WO2020256399A1

WO2020256399A1 - Video or image coding based on mapping of luma samples and scaling of chroma samples

Info

Publication number: WO2020256399A1
Application number: PCT/KR2020/007830
Authority: WO
Inventors: 자오지에; 김승환
Original assignee: 엘지전자 주식회사
Priority date: 2019-06-17
Filing date: 2020-06-17
Publication date: 2020-12-24

Abstract

According to the disclosure of the present document, a procedure of deriving an inverse mapping index for a luma component in a procedure of luma mapping with chroma scaling (LMCS) may be simplified, and linear LMCS may also be applied. Therefore, the complexity of the LMCS may be reduced, and the video/image coding efficiency may be increased.

Description

Video or image coding based on mapping of luma samples and scaling of chroma samples

The present technology relates to video or picture coding based on mapping of luma samples and scaling of chroma samples.

Recently, demand for high-resolution, high-quality video/video such as 4K or 8K or higher UHD (Ultra High Definition) video/video is increasing in various fields. As the video/video data becomes high-resolution and high-quality, the amount of information or bits to be transmitted increases relative to the existing video/video data. Therefore, the video data can be transmitted using a medium such as a wired/wireless broadband line or an existing storage medium. When video/video data is stored by using it, the transmission cost and storage cost increase.

In addition, interest and demand for immersive media such as VR (Virtual Reality) and AR (Artificial Realtiy) contents or holograms are increasing in recent years, and videos/videos having different image characteristics from real images such as game images. Broadcasting about is increasing.

Accordingly, high-efficiency video/video compression technology is required in order to effectively compress, transmit, store, and reproduce information of high-resolution, high-quality video/video having various characteristics as described above.

In addition, a luma mapping with chroma scaling (LMCS) procedure is performed in order to improve compression efficiency and increase subjective/objective visual quality, and there is discussion to increase the efficiency of the LMCS procedure.

According to an embodiment of the present document, a method and apparatus for increasing video/video coding efficiency is provided.

According to an embodiment of the present document, an efficient method and apparatus for applying filtering are provided.

According to an embodiment of the present document, an efficient method and apparatus for applying LMCS is provided.

According to an embodiment of the present document, the LMCS codewords (or ranges thereof) may be limited.

According to an embodiment of this document, a single chroma residual scaling factor signaled directly in chroma scaling of the LMCS may be used.

According to an embodiment of this document, linear mapping (linear LMCS) may be used.

According to an embodiment of the present document, information on pivot points necessary for linear mapping may be explicitly signaled.

According to an embodiment of the present document, a flexible number of bins may be used for luma mapping.

According to an embodiment of the present document, a procedure for deriving bin indices for inverse mapping or chroma residual scaling for luma samples may be simplified.

According to an embodiment of the present document, a video/video decoding method performed by a decoding apparatus is provided.

According to an embodiment of the present document, a decoding apparatus for performing video/video decoding is provided.

According to an embodiment of the present document, a video/video encoding method performed by an encoding device is provided.

According to an embodiment of the present document, there is provided an encoding device that performs video/video encoding.

According to an embodiment of the present document, a computer-readable digital storage medium in which encoded video/image information generated according to the video/image encoding method disclosed in at least one of the embodiments of the present document is stored is provided.

According to an embodiment of the present document, encoded information causing to perform the video/image decoding method disclosed in at least one of the embodiments of the present document by a decoding device or a computer-readable digital storing encoded video/image information Provide a storage medium.

According to an embodiment of the present document, it is possible to increase overall image/video compression efficiency.

According to an embodiment of the present document, subjective/objective visual quality may be improved through efficient filtering.

According to an embodiment of the present document, an LMCS procedure for video/video coding can be efficiently performed.

According to an embodiment of the present document, it is possible to minimize the resource/cost (of software or hardware) required for the LMCS procedure.

According to an embodiment of this document, it is possible to facilitate hardware implementation for an LMCS procedure.

According to an embodiment of the present document, a division operation required for deriving LMCS codewords in mapping (reshaping) may be removed or minimized through the restriction of the LMCS codewords (or their range).

According to an embodiment of the present document, the latency according to the piecewise index identification may be removed through the use of a single chroma residual scaling factor.

According to an embodiment of the present document, a chroma residual scaling procedure may be performed without relying on a luma block (reconstruction of) through the use of linear mapping in the LMCS, and thus latency in scaling may be removed.

According to an embodiment of the present document, mapping efficiency in LMCS may be improved.

According to an embodiment of the present document, the complexity of LMCS may be reduced through simplification of a procedure for deriving bin indices for inverse mapping or chroma residual scaling for luma samples, and thus video/image coding efficiency is increased can do.

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.

4 exemplarily shows an inter prediction procedure.

5 exemplarily shows a hierarchical structure for a coded image/video.

6 exemplarily shows a hierarchical structure of a CVS according to an embodiment of the present document.

7 shows an exemplary LMCS structure according to an embodiment of the present document.

8 illustrates an LMCS structure according to another embodiment of this document.

9 shows a graph showing exemplary forward mapping.

10 is a flowchart illustrating a method of deriving a chroma residual scaling index according to an embodiment of the present document.

11 shows a linear fit of pivot points according to an embodiment of the present document.

12 shows an example of a linear reshaper according to an embodiment of the present document.

13 shows an example of linear forward mapping in an embodiment of this document.

14 shows an example of inverse forward mapping according to an embodiment of this document.

15 and 16 schematically illustrate an example of a video/video encoding method and related components according to the embodiment(s) of this document.

17 and 18 schematically illustrate an example of a video/video decoding method and related components according to an embodiment of the present document.

19 shows an example of a content streaming system to which embodiments disclosed in this document can be applied.

The disclosure of the present document is intended to illustrate specific embodiments in the drawings and describe in detail since various modifications may be made and various embodiments may be provided. However, this is not intended to limit the present disclosure to specific embodiments. The terms used in this document are only used to describe specific embodiments, and are not intended to limit the technical idea of the embodiments of the present document. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this document, terms such as "comprise" or "have" are intended to designate the existence of features, numbers, steps, actions, components, parts, or combinations thereof, described in the document, and one or more other features or numbers. It is to be understood that the possibility of addition or presence of, steps, actions, components, parts, or combinations thereof is not preliminarily excluded.

Meanwhile, each of the components in the drawings described in this document 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 disclosure.

Hereinafter, exemplary embodiments of the present document will be described with reference to the accompanying drawings. Hereinafter, the same reference numerals may be used for the same constituent elements in the drawings, and duplicate descriptions for the same constituent elements may be omitted.

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

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

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

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

The transmission unit may transmit the encoded image/video information or data output in the form of a bitstream to the reception unit of the reception device through a digital storage medium or a network in a file or streaming format. 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 may be applied to a method disclosed in the VVC (versatile video coding) standard. In addition, the method/embodiment disclosed in this document is an EVC (essential video coding) standard, AV1 (AOMedia Video 1) standard, AVS2 (2nd generation of audio video coding standard), or next-generation video/image coding standard (ex. H.267). or H.268, etc.).

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

In this document, a video may mean a set of a series 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 an integer number of complete tiles, which may be contained exclusively in a single NAL unit, or an integer number of consecutive complete CTU rows in a tile of a picture (A slice includes an integer number of complete tiles or an integer number of consecutive tiles). complete CTU rows within a tile of a picture that may be exclusively contained in a single NAL unit)

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.

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

A forward slash (/) or comma (comma) used in this document may mean "and/or". For example, "A/B" can mean "A and/or B". Accordingly, "A/B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B or C".

In this document, "at least one of A and B" may mean "only A", "only B", or "both A and B". In addition, in this document, the expression "at least one of A or B" or "at least one of A and/or B" means "at least one A and B (at least one of A and B)" can be interpreted the same.

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

In addition, parentheses used in this document 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 this document 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 this document, technical features that are individually described in one drawing may be implemented individually or at the same time.

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

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

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

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

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

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

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

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

The prediction signal generated through the prediction unit (including the inter prediction unit 221 and/or the intra prediction unit 222) may be used to generate a reconstructed signal or may be used to generate a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transformation technique may include at least one of Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), Graph-Based Transform (GBT), or Conditionally Non-linear Transform (CNT). 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 of 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 (ex. encoded image/video information) may be transmitted or stored in a bitstream format in units of network abstraction layer (NAL) units. The image/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 image/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 image/video information. The image/video information may be encoded through the above-described encoding procedure and included in the bitstream. The bitstream may be transmitted through a network or may be stored in a digital storage medium. Here, the network may include a broadcasting network and/or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD. For the signal output from the entropy encoding unit 240, a transmission unit (not shown) for transmitting and/or a storage unit (not shown) for storing may be configured as an internal/external element of the encoding apparatus 200, or the transmission unit It may be included in the entropy encoding unit 240.

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

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

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

The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter prediction unit 221. When inter prediction is applied through this, the encoding device may avoid prediction mismatch between the encoding device 200 and the decoding device, 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/image decoding apparatus to which embodiments of the present document can be applied. Hereinafter, the decoding device may include an image decoding device and/or a video decoding device.

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 (memoery) 360. The prediction unit 330 may include an inter prediction unit 331 and an intra prediction unit 332. The residual processing unit 320 may include a dequantizer 321 and an inverse transformer 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 image/video information is input, the decoding apparatus 300 may reconstruct an image in response to a process in which the image/video information is processed by the encoding device of FIG. 2. For example, the decoding apparatus 300 may derive units/blocks based on block division related information obtained from the bitstream. The decoding device 300 may perform decoding using a processing unit applied in the encoding device. Thus, the processing unit of decoding may be, for example, a coding unit, and the coding unit may be divided from a coding tree unit or a maximum coding unit along a quad tree structure, a binary tree structure and/or a ternary tree structure. One or more transform units may be derived from the coding unit. In addition, the reconstructed image signal decoded and output through the decoding device 300 may be reproduced through the playback device.

The decoding apparatus 300 may receive a signal output from the encoding apparatus of FIG. 2 in the form of a bitstream, and the received signal may be decoded through the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (eg, image/video information) necessary for image restoration (or picture restoration). The image/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 image/video information may further include general constraint information. The decoding apparatus may further decode the picture based on the information on the parameter set and/or the general restriction information. Signaled/received information and/or syntax elements described later in this document may be decoded through the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 decodes information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and a value of a syntax element required for image restoration, a quantized value of a transform coefficient related to a residual. Can be printed. In more detail, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and includes information on a syntax element to be decoded and information on a neighboring and decoding target block or information on 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 320 may generate a prediction signal based on various prediction methods to be described later. For example, the prediction unit may apply intra prediction or inter prediction for prediction of one block, as well as simultaneously apply intra prediction and inter prediction. This can be called combined inter and intra prediction (CIIP). In addition, the prediction unit may be based on an intra block copy (IBC) prediction mode or a palette mode to predict a block. The IBC prediction mode or the palette mode may be used for content image/video coding such as a game, for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction in that it derives a reference block in the current picture. That is, the IBC may use at least one of the inter prediction techniques described in this document. The palette mode can be viewed as an example of intra coding or intra prediction. When the palette mode is applied, information about a palette table and a palette index may be included in the image/video information and signaled.

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

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

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

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

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

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

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

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

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.

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

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

Intra prediction may indicate prediction of generating prediction samples for a current block based on reference samples in a picture (hereinafter, referred to as a current picture) to which the current block belongs. When intra prediction is applied to the current block, surrounding reference samples to be used for intra prediction of the current block may be derived. The neighboring reference samples of the current block are a sample adjacent to the left boundary of the current block of size nWxnH, a total of 2xnH samples adjacent to the bottom-left, and a sample adjacent to the top boundary of the current block. And a total of 2xnW samples adjacent to the top-right side and one sample adjacent to the top-left side of the current block. Alternatively, the peripheral reference samples of the current block may include a plurality of columns of upper peripheral samples and a plurality of rows of left peripheral samples. In addition, the neighboring reference samples of the current block are a total of nH samples adjacent to the right boundary of the current block of size nWxnH, a total of nW samples adjacent to the bottom boundary of the current block, and the lower right side of the current block. It may include one sample adjacent to (bottom-right).

However, some of the neighboring reference samples of the current block have not yet been decoded or may not be available. In this case, the decoder may construct neighboring reference samples to be used for prediction by substituting samples that are not available with available samples. Alternatively, surrounding reference samples to be used for prediction may be configured through interpolation of available samples.

When neighboring reference samples are derived, (i) a prediction sample can be derived based on an average or interpolation of neighboring reference samples of the current block, and (ii) neighboring reference samples of the current block Among them, the prediction sample may be derived based on a reference sample existing in a specific (prediction) direction with respect to the prediction sample. The case of (i) may be referred to as a non-directional mode or a non-angular mode, and the case of (ii) may be referred to as a directional mode or an angular mode.

In addition, among the neighboring reference samples, a first neighboring sample positioned in a prediction direction of an intra prediction mode of the current block and a second neighboring sample positioned in a direction opposite to the prediction direction based on the prediction sample of the current block. The prediction sample may be generated through interpolation. The above-described case may be referred to as linear interpolation intra prediction (LIP). Also, chroma prediction samples may be generated based on luma samples using a linear model. This case may be referred to as LM mode.

In addition, a temporary prediction sample of the current block is derived based on the filtered surrounding reference samples, and at least one of the existing surrounding reference samples, that is, unfiltered surrounding reference samples, derived according to the intra prediction mode. A prediction sample of the current block may be derived by weighted sum of a reference sample and the temporary prediction sample. The above case may be referred to as PDPC (Position dependent intra prediction).

In addition, a reference sample line with the highest prediction accuracy is selected among the neighboring multi-reference sample lines of the current block, and a prediction sample is derived from the reference sample located in the prediction direction from the line, and at this time, the used reference sample line is decoded. Intra prediction coding may be performed by instructing (signaling) the device. The above-described case may be referred to as multi-reference line intra prediction or MRL-based intra prediction.

