Image Compilation Device and Method Based on In-Loop Filtering

Abstract

According to an embodiment of this document, a method for improving the accuracy of in-loop filtering is proposed. In an example, the filtering accuracy of a chrominance block can be improved on the basis of a luminance block by performing a cross-component adaptive loop filtering process.

Description

Technical Field

[0001] The present disclosure relates to an image encoding apparatus and method based on in-loop filtering. Background Art

[0002] Recently, there has been 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 compared to existing image / video data. 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 the transmission cost and storage cost.

[0003] In addition, there has been an increasing interest in and demand for virtual reality (VR) and augmented reality (AR) content and immersive media such as holograms, and there has also been an increasing broadcast of images / videos having characteristics different from real images (such as game images).

[0004] Therefore, highly efficient image / video compression techniques are needed to effectively compress, transmit, store, or reproduce information of high-resolution, high-quality images / videos having various characteristics as described above.

[0005] In addition, a cross-component adaptive loop filtering (CCALF) process is performed to improve compression efficiency and enhance subjective / objective visual quality, and methods for improving the data transmission efficiency of the CCALF process are being discussed. Summary of the Invention

[0006] The present disclosure provides a method and apparatus for improving image / video encoding efficiency.

[0007] The present disclosure also provides an efficient filtering application method and apparatus.

[0008] The present disclosure also provides an efficient ALF application method and apparatus.

[0009] According to an embodiment of the present disclosure, a filtering process may be performed on reconstructed chrominance samples based on reconstructed luminance samples.

[0010] According to an embodiment of the present disclosure, the filtered reconstructed chrominance samples may be modified based on the reconstructed luminance samples.

[0011] According to an embodiment of the present disclosure, information on whether CCALF is available may be signaled in the SPS.

[0012] According to an embodiment of the present disclosure, information on values of cross-component filter coefficients may be derived from ALF data (normal ALF data or CCALF data).

[0013] According to an embodiment of the present disclosure, the identifier (ID) information of the APS including ALF data for deriving cross-component filter coefficients in a slice may be signaled.

[0014] According to an embodiment of the present disclosure, information on the filter set index of CCALF may be signaled in units of CTUs (blocks).

[0015] According to an embodiment of this document, a video / image decoding method performed by a decoding device is provided.

[0016] According to an embodiment of this document, a decoding device for performing video / image decoding is provided.

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

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

[0019] According to an 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 of the embodiments of this document is stored.

[0020] According to an embodiment of this document, a computer-readable digital storage medium is provided, in which encoded information or encoded video / image information for causing a decoding device to execute the video / image decoding method disclosed in at least one of the embodiments of this document is stored.

[0021] Advantageous Effects

[0022] According to an embodiment of this document, the overall image / video compression efficiency may be improved.

[0023] According to an embodiment of this document, the subjective / objective visual quality may be improved through efficient filtering.

[0024] According to an embodiment of the present disclosure, the ALF process may be efficiently performed and the filtering performance may be improved.

[0025] According to an embodiment of the present disclosure, the reconstructed chrominance samples filtered based on the reconstructed luminance samples may be modified to improve the picture quality and coding accuracy of the chrominance component of the decoded picture.

[0026] According to an embodiment of the present disclosure, the CCALF process may be efficiently performed.

[0027] According to an embodiment of the present disclosure, the ALF-related information may be efficiently signaled.

[0028] According to an embodiment of the present disclosure, CCALF-related information can be signaled efficiently.

[0029] According to an embodiment of the present disclosure, ALF and / or CCALF can be adaptively applied in units of pictures, slices, and / or coding blocks.

[0030] According to an embodiment of this document, when CCALF is used in an encoding and decoding method and apparatus for still images or videos, the filter coefficients for CCALF and the on / off transmission method in a block or CTU unit can be improved, thereby improving the encoding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 An example of a video / image coding system to which embodiments of the present disclosure can be applied is schematically shown.

[0032] Figure 2 FIG. schematically illustrates the configuration of a video / image encoding apparatus to which embodiments of the present disclosure can be applied.

[0033] Figure 3 FIG. schematically illustrates the configuration of a video / image decoding apparatus to which embodiments of the present disclosure can be applied.

[0034] Figure 4 An exemplary hierarchical structure of coded images / videos is shown.

[0035] Figure 5 FIG. is a flowchart illustrating a method for reconstructing an intra-predicted block in an encoding apparatus.

[0036] Figure 6 FIG. is a diagram illustrating an intra-predictor in an encoding apparatus.

[0037] Figure 7 FIG. is a flowchart illustrating a method for reconstructing an intra-predicted block in a decoding apparatus.

[0038] Figure 8 FIG. is a diagram illustrating an intra-predictor in a decoding apparatus.

[0039] Figure 9 FIG. is a flowchart for describing a method for reconstructing an intra-predicted block in an encoding apparatus.

[0040] Figure 10 FIG. is a diagram illustrating an inter-predictor in an encoding apparatus.

[0041] Figure 11 FIG. is a flowchart for describing a method for reconstructing an inter-predicted block in a decoding apparatus.

[0042] Figure 12 It is a diagram of an inter - frame predictor in a picture decoding device.

[0043] Figure 13 It is a diagram showing an example of the shape of an ALF filter.

[0044] Figure 14 It is a diagram for describing a virtual boundary applied to a filtering process according to an embodiment of the present disclosure.

[0045] Figure 15 It is a diagram showing an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure.

[0046] Figure 16 It is a diagram for describing a cross - component adaptive loop filtering (CC - ALF(CCALF)) process according to an embodiment of the present disclosure.

[0047] Figure 17 and Figure 18 It is a diagram schematically showing an example of a video / image decoding method and related components according to an embodiment of the present disclosure.

[0048] Figure 19 and Figure 20 It is a diagram schematically showing an example of an image / video decoding method and related components according to an embodiment of the present disclosure.

[0049] Figure 21 It is a diagram showing an example of a content streaming system to which the embodiments disclosed in the present disclosure can be applied. Detailed implementation manners

[0050] This document can be modified in various ways and can have various embodiments, and specific embodiments will be illustrated and described in detail in the accompanying drawings. However, this is not intended to limit this document to specific embodiments. Commonly used terms in this specification are used to describe specific embodiments and do not limit the technical spirit of this document. Singular expressions include plural expressions unless clearly stated otherwise in the context. Terms such as "including" or "having" in this specification should be understood to indicate the presence of the features, quantities, steps, operations, elements, parts, or combinations thereof described in the specification, rather than excluding the presence or possibility of adding one or more other features, quantities, steps, operations, elements, parts, or combinations thereof.

[0051] Meanwhile, for ease of description of the descriptions related to different feature functions, the elements in the drawings described in this document are illustrated independently. This does not mean that each element is implemented as a separate hardware or a separate software. For example, at least two elements can be combined to form a single element, or a single element can be divided into multiple elements. Embodiments in which elements are combined and / or separated are also included within the scope of the rights of this document, unless it deviates from the essence of this document.

[0052] Hereinafter, the preferred embodiments of this document will be described more specifically with reference to the drawings. Hereinafter, in the drawings, the same reference numerals are used for the same elements, and the repeated description of the same elements is omitted.

[0053] This document relates to video / image compilation. For example, the methods / embodiments disclosed in this document may be related to the General Video Compilation (VVC) standard (ITU-T Rec. H.266), the next-generation video / image compilation standard after VVC, or other video compilation-related standards (e.g., the High Efficiency Video Compilation (HEVC) standard (ITU-T Rec. H.265), the Essential Video Compilation (EVC) standard, and the AVS2 standard).

[0054] This document presents various embodiments of video / image compilation, and the embodiments can be executed in combination with each other unless otherwise stated.

[0055] In this document, video may mean a collection of a series of images over time. A picture generally means a unit representing one image in a specific time region, and a slice / tile is a unit that forms part of a picture in compilation. A slice / tile can include one or more Compilation Tree Units (CTUs). A picture can be composed of one or more slices / tiles. A picture can be composed of one or more tile groups. A tile group can include one or more tiles.

[0056] A pixel or pel can mean the smallest unit that constitutes a picture (or image). Additionally, "sample" can be used as a term corresponding to a pixel. A sample generally can represent a pixel or the value of a pixel, and can represent only the pixel / pixel value of the luminance component, or only the pixel / pixel value of the chrominance component. Furthermore, a sample can mean a pixel value in the spatial domain, or in the case of transforming such a pixel value to the frequency domain, can mean a transform coefficient in the frequency domain.

[0057] 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, terms such as unit and terms like block, area, etc. may be used interchangeably. Generally, an M×N block may include a set (or array) of samples (or sample arrays) or transform coefficients consisting of M columns and N rows.

[0058] In this document, the terms " / " and "," are interpreted as indicating "and / or". For example, the expression "A / B" is interpreted as indicating "A and / or B", and "A, B" is interpreted as indicating "A and / or B". Additionally, "A / B / C" may mean "at least one of A, B, and / or C". Moreover, "A, B, C" may mean "at least one of A, B, and / or C".

[0059] Furthermore, in this document, the term "or" should be interpreted as indicating "and / or". For example, the expression "A or B" may mean 1) only A, 2) only B, and / or 3) both A and B. In other words, the term "or" in this document may mean "additionally or alternatively".

