Encoding / decoding devices, devices for transmitting data, and storage media

Abstract

The present disclosure relates to a coding / decoding device, a device for sending data, and a storage medium. According to one embodiment of the present document, a cross-component adaptive loop filtering (CCALF) process may be performed. The CCALF process may enhance the filtering performance for chrominance components and improve the subjective / objective image quality of a picture.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080075244.X (international application number: PCT / KR2020 / 011598, application date: August 31, 2020, invention name: Image encoding device and method based on cross-component filtering). Technical Field

[0002] The present disclosure relates to an image encoding device and method based on cross-component filtering. Background Art

[0003] Recently, there is an increasing demand for high-resolution, high-quality images / videos such as 4K or 8K or higher ultra-high definition (UHD) images / videos in various fields. As image / video data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to existing image / video data, and therefore, transmitting image data using a medium such as an existing wired / wireless broadband line or an existing storage medium or storing image / video data using an existing storage medium increases transmission costs and storage costs.

[0004] In addition, interest in and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content and holograms are growing, and broadcasting of images / videos having characteristics different from real images (such as game images) is also growing.

[0005] Therefore, highly efficient image / video compression technology is required to effectively compress, transmit, store or reproduce information of high-resolution, high-quality images / videos having various characteristics as described above.

[0006] In addition, the improvement of compression efficiency and improvement of subjective / objective visual quality based on the implementation of the cross-component adaptive loop filtering (CCALF) process are also discussed. Summary of the invention

[0007] Technical Solution

[0008] The present disclosure provides a method and apparatus for improving image / video encoding efficiency.

[0009] The present disclosure also provides an efficient filtering application method and device.

[0010] The present disclosure also provides an efficient ALF application method and device.

[0011] According to an embodiment of the present disclosure, a filtering process may be performed on the reconstructed chrominance samples based on the reconstructed luma samples.

[0012] According to an embodiment of the present disclosure, the filtered reconstructed chroma samples may be modified based on the reconstructed luma samples.

[0013] According to an embodiment of the present disclosure, information on whether CCALF is available may be signaled in the SPS.

[0014] According to an embodiment of the present disclosure, information on the values ​​of cross-component filter coefficients may be derived from ALF data (normal ALF data or CCALF data).

[0015] According to an embodiment of the present disclosure, identifier (ID) information of an APS including ALF data for deriving cross-component filter coefficients in a slice may be signaled.

[0016] According to an embodiment of the present disclosure, information on a filter set index of a CCALF can be signaled in units of CTU (block).

[0017] According to an embodiment of this document, a video / image decoding method performed by a decoding device is provided.

[0018] According to an embodiment of this document, a decoding device for performing video / image decoding is provided.

[0019] According to an embodiment of this document, a video / image encoding method performed by an encoding device is provided.

[0020] According to an embodiment of this document, there is provided an encoding device for performing video / image encoding.

[0021] According to one embodiment of this document, a computer-readable digital storage medium is provided, in which encoded video / image information generated according to the video / image encoding method disclosed in at least one embodiment of the embodiments of this document is stored.

[0022] According to an embodiment of the present document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information is stored for enabling a decoding device to execute a video / image decoding method disclosed in at least one embodiment of the present document.

[0023] Beneficial Effects

[0024] According to the implementation of this document, the overall image / video compression efficiency can be improved.

[0025] According to the implementation of this document, subjective / objective visual quality can be improved through efficient filtering.

[0026] According to an embodiment of the present disclosure, the ALF process may be efficiently performed and filtering performance may be improved.

[0027] According to an embodiment of the present disclosure, reconstructed chroma samples filtered based on reconstructed luma samples may be modified to improve picture quality and encoding accuracy of chroma components of a decoded picture.

[0028] According to an embodiment of the present disclosure, the CCALF process may be efficiently performed.

[0029] According to the embodiments of the present disclosure, ALF-related information may be efficiently signaled.

[0030] According to an embodiment of the present disclosure, CCALF-related information may be efficiently signaled.

[0031] According to an embodiment of the present disclosure, ALF and / or CCALF may be adaptively applied in units of pictures, slices, and / or coding blocks.

[0032] According to an embodiment of the present document, when CCALF is used in a coding and decoding method and apparatus for still images or videos, the filter coefficients used for CCALF and the on / off transmission method in a block or CTU unit can be improved, thereby improving coding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 An example of a video / image encoding system that can be applied to an embodiment of the present disclosure is schematically shown.

[0034] Figure 2 is a diagram schematically illustrating a configuration of a video / image encoding device that can be applied to an embodiment of the present disclosure.

[0035] Figure 3 is a diagram schematically illustrating a configuration of a video / image decoding device that can be applied to an embodiment of the present disclosure.

[0036] Figure 4 The hierarchical structure of the encoded image / video is shown as an example.

[0037] Figure 5 The present invention is a flowchart for describing a block reconstruction method based on intra-frame prediction in a decoding device.

[0038] Figure 6 An intra predictor in a decoding device is illustrated.

[0039] Figure 7 is a flowchart for describing a block reconstruction method based on inter-frame prediction in an encoding device.

[0040] Figure 8 The present invention is a flowchart for describing a block reconstruction method based on inter-frame prediction in a decoding device.

[0041] Fig. 9An inter-frame predictor in a decoding device is illustrated.

[0042] Fig.10 is a diagram illustrating an example of the shape of an ALF filter.

[0043] Fig.11 is a diagram for describing a virtual boundary applied to a filtering process according to an embodiment of the present disclosure.

[0044] Fig.12 is a diagram illustrating an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure.

[0045] Fig.13 is a diagram for describing a cross-component adaptive loop filtering (CC-ALF (CCALF)) process according to an embodiment of the present disclosure.

[0046] Fig.14 and Fig.15 is a diagram schematically illustrating an example of a video / image encoding method and related components according to an embodiment of the present disclosure.

[0047] Fig.16 and Fig.17 is a diagram schematically illustrating an example of an image / video decoding method and related components according to an embodiment of the present disclosure.

[0048] Fig.18 is a diagram illustrating an example of a content streaming system to which an embodiment disclosed in the present disclosure can be applied. DETAILED DESCRIPTION

[0049] Since the present disclosure can be modified differently and has several exemplary embodiments, specific exemplary embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present disclosure to specific embodiments. The terms used in the present disclosure are only used to describe specific embodiments and are not intended to limit the technical ideas of the embodiments of the present disclosure. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form. It should be further understood that the terms "including" or "having" used in this specification specify the presence of stated features, steps, operations, components, parts or combinations thereof mentioned in this specification, but do not exclude the presence or addition of one or more other features, values, steps, operations, components, parts or combinations thereof.

[0050] In addition, each configuration in the drawings described in the present disclosure is independently illustrated for the convenience of describing different feature functions, and does not mean that each configuration is implemented as separate hardware or separate software. For example, two or more components in each component can be combined to form a component, or a component can be divided into multiple components. Embodiments in which each configuration is integrated and / or separated are also included in the scope of the disclosure of the present disclosure.

[0051] This document relates to video / image coding. For example, the methods / implementations disclosed in this document may be applied to methods disclosed in the Versatile Video Coding (VVC) standard. In addition, the methods / implementations disclosed in this document may be applied to methods disclosed in the Basic Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second generation Audio Video Coding standard (AVS2), or the next generation video / image coding standard (e.g., H.267, H.268, etc.).

[0052] Various embodiments related to video / image coding are presented in this document, and unless stated otherwise, the embodiments may be combined with each other.

[0053] In this document, video may refer to a series of images over time. A picture generally refers to a unit representing an image in a specific time frame, and a slice / tile refers to a unit that constitutes a part of a picture in terms of coding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / tiles. A tile is a rectangular area of ​​a CTU within a specific tile column and a specific tile row in a picture. A tile column is a rectangular area of ​​a CTU having a height equal to the height of the picture and a width specified by a syntax element in a picture parameter set. A tile row is a rectangular area of ​​a CTU having a height specified by a syntax element in a picture parameter set and a width equal to the width of the picture. Tile scanning is a specific ordering of CTUs that partition a picture, where CTUs are continuously ordered in a tile with a CTU raster scan, and tiles in a picture are continuously ordered in a raster scan of tiles of a picture. A slice includes an integer number of complete tiles that may be exclusively contained in a single NAL unit or an integer number of continuous complete CTU rows within a tile of a picture.

[0054] In addition, a picture can be divided into two or more sub-pictures. A sub-picture can be a rectangular area of ​​one or more slices within a picture.

[0055] A pixel or a picture element (pel) may mean the smallest unit constituting a picture (or image). In addition, a "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may represent a pixel / pixel value of only a luminance component or a pixel / pixel value of only a chrominance component.

[0056] A unit may represent a basic unit of image processing. A unit may include at least one of a specific area of ​​a picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit may be used interchangeably with terms such as a block or an area. In general, an M×N block may include a set (or array) of transform coefficients of M columns and N rows.

[0057] In this document, "A or B" may mean "only A", "only B", or "both A and B". In other words, "A or B" in this document may be interpreted as "A and / or B". For example, in this document, "A, B, or C" means "only A", "only B", "only C", or "any one and any combination of A, B, and C".

[0058] A slash ( / ) or a comma (,) as used in this document may mean "and / or". For example, "A / B" may mean "A and / or B". Thus, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B, or C".

[0059] 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" may be interpreted as being the same as "at least one of A and B".

[0060] Furthermore, in this document, “at least one of A, B, and C” may mean “only A,” “only B,” “only C,” or “any combination of A, B, and C.” Furthermore, “at least one of A, B, or C” or “at least one of A, B and / or C” may mean “at least one of A, B, and C.”

[0061] In addition, brackets used in this specification may mean "for example". Specifically, in the case of expressing "prediction (intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In other words, the term "prediction" in this specification is not limited to "intra-frame prediction", and it may indicate that "intra-frame prediction" is proposed as an example of "prediction". In addition, even in the case of expressing "prediction (ie, intra-frame prediction)", it may indicate that "intra-frame prediction" is proposed as an example of "prediction".

[0062] In this specification, technical features described individually in one drawing may be implemented individually, or may be implemented simultaneously.

[0063] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, like reference numerals are used to indicate like elements in all drawings, and the same description of like elements may be omitted.

[0064] Figure 1 An example of a video / image encoding system to which embodiments of this document can be applied is schematically illustrated.

[0065] Reference Figure 1 The video / image coding system may include a source device and a receiving device. The source device may deliver the coded video / image information or data to the receiving device in the form of a file or stream via a digital storage medium or a network.

[0066] The source device may include a video source, an encoding device, and a transmitter. The receiving device may include a receiver, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display, and the display may be configured as a separate device or an external component.

[0067] The video source can obtain the video / image by capturing, synthesizing or generating the video / image process. The video source may include a video / image capturing device and / or a video / image generating device. For example, the video / image capturing device may include one or more cameras, a video / image archive including previously captured videos / images, etc. For example, the video / image generating device may include a computer, a tablet computer, and a smart phone, and may generate the video / image (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process that generates relevant data.

[0068] The encoding device can encode the input video / image. For compression and coding efficiency, the encoding device can perform a series of processes such as prediction, transformation and quantization. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0069] The transmitter may transmit the encoded image / image information or data output in the form of a bit stream to a receiver of a receiving device in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include an element for generating a media file in a predetermined file format, and may include an element for transmitting through a broadcast / communication network. The receiver may receive / extract a bit stream and transmit the received bit stream to a decoding device.

[0070] The decoding device may decode a video / image by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0071] The renderer may render the decoded video / image. The rendered video / image may be displayed by a display.

[0072] Figure 2 is a diagram schematically explaining a configuration of a video / image encoding device to which this document is applicable. Hereinafter, a video encoding device may include an image encoding device.

[0073] Reference Figure 2 , the encoding device 200 includes an image segmenter 210, a predictor 220, a residual processor 230 and an entropy encoder 240, an adder 250, a filter 260 and a memory 270. The predictor 220 may include an inter-frame predictor 221 and an intra-frame predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234 and an inverse transformer 235. The residual processor 230 may also include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. According to an embodiment, the image segmenter 210, the predictor 220, the residual processor 230, the entropy encoder 240, the adder 250 and the filter 260 may be configured by at least one hardware component (e.g., an encoder chipset or processor). In addition, the memory 270 may include a decoded picture buffer (DPB), or may be configured by a digital storage medium. The hardware component may also include a memory 270 as an internal / external component.