In addition, while dividing the current block into vertical or horizontal subpartitions, intra prediction is performed based on the same intra prediction mode, and neighboring reference samples may be derived and used in units of the subpartition. That is, in this case, the intra prediction mode for the current block is equally applied to the subpartitions, but by deriving and using neighboring reference samples in units of the subpartitions, intra prediction performance may be improved in some cases. This prediction method may be referred to as intra-prediction based on ISP (intra sub-partitions).

The above-described intra prediction methods may be referred to as an intra prediction type in distinction from the intra prediction mode. The intra prediction type may be referred to as various terms such as an intra prediction technique or an additional intra prediction mode. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the aforementioned LIP, PDPC, MRL, and ISP. A general intra prediction method excluding specific intra prediction types such as LIP, PDPC, MRL, and ISP may be referred to as a normal intra prediction type. The normal intra prediction type may be generally applied when the specific intra prediction type as described above is not applied, and prediction may be performed based on the aforementioned intra prediction mode. Meanwhile, post-processing filtering may be performed on the derived prediction samples as necessary.

Specifically, the intra prediction procedure may include determining an intra prediction mode/type, deriving a neighboring reference sample, and deriving an intra prediction mode/type based prediction sample. Also, a post-filtering step may be performed on the derived prediction samples as necessary.

When intra prediction is applied, an intra prediction mode applied to the current block may be determined using an intra prediction mode of a neighboring block. For example, the decoding apparatus receives one of the MPM candidates in the most probable mode (MPM) list derived based on the intra prediction mode of the neighboring block (ex. left and/or upper neighboring block) of the current block and additional candidate modes. The selected MPM index may be selected, or one of the remaining intra prediction modes not included in the MPM candidates (and the planner mode) may be selected based on the remaining intra prediction mode information. The MPM list may be configured to include or not include a planner mode as a candidate. For example, when the MPM list includes a planner mode as candidates, the MPM list may have 6 candidates, and when the MPM list does not include a planner mode as candidates, the MPM list has 5 candidates. I can. When the MPM list does not include a planar mode as a candidate, a not planar flag (ex. intra_luma_not_planar_flag) indicating whether the intra prediction mode of the current block is not a planar mode may be signaled. For example, the MPM flag may be signaled first, and the MPM index and the not planner flag may be signaled when the value of the MPM flag is 1. In addition, the MPM index may be signaled when the value of the not planner flag is 1. Here, the MPM list is configured not to include a planar mode as a candidate, rather than that the planner mode is not an MPM, but a planar mode is always considered as an MPM. This is to first check whether or not.

For example, whether the intra prediction mode applied to the current block is among the MPM candidates (and planner mode) or the remaining mode may be indicated based on the MPM flag (ex. intra_luma_mpm_flag). A value of 1 of the MPM flag may indicate that the intra prediction mode for the current block is within MPM candidates (and planner mode), and a value of 0 of the MPM flag indicates that the intra prediction mode for the current block is MPM candidates (and planner mode). ) Can indicate not within. The not planar flag (ex. intra_luma_not_planar_flag) value 0 may indicate that the intra prediction mode for the current block is a planar mode, and the not planner flag value 1 indicates that the intra prediction mode for the current block is not a planar mode. I can. The MPM index may be signaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element, and the remaining intra prediction mode information may be signaled in the form of rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element. For example, the remaining intra prediction mode information may indicate one of all intra prediction modes by indexing the remaining intra prediction modes not included in the MPM candidates (and the planar mode) in the order of prediction mode numbers. The intra prediction mode may be an intra prediction mode for a luma component (sample). Hereinafter, the intra prediction mode information includes the MPM flag (ex. intra_luma_mpm_flag), the not planar flag (ex. intra_luma_not_planar_flag), the MPM index (ex. mpm_idx or intra_luma_mpm_idx), and the remaining intra prediction mode information (rem_intra_remainder_mpm_mainder_). It may include at least one. In this document, the MPM list may be referred to in various terms such as an MPM candidate list and candModeList. When MIP is applied to the current block, a separate mpm flag (ex. intra_mip_mpm_flag) for MIP, an mpm index (ex. intra_mip_mpm_idx), and remaining intra prediction mode information (ex. intra_mip_mpm_remainder) may be signaled, and the not planar The flag is not signaled.

In other words, in general, when a block is divided for an image, the current block to be coded and the neighboring block have similar image characteristics. Accordingly, it is highly likely that the current block and the neighboring block have the same or similar intra prediction modes. Accordingly, the encoder can use the intra prediction mode of the neighboring block to encode the intra prediction mode of the current block.

For example, the encoder/decoder can construct a list of most probable modes (MPM) for the current block. The MPM list may also be referred to as an MPM candidate list. Here, MPM may mean a mode used to improve coding efficiency in consideration of similarity between a current block and a neighboring block during intra prediction mode coding. As described above, the MPM list may be configured including a planner mode, or may be configured excluding a planner mode. For example, when the MPM list includes a planner mode, the number of candidates in the MPM list may be six. In addition, when the MPM list does not include the planner mode, the number of candidates in the MPM list may be five.

The encoder/decoder can configure an MPM list including 5 or 6 MPMs.

In order to construct the MPM list, three types of modes can be considered: default intra modes, neighbor intra modes, and derived intra modes.

For the peripheral intra modes, two neighboring blocks, that is, a left neighboring block and an upper neighboring block may be considered.

As described above, if the MPM list is configured not to include the planar mode, the planar mode is excluded from the list, and the number of MPM list candidates may be set to five.

In addition, the non-directional mode (or non-angular mode) of the intra prediction modes may include a DC mode based on an average of neighboring reference samples of the current block or a planar mode based on interpolation. have.

When inter prediction is applied, the prediction unit of the encoding device/decoding device may derive a prediction sample by performing inter prediction in block units. Inter prediction may represent a prediction derived in a method dependent on data elements (ex. sample values or motion information) of a picture(s) other than the current picture (Inter prediction can be a prediction derived in a manner that is dependent on data elements (ex. sample values or motion information) of picture(s) other than the current picture). When inter prediction is applied to the current block, a predicted block (prediction sample array) for the current block is derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. I can. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, motion information of the current block may be predicted in units of blocks, subblocks, or samples based on correlation between motion information between neighboring blocks and current blocks. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter prediction is applied, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block existing in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a co-located CU (colCU), and the like, and a reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). May be. For example, a motion information candidate list may be constructed based on neighboring blocks of the current block, and a flag indicating which candidate is selected (used) to derive a motion vector and/or a reference picture index of the current block Alternatively, index information may be signaled. Inter prediction may be performed based on various prediction modes. For example, in the case of a skip mode and a merge mode, motion information of a current block may be the same as motion information of a selected neighboring 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, a motion vector of a selected neighboring block is used as a motion vector predictor, and a motion vector difference may be signaled. In this case, the motion vector of the current block may be derived by using the sum of the motion vector predictor and the motion vector difference.

The motion information may include L0 motion information and/or L1 motion information according to an inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). The motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. The prediction based on the L0 motion vector may be referred to as L0 prediction, the prediction based on the L1 motion vector may be referred to as the L1 prediction, and the prediction based on both the L0 motion vector and the L1 motion vector may be referred to as a pair (Bi) prediction. I can. Here, the motion vector L0 may represent a motion vector associated with the reference picture list L0 (L0), and the motion vector L1 may represent a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include pictures prior to the current picture in output order as reference pictures, and the reference picture list L1 may include pictures after the current picture in output order. The previous pictures may be referred to as forward (reference) pictures, and the subsequent pictures may be referred to as reverse (reference) pictures. The reference picture list L0 may further include pictures later in output order than the current picture as reference pictures. In this case, the previous pictures in the reference picture list L0 may be indexed first, and the subsequent pictures may be indexed next. The reference picture list L1 may further include pictures preceding the current picture in an output order as reference pictures. In this case, the subsequent pictures in the reference picture list 1 may be indexed first, and the previous pictures may be indexed next. Here, the output order may correspond to a picture order count (POC) order.

4 exemplarily shows an inter prediction procedure.

Referring to FIG. 4, as described above, the inter prediction procedure may include determining an inter prediction mode, deriving motion information according to the determined prediction mode, and performing prediction based on the derived motion information (generating a prediction sample). The inter prediction procedure may be performed in an encoding device and a decoding device as described above. In this document, the coding device may include an encoding device and/or a decoding device.

Referring to FIG. 4, the coding apparatus determines an inter prediction mode for a current block (S400). Various inter prediction modes may be used for prediction of a current block in a picture. For example, various modes, such as a merge mode, a skip mode, a motion vector prediction (MVP) mode, an affine mode, a subblock merge mode, and an MMVD (merge with MVD) mode, may be used. Decoder side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, Bi-prediction with CU-level weight (BCW), and Bi-directional optical flow (BDOF) are additional modes that can be used more or instead. have. The afine mode may also be referred to as an affine motion prediction mode. The MVP mode may also be called an advanced motion vector prediction (AMVP) mode. In this document, some modes and/or motion information candidates derived by some modes may be included as one of motion information related candidates of other modes. For example, the HMVP candidate may be added as a merge candidate of the merge/skip mode, or may be added as an mvp candidate of the MVP mode. When the HMVP candidate is used as a motion information candidate of the merge mode or skip mode, the HMVP candidate may be referred to as an HMVP merge candidate.

Prediction mode information indicating the inter prediction mode of the current block may be signaled from the encoding device to the decoding device. The prediction mode information may be included in a bitstream and received by a decoding apparatus. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated through hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag is signaled to indicate whether to apply the skip mode, and when the skip mode is not applied, the merge flag is signaled to indicate whether to apply the merge mode, and when the merge mode is not applied, the MVP mode is indicated to be applied. Alternatively, a flag for additional classification may be further signaled. The afine mode may be signaled as an independent mode, or may be signaled as a mode dependent on a merge mode or an MVP mode. For example, the afine mode may include an afine merge mode and an afine MVP mode.

Meanwhile, information indicating whether the above-described list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current coding unit) may be signaled to the current block. The information may be referred to as motion prediction direction information, inter prediction direction information, or inter prediction indication information, and may be configured/encoded/signaled in the form of an inter_pred_idc syntax element, for example. That is, the inter_pred_idc syntax element may indicate whether the above-described list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current coding unit). In this document, for convenience of description, an inter prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by an inter_pred_idc syntax element may be indicated as a motion prediction direction. L0 prediction may be represented by pred_L0, L1 prediction by pred_L1, and bi prediction by pred_BI. For example, the following prediction types may be indicated according to the value of the inter_pred_idc syntax element.

As described above, one picture may include one or more slices. A slice may have one of slice types including an I (intra) slice, a P (predictive) slice, and a B (bi-predictive) slice. The slice type may be indicated based on slice type information. For the blocks in the I slice, inter prediction is not used for prediction, only intra prediction can be used. Of course, even in this case, the original sample value may be coded and signaled without prediction. For blocks in a P slice, intra prediction or inter prediction may be used, and when inter prediction is used, only uni prediction may be used. Meanwhile, intra prediction or inter prediction may be used for blocks in a B slice, and when inter prediction is used, up to a maximum bi prediction may be used.

L0 and L1 may include reference pictures encoded/decoded before the current picture. For example, L0 may include reference pictures before and/or after the current picture in POC order, and L1 may include reference pictures after and/or before the current picture in POC order. In this case, a lower reference picture index may be allocated to L0 than the current picture in POC order, and a lower reference picture index may be allocated to L1 to reference pictures later than the current picture in POC order. Can be. In the case of B slice, bi-prediction may be applied, and even in this case, unidirectional bi-prediction may be applied, or bi-directional bi-prediction may be applied. Bi-directional bi-prediction can be called true bi-prediction.

The coding apparatus derives motion information for the current block (S410). The motion information may be derived based on the inter prediction mode.

The coding apparatus may perform inter prediction using motion information of the current block. The encoding apparatus may derive optimal motion information for the current block through a motion estimation procedure. For example, the encoding device may search for a similar reference block with high correlation using the original block in the original picture for the current block in units of fractional pixels within a predetermined search range in the reference picture, and derive motion information through this. I can. The similarity of the block can be derived based on the difference between the phase-based sample values. For example, the similarity of blocks may be calculated based on the SAD between a current block (or a template of a current block) and a reference block (or a template of a reference block). In this case, motion information may be derived based on the reference block having the smallest SAD in the search area. The derived motion information may be signaled to the decoding apparatus according to various methods based on the inter prediction mode.

The coding apparatus performs inter prediction based on the motion information for the current block (S420). The coding apparatus may derive the prediction sample(s) for the current block based on the motion information. The current block including the prediction samples may be referred to as a predicted block.

When the merge mode is applied, motion information of the current prediction block is not directly transmitted, and motion information of the current prediction block is derived using motion information of a neighboring prediction block. Accordingly, the motion information of the current prediction block can be indicated by transmitting flag information indicating that the merge mode has been used and a merge index indicating which prediction block is used. The merge mode may be called a regular merge mode.

In order to perform the merge mode, the encoder must search for a merge candidate block used to derive motion information of the current prediction block. For example, up to five merge candidate blocks may be used, but embodiments of this document are not limited thereto. In addition, the maximum number of merge candidate blocks may be transmitted in a slice header or a tile group header. After finding the merge candidate blocks, the encoder may generate a merge candidate list and select a merge candidate block having the lowest cost among them as a final merge candidate block.

The merge candidate list may use, for example, five merge candidate blocks. For example, four spatial merge candidates and one temporal merge candidate can be used. Hereinafter, the spatial merge candidate or the spatial MVP candidate to be described later may be referred to as an SMVP, and the temporal merge candidate or the temporal MVP candidate to be described later may be referred to as TMVP.

5 exemplarily shows a hierarchical structure for a coded image/video.

Referring to FIG. 5, the coded image/video is a video coding layer (VCL) that deals with decoding processing of the image/video and itself, a subsystem for transmitting and storing coded information, and a VCL and subsystem. It exists between and is divided into a network abstraction layer (NAL) responsible for the network adaptation function.

In VCL, VCL data including compressed video data (slice data) is generated, or a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (Video Parameter Set: A parameter set including information such as VPS) or a Supplemental Enhancement Information (SEI) message additionally required for a video decoding process may be generated.