[0060] In this specification, "at least one of A and B" may mean "only A", "only B", or "both A and B". Additionally, in this specification, the expression "at least one of A or B" or "at least one of A and / or B" may be interpreted the same as "at least one of A and B".

[0061] Moreover, in this specification, "at least one of A, B, and C" may mean "only A", "only B", "only C", or "any combination of A, B, and C". Additionally, "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".

[0062] Furthermore, the parentheses used in this specification may mean "for example". Specifically, in the case of the expression "prediction (intra prediction)", it may indicate that "intra prediction" is presented as an example of "prediction". In other words, the term "prediction" in this specification is not limited to "intra prediction" and may indicate that "intra prediction" is presented as an example of "prediction". Additionally, even in the case of the expression "prediction (i.e., intra prediction)", it may indicate that "intra prediction" is presented as an example of "prediction".

[0063] In this specification, technical features separately explained in one drawing may be implemented separately or may be implemented simultaneously.

[0064] Figure 1Schematically illustrate an example of a video / image compilation system to which embodiments of this document can be applied.

[0065] Reference Figure 1 , the video / image compilation system may include a source device and a receiving device. The source device may deliver encoded video / image information or data to the receiving device in the form of a file or a 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 may obtain video / images through processes such as capturing, synthesizing, or generating video / images. The video source may include a video / image capture device and / or a video / image generation device. For example, the video / image capture device may include one or more cameras, a video / image archive including previously captured video / images, etc. For example, the video / image generation device may include a computer, a tablet computer, and a smart phone, and may (electronically) generate video / images. For example, virtual video / images may be generated by a computer or the like. In this case, the video / image capture process may be replaced by a process of generating relevant data.

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

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

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

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

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

[0073] Reference Figure 2 , the encoding device 200 includes an image splitter 210, a predictor 220, a residual processor 230, 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, an inverse quantizer 234, and an inverse transformer 235. The residual processor 230 may further 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 splitter 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 a processor). Additionally, 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 the memory 270 as an internal / external component.

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

[0075] In some cases, a unit may be used interchangeably with terms such as a block or a region. In general, an M×N block may represent a set of samples or transformation coefficients composed of M columns and N rows. A sample may generally represent a pixel or a pixel value, which may be a pixel / pixel value representing only a luminance component or a pixel / pixel value representing only 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 may 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 may send the generated residual signal to the transformer 232. The predictor 220 may perform prediction on a processing target block (hereinafter referred to as “current block”), and may generate a prediction block including prediction samples for the current block. The predictor 220 may determine whether to apply intra prediction or inter prediction in units of the current block or CU. The predictor may generate and transmit various information about the prediction, such as prediction mode information described later in the explanation of each prediction mode, to the entropy encoder 240. The information about the prediction may be encoded by the entropy encoder 240 and output in the form of a bitstream.

[0077] The intra predictor 222 can predict the current block by referring to samples in the current picture. Depending on the prediction mode, the samples referred to may be located near the current block or may be separated. In intra prediction, the prediction mode may include a plurality of non - directional modes and a plurality of directional modes. For example, the non - directional modes may include the DC mode and the planar mode. For example, depending on the level of detail of the prediction direction, the directional modes 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 according to settings. The intra predictor 222 can determine the prediction mode applied to the current block by using the prediction mode applied to neighboring blocks.

[0078] The inter predictor 221 can derive the predicted 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 transmitted in the inter - 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 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 - prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter - prediction, 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 predictor 221 can configure a motion information candidate list based on 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 - prediction can be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter predictor 221 can use the motion information of neighboring blocks as the motion information of the current block. In the skip mode, different from the merge mode, the residual signal may not be sent. In the case of the motion vector prediction (MVP) mode, the motion vector of the neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0079] Predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may not only apply intra prediction or inter prediction to predict a block, but may also apply intra prediction and inter prediction simultaneously. This may be referred to as combined inter and intra prediction (CIIP). In addition, the predictor may perform intra block copy (IBC) for prediction of a block. Intra block copy may be used for content image / video compilation such as games, for example, screen content compilation (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction at points where reference blocks are derived in the current picture. That is, IBC may use at least one of the inter prediction techniques described in this document.

[0080] The prediction signal generated by the inter predictor 221 and / or the intra predictor 222 may be used to generate a reconstructed signal or to generate a residual signal. The transformer 232 may generate transform coefficients 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 non-linear transform (CNT). Here, GBT means a transform obtained from a graph when relationship information between pixels is represented by the graph. CNT means a transform generated based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to a square pixel block having the same size, or may be applied to a block having a variable size rather than a square.

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

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

[0083] Meanwhile, luminance mapping and chrominance scaling (LMCS) can be applied during picture encoding and / or reconstruction.

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

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

[0086] The DPB of memory 270 can store the modified reconstructed picture to be used as a reference picture in inter-frame predictor 221. Memory 270 can store the motion information of the blocks from which the motion information in the current picture is derived (or encoded) and / or the motion information of the blocks in the already reconstructed pictures. The stored motion information can be sent to inter-frame predictor 221 and used as the motion information of spatially adjacent blocks or temporally adjacent blocks. Memory 270 can store the reconstructed samples of the reconstructed blocks in the current picture and can pass the reconstructed samples to intra-frame predictor 222.

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

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

[0089] When the input includes a bitstream of video / image information, the decoding device 300 may reconstruct an image corresponding to the processing of the video / image information in the Figure 2 encoding device. For example, the decoding device 300 may derive units / blocks based on the block partitioning related information obtained from the bitstream. The decoding device 300 may use the processor applied in the encoding device to perform decoding. Thus, the decoding processor may be, for example, a compilation unit, and the compilation unit may be partitioned from the compilation tree unit or the largest compilation unit according to a quadtree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units may be derived from the compilation unit. The reconstructed image signal decoded and output by the decoding device 300 may be reproduced by a reproduction device.

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

[0091] The dequantizer 321 can dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 321 can rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement can be performed based on the coefficient scan order executed in the encoding device. The dequantizer 321 can perform dequantization on the quantized transform coefficients by using quantization parameters (e.g., quantization step information) and obtain the transform coefficients.

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

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

[0094] The predictor 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 simultaneously. This can be referred to as combined inter and intra prediction (CIIP). In addition, the predictor can perform intra block copy (IBC) for prediction of a block. Intra block copy can be used for content image / video compilation such as games, for example, screen content compilation (SCC). IBC basically performs prediction in the current picture, but can be performed similar to inter prediction because a 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 predictor 331 can predict the current block by referring to samples in the current picture. The samples referred to can be located near the current block or can be located at separate positions according to the prediction mode. In intra prediction, the prediction mode can include a plurality of non-directional modes and a plurality of directional modes. The intra predictor 331 can determine the prediction mode applied to the current block by using the prediction mode applied to neighboring blocks.

[0096] The inter - frame predictor 332 can 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 transmitted 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 neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter - frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter - frame prediction, neighboring blocks can 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 can configure a motion information candidate list based on neighboring blocks and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter - frame prediction can be performed based on various prediction modes, and the information about the prediction can include information indicating the mode used for the inter - frame prediction of 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 there is no residual for the block to be processed, such as when the skip mode is applied, the prediction block can be used as the reconstructed block.

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

[0099] Meanwhile, luminance mapping and chrominance scaling (LMCS) can be applied during the picture decoding process.

[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). Various filtering methods can include, for example, de - blocking 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 blocks from which the motion information in the current picture is derived (or decoded) and / or the motion information of the blocks in the already - reconstructed pictures. The stored motion information can be sent to the inter - frame predictor 332 so as to be used as the motion information of spatially - adjacent blocks or temporally - adjacent blocks. 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 this specification, the embodiments explained in the predictor 330, de - quantizer 321, inverse transformer 322, and filter 350 of the decoding device 300 can be applied to or correspond to the predictor 220, de - quantizer 234, inverse transformer 235, and filter 260 of the encoding device 200 in the same way respectively.

[0103] As described above, in video coding, prediction is performed to improve the compression efficiency. Through this operation, a prediction block including prediction samples for the current block (i.e., the block to be coded) can be generated. Here, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived identically in the encoding device and the decoding device, and the encoding device decodes the information (residual information) regarding the residual between the original block and the prediction block (rather than the original sample values of the original block itself). Signaling to the device can improve the image coding efficiency. 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 through transformation processing and quantization processing. For example, the encoding device can derive a residual block between the original block and the prediction block, perform transformation processing on the residual samples (residual sample array) included in the residual block to derive transform coefficients, and then derive quantized transform coefficients by performing quantization processing on the transform coefficients to signal the residual - related information (via the bitstream) to the decoding device. Here, the residual information can include value information, position information, transformation technique, transformation core, and quantization parameters, etc., of the quantized transform coefficients. The decoding device can perform de - quantization / inverse - transformation processing based on the residual information and derive the residual samples (or residual block). The decoding device can generate a reconstructed picture based on the prediction block and the residual block. The encoding device can also de - quantize / inverse - transform the quantized transform coefficients for inter - frame prediction reference of subsequent pictures to derive a residual block and generate a reconstructed picture 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 coefficients may be referred to as transform coefficients. When transform / inverse transform is omitted, the transform coefficients may be referred to as coefficients or residual coefficients, or, for the sake of uniformity of expression, may still be referred to as transform coefficients.

