoded, and may be directly encoded as dec_abs_level as shown in Table 6 described later. 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 encoded, and may be directly encoded as dec_abs_level as shown in Table 6 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. Also, the mts_idx may represent transform kernels applied in a horizontal direction and a vertical direction to residual samples in a current transform block.

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.

For example, encoding results of coefficients scanned inverse diagonally in FIG. 5 may be as shown in the following table.

In Table 7 described above, scan_pos indicates the position of the coefficient according to the inverse diagonal scan. scan_pos 15 may be the transform coefficient of the first scan, that is, the lower right corner, in the 4x4 block, and scan_pos 0 may be the transform coefficient of the last scan, that is, the upper left corner. Meanwhile, in an embodiment, the scan_pos may be referred to as a scan position. For example, the scan_pos 0 may be referred to as a scan position 0.

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, for example, when there is a suffix empty string for the 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 follows.

Here, prefixVal may represent the prefix value of the symbolVal. A prefix (ie, prefix empty string) of the TR bin string of the syntax element 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 the following equation.

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 precisely 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.

First, lastAbsRemainder and lastRiceParam for abs_remainder[n] can be derived as follows. Here, the lastAbsRemainder may indicate a value of abs_remainder derived before abs_remainder[n], and the lastRiceParam may indicate a Rice parameter cRiceParam for abs_remainder derived before abs_remainder[n].

For example, when the process of deriving the lastAbsRemainder and lastRiceParam for the abs_remainder[n] is first called for the current subblock, that is, for the first transform coefficient in the scanning order among the transform coefficients of the current subblock. When the process of abs_remainder[n] is performed, both the lastAbsRemainder and the lastRiceParam may be set to 0.

In addition, if this is not the case, that is, if the process is not called for the first time for the current subblock, the lastAbsRemainder and the lastRiceParam are set equal to the values of abs_remainder[n] and cRiceParam derived from each last call. Can be. That is, the lastAbsRemainder may be derived with the same value as abs_remainder[n] coded before abs_remainder[n] currently coded, and the lastRiceParam is cRiceParam for abs_remainder[n] coded before abs_remainder[n] currently coded Can be derived with the same value as

Thereafter, a Rice parameter cRiceParam for abs_remainder[n] that is currently coded may be derived based on the lastAbsRemainder and the lastRiceParam. For example, the Rice parameter cRiceParam for abs_remainder[n] that is currently coded may be derived as the following equation.

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.

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. Or, when transformation is applied to the current TB including the current CG, that is, when transformation skip is not applied to the current TB including the current CG, the currently coded abs_remainder[n The Rice parameter cRiceParam for] can be derived with the same value as cRiceParam for abs_remainder[n] coded previously.

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.

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.

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), log2TbWidth, which is a binary logarithm of the width of a transform block, 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 syntax elements sig_coeff_flag[x][y], the component index cIdx, and the array AbsLevel[x][y] for transform blocks having the upper left luma position (x0, y0), the variable locSumAbs is It can be derived as a pseudo code disclosed in the following table.

The Rice parameter cRiceParam may be derived as follows.

For example, the Rice parameter cRiceParam may be derived based on the derived variable locSumAbs and the variable s. The variable s may be set to Max(0, QState-1). That is, the s may be set to a maximum value of 0 and QState-1.

The Rice parameters cRiceParam and ZeroPos[n] derived based on the variable locSumAbs and the variable s may be as shown in the following table.

For example, referring to Table 15 above, when the locSumAbs is 6 or less, the cRiceParam may be set to 0, and when the locSumAbs is 7 or more and 13 or less, the cRiceParam may be set to 1, and the locSumAbs When is 14 or more and 27 or less, the cRiceParam may be set to 2, and when the locSumAbs is 28 or more, the cRiceParam may be set to 3.