[0074] The image divider 210 may divide the input image (or picture or frame) input to the encoding device 200 into one or more processors. For example, the processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively divided from a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QTBTTT) structure. For example, a coding unit may be divided into a plurality of coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. In this case, for example, a quadtree structure may be applied first, and / or a binary tree structure and / or a ternary tree structure may be applied later. Alternatively, a binary tree structure may also be applied first. The encoding process according to the present disclosure may be performed based on a final coding unit that is no longer divided. In this case, based on the encoding efficiency according to the image feature, the maximum coding unit may be used as the final coding unit, or, if necessary, the coding unit may be recursively divided into coding units of a deeper depth, and a coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processor may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be partitioned or split from the aforementioned final coding unit. The prediction unit may be a unit for sample prediction, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0075] In some cases, a unit may be used interchangeably with terms such as a block or region. In general, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component. A sample may be used as a term corresponding to a pixel or a pixel element of a picture (or image).

[0076] The subtractor 231 can generate a residual signal (residual block, residual sample or residual sample array) by subtracting the prediction signal (prediction block, prediction sample or prediction sample array) output from the predictor 220 from the input image signal (original block, original sample or original sample array), and can send the generated residual signal to the transformer 232. The predictor 220 can perform prediction on the processing target block (hereinafter referred to as the "current block"), and can generate a prediction block including prediction samples for the current block. The predictor 220 can determine whether to apply intra-frame prediction or inter-frame prediction in units of the current block or CU. The predictor can generate and pass various information about the prediction to the entropy encoder 240, such as prediction mode information that will be described later in the explanation of each prediction mode. The information about the prediction can be encoded by the entropy encoder 240 and can be output in the form of a bitstream.

[0077] The intra-frame predictor 222 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the referenced samples can be located near the current block or can be spaced apart. In intra-frame prediction, the prediction mode may include multiple non-directional modes and multiple directional modes. For example, the non-directional mode may include a DC mode and a plane mode. For example, depending on the level of detail of the prediction direction, the directional mode may include 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used depending on the settings. The intra-frame predictor 222 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0078] The inter-frame predictor 221 can derive the prediction block of the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. Here, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information can be predicted in units of blocks, sub-blocks or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame predictor 221 may use the motion information of the neighboring block as the motion information of the current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling a motion vector difference.

[0079] The predictor 220 can generate a prediction signal based on various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply intra prediction and inter prediction at the same time. This can be called combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copying (IBC) for prediction of blocks. Intra block copying can be used for content image / video encoding of games, etc., for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction at the point where the reference block is derived in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document.

[0080] The prediction signal generated by the inter-frame predictor 221 and / or the intra-frame predictor 222 can be used to generate a reconstruction signal or to generate a residual signal. The transformer 232 can generate a transform coefficient by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT means a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT means a transform generated based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process can be applied to square pixel blocks of the same size, or can be applied to blocks of variable size instead of squares.

[0081] The quantizer 233 may quantize the transform coefficients and send them to the entropy encoder 240 and the entropy encoder 240 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. Information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the block-type quantized transform coefficients into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 may perform various encoding methods, such as exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 may encode information required for video / image reconstruction in addition to the quantized transform coefficients (e.g., the values ​​of syntax elements, etc.) together or separately. The encoding information (e.g., encoded video / image information) can be transmitted or stored in units of NAL (network abstraction layer) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. In this document, the information and / or syntax elements to be transmitted / transmitted by the signal described later in this document may be encoded by the above-mentioned encoding process and may be included in the bitstream. The bitstream may be transmitted through a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 240 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the encoding device 200, and alternatively, the transmitter may be included in the entropy encoder 240.

[0082] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, the residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients by the dequantizer 234 and the inverse transformer 235. The adder 250 adds the reconstructed residual signal to the prediction signal output from the predictor 220 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample or reconstructed sample array). If the block to be processed has no residual, such as the case where the skip mode is applied, the prediction block can be used as the reconstructed block. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0083] Furthermore, luma mapping and chroma scaling (LMCS) may be applied during picture encoding and / or reconstruction.

[0084] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 270 (specifically, the DPB of the memory 270). Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 260 can generate various information related to filtering and send the generated information to the entropy encoder 240, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 240 and output in the form of a bit stream.

[0085] The modified reconstructed picture transmitted to the memory 270 may be used as a reference picture in the inter predictor 221. When inter prediction is applied by the encoding apparatus, prediction mismatch between the encoding apparatus 200 and the decoding apparatus 300 may be avoided, and encoding efficiency may be improved.

[0086] The DPB of the memory 270 may store the modified reconstructed picture for use as a reference picture in the inter-frame predictor 221. The memory 270 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the block in the reconstructed picture. The stored motion information may be sent to the inter-frame predictor 221 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 270 may store the reconstructed samples of the reconstructed blocks in the current picture and may pass the reconstructed samples to the intra-frame predictor 222.

[0087] Figure 3 is a diagram schematically explaining a configuration of a video / image decoding device to which this document is applicable.

[0088] Reference Figure 3 , the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter-frame predictor 332 and an intra-frame predictor 331. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured by a hardware component (e.g., a decoder chipset or a processor). In addition, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware component may also include a memory 360 as an internal / external component.

[0089] When a bit stream including video / image information is input, the decoding device 300 can be used with Figure 2 The image is reconstructed correspondingly to the processing of the video / image information in the encoding device. For example, the decoding device 300 can derive the unit / block based on the block partition related information obtained from the bit stream. The decoding device 300 can perform decoding using a processor applied in the encoding device. Therefore, the processor used for decoding can be, for example, a coding unit, and the coding unit can be partitioned from the coding tree unit or the largest coding unit according to a quadtree structure, a binary tree structure and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a reproduction device.

[0090] The decoding device 300 may receive the bit stream from Figure 2The received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The information and / or syntax elements sent / received by the signal described later in this document may be decoded and obtained from the bitstream by the decoding process. For example, the entropy decoder 310 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and the output values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients for the residual. More specifically, the CABAC entropy decoding method may receive a bin corresponding to each syntax element in the bitstream, determine a context model using information of the decoding target syntax element, information of the decoding of the neighboring and decoding target blocks, or information of the symbol / bin decoded in the previous stage, and perform arithmetic decoding on the bin by predicting the probability of the bin appearing according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Information about prediction among the information decoded by the entropy decoder 310 may be provided to the predictor 330, and information about the residual on which entropy decoding has been performed in the entropy decoder 310, that is, quantized transform coefficients and related parameter information may be input to the dequantizer 321. In addition, information about filtering among the information decoded by the entropy decoder 310 may be provided to the filter 350. In addition, a receiver (not shown) for receiving a signal output from the encoding device may also be configured as an internal / external element of the decoding device 300, or the receiver may be a component of the entropy decoder 310. In addition, the decoding device according to this document may be referred to as a video / image / picture decoding device, and the decoding device may be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, a predictor 330, an adder 340, a filter 350, and a memory 360.

[0091] The dequantizer 321 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 321 may rearrange the quantized transform coefficient in the form of a two-dimensional block. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The dequantizer 321 may perform dequantization on the quantized transform coefficient by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0092] The inverse transformer 322 performs an inverse transformation on the transformation coefficients to obtain a residual signal (residual block, residual sample array).

[0093] The predictor may perform prediction on the current block and generate a prediction block including prediction samples for the current block. The predictor may determine whether to apply intra prediction or inter prediction to the current block based on information on prediction output from the entropy decoder 310 and may determine a specific intra / inter prediction mode.

[0094] The predictor can generate a prediction signal based on the various prediction methods described below. For example, the predictor can not only apply intra prediction or inter prediction to predict a block, but also apply intra prediction and inter prediction at the same time. This can be called combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copying (IBC) for prediction of blocks. Intra block copying can be used for content image / video encoding of games, etc., for example, screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similar to inter prediction because the reference block is derived in the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document.

[0095] The intra-frame predictor 331 can predict the current block by referring to samples in the current picture. The referenced samples can be located near the current block or can be located at a separate position according to the prediction mode. In intra-frame prediction, the prediction mode can include multiple non-directional modes and multiple directional modes. The intra-frame predictor 331 can determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

[0096] The inter-frame predictor 332 may derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter-frame predictor 332 may configure a motion information candidate list based on neighboring blocks and derive a motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating a mode of inter-frame prediction for the current block.

[0097] The adder 340 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (330). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block.

[0098] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra-frame prediction of the next block to be processed in the current picture, may be output through filtering as described below, or may be used for inter-frame prediction of the next picture.

[0099] In addition, luma mapping and chroma scaling (LMCS) can be applied during picture decoding.

[0100] The filter 350 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 360 (specifically, the DPB of the memory 360). The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0101] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter-frame predictor 332. The memory 360 can store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the block in the reconstructed picture. The stored motion information can be sent to the inter-frame predictor 332 so as to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 360 can store the reconstructed samples of the reconstructed blocks in the current picture and pass the reconstructed samples to the intra-frame predictor 331.

[0102] In the present specification, the embodiments explained in the predictor 330, the dequantizer 321, the inverse transformer 322, and the filter 350 of the decoding device 300 can be respectively applied to or correspond to the predictor 220, the dequantizer 234, the inverse transformer 235, and the filter 260 of the encoding device 200 in the same manner.

[0103] As described above, in video coding, prediction is performed to improve compression efficiency. Through this operation, a prediction block including prediction samples for a current block (i.e., a block to be encoded) can be generated. Here, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived identically 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 prediction block (rather than the original sample value of the original block itself). Image coding efficiency can be improved by notifying the device with a signal. The decoding device can derive a residual block including residual samples based on the residual information, generate a reconstructed block including reconstructed samples by adding the residual block and the prediction block, and generate a reconstructed picture including the reconstructed block.

[0104] The residual information can be generated by a transform process and a quantization process. For example, the encoding device can derive a residual block between the original block and the prediction block, perform a transform process on the residual samples (residual sample array) included in the residual block to derive the transform coefficients, and then derive the quantized transform coefficients by performing a quantization process on the transform coefficients to signal the residual related information (via a bitstream) to the decoding device. Here, the residual information may include value information, position information, transform technology, transform core, and quantization parameters of the quantized transform coefficients. The decoding device can perform a dequantization / inverse transform process based on the residual information and derive residual samples (or residual blocks). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. The encoding device can also dequantize / inverse transform the quantized transform coefficients for inter-frame prediction reference of subsequent pictures to derive residual blocks, and generate reconstructed pictures based on this.

[0105] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When quantization / dequantization is omitted, the quantized transform coefficient may be referred to as a transform coefficient. When transform / inverse transform is omitted, the transform coefficient may be referred to as a coefficient or a residual coefficient, or may still be referred to as a transform coefficient for the sake of uniformity of expression.

[0106] 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, and the information about the transform coefficient may be signaled through a residual coding syntax. The transform coefficient may be derived based on the residual information (or information about the transform coefficient), and the scaled transform coefficient may be derived by inversely transforming (scaling) the transform coefficient. The residual sample may be derived based on the inverse transform (transform) of the scaled transform coefficient. This may also be applied / expressed in other parts of this document.

[0107] The predictor of the encoding device / decoding device can derive prediction samples by performing inter-frame prediction in units of blocks. Inter-frame prediction can be a prediction derived in a manner that depends on data elements (e.g., sample values ​​or motion information) of pictures other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. Here, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and a reference picture including a temporally neighboring block may be referred to as a collocated picture (colPic). For example, a motion information candidate list may be configured based on a neighboring block of the current block, and a flag or index information indicating which candidate is selected (used) may be signaled to derive a motion vector and / or a reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of a skip mode and a merge mode, the motion information of the current block may be the same as the motion information of the neighboring block. In the skip mode, unlike the merge mode, a residual signal may not be sent. In the case of a motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0108] According to the inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. The motion vector in the L0 direction may be referred to as the L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as the L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as the L0 prediction, prediction based on the L1 motion vector may be referred to as the L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bidirectional prediction. Here, the L0 motion vector may indicate a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may indicate a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include a picture earlier than the current picture in output order as a reference picture, and the reference picture list L1 may include a picture later than the current picture in output order. The preceding picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. The reference picture list L0 may also include a picture later than the current picture in output order as a reference picture. In this case, the previous picture may be indexed first in the reference picture list L0, and the subsequent picture may be indexed later. The reference picture list L1 may also include pictures earlier than the current picture in the output order as reference pictures. In this case, the subsequent picture may be indexed first in the reference picture list 1, and the previous picture may be indexed later. The output order may correspond to a picture order count (POC) order.