[0106] In this document, the quantized transform coefficients and the transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, the residual information may include information about the transform coefficients, and the information about the transform coefficients may be signaled by the residual coding syntax. The transform coefficients may be derived based on the residual information (or the information about the transform coefficients), and the scaled transform coefficients may be derived by inverse-transforming (scaling) the transform coefficients. The residual samples may be derived based on the inverse-transform (transform) of the scaled transform coefficients. This may also be applied / expressed in other parts of this document.

[0107] The predictor of an encoding device / decoding device may derive a prediction sample by performing inter-frame prediction in units of blocks. Inter-frame prediction may be 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 applying inter-frame prediction to a current block, a prediction block (prediction sample array) for the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. Here, in order to reduce the amount of motion information transmitted in an inter-frame prediction mode, the motion information of the current block may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the 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, 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, a motion information candidate list may be configured based on neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) may be signaled to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the 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, different from the merge mode, a residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector 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-frame 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. The prediction based on the L0 motion vector may be referred to as L0 prediction, the prediction based on the L1 motion vector may be referred to as L1 prediction, and the 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 the motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may indicate the motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include pictures earlier than the current picture in the output order as reference pictures, and the reference picture list L1 may include pictures later than the current picture in the output order. The previous pictures may be referred to as forward (reference) pictures, and the subsequent pictures may be referred to as backward (reference) pictures. The reference picture list L0 may also include pictures later than the current picture in the output order as reference pictures. In this case, the previous pictures may be indexed first in the reference picture list L0, and the subsequent pictures 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 pictures may be indexed first in the reference picture list 1, and the previous pictures may be indexed later. The output order may correspond to the picture order count (POC) order.

[0109] Figure 4 Exemplarily shows the hierarchical structure of the compiled image / video.

[0110] Reference Figure 4 , the compiled image / video is divided into a video coding layer (VCL) that processes the image / video and its own decoding process, a subsystem that transmits and stores the compiled information, and a 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) may be generated, or parameter sets including a picture parameter set (PSP), a sequence parameter set (SPS), and a video parameter set (VPS), or supplementary enhancement information (SEI) messages additionally required for the image decoding process may be generated.

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

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

[0114] The aforementioned VCL NAL units and non-VCL NAL units can be sent over a network by attaching header information according to the data standards of the subsystem. For example, the NAL units can be transformed into a data format of a predetermined standard such as the H.266 / VVC file format, Real-Time Transport Protocol (RTP), Transport Stream (TS), etc., and sent over various networks.

[0115] As described above, the NAL unit can be specified using the NAL unit type according to the RBSP data structure included in the corresponding NAL unit, and information about the NAL unit type can be stored and signaled in the 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 an image (slice data). The VCL NAL unit types can be classified according to the nature and type of the pictures included in the VCL NAL units, and the non-VCL NAL unit types can be classified according to the type of the parameter sets.

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

[0118] - APS (Adaptive Parameter Set) NAL unit: The type for NAL units including APS

[0119] - DPS (Decoding Parameter Set) NAL unit: The type for NAL units including DPS

[0120] - VPS (Video Parameter Set) NAL unit: The type for NAL units including VPS

[0121] -SPS (Sequence Parameter Set) NAL unit: The type of NAL unit used to include SPS

[0122] -PPS (Picture Parameter Set) NAL unit: The type of NAL unit used to include PPS

[0123] -PH (Picture Header) NAL unit: The type of NAL unit used to include PH

[0124] The aforementioned NAL unit types may have syntax information for the NAL unit type and may store and signal the syntax information 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] Meanwhile, 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 the multiple slices (slice header 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 used interchangeably or replaced with tile groups. Additionally, in this document, slice headers may be used interchangeably or replaced with tile 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 the compiled video sequence (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 by the encoding device and signaled to the decoding device in the form of a bitstream includes not only information related to partitions in the picture, intra / inter prediction information, residual information, in-loop filtering information, etc., but also information included in the slice header, information included in APS, information included in PPS, information included in SPS, and / or information included in VPS.

[0128] Meanwhile, in order to compensate for the difference between the original image and the reconstructed image caused by errors occurring during compression encoding such as quantization, an in-loop filtering process may be performed on the reconstructed samples or the reconstructed picture as described above. As described above, the in-loop filtering may be performed by the filter of the encoding device and the filter of the 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. 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 may be generated based on intra prediction / inter prediction for each block, and a reconstructed picture including the reconstructed blocks may be generated. When the current picture / slice is an I picture / slice, the blocks included in the current picture / slice may be reconstructed only based on intra prediction. Meanwhile, when the current picture / slice is a P or B picture / slice, the blocks included in the current picture / slice may be reconstructed based on intra prediction or inter prediction. In this case, intra prediction may be applied to some of the blocks in the current picture / slice, and inter prediction may be applied to the remaining blocks.

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

[0131] However, some of the neighboring reference samples of the current block may still not be decoded or available. In this case, the decoder may 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 may be configured by interpolation of the available samples.

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

[0134] Figure 5 is a flowchart of a block reconstruction method based on intra prediction in an encoding device. Figure 6 is a diagram of an inter predictor in an encoding device.

[0135] S500 may be executed by the intra predictor 222 of the encoding device, and S510 to S530 may be executed by the residual processor 230 of the encoding device. Specifically, S510 may be executed by the subtractor 231 of the encoding device, S520 may be executed by the transformer 232 and quantizer 233 of the encoding device, and S530 may be executed by the dequantizer 234 and inverse transformer 235 of the encoding device. In S500, the prediction information may be derived by the inter predictor 222 and encoded by the entropy encoder 240. The residual information may be derived through S510 and S520 and encoded by the entropy encoder 240. The residual information is information about the residual samples. The residual information may include information about the quantization transform coefficients for the residual samples. As described above, the residual samples may be derived as transform coefficients by the transformer 232 of the encoding device, and the transform coefficients may be derived as quantization transform coefficients by the quantizer 233. The information about the quantization transform coefficients may be encoded by the entropy encoder 240 through a residual compilation process.

[0136] The encoding device performs intra prediction for the current block (S500). 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 processes of determining the intra prediction mode, deriving the neighboring reference samples, and generating the prediction samples may be performed simultaneously, or 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 222-1, a reference sample derivation unit 222-2, and a prediction sample derivation unit 222-3, and may determine the intra prediction mode / type for the current block in the prediction mode / type determiner 222-1, derive the neighboring reference samples of the current block in the reference sample derivator 222-2, and derive the motion samples of the current block from the prediction sample derivator 222-3. At the same time, although not shown, when performing the prediction sample filtering process to be described later, the intra predictor 222 may also include a prediction sample filter unit (not shown). The encoding device may determine a mode to be applied to the current block from among a plurality of intra prediction modes. The encoding device may compare the RD costs for the intra prediction modes and determine the best intra prediction mode for the current block.

[0137] At the same time, the encoding device may perform a prediction sample filtering process. The prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered through the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0138] The encoding device derives residual samples for the current block based on the prediction samples (S510). The encoding device may compare the prediction samples in the original samples of the current block based on the phase and derive the residual samples.

[0139] The encoding device may transform / quantize the residual samples to derive quantized transform coefficients (S520), and then dequantize / inverse-transform the quantized transform coefficients again to derive (modified) residual samples (S530). The reason for performing dequantization / inverse-transformation again after transformation / quantization is to derive the same residual samples as the residual samples derived from the decoding device as described above.

[0140] The encoding device may generate a reconstructed block including the reconstructed samples of the current block based on the prediction samples and the (modified) residual samples (S540). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0141] As described above, the encoding device may encode image information including prediction information regarding intra prediction (e.g., prediction mode information indicating a prediction mode) and residual information regarding intra and residual samples, and output the encoded image information in the form of a bitstream. The residual information may include residual compilation syntax. The encoding device may perform transform / quantization on the residual samples to derive quantized transform coefficients. The residual information may include information regarding the quantized transform coefficients.

[0142] Figure 7 is a flowchart illustrating a block reconstruction method based on intra prediction in a decoding device. Figure 8 is a diagram of an intra predictor in a decoding device.

[0143] The decoding device may perform operations corresponding to those performed by the encoding device.

[0144] S700 to S720 may be performed by the intra predictor 331 of the decoding device, and the prediction information of S700 and the residual information of S730 may be obtained by the entropy decoder 310 of the decoding device from the bitstream. 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 transform coefficients by performing dequantization based on the quantized transform coefficients derived based on the residual information, and the inverse transformer 322 of the residual processor may derive residual samples for the current block by performing an inverse transform on the transform coefficients. S740 may be performed by the adder 340 or the reconstructor of the decoding device.

[0145] Specifically, the decoding device may derive an intra prediction mode for the current block based on the received prediction mode information (S700). The decoding device may derive neighboring reference samples of the current block (S710). The decoding device generates prediction samples in the current block based on the intra prediction mode and the neighboring reference samples (S720). In this case, the decoding device may perform a prediction sample filtering process. The prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered through the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0146] The decoding device generates residual samples for the current block based on the received residual information (S730). The decoding device may generate reconstruction samples for the current block based on the prediction samples and the residual samples, and derive a reconstruction block including the reconstruction samples (S740). A reconstructed picture for the current picture may be generated based on the reconstruction block.