In addition, referring to Table 15 above, when s is 0 and locSumAbs is 4 or less, ZeroPos[n] may be set to 0, and when s is 0 and locSumAbs is 5, the ZeroPos [n] may be set to 1, and when s is 0 and locSumAbs is 6 or more and 11 or less, ZeroPos[n] may be set to 2, s is 0, and locSumAbs is 12 If it is greater than or equal to 22, the ZeroPos[n] may be set to 4, and if the s is 0 and the locSumAbs is greater than or equal to 23 and less than or equal to 27, the ZeroPos[n] may be set to 8, and the s When is 0 and the locSumAbs is 28 or more, the ZeroPos[n] may be set to 16. Further, referring to Table 15 above, when s is 1 and locSumAbs is 3 or less, ZeroPos[n] may be set to 1, and when s is 1 and locSumAbs is 4, the ZeroPos [n] may be set to 2, and when s is 1 and locSumAbs is 5, ZeroPos[n] may be set to 3, s is 1, and locSumAbs is 6 or more and 8 In the following cases, the ZeroPos[n] may be set to 4, the s is 1, and the locSumAbs is 9 or more and 11 or less, the ZeroPos[n] may be set to 6, and the s is 1 , When the locSumAbs is 12 or more and 15 or less, the ZeroPos[n] may be set to 8, and when s is 1 and the locSumAbs is 16 or more and 17 or less, the ZeroPos[n] is set to 4 In the case where s is 1 and locSumAbs is 18 or more and 25 or less, ZeroPos[n] may be set to 12, and when locSumAbs is 26 or more and 31 or less, ZeroPos[n] is 16 Can be set. In addition, referring to Table 15 above, when s is 2 and locSumAbs is 1 or less, ZeroPos[n] may be set to 1, s is 2, and locSumAbs is 2 or more and 4 or less. , The ZeroPos[n] may be set to 2, the s is 2, and the locSumAbs is 5, the ZeroPos[n] may be set to 3, the s is 2, and the locSumAbs is 6 If it is greater than or equal to 8, the ZeroPos[n] may be set to 4, and if the s is 2 and the locSumAbs is greater than or equal to 9 and less than or equal to 11, the ZeroPos[n] may be set to 6, and the s Is 2, the locSumAbs is 12 or more and 17 or less, the ZeroPos[n] may be set to 8, and when s is 2 and the locSumAbs is 18 or more and 24 or less, the ZeroPos[n] is 12 When s is 2 and locSumAbs is 25 or more, the ZeroPos[n] may be set to 16.

Alternatively, for example, ZeroPos[n] may be derived as the following equation, where cRiceParam included in the equation to be described later may be derived with reference to Table 15.

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

In the suffix of the empty string of dec_abs_level[n], the empty string k is set to cRiceParam+1, riceParam is set to cRiceParam, log2TransformRange is set to 15, and maxPreExtLen is set to 11 Limited EGk binarization for the suffixVal. It can be derived through the process.

In addition, in order to adapt statistics and signal characteristics of the transform skip level (i.e., the residual in the spatial domain) representing the quantized prediction residual to residual coding, the contents described later in the existing residual coding scheme are modified. Suggest a plan.

Scanning order: For example, the scanning order of the sub-block in the TB block and the residual coefficient in the sub-block may be a diagonal scan order moving from the lower right to the upper left. That is, the scanning order of the sub-block in the TB block and the residual coefficient in the sub-block may be a diagonal scan order of scanning from the lower right to the upper left. Alternatively, for example, the scanning order of the sub-block in the TB block and the residual coefficient in the sub-block may be a diagonal scan order moving from the upper left to the lower right. That is, the scanning order of the sub-block in the TB block and the residual coefficient in the sub-block may be a diagonal scan order of scanning from the upper left to the lower right.

No last non-zero transform coefficient position: Since the residual signal (i.e., residual sample) reflects the spatial residual after prediction, and energy compression by transform is not performed by transform skip , A high probability for a trailing zero or an insignificant level in the lower right corner of the transform block may no longer occur. Accordingly, in this case, signaling information on the scanning position of the last non-zero transform coefficient may be omitted. Instead, the first sub-block to be coded first may be the upper left sub-block in the transform block. Meanwhile, the non-zero transform coefficient may be expressed as a significant coefficient.

Subblock CBF: Transform skip is applied to the absence of signaling information on the scanning position of the last non-zero transform coefficient, and CBF signaling of a subblock having coded_sub_block_flag should be modified as follows.

Due to quantization, the above-described non-critical level sequence can still occur locally within the transform block. Accordingly, information on the scanning position of the last non-zero transform coefficient is removed as described above, and coded_sub_block_flag can be coded for all sub-blocks.

In addition, coded_sub_block_flag for a sub-block (top left sub-block) for a DC frequency position may indicate a special case. For example, in VVC Draft 3, it may be derived that the coded_sub_block_flag for the upper left subblock is not signaled and is always equal to 1. When the scanning position of the last non-zero transform coefficient is located in a subblock other than the upper left subblock, it may indicate that there is at least one significant level outside the DC subblock (ie, the upper left subblock). . As a result, it is derived that the coded_sub_block_flag for the DC subblock is 1, but only the 0/non-significant level may be included. As described above, if the transform skip is applied to the current block and there is no information on the scanning position of the last non-zero transform coefficient, a coded_sub_block_flag for each sub-block may be signaled. Here, a coded_sub_block_flag for a DC sub-block may also be included except when the coded_sub_block_flag for all sub-blocks other than the DC sub-block is already 0. On the other hand, for example, when a diagonal scan order moving from the lower right to the upper left is applied as the scanning order of the transform block, and the coded_sub_block_flag for the DC subblock is not signaled, it is derived that the coded_sub_block_flag for the DC subblock is equal to 1. Can be (inferDcSbCbf = 1). Therefore, since there must be at least one effective level in the DC sub-block, if all sig_coeff_flag other than sig_coeff_flag for the first position of (0,0) in the DC sub-block are 0, the first position of (0,0) is The sig_coeff_flag for is not signaled and may be derived as equal to 1 (inferSbDcSigCoeffFlag = 1).