[0109] Figure 4 The hierarchical structure of a coded image / video is shown exemplarily.

[0110] Reference Figure 4 , the coded image / video is divided into the Video Coding Layer (VCL) that handles the image / video and its own decoding process, the subsystem that sends and stores the coded information, and the NAL (Network Abstraction Layer) that is responsible for the network adaptation function and exists between the VCL and the subsystem.

[0111] In the VCL, VCL data including compressed image data (slice data) is generated, or a parameter set including a picture parameter set (PSP), a sequence parameter set (SPS), and a video parameter set (VPS), or a supplemental enhancement information (SEI) message additionally required for the image decoding process may be generated.

[0112] In NAL, a NAL unit may be generated by adding header information (NAL unit header) to a raw byte sequence payload (RBSP) generated in a VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated in a VCL. The NAL unit header may include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0113] As shown in the figure, the NAL unit can be divided into a VCL NAL unit and a non-VCL NAL unit according to the RBSP generated in the VCL. The VCL NAL unit may refer to a NAL unit including information about an image (slice data), and the non-VCL NAL unit may refer to a NAL unit including information (parameter set or SEI message) required for decoding the image.

[0114] The aforementioned VCL NAL unit and non-VCL NAL unit can be sent through the network by adding header information according to the data standard of the subsystem. For example, the NAL unit can be transformed into a predetermined standard data format such as H.266 / VVC file format, real-time transport protocol (RTP), transport stream (TS), etc., and sent through various networks.

[0115] As described above, a NAL unit may be specified using a NAL unit type according to an RBSP data structure included in a corresponding NAL unit, and information about the NAL unit type may be stored and signaled in a NAL unit header.

[0116] For example, NAL units can be classified into VCL NAL unit types and non-VCL NAL unit types according to whether the NAL unit includes information about the image (slice data). VCL NAL unit types can be classified according to the nature and type of the picture included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0117] The following are examples of NAL unit types specified according to the type of parameter sets included in the non-VCL NAL unit type.

[0118] -APS (Adaptation Parameter Set) NAL unit: type used for NAL units that include APS

[0119] -DPS (Decoding Parameter Set) NAL unit: type used for NAL units that include DPS

[0120] - VPS (Video Parameter Set) NAL unit: Type used for NAL units that include VPS

[0121] - SPS (Sequence Parameter Set) NAL unit: type used for NAL units that include SPS

[0122] -PPS (Picture Parameter Set) NAL unit: Type used for NAL units that include PPS

[0123] - PH (Picture Header) NAL unit: type used for NAL units including PH

[0124] The aforementioned NAL unit type may have syntax information for the NAL unit type, and the syntax information may be stored and signaled in the NAL unit header. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified by the nal_unit_type value.

[0125] In addition, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to multiple slices (slice headers and slice data sets) in a picture. The picture header (picture header syntax) may include information / parameters that are commonly applicable to the picture. In this document, slices may be mixed or replaced with tiling groups. In addition, in this document, slice headers may be mixed or replaced with tiling group headers.

[0126] The slice header (slice header syntax, slice header information) may include information / parameters that can be commonly applied to the slice. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that can be commonly applied to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that can be commonly applied to one or more sequences. VPS (VPS syntax) may include information / parameters that can be commonly applied to multiple layers. DPS (DPS syntax) may include information / parameters that can be commonly applied to the entire video. DPS may include information / parameters related to the concatenation of coded video sequences (CVS). The high-level syntax (HLS) in this document may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[0127] In this document, the image / image information encoded from the encoding device and notified to the decoding device by a signal in the form of a bit stream includes not only partition-related information in the picture, intra-frame / inter-frame prediction information, residual information, in-loop filtering information, etc., but also includes information included in the slice header, information included in the APS, information included in the PPS, information included in the SPS and / or information included in the VPS.

[0128] In addition, in order to compensate for the difference between the original image and the reconstructed image due to errors occurring in the compression coding process such as quantization, an in-loop filtering process may be performed on the reconstructed sample or the reconstructed picture as described above. As described above, the in-loop filtering may be performed by a filter of an encoding device and a filter of a decoding device, and a deblocking filter, SAO, and / or an adaptive loop filter (ALF) may be applied. For example, the ALF process may be performed after the deblocking filtering process and / or the SAO process are completed. However, even in this case, the deblocking filtering process and / or the SAO process may be omitted.

[0129] Hereinafter, a detailed description of picture reconstruction and filtering will be described. In image / video encoding, a reconstructed block can be generated based on intra-frame prediction / inter-frame prediction for each block, and a reconstructed picture including the reconstructed block can be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice can be reconstructed based only on intra-frame prediction. In addition, when the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice can be reconstructed based on intra-frame prediction or inter-frame prediction. In this case, intra-frame prediction can be applied to some blocks in the current picture / slice, and inter-frame prediction can be applied to the remaining blocks.

[0130] Intra-frame prediction may refer to the prediction of the prediction samples of the current block generated based on the reference samples in the picture to which the current block belongs (hereinafter referred to as the current picture). When intra-frame prediction is applied to the current block, the neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary of the current block having a size of nWxnH and a total of 2xnH samples adjacent to the lower left, samples adjacent to the upper boundary of the current block and a total of 2xnW samples adjacent to the upper right, and one sample adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple upper neighboring samples and multiple left neighboring samples. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block having a size of nWxnH, a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right of the current block.

[0131] However, some neighboring reference samples of the current block may not yet be decoded or available. In this case, the decoder can configure the neighboring reference samples to be used for prediction by replacing the unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction can be configured by interpolation of available samples.

[0132] When deriving neighboring reference samples, the prediction samples can be derived based on the average or interpolation of the neighboring reference samples of the current block and (ii) the prediction among the neighboring reference samples of the current block. The prediction samples can be derived based on the reference samples existing in a specific (prediction) direction relative to the sample. The case of (i) can be referred to as a non-directional mode or a non-angle mode, and the case of (ii) can be referred to as a directional mode or an angle mode. In addition, based on the prediction samples of the current block among the neighboring reference samples, the first neighboring samples and the second neighboring samples located in the direction opposite to the prediction direction of the intra-frame prediction mode of the current block are interpolated. The prediction samples can be generated. The above situation can be referred to as linear interpolation intra-frame prediction (LIP). In addition, a linear model can be used to generate chrominance prediction samples based on luminance samples. This situation can be referred to as LM mode. In addition, the temporary prediction samples of the current block can be derived based on the filtered neighboring reference samples, and at least one reference sample (i.e., an unfiltered neighboring reference sample) derived according to the intra-frame prediction mode among the existing neighboring reference samples and the temporary prediction samples can be weighted summed to derive the prediction samples of the current block. The above situation may be referred to as position-dependent intra prediction (PDPC). In addition, a reference sample line with the highest prediction accuracy among the neighboring multiple reference sample lines of the current block may be selected to derive a prediction sample by using a reference sample located in the prediction direction on the corresponding line, and then the reference sample line used herein may be indicated (signaled) to the decoding device, thereby performing intra prediction coding. The above situation may be referred to as multi-reference line (MRL) intra prediction or MRL-based intra prediction. In addition, intra prediction may be performed based on the same intra prediction mode by dividing the current block into vertical or horizontal sub-partitions, and neighboring reference samples may be derived and used in the sub-partition unit. That is, in this case, the intra prediction mode for the current block is equally applied to the sub-partition, and the intra prediction performance may be improved in some cases by deriving and using neighboring reference samples in the sub-partition unit. Such a prediction method may be referred to as intra sub-partition (ISP) or intra prediction based on ISP. The aforementioned intra prediction method may be referred to as an intra prediction type separately from the intra prediction mode. The intra prediction type may be referred to in 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) may include at least one of the aforementioned LIP, PDPC, MRL, and ISP. A general intra prediction method other than a specific intra prediction type such as LIP, PDPC, MRL, or ISP may be referred to as a normal intra prediction type. When a specific intra prediction type cannot be applied, a normal intra prediction type may be generally applied, and prediction may be performed based on the above intra prediction mode. In addition, post filtering may be performed on the derived prediction sample as needed.

[0133] Specifically, the intra prediction process may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and a prediction sample derivation step based on the intra prediction mode / type. In addition, a post-filtering step may be performed on the derived prediction samples as needed.

[0134] In the following, intra prediction in an encoding device will be described. The encoding device performs intra prediction on a current block. The encoding device may derive an intra prediction mode for the current block, derive neighboring reference samples of the current block, and generate prediction samples in the current block based on the intra prediction mode and the neighboring reference samples. Here, the process of determining the intra prediction mode, deriving neighboring reference samples, and generating prediction samples may be performed simultaneously, or any one process may be performed before another process. For example, the intra predictor 222 of the encoding device may include a prediction mode / type determiner, a reference sample deriver, and a prediction sample deriver, the prediction mode / type determiner may determine the intra prediction mode / type for the current block, the reference sample deriver may derive neighboring reference samples of the current block, and the prediction sample deriver may derive motion samples of the current block. In addition, although not illustrated, when the prediction sample filtering process to be described later is performed, the intra predictor 222 may also include a prediction sample filter. The encoding device may determine the mode applied to the current block from among a plurality of intra prediction modes. The encoding apparatus may compare RD costs for intra prediction modes and determine an optimal intra prediction mode for the current block.

[0135] In addition, the encoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all prediction samples may be filtered by the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0136] The encoding device derives residual samples for the current block based on the prediction samples. The encoding device may compare the prediction samples among the original samples of the current block based on a phase and derive the residual samples.

[0137] The encoding device may transform / quantize the residual samples to derive quantized transform coefficients, and then perform a dequantization / inverse transform process on the quantized transform coefficients to derive (modified) residual samples. The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual samples as the residual samples derived from the decoding device as described above.

[0138] The encoding device may generate a reconstructed block including reconstructed samples for the current block based on the prediction samples and the (modified) residual samples. A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0139] As described above, the encoding device encodes image information including prediction information about intra prediction (e.g., prediction mode information indicating a prediction mode) and residual information about intra and residual samples to output the encoded image information in the form of a bit stream. The residual information may include residual coding syntax. The encoding device may transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information about the quantized transform coefficients.

[0140] Figure 5 The present invention is a flowchart for describing a block reconstruction method based on intra-frame prediction in a decoding device. Figure 6 An intra predictor in a decoding device is illustrated.

[0141] The decoding device may perform operations corresponding to those performed by the encoding device.

[0142] S500 to S520 may be performed by the intra-frame predictor 331 of the decoding device, and the prediction information of S500 and the residual information of S530 may be obtained from the bitstream by the entropy decoder 310 of the decoding device. The residual processor 320 of the decoding device may derive residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 may derive the transform coefficient by performing dequantization based on the quantized transform coefficient derived based on the residual information, and the inverse transformer 322 of the residual processor may derive the residual sample for the current block by performing inverse transformation on the transform coefficient. S540 may be performed by the adder 340 or the reconstructor of the decoding device.

[0143] In detail, the decoding device may derive an intra prediction mode for the current block based on the received prediction mode information (S500). The decoding device may derive neighboring reference samples of the current block (S510). The decoding device generates prediction samples in the current block based on the intra prediction mode and the neighboring reference samples (S520). In this case, the decoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post filtering. Some or all prediction samples may be filtered by a prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0144] The decoding device generates residual samples for the current block based on the received residual information (S530). The decoding device may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S540). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0145] Here, the intra predictor 331 of the decoding device may include a prediction mode / type determiner 331-1, a reference sample deriver 331-2, and a prediction sample deriver 331-3, the prediction mode / type determiner 331-1 may determine the intra prediction mode for the current block based on the prediction mode information obtained from the entropy decoder 310 of the decoding device, the reference sample deriver 331-2 may derive the neighboring reference samples of the current block, and the prediction sample deriver 331-3 may derive the prediction sample of the current block. In addition, although not shown, when performing the above-mentioned prediction sample filtering process, the intra predictor 331 may also include a prediction sample filter unit (not shown).