[0147] Here, the intra predictor 331 of the decoding device may include a prediction mode / type determiner 331-1, a reference sample derivator 331-2, and a predicted sample derivator 331-3. The prediction mode / type determiner 331-1 may determine an intra prediction mode for a current block based on prediction mode information obtained from the entropy decoder 310 of the decoding device. The reference sample derivator 331-2 may derive neighboring reference samples of the current block, and the predicted sample derivator 331-3 may derive predicted samples of the current block. Meanwhile, although not shown, when performing the above-described predicted sample filtering process, the intra predictor 331 may further include a predicted sample filter unit (not shown).

[0148] The prediction information may include intra prediction mode information and / or intra prediction type information. The intra prediction mode information may include, for example, flag information (e.g., Intra_luma_mpm_flag) indicating whether to apply the most probable mode (MPM) or the remaining mode to the current block, and when applying MPM to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra prediction mode candidates (MPM candidates). The intra prediction mode candidates (MPM candidates) may include an MPM candidate list or an MPM list. Additionally, when not applying MPM to the current block, the intra prediction mode information may further include remaining mode information (e.g., Intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes other than the intra prediction mode candidates (MPM candidates). The decoding device may determine the intra prediction mode of the current block based on the intra prediction mode information. A separate MPM list may be configured for the foregoing MIP.

[0149] Additionally, 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 (e.g., Intra_luma_ref_idx) indicating whether to apply MRL to the current block and indicating which reference sample line is used in the case of application, ISP flag information (e.g., Intra_subpartitions_mode_flag) indicating whether to apply ISP to the current block, ISP type information (e.g., Intra_subpartitions_split_flag) indicating the split type of the subpartition when ISP is applied, flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. Additionally, the intra prediction type information may include an MIP flag indicating whether to apply MIP to the current block.

[0150] The intra prediction mode information and / or intra prediction type information can be encoded / decoded by the encoding / decoding methods described in this disclosure. For example, the intra prediction mode information and / or intra prediction type information can be encoded / decoded by entropy encoding (e.g., CABAC, CAVLC) based on truncated (Rice) binary codes.

[0151] The predictor of the encoding / decoding apparatus can derive a predicted sample by performing inter prediction on a block-by-block basis. The inter 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 applying inter prediction to the current block, a predicted block (predicted 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 transmitted in the inter 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 the motion information between neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can also include inter prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. When applying inter prediction, neighboring blocks can 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 can be the same as or different from each other. The temporal neighboring block can be referred to by names such as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block can be referred to as a collocated picture (colPic). For example, a motion information candidate list can be configured based on neighboring blocks of the current block and flag or index information indicating which candidate is selected (used) to derive the motion vector and / or reference picture index of the current block can be signaled. Inter prediction can be performed based on various prediction modes, and for example, in the case of the skip mode and the merge mode, the motion information of the current block can be the same as the motion information of the neighboring block. In the case of the skip mode, different from the merge mode, a residual signal may not be transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of the selected neighboring block is used as a motion vector predictor and a motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference.

[0152] Figure 9 is a flowchart for describing a block reconstruction method based on intra prediction in an encoding apparatus. Figure 10 is a diagram illustrating an inter predictor in an encoding apparatus.

[0153] S900 can be performed by the inter - frame predictor 221 of the encoding device, and S910 to S930 can be performed by the residual processor 230 of the encoding device. Specifically, S910 can be performed by the subtractor 231 of the encoding device, S920 can be performed by the transformer 232 and the quantizer 233 of the encoding device, and S930 can be performed by the de - quantizer 234 and the inverse transformer 235 of the encoding device. In S900, the prediction information can be derived by the inter - frame predictor 221 and encoded by the entropy encoder 240. The residual information can be derived through S910 and S920 and encoded by the entropy encoder 240. The residual information is information about the residual samples. The residual information can include information about the quantized transform coefficients for the residual samples. As described above, the residual samples can be derived as transform coefficients by the transformer 232 of the encoding device, and the transform coefficients can be derived as quantized transform coefficients by the quantizer 233. The information about the quantized transform coefficients can be encoded by the entropy encoder 240 through the residual encoding process.

[0154] The encoding device performs inter - frame prediction (S900) on the current block. The encoding device can derive the inter - frame prediction mode and motion information of the current block and generate the prediction samples of the current block. Here, the processes for determining the inter - frame prediction mode, deriving the motion information, and generating the prediction samples can be performed simultaneously, or one process can be performed before another process. For example, the inter - frame predictor 221 of the encoding device can include a prediction mode determiner 221 - 1, a motion information deriver 221 - 2, and a prediction sample deriver 221 - 3. The prediction mode determiner 221 - 1 can determine the prediction mode for the current block, the motion information deriver 221 - 2 can derive the motion information of the current block, and the prediction sample deriver 221 - 3 can derive the motion samples of the current block. For example, the inter - frame predictor 221 of the encoding device can search for a block similar to the current block within a predetermined region (search region) of the reference picture through motion estimation and derive a reference block whose difference from the current block is equal to or less than a minimum value or a specific criterion. Based on this, a reference picture index indicating the reference picture in which the reference block is located can be derived, and a motion vector can be derived based on the difference between the position of the reference block and the position of the current block. The encoding device can determine the mode applied to the current block from among various prediction modes. The encoding device can compare the RD costs for various prediction modes and determine the best prediction mode for the current block.

[0155] For example, when applying a skip mode or a merge mode to a current block, an encoding device may construct a merge candidate list to be described later, and derive a reference block that has a minimum value or a difference less than or equal to a predetermined criterion from among the reference blocks indicated by the merge candidates included in the merge candidate list with respect to the current block. In such a 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 a decoding device. Motion information of the selected merge candidate may be used to derive motion information of the current block.

[0156] As another example, when applying an (A)MVP mode to a current block, an encoding device may construct an (A)MVP candidate list to be described later, and may use a motion vector of an mvp candidate selected from among the motion vector predictors (mvps) included in the (A)MVP candidate list as the mvp of the current block. In such a case, for example, a motion vector indicating a reference block derived through the above-described motion estimation may be used as the motion vector of the current block, and an mvp candidate having a minimum difference from the motion vector of the current block among the mvp candidates may be the selected mvp candidate. A motion vector difference (MVD) that is a difference obtained by subtracting the mvp from the motion vector of the current block may be derived. In such a case, information regarding the MVD may be signaled to the decoding device. Additionally, when applying the (A)MVP mode, a value of a reference picture index may be separately signaled to the decoding device by constructing reference picture index information.

[0157] The encoding device may derive a residual sample based on a prediction sample (S910). The encoding device may derive the residual sample by comparing an original sample of the current block with the prediction sample.

[0158] The encoding device performs transform / quantization on the residual sample to derive quantized transform coefficients (S920), and then performs dequantization / inverse transform on the quantized transform coefficients again to derive a (modified) residual sample (S930). The reason for performing dequantization / inverse transform again after transform / quantization is to derive the same residual sample as the residual sample derived from the decoding device as described above.

[0159] The encoding device may generate a reconstructed block including reconstructed samples for the current block based on the prediction sample and the (modified) residual sample (S940). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0160] 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., skip flag, merge flag, or mode index, etc.) and motion information. Information about the motion information may include candidate selection information (e.g., merge index, mvp flag, or mvp index) as information for deriving a motion vector. Additionally, information about the motion information may include the above-mentioned MVD information and / or reference picture index information. Additionally, 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 residual samples. The residual information may include information about quantization transform coefficients for the residual samples.

[0161] 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 via a network.

[0162] Figure 11 is a flowchart for describing a block reconstruction method based on inter-frame prediction in a decoding device. Figure 12 is a diagram illustrating an inter-frame predictor in a decoding device.

[0163] The decoding device may perform operations corresponding to those performed by the encoding device.

[0164] S1100 to S1120 may be performed by the inter-frame predictor 332 of the decoding device, and the prediction information of S1100 and the residual information of S1130 may be obtained by the entropy decoder 310 of the decoding device from the bitstream. 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 transform coefficients by performing dequantization based on the quantization transform coefficients derived based on the residual information, and the inverse transformer 322 of the residual processor may derive residual samples for the current block by performing an inverse transform on the transform coefficients. S1140 may be performed by the adder 340 or the reconstructor of the decoding device.

[0165] Specifically, the decoding device may determine a prediction mode for the current block based on the received prediction information (S1100). The decoding device may determine which inter-frame prediction mode to apply to the current block based on the prediction mode information in the prediction information.

[0166] For example, based on the merge flag, it can be determined whether to apply the merge mode to the current block or whether the (A)MVP mode is determined. Alternatively, one of various inter prediction mode candidates can be selected based on the mode index. The inter prediction mode candidates can include the skip mode, the merge mode, and / or the (A)MVP mode, or can include various inter prediction modes to be described later.

[0167] The decoding device derives the motion information of the current block based on the determined inter prediction mode (S1110). For example, when applying the skip mode or the merge mode to the current block, the decoding device can construct a merge candidate list and select one merge candidate from among the merge candidates included in the merge candidate list. The selection can be performed based on the above selection information (merge index). The motion information of the selected merge candidate can be used to derive the motion information of the current block. The motion information of the selected merge candidate can be used as the motion information of the current block.