Also, context modeling of coded_sub_block_flag may be changed. For example, the context model index may be calculated as a sum of the coded_sub_block_flag of the left sub-block of the current sub-block and the coded_sub_block_flag of the upper sub-block of the current sub-block, and logical separation of the coded_sub_block_flags.

sig_coeff_flag context modeling: The local template of sig_coeff_flag context modeling may be modified to include only the left position NB0 and the upper position NB1 of the current scanning position. The context model offset may be derived by the number of sig_coeff_flag [NB0] + sig_coeff_flag [NB1] of the effective surrounding location. Thus, selection of different context sets may be eliminated according to the diagonal d of the current transform block. As a result, three context models and a single context model can be set to code sig_coeff_flag.

abs_level_gt1_flag and par_level_flag context modeling: A single context model can be used for abs_level_gt1_flag and par_level_flag. Alternatively, abs_level_gt1_flag may be determined by the number of non-zero coefficients of surrounding coefficients.

abs_remainder coding: The empirical distribution of the transform skip residual absolute level still fits the Laplacian or geometric distribution, but there may be greater instability than the transform coefficient absolute level. In particular, the variance within the window of successive realization can be higher for the residual absolute level. Accordingly, the binarization and context modeling of abs_remainder can be modified as follows.

For example, a higher cutoff value can be used for binarization of abs_remainder. Through this, higher compression efficiency can be provided to a conversion point from coding using sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag to rice code for abs_remainder and a dedicated context model for each bin location. Increasing the cutoff may cause more flags "greater than X" (eg, abs_level_gt5_flag, abs_level_gt7_flag, etc.) to occur until the cutoff is reached. The cutoff can be fixed to 5 (numGtFlags = 5).

In addition, the template for deriving rice parameters may be modified. That is, only the right peripheral position and the lower peripheral position of the current scanning position may be considered as a local template for sig_coeff_flag context modeling. Alternatively, depending on whether the transform skip is applied, the Rice parameter may be fixed to 1 in the case of a block to which the transform skip is applied.

coeff_sign_flag Context Modeling: Instability inside the sign sequence and prediction residuals are often biased, so even when the global empirical distribution is almost uniformly distributed, the context model is used for sign-related information. Can be coded by A single-only context model may be used for coding the code related information, and the code related information may be parsed after sig_coeff_flag and maintained together with all context coded bins.

Reduction of context encoding bins: Transmission of syntax elements for the first scanning path, that is, sig_coeff_flag, abs_level_gt1_flag, and par_level_flag may not be changed. However, the limit of the maximum value of the context coded bins per sample (CCBs) may be removed and adjusted differently. The reduction of CCB can be derived by designating an invalid mode when CCB> k. Here, k may be a positive integer. For example, in the case of a regular level coding mode, k = 2 may be used. The above limitation may correspond to a reduction in quantization space.

Meanwhile, a context index (ctxIdx) indicating a context model of a syntax element coded based on a context included in the above-described residual information may be derived as described below.

For example, the input of the process of deriving the context index for the syntax element may be binIdx indicating the position of the current bin in the bin string for the syntax element, and ctxTable, ctxIdx, and bypassFlag may be derived as outputs.

First, a context index increment (ctxInc) for a current bean for a syntax element may be derived. That is, ctxInc may be derived based on binIdx indicating the location of the current bin for the syntax element. The ctxInc may be expressed as a context increment parameter.

CtxInc derived according to binIdx for the syntax element may be as shown in the following table.

In Table 16, the context index of a bean having a value other than "bypass", "terminate", or "na" can be derived as follows.

The ctxInc for the current bean of the syntax element may be derived as a value designated as an item for the current bean in Table 16. In addition, when there are a plurality of values designated as the item for the current bin, the ctxInc may be derived through the process of clauses in parentheses in the item. The above clause may mean a clause disclosed in the VVC standard. Thereafter, the variable ctxIdxOffset may be designated as the lowest value of ctxIdx according to the current value of initType. The initType may be determined according to a slice type of a current slice including a current block. For example, if the slice type is an I slice, initType may be 0, if the slice type is P slice, initType may be 2, and in other cases, initType may be 1. In addition, the context index (ctxIdx) for the current bin of the syntax element may be set equal to the sum of ctxInc and ctxIdxOffset. That is, the context index for the current block may be determined based on ctxInc. Also, bypassFlag can be set to 0.

Meanwhile, in Table 16, when the item for the current bin is "bypass", the context index of the bin may be derived as follows. For example, ctxTable for the current bin may be set to 0. Also, the context index (ctxIdx) for the current bin may be set to 0. Also, bypassFlag may be set to 1.

Meanwhile, in Table 16, when the item for the current bean is "terminate", the context index of the bean may be derived as follows. For example, ctxTable for the current bin may be set to 0. Also, the context index (ctxIdx) for the current bin may be set to 0. Also, bypassFlag can be set to 0.