In NAL, a NAL unit can be generated by adding header information (NAL unit header) to a Raw Byte Sequence Payload (RBSP) generated in VCL. In this case, RBSP refers to slice data, parameter set, SEI message, etc. generated in the VCL. The NAL unit header may include NAL unit type information specified according to RBSP data included in the corresponding NAL unit.

As shown in the figure, the NAL unit may be divided into a VCL NAL unit and a Non-VCL NAL unit according to the RBSP generated from the VCL. The VCL NAL unit may mean a NAL unit including information (slice data) on an image, and the Non-VCL NAL unit is a NAL unit including information (parameter set or SEI message) necessary for decoding an image. Can mean

The above-described VCL NAL unit and Non-VCL NAL unit may be transmitted through a network by attaching header information according to the data standard of the sub-system. For example, the NAL unit may be transformed into a data format of a predetermined standard, such as an H.266/VVC file format, Real-time Transport Protocol (RTP), Transport Stream (TS), and the like, and transmitted through various networks.

As described above, the NAL unit type may be specified according to the RBSP data structure included in the NAL unit, and information on the NAL unit type may be stored and signaled in the NAL unit header.

For example, depending on whether the NAL unit includes information about an image (slice data), it may be largely classified into a VCL NAL unit type and a Non-VCL NAL unit type. The VCL NAL unit type may be classified according to the nature and type of a picture included in the VCL NAL unit, and the non-VCL NAL unit type may be classified according to the type of a parameter set.

The following is an example of a NAL unit type specified according to the type of a parameter set included in the Non-VCL NAL unit type.

-APS (Adaptation Parameter Set) NAL unit: Type for NAL unit including APS

-DPS (Decoding Parameter Set) NAL unit: a type for a NAL unit including DPS

-Video Parameter Set (VPS) NAL unit: A type for a NAL unit including a VPS

-SPS (Sequence Parameter Set) NAL unit: a type for a NAL unit including SPS

-PPS (Picture Parameter Set) NAL unit: A type for a NAL unit including PPS

-PH (Picture header) NAL unit: A type for a NAL unit including PH

The above-described NAL unit types have syntax information for the NAL unit type, and the syntax information may be stored in the NAL unit header and signaled. For example, the syntax information may be nal_unit_type, and NAL unit types may be specified as nal_unit_type values.

Meanwhile, as described above, one picture may include a plurality of slices, and one slice may include a slice header and slice data. In this case, one picture header may be further added to a plurality of slices (slice header and slice data set) in one picture. The picture header (picture header syntax) may include information/parameters commonly applicable to the picture. In this document, slices can be mixed or replaced with tile groups. Also, in this document, the slice header may be mixed or replaced with a type group header.

The slice header (slice header syntax) may include information/parameters commonly applicable to the slice. The APS (APS syntax) or PPS (PPS syntax) may include information/parameters commonly applicable to one or more slices or pictures. The SPS (SPS syntax) may include information/parameters commonly applicable to one or more sequences. The VPS (VPS syntax) may include information/parameters commonly applicable to multiple layers. The DPS (DPS syntax) may include information/parameters commonly applicable to the entire video. The DPS may include information/parameters related to concatenation of a coded video sequence (CVS). In this document, a high level syntax (HLS) may include at least one of the APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, picture header syntax, and slice header syntax.

In this document, the image/video information encoded by the encoding device to the decoding device and signaled in the form of a bitstream not only includes intra-picture partitioning information, intra/inter prediction information, residual information, in-loop filtering information, etc. Information included in the slice header, information included in the picture header, information included in the APS, information included in the PPS, information included in the SPS, information included in the VPS, and/or information included in the DPS can do. In addition, the image/video information may further include information on a NAL unit header.

Meanwhile, in order to compensate for a difference between an original image and a reconstructed image due to an error occurring in a compression encoding process such as quantization, an in-loop filtering procedure may be performed on reconstructed samples or reconstructed pictures as described above. As described above, in-loop filtering may be performed in the filter unit of the encoding device and the filter unit of the decoding device, and a deblocking filter, SAO, and/or adaptive loop filter (ALF) may be applied. For example, the ALF procedure may be performed after the deblocking filtering procedure and/or the SAO procedure is completed. However, even in this case, the deblocking filtering procedure and/or the SAO procedure may be omitted.

Meanwhile, in order to increase coding efficiency, luma mapping wth chroma scaling (LMCS) may be applied as described above. LMCS can be referred to as a loop reshaper (reshaping). In order to increase coding efficiency, LMCS control and/or LMCS-related information signaling may be hierarchically performed.

6 exemplarily shows a hierarchical structure of a CVS according to an embodiment of the present document. Coded video suquence (CVS) may include a sequence parameter set (SPS), a picture parameter set (PPS), a tile group header, tile data, and/or CTU(s). Here, the tile group header and tile data may be referred to as a slice header and slice data, respectively.

The SPS can natively contain flags to enable tools to be used in CVS. Also, the SPS may be referred to by a PPS including information on parameters that change for each picture. Each of the encoded pictures may include tiles of one or more encoded rectangular domains. The tiles may be grouped in a raster scan forming tile groups. Each tile group is encapsulated with header information called a tile group header. Each tile is composed of a CTU containing coded data. Here, the data may include original sample values, predicted sample values, and luma and chroma components thereof (luma predicted sample values and chroma predicted sample values).

7 shows an exemplary LMCS structure according to an embodiment of the present document. The LMCS structure 700 of FIG. 7 shows luma for an in-loop mapping portion 710 and chroma components of luma components based on adaptive piecewise linear (adaptive PWL) models. -May include a luma-dependent chroma residual scaling portion 720. The inverse quantization and inverse transform 711, reconstruction 712, and intra prediction 713 blocks of the in-loop mapping portion 710 represent processes applied in the mapped (reshaped) domain. Loop filters 715 of the in-loop mapping portion 710, blocks of motion compensation or inter prediction 717, and restoration 722 of the chroma residual scaling portion 620, intra prediction 723, motion compensation Or inter prediction 724, loop filters 725 blocks represent processes applied in the original (non-mapped, non-reshaped) domain.

As described in FIG. 7, when the LMCS is enabled, at least one of an inverse reshaping (mapping) process 714, a forward reshaping (mapping) process 718, and a chroma scaling process 721 may be applied. . For example, the inverse reshaping process can be applied to the (restored) luma sample (or luma samples or luma sample array) of the reconstructed picture. The inverse reshaping process may be performed based on a piecewise function (inverse) index of a luma sample. The partial function (inverse) index can identify the fragment (or part) to which the luma sample belongs. The output of the inverse reshaping process is a modified (restored) luma sample (or modified luma samples or modified luma sample array). The LMCS may be enabled or disabled at a tile group (or slice), picture, or higher level.

A forward reshaping process and/or a chroma scaling process may be applied to generate the reconstructed picture. A picture may include luma samples and chroma samples. A reconstructed picture having luma samples may be referred to as a reconstructed luma picture, and a reconstructed picture having chroma samples may be referred to as a reconstructed chroma picture. The combination of the reconstructed luma picture and the reconstructed chroma picture may be referred to as a reconstructed picture. The restored luma picture can be created based on the forward reshaping process. For example, if inter prediction is applied to the current block, forward reshaping is applied to the luma prediction samples derived based on the (restored) luma samples of the reference picture. Since the (restored) luma sample of the reference picture is generated based on the inverse reshaping process, forward reshaping is applied to the luma prediction sample to derive a reshaped (mapped) luma prediction sample. The forward reshaping process may be performed based on the partial function index of the luma prediction sample. The partial function index may be derived based on a value of a luma prediction sample or a value of a luma sample of a reference picture used for inter prediction. When intra prediction (or intra block copy (IBC)) is applied to the current block, forward mapping is not necessary because the inverse reshaping process has not yet been applied to reconstructed samples of the current picture. In the reconstructed luma picture, a (restored) luma sample is generated based on the reshaped luma prediction sample and the corresponding luma residual sample.

The reconstructed chroma picture may be generated based on a chroma scaling process. For example, a (restored) chroma sample in the reconstructed coma picture may be derived based on a chroma prediction sample and a chroma residual sample (c _res ) in the current block. The chroma residual sample (c _res ) is derived based on the (scaled) chroma residual sample (c _resScale ) for the current block and the chroma residual scaling factor (cScaleInv may be referred to as varScale). The chroma residual scaling factor may be calculated based on the reshaped luma prediction sample values in the current block. For example, the scaling factor may be calculated based on the average luma value (ave(Y' _pred )) of the _reshaped luma prediction sample values (Y' _pred ). For reference, the (scaled) chroma residual sample derived based on the inverse transform/inverse quantization in FIG. 7 is c _resScale , the chroma residual derived by performing the (inverse) scaling procedure on the (scaled) chroma residual sample. The sample can be referred to as c _res .

8 illustrates an LMCS structure according to another embodiment of this document. FIG. 8 will be described with reference to FIG. 7. Here, the difference between the LMCS structure of FIG. 8 and the LMCS structure 700 of FIG. 7 will be mainly described. The in-loop mapping portion and luma-dependent chroma residual scaling portion of FIG. 8 may operate in the same/similar manner as the in-loop mapping portion 710 and luma-dependent chroma residual scaling portion 720 of FIG. 7. I can.

Referring to FIG. 8, a chroma residual scaling factor may be derived based on luma reconstructed samples. In this case, the average luma value (avgY _r ) can be obtained based on the surrounding luma reconstructed samples outside the reconstructed block, not the internal luma reconstructed samples of the reconstructed block, and chroma residual scaling is based on the average luma value (avgY _r ). Factors can be derived. Here, the peripheral luma reconstructed samples may be peripheral luma reconstructed samples of the current block, or may be peripheral luma reconstructed samples of virtual pipeline data units (VPDUs) including the current block. For example, when intra prediction is applied to a target block, reconstructed samples may be derived based on prediction samples derived based on the intra prediction. Also, for example, when inter prediction is applied to the target block, forward mapping is applied to prediction samples derived based on the inter prediction, and reconstructed based on reshaped (or forward mapped) luma prediction samples. Samples can be generated.

The video/video information signaled through the bitstream may include LMCS parameters (information on LMCS). The LMCS parameters may be composed of HLS (high level syntax, including slice header syntax) or the like. A detailed description of the LMCS parameters and configuration will be described later. As described above, the syntax tables described in this document (and the following embodiments) may be configured/encoded at the encoder end and signaled to the decoder end through a bitstream. The decoder may parse/decode information about the LMCS (in the form of syntax elements) in the syntax tables. One or more of the embodiments described below may be combined. The encoder can encode the current picture based on the information about the LMCS, and the decoder can decode the current picture based on the information about the LMCS.

In-loop mapping of luma components can adjust the dynamic range of the input signal by redistributing codewords over the dynamic range to improve compression efficiency. For luma mapping, a forward mapping (reshaping) function (FwdMap) and an inverse mapping (reshaping) function (InvMap) corresponding to the forward mapping function (FwdMap) may be used. The forward mapping function (FwdMap) can be signaled using partial linear models, for example, partial linear models can have 16 pieces or bins. The pieces can have the same length. In an example, the inverse mapping function InvMap may not be signaled separately, and instead may be derived from the forward mapping function FwdMap. That is, inverse mapping may be a function of forward mapping. For example, the inverse mapping function may be a function in which the forward mapping function is symmetrical based on y=x.

In-loop (luma) reshaping can be used to map input luma values (samples) to changed values in the reshaped domain. The reshaped values can be encoded and mapped back to the original (unmapped, unreshaped) domain after reconstruction. Chroma residual scaling can be applied to compensate for a difference between a luma signal and a chroma signal. In-loop reshaping can be performed by specifying a high level syntax for the reshaper model. Reshaper model syntax can signal a partial linear model (PWL model). A forward lookup table (FwdLUT) and/or an inverse lookup table (InvLUT) may be derived based on the partial linear model. As an example, when a forward lookup table (FwdLUT) is derived, an inverse lookup table (InvLUT) may be derived based on the forward lookup table (FwdLUT). The forward lookup table (FwdLUT) maps the input luma values Y _i to the changed values Y _r , and the inverse lookup table (InvLUT) maps the restored values Y _r based on the changed values to the restored values Y′ _i . Restored values Y _'i may be derived based on the luma input values Y _i.

In one example, the SPS may include the syntax of Table 2 below. The syntax of Table 2 may include sps_reshaper_enabled_flag as a tool enabling flag. Here, sps_reshaper_enabled_flag may be used to designate whether the reshaper is used in a coded video sequence (CVS). That is, sps_reshaper_enabled_flag may be a flag for enabling reshaper in the SPS. In one example, the syntax of Table 2 may be part of the SPS.

In one example, semantics that sps_seq_parameter_set_id and sps_reshaper_enabled_flag may indicate may be as shown in Table 3 below.

In one example, the tile group header or the slice header may include the syntax of Table 4 or Table 5 below.

The semantics of syntax elements included in the syntax of Table 4 or 5 may include, for example, items disclosed in the following tables.

As an example, when sps_reshaper_enabled_flag is parsed, the tile group header may parse additional data (e.g., information included in Table 6 or 7) used to configure lookup tables (FwdLUT and/or InvLUT). To this end, the state of the SPS reshaper flag may be checked in the slice header or the tile group header. When sps_reshaper_enabled_flag is true (or 1), an additional flag, tile_group_reshaper_model_present_flag (or slice_reshaper_model_present_flag) may be parsed. The purpose of tile_group_reshaper_model_present_flag (or slice_reshaper_model_present_flag) may be to indicate the existence of a reshaper model. For example, when tile_group_reshaper_model_present_flag (or slice_reshaper_model_present_flag) is true (or 1), it may be indicated that a reshaper exists for the current tile group (or current slice). If tile_group_reshaper_model_present_flag (or slice_reshaper_model_present_flag) is false (or 0), it may be indicated that there is no reshaper for the current tile group (or current slice).