[0168] As another example, when applying the (A)MVP mode to the current block, the decoding device can construct an (A)MVP candidate list to be described later, and can use the motion vector of the mvp candidate selected from among the motion vector predictors (mvps) included in the (A)MVP candidate list as the mvp of the current block. The selection can be performed based on the above selection information (mvp flag or mvp index). In this case, the MVD of the current block can be derived based on the information about the MVD, and the motion vector of the current block can be derived based on the mvp and the MVD of the current block. Additionally, the reference picture index of the current block can 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 can be derived as the reference picture referred to for the inter prediction of the current block.

[0169] Meanwhile, 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 described above can be omitted.

[0170] The decoding device can generate a prediction sample of the current block based on the motion information of the current block (S1120). In this case, the reference picture can be derived based on the reference picture index of the current block, and the sample of the reference block indicated by the motion vector of the current block on the reference picture can be used to derive the prediction sample of the current block. In this case, as described below, in some cases, a prediction sample filtering process can be further performed on all or some of the prediction samples of the current block.

[0171] For example, the inter - frame predictor 332 of the decoding device may include a prediction mode determiner 332_1, a motion information derivator 332_2, and a predicted sample derivator 332_3. The prediction mode determiner 332_1 may determine a prediction mode for a current block based on the received prediction mode information. The motion information derivator 332_2 may derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received information about the motion information. And the predicted sample derivator 332_3 may derive the predicted samples of the current block.

[0172] The decoding device generates residual samples for the current block based on the received residual information (S1130). The decoding device may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and derive a reconstructed block including the reconstructed samples (S1140). A reconstructed picture for the current picture may be generated based on the reconstructed block.

[0173] Various inter - frame prediction modes may be used for the prediction of a current block in a picture. For example, various modes such as the merge mode, the skip mode, the motion vector prediction (MVP) mode, the affine mode, the sub - block merge mode, and the merge with MVD (MMVD) mode, etc. may be used. Additionally or alternatively, the decoder - side motion vector refinement (DMVR) mode, the adaptive motion vector resolution (AMVR) mode, the bi - prediction with CU - level weight (BCW), the bidirectional optical flow (BDOF), etc. may be used as additional modes. The affine mode may be referred to as the affine motion prediction mode. The MVP mode may be called the advanced motion vector prediction (AMVP) mode. In this document, some modes and / or motion information candidates derived by some modes may be included as one of the motion information candidates of other modes. For example, the HMVP candidate may be added as a merge candidate in the merge / skip mode or may be added as an mvp candidate in the MVP mode.

[0174] Prediction mode information indicating an inter - prediction mode of a current block can be signaled from an encoding device to a decoding device. The prediction mode information can be included in a bitstream and received by the decoding device. The prediction mode information can include index information indicating one of a plurality of candidate modes. Alternatively, the inter - prediction mode can be indicated by hierarchical signaling of flag information. In this case, the prediction mode information can include one or more flags. For example, a skip flag can be signaled to indicate whether the skip mode is applied, and if the skip mode is not applied, a merge flag can be signaled to indicate whether the merge mode is applied, and if the merge mode is not applied, it indicates that the MVP mode is to be applied or flags for additional classification can be further signaled. The affine mode can be signaled in an independent mode or can be signaled in a mode dependent on the merge mode or the MVP mode. For example, the affine mode can include an affine merge mode and an affine MVP mode.

[0175] Meanwhile, information indicating whether the above - mentioned list0 (L0) prediction, list1 (L1) prediction, or bi - prediction is used in the current block (current coding unit) can be signaled in the current block. This information can be referred to as motion prediction direction information, inter - prediction direction information, or inter - prediction indication information, and can be configured / encoded / signaled in the form of, for example, the inter_pred_idc syntax element. That is, the inter_pred_idc syntax element can indicate whether the aforementioned 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 can be referred to as the motion prediction direction. The L0 prediction can be represented as pred_L0, the L1 prediction can be represented as pred_L1, and the bi - prediction can be represented as pred_BI. For example, the following prediction types can be determined according to the value of the inter_pred_idc syntax element.

[0176] [Table 1]

[0177]

[0178] 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 predictive (P) slice, and a bi-predictive (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 compiled and signaled without prediction. Intra prediction or inter prediction may be used for blocks in a P slice, and only uni-directional prediction may be used when using inter prediction. Meanwhile, intra prediction or inter prediction may be used for blocks in a B slice, and up to bi-prediction may be used when using inter prediction.

[0179] 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 POC order, and L1 may include reference pictures after and / or before the current picture in POC order. In this case, L0 may be assigned a reference picture index lower than the current picture with respect to a previous reference picture in POC order, and L1 may be assigned a reference picture index lower than the current picture with respect to a subsequent reference picture in POC order. In the case of a B slice, bi-prediction may be applied, and in this case, uni-directional bi-prediction or bi-directional bi-prediction may be applied. Bi-directional bi-prediction may be referred to as true bi-prediction.

[0180] As described above, a residual block (residual sample) may be derived based on a predicted block (predicted sample) derived by prediction at the encoding stage, and a residual sample transformed / quantized by residual information may be generated. The residual information may include information on quantized transform coefficients. The residual information may be included in 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 a residual sample based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information and may derive a residual block (residual sample) through an inverse quantization / inverse transform process.

[0181] Meanwhile, at least one of the (inverse) transform and / or (de)quantization processes may be omitted.

[0182] In the following, the in-loop filtering process performed on the reconstructed picture will be described. The modified reconstructed samples, blocks, pictures (or modified filtered samples, blocks, pictures) can be generated through the in-loop filtering process, and the modified (modified and filtered) reconstructed picture can be output as a decoded picture at the decoding device and can also be stored in the decoded picture buffer or memory of the encoding device / decoding device and used as a reference picture in the inter prediction process when encoding / decoding pictures later. The in-loop filtering process can include the deblocking filtering process, sample adaptive offset (SAO) process, and / or adaptive loop filter (ALF) process as described above. In this case, one or some of the deblocking filtering process, sample adaptive offset (SAO) process, adaptive loop filter (ALF) process, and bilateral filter process can be applied sequentially or all can be applied sequentially. For example, the SAO process can be performed after applying the deblocking filtering process to the reconstructed picture. Or, for example, the ALF process can be performed after applying the deblocking filtering process to the reconstructed picture. This can also be performed in the encoding device.

[0183] Deblocking filtering is a filtering technique for removing distortions at the boundaries between blocks in the reconstructed picture. For example, the deblocking filtering process can derive a target boundary based on the reconstructed picture, determine the boundary strength (bS) of the target boundary, and perform deblocking filtering on the target boundary based on bS. The bS can be determined based on the prediction modes of two blocks adjacent to the target boundary, the motion vector difference, whether the reference pictures are the same, whether there are non-zero valid coefficients, etc.

[0184] SAO is a method for compensating the offset difference between the reconstructed picture and the 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 filtering information for SAO can include information on whether SAO is applied, SAO type information, and SAO offset value information. SAO can be applied to the reconstructed picture after applying deblocking filtering.

[0185] Adaptive loop filter (ALF) is a technique for filtering the reconstructed picture on a sample basis according to the filter shape based on filter coefficients. The encoding device can determine whether to apply ALF, the ALF shape, and / or the ALF filtering coefficients, etc. by comparing the reconstructed picture and the original picture and can signal them to the decoding device. That is, the filtering information for ALF can include information on whether ALF is applied, ALF filter shape information, ALF filtering coefficient information, etc. ALF can be applied to the reconstructed picture after applying deblocking filtering.

[0186] Figure 13Shows an example of the shape of the ALF filter.

[0187] Figure 13 (a) of shows the shape of a 7x7 rhombus filter, Figure 13 (b) of shows the shape of a 5x5 rhombus filter. In Figure 13 , Cn in the filter shape 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 where the filter coefficient can be assigned according to the filter shape of the ALF can be referred to as a filter tab. In this case, one filter coefficient can be assigned to each filter tab, and the arrangement of the filter tabs can correspond to the filter shape. The filter tab located at the center of the filter shape can be referred to as the central filter tab. The same filter coefficient can be assigned to two filter tabs existing at positions corresponding to each other with respect to the central filter tab for the same n value. For example, in the case of a 7x7 rhombus filter shape, including 25 filter tabs, and since the filter coefficients C0 to C11 are assigned in a centrosymmetric form, only 13 filter coefficients can be used to assign the filter coefficients to 25 filter tabs. Additionally, for example, in the case of a 5x5 rhombus filter shape, including 13 filter tabs, and since the filter coefficients C0 to C5 are distributed in a centrosymmetric form, only 7 filter coefficients can be used to assign the filter coefficients to 13 filter tabs. For example, in order to reduce the amount of data on the information of the filter coefficients signaled, 12 out of 13 filter coefficients for the 7x7 rhombus filter shape are (explicitly) signaled, and 1 filter coefficient can be (implicitly) derived. Additionally, for example, 6 out of 7 coefficients for the 5x5 rhombus filter shape can be (explicitly) signaled and 1 filter coefficient can be (implicitly) derived.