Meanwhile, in Table 16, when the item for the current bean is “na”, syntax elements for the bean, that is, the context index for the bean may be derived as follows. For example, ctxIdx, ctxTable, and/or bypassFlag for the current bin may not occur.

The procedures of the clauses for deriving ctxInc for a bin having a value other than "bypass", "terminate" or "na" may be described later.

For example, the process of deriving ctxInc according to Section 9.5.4.2.2 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.3 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.4 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.5 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.6 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.7 may be as shown in the following table.

Also, for example, the process of deriving ctxInc according to Section 9.5.4.2.8 may be as shown in the following table.

On the other hand, as described above, a block that does not perform transform encoding, that is, a transform block including residual coefficients to which transform is not applied, has different characteristics of residual information from a block in which normal transform encoding has been performed. There is a need for an efficient residual data encoding method for blocks that do not perform. Meanwhile, as described above, the transform skip flag indicating whether to apply the transform may be transmitted in units of transform blocks, and the size of the transform block is not limited in this document. For example, if the value of the transform skip flag is 1, the residual information encoding/decoding scheme proposed in this document may be performed, and if the value of the transform skip flag is 0, the existing information described in Table 4 above. The residual information encoding/decoding scheme of may be performed. Alternatively, when the transform skip flag indicates that no transform is applied to the current block (transform is skipped), the residual information encoding/decoding scheme in the transform skip mode disclosed in Table 5 may be performed.

Here, the transform skip flag of the current block may have a correlation with the prediction mode of the current block. Alternatively, the transform skip flag of the current block may have correlation with prediction modes of neighboring blocks on the left or above the current block. For example, when an intra block copy (IBC) prediction mode is used, the frequency of occurrence of a transform skip block may increase.

Accordingly, in an embodiment of the present specification, the context model for the transform skip flag is determined based on prediction mode information of the current block or at least one of neighboring blocks of the current block, and the transform skip flag is coded based on the determined context model. Suggest a way to do it.

An embodiment of deriving a context model for a transform skip flag based on prediction mode information of the current block may be defined as shown in Table 24 below.

Referring to Table 24 above, a context model for a bin of a syntax element transform skip flag (transform_skip_flag) indicating whether a transform skip is applied to a current block may be determined based on a prediction mode (CuPredMode) of the current block.

The context model for a bin of the transform skip flag may be determined based on a context index increment (ctxInc) for the transform skip flag.

For example, ctxInc for the transform skip flag is '0' when the prediction mode of the current block is not the intra block copy (IBC) prediction mode, and '1' when the prediction mode of the current block is the IBC prediction mode. Can be derived as

Meanwhile, after the ctxInc for the transform skip flag of the current residual coefficient is derived as described above, a process of deriving a context model based on the ctxInc may be as follows.

For example, ctxIdxOffset for the transform skip flag may be derived as one of 0, 2, and 4 values. For example, when the slice type of the current slice is an I slice, the ctxIdxOffset may be derived as 0, when the slice type of the current slice is a P slice, the ctxIdxOffset may be derived as 4, and otherwise, the ctxIdxOffset may be derived as 2. However, this is an example, and ctxIdxOffset may be determined in advance as another value. Accordingly, a context model (or ctxIdx) for the transform skip flag for blocks in the same slice may be determined based on ctxInc.

For example, in the above description, ctxIdx (a context model index indicating a context model) may be derived based on

ctxInc

0 or 1, and accordingly, one of a first context model to a second context model may be derived. Alternatively, for example, ctxIdx (context model index indicating a context model) for the transform skip flag may be derived based on one of ctxInc 0 to ctxInc N, and accordingly, the first context model to the N+th 1 One of the context models can be derived.

Therefore, when the prediction mode of the current block is not the IBC prediction mode, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is derived as the first ctxIdx (that is, derived as a first context model. ) Can be. In addition, when the prediction mode of the current block is the IBC prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is derived as a second ctxIdx (that is, derived as a second context model). Can be.

Alternatively, another embodiment of deriving a context model for a transform skip flag based on prediction mode information of the current block may be defined as shown in Table 25 below.

Referring to Table 25, the ctxInc for the transform skip flag is '0' when the prediction mode of the current block is not the inter prediction mode, and 1'when the prediction mode of the current block is the inter prediction mode. Can be derived.

Therefore, when the prediction mode of the current block is not the inter prediction mode, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is derived as the first ctxIdx (that is, derived as a first context model. ) Can be. In addition, when the prediction mode of the current block is the inter prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is derived as a second ctxIdx (that is, derived as a second context model). Can be.

Another embodiment of deriving a context model for a transform skip flag based on prediction mode information of the current block may be defined as shown in Table 26 below.

Referring to Table 26, the ctxInc for the transform skip flag is '0' when the prediction mode of the current block is not the intra prediction mode, and 1'when the prediction mode of the current block is the intra prediction mode. Can be derived.