If a reshaper exists and the reshaper is enabled in the current tile group (or current slice), the reshaper model (e.g. tile_group_reshaper_model() or slice_reshaper_model()) can be processed, in addition to an additional flag, tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) can also be parsed. tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) may indicate whether the reshaper model is currently used for the tile group (or slice). For example, if tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) is 0 (or false), the reshaper model may be indicated as not being used for the current tile group (or current slice). If tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) is 1 (or true), the reshaper model may be indicated as being used for the current tile group (or slice).

As an example, for example, tile_group_reshaper_model_present_flag (or slice_reshaper_model_present_flag) is true (or 1), and tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) may be false (or 0). This means that a reshaper model exists but is not currently used in a tile group (or slice). In this case, the reshaper model can be used in the next tile groups (or slices). As another example, tile_group_reshaper_enable_flag may be true (or 1) and tile_group_reshaper_model_present_flag may be false (or 0).

When the reshaper model (e.g., tile_group_reshaper_model() or slice_reshaper_model()) and tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) are parsed, it may be determined (evaluated) whether or not conditions necessary for chroma scaling exist. The above conditions were condition 1 (the current tile group/slice would not have been intra-coded) and/or condition 2 (the current tile group/slice would not have been split into two separate coding quad tree structures for luma and chroma, i.e. The current tile group/slice may not have a dual tree structure). If condition 1 and/or condition 2 is true and/or tile_group_reshaper_enable_flag (or slice_reshaper_enable_flag) is true (or 1), tile_group_reshaper_chroma_residual_scale_flag (or slice_reshaper_chroma_residual_scale_flag) may be parsed. When tile_group_reshaper_chroma_residual_scale_flag (or slice_reshaper_chroma_residual_scale_flag) is enabled (1 or true), it may be indicated that chroma residual scaling is enabled for the current tile group (or slice). When tile_group_reshaper_chroma_residual_scale_flag (or slice_reshaper_chroma_residual_scale_flag) is disabled (0 or false), it may be indicated that chroma residual scaling is disabled for the current tile group (or slice).

The purpose of the reshaping described above is to parse the data necessary to construct the lookup tables (FwdLUT and/or InvLUT). In an example, the lookup tables configured based on the parsed data may divide the distribution of an allowable luma value range into a plurality of bins (eg, 16). Thus, luma values within given bins can be mapped to changed luma values.

9 shows a graph showing exemplary forward mapping. In FIG. 9, only five bins are shown by way of example.

Referring to FIG. 9, the x-axis represents input luma values, and the y-axis represents changed output luma values. The x-axis is divided into 5 bins or pieces, and each bin has a length L. That is, five bins mapped to the changed luma values have the same length. The forward lookup table (FwdLUT) may be constructed using data available in the tile group header (eg, reshaper data), from which mapping may be facilitated.

In one embodiment, output pivot points related to the bin indices may be calculated. The output pivot points can set (mark) the minimum and maximum boundaries of the output range of luma codeword reshaping. The process of calculating the output pivot points may be performed based on a piecewise cumulative distribution function of the number of codewords. The output pivot range may be divided based on the maximum number of bins to be used and the size of a lookup table (FwdLUT or InvLUT). As an example, the output pivot range may be divided based on a product between the maximum number of bins and the size of the lookup table. For example, when the product between the maximum number of bins and the size of the lookup table is 1024, the output pivot range may be divided into 1024 entries. The division of the output pivot range may be performed (applied or achieved) based on (using) a scaling factor. In an example, the scaling factor may be derived based on Equation 1 below.

In Equation 1, SF denotes a scaling factor, and y1 and y2 denote output pivot points corresponding to each bin. Also, FP_PREC and c may be predetermined constants. The scaling factor determined based on Equation 1 may be referred to as a scaling factor for forward reshaping.

In another embodiment, with respect to inverse reshaping (inverse mapping), for a defined range of bins (e.g., from reshaper_model_min_bin_idx to reshape_model_max_bin_idx), the input reshape corresponding to the mapped pivot points of the forward lookup table (FwdLUT). The mapped pivot points and mapped inverse output pivot points (given by empty index*number of initial codewords) are patched. In another example, the scaling factor SF may be derived based on Equation 2 below.

In Equation 2, SF denotes a scaling factor, x1 and x2 denote input pivot points, and y1 and y2 denote output pivot points corresponding to each piece (bin). Here, the input pivot points may be pivot points mapped based on the forward lookup table (FwdLUT), and the output pivot points may be pivot points mapped inversely based on the inverse lookup table (InvLUT). Also, FP_PREC may be a predetermined constant. FP_PREC of Equation 2 may be the same as or different from FP_PREC of Equation 1. The scaling factor determined based on Equation 2 may be referred to as a scaling factor for inverse reshaping. During inverse reshaping, division of input pivot points may be performed based on the scaling factor of Equation 2. Based on the divided input pivot points, correspond to the minimum and maximum bin values for bin indices in the range from 0 to the minimum bin index (reshaper_model_min_bin_idx) and/or from the minimum bin index (reshaper_model_min_bin_idx) to the maximum bin index (reshape_model_max_bin_idx). Pivot values are specified.

Table 8 below shows the syntax of the reshaper model according to an embodiment. The reshaper model may be referred to as an LMCS model. Here, the reshaper model has been exemplarily described as a tile group reshaper, but the present specification is not necessarily limited by this embodiment. For example, the reshaper model may be included in the APS, or the tile group reshaper model may be referred to as a slice reshaper model or LMCS data. Also, the prefix reshaper_model or Rsp can be used interchangeably with lmcs. For example, in the following tables and the following description, reshaper_model_min_bin_idx, reshaper_model_delta_max_bin_idx, reshaper_model_max_bin_idx, RspCW, RsepDeltaCW can be used as lmcs_min_bin_idx, lmcs_delta_max_bin_C_idx, lmcsmax_bin_Widx, and lmcsmax_bin_Widx.

The semantics of syntax elements included in the syntax of Table 8 may include, for example, items disclosed in the following table.

The inverse mapping procedure for luma samples according to this document can be described in a standard document format as shown in the table below.

Identification of a piecewise function index procedure for a luma sample according to this document can be described in a standard document format as shown in the table below. In Table 11, idxYInv may be referred to as an inverse mapping index, and the inverse mapping index may be derived based on reconstructed luma samples (lumaSample).

Luma mapping may be performed based on the above-described embodiments and examples, and the above-described syntax and components included therein may be merely exemplary expressions, and the embodiments are limited by the above-described tables or equations. no. Hereinafter, a method of performing chroma residual scaling (scaling a chroma component of residual samples) based on luma mapping will be described.

The (luma-dependent) chroma residual scaling is to compensate for a difference between luma samples and corresponding chroma samples. For example, whether chroma residual scaling is enabled may be signaled at the tile group level or the slice group level. In one example, if luma mapping is enabled and dual tree partitioning is not applied to the current tile group, an additional flag may be signaled to indicate whether luma-dependent chroma residual scaling is enabled. have. In another example, if luma mapping is not used, or if dual tree splitting is not used for the current tile group, luma-dependent chroma residual scaling may be disabled. In another example, chroma residual scaling may always be disabled for chroma blocks having a size less than or equal to 4.

The chroma residual scaling may be based on an average value of a corresponding luma prediction block (a luma component of a prediction block to which an intra prediction mode and/or an inter prediction mode is applied). Scaling operations at the encoder stage and/or the decoder stage may be implemented as fixed-point integer operations based on Equation 3 below.

In the above-described Equation 3, c'represents a scaled chroma residual sample (scaled chroma component of the residual sample), c represents a chroma residual sample (chroma component of the residual sample), and s represents a chroma residual. Represents a dual scaling factor, and CSCALE_FP_PREC may indicate a predetermined constant. For example, CSCALE_FP_PREC may be 11.

10 is a flowchart illustrating a method of deriving a chroma residual scaling index according to an embodiment of the present document. The method described in conjunction with FIG. 10 may be performed based on tables, equations, variables, arrays, and functions included in FIG. 7 and related descriptions.

In step S1010, it may be determined whether the prediction mode is an intra prediction mode or an inter prediction mode based on the prediction mode information. If the prediction mode is an intra prediction mode, the current block or prediction samples of the current block are considered to be in an already reshaped (mapped) region. If the prediction mode is an inter prediction mode, the current block or prediction samples of the current block are considered to be in the original (unmapped, unreshaped) region.

In step S1020, when the prediction mode is an intra prediction mode, an average of the current block (or luma prediction samples of the current block) may be calculated (derived). That is, the average of the current blocks in the already reshaped area is calculated directly. The average may also be referred to as the average value.

In step S1021, when the prediction mode is the inter prediction mode, forward reshaping (forward mapping) may be performed (applied) on luma prediction samples of the current block. Through forward reshaping, luma prediction samples based on the inter prediction mode may be mapped from an original region to a reshaped region. In one example, forward reshaping for luma prediction samples may be performed based on the reshaper model described in conjunction with Table 4 above.

In step S1022, an average of the forward-reshaped (forward-mapped) luma prediction samples may be calculated (derived). That is, the averaging process may be performed on the forward reshaped result.

In step S1030, a chroma residual scaling index may be calculated. When the prediction mode is an intra prediction mode, the chroma residual scaling index may be calculated based on an average of the luma prediction samples. When the prediction mode is the inter prediction mode, the chroma residual scaling index may be calculated based on an average of forward-reshaped luma prediction samples.

In an embodiment, the chroma residual scaling index may be calculated based on a for loop syntax. The table below shows an exemplary for loop syntax for derivation (calculation) of the chroma residual scaling index.

In Table 12, idxS represents the chroma residual scaling index, idxS represents an index that identifies whether a chroma residual scaling index that satisfies the condition of an if statement has been obtained, S represents a predetermined constant, and MaxBinIdx represents the maximum allowable bin index. ReshapPivot[idxS+1] may be derived based on Tables 8 and/or 9 described above.

In an embodiment, a chroma residual scaling factor may be derived based on the chroma residual scaling index. Equation 4 below is an example for deriving the chroma residual scaling factor.

In Equation 4, s denotes the chroma residual scaling factor, and ChromaScaleCoef may be a variable (or array) derived based on Tables 8 and 9 described above.

As described above, an average luma value of the reference samples may be obtained, and a chroma residual scaling factor may be derived based on the average luma value. As described above, scaling of chroma component residual samples may be performed based on the chroma residual scaling factor, and a chroma component reconstructed sample may be generated based on the scaled chroma component residual samples.

In an embodiment of this document, a signaling structure for efficiently applying the above-described LMCS is proposed. According to an embodiment of the present document, for example, LMCS data may be included in HLS (eg, APS), and APS referred to through header information (ex. picture header, slice header) that is a lower level of APS By signaling the ID, an LMCS model (reshaper model) can be adaptively derived. The LMCS model may be derived based on LMCS parameters. Further, for example, a plurality of APS IDs may be signaled through the header information, and different LMCS models may be applied in units of blocks within the same picture/slice through this.

In an embodiment according to this document, a method of efficiently performing an operation required for an LMCS is proposed. According to the semantics described above in Table 9, a division operation by a piece length lmcsCW[i] is required to derive InvScaleCoeff[i]. However, when the length of the piece is not a power of 2, the division operation cannot be performed by bit shifting.

For example, calculation of InvScaleCoeff may require up to 16 division operations per slice. According to Table 8 above, in the case of 10-bit coding, the range of lmcsCW[i] ranges from 8 to 511, so the size of the LUT must be 504 to implement the division operation by lmcsCW[i] using the LUT. In addition, in the case of 12-bit coding, since lmcsCW[i] ranges from 32 to 2047, the LUT size must be 2016 to implement the division operation by lmcsCW[i] using the LUT. That is, the division operation can incur considerable cost in hardware implementation, and thus division operation should be omitted if possible.

In one aspect of the present embodiment, lmcsCW[i] may be limited to a fixed number (or a multiple of a predetermined number or pre-determined number). Accordingly, a lookup table (LUT) for a division operation (capacity or size of the LUT) can be reduced. For example, if lmcsCW[i] is a multiple of 2, the size of the LUT to replace the division operation may be reduced by half.

In another aspect of this embodiment, high internal bit depth coding is proposed. High internal bit depth coding may be an upper condition of the range limitation of lmcsCW[i]. For example, when the coding bit depth is higher than 10, lmcsCW[i] may be limited to a multiple of 1<<(BitDepthY-10). Here, BitDepthY may be a luma bit depth. Accordingly, the possible value of lmcsCW[i] does not change according to the coding bit depth, and thus the size of the LUT for calculating InvScaleCoeff does not increase even if the coding bit depth is high. In one example, for a 12-bit internal coding bit depth, the value of lmcsCW[i] may be limited to a multiple of 4, and accordingly, the size of the LUT for replacing the division operation is of the LUT used for 10-bit coding. It can be the same size. This aspect may be implemented alone, but may be implemented in combination with the above-described aspect.

In another aspect of this embodiment, lmcsCW[i] can be limited to a narrower range. For example, lmcsCW[i] may be limited within a range from (OrgCW>>1) to (OrgCW<<1)-1. In the case of 10-bit coding, the range of lmcsCW[i] may be [32, 127], and InvScaleCoeff can be calculated using only an LUT having a size of 96.

In another aspect of the present embodiment, lmcsCW[i] can be approximated to a power of 2 and used in the design of a reshaper. Accordingly, the division operation in the inverse mapping procedure can be performed by bit shifting (can be substituted).

In an embodiment according to this document, a limitation of the range of the LMCS codeword is proposed. According to Table 9 described above, values of LMCS codewords range from (OrgCW>>3) to (OrgCW<<3)-1. Due to the wide range of LMCS fragment lengths, visual deterioration may result if a large difference between RspCW[i] and OrgCW occurs.

According to an embodiment according to this document, it is proposed to limit the codeword of LMCS PWL mapping to a narrow range. For example, the range of lmcsCW[i] may be in the range from (OrgCW>>1) to (OrgCW<<1)-1.