[0188] According to an embodiment of the present disclosure, the ALF parameters for the ALF process can be signaled through an Adaptive Parameter Set (APS). The ALF parameters can be derived based on the filter information or ALF data for the ALF.

[0189] ALF is an in-loop filtering technique that can be applied in video / image coding as described above. An adaptive filter based on Wiener can be used to perform ALF. This can be to minimize the Mean Square Error (MSE) between the original samples and the decoded samples (or reconstructed samples). The advanced design for the ALF tool can incorporate syntax elements accessible in the SPS and / or slice header (or tile group header).

[0190] In an example, before filtering each 4x4 luma block, geometric transformations such as rotation or diagonal and vertical flipping can be applied to the filter coefficients f(k,l) and the corresponding filter clipping values c(k,l) depending on the gradient value computed for the block. This is equivalent to applying these transformations to the samples in the filter support region. Creating other blocks to which ALF is applied can be similar to arranging these blocks according to their directionality.

[0191] For example, three transformations can be performed based on the following equations: diagonal, vertical flipping, and rotation.

[0192] [Equation 1]

[0193] Diagonal: f_D(k,l) = f(l,k), c_D(k,l) = c(l,k)

[0194] [Equation 2]

[0195] Vertical flipping: f_V(k,l) = f(k,K-l-1), c_V(k,l) = c(k,K-l-1)

[0196] [Equation 3]

[0197] Rotation: f_R(k,l) = f(K-l-1,k), c_R(k,l) = c(K-l-1,k)

[0198] In Equations 1 to 3, K can be the size of the filter. 0 ≤ k and 1 ≤ K-1 can be the coefficient coordinates. For example, (0,0) can be the top-left coordinate, and / or (K-1,K-1) can be the bottom-right coordinate. The relationship between the transformations and the four gradients in the four directions can be summarized in the following table.

[0199] [Table 2]

[0200] Gradient value Transformation <![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 > Vertical flip <![CDATA[g d1 <g d2 and g v <g h > Rotation

[0201] The ALF filter parameters can be signaled in the 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. To reduce the bit overhead, the filter coefficients for different classifications of the luma component can be merged. In the slice header, the index of the APS (referenced by the current slice) for the current slice can be signaled.

[0202] The clipping value indices decoded from the APS can make it possible to determine the clipping values using the luma table of clipping values and the chroma table of clipping values. These clipping values may depend on the internal bit depth. More specifically, the luma table of clipping values and the chroma table of clipping values can be derived based on the following equations.

[0203] [Equation 4]

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

[0205] [Equation 5]

[0206] AlfClipC = {round(2^((B - 8)+8((N - n)) / (N - 1))) for n ∈ [1..N]}

[0207] In the above equations, B can be the internal bit depth, and N can be the number of allowed clipping values (predetermined number). For example, N can be 4.

[0208] In the slice header, up to 7 APS indices can be signaled to indicate the luminance filter set for the current slice. The filtering process can be further controlled at the CTB level. For example, a flag indicating whether to apply ALF to the luminance CTB can be signaled. The luminance CTB can select one of 16 fixed filter sets and the filter set from the APS. A filter set index can be signaled for the luminance CTB to indicate which filter set is applied. The 16 fixed filter sets can be predefined and hard-compiled in both the encoder and the decoder.

[0209] For the chrominance component, an APS index can be signaled in the slice header to indicate the chrominance filter set for the current slice. At the CTB level, when there are two or more chrominance filter sets in the APS, a filter index can be signaled for each chrominance CTB.

[0210] 128 can be used as the norm ( norm ) to quantize the filter coefficients. To limit the multiplication complexity, bitstream consistency (bitstrea m con formanc e ) can be applied such that the coefficient values at non-central positions can vary from 0 to 28 and / or the coefficient values at the remaining positions can be in the range from -27 to 27 - 1. The central position coefficient can be not signaled in the bitstream and can be pre-determined (considered) as 128.

[0211] When ALF is available for the current block, each sample R(i, j) can be filtered, and the filtered result R'(i, j) can be represented by the following equation.

[0212] [Equation 6]

[0213] R′(i, j) = R(i, j)+((Σ k≠0Σ l≠0 f(k, l) × K(R(i + k, j + l) - R(i, j), c(k, l)) + 64) >> 7)

[0214] In the above equation, f(k, l) can be decoding filter coefficients, K(x, y) can be a clipping function, and c(k, l) can be a decoding 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).

[0215] In an example, to reduce the row buffer requirements of the ALF, modified block classification and filtering can be applied to samples adjacent to the horizontal CTU boundary. For this purpose, a virtual boundary can be defined.

[0216] Figure 14 is a diagram for describing a virtual boundary applied to a filtering process according to an embodiment of the present disclosure. Figure 15 is a diagram illustrating an example of an ALF process using a virtual boundary according to an embodiment of the present disclosure. It will be described in conjunction with Figure 14 description Figure 15 .

[0217] Reference Figure 14 , the virtual boundary can be a line defined by shifting the horizontal CTU boundary by N samples. In one example, N can be 4 for the luminance component and / or N can be 2 for the chrominance component.

[0218] In Figure 14 , modified block classification can be applied to the luminance component. For the 1D Laplacian gradient calculation of 4x4 blocks on the virtual boundary, only the samples above the virtual boundary can be used. Similarly, to calculate the 1D Laplacian gradient of 4x4 blocks below the virtual boundary, only the samples below the virtual boundary can be used. Considering the reduction in the number of samples used in the 1D Laplacian gradient calculation, the quantization of the activity value A can be scaled accordingly.

[0219] For the filtering process, symmetric padding operations at the virtual boundary can be used for both the luminance component and the chrominance component. Referring to Figure 15 , when the filtered sample is below the virtual boundary, the neighboring samples above the virtual boundary can be filled. At the same time, the corresponding samples on the other side can also be symmetrically filled.

[0220] When no filter is enabled across the boundary, referring to Figure 15The described process can also be used for the boundaries of slices, bricks, and / or tiles. For ALF block classification, samples included only within the same slice, brick, and / or tile can be used and the activity values can be scaled accordingly. For ALF filtering, symmetric padding can be applied for each of the horizontal direction and / or vertical direction with respect to the horizontal boundary and / or vertical boundary.

[0221] Figure 16 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 can be referred to as a cross-component filtering process.

[0222] In one aspect, the ALF process can include a general ALF process and a CCALF process. That is, the CCALF process can be referred to as some processes of the ALF process. In another aspect, the filtering process can include a deblocking process, a SAO process, an ALF process, and / or a CCALF process.

[0223] CC-ALF can use luminance sample values to refine each chrominance component. CC-ALF is controlled by the (picture) information of the bitstream, and the picture information can include (a) information about the filter coefficients for each chrominance component and (b) information about the mask for controlling the filter application to the blocks of samples. The filter coefficients can be signaled at the APS, and the block size and mask can be signaled at the slice level.

[0224] Reference Figure 16 , CC-ALF can be operated by applying a linear diamond filter ( Figure 16 's (b)) to the luminance channel for each chrominance component. The filter coefficients are sent to the APS, scaled by 210 times, and rounded up to obtain a fixed-point representation. The application of the filter can be controlled at variable block sizes and signaled by the context compilation flag received for each block of samples. The block size and the CC-ALF enable flag can be received at the slice level for each chrominance component. The block size (for chrominance samples) can be 16x16, 32x32, 64x64, or 128x128.

[0225] In the following embodiments, a method for re-filtering or modifying the reconstructed chrominance samples filtered by ALF based on the reconstructed luminance samples will be proposed.

[0226] Embodiments of the present disclosure relate to filter on / off transmission and filter coefficient transmission in CC-ALF. As described above, the information (syntax elements) in the syntax tables disclosed in the present disclosure can be included in image / video information, can be configured / encoded in an encoding device, and can be sent to a 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 a picture / image / video decoding process (specifically, for example, a CC-ALF process) based on the decoded information. Hereinafter, the same applies to other examples.

[0227] 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 can be sent independently of the ALF enable flag (sps_alf_enabled_flag) used to determine whether to use (apply) ALF.

[0228] The following table shows an exemplary syntax of the SPS according to this embodiment.

[0229] [Table 3]

[0230]

[0231]

[0232]

[0233]

[0234] The following table shows an exemplary semantics of the CC-ALF enable flag included in the table. The CC-ALF enable flag can indicate whether CC-ALF is enabled (can be related to whether CC-ALF is enabled).

[0235] [Table 4]

[0236]

[0237] In another example of this embodiment, when sending the CC-ALF enable flag, the conditions for ChromaArrayType can be determined as shown in the following table.

[0238] [Table 5]

[0239]

[0240]

[0241]

[0242]

[0243] 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 signaled via the SPS.

[0244] The following table shows exemplary semantics of the CC-ALF enable flag included in the table.

[0245] [Table 6]

[0246]

[0247] The picture information may include the SPS. The SPS may include a first ALF enable flag (sps_alf_enabled_flag) related to whether ALF is enabled. For example, based on the determination that the value of the first ALF enable flag is 1, the SPS may include a CCALF enable flag related to whether cross-component filtering is enabled.

[0248] 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.