Therefore, when the prediction mode of the current block is not the intra prediction mode, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is derived as the first ctxIdx (that is, derived as a first context model). ) Can be. In addition, when the prediction mode of the current block is an intra prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is derived as a second ctxIdx (that is, derived as a second context model). Can be.

Meanwhile, when a context model for a transform skip flag is derived based on prediction mode information of an upper neighboring block of the current block and prediction mode information of a left neighboring block, for example, ctxInc is 0, 1, and as shown in Table 27 below. It can be derived from either of two.

In this case, an embodiment of deriving the ctxInc may be defined as shown in Tables 28 and 29 below. According to Tables 28 and 29, the ctxInc may be derived according to whether each of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block is an IBC prediction mode.

Referring to Equation (28-2) and Table 29 of Table 28 above, the ctxInc is that the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not IBC (Intra block copy) prediction mode. In this case, it may be derived as '0', and when either of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an IBC prediction mode, it may be derived as '1', and the prediction mode of the upper neighboring block and the When all of the prediction modes of the left neighboring block are IBC prediction modes, it may be derived as '2'.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both IBC prediction modes, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when any one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an IBC prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model). In addition, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block are both IBC prediction modes, ctxIdc for the transform skip flag may be derived as 2, and ctxIdx for the transform skip flag is a third ctxIdx Can be derived (that is, derived as a third context model).

In addition, another embodiment for deriving the ctxInc may be defined as in Table 28 and Table 30 below. According to Tables 28 and 30, the ctxInc may be derived according to whether the prediction mode of the upper neighboring block of the current block and the prediction mode of the left neighboring block are inter prediction modes.

Referring to Equation (28-2) and Table 30 of Table 28 above, ctxInc is '0' when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both inter prediction mode. As a result, when any one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an inter prediction mode, it may be derived as '1', and the prediction mode of the upper neighboring block and the prediction of the left neighboring block When all the modes are inter prediction modes, it may be derived as '2'.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both inter prediction mode, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when any one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an inter prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model). In addition, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block are both inter prediction modes, ctxIdc for the transform skip flag may be derived as 2, and ctxIdx for the transform skip flag is a third ctxIdx Can be derived (that is, derived as a third context model).

In addition, another embodiment for deriving the ctxInc may be defined as in Table 28 and Table 31 below. According to Tables 28 and 31, the ctxInc may be derived according to whether each of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block is an intra prediction mode.

Referring to Equation (28-2) and Table 31 of Table 28 above, ctxInc is '0' when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not all intra prediction modes. As a result, if any one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an intra prediction mode, it may be derived as '1', and the prediction mode of the upper neighboring block and the prediction of the left neighboring block When all the modes are intra prediction modes, it may be derived as '2'.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both intra prediction modes, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when any one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an intra prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model). In addition, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block are both intra prediction modes, ctxIdc for the transform skip flag may be derived as 2, and ctxIdx for the transform skip flag is a third ctxIdx Can be derived (that is, derived as a third context model).

On the other hand, when the context model for the transform skip flag is derived based on the prediction mode of the upper neighboring block of the current block and the prediction mode information of the left neighboring block, the ctxInc is derived as one of 0 and 1 unlike Table 27 above. It may be, which is shown in Table 32 below.

In this case, an embodiment of deriving the ctxInc may be defined as shown in Table 33 and Table 29 below. According to Tables 33 and 29, the ctxInc may be derived according to whether each of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block is an IBC prediction mode.

Referring to Equation (33-3) and Table 29 of Table 33, the ctxInc is that the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not IBC (Intra block copy) prediction mode. In this case, it may be derived as '0', and '1' when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is the IBC prediction mode.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both IBC prediction modes, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an IBC prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model).

In addition, another embodiment for deriving the ctxInc may be defined as shown in Tables 33 and 30. According to Tables 33 and 30, the ctxInc may be derived according to whether each of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block is an inter prediction mode.

Referring to Equation (33-3) and Table 30 of Table 33 above, ctxInc is '0' when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both inter prediction mode. As a result, when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an inter prediction mode, it may be derived as '1'.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both inter prediction mode, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an inter prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model).

Another embodiment for deriving the ctxInc may be defined as in Tables 33 and 31 above. According to Tables 33 and 31, the ctxInc may be derived according to whether each of the prediction modes of the upper neighboring block and the left neighboring block of the current block is an intra prediction mode.

Referring to Equation (33-3) and Table 31 of Table 33, ctxInc is '0' when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not all intra prediction modes. As a result, when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an intra prediction mode, it may be derived as '1'.

Therefore, when the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block of the current block are not both intra prediction modes, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is zero. It can be derived as 1 ctxIdx (that is, derived as a first context model). In addition, when at least one of the prediction mode of the upper neighboring block and the prediction mode of the left neighboring block is an intra prediction mode, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model).