[0146] The prediction information may include intra-frame prediction mode information and / or intra-frame prediction type information. The intra-frame prediction mode information may include, for example, flag information (e.g., Intra_luma_mpm_flag) indicating whether the most probable mode (MPM) is applied to the current block or the residual mode is applied, and when MPM is applied to the current block, the prediction mode information may also include index information (e.g., intra_luma_mpm_idx) indicating one of the intra-frame prediction mode candidates (MPM candidates). The intra-frame prediction mode candidate (MPM candidate) may include an MPM candidate list or an MPM list. In addition, when MPM is not applied to the current block, the intra-frame prediction mode information may also include residual mode information (e.g., Intra_luma_mpm_remainder) indicating one of the remaining intra-frame prediction modes other than the intra-frame prediction mode candidate (MPM candidate). The decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction mode information. A separate MPM list may be configured for the aforementioned MIP.

[0147] In addition, the intra prediction type information can be implemented in various forms. For example, the intra prediction type information may include intra prediction type index information indicating one of the intra prediction types. As another example, the intra prediction type information may include at least one of the following: reference sample line information indicating whether MRL is applied to the current block and indicating which reference sample line is used if applied (e.g., Intra_luma_ref_idx), ISP flag information indicating whether ISP is applied to the current block (e.g., Intra_subpartitions_mode_flag), ISP type information indicating the segmentation type of the sub-partition when ISP is applied (e.g., Intra_subpartitions_split_flag), flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. In addition, the intra prediction type information may include a MIP flag indicating whether MIP is applied to the current block.

[0148] The intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by the encoding method described in the present disclosure. For example, the intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by entropy encoding (e.g., CABAC, CAVLC) based on truncated (Rice) binary code.

[0149] The predictor of the encoding device / decoding device can derive the prediction sample by performing inter-frame prediction on a block-by-block basis. Inter-frame prediction can be a prediction derived in a manner that depends on data elements (e.g., sample values ​​or motion information) of pictures other than the current picture. When inter-frame prediction is applied to the current block, a prediction block (prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information of the current block can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When inter-frame prediction is applied, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same as or different from each other. The temporally neighboring blocks may be referred to as names such as collocated reference blocks, collocated CUs (colCUs), and the like, and the reference pictures including the temporally neighboring blocks may be referred to as collocated pictures (colPic). For example, a motion information candidate list may be configured based on the neighboring blocks of the current block and a flag or index information indicating which candidate is selected (used) to derive the motion vector and / or reference picture index of the current block may be signaled. Inter-frame prediction may be performed based on various prediction modes, and for example, in the case of skip mode and merge mode, the motion information of the current block may be the same as the motion information of the neighboring blocks. In the case of skip mode, unlike the merge mode, a residual signal may not be sent. In the case of a motion vector prediction (MVP) mode, the motion vector of the selected neighboring block is used as a motion vector predictor and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0150] Figure 7 is a flowchart for describing a block reconstruction method based on inter-frame prediction in an encoding device.

[0151] S700 may be performed by the inter-frame predictor 221 of the encoding device, and S710 to S730 may be performed by the residual processor 230 of the encoding device. Specifically, S710 may be performed by the subtractor 231 of the encoding device, S720 may be performed by the transformer 232 and the quantizer 233 of the encoding device, and S730 may be performed by the dequantizer 234 and the inverse transformer 235 of the encoding device. In S700, the prediction information may be derived by the inter-frame predictor 221 and encoded by the entropy encoder 240. The residual information may be derived by S710 and S720 and encoded by the entropy encoder 240. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample. As described above, the residual sample may be derived as a transform coefficient by the transformer 232 of the encoding device, and the transform coefficient may be derived as a quantized transform coefficient by the quantizer 233. Information about the quantized transform coefficients may be encoded by the entropy encoder 240 through a residual encoding process.

[0152] The encoding device performs inter prediction on the current block (S700). The encoding device may derive the inter prediction mode and motion information of the current block, and generate a prediction sample of the current block. Here, the process of determining the inter prediction mode, deriving motion information, and generating prediction samples may be performed simultaneously, or any process may be performed before another process. For example, the inter predictor 221 of the encoding device may include a prediction mode determiner, a motion information deriver, and a prediction sample deriver, the prediction mode determiner may determine the prediction mode of the current block, the motion information deriver may derive the motion information of the current block, and the prediction sample deriver may derive the motion sample of the current block. For example, the inter predictor 221 of the encoding device searches for a block similar to the current block in a predetermined area (search area) of the reference picture by motion estimation, and may derive a reference block whose difference with the current block is equal to or less than a minimum value or a predetermined standard. Based on this, a reference picture index indicating a reference picture in which the reference block is located may be derived, and a motion vector may be derived based on the position difference between the reference block and the current block. The encoding device may determine the mode applied to the current block from among various prediction modes. The encoding device may compare RD costs for various prediction modes and determine an optimal prediction mode for the current block.

[0153] For example, when a skip mode or a merge mode is applied to the current block, the encoding device may construct a merge candidate list to be described later, and derive a reference block having a minimum value or a predetermined criterion or less difference with the current block among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the current block may be derived using the motion information of the selected merge candidate.

[0154] As another example, when the (A)MVP mode is applied to the current block, the encoding device may construct an (A)MVP candidate list to be described later, and may use the motion vector of the MVP candidate selected from the motion vector predictor (MVP) candidates included in the (A)MVP candidate list as the MVP of the current block. In this case, for example, the motion vector indicating the reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block, and the MVP candidate having the motion vector with the smallest difference from the motion vector of the current block among the MVP candidates may be the selected MVP candidate. A motion vector difference (MVD) as a difference obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, information about the MVD may be signaled to the decoding device. In addition, when the (A)MVP mode is applied, the value of the reference picture index may be separately signaled to the decoding device by constructing reference picture index information.

[0155] The encoding apparatus may induce residual samples based on the prediction samples (S710). The encoding apparatus may induce residual samples by comparing the prediction samples with original samples of the current block.

[0156] The encoding device may transform / quantize the residual samples to derive quantized transform coefficients (S720), and then perform a dequantization / inverse transform process on the quantized transform coefficients to derive (modified) residual samples (S730). The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual samples as the residual samples derived from the decoding device as described above.

[0157] The encoding apparatus may generate a reconstructed block including reconstructed samples for the current block based on the prediction samples and the (modified) residual samples (S740). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0158] Although not shown, as described above, the encoding device may encode image information including prediction information and residual information. The encoding device can output the encoded image information in the form of a bitstream. The prediction information is information related to the prediction process and may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and motion information. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. In addition, the information about the motion information may include the above-mentioned MVD information and / or reference picture index information. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or bi prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0159] The output bitstream may be stored in a (digital) storage medium and sent to the decoding device, or may be sent to the decoding device over a network.

[0160] Figure 8 The present invention is a flowchart for describing a block reconstruction method based on inter-frame prediction in a decoding device. Fig. 9 An inter-frame predictor in a decoding device is illustrated.

[0161] The decoding device may perform operations corresponding to those performed by the encoding device.

[0162] S800 to S820 may be performed by the inter-frame predictor 332 of the decoding device, and the prediction information of S800 and the residual information of S830 may be obtained from the bitstream by the entropy decoder 310 of the decoding device. The residual processor 320 of the decoding device may derive residual samples for the current block based on the residual information. Specifically, the dequantizer 321 of the residual processor 320 may derive the transform coefficient by performing dequantization based on the quantized transform coefficient, which is derived based on the residual information, and the inverse transformer 322 of the residual processor may derive the residual sample for the current block by performing inverse transformation on the transform coefficient. S840 may be performed by the adder 340 or the reconstructor of the decoding device.

[0163] Specifically, the decoding device may determine a prediction mode for the current block based on the received prediction mode information (S800). The decoding device may determine which inter prediction mode to apply to the current block based on the prediction mode information in the prediction information.

[0164] For example, based on a merge flag, it may be determined whether a merge mode is applied to the current block or whether the (A) MVP mode is determined. Alternatively, one of various inter prediction mode candidates may be selected based on a mode index. The inter prediction mode candidate may include a skip mode, a merge mode, and / or an (A) MVP mode, or may include various inter prediction modes to be described later.

[0165] The decoding device may derive motion information of the current block based on the determined inter prediction mode (S810). For example, when the skip mode or merge mode is applied to the current block, the decoding device may construct a merge candidate list to be described later, and select a merge candidate from the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0166] As another example, when the (A)MVP mode is applied to the current block, the decoding device may construct an (A)MVP candidate list to be described later, and may use the motion vector of the mvp candidate selected from the motion vector predictor (mvp) candidates included in the (A)MVP candidate list as the mvp of the current block. The selection may be performed based on the above-mentioned selection information (mvp flag or mvp index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the mvp and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list for the current block may be derived as the reference picture referenced for inter-frame prediction of the current block.

[0167] In addition, as described below, the motion information of the current block can be derived without constructing a candidate list, and in this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode to be described later. In this case, the candidate list configuration as described above can be omitted.

[0168] The decoding device may generate a prediction sample for the current block based on the motion information of the current block (S820). In this case, the reference picture may be derived based on the reference picture index of the current block, and the prediction sample of the current block may be derived using the sample of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as described below, in some cases, a prediction sample filtering process may also be performed on all or some of the prediction samples of the current block.

[0169] For example, the inter-frame predictor 332 of the decoding device may include a prediction mode determiner 332-1, a motion information deriver 332-2 and a prediction sample deriver 332-3, wherein the prediction mode determiner 332-1 can determine the prediction mode of the current block based on the received prediction mode information, the motion information deriver 332-2 can derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received motion information, and the prediction sample deriver 332-3 can derive the prediction sample of the current block.

[0170] The decoding device generates residual samples for the current block based on the received residual information (S830). The decoding device may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and may derive a reconstructed block including the reconstructed samples (S840). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0171] Various inter prediction modes can be used for the prediction of the current block in the picture. For example, various modes such as merge mode, skip mode, motion vector prediction (MVP) mode, affine mode, sub-block merge mode, and merge with MVD (MMVD) mode can be used. Decoder-side motion vector refinement (DMVR) mode, adaptive motion vector resolution (AMVR) mode, bi-prediction with CU-level weights (BCW), bidirectional optical flow (BDOF), etc. can also be used in addition or alternatively as additional modes. Affine mode can be referred to as affine motion prediction mode. MVP mode can be referred to as advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived by some modes can be included as one of the motion information candidates of other modes. For example, an HMVP candidate can be added as a merge candidate in merge / skip mode or can be added as an MVP candidate in MVP mode.

[0172] 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 the decoding device. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated by hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag may be signaled to indicate whether the skip mode is applied, and if the skip mode is not applied, a merge flag may be signaled to indicate whether the merge mode is applied, and if the merge mode is not applied, an MVP mode is indicated to be applied or a flag for additional classification may also be signaled. Affine mode may be signaled in an independent mode or may be signaled in a mode dependent on a merge mode or an MVP mode. For example, an affine mode may include an affine merge mode and an affine MVP mode.

[0173] In addition, information indicating whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction or bi-prediction is used in the current block (current coding unit) may be signaled in the current block. This 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, for example, an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element may indicate whether the above-mentioned list0 (L0) prediction, list1 (L1) prediction or bi-prediction is used for the current block (current coding unit). In this document, for the convenience of description, the inter-prediction type (L0 prediction, L1 prediction or BI prediction) indicated by the inter_pred_idc syntax element may be indicated as a motion prediction direction. The L0 prediction may be represented as pred_L0, the L1 prediction may be represented as pred_L1, and the paired prediction may be represented as pred_BI. For example, the following prediction types may be determined according to the value of the inter_pred_idc syntax element.

[0174] [Table 1]

[0175]

[0176] As described above, a picture may include one or more slices. A slice may have one of slice types including an intra (I) slice, a predicted (P) slice, and a bidirectional predicted (B) slice. The slice type may be indicated based on slice type information. For blocks in an I slice, inter prediction may not be used for prediction, and only intra prediction may be used. Of course, even in this case, the original sample values ​​may be encoded and signaled without prediction. Intra prediction or inter prediction may be used for blocks in a P slice, and only unidirectional prediction may be used when inter prediction is used. In addition, intra prediction or inter prediction may be used for blocks in a B slice, and up to bidirectional prediction may be used when inter prediction is used.

[0177] L0 and L1 may include reference pictures previously encoded / decoded before the current picture. For example, L0 may include reference pictures before and / or after the current picture in the POC order, and L1 may include reference pictures after and / or before the current picture in the POC order. In this case, L0 may be assigned a reference picture index lower than the current picture relative to the previous reference picture in the POC order, and L1 may be assigned a reference picture index lower than the current picture relative to the subsequent reference picture in the POC order. In the case of B slices, bi-prediction may be applied, and in this case, unidirectional bi-prediction may be applied or bidirectional bi-prediction may be applied. Bidirectional bi-prediction may be referred to as true bi-prediction.