[0249] [Table 7]

[0250]

[0251] The following table shows exemplary semantics of the CC-ALF constraint flag included in the table.

[0252] [Table 8]

[0253]

[0254] The picture 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.

[0255] According to an embodiment of the present disclosure, the slice_cross_component_alf_cb_enabled_flag flag can be added on a slice-by-slice basis to determine whether CC-ALF is used. The slice_cross_component_alf_cb_enabled_flag flag can be sent when the sps_ccalf_enabled_flag flag is 1. Alternatively, the slice_ccalf_enable_flag flag can be sent when the sps_ccalf_enabled_flag flag is 1 and the ChromaArrayType is not 0.

[0256] For example, when the value of the slice_cross_component_alf_cb_enabled_flag flag is 1, the syntax slice_cross_component_alf_cb_reuse_temporal_layer_filter can be additionally sent. When this syntax value is 0, the syntax slice_cross_component_alf_cb_aps_id can be sent. The slice_cross_component_alf_cb_log2_control_size_minus4 syntax for the block size used for CC-ALF can be sent.

[0257] The following table is an exemplary syntax of the slice header information according to the above embodiment.

[0258] [Table 9]

[0259]

[0260]

[0261]

[0262]

[0263] The following table is an exemplary syntax of the slice header information according to the above embodiment.

[0264] [Table 10]

[0265]

[0266]

[0267] According to an embodiment of the present disclosure, the slice_ccalf_enable_flag flag can be added on a slice-by-slice basis to determine whether CC-ALF is used. When the sps_ccalf_enabled_flag flag is 1, the slice_ccalf_enable_flag flag can be sent. Alternatively, when the sps_ccalf_enabled_flag flag is 1 and the ChromaArrayType is not 0, the slice_ccalf_enable_flag flag can be sent.

[0268] For example, when the value of the slice_ccalf_enable_flag flag is 1, the slice_ccalf_chroma_idc syntax and the slice_ccalf_aps_id_chroma syntax can be additionally sent. The slice_ccalf_chroma_idc syntax indicates whether Cb or Cr is applied, and the slice_ccalf_aps_id_chroma syntax indicates the APS id referred to by CC-ALF for the corresponding slice.

[0269] The following table shows the syntax of the slice header information according to this embodiment.

[0270] [Table 11]

[0271]

[0272]

[0273]

[0274]

[0275] The following table shows the semantics of the syntax elements included in the table.

[0276] [Table 12]

[0277]

[0278]

[0279] Alternatively, the syntax element slice_ccalf_chroma_idc in the above table can be described based on the semantics shown in the following table.

[0280] [Table 13]

[0281]

[0282] According to an embodiment of the present disclosure, CC-ALF can be performed at the slice level without an additional enable flag (or similar information). The following table shows some syntax of the slice header information according to this embodiment.

[0283] [Table 14]

[0284]

[0285] The following table shows the semantics of the syntax elements included in the table.

[0286] [Table 15]

[0287]

[0288] According to an embodiment of the present disclosure, the syntax element slice_ccalf_chroma_idc can be included in the slice header information based on the condition of ChromaArrayType. The following table shows some syntax of the slice header information according to this embodiment.

[0289] [Table 16]

[0290]

[0291] In the 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 is available for the Cr color component of the filtered reconstructed chroma samples.

[0292] In the example, based on the determination that the 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) related to the identifier of the APS used to derive the cross-component filter coefficients for the Cb color component.

[0293] In one example, based on the 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 related to the identifier of the APS used to derive the cross-component filter coefficients for the Cr color component (slice_cross_component_id_cross_component_id_flag or sh_cc_alf_cr_aps_id).

[0294] According to an embodiment of the present disclosure, the cross-component filter coefficients for CC-ALF may be sent via the APS. In one example, an APS for CC-ALF may be defined.

[0295] The following table shows an exemplary syntax of the APS according to this embodiment.

[0296] [Table 17]

[0297]

[0298] In the above table, alf_data() may be referred to as general ALF data, and ccalf_data() may be referred to as CCALF data. The ALF data may include general ALF data and / or CCALF data. In one example, the ALF data may be the same as the CCALF data. In another example, the ALF data may be different from the CCALF data.

[0299] The following table shows the semantics of the syntax elements included in the table.

[0300] [Table 18]

[0301]

[0302] The ALF data according to an embodiment of the present disclosure may be expressed in the syntax shown in the following table.

[0303] [Table 19]

[0304]

[0305] The semantics of the syntax elements included in the table may be expressed as shown in the following table.

[0306] [Table 20]

[0307]

[0308]

[0309]

[0310] In another example, the syntax related to the ALF data can be expressed as shown in the following table.

[0311] [Table 21]

[0312]

[0313] The semantics of the syntax elements included in the table can be as shown in the following table.

[0314] [Table 22]

[0315]

[0316]

[0317] In the table, the order of the exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] can be defined as one of the values from 0 to 9.

[0318] In another example, the syntax related to the ALF data can be expressed as shown in the following table.

[0319] [Table 23]

[0320]

[0321] In the table, the information related to the absolute value of the filter coefficients and / or the information related to the sign of the filter coefficients can 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 the example, the information about the number of filters, the information related to the absolute value of the filter coefficients, and / or the information related to the sign of the filter coefficients can be included in the general ALF data.

[0322] The semantics of the syntax elements included in the table can be as shown in the following table.

[0323] [Table 24]

[0324]

[0325]

[0326] The order of the exp-Golomb binarization used to parse the syntax of alf_cross_component_cb_coeff_abs[j] and alf_cross_component_cr_coeff_abs[j] can be defined as one of the values from 0 to 9.

[0327] The cross-component filter coefficients can be referred to as CCALF filter coefficients. The cross-component filter coefficients can include the cross-component filter coefficients for the Cb color component and the cross-component filter coefficients for the Cr color component. Information about the value of the cross-component filter coefficients for the Cb color component (Cr color component) can include information about the value of the cross-component filter coefficients for the Cb color component (Cr color component) and / or information about the sign of the cross-component filter coefficients for the Cb color component (Cr color component).

[0328] In one example, the ALF data included in the APS for deriving cross-component filter coefficients 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 signaling for the cross-component filter for the Cb color component is used. Based on the Cb filter signal flag, the ALF data included in the APS for deriving cross-component filter coefficients 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 related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving cross-component filter coefficients for the Cb color component may include information about the absolute value of the cross-component filter coefficients 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 coefficients for the Cb color component (alf_cross_component_cb_coeff_sign or alf_cc_cb_coeff_sign). The cross-component filter coefficients for the Cb color component (ccalfcoeff or ccalfapscoeff) may be derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component. For example, the information related to the number of cross-component filters for the Cb color component may be compiled in zero-order exponential Golomb (0EG, ue(v) or ue(k)).

[0329] In one example, the ALF data included in the APS for deriving 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 to signal a cross-component filter for the Cr color component. Based on the Cr filter signal flag, the ALF data included in the APS for deriving 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 related to the number of cross-component filters for the Cr color component, the ALF data included in the APS for deriving 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 related to the number of cross-component filters for the Cr color component may be coded in zero-order exponential Golomb (0EG, ue(v) or ue(k)).

[0330] According to an embodiment of the present disclosure, CC-ALF related information can be sent in units of CTUs (blocks) to control the filter on / off of CC-ALF.

[0331] The following table shows an exemplary syntax of a compilation tree unit according to this embodiment.

[0332] [Table 25]

[0333]

[0334] The following table shows exemplary semantics of the syntax elements included in the table.

[0335] [Table 26]

[0336]

[0337] In another example of this embodiment, the syntax related to the coding tree unit can be expressed as the following table.

[0338] [Table 27]

[0339]

[0340]

[0341] The following table shows the exemplary semantics of the syntax elements included in the table.

[0342] [Table 28]

[0343]

[0344] In the example, the image information may include information about the coding tree unit (coding_tree_unit()). The information about the coding tree unit may include information about whether to apply a cross-component filter to the current block of the Cb color component (ccalf_ctb_flag[0]) and / or information about whether to apply a cross-component filter to the current block of the Cr color component (ccalf_ctb_flag[1]). Additionally, the information about the coding tree unit may include information about the filter set index of the cross-component filter applied to the current block of the Cb color component (ccalf_ctb_filter_alt_idx[0]) and / or information about the filter set index of the cross-component filter applied to the current block of the Cr color component (ccalf_ctb_filter_alt_idx[1]).

[0345] Figure 17 and Figure 18 is a diagram schematically illustrating an example of a video / image coding method and related components according to an embodiment of the present disclosure.

[0346] Figure 17 The method disclosed in Figure 2 or Figure 18 can be executed by the coding device disclosed in Figure 17 Specifically, for example, Figure 18 S1700 to S1730 of Figure 17 can be executed by the residual processor 230 of the coding device of Figure 18 S1740 of Figure 17 can be executed by the adder 250 of the coding device of Figure 18 S1750 of Figure 17 can be executed by the filter 260 of the coding device ofFigure 18 is performed by the entropy encoder 240 of the encoding apparatus. Additionally, although not shown in Figure 17 , the predicted sample or prediction-related information may be derived by the predictor 220 of the Figure 17 encoding apparatus, and the entropy encoder 240 of the encoding apparatus may generate a bitstream based on the residual information or prediction-related information. Figure 17 The method disclosed in

[0347] Reference Figure 17 , the encoding apparatus may generate a residual sample (S1700). The encoding apparatus may generate a residual sample for the current block and may generate the residual sample for the current block based on the original sample and the predicted sample of the current block. Specifically, the encoding apparatus may generate a predicted sample for the current block based on the prediction mode. In this case, various prediction methods disclosed in the present disclosure, such as inter prediction or intra prediction, may be applied. The residual sample may be generated based on the predicted sample and the original sample.