Meanwhile, the context model for the transform skip flag of the current block may be derived based on transform skip flag information of the upper neighboring block of the current block and transform skip flag information of each of the left neighboring blocks.

Accordingly, in an embodiment of the present specification, the context model for the transform skip flag is determined based on the transform skip flag information of the upper neighboring block and the transform skip flag information of the left neighboring blocks, and the transform skip flag is determined based on the determined context model. We propose a coding scheme.

When the context model for the transform skip flag of the current block is derived based on the transform skip flag of the upper neighboring block of the current block and the transform skip flag of the left neighboring block, for example, ctxInc is 0 and 1 as shown in Table 34 below. And any one of 2.

In this case, an embodiment of deriving the ctxInc may be defined as in Table 28 and Table 35 below. According to Tables 28 and 35, the ctxInc may be derived based on the transform skip flag information of the upper neighboring block of the current block and the transform skip flag of each of the left neighboring blocks.

Referring to Equation (28-2) and Table 35 of Table 28 above, ctxInc is '0' when the transform skip flag information of the upper neighboring block and the transform skip flag of the left neighboring block are not all 1. ', if any one of the transform skip flag information of the upper neighboring block and the transform skip flag of the left neighboring block is 1, it can be derived as '1', and the transform skip flag information of the upper neighboring block and the transformation of the left neighboring block When all of the skip flags are 1, it may be derived as '2'.

Accordingly, when the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are not all 1, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is first It can be derived as ctxIdx (that is, derived as a first context model). In addition, when any one of the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block is 1, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model). In addition, when both the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are 1, ctxIdc for the transform skip flag may be derived as 2, and ctxIdx for the transform skip flag is a third ctxIdx Can be derived (that is, derived as a third context model).

When the context model for the transform skip flag of the current block is derived based on the transform skip flag of the upper neighboring block of the current block and the transform skip flag of the left neighboring block, the ctxInc is one of 0 and 1, unlike Table 34. It may be derived as one, which is shown in Table 36 below.

In this case, an embodiment of deriving the ctxInc may be defined as in Tables 33 and 35 described above. According to Tables 33 and 35, the ctxInc may be derived based on the transform skip flag of the upper neighboring block of the current block and the transform skip flag of each of the left neighboring blocks.

Referring to Equations (33-3) and Table 35 of Table 33, the ctxInc is '0' when the transform skip flag information of the upper neighboring block of the current block and the transform skip flag of the left neighboring block are not all 1. When at least one of the transform skip flag information of the upper neighboring block and the transform skip flag of the left neighboring block is 1, it may be derived as '1'.

Accordingly, when the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are not all 1, ctxIdc for the transform skip flag may be derived as 0, and ctxIdx for the transform skip flag is first It can be derived as ctxIdx (that is, derived as a first context model). In addition, when at least one of the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block is 1, ctxIdc for the transform skip flag may be derived as 1, and ctxIdx for the transform skip flag is zero. It can be derived as 2 ctxIdx (that is, derived as a second context model).

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. For example, S610 to S630 of FIG. 6 may be performed by the entropy encoding unit of the encoding device. 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 residual sample for the current block is derived based on the original sample and the prediction sample for the current block. The process of generating a reconstructed sample and a reconstructed picture for the current block based on a residual sample and a prediction sample for the current block may be performed by a subtraction unit of the encoding device. It can be done by wealth.

The encoding device may derive a context model for a transform skip flag indicating whether transform skip is applied to the current block (S610).

First, 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.

Thereafter, the encoding device may determine whether or not transformation is applied to the current block. That is, the encoding device may determine whether or not the transformation is applied to the residual sample of the current block. The encoding apparatus may determine whether to apply the transform to the current block in consideration of coding efficiency. For example, the encoding device may determine that the transformation is not applied to the current block.

The encoding apparatus may generate residual information based on a residual sample and whether the transform skip is applied. The residual information may include a transform skip flag for the current block. The transform skip flag may indicate whether transform skip is applied to the current block. The syntax element representing the transform skip flag may be transform_skip_flag described above.

For example, the context model for the transform skip flag may be determined based on a context index increment for the transform skip flag. For example, the increment of the context index with respect to the transform skip flag may be derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.

As an example, when the prediction mode of the current block is not an intra block copy (IBC) prediction mode, the context index increment for the transform skip flag is derived as 0, and the prediction mode of the current block is an IBC prediction mode. In this case, the context index increment for the transform skip flag may be derived as 1.

For example, the neighboring blocks include an upper neighboring block and a left neighboring block of the current block, and the context index increment for the transform skip flag is prediction mode information of the upper neighboring block and a prediction mode of the left neighboring block. It is derived based on information, and when the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0, When any one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag is derived as 1,

When the prediction modes of the upper neighboring block and the left neighboring block are both IBC prediction modes, the context index increment for the transform skip flag may be derived by 2.