[0178] As described above, a residual block (residual sample) can be derived based on a prediction block (prediction sample) derived by prediction at the encoding stage, and a residual sample transformed / quantized by residual information can be generated. The residual information may include information about quantized transform coefficients. The residual information may be included in the video / image information, and the video / image information may be encoded and sent to a decoding device in the form of a bitstream. The decoding device may obtain the residual information from the bitstream, and may derive the residual sample based on the residual information. Specifically, the decoding device may derive the quantized transform coefficient based on the residual information, and may derive the residual block (residual sample) through a dequantization / inverse transform process.

[0179] Furthermore, at least one process of (inverse) transformation and / or (de)quantization may be omitted.

[0180] In the following, the in-loop filtering process performed on the reconstructed picture will be described. Modified reconstructed samples, blocks, pictures (or modified filtered samples, blocks, pictures) can be generated by the in-loop filtering process, and the modified (modified filtered) reconstructed pictures can be output as decoded pictures at the decoding device and can also be stored in the decoded image buffer or memory of the encoding device / decoding device and used as reference pictures in the inter-frame prediction process when the picture is encoded / decoded later. The in-loop filtering process may include a deblocking filtering process, a sample adaptive offset (SAO) process, and / or an adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filter (ALF) process, and the bilateral filter process may be applied sequentially or all may be applied sequentially. For example, the SAO process may be performed after the deblocking filtering process is applied to the reconstructed picture. Or, for example, the ALF process may be performed after the deblocking filtering process is applied to the reconstructed picture. This can also be performed in the encoding device.

[0181] Deblocking filtering is a filtering technique that removes distortion at the boundaries between blocks in a reconstructed picture. For example, the deblocking filtering process can derive a target boundary from the reconstructed picture, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on the bS. The bS can be determined based on the prediction mode of two blocks adjacent to the target boundary, the motion vector difference, whether the reference picture is the same, whether there is a non-zero significant coefficient, etc.

[0182] SAO is a method for compensating for the offset difference between a reconstructed picture and an original picture on a sample basis. For example, SAO can be applied based on types such as band offset, edge offset, etc. According to SAO, samples can be classified into different categories according to each SAO type, and an offset value can be added to each sample based on the category. The filter information for SAO may include information on whether SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed picture after deblocking filtering is applied.

[0183] Adaptive loop filter (ALF) is a technique for filtering a reconstructed picture on a sample basis based on filter coefficients according to a filter shape. The encoding device can determine whether to apply ALF, ALF shape and / or ALF filter coefficients, etc. by comparing the reconstructed picture and the original picture, and can notify the decoding device with a signal. That is, the filter information for ALF may include information on whether to apply ALF, ALF filter shape information, ALF filter coefficient information, etc. ALF can be applied to the reconstructed picture after applying deblocking filtering.

[0184] Fig.10An example of the shape of the ALF filter is shown.

[0185] Fig.10 (a) shows the shape of a 7×7 diamond filter, Fig.10 (b) shows the shape of a 5×5 diamond filter. Fig.10 In the filter shape, Cn represents the filter coefficient. When n in Cn is the same, this indicates that the same filter coefficient can be assigned. In this document, the position and / or unit of assigning the filter coefficient according to the filter shape of the ALF may be referred to as a filter tap. In this case, one filter coefficient may be assigned to each filter tap, and the arrangement of the filter taps may correspond to the filter shape. The filter tap located at the center of the filter shape may be referred to as a central filter tap. The same filter coefficient may be assigned to two filter taps of the same n value, which exist at positions corresponding to each other relative to the central filter tap. For example, in the case of a 7×7 diamond filter shape, 25 filter taps are included, and since the filter coefficients C0 to C11 are assigned in a centrally symmetric form, only 13 filter coefficients may be used to assign the filter coefficients to the 25 filter taps. Furthermore, for example, in the case of a 5×5 diamond filter shape, 13 filter taps are included, and since the filter coefficients C0 to C5 are allocated in a centrally symmetrical form, the filter coefficients can be allocated to the 13 filter taps using only 7 filter coefficients. For example, in order to reduce the amount of data of information about the filter coefficients to be signaled, 12 of the 13 filter coefficients of the 7×7 diamond filter shape are (explicitly) signaled, and 1 filter coefficient can be (implicitly) derived. Furthermore, for example, 6 of the 7 filter coefficients of the 5×5 diamond filter shape can be (explicitly) signaled, and 1 filter coefficient can be (implicitly) derived.

[0186] According to an embodiment of the present disclosure, ALF parameters for an ALF process may be signaled through an adaptive parameter set (APS). The ALF parameters may be derived from filter information for ALF or ALF data.

[0187] ALF is an in-loop filtering technique that can be applied in video / image coding as described above. ALF can be performed using an adaptive filter based on Wiener. This can be to minimize the mean square error (MSE) between the original sample and the decoded sample (or reconstructed sample). The advanced design for the ALF tool can be incorporated into the syntax elements accessible in the SPS and / or slice header (or tile group header).

[0188] In the example, before filtering for each 4x4 luma block, geometric transformations such as rotation or diagonal and vertical flipping may be applied to the filter coefficients f(k,l) and corresponding filter clipping values ​​c(k,l) that depend on the gradient values ​​calculated for the block. This is equivalent to applying these transformations to the samples in the filter support region. Creating other blocks to which the ALF is applied may be similar to arranging these blocks according to their directionality.

[0189] For example, three transformations can be performed based on the following formulas: diagonal, vertical flip, and rotation.

[0190] [Formula 1]

[0191] Diagonal: f_D(k,1)=f(1,k), c_D(k,1)=c(1,k)

[0192] [Formula 2]

[0193] Vertical flip: f_V(k, l) = f(k, K-1-1), c_V(k, l) = c(k, Kl-1)

[0194] [Formula 3]

[0195] Rotation: f_R(k, l) = f(Kl-1, k), c_R(k, l) = c(Kl-1, k)

[0196] In equations 1 to 3, K may be the size of the filter. 0≤k and 1≤K-1 may be coefficient coordinates. For example, (0,0) may be the upper left corner coordinate, and / or (K-1,K-1) may be the lower right corner coordinate. The relationship between the transform and the four gradients in the four directions may be summarized in the following table.

[0197] [Table 2]

[0198] Gradient Value Transform <![CDATA[g d2 <g d1 And g h <g v ]]> No transformation <![CDATA[g d2 <g d1 And g v <g h ]]> diagonal <![CDATA[g d1 <g d2 And g h <g v ]]> Flip Vertically <![CDATA[g d1 <g d2 And g v <g h ]]> Rotation

[0199] ALF filter parameters can be signaled in APS and slice headers. In one APS, up to 25 luma filter coefficients and clipping value indices can be signaled. In one APS, up to 8 chroma filter coefficients and clipping value indices can be signaled. In order to reduce bit overhead, filter coefficients of different classifications for luma components can be merged. In the slice header, the index of the APS for the current slice (referenced by the current slice) can be signaled.

[0200] The clip value index decoded from the APS may make it possible to determine the clip value using a brightness table of the clip value and a chrominance table of the clip value. These clip values ​​may depend on the internal bit depth. More specifically, the brightness table of the clip value and the chrominance table of the clip value may be derived based on the following formula.

[0201] [Formula 4]

[0202] AlfClipL = {round(2^(B(N-n+1) / N)) for n∈[1..N]}

[0203] [Formula 5]

[0204] AlfClipC={round(2^((B-8)+8((Nn)) / (N-1))) for n∈[1..N]}

[0205] In the above formula, B may be the internal bit depth, and N may be the number of allowable clipping values ​​(predetermined number). For example, N may be 4.

[0206] In the slice header, up to 7 APS indices can be signaled to indicate the luma filter set for the current slice. The filtering process can also be controlled at the CTB level. For example, a flag indicating whether the ALF is applied to the luma CTB can be signaled. The luma CTB can select one of 16 fixed filter sets and a filter set from the APS. The filter set index can be signaled for the luma CTB to indicate which filter set is applied. The 16 fixed filter sets can be predefined and hard-coded in both the encoder and the decoder.

[0207] For chroma components, an APS index may be signaled in a slice header to indicate the chroma filter set used for the current slice. At the CTB level, when there are two or more chroma filter sets in an APS, a filter index may be signaled for each chroma CTB.

[0208] The filter coefficients may be quantized with a norm of 128. To limit the multiplication complexity, bitstream conformance may be applied so that the coefficient values ​​for non-center positions may vary from 0 to 28 and / or the coefficient values ​​for the remaining positions may range from -27 to 27-1. The center position coefficient may not be signaled in the bitstream and may be predetermined (considered) to be 128.

[0209] When ALF is available for the current block, each sample R(i, j) may be filtered, and the filtering result R'(i, j) may be expressed by the following formula.

[0210] [Formula 6]

[0211] R′(i, j)=R(i, j)+((∑ k≠0 ∑ l≠0 f(k,l)×K(R(i+k,j+l)-R(i,j),c(k,l))+64)>>7)

[0212] In the above formula, f(k,l) can be a decoded filter coefficient, K(x,y) can be a clipping function, and c(k,l) can be a decoded clipping parameter. For example, the variables k and / or l can vary from -L / 2 to L / 2. Here, L can represent the filter length. The clipping function K(x,y)=min(y,max(-y,x)) can correspond to the function Clip3(-y,y,x).

[0213] In an example, to reduce the line buffer requirements of the ALF, modified block classification and filtering may be applied for samples adjacent to horizontal CTU boundaries. For this purpose, a virtual boundary may be defined.

[0214] Fig.11 is a diagram for describing a virtual boundary applied to a filtering process according to an embodiment of the present disclosure. Fig.12 FIG. 1 is a diagram illustrating an ALF process using a virtual boundary according to an embodiment of the present disclosure. Fig.11 Combined description Fig.12 .

[0215] Reference Fig.11 , the virtual boundary may be a line defined by shifting the horizontal CTU boundary by N samples. In one example, N may be 4 for luma components and / or 2 for chroma components.

[0216] exist Fig.11 In , the modified block classification can be applied to the luma component. For the 1D Laplacian gradient calculation for the 4×4 block on the virtual boundary, only the samples above the virtual boundary can be used. Similarly, for the 1D Laplacian gradient calculation for the 4×4 block below the virtual boundary, only the samples below the virtual boundary can be used. The quantization of the vitality value A can be scaled by considering the reduced number of samples used in the 1D Laplacian gradient calculation.

[0217] For the filtering process, symmetric padding operations at virtual boundaries can be used for luma and chroma components. Fig.12 When the filtered sample is below the virtual boundary, the adjacent sample above the virtual boundary can be filled in. In addition, the corresponding samples on the other side can also be filled symmetrically.

[0218] When no filter is available across the boundary, Fig.12The described process may also be used for slice, tile, and / or brick boundaries. For ALF block classification, only samples included in the same slice, tile, and / or brick may be used, and the activity values ​​may be scaled accordingly. For ALF filtering, symmetric padding may be applied in each of the horizontal and / or vertical directions relative to the horizontal and / or vertical boundaries.

[0219] Fig.13 2 is a diagram for describing a cross-component adaptive loop filtering (CCALF (CC-ALF)) process according to an embodiment of the present disclosure. The CCALF process may be referred to as a cross-component filtering process.

[0220] In one aspect, the ALF process may include a general ALF process and a CCALF process. That is, the CCALF process may be referred to as some processes of the ALF process. In another aspect, the filtering process may include a deblocking process, a SAO process, an ALF process and / or a CCALF process.

[0221] CC-ALF may use luma sample values ​​to refine each chroma component. CC-ALF is controlled by (image) information of the bitstream, and the image information may include (a) information about filter coefficients for each chroma component and (b) information about masks for controlling filter application to blocks of samples. The filter coefficients may be signaled at the APS, and the block size and mask may be signaled at the slice level.

[0222] Reference Fig.13 , CC-ALF can be achieved by replacing the linear diamond filter ( Fig.13 (b)) is applied to the luma channel of each chroma component. The filter coefficients are sent to the APS with a scaling factor of 210 and are rounded for fixed point representation. The application of the filter can be controlled at a variable block size and is signaled by a context coding flag received for each block of samples. For each chroma component, the block size can be received at the slice level together with the CC-ALF enable flag. The block size (for chroma samples) can be 16×16, 32×32, 64×64, or 128×128.