In an embodiment according to this document, it is proposed to use a single chroma residual scaling factor for chroma residual scaling in LMCS. The existing method for deriving the chroma residual scaling factor uses the average value of the corresponding luma block and derived the slope of each piece in the inverse luma mapping as the corresponding scaling factor. In addition, a latency problem has occurred due to a procedure for identifying a piecewise index that requires availability of the corresponding luma block. This is not desirable for hardware implementation. Through an embodiment of the present document, scaling in a chroma block does not depend on a luma block value, and piecewise index identification may not be required. Therefore, a chroma residual scaling procedure in LMCS can be performed without latency issues.

In one embodiment according to this document, a single chroma scaling factor can be derived in both the encoder and the decoder based on luma LMCS information. When the LMCS luma model is received, the chroma residual scaling factor may be updated. For example, when the LMCS model is updated, a single chroma residual scaling factor may be updated.

The table below shows an example for obtaining a single chroma scaling factor according to the present embodiment.

Referring to Table 13, a single chroma scaling factor (ex.ChromaScaleCoeff or ChromaScaleCoeffSingle) can be obtained by averaging the inverse luma mapping slopes of all pieces within the range between lmcs_min_bin_idx and lmcs_max_bin_idx.

11 shows a linear fit of pivot points according to an embodiment of the present document. In FIG. 11, pivot points P1, Ps, and P2 are shown. The following embodiments or examples thereof will be described with reference to FIG. 11.

In an example of this embodiment, a single chroma scaling factor may be obtained based on a linear approximation of the luma PWL mapping between the pivot points lmcs_min_bin_idx and lmcs_max_bin_idx+1. That is, the inverse slope of the linear mapping can be used as a chroma residual scaling factor. For example, linear line 1 of FIG. 11 may be a straight line connecting pivot points P1 and P2. Referring to FIG. 11, in P1, the input value is x1 and the mapped value is 0, and in P2, the input value is x2 and the mapped value is y2. The inverse slope (inverse scale) of linear line 1 is (x2-x1)/y2, and the single chroma scaling factor ChromaScaleCoeffSingle is calculated based on the input values and mapped values of the pivot points P1 and P2, and the following equation. I can.

In Equation 5, CSCALE_FP_PREC represents a shift factor, and for example, CSCALE_FP_PREC may be a predetermined constant. In one example, CSCALE_FP_PREC may be 11.

In another example according to this embodiment, referring to FIG. 11, the input value at the pivot point Ps is min_bin_idx+1 and the mapped value is ys. Accordingly, the inverse slope (inverse scale) of linear line 1 can be calculated as (xs-x1)/ys, and a single chroma scaling factor ChromaScaleCoeffSingle is the input values and mapped values of the pivot points P1, Ps, and the following math It can be calculated based on the equation.

In Equation 6, CSCALE_FP_PREC represents a shift factor (a factor for bit shifting), and for example, CSCALE_FP_PREC may be a predetermined constant. In one example, CSCALE_FP_PREC may be 11, and bit shifting for inverse scale may be performed based on CSCALE_FP_PREC.

In another example according to this embodiment, a single chroma residual scaling factor may be derived based on a linear approximation line. An example for deriving a linear approximation line may include linear connection of pivot points (ex. lmcs_min_bin_idx, lmcs_max_bin_idx+1). For example, the linear trend result can be represented by codewords of PWL mapping. The mapped value y2 in P2 can be the sum of the codewords of all bins (slices), and the difference (x2-x1) between the input value in P2 and the input value in P1 is OrgCW*(lmcs_max_bin_idx-lmcs_min_bin_idx+1) ) (OrgCW, see Table 9 described above). The table below shows an example of obtaining a single chroma scaling factor according to the above-described embodiment.

Referring to Table 14, a single chroma scaling factor (ex. ChromaScaleCoeffSingle) may be obtained from two pivot points (i.e., lmcs_min_bin_idx, lmcs_max_bin_idx). For example, the inverse slope of linear mapping can be used as a chroma scaling factor.

In another example of this embodiment, a single chroma scaling factor may be obtained by linear fitting of pivot points to minimize an error (or mean square error) between linear fitting and conventional PWL mapping. This example may be more accurate than simply connecting two pivot points of lmcs_min_bin_idx and lmcs_max_bin_idx. There may be various methods for finding the optimal linear mapping, and an example will be described below.

In an example, parameters b1 and b0 of a linear fitting equation y=b1*x + b0 for minimizing the sum of least squares errors may be calculated based on the following equations 7 and/or 8 .

Here, x is the original luma values, and y is the reshaped luma values. Specifically,

,

Denotes the average of x and y, respectively, and xi and yi denote values of the i-th pivot points.

Referring to Fig. 11, another approximation for identifying the linear mapping can be given as follows:

-Obtain linear line 1 by connecting the pivot points of the PWL mapping at lmcs_min_bin_idx and lmcs_max_bin_idx+1, and calculate lmcs_pivots_linear[i] on a linear line with input values that are multiples of OrgCW.

-Summing the difference between the mapped values of the pivot points using linear line 1 and PWL mapping

-Acquire the mean difference (avgDiff)

-Adjust the last pivot point of the linear line according to the mean difference (e.g. 2*avgDiff)

-Use the inverse slope of the adjusted linear line as the chroma residual scale

According to the above-described linear fitting, the chroma scaling factor (i.e., inverse slope of forward mapping) may be derived (obtained) based on

Equation

9 or 10 below.

In the above equations, lmcs_pivots_lienar[i] may be mapped values of linear mapping. Through linear mapping, all pieces of the PWL mapping between the minimum and maximum bin indexes can have the same LMCS codeword (lmcsCW). That is, lmcs_pivots_linear[lmcs_min_bin_idx + 1] may be the same as lmcsCW[lmcs_min_bin_idx].

In addition, in

Equations

9 and 10, CSCALE_FP_PREC represents a shift factor (a factor for bit shifting), and for example, CSCALE_FP_PREC may be a predetermined constant. In one example, CSCALE_FP_PREC may be 11.

With a single chroma residual scaling factor (ChromaScaleCoeffSingle), there is no need to calculate the average of the corresponding luma block and there is no need to find an index in PWL linear mapping. Accordingly, the efficiency of coding using chroma residual scaling can be increased.

In another embodiment of this document, the encoder may determine parameters for a single chroma scaling factor and may signal the parameters to the decoder. Through signaling, the encoder can make use of other information available in the encoder to derive a chroma residual scaling factor. The present embodiment aims to eliminate the problem of chroma residual scaling latency.

For example, the procedure for identifying the linear mapping used to determine the chroma residual scaling factor can be given as follows:

-A weighted sum of the differences between the mapped values of the pivot points is obtained using the pivot points of linear line 1 and luma PWL mapping.

-Acquiring weighted average difference (avgDiff)

-Adjust the last pivot point of linear line 1 according to the weighted mean difference (e.g. 2*avgDiff)

-Use the inverse slope of the adjusted linear line as the chroma residual scale

The table below shows an exemplary syntax for signaling a y value to derive a chroma scaling factor.

In Table 15, the syntax element lmcs_chroma_scale may specify a single chroma (residual) scaling factor used for LMCS chroma residual scaling (ChromaScaleCoeffSingle = lmcs_chroma_scale). That is, information on a chroma residual scaling factor may be directly signaled and the signaled information may be derived as a chroma residual scaling factor. In other words, the value of the information on the signaled chroma residual scaling factor may be derived (directly) as the value of the single chroma residual scaling factor. Here, the syntax element lmcs_chroma_scale may be signaled together with other LMCS data (eg, an absolute value of a codeword, a syntax element related to a code, etc.).

Alternatively, the encoder can signal to the decoder only the parameters necessary to derive the chroma residual scaling factor. In order to derive the chroma residual scaling factor in the decoder, the input value x and the mapped value y are required. Since the x value represents the empty length, it is already known to the decoder stage and does not need to be signaled. After all, only y values need to be signaled in order to derive the chroma residual scaling factor. Here, the y value may be a mapped value of an arbitrary pivot point in linear mapping (e.g. mapped values of P2 or Ps in FIG. 11).

The following tables show examples of signaling mapped values to derive a chroma residual scaling factor.

One of the syntaxes of Tables 16 and 17 described above may be used to signal the y value at any linear pivot points specified by the encoder and decoder. That is, the encoder and the decoder can derive the y value using the same syntax.

First, an embodiment according to Table 16 will be described. In Table 16, lmcs_cw_linear may represent a value mapped to Ps or P2. That is, in the embodiment according to Table 16, a fixed number may be signaled through lmcs_cw_linear.

In an example according to the present embodiment, if lmcs_cw_linear represents a value mapped to one bin (ie lmcs_pivots_linear[lmcs_min_bin_idx + 1] in Ps in FIG. 11), the chroma scaling factor may be derived based on the following equation. .

In another example according to the present embodiment, if lmcs_cw_linear represents lmcs_max_bin_idx+1 (i.e. lmcs_pivots_linear [lmcs_max_bin_idx + 1] in P2 of FIG. 11), the chroma scaling factor may be derived based on the following equation.

In the above-described equations, CSCALE_FP_PREC represents a shift factor (a factor for bit shifting), and, for example, CSCALE_FP_PREC may be a predetermined constant. In one example, CSCALE_FP_PREC may be 11.

Next, an embodiment according to Table 17 will be described. In this embodiment, lmcs_cw_linear may be signaled as a delta value (i.e. lmcs_delta_abs_cw_linear, lmcs_delta_sign_cw_linear_flag) associated with a fixed number. In an example of the present embodiment, when lmcs_cw_linear represents a mapped value in lmcs_pivots_linear[lmcs_min_bin_idx+1] (i.e. Ps in FIG. 11), lmcs_cw_linear_delta and lmcs_cw_linear may be derived based on the following equations.

In another example of the present embodiment, when lmcs_cw_linear represents the mapped value in lmcs_pivots_linear[lmcs_max_bin_idx+1] (i.e. P2 in FIG. 11), lmcs_cw_linear_delta and lmcs_cw_linear may be derived based on the following equations.

In the above equations, OrgCW may be a value derived based on Table 9 described above.

12 shows an example of linear reshaping (or linear reshaper, linear mapping) according to an embodiment of the present document. That is, in an embodiment of this document, the use of a linear reshaper in LMCS is proposed. For example, the example of FIG. 12 may relate to forward linear reshaping (mapping).

In the existing example, the LMCS can use piecewise linear mapping with fixed 16 pieces. Accordingly, inevitable deterioration may occur due to a sudden transition between pivot points, which may increase the complexity of the reshaper design. Also, for Reshaper's inverse luma mapping, you need to identify the piecewise function index. The peacewise function index identification procedure is an iteration process that includes many comparison execution procedures. In addition, for chroma residual scaling using the corresponding luma block average, a luma piecewise index identification procedure is required. This not only brings about a complexity problem, but also may cause a latency of chroma residual scaling that depends on the restoration of the entire luma block. In order to solve this problem, the use of a linear reshaper in LMCS is proposed, and a detailed description of the linear reshaper will be described later.

Referring to FIG. 12, the linear reshaper may include two pivot points (i.e., P1, P2). P1 and P2 may represent input and mapped values, for example, P1 may be (minInput, 0) and P2 may be (maxInput, maxMapped). Here, minInput represents the minimum input value and maxInput represents the maximum input value. If the input value is less than or equal to minInput, it is mapped to 0, and if the input value is greater than maxInput, it is mapped to maxMapped. Input (luma) values between minInput and maxInput can be mapped linearly to other values. 12 shows an example of mapping. Pivot points P1, P2 can be determined in the encoder, for which a linear fit can be used to approximate a piecewise linear mapping.

There can be various ways of signaling a linear reshaper. In one example of a method of signaling a linear reshaper, each luma range can be divided by an equal number of bins. In other words, luma mapping between the minimum and maximum bins can be evenly distributed (can be achieved). For example, all beans may have the same LMCS codeword (lmcsCW). To this end, the minimum and maximum bin indices can be signaled. In addition, only one set of reshape_model_bin_delta_abs_CW (or reshaper_model_delta_abs_CW, lmcs_delta_abs_CW) and reshaper_model_bin_delta_sign_CW_flag (or reshaper_model_delta_sign_CW_flag, lmcs_flag) need to be signaled.

The following tables exemplarily show syntax and semantics for signaling a linear reshaper according to this example.

Referring to Tables 18 and 19, the syntax element log2_lmcs_num_bins_minus4 may be information on the number of bins. The number of bins may be signaled based on the information, and thus better control of the minimum and maximum pivot points may be possible. In another existing example, the encoder and/or decoder can derive (specify) the (fixed) number of bins without signaling, for example the number of bins was derived as 16 or 32. However, according to the examples of Tables 18 and 19, log2_lmcs_num_bins_minus4 plus 4 may represent a binary logarithm of the number of bins. The number of bins derived based on the syntax element may range from 4 to a value of the luma bit depth (BitDepthY).

In Table 19, ScaleCoeffSingle may be referred to as a single luma forward scaling factor, and InvScaleCoeffSingle may be referred to as a single luma inverse scaling factor. (Forward) mapping may be performed on predicted luma samples based on a single luma forward scaling factor, and (inverse) mapping may be performed on reconstructed luma samples based on a single luma inverse scaling factor. ChromaSclaeCoeffSingle may be referred to as a single chroma residual scaling factor, as described above. ScaleCoeffSingle, InvScaleCoeffSingle, and ChromaSclaeCoeffSingle can be used for forward luma mapping, inverse luma mapping, and chroma residual scaling, respectively. ScaleCoeffSingle, InvScaleCoeffSingle, and ChromaSclaeCoeffSingle are a single factor and can be uniformly applied to all bins (16 bins PWL mappings).

Referring to Table 19, FP_PREC and CSCALE_FP_PREC may be constants for bit shifting. FP_PREC and CSCALE_FP_PREC may or may not be the same as each other. For example, FP_PREC may be greater than or equal to CSCALE_FP_PREC. In one example, both FP_PREC and CSCALE_FP_PREC may be 11. In another example, FP_PREC may be 15 and CSCALE_FP_PREC may be 11.