For example, the neighboring blocks include an upper neighboring block and a left neighboring block of the current block, and the context index increment for the transform skip flag is prediction mode information of the upper neighboring block and a prediction mode of the left neighboring block. It is derived based on information, and when the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0, When at least one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag may be derived as 1.

As an example, the neighboring blocks include an upper neighboring block and a left neighboring block of the current block, and the context index increment for the transform skip flag is transformed skip flag information of the upper neighboring block and the left neighboring block. It may be derived based on the transform skip flag information.

As an example, when the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are not all 1, the context index increment of the transform skip flag is derived as 0, and the When any one of the transform skip flag and the transform skip flag of the left neighboring block is 1, the context index increment for the transform skip flag is derived as context model 1, and the upper neighboring block and the left neighboring block When all of the transform skip flags are 1, the context index increment for the transform skip flag may be derived as 2.

For example, when the transform skip flags of the upper neighboring block and the left neighboring block are not all 1, the context index increment of the transform skip flag is derived as 0, and the upper neighboring block and the left neighboring block are When at least one of the transform skip flags is in the IBC prediction mode, the context index increment for the transform skip flag may be derived as 1.

For example, when the transform skip flags of the upper neighboring block and the left neighboring block are not all 1, the context model for the transformed skip flag is derived as a context model 0, and the upper neighboring block and the left neighboring block When at least one of the transform skip flags is 1, the context model for the transform skip flag may be derived as a context model 1.

The encoding device may encode the transform skip flag based on the context model (S620).

The encoding device may output encoded image information including the encoded transform skip flag (S630).

For example, the encoding device may output image information including residual information including the transform skip flag as a bitstream. The bitstream may include residual information.

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. Alternatively, the bitstream may be stored in a computer-readable storage medium. For example, the bitstream may be represented by image information or video information.

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 entropy encoding unit of the encoding device of FIG. 7 may perform S610 to 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, S810 to S830 of FIG. 8 may be performed by the entropy decoding unit of the decoding device, S840 may be performed by the residual processing unit of the decoding device, and S850 is the addition of the decoding device. It can be done by wealth. Further, although not shown, the process of deriving a prediction sample may be performed by the prediction unit of the decoding apparatus.

The decoding apparatus receives image information including a transform skip flag (S810). The decoding apparatus may receive image information including residual information on the current block through a bitstream. Here, the current block may be a coding block (CB) or a transform block (TB).

For example, the image information may include a transform skip flag for the current block. For example, the residual information may include a transform skip flag for the current block. The transform skip flag may indicate whether transform skip is applied to the current block. Alternatively, the transform skip flag may be represented by a transform_skip_flag syntax element. For example, when a value of the transform_skip_flag syntax element is 1, a transform skip may be applied to the current block, and if it is 0, a transform skip may not be applied to the current block. Alternatively, depending on the setting, when the value of the transform_skip_flag syntax element is 0, the transform skip may be applied to the current block, and when 1, the transform skip may not be applied to the current block.

The decoding apparatus may derive a context model for the transform skip flag indicating whether transform skip is applied to the current block (S820).

The decoding apparatus may decode the transform skip flag based on the context model (S830).

The decoding apparatus may derive a residual sample based on the decoded transform skip flag (S840).

For example, when the value of the transform_skip_flag syntax element is 1, the residual signal (or information on the residual) for the current block may be signaled on the pixel domain (spatial domain) without transformation. Alternatively, when the value of the transform_skip_flag syntax element is 0, the residual signal (or information on the residual) for the current block may be transformed and signaled in the transform domain. For example, the decoding apparatus may derive residual samples based on the signaled residual signal without the conversion or after conversion.

The decoding apparatus may generate a reconstructed picture based on the residual sample (S850).

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 picture may be generated through addition. Also, for example, the prediction information may include information indicating an intra prediction mode of the current block. The decoding apparatus may derive the intra prediction mode of the current block based on information indicating the intra prediction mode of the current block, and predict the current block based on reference samples of the current block and the intra prediction mode. Samples can be derived. The reference samples may include upper reference samples and left reference samples of the current block. For example, when the size of the current block is NxN and the x component of the top-left sample position of the current block is 0 and the y component is 0, the left reference samples are p[-1][0 ] To p[-1][2N-1], and the upper reference samples may be p[0][-1] to p[2N-1][-1].

Thereafter, as described above, an in-loop filtering procedure such as deblocking filtering, SAO and/or ALF procedure can be applied to the reconstructed picture 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 S810 to S830 of FIG. 8, and the residual processing unit of the decoding apparatus of FIG. 9 may perform S840 of FIG. 8, and The adder of the decoding apparatus of 9 may perform S850 of FIG. 8. Further, although not shown, the process of deriving the prediction sample may be performed by the prediction unit of the decoding apparatus of FIG. 9.

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).