[0223] In the following embodiments, a method of re-filtering or modifying the reconstructed chroma samples after ALF filtering based on the reconstructed luma samples will be proposed.

[0224] Embodiments of the present disclosure relate to filter on / off transmission and filter coefficient transmission between CC-ALF. As described above, the information (syntax elements) in the syntax table disclosed in the present disclosure can be included in the image / video information, can be configured / encoded in the encoding device and sent to the decoding device in the form of a bitstream. The decoding device can parse / decode the information (syntax elements) in the corresponding syntax table. The decoding device can perform picture / image / video decoding processing (specifically, for example, CCALF process) based on the decoded information. Hereinafter, this also applies to other embodiments.

[0225] According to an embodiment of the present disclosure, in order to determine whether to use (apply) CCALF, a sequence parameter set (SPS) may include a CCALF enable flag (sps_ccalf_enable_flag). The CCALF enable flag may be transmitted independently of an ALF enable flag (sps_alf_enabled_flag) used to determine whether to use (apply) ALF.

[0226] The following table shows an exemplary syntax of the SPS according to the present embodiment.

[0227] [Table 3]

[0228]

[0229]

[0230]

[0231]

[0232] The following table shows exemplary semantics of the CC-ALF enabled flag included in the table: The CC-ALF enabled flag may indicate (may be related to) whether CC-ALF is enabled.

[0233] [Table 4]

[0234]

[0235] In another example of this embodiment, when the CC-ALF enable flag is sent, the conditions for ChromaArrayType may be determined as shown in the following table.

[0236] [Table 5]

[0237]

[0238]

[0239]

[0240]

[0241] Referring to the above table, when ChromaArrayType is not 0, the SPS may include a CC-ALF enable flag. For example, when ChromaArrayType is not 0, the chroma format may not be monochrome, and in this case, the CCALF enable flag may be transmitted through the SPS.

[0242] The following table shows exemplary semantics of the CC-ALF enabled flags included in the table.

[0243] [Table 6]

[0244]

[0245] The image information may include an SPS. The SPS may include a first ALF enable flag (sps_alf_enabled_flag) regarding whether ALF is enabled. For example, based on a determination that a value of the first ALF enable flag is 1, the SPS may include a CCALF enable flag regarding whether cross component filtering is enabled.

[0246] In an embodiment of the present disclosure, general constraint information for defining profiles and levels may include a constraint flag for CC-ALF. In one example, the syntax of the general constraint information may be expressed as in the following table.

[0247] [Table 7]

[0248]

[0249] The following table shows exemplary semantics of the CC-ALF constraint flags included in the table.

[0250] [Table 8]

[0251]

[0252] The image information may include general constraint information. For example, the general constraint information may include a CCALF constraint flag for constraining cross component filtering based on the value of the CCALF enable flag included in the SPS. When the value of the CCALF constraint flag is 0, the CCALF constraint may not be applied. A CCALF constraint flag having a value of 1 may indicate that the value of the CCALF enable flag included in the SPS is 0.

[0253] According to an embodiment of the present disclosure, a slice_cross_component_alf_cb_enabled_flag flag may be added in slice units to determine whether CC-ALF is used. The slice_cross_component_alf_cb_enabled_flag flag may be transmitted when the sps_ccalf_enabled_flag flag is 1. Alternatively, the slice_ccalf_enable_flag flag may be transmitted when the sps_ccalf_enabled_flag flag is 1 and the ChromaArrayType is not 0.

[0254] For example, when the slice_cross_component_alf_cb_enabled_flag flag value is 1, the syntax slice_cross_component_alf_cb_reuse_temporal_layer_filter may be additionally transmitted. When this syntax value is 0, the syntax slice_cross_component_alf_cb_aps_id may be transmitted. The slice_cross_component_alf_cb_log2_control_size_minus4 syntax for the block size for CC-ALF may be transmitted.

[0255] The following table is an exemplary syntax of slice header information according to the above embodiment.

[0256] [Table 9]

[0257]

[0258]

[0259]

[0260]

[0261] The following table is an exemplary syntax of slice header information according to the above embodiment.

[0262] [Table 10]

[0263]

[0264]

[0265] According to an embodiment of the present disclosure, a slice_ccalf_enable_flag flag may be added in slice units to determine whether CC-ALF is used. The slice_ccalf_enable_flag flag may be transmitted when the sps_ccalf_enabled_flag flag is 1. Alternatively, the slice_ccalf_enable_flag flag may be transmitted when the sps_ccalf_enabled_flag flag is 1 and ChromaArrayType is not 0.

[0266] For example, when the slice_ccalf_enable_flag flag value is 1, slice_ccalf_chroma_idc syntax and slice_ccalf_aps_id_chroma syntax may be additionally transmitted. The slice_ccalf_chroma_idc syntax indicates whether Cb or Cr is applied, and the slice_ccalf_aps_id_chroma syntax indicates an APS id referenced by CC-ALF for a corresponding slice.

[0267] The following table shows the syntax of slice header information according to the present embodiment.

[0268] [Table 11]

[0269]

[0270]

[0271]

[0272]

[0273] The following table shows the semantics of the syntax elements included in the table.

[0274] [Table 12]

[0275]

[0276]

[0277] Alternatively, the syntax element slice_ccalf_chroma_idc in the above table may be described based on semantics as shown in the following table.

[0278] [Table 13]

[0279]

[0280] According to an embodiment of the present disclosure, CC-ALF may be performed at a slice level without an additional enabling flag (or information similar thereto). The following table shows some syntaxes of slice header information according to the present embodiment.

[0281] [Table 14]

[0282]

[0283] The following table shows the semantics of the syntax elements included in the table.

[0284] [Table 15]

[0285]

[0286] According to an embodiment of the present disclosure, the syntax element slice_ccalf_chroma_idc may be included in the slice header information based on the condition of ChromaArrayType. The following table shows some syntaxes of the slice header information according to the present embodiment.

[0287] [Table 16]

[0288]

[0289] In an example, the header information (slice_header()) includes a first flag (slice_cross_component_alf_cb_enabeld_flag or sh_cc_alf_cb_enabeld_flag) related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chroma samples and a second flag (slice_cross_component_alf_cr_enabeld_flag or sh_cc_alf_cr_enabeld_flag) related to whether CCALF can be used for the Cr color component of the filtered reconstructed chroma samples.

[0290] In an example, based on determination that a value of the first flag (slice_cross_component_alf_cb_enabeld_flag or sh_cc_alf_cb_enabeld_flag) is 1, the header information may include information (slice_cross_cb_aps_id_id or sh_cc_alf_cb_aps_id) about an identifier of an APS for deriving a cross component filter coefficient for a Cb color component.

[0291] In one example, based on determination that the value of the second flag (slice_cross_component_alf_cr_enabeld_flag or sh_cc_alf_cr_enabeld_flag) is 1, the header information may include information (slice_cross_component_id_cross_component_id_flag or sh_cc_alf_cr_aps_id) about an identifier of an APS for deriving a cross-component filter coefficient for a Cr color component.

[0292] According to an embodiment of the present disclosure, cross-component filter coefficients for CC-ALF may be transmitted through an APS. In one example, an APS for CC-ALF may be defined.

[0293] The following table shows an exemplary syntax of the APS according to the present embodiment.

[0294] [Table 17]

[0295]

[0296] In the above table, alf_data() may be referred to as general ALF data, and ccalf_data() may be referred to as CCALF data. ALF data may include general ALF data and / or CCALF data. In one example, ALF data may be the same as CCALF data. In another example, ALF data may be different from CCALF data.

[0297] The following table shows the semantics of the syntax elements included in the table.

[0298] [Table 18]

[0299]

[0300] The ALF data according to the embodiment of the present disclosure may be expressed using the syntax shown in the following table.

[0301] [Table 19]

[0302]

[0303] The semantics of the syntax elements included in the table can be expressed as shown in the following table.

[0304] [Table 20]

[0305]

[0306]

[0307]

[0308] In another example, the syntax related to the ALF data may be expressed as shown in the following table.

[0309] [Table 21]

[0310]

[0311] The semantics of the syntax elements included in the table can be shown in the following table.

[0312] [Table 22]

[0313]

[0314]

[0315] In the table, the order of exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] may be defined as one of the values ​​0 to 9.

[0316] In another example, the syntax related to the ALF data may be expressed as shown in the following table.

[0317] [Table 23]

[0318]

[0319] In the table, information about the absolute value of the filter coefficient and / or information about the sign of the filter coefficient may be expressed as a quadratic vector, a quadratic matrix, or a quadratic array (e.g., alf_cross_component_cb_coeff_abs[altIdx][j], alf_cross_component_cb_coeff_sign[altIdx][j], alf_cross_component_cr_coeff_abs[altIdx][j], alf_cross_component_cr_coeff_sign[altIdx][j]). In an example, information about the number of filters, information about the absolute value of the filter coefficient, and / or information about the sign of the filter coefficient may be included in general ALF data.

[0320] The semantics of the syntax elements included in the table can be shown in the following table.

[0321] [Table 24]

[0322]

[0323]

[0324] The order of exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] may be defined as one of the values ​​0 to 9.

[0325] The cross component filter coefficient may be referred to as a CCALF filter coefficient. The cross component filter coefficient may include a cross component filter coefficient for a Cb color component and a cross component filter coefficient for a Cr color component. The information about the value of the cross component filter coefficient for the Cb color component (Cr color component) may include information about the value of the cross component filter coefficient for the Cb color component (Cr color component) and / or information about the sign of the cross component filter coefficient for the Cb color component (Cr color component).

[0326] In one example, the ALF data included in the APS for deriving the cross-component filter coefficient for the Cb color component may include a Cb filter signal flag (alf_cross_component_cb_filter_signal_flag or alf_cc_cb_filter_signal_flag) related to whether the cross-component filter for the Cb color component is signaled. Based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficient for the Cb color component may include information related to the number of cross-component filters for the Cb color component (ccalf_cb_num_alt_filters_minus1 or alf_cc_cb_filters_signalled_minus1). Based on the information about the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficient for the Cb color component may include information about the absolute value of the cross-component filter coefficient for the Cb color component (alf_cross_component_cb_coeff_abs or alf_cc_cb_mapped_coeff_abs) and information about the sign of the cross-component filter coefficient for the Cb color component (alf_cross_component_cb_coeff_sign or alf_cc_cb_coeff_sign). The cross-component filter coefficient for the Cb color component (ccalfcoeff or ccalfapscoeff) may be derived based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component. For example, the information about the number of cross-component filters for the Cb color component may be zero-order exponential Golomb (0EG, ue(v) or ue(k)) coded.

[0327] In one example, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cr color component may include a Cr filter signal flag (alf_cross_component_cr_filter_signal_flag or alf_cc_cr_filter_signal_flag) related to whether the cross-component filter for the Cr color component is signaled. Based on the Cr filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cr color component may include information related to the number of cross-component filters for the Cr color component (ccalf_cr_num_alt_filters_minus1 or alf_cc_cr_filters_signalled_minus1). Based on the information about the number of cross-component filters for the Cr color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cr color component may include information about the absolute value of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_abs or alf_cc_cr_mapped_coeff_abs) and information about the sign of the cross-component filter coefficients for the Cr color component (alf_cross_component_cr_coeff_sign or alf_cc_cr_coeff_sign). The cross-component filter coefficients for the Cr color component (ccalfcoeff or ccalfapscoeff) may be derived based on the information about the absolute value of the cross-component filter coefficients for the Cr color component and the information about the sign of the cross-component filter coefficients for the Cr color component. For example, the information about the number of cross-component filters for the Cr color component may be zero-order exponential Golomb (0EG, ue(v) or ue(k)) coded.

[0328] According to an embodiment of the present disclosure, CC-ALF related information can be transmitted in CTU (block) units to control filter on / off of CC-ALF.

[0329] The following table shows an exemplary syntax of a coding tree unit according to the present embodiment.

[0330] [Table 25]

[0331]

[0332] The following table shows exemplary semantics of the syntax elements included in the table.

[0333] [Table 26]

[0334]

[0335]

[0336] In another example of this embodiment, the syntax of the coding tree unit can be expressed as the following table.