In another example of a method of signaling a linear reshaper, an LMCS codeword (lmcsCWlinearALL) may be derived based on the following equations. In this example, the linear reshaping syntax elements signaled according to the syntax of Table 18 described above may be used. The following table shows an example of semantics described according to this example.

Referring to Table 20, FP_PREC and CSCALE_FP_PREC may be constants for bit shifting. FP_PREC and CSCALE_FP_PREC may or may not be the same as each other. For example, FP_PREC may be greater than or equal to CSCALE_FP_PREC. In one example, both FP_PREC and CSCALE_FP_PREC may be 11. In another example, FP_PREC may be 15 and CSCALE_FP_PREC may be 11.

In Table 20, lmcs_max_bin_idx may be used interchangeably with LmcsMaxBinIdx. The lmcs_max_bin_idx and LmcsMaxBinIdx may be derived with reference to Table 19 described above based on the lmcs_delta_max_bin_idx of the syntax of Table 18 described above. As such, Table 20 can be interpreted with reference to Table 19.

In another embodiment according to the present document, another example of a method of signaling a linear reshaper may be proposed. The pivot points P1 and P2 of the linear reshaper model can be explicitly signaled. The following tables show an example of syntax and semantics for explicitly signaling a linear reshaper model according to this example.

Referring to Tables 21 and 22, the input value of the first pivot point may be derived based on the syntax element lmcs_min_input, and the input value of the second pivot point may be derived based on the syntax element lmcs_max_input. The mapped value of the first pivot point may be a predetermined value (a value known to both the encoder and the decoder), and may be 0, for example. A mapped value of the second pivot point may be derived based on the syntax element lmcs_max_mapped. That is, the linear reshaper model may be explicitly (directly) signaled based on the information signaled based on the syntax of Table 21.

Alternatively, lmcs_max_input and lmcs_max_mapped can be signaled as delta values. The following tables show an example of syntax and semantics for signaling a linear reshaper model as a delta value.

Referring to Table 24, the input value of the first pivot point may be derived based on the syntax element lmcs_min_input. For example, lmcs_min_input may have a mapped value of 0. lmcs_max_input_delta may represent a difference between the input value of the second pivot point and the maximum luma value (i.e., (1<<bitdepthY)-1). lmcs_max_mapped_delta may represent a difference between the mapped value of the second pivot point and the maximum luma value (i.e., (1<<bitdepthY)-1).

According to an embodiment of the present document, forward mapping for luma prediction samples, inverse mapping for luma reconstructed samples, and chroma residual scaling may be performed based on examples of the linear reshaper described above. In one example, only one inverse scaling factor may be needed for inverse scaling for luma (restored) samples (pixels) in linear reshaper based inverse mapping. This is the same for forward mapping and chroma residual scaling. That is, the steps of determining ScaleCoeff[i], InvScaleCoeff[i] and ChromaScaleCoeff[i] for the bin index i may be replaced with using only one factor. Here, one factor may refer to a (forward) slope or an inverse slope of a linear mapping expressed as a fixed point. In an example, an inverse luma mapping scaling factor (an inverse scaling factor in inverse mapping for luma reconstructed samples) may be derived based on at least one of the following equations.

LmcsCWLinear of Equation 17 may be derived from Tables 18 and 19 described above. LmcsCWLinearALL of Equations 18 and 19 may be derived from at least one of Tables 20 to 24 described above. In Equation 17 or 18, OrgCW may be derived from Table 9 or 18.

The following tables describe equations and syntax (conditional statements) representing a forward mapping procedure for luma samples (i.e. luma prediction samples) in picture restoration. In the following tables and equations, FP_PREC is a constant for bit shifting and may be a predetermined value. For example, FP_PREC may be 11 or 15.

Table 25 may be for deriving forward-mapped luma samples in the luma mapping procedure based on Tables 8 and 9 described above. That is, Table 25 may be described together with Tables 8 and 9. In Table 25, forward mapped luma (prediction) samples PredmAPSamples[i][j] as output can be derived from luma (predictive) samples predSamples[i][j] as input. IdxY in Table 25 may be referred to as a (forward) mapping index, and the mapping index may be derived based on predicted luma samples.

Table 26 may be for deriving forward-mapped luma samples from luma mapping according to the application of the linear reshaper. For example, lmcs_min_input, lmcs_max_input, lmcs_max_mapped, and ScaleCoeffSingle of Table 26 may be derived by at least one of Tables 21 to 24. In Table 26, in the case of lmcs_min_input<predSamples[i][j]< lmcs_max_input, luma (prediction) samples as input from predSamples[i][j] forward mapped luma (prediction) samples as output PredmAPSamples[i][ j] can be derived. Through the comparison between Tables 25 and 26, the change from the existing LMCS according to the application of the linear reshaper can be seen from the perspective of forward mapping.

The following equations describe an inverse mapping procedure for luma samples (i.e. luma reconstructed samples). In the following equations, lumaSample as an input may be a luma restoration sample before inverse mapping (before modification). InvSample as output may be an inverse mapped (modified) luma reconstructed sample. In other cases, the clipped invSample may be referred to as a modified luma reconstructed sample.

Referring to Equation 20, the index idxInv may be derived based on Table 11 described above. That is, Equation 20 may be for deriving inverse-mapped luma samples in the luma mapping procedure based on Tables 8 and 9 described above. Equation 20 may be described together with Table 10 described above.

Equation 21 may be for deriving inverse-mapped luma samples from luma mapping according to the application of a linear reshaper. For example, lmcs_min_input of Equation 21 may be derived by at least one of Tables 21 to 24. Through the comparison between Equation 20 and Equation 21, a change from the existing LMCS according to the application of the linear reshaper can be seen from a forward mapping perspective.

A piecewise index identification procedure may be omitted based on the above-described examples of the linear reshaper. That is, since there is only one fragment having a reshaped luma pixel in the examples, a piecewise index identification procedure used for inverse luma mapping and chroma residual scaling may be eliminated. Accordingly, the complexity of the inverse luma mapping can be reduced. In addition, the latency problem caused by relying on luma piecewise index identification can be eliminated during chroma residual scaling.

Depending on the embodiment of the use of the linear reshaper described above, the following advantages may be provided for the LMCS. i) By simplifying the encoder's reshaper design, it is possible to prevent deterioration due to sudden changes occurring between the piecewise linear pieces. ii) It is possible to simplify the decoder inverse mapping procedure by removing the piecewise index identification procedure. iii) By removing the peacewise index identification procedure, a latency problem in chroma residual scaling caused by relying on corresponding luma blocks can be eliminated. iv) Reduce the signaling overhead and make frequent reshaper updates more feasible. v) You can remove loops in many areas where a 16-piece loop (eg, for statement) was needed. For example, the number of division operations by lmcsCW[i] can be reduced to 1 to derive InvScaleCoeff[i].

In another embodiment according to this document, an LMCS based on flexible beans is proposed. Here, the flexible bins may mean that the number of bins is not fixed to a predetermined number. In an existing embodiment, the number of bins in the LMCS is fixed to 16, and the 16 bins are evenly distributed for input sample values. In this embodiment, a flexible number of bins is proposed, and fragments (bins) will not be evenly distributed to original pixel values.

The following tables exemplarily show syntax for LMCS data (data field) and semantics for syntax elements included therein according to the present embodiment.

Referring to Table 27, information about the number of bins lmcs_num_bins_minus1 may be signaled. Referring to Table 28, lmcs_num_bins_minus1+1 may be equal to the number of bins, and the number of bins may range from 1 to (1<<BitDepthY)-1. For example, lmcs_num_bins_minus1 or lmcs_num_bins_minus1+1 may be a multiple of 2.

In the embodiment described with Tables 27 and 28, the number of pivot points can be derived based on lmcs_num_bins_minus1 (information on the number of bins), regardless of whether the reshaper is linear (signaling of lmcs_num_bins_minus1) and The input values of the pivot points and the mapped values (LmcsPivot_input[i], LmcsPivot_mapped[i]) can be derived based on the summation of the signaled codeword values (lmcs_delta_input_cw[i], lmcs_delta_mapped_cw[i]) (here, the initial The input value LmcsPivot_input[0] and the initial output value LmcsPivot_mapped[0] are 0).

13 shows an example of linear forward mapping in an embodiment of this document. 14 shows an example of inverse forward mapping according to an embodiment of this document.

In the embodiment according to FIGS. 13 and 14, a method of supporting both regular LMCS and linear LMCS is proposed. In an example according to the present embodiment, a regular LMCS and/or a linear LMCS may be indicated based on the syntax element lmcs_is_linear. In the encoder, after the linear LMCS line is determined, the mapped value (ex. the mapped value in pL of FIGS. 13 and 14) may be divided into equal pieces (ex. LmcsMaxBinIdx-lmcs_min_bin_idx+1). The codeword in the bin LmcsMaxBinIdx may be signaled using syntaxes related to the lmcs data or Reshaper mode described above.

The following tables exemplarily show syntax for LMCS data (data field) and semantics for syntax elements included therein according to an example of the present embodiment.

The following tables exemplarily show syntax for LMCS data (data field) and semantics for syntax elements included therein according to another example of the present embodiment.

Referring to Tables 29 to 32, if lmcs_is_linear_flag is true, all lmcsDeltaCW[i] between lmcs_min_bin_idx and LmcsMaxBinIdx may have the same value. That is, lmcsCW[i] among all fragments between lmcs_min_bin_idx and LmcsMaxBinIdx may have the same value. The scale and inverse scale and chroma scale of all fragments between lmcs_min_bin_idx and lmcsMaxBinIdx may be the same. If the linear reshaper is true, there is no need to derive the fragment index, and the scale, inverse scale on one of the fragments can be used.

The following table exemplarily shows a procedure for identifying a piecewise index according to the present embodiment.

According to another embodiment of this document, the application of regular 16-piece PWL LMCS and linear LMCS may rely on high level syntax (eg, sequence level).

The following tables exemplarily show the syntax for the SPS according to the present embodiment and the semantics for the syntax elements included therein.

Referring to Tables 34 and 35, whether a regular LMCS and/or a linear LMCS are available may be determined (signaled) by a syntax element included in the SPS. Referring to Table 35, based on the syntax element sps_linear_lmcs_enabled_flag, one of a regular LMCS or a linear LMCS may be available in a sequence unit.

In addition, whether one or both of linear LMCS or regular LMCS are available may depend on the profile level. In one example, for a specific profile (eg SDR profile), only linear LMCS may be allowed, and for another profile (eg HDR profile), only regular LMCS may be allowed, and for another profile, regular LMCS And/or both linear LMCS may be allowed.

According to another embodiment of the present document, an LMCS piecewise index identification procedure may be used in inverse luma mapping and chroma residual scaling. In this embodiment, the identification procedure of the piecewise index may be used for a block for which chroma residual scaling is available, and the identification procedure may also be used for all luma samples in the reshaped (mapped) region. The present embodiment aims to reduce the complexity for deriving the index.

The following table shows the identification procedure (derived procedure) of the existing piecewise function index.

In one example, in the piecewise index identification procedure, input samples may be classified into at least two or more categories. For example, the input samples may be classified into three categories, first, second, and third categories. For example, the first category may represent samples (values of) smaller than LmcsPivot[lmcs_min_bin_idx+1], and the second category may represent samples (values of) greater than or equal to LmcsPivot[LmcsMaxBinIdx], The third category may represent samples (values of) between LmcsPivot[lmcs_min_bin_idx+1] and LmcsPivot[LmcsMaxBinIdx].

In this embodiment, a method of optimizing the identification procedure by removing the category classification is proposed. Since the input to the piecewise index identification procedure is a reshaped (mapped) luma value, there should be no values exceeding the mapped values in the pivot points lmcs_min_bin_idx and LmcsMaxBinIdx+1. Accordingly, the conditional procedure for classifying samples by category may be omitted from the existing piecewise index identification procedure, and specific examples will be described below with tables.

In an example according to this embodiment, the identification procedure included in Table 35 may be replaced with one of Tables 37 or 38 below. Referring to Tables 36 and 37, the preceding two categories of Table 35 may be deleted, and the boundary value (the second boundary value or ending point) in the loop (for statement) repetitive for the last category is LmcsMaxBinIdx to LmcsMaxBinIdx Can be modified to +1. That is, the identification procedure can be simplified and the complexity for deriving the piecewise index can be reduced. Accordingly, LMCS-related coding can be efficiently performed according to this embodiment.

Referring to Table 37, a comparison procedure corresponding to the condition of the if clause (an equation corresponding to the condition of the if clause) may be repeatedly performed for all of the empty indexes from the minimum empty index to the maximum empty index. When the equation corresponding to the condition of the if clause is true, the bin index may be derived as an inverse mapping index for inverse luma mapping (or an inverse scaling index for chroma residual scaling). Corrected reconstructed luma samples (or scaled chroma residual samples) may be derived based on the inverse mapping index.

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

15 and 16 schematically illustrate an example of a video/video encoding method and related components according to the embodiment(s) of this document. The method disclosed in FIG. 15 may be performed by the encoding apparatus disclosed in FIG. 2. Specifically, for example, S1500 of FIG. 15 may be performed by 220 of the encoding device, and S1510 and S1520 may be performed by the prediction unit 220 or the residual processing unit 230 of the encoding device. In addition, S1530 and S1540 may be performed by the residual processing unit 230 or the adding unit 250 of the encoding apparatus, and S1550 to S1570 may be performed by the residual processing unit 230 of the encoding apparatus, S1580 may be performed by the entropy encoding unit 240 of the encoding device. The method disclosed in FIG. 15 may include the embodiments described above in this document.

Referring to FIG. 15, the encoding device may generate predictive luma samples (S1500). In relation to the prediction luma samples, the encoding apparatus may derive the prediction luma samples of the current block based on the prediction mode. In this case, various prediction methods disclosed in this document, such as inter prediction or intra prediction, may be applied.

The encoding device may derive predictive chroma samples. The encoding apparatus may derive the residual chroma samples based on the original chroma samples and the predicted chroma samples of the current block. For example, the encoding apparatus may derive residual chroma samples based on a difference between the predicted chroma samples and the original chroma samples.