[0348] In one example, the encoding apparatus may generate a residual luminance sample. The residual luminance sample may be generated based on the original luminance sample and the predicted luminance sample. In one example, the encoding apparatus may generate a residual chrominance sample. The residual chrominance sample may be generated based on the original chrominance sample and the predicted chrominance sample.

[0349] The encoding apparatus may derive transform coefficients (S1710). The encoding apparatus may derive transform coefficients based on the transform process for the residual sample. The encoding apparatus may derive transform coefficients for the residual luminance sample (luminance transform coefficients) and / or transform coefficients for the residual chrominance sample (chrominance transform coefficients). For example, the transform process may include at least one of DCT, DST, GBT, or CNT.

[0350] The encoding apparatus may derive quantized transform coefficients (S1720). The encoding apparatus may derive quantized transform coefficients based on the quantization process for the transform coefficients. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order. The quantized transform coefficients may include quantized luminance transform coefficients and / or quantized chrominance transform coefficients.

[0351] The encoding apparatus may generate residual information (S1730). The encoding apparatus may generate residual information indicating (including) the quantized transform coefficients. The residual information may be generated by various coding methods such as exponential Golomb, CAVLC, CABAC, etc.

[0352] The encoding device may generate reconstructed samples (S1740). The reconstructed samples may include reconstructed luminance samples and / or reconstructed chrominance samples. The encoding device may generate the reconstructed samples based on residual information. The reconstructed samples may be generated by adding residual samples based on the residual information to the prediction samples. Specifically, the encoding device may perform prediction (intra prediction or inter prediction) on a current block, and generate the reconstructed samples based on the original samples and the prediction samples generated according to the prediction.

[0353] The encoding device may generate ALF-related information and / or CCALF (CC-ALF)-related information for the reconstructed samples (S1750). The encoding device may generate ALF-related information for the reconstructed samples. The encoding device may derive ALF-related parameters that can be applied to filter the reconstructed samples, and generate the ALF-related information. For example, the ALF-related information may include the ALF-related information described above in this disclosure. The encoding device may generate CCALF-related information for the reconstructed chrominance samples among the reconstructed samples.

[0354] The encoding device may encode video / image information (S1760). The image information may include residual information, ALF-related information, and / or CCALF-related information. The encoded video / image information can be output in the form of a bitstream. The bitstream can be sent to a decoding device via a network or a storage medium.

[0355] In one example, the CCALF-related information may include a CCALF enable flag, a flag related to whether CCALF is enabled for the Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether to signal a cross-component filter for the Cb (or Cr) color component, information related to the number of cross-component filters for the Cb (or Cr) color component, information about the values of the cross-component filter coefficients for the Cb (or Cr) color component, information about the absolute values of the cross-component filter coefficients for the Cb (or Cr) color component, information about the signs of the cross-component filter coefficients for the Cb (or Cr) color component, and / or information about whether to apply a cross-component filter to the current block of the Cb (or Cr) color component in the information (compilation tree unit syntax) about the compilation tree unit.

[0356] The image / video information may include each piece of information according to the embodiments of the present disclosure. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 28 above.

[0357] 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 header information may include information related to an identifier of the APS including the ALF data. For example, the cross-component filter coefficients may be derived based on the ALF data.

[0358] 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.

[0359] 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 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.

[0360] In an embodiment, the header information may include: a first flag related to whether CCALF is enabled for the Cb color component of the reconstructed chrominance samples for filtering, and a second flag related to whether CCALF is enabled for the Cr color component of the reconstructed chrominance samples for filtering.

[0361] In an embodiment, based on a determination that the value of the first flag is 1, the header information may include information related to an identifier of the APS used to derive the cross-component filter coefficients for the Cb color component.

[0362] In an example, the ALF data included in the APS used to derive the cross-component filter coefficients for the Cb color component may include a 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 used to derive the cross-component filter coefficients for the Cb color component 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 ALF data included in the APS used to derive the cross-component filter coefficients for the Cb color component may include information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component. The cross-component filter coefficients for the Cb color component may be derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component.

[0363] In an embodiment, information related to the number of cross-component filters for the Cb color component may be coded in zero-order exponential Golomb (0EG).

[0364] In an example, the picture information may include information about a coding tree unit. The information about the coding tree unit may include information about whether to apply a cross-component filter to a current block of the Cb color component and / or information about whether to apply a cross-component filter to a current block of the Cr color component.

[0365] 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 a current block of the Cb color component and / or information about a filter set index of a cross-component filter applied to a current block of the Cr color component.

[0366] Figure 19 and Figure 20 are diagrams schematically illustrating examples of a video / image decoding method and related components according to an embodiment of the present disclosure.

[0367] Figure 19 The method disclosed in Figure 3 or Figure 20 may be performed by the decoding device disclosed in. Specifically, for example, Figure 19 S1900 of Figure 19 The method disclosed in may include the embodiments described above in the present disclosure.

[0368] Refer to Figure 19, the decoding device may receive / acquire video / image information (S1900). The video / image information may include residual information. The decoding device may receive / acquire the image / video information through a bitstream. In one example, the video / image information may further include CCAL-related information. For example, the CCALF-related information may include a CCALF enable flag, a flag related to whether CCALF is enabled for the Cb (or Cr) color component, a Cb (or Cr) filter signal flag related to whether to signal the cross-component filter for the Cb (or Cr) color component, information related to the number of cross-component filters for the Cb (or Cr) color component, information about the values of the coefficients of the cross-component filter for the Cb (or Cr) color component, information about the absolute values of the coefficients of the cross-component filter for the Cb (or Cr) color component, information about the signs of the coefficients of the cross-component filter for the Cb (or Cr) color component, and / or information about whether to apply the cross-component filter to the current block of the Cb (or Cr) color component in the information (compilation tree unit syntax) about the compilation tree unit.

[0369] The image / video information may include each piece of information according to the embodiments of the present disclosure. For example, the image / video information may include the information disclosed in at least one of Tables 1 to 28 above.

[0370] The decoding device may derive quantized transform coefficients (S1910). The decoding device may derive the quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order.

[0371] The decoding device may derive transform coefficients (S1920). The decoding device may derive the transform coefficients based on the dequantization process for the quantized transform coefficients.

[0372] The decoding device may generate / derive residual samples (S1930). The decoding device may derive the residual samples based on the inverse transform process for the transform coefficients.

[0373] The decoding device may generate / derive reconstructed samples (S1940). The decoding device may generate the reconstructed samples based on the residual samples. The reconstructed samples may include reconstructed luminance samples and / or reconstructed chrominance samples. The luminance component of the reconstructed samples may correspond to the reconstructed luminance samples, and the chrominance component of the reconstructed samples may correspond to the reconstructed chrominance samples.

[0374] The decoding device may derive the ALF filter coefficients for the ALF process for the reconstructed chrominance samples (S1950). Additionally, the decoding device may derive the ALF filter coefficients for the ALF process for the reconstructed luminance samples. The ALF filter coefficients may be derived based on the ALF parameters included in the ALF data in the APS.

[0375] The decoding device may generate filtered reconstructed chrominance samples (S1960). The decoding device may generate filtered reconstructed samples based on the reconstructed chrominance samples and the ALF filter coefficients.

[0376] The decoding device may derive cross-component filter coefficients for cross-component filtering (S1970). 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 (and signaled through the slice header).

[0377] The decoding device may generate modified-filtered reconstructed chrominance samples (S1980). The decoding device may generate modified-filtered reconstructed chrominance samples based on the reconstructed luma samples, the filtered reconstructed chrominance samples, and the cross-component filter coefficients. In an example, the decoding device may derive the difference between two reconstructed luma samples and multiply the difference by one of the filter coefficients of the cross-component filter coefficients. Based on the result of the multiplication and the filtered reconstructed chrominance samples, the decoding device may generate modified-filtered reconstructed chrominance samples. For example, the decoding device may generate modified-filtered reconstructed chrominance samples based on the sum between the multiplication and one of the filtered reconstructed chrominance samples.

[0378] 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 header information may include information related to the identifier of the APS including the ALF data. For example, the cross-component filter coefficients may be derived based on the ALF data. The ALF data may be general ALF data or CCALF data.

[0379] In an embodiment, the image information may include an SPS. The SPS may include a CCALF enable flag related to whether cross-component filtering is enabled.

[0380] 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 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.

[0381] In an embodiment, the header information may include: a first flag related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chrominance samples, and a second flag related to whether CCALF is enabled for the Cr color component of the filtered reconstructed chrominance samples.

[0382] In an embodiment, based on the determination that the value of the first flag is 1, the header information may include information related to an identifier of an APS used to derive cross-component filter coefficients for the Cb color component.

[0383] In an example, the ALF data included in the APS used to derive cross