Further, 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 may be stored in a computer-readable recording medium. Multimedia data having the 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 includes, 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. Further, the computer-readable recording medium includes 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 a transform skip flag;

Deriving a context model for the transform skip flag indicating whether transform skip has been applied to the current block;

Decoding the transform skip flag based on the context model;

Deriving a residual sample based on the decoded transform skip flag; And

Including the step of generating a reconstructed picture based on the residual sample,

The context model for the transform skip flag is determined based on a context index increment for the transform skip flag,

The context index increment for the transform skip flag,

The image decoding method, which is derived based on prediction mode information of the current block or at least one of neighboring blocks of the current block.
The method of claim 1,

When the prediction mode of the current block is not an intra block copy (IBC) prediction mode, the context index increment for the transform skip flag is derived as 0,

When the prediction mode of the current block is the IBC prediction mode, the context index increment for the transform skip flag is derived as 1.
The method of claim 1,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag is derived based on prediction mode information of the upper neighboring block and prediction mode information of the left neighboring block,

When the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0,

When any one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag is derived as 1,

When the prediction modes of the upper neighboring block and the left neighboring block are both IBC prediction modes, the context index increment with respect to the transform skip flag is derived by 2.
The method of claim 1,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag is derived based on prediction mode information of the upper neighboring block and prediction mode information of the left neighboring block,

When the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0,

When at least one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag is derived to be 1.
The method of claim 1,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag,

The image decoding method, which is derived based on transform skip flag information of the upper neighboring block and transform skip flag information of the left neighboring block.
The method of claim 5,

When both the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are not 1, the context index increment for the transform skip flag is derived as 0,

When any one of the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block is 1, the context index increment for the transform skip flag is derived as 1,

When both the upper neighboring block and the transform skip flag of the left neighboring block are 1, the context index increment for the transform skip flag is derived as 2.
The method of claim 5,

When the transform skip flags of the upper neighboring block and the left neighboring block are not all 1, the context index increment for the transform skip flag is derived as 0,

When at least one of the transform skip flag of the upper neighboring block and the left neighboring block is 1, the context index increment of the transform skip flag is derived as 1.
In the video encoding method performed by the encoding device,

Deriving a context model for a transform skip flag indicating whether transform skip has been applied to the current block;

Encoding the transform skip flag based on the context model; And

Including the step of outputting the encoded video information including the encoded transform skip flag,

The context model for the transform skip flag is determined based on a context index increment for the transform skip flag,

The context index increment for the transform skip flag,

An image encoding method that is derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.
The method of claim 8,

When the prediction mode of the current block is not an intra block copy (IBC) prediction mode, the context index increment for the transform skip flag is derived as 0,

When the prediction mode of the current block is the IBC prediction mode, the context index increment for the transform skip flag is derived as 1.
The method of claim 8,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag is derived based on prediction mode information of the upper neighboring block and prediction mode information of the left neighboring block,

When the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0,

When any one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag is derived as 1,

When the prediction modes of the upper neighboring block and the left neighboring block are both IBC prediction modes, the context index increment for the transform skip flag is derived as 2.
The method of claim 8,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag is derived based on prediction mode information of the upper neighboring block and prediction mode information of the left neighboring block,

When the prediction modes of the upper neighboring block and the left neighboring block are not both intra block copy (IBC) prediction modes, the context index increment for the transform skip flag is derived as 0,

When at least one of the prediction modes of the upper neighboring block and the left neighboring block is an IBC prediction mode, the context index increment for the transform skip flag is derived to be 1.
The method of claim 8,

The neighboring blocks include an upper neighboring block and a left neighboring block of the current block,

The context index increment for the transform skip flag,

The image encoding method, which is derived based on transform skip flag information of the upper neighboring block and transform skip flag information of the left neighboring block.
The method of claim 12,

When both the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block are not 1, the context index increment for the transform skip flag is derived as 0,

When any one of the transform skip flag of the upper neighboring block and the transform skip flag of the left neighboring block is 1, the context index increment for the transform skip flag is derived as 1,

When both the upper neighboring block and the transform skip flag of the left neighboring block are 1, the context index increment for the transform skip flag is derived as 2.
The method of claim 12,

When the transform skip flags of the upper neighboring block and the left neighboring block are not all 1, the context index increment for the transform skip flag is derived as 0,

When at least one of the transform skip flag of the upper neighboring block and the left neighboring block is in the IBC prediction mode, the context index increment for the transform skip flag is derived to be 1.
A computer-readable digital storage medium storing a bitstream containing image information causing a decoding device to perform an image decoding method, the image decoding method comprising:

Receiving image information including a transform skip flag;

Deriving a context model for the transform skip flag indicating whether transform skip has been applied to the current block;

Decoding the transform skip flag based on the context model;

Deriving a residual sample based on the decoded transform skip flag; And

Including the step of generating a reconstructed picture based on the residual sample,

The context model for the transform skip flag is determined based on a context index increment for the transform skip flag,

The context index increment for the transform skip flag,

A computer-readable digital storage medium derived based on at least one of prediction mode information of the current block or neighboring blocks of the current block.