The encoding apparatus may derive bins and LMCS codewords for luma mapping (S1510). The encoding device may derive the bins and/or LMCS codewords based on SDR or HDR.

The encoding apparatus may generate mapped prediction luma samples based on bins and/or LMCS codewords for luma mapping (S1520). For example, the encoding apparatus may derive input values and mapping values (output values) of pivot points for luma mapping, and may generate mapped prediction luma samples based on the input values and mapping values. In one example, the encoding device may derive a mapping index (idxY) based on a first prediction luma sample, and a first mapped prediction luma sample based on an input value and a mapping value of a pivot point corresponding to the mapping index Can be created. In another example, linear mapping (linear reshaping, linear LMCS) can be used and mapped predictive luma samples based on the forward mapping scaling factor derived from the two pivot points in the linear mapping can be generated, and thus The index derivation procedure may be omitted due to linear mapping.

The encoding device may generate scaled residual chroma samples. Specifically, the encoding apparatus may derive a chroma residual scaling factor and generate scaled residual chroma samples based on the chroma residual scaling factor. Here, chroma residual scaling of the encoding stage may be referred to as forward chroma residual scaling. Accordingly, the chroma residual scaling factor derived by the encoding apparatus may be referred to as a forward chroma residual scaling factor, and forward-scaled residual chroma samples may be generated.

The encoding device may generate reconstructed luma samples (S1530). The encoding device may generate reconstructed luma samples based on the mapped prediction luma samples. Specifically, the encoding apparatus may sum the above-described residual luma samples with mapped prediction luma samples, and may generate reconstructed luma samples based on the summation result.

The encoding apparatus may generate reconstructed luma samples based on the bins for the luma mapping, the LMCS codewords, and the reconstructed luma samples (S1540). The encoding apparatus may generate the modified reconstructed luma samples through an inverse mapping procedure for the reconstructed luma samples. For example, the encoding device is an inverse mapping index based on mapping values (ex. LmcsPivot[i], i=lmcs_min_bin_idx...LmcsMaxBinIdx+1) allocated to each of the restored luma samples and/or bin indexes in the inverse mapping procedure. (ex. invYIdx) can be derived. The encoding device may generate reconstructed luma samples based on a mapping value (LmcsPivot[invYIdx]) allocated to the inverse mapping index.

The encoding apparatus may derive information on LMCS data based on the bins for the luma mapping and the LMCS codewords (S1550). Alternatively, the encoding apparatus may generate LMCS related information based on the mapped prediction luma samples and/or the scaled residual chroma samples. The encoding device may generate LMCS related information for the reconstructed samples. The encoding apparatus may derive LMCS-related parameters that can be applied to filter the reconstructed samples, and may generate LMCS-related information based on the LMCS-related parameters. For example, the LMCS-related information is information on luma mapping (ex.forward mapping, inverse mapping, linear mapping), information on chroma residual scaling, and/or LMCS (or reshaping, reshaper). It may include indexes (ex. a maximum bin index, a minimum bin index).

The encoding apparatus may generate residual luma samples based on the mapped prediction luma samples (S1560). For example, the encoding apparatus may derive residual luma samples based on a difference between the mapped prediction luma samples and original luma samples.

The encoding device may derive residual information (S1570). The encoding apparatus may derive residual information based on the scaled residual chroma samples and/or the residual luma samples. The encoding apparatus may derive transform coefficients based on a transform procedure for the scaled residual chroma samples and/or the residual luma samples. For example, the conversion procedure may include at least one of DCT, DST, GBT, or CNT. The encoding apparatus may derive quantized transform coefficients based on a quantization procedure for the transform coefficients. The quantized transform coefficients may have a one-dimensional vector shape based on the coefficient scan order. The encoding apparatus may generate residual information indicating the quantized transform coefficients. The residual information may be generated through various encoding methods such as exponential Golom, CAVLC, CABAC, and the like.

The encoding device may encode image/video information (S1580). The image information may include information on LMCS data and/or residual information. For example, the LMCS-related information may include information on the linear LMCS. In an example, at least one LMCS codeword may be derived based on information about the linear LMCS. The encoded video/video information may be output in the form of a bitstream. The bitstream may be transmitted to a decoding device through a network or a storage medium.

The image/video information may include various information according to an embodiment of the present document. For example, the image/video information may include information disclosed in at least one of Tables 1 to 38 described above.

In an embodiment, mapping values based on bin indices from a minimum bin index to a maximum bin index may be derived based on LMCS codewords. For example, the mapped prediction luma samples and the modified reconstructed luma samples may be generated based on the mapping values based on the bin indices from the minimum bin index to the maximum bin index.

In one embodiment, the bin indexes include a first bin index indicating a first mapping value, mapping values based on the bin indices from the minimum bin index to the maximum bin index and values of the reconstructed luma samples The first bin index may be derived based on a comparison between, and at least one of the reconstructed luma samples may be derived based on the reconstructed luma samples and the first mapping value.

In one embodiment, the bin indexes include a first bin index indicating a first mapping value, and the first bin index is based on a comparison equation (lumaSample<LmcsPivot[idxYInv + 1]) included in Table 37. Can be derived. For example, in the above equation, lumaSample represents a value of a target luma sample among the reconstructed luma samples, idxYInv represents one of the bin indices, and LmcsPivot[idxYinv + 1] represents the minimum bin index to the maximum bin It may represent one of mapping values based on the bin indices up to the index. At least one of the modified reconstructed luma samples may be derived based on the reconstructed luma samples and the first mapping value.

In an embodiment, the comparison procedure (lumaSample<LmcsPivot[idxYInv + 1]) included in Table 37 may be performed on all of the bin indices from the minimum bin index to the maximum bin index.

In one embodiment, residual chroma samples are generated based on the residual information, the bin indexes include a first bin index indicating a first mapping value, and the range from the minimum bin index to the maximum bin index The first bin index is derived based on a comparison between mapping values based on bin indices and values of the reconstructed luma samples, a chroma residual scaling factor is derived based on the first bin index, and the residual chroma Scaled residual chroma samples may be generated based on samples and the chroma residual scaling factor, and reconstructed chroma samples may be generated based on the scaled residual chroma samples.

In one embodiment, the image information includes information on a linear LMCS, the information on the LMCS data includes a linear LMCS flag indicating whether a linear LMCS is applied, and the mapped prediction luma samples are the linear LMCS When it is generated based on the information on, the value of the linear LMCS flag may be 1.

In an embodiment, the information on the linear LMCS may include information on a first pivot point (eg, P1 in FIG. 12) and information on a second pivot point (eg, P2 in FIG. 12 ). For example, the input value and the mapping value of the first pivot point may be a minimum input value and a minimum mapping value, respectively. The input value and the mapping value of the second pivot point may be a maximum input value and a maximum mapping value, respectively. An input value between the minimum input value and the maximum input value may be linearly mapped.

In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a linear LMCS available flag indicating whether the linear LMCS is available.

In an embodiment, a minimum bin index (ex. lmcs_min_bin_idx) and/or a maximum bin index (ex. LmcsMaxBinIdx) may be derived based on the LMCS-related information. A first mapping value (LmcsPivot[lmcs_min_bin_idx]) may be derived based on the minimum bin index. A second mapping value (LmcsPivot[LmcsMaxBinIdx] or LmcsPivot[LmcsMaxBinIdx+1]) may be derived based on the maximum bin index. Values of the reconstructed luma samples (eg, lumaSample in Table 37 or 38) may be in a range from a first mapping value to a second mapping value. In an example, values of all reconstructed luma samples may be in a range from a first mapping value to a second mapping value. In another example, values of some of the reconstructed luma samples may be in a range from the first mapping value to the second mapping value.

In an embodiment, the encoding device may generate a piecewise index for chroma residual scaling. The encoding apparatus may derive a chroma residual scaling factor based on the piecewise index. The encoding apparatus may generate scaled residual chroma samples based on the residual chroma samples and the chroma residual scaling factor.

In an embodiment, the chroma residual scaling factor may be a single chroma residual scaling factor.

In an embodiment, the LMCS related information may include an LMCS data field and information about a linear LMCS. The information on the linear LMCS may be referred to as information on linear mapping. The LMCS data field may include a linear LMCS flag indicating whether the linear LMCS is applied. When the value of the linear LMCS flag is 1, the mapped prediction luma samples may be generated based on information on the linear LMCS.

In an embodiment, the image information may include information on the maximum input value and information on the maximum mapping value. The maximum input value may be the same as a value of information on the maximum input value (ex. lmcs_max_input in Table 21). The maximum mapping value may be the same as a value of information on the maximum mapping value (ex. lmcs_max_mapped in Table 21).

In one embodiment, the information on the linear mapping includes information on an input delta value of the second pivot point (ex. lmcs_max_input_delta in Table 23) and information on a mapping delta value of the second pivot point (ex. Table 23). Lmcs_max_mapped_delta) may be included. The maximum input value may be derived based on the input delta value of the second pivot point, and the maximum mapping value may be derived based on the mapping delta value of the second pivot point.

In an embodiment, the maximum input value and the maximum mapping value may be derived based on at least one equation included in Table 24 described above.

In an embodiment, the generating of the mapped prediction luma samples includes deriving a forward mapping scaling factor (ex. ScaleCoeffSingle described above) for the prediction luma samples, and the forward mapping scaling factor based on the forward mapping scaling factor. The mapped predictive luma samples may include generating. The forward mapping scaling factor may be a single factor for the prediction luma samples.

In an embodiment, the forward mapping scaling factor may be derived based on at least one equation included in Tables 22 and/or 24 described above.

In an embodiment, the mapped prediction luma samples may be derived based on at least one equation included in Table 26 described above.

In an embodiment, the encoding apparatus may derive an inverse mapping scaling factor (eg, InvScaleCoeffSingle) for the reconstructed luma samples (eg, the aforementioned lumaSample). In addition, the encoding apparatus may generate reconstructed luma samples (ex. invSample) modified based on the reconstructed luma samples and the inverse mapping scaling factor. The inverse mapping scaling factor may be a single factor for the reconstructed luma samples.

In an embodiment, the inverse mapping scaling factor may be derived using a piecewise index derived based on the reconstructed luma samples.

In one embodiment, the piecewise index may be derived based on Table 36 described above. That is, the comparison procedure (lumaSample<LmcsPivot[idxYInv + 1]) included in Table 37 can be repeatedly performed from the case where the piecewise index is the minimum empty index to the case where the piecewise index is the maximum empty index. have.

In an embodiment, the inverse mapping scaling factor may be derived based on at least one equation or

equation

11 or 12 included in Tables 19, 20, 22, and 24 described above.

In an embodiment, the modified reconstructed luma samples may be derived based on Equation 21 described above.

In an embodiment, the LMCS-related information may include information on the number of bins for deriving the mapped prediction luma samples (ex. lmcs_num_bins_minus1 in Table 27). For example, the number of pivot points for luma mapping may be set equal to the number of bins. In an example, the encoding apparatus may generate delta input values and delta mapping values of the pivot points as much as the number of bins. In one example, input values and mapping values of the pivot points are derived based on the delta input values (ex. lmcs_delta_input_cw[i] in Table 27) and the delta mapping values (ex. lmcs_delta_mapped_cw[i] in Table 28). , Based on the input values (ex. LmcsPivot_input[i] in Table 28, or InputPivot[i] in Table 10) and the mapping values (ex. LmcsPivot_mapped[i] in Table 28, or LmcsPivot[i] in Table 10) As a result, the mapped prediction luma samples may be generated.

In one embodiment, the encoding device may derive an LMCS delta codeword based on at least one LMCS codeword and an original codeword (OrgCW) included in the LMCS-related information, and at least one LMCS codeword and an original code Mapped luma prediction samples may be derived based on the word. In one example, the information on the linear mapping may include information on an LMCS delta codeword.

In one embodiment, the at least one LMCS codeword may be derived based on the sum of the LMCS delta codeword and OrgCW, for example, OrgCW is (1<<BitDepthY) / 16, where BitDepthY is luma bit Depth can be indicated. This embodiment may be based on Equation 12.

In one embodiment, the at least one LMCS codeword may be derived based on the sum of the LMCS delta codeword and OrgCW* (lmcs_max_bin_idx-lmcs_min_bin_idx+1), and lmcs_max_bin_idx and lmcs_min_bin_idx are respectively a maximum bin index and a minimum bin index And OrgCW may be (1<<BitDepthY) / 16. This embodiment may be based on Equations 15 and 16.

In one embodiment, the at least one LMCS codeword may be a multiple of 2.

In an embodiment, when the luma bit depth (BitDepthY) of the reconstructed luma samples is higher than 10, the at least one LMCS codeword may be a multiple of 1<<(BitDepthY-10).

In one embodiment, the at least one LMCS codeword may be in a range from (OrgCW>>1) to (OrgCW<<1)-1.

17 and 18 schematically illustrate an example of a video/video decoding method and related components according to an embodiment of the present document. The method disclosed in FIG. 17 may be performed by the decoding apparatus disclosed in FIG. 3. Specifically, for example, S1700 of FIG. 17 may be performed by the entropy decoding unit 310 of the decoding device, and S1710 may be performed by the residual processing unit 320 or the prediction unit 330 of the decoding device. S1720 may be performed by the residual processing unit 320, the prediction unit 330, and/or the addition unit 340 of the decoding device, and S1730 and S1740 are the residual processing unit 320 of the decoding device and / Or may be performed by the addition unit 340. The method disclosed in FIG. 17 may include the embodiments described above in this document.

Referring to FIG. 17, the decoding apparatus may receive/obtain video/video information (S1700). The video/video information may include information on LMCS data and/or residual information. For example, the LMCS-related information is information on luma mapping (ex.forward mapping, inverse mapping, linear mapping), information on chroma residual scaling, and/or LMCS (or reshaping, reshaper). Indices (ex. maximum bin index, minimum bin index, mapping index) may be included. The decoding apparatus may receive/acquire the image/video information through a bitstream.