[0337] [Table 27]

[0338]

[0339]

[0340] The following table shows exemplary semantics of the syntax elements included in the table.

[0341] [Table 28]

[0342]

[0343] In an example, the image information may include information about a coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether a cross-component filter is applied to a current block of a Cb color component (ccalf_ctb_flag[0]) and / or information about whether a cross-component filter is applied to a current block of a Cr color component (ccalf_ctb_flag[1]). In addition, the information about the coding tree unit may include information about a filter set index of a cross-component filter applied to a current block of a Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about a filter set index of a cross-component filter applied to a current block of a Cr color component (ccalf_ctb_filter_alt_idx[1]).

[0344] Fig.14 and Fig.15 is a diagram schematically illustrating an example of a video / image encoding method and related components according to an embodiment of the present disclosure. Fig.14 The method disclosed in Figure 2 Specifically, for example, Fig.14 S1400 may be performed by the adder 250 of the encoding device, S1410 to S1440 may be performed by the filter 260 of the encoding device, and S1450 may be performed by the entropy encoder 240 of the encoding device. Fig.14 The method disclosed in may include the above-mentioned embodiments in the present disclosure.

[0345] Reference Fig.14, the encoding device may generate a reconstructed luma sample and a reconstructed chroma sample of the current block (S1400). The encoding device may generate a residual luma sample and / or a residual chroma sample. The encoding device may generate a reconstructed luma sample based on the residual luma sample, and may generate a reconstructed chroma sample based on the residual chroma sample.

[0346] In the example, the residual samples for the current block can be generated based on the original samples and the predicted samples of the current block. Specifically, the encoding device can generate the predicted samples of the current block based on the prediction mode. In this case, various prediction methods such as inter-frame prediction or intra-frame prediction disclosed in the present disclosure can be applied. The residual samples can be generated based on the predicted samples and the original samples.

[0347] In one example, the encoding device may generate residual luma samples. The residual luma samples may be generated based on the original luma samples and the predicted luma samples. In one example, the encoding device may generate residual chroma samples. The residual chroma samples may be generated based on the original chroma samples and the predicted chroma samples.

[0348] The encoding device may derive transform coefficients. The encoding device may derive transform coefficients based on a transform process for the residual samples. The encoding device may derive transform coefficients for residual luma samples (luminance transform coefficients) and / or transform coefficients for residual chroma samples (chroma transform coefficients). For example, the transform process may include at least one of DCT, DST, GBT, or CNT.

[0349] The encoding device may derive (quantized) transform coefficients. The encoding device may derive quantized transform coefficients based on a quantization process for the transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on a coefficient scanning order. The quantized transform coefficients may include quantized luminance transform coefficients and / or quantized chrominance transform coefficients.

[0350] The encoding device may generate residual information. The encoding device may generate residual information indicating (including) the quantized transform coefficient. The residual information may be generated by various encoding methods such as exponential Golomb, CAVLC, and CABAC.

[0351] The encoding device may generate prediction related information. The encoding device may generate prediction related information based on the prediction sample and / or the mode applied to the prediction sample. The prediction related information may include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0352] The encoding device may derive ALF filter coefficients for the ALF process (S1410). The ALF filter coefficients may include ALF luminance filter coefficients for reconstructed luminance samples and ALF chrominance filter coefficients for reconstructed chrominance samples. Filtered reconstructed luminance samples and / or filtered reconstructed chrominance samples may be generated based on the ALF filter coefficients.

[0353] The encoding device may generate ALF related information (S1420). The encoding device may generate ALF related information based on ALF filter coefficients. The encoding device derives ALF related parameters that can be applied to the filter on the reconstructed sample and generates ALF related information. For example, the ALF related information may include the ALF related information described above in the present disclosure.

[0354] The encoding device may derive a cross component filter (CCALF filter) and / or a cross component filter coefficient (CCALF filter coefficient) (S1430). The cross component filter and / or the cross component filter coefficient may be used in the CCALF process. The modified filtered reconstructed chroma samples may be generated based on the cross component filter and / or the cross component filter coefficient.

[0355] The encoding device may generate cross-component filtering related information (or CCFL related information) (S1440). In an example, the cross-component filtering related information may include information about the number of cross-component filters and information about cross-component filter coefficients. The cross-component filter may include a cross-component filter for the Cb color component and a cross-component filter for the Cr color component.

[0356] In an example, cross-component filtering related information may include a CCALF enable flag, a flag related to whether CCALF is enabled for a Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether a cross-component filter for a Cb (or Cr) color component is signaled, information about the number of cross-component filters for a Cb (or Cr) color component, information about the values ​​of the cross-component filter coefficients for a Cb (or Cr) color component, information about the absolute values ​​of the cross-component filter coefficients for a Cb (or Cr) color component, information about the signs of the cross-component filter coefficients for a Cb (or Cr) color component, and / or information about whether a cross-component filter is applied to a current block of a Cb (or Cr) color component in information about a coding tree unit (coding tree unit syntax).

[0357] The encoding device may encode the video / image information (S1450). The image information may include residual information and / or ALF related information. The encoded video / image information may be output in the form of a bitstream. The bitstream may be sent to the decoding device via a network or a storage medium.

[0358] The image / video information may include various information according to an embodiment of the present disclosure. For example, the image / video information may include information disclosed in at least one of Tables 1 to 28 above.

[0359] In an embodiment, the image information may include a first adaptive parameter set (APS) including first ALF data and a second APS including second ALF data. The first ALF data may include information about the number of cross component filters for the Cb color component. The second ALF data may include information about the number of cross component filters for the Cr color component.

[0360] In an embodiment, the image information may include header information and an adaptive parameter set (APS). The header information may be slice header information. The slice header information may include information related to an identifier of an APS containing ALF data. For example, cross-component filter coefficients may be derived based on the ALF data.

[0361] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a CCALF enable flag related to whether cross-component filtering is enabled. For example, based on the CC-ALF enable flag, ID information of an adaptive parameter set (APS) containing ALF data for deriving cross-component filter coefficients for CC-ALF may be derived.

[0362] In an embodiment, the image information may include general constraint information. For example, the general constraint information may include a CCALF constraint flag for constraining cross component filtering based on the value of a CCALF enable flag included in the SPS. When the value of the CCALF constraint flag is 0, the CCALF constraint may not be applied. A CCALF constraint flag having a value of 1 may indicate that the value of the CCALF enable flag included in the SPS is 0.

[0363] In an embodiment, the slice header information may include a first flag related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chroma samples, and a second flag related to whether CCALF is enabled for the Cr color component of the filtered reconstructed chroma samples.

[0364] In an embodiment, the image information may include an adaptive parameter set (APS). In an example, based on a determination that the value of the first flag is 1, the slice header information may include ID information of a first APS including first ALF data for deriving a cross-component filter coefficient for a Cb color component. In an example, based on a determination that the value of the first flag is 1, the slice header information may include ID information of a second APS including second ALF data for deriving a cross-component filter coefficient for a Cr color component.

[0365] In an embodiment, the first ALF data may include a Cb filter signal flag related to whether to signal a cross-component filter for the Cb color component. Based on the Cb filter signal flag, the first ALF data may include information related to the number of cross-component filters for the Cb color component. Based on the information related to the number of cross-component filters for the Cb color component, the first ALF data may include information about the absolute value of the cross-component filter coefficient for the Cb color component and information about the sign of the cross-component filter coefficient for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component can be derived.

[0366] In an embodiment, the information related to the number of cross-component filters for the Cb color component may be processed by zero-order exponential Golomb (0 th EG) encoding.

[0367] In an embodiment, the second ALF data may include a Cr filter signal flag related to whether to signal a cross-component filter for a Cr color component. Based on the Cr filter signal flag, the second ALF data may include information related to the number of cross-component filters for the Cr color component. Based on the information related to the number of cross-component filters for the Cr color component, the second ALF data may include information about the absolute value of the cross-component filter coefficient for the Cr color component and information about the sign of the cross-component filter coefficient for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0368] In an embodiment, the information related to the number of cross-component filters for the Cr color component may be processed by zero-order exponential Golomb (0 th EG) encoding.

[0369] In an embodiment, the image information may include information about a coding tree unit. The information about the coding tree unit may include information about whether a cross component filter is applied to a current block of a Cb color component and / or information about whether a cross component filter is applied to a current block of a Cr color component.

[0370] In an embodiment, the information about the coding tree unit may include information about a filter set index of a cross-component filter applied to the current block of the Cb color component, and / or information about a filter set index of a cross-component filter applied to the current block of the Cr color component.

[0371] Fig.16 and Fig.17 is a diagram schematically illustrating an example of a video / image decoding method and related components according to an embodiment of the present disclosure. Fig.16 The method disclosed in can be Figure 3 or Fig.17 Specifically, for example, Fig.16 S1600 may be performed by the entropy decoder 310 of the decoding device, S1610 may be performed by the adder 340 of the decoding device, and S1620 and S1630 may be performed by the filter 350 of the encoding device.

[0372] Reference Fig.16 , the decoding device can receive / obtain video / image information (S1600). The video / image information may include prediction related information and / or residual information. The decoding device may receive / obtain image / video information through a bitstream. Residual information may be generated by various coding methods such as exponential Golomb, CAVLC, and CABAC. In an example, the video / image information may also include CCAL related information. For example, CCALF related information may include a CCALF enable flag, a flag related to whether CCALF is enabled for a Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether a cross component filter for a Cb (or Cr) color component is signaled, information related to the number of cross component filters for a Cb (or Cr) color component, information about the absolute value of the cross component filter coefficient for a Cb (or Cr) color component, information about the sign of the cross component filter coefficient for a Cb (or Cr) color component, and / or information about whether a cross component filter is applied to a current block of a Cb (or Cr) color component in information about a coding tree unit (coding tree unit syntax).

[0373] The image / video information may include various information according to an embodiment of the present disclosure. For example, the image / video information may include information disclosed in at least one of Tables 1 to 28 above.

[0374] The decoding device may derive the transform coefficient. Specifically, the decoding device may derive the quantized transform coefficient based on the residual information. The quantized transform coefficient may have a one-dimensional vector form based on the coefficient scanning order. The decoding device may derive the transform coefficient based on the dequantization process of the quantized transform coefficient.

[0375] The decoding device may derive residual samples. The decoding device may derive residual samples based on transform coefficients. In addition, residual samples for the current block may be derived based on original samples and predicted samples of the current block.

[0376] The decoding device may perform prediction based on the image / video information and derive a prediction sample of the current block. The decoding device may derive a prediction sample of the current block based on the prediction mode information. The decoding device may determine whether to apply inter-frame prediction or intra-frame prediction to the current block based on the prediction mode information, and may perform prediction based on this.

[0377] The decoding device may generate / derive a reconstructed luma sample and / or a reconstructed chroma sample (S1610). The decoding device may generate / derive a reconstructed luma sample and / or a reconstructed chroma sample based on the image information. The decoding device may generate a reconstructed luma (or chroma) sample from the residual sample based on the image information. The luma component of the reconstructed sample may correspond to the reconstructed luma sample, and the chroma component of the reconstructed sample may correspond to the reconstructed chroma sample.

[0378] The decoding device may perform an adaptive loop filtering ALF process on the reconstructed chroma samples to generate filtered reconstructed chroma samples (S1620). In the ALF process, the decoding device may derive ALF filter coefficients for the ALF process of the reconstructed chroma samples. In addition, the decoding device may derive ALF filter coefficients for the ALF process of the reconstructed luminance samples. The ALF filter coefficients may be derived based on the ALF parameters in the ALF data included in the APS.

[0379] The decoding device may generate filtered reconstructed chroma samples. The decoding device may generate filtered reconstructed samples based on the reconstructed chroma samples and the ALF filter coefficients.

[0380] The decoding device may perform a cross-component filtering process on the filtered reconstructed chroma samples to generate modified filtered reconstructed chroma samples (S1630). In the cross-component filtering process, the decoding device may derive cross-component filter coefficients for cross-component filtering. The cross-component filter coefficients may be derived based on CCALF-related information included in the ALF data in the above-mentioned APS, and the identifier (ID) information of the corresponding APS may be included in the slice header (which may be notified by a signal through the slice header).