The decoding apparatus may generate predictive luma samples. The decoding apparatus may derive prediction luma samples of the current block based on the prediction mode. In this case, various prediction methods disclosed in this document, such as inter prediction or intra prediction, may be applied.

The decoding apparatus may generate mapped prediction luma samples (S1710). For example, the decoding apparatus may derive input values and mapping values (output values) of pivot points for luma mapping, and may generate mapped prediction luma samples based on the input values and mapping values. In one example, the decoding apparatus may derive a (forward) mapping index (idxY) based on the first predicted luma sample, and the first mapped based on the input value and the mapping value of the pivot point corresponding to the mapping index. Predictive luma samples can be generated. In another example, linear mapping (linear reshaping, linear LMCS) can be used and mapped predictive luma samples based on the forward mapping scaling factor derived from the two pivot points in the linear mapping can be generated, and thus The index derivation procedure may be omitted due to linear mapping.

The decoding apparatus may generate residual luma samples based on the residual information (S1720). For example, the decoding apparatus may derive quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector shape based on the coefficient scan order. The decoding apparatus may derive transform coefficients based on an inverse quantization procedure for the quantized transform coefficients. The decoding apparatus may derive residual samples based on an inverse transform procedure for the transform coefficients. The residual samples may include residual luma samples and/or residual chroma samples.

The decoding apparatus may generate reconstructed luma samples (S1730). The decoding apparatus may generate reconstructed luma samples based on the mapped prediction luma samples. Specifically, the decoding apparatus may sum the above-described residual luma samples with the mapped prediction luma samples, and may generate reconstructed luma samples based on the summation result.

The decoding apparatus may generate reconstructed luma samples based on the information on the LMCS data and the reconstructed luma samples (S1740). The decoding apparatus may generate the modified reconstructed luma samples through an inverse mapping procedure for the reconstructed luma samples.

The decoding apparatus may generate scaled residual chroma samples. Specifically, the decoding apparatus may derive a chroma residual scaling factor and generate scaled residual chroma samples based on the chroma residual scaling factor. Here, the chroma residual scaling of the decoding stage may be referred to as inverse chroma residual scaling, as opposed to the encoding stage. Accordingly, the chroma residual scaling factor derived by the decoding apparatus may be referred to as an inverse chroma residual scaling factor, and inverse-scaled residual chroma samples may be generated.

The decoding apparatus may generate reconstructed chroma samples. The decoding apparatus may generate reconstructed chroma samples based on the scaled residual chroma samples. Specifically, the decoding apparatus may perform a prediction procedure on a chroma component and may generate predicted chroma samples. The decoding apparatus may generate reconstructed chroma samples based on the summation between the predicted chroma samples and the scaled residual chroma samples.

In an embodiment, the information on the LMCS data may include information on the linear LMCS. The information on the linear LMCS may be referred to as information on linear mapping. The information on the LMCS data may include a linear LMCS flag indicating whether linear LMCS is applied. When the value of the linear LMCS flag is 1, the mapped prediction luma samples may be generated based on information on the linear LMCS.

In an embodiment, a minimum bin index (ex. lmcs_min_bin_idx) and/or a maximum bin index (ex. LmcsMaxBinIdx) may be derived based on the LMCS-related information. A first mapping value (LmcsPivot[lmcs_min_bin_idx]) may be derived based on the minimum bin index. A second mapping value (LmcsPivot[LmcsMaxBinIdx] or LmcsPivot[LmcsMaxBinIdx+1]) may be derived based on the maximum bin index. Values of the reconstructed luma samples (ex. lumaSample in Table 36 or 37) may be in a range from a first mapping value to a second mapping value. In an example, values of all reconstructed luma samples may be in a range from a first mapping value to a second mapping value. In another example, values of some of the reconstructed luma samples may be in a range from the first mapping value to the second mapping value.

In an embodiment, a piecewise index (ex. idxYInv in Tables 35, 36, or 37) may be identified based on the LMCS-related information. The decoding apparatus may derive a chroma residual scaling factor based on the piecewise index. The decoding apparatus may generate scaled residual chroma samples based on the residual chroma samples and the chroma residual scaling factor.

In one embodiment, the information on the linear mapping includes information on an input delta value of the second pivot point (ex. lmcs_max_input_delta in Table 23) and information on a mapping delta value of the second pivot point (ex. Table 23). Lmcs_max_mapped_delta) of may be included. The maximum input value may be derived based on the input delta value of the second pivot point, and the maximum mapping value may be derived based on the mapping delta value of the second pivot point.

In an embodiment, the decoding apparatus may derive an inverse mapping scaling factor (eg, InvScaleCoeffSingle) for the reconstructed luma samples (eg, the aforementioned lumaSample). Also, the decoding apparatus may generate reconstructed luma samples (ex. invSample) modified based on the reconstructed luma samples and the inverse mapping scaling factor. The inverse mapping scaling factor may be a single factor for the reconstructed luma samples.

equation

11 or 12 included in Tables 19, 20, 22, and 24 described above.

In one embodiment, the decoding apparatus may derive an LMCS delta codeword based on at least one LMCS codeword and an original codeword (OrgCW) included in the LMCS-related information, and at least one LMCS codeword and an original code Mapped luma prediction samples may be derived based on the word. In one example, the information on the linear mapping may include information on an LMCS delta codeword.

In one embodiment, the at least one LMCS codeword may be a multiple of 2.

In the above-described embodiment, the methods are described on the basis of a flowchart as a series of steps or blocks, but the embodiment 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. I can. In addition, those skilled in the art will appreciate that the steps shown in the flowchart are not exclusive, other steps are included, or one or more steps in the flowchart may be deleted without affecting the scope of the embodiments of the present document.

The method according to the embodiments of the present document described above may be implemented in the form of software, and the encoding device and/or the decoding device according to the present document is, for example, an image such as a TV, computer, smartphone, set-top box, It may be included in the device that performs the processing.

When the embodiments in this document are implemented as software, the above-described method may be implemented as a module (process, function, etc.) performing the above-described functions. The modules are stored in memory and can be executed by the processor. The memory may be inside or outside the processor, and may be connected to the processor by various well-known means. The processor may include an application-specific integrated circuit (ASIC), another chipset, a logic circuit, and/or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and/or other storage device. That is, 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 embodiment(s) of the present document is 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, and a video communication device. Real-time communication device, mobile streaming device, storage medium, camcorder, video-on-demand (VoD) service provider, OTT video (over the top video) device, internet streaming service provider, 3D (3D) video device, virtual reality (VR) ) Device, AR (argumente reality) device, video telephony video device, vehicle terminal (ex. vehicle (including autonomous vehicle) terminal, airplane terminal, ship terminal, etc.) and medical video devices, and video signals or data It can be used to process signals. For example, an OTT video (Over the top video) device may include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smartphone, a tablet PC, and a digital video recorder (DVR).

In addition, the processing method to which the embodiment(s) of this document is 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 a data structure according to the embodiment(s) of this document may 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.

In addition, the embodiment(s) of this document may be implemented as a computer program product by program code, and the program code may be executed in a computer according to the embodiment(s) of this document. The program code may be stored on a carrier readable by a computer.

Referring to FIG. 19, a content streaming system to which embodiments of the present 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,

Obtaining image information including information on luma mapping with chroma scaling (LMCS) data and residual information from the bitstream;

Generating mapped prediction luma samples based on the information on the LMCS data and prediction luma samples; And

Deriving residual luma samples based on the residual information;

Generating reconstructed luma samples based on the mapped prediction luma samples and the residual luma samples; And

Further comprising the step of generating modified reconstructed luma samples based on the information on the LMCS data and the reconstructed luma samples,

The information on the LMCS data includes information on bins for luma mapping and information on LMCS codewords,

A minimum bin index and a maximum bin index are derived based on the information on the bins,

Mapping values based on bin indices from the minimum bin index to the maximum bin index are derived based on the information on the LMCS codewords,

The modified reconstructed luma samples are generated based on the mapping values based on the bin indices from the minimum bin index to the maximum bin index.
The method of claim 1,

The bin indices include a first bin index indicating a first mapping value,

The first bin index is derived based on a comparison between mapping values based on the bin indices from the minimum bin index to the maximum bin index and values of the reconstructed luma samples,

At least one of the reconstructed luma samples is derived based on the reconstructed luma samples and the first mapping value.
The method of claim 1,

The bin indices include a first bin index indicating a first mapping value,

The first bin index is derived based on the following equation,

In the above equation, lumaSample represents a value of a target luma sample among the reconstructed luma samples, idxYInv represents one of the bin indices, and LmcsPivot[idxYinv + 1] represents the minimum bin index to the maximum bin index. Represents one of the mapping values based on empty indexes,

At least one of the reconstructed luma samples is derived based on the reconstructed luma samples and the first mapping value.
The method of claim 3,

The comparison procedure of the equation is characterized in that it is performed on all of the bin indices from the minimum bin index to the maximum bin index.
The method of claim 1,

Residual chroma samples are generated based on the residual information,

The bin indices include a first bin index indicating a first mapping value,

The first bin index is derived based on a comparison between mapping values based on the bin indices from the minimum bin index to the maximum bin index and values of the reconstructed luma samples,

A chroma residual scaling factor is derived based on the first bin index,

Scaled residual chroma samples are generated based on the residual chroma samples and the chroma residual scaling factor,

The image decoding method, characterized in that the reconstructed chroma samples are generated based on the scaled residual chroma samples.
The method of claim 1,

The image information includes information on a linear LMCS,

The information on the LMCS data includes a linear LMCS flag indicating whether linear LMCS is applied,

When the value of the linear LMCS flag is 1, the mapped prediction luma samples are generated based on the information on the linear LMCS.
The method of claim 6,

The information on the linear LMCS includes information on a first pivot point and information on a second pivot point,

The input value and the mapping value of the first pivot point are a minimum input value and a minimum mapping value, respectively,

The input value and the mapping value of the second pivot point are a maximum input value and a maximum mapping value, respectively,

An input value between the minimum input value and the maximum input value is linearly mapped.
The method of claim 1,

The image information includes a sequence parameter set (SPS),

The SPS comprises a linear LMCS available flag indicating whether the linear LMCS is available.
In the video encoding method performed by the encoding device,

Generating predictive luma samples;

Deriving bins and LMCS codewords for luma mapping;

Generating mapped prediction luma samples based on the bins and the LMCS codewords for the luma mapping;

Generating reconstructed luma samples based on the mapped prediction luma samples;

The bins for the luma mapping. Generating the modified reconstructed luma samples based on the LMCS codewords and the reconstructed luma samples;

Deriving information about LMCS data based on the bins and the LMCS codewords for the luma mapping;

Generating residual luma samples based on the mapped prediction luma samples;

Generating residual information based on the residual luma samples; And

Including the step of encoding video information including the information on the LMCS data and the residual information,

Mapping values based on bin indices from a minimum bin index to a maximum bin index are derived based on the LMCS codewords,

The mapped prediction luma samples and the modified reconstructed luma samples are generated based on the mapping values based on the bin indices from the minimum bin index to the maximum bin index.
The method of claim 9,

The bin indexes include a first bin index indicating a first mapping value,

The first bin index is derived based on a comparison between mapping values based on the bin indices from the minimum bin index to the maximum bin index and values of the reconstructed luma samples,

At least one of the reconstructed luma samples is derived based on the reconstructed luma samples and the first mapping value.
The method of claim 9,

The bin indices include a first bin index indicating a first mapping value,

The first bin index is derived based on the following equation,

In the above equation, lumaSample represents a value of one of the restored luma samples, idxYInv represents one of the bin indices, and LmcsPivot[idxYinv + 1] is the bin index from the minimum bin index to the maximum bin index Represents one of the mapping values based on

At least one of the reconstructed luma samples is derived based on the reconstructed luma samples and the first mapping value.
The method of claim 11,

Wherein the comparison procedure of the equation is performed for all of the bin indices from the minimum bin index to the maximum bin index.
The method of claim 9,

Residual chroma samples are generated based on the residual information,

The bin indexes include a first bin index indicating a first mapping value,

The first bin index is derived based on a comparison between mapping values based on the bin indices from the minimum bin index to the maximum bin index and values of the reconstructed luma samples,

A chroma residual scaling factor is derived based on the first bin index,

Scaled residual chroma samples are generated based on the residual chroma samples and the chroma residual scaling factor,

An image encoding method, characterized in that reconstructed chroma samples are generated based on the scaled residual chroma samples.
The method of claim 9,

The image information includes information on a linear LMCS,

The information on the LMCS data includes a linear LMCS flag indicating whether linear LMCS is applied,

When the mapped prediction luma samples are generated based on information on the linear LMCS, the value of the linear LMCS flag is 1.
The method of claim 14,

The information on the linear LMCS includes information on a first pivot point and information on a second pivot point,

The input value and the mapping value of the first pivot point are a minimum input value and a minimum mapping value, respectively,

The input value and the mapping value of the second pivot point are a maximum input value and a maximum mapping value, respectively,

An input value between the minimum input value and the maximum input value is linearly mapped.
The method of claim 9,

The image information includes a sequence parameter set (SPS),

Wherein the SPS includes a linear LMCS available flag indicating whether or not the linear LMCS is available.
A computer-readable storage medium storing encoded information that causes an image decoding device to perform an image decoding method, the image decoding method comprising:

Obtaining image information including information on luma mapping with chroma scaling (LMCS) data and residual information from the bitstream;

Generating mapped prediction luma samples based on the information on the LMCS data and prediction luma samples; And

Deriving residual luma samples based on the residual information;

Generating reconstructed luma samples based on the mapped prediction luma samples and the residual luma samples; And

Further comprising the step of generating modified reconstructed luma samples based on the information on the LMCS data and the reconstructed luma samples,

The information on the LMCS data includes information on bins for luma mapping and information on LMCS codewords,

A minimum bin index and a maximum bin index are derived based on the information on the bins,

Mapping values based on bin indices from the minimum bin index to the maximum bin index are derived based on the information on the LMCS codewords,

The mapped prediction luma samples and the modified reconstructed luma samples are generated based on the mapping values based on the bin indices from the minimum bin index to the maximum bin index. media.