[0381] The decoding device can generate a modified filtered reconstructed chroma sample. The decoding device can generate a modified filtered reconstructed chroma sample based on the reconstructed luminance sample, the filtered reconstructed chroma sample and the cross-component filter coefficient. In an example, the decoding device can derive the difference between two of the reconstructed luminance samples and multiply the difference by the filter coefficient of one of the cross-component filter coefficients. Based on the result of the multiplication and the filtered reconstructed chroma sample, the decoding device can generate a modified filtered reconstructed chroma sample. For example, the decoding device can generate a modified filtered reconstructed chroma sample based on the sum between the product and one of the filtered reconstructed chroma samples.

[0382] In an embodiment, the image information may include an adaptive parameter set (APS) including ALF data, the ALF data including information about cross-component filtering. The ALF data may include information about the number of cross-component filters for cross-component filtering and information about cross-component filter coefficients. Modified filtered reconstructed chroma samples may be generated based on the filtered reconstructed chroma samples and the cross-component filter coefficients.

[0383] In an embodiment, the cross component filter may include a cross component filter for a Cb color component and a cross component filter for a Cr color component. The image information may include a first adaptive parameter set (APS) including first ALF data and a second APS including second ALF data. The first ALF data may include information about the number of cross component filters for the Cb color component. The second ALF data may include information about the number of cross component filters for the Cr color component.

[0384] In an embodiment, the image information may include header information and an adaptive parameter set (APS). The header information may be slice header information. The slice header information may include information related to an identifier of an APS containing ALF data. For example, cross-component filter coefficients may be derived based on the ALF data.

[0385] In an embodiment, the image information may include a sequence parameter set (SPS). The SPS may include a cross-component adaptive loop filter (CCALF) enable flag related to whether cross-component filtering is enabled. For example, based on the CC-ALF enable flag, the ID information of an adaptive parameter set (APS) containing ALF data for deriving cross-component filter coefficients for CC-ALF may be derived.

[0386] In an embodiment, the image information may include general constraint information. For example, the general constraint information may include a CCALF constraint flag for constraining cross component filtering based on the value of a CCALF enable flag included in the SPS. When the value of the CCALF constraint flag is 0, the CCALF constraint may not be applied. A CCALF constraint flag having a value of 1 may indicate that the value of the CCALF enable flag included in the SPS is 0.

[0387] In an embodiment, the slice header information may include a first flag related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chroma samples, and a second flag related to whether CCALF is enabled for the Cr color component of the filtered reconstructed chroma samples.

[0388] In an embodiment, the image information may include an adaptive parameter set (APS). In an example, based on a determination that the value of the first flag is 1, the slice header information may include ID information of a first APS, the first APS including first ALF data for deriving a cross-component filter coefficient for a Cb color component. In an example, based on a determination that the value of the first flag is 1, the slice header information may include ID information of a second APS including second ALF data for deriving a cross-component filter coefficient for a Cr color component.

[0389] In an embodiment, the first ALF data may include a Cb filter signal flag related to whether to signal a cross-component filter for a Cb color component. Based on the Cb filter signal flag, the first ALF data may include information related to the number of cross-component filters for the Cb color component. Based on the information related to the number of cross-component filters for the Cb color component, the first ALF data may include information about the absolute value of the cross-component filter coefficient for the Cb color component and information about the sign of the cross-component filter coefficient for the Cb color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cb color component and the information about the sign of the cross-component filter coefficient for the Cb color component, the cross-component filter coefficient for the Cb color component may be derived.

[0390] In an embodiment, the information about the number of cross-component filters for the Cb color component may be zero-order exponential-Golomb (0th EG) encoded.

[0391] In an embodiment, the second ALF data may include a Cr filter signal flag related to whether to signal a cross-component filter for a Cr color component. Based on the Cr filter signal flag, the second ALF data may include information related to the number of cross-component filters for the Cr color component. Based on the information related to the number of cross-component filters for the Cr color component, the second ALF data may include information about the absolute value of the cross-component filter coefficient for the Cr color component and information about the sign of the cross-component filter coefficient for the Cr color component. Based on the information about the absolute value of the cross-component filter coefficient for the Cr color component and the information about the sign of the cross-component filter coefficient for the Cr color component, the cross-component filter coefficient for the Cr color component can be derived.

[0392] In an embodiment, the information about the number of cross-component filters for the Cr color component may be zero-order exponential-Golomb (0th EG) encoded.

[0393] In an embodiment, the image information may include information about a coding tree unit. The information about the coding tree unit may include information about whether a cross component filter is applied to a current block of a Cb color component and / or information about whether a cross component filter is applied to a current block of a Cr color component.

[0394] In an embodiment, the information about the coding tree unit may include information about a filter set index of a cross-component filter applied to the current block of the Cb color component, and / or information about a filter set index of a cross-component filter applied to the current block of the Cr color component.

[0395] In the presence of residual samples for the current block, the decoding device may receive information about the residual for the current block. The information about the residual may include a transform coefficient for the residual sample. The decoding device may derive the residual sample (or residual sample array) for the current block based on the residual information. Specifically, the decoding device may derive the quantized transform coefficient based on the residual information. The quantized transform coefficient may have a one-dimensional vector form based on the coefficient scanning order. The decoding device may derive the transform coefficient based on the dequantization process for the quantized transform coefficient. The decoding device may derive the residual sample based on the transform coefficient.

[0396] The decoding device may generate a reconstructed sample based on the (intra-frame) prediction sample and the residual sample, and may derive a reconstructed block or a reconstructed picture based on the reconstructed sample. Specifically, the decoding device may generate a reconstructed sample based on the sum of the (intra-frame) prediction sample and the residual sample. Thereafter, as described above, if necessary, the decoding device may apply a loop filtering process (e.g., deblocking filtering and / or SAO process) to the reconstructed picture to improve the subjective / objective picture quality.

[0397] For example, the decoding device can obtain image information including all or some of the above information (or syntax elements) by decoding the bit stream or the encoded information. In addition, the bit stream or the encoded information can be stored in a computer-readable storage medium, or the above decoding method can be executed.

[0398] In the above-mentioned embodiment, the method is described based on a flow chart with a series of steps or frames. The present disclosure is not limited to the order of the above-mentioned steps or frames. Some steps or frames may occur simultaneously with other steps or frames as described above or in an order different from other steps or frames as described above. In addition, it will be understood by those skilled in the art that the steps shown in the above-mentioned flow chart are not exclusive, and additional steps may be included, or one or more steps in the flow chart may be deleted without affecting the scope of this document.

[0399] The method according to the above-mentioned embodiment of the present document can be implemented in the form of software, and the encoding device and / or decoding device according to the present document can be included in a device for performing image processing such as a TV, a computer, a smart phone, a set-top box, and a display device.

[0400] When the embodiments in this document are implemented in software, the above methods can be implemented as modules (processing, functions, etc.) that perform the above functions. The module can be stored in a memory and executed by a processor. The memory can be inside or outside the processor and can be connected to the processor by various known means. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices. The memory may include a read-only memory (ROM), a random access memory (RAM), flash memory, a memory card, a storage medium, and / or other storage devices. In other words, the embodiments described in this document can be implemented and executed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in each of the accompanying drawings can be implemented and executed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information about instructions or algorithms for the implementation can be stored in a digital storage medium.

[0401] In addition, the decoding device and the encoding device to which this document is applied may be included in a multimedia broadcast transmission / reception device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service provider, an over-the-top (OTT) video device, an Internet streaming service provider, a three-dimensional (3D) video device, a virtual reality (VR) device, an augmented reality (AR) device, an image phone video, a vehicle terminal (e.g., a vehicle (including an autonomous vehicle) terminal, an aircraft terminal or a ship terminal), and a medical video device, and may be used to process video signals and data signals. For example, an OTT video device may include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smart phone, a tablet PC, a digital video recorder (DVR), etc.

[0402] In addition, the processing method of applying this document can be generated in the form of a program executed by a computer and can be stored in a computer-readable recording medium. Multimedia data with a data structure according to the present disclosure can also be stored in a computer-readable recording medium. Computer-readable recording media include all kinds of storage devices that store data readable by a computer system. For example, computer-readable recording media may include BD, universal serial bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage device. In addition, computer-readable recording media include media implemented in the form of carrier waves (i.e., transmission via the Internet). In addition, the bit stream generated by the encoding method can be stored in a computer-readable recording medium or can be sent via a wired or wireless communication network.

[0403] In addition, the embodiments of this document can be implemented using a computer program product according to the program code, and the program code can be executed in a computer according to the embodiments of this document. The program code can be stored on a computer-readable carrier.

[0404] Fig.18 An example of a content streaming system to which embodiments of this document may be applied is shown.

[0405] Reference Fig.18 A content streaming system to which embodiments of this document are applied may generally include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0406] The encoding server compresses the content input from the multimedia input device (e.g., a smart phone, a camera, a camcorder, etc.) into digital data to generate a bit stream, and sends the bit stream to the streaming server. As another example, when the multimedia input device such as a smart phone, a camera, a camcorder, etc. directly generates a bit stream, the encoding server can be omitted.

[0407] A bitstream may be generated by applying the encoding method or the bitstream generating method of the embodiment of the present disclosure, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0408] The streaming server sends multimedia data to the user device through the web server based on the user's request, and the web server serves as a medium for notifying the user of the service. When the user requests the desired service from the web server, the web server passes the request to the streaming server, and the streaming server sends the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control the command / response between the devices in the content streaming system.

[0409] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from an encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time.

[0410] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation, tablet PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital TVs, desktop 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 distributed.

[0411] 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 processed in a distributed manner.

[0412] The claims described herein may be combined in various ways. For example, the technical features of the method claims of this document may be combined and implemented as a device, and the technical features of the device claims of this document may be combined and implemented as a method. In addition, the technical features of the method claims of this document and the technical features of the device claims of this document may be combined to be implemented as a device, and the technical features of the method claims of this document and the technical features of the device claims of this document may be combined and implemented as a method.

Claims

1. A decoding device for image decoding, the decoding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: receiving image information via a bit stream; generating a reconstructed luminance sample and a reconstructed chrominance sample based on the image information; performing an adaptive loop filtering (ALF) process on the reconstructed chroma samples to generate filtered reconstructed chroma samples; as well as performing a cross-component filtering process on the filtered reconstructed chroma samples to generate modified filtered reconstructed chroma samples, The image information includes an adaptive parameter set APS including ALF data, and the ALF data includes information about cross-component filtering, wherein the ALF data includes information about the number of cross-component filters for the cross-component filtering and information about cross-component filter coefficients, and Wherein the modified filtered reconstructed chroma samples are generated based on the filtered reconstructed chroma samples and the cross-component filter coefficients.

2. A coding device for image coding, the coding device comprising: Memory; as well as at least one processor, the at least one processor connected to the memory, the at least one processor configured to: generating a reconstructed sample including a reconstructed luma sample and a reconstructed chroma sample of a current block in a current picture; deriving ALF filter coefficients for an adaptive loop filtering (ALF) process; generating ALF related information based on the ALF filter coefficients; deriving cross-component filter coefficients for a cross-component filtering process; generating cross-component filtering related information based on the cross-component filter coefficients; as well as encoding the image information including the information for generating the reconstructed samples, the ALF related information and the cross component filtering related information, The cross-component filtering related information includes information about the number of cross-component filters and information about cross-component filter coefficients.

3. A device for sending data for an image, the device comprising: at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on the following steps: generating reconstructed samples including reconstructed luminance samples and reconstructed chrominance samples of a current block in a current picture, deriving ALF filter coefficients for an adaptive loop filtering ALF process, generating ALF related information based on the ALF filter coefficients, deriving cross-component filter coefficients for a cross-component filtering process, generating cross-component filtering related information based on the cross-component filter coefficients, and encoding image information to generate a bitstream, wherein the image information includes information for generating the reconstructed samples, the ALF related information, and the cross-component filtering related information; and a transmitter configured to transmit said data including said bit stream, The cross-component filtering related information includes information about the number of cross-component filters and information about cross-component filter coefficients.

4. A non-transitory computer-readable storage medium storing a bit stream generated by an image encoding method, the image encoding method comprising the following steps: Determine the prediction mode of the current block; generating a prediction sample of the current block based on the prediction mode; Generate a reconstructed sample including a reconstructed luma sample and a reconstructed chroma sample of the current block based on the predicted sample; deriving cross-component filter coefficients for a cross-component filtering process; generating cross-component filtering related information based on the cross-component filter coefficients; as well as encoding image information including information for generating the reconstructed samples and information related to the cross-component filtering, The cross-component filtering related information includes information about the number of cross-component filters and information about cross-component filter coefficients.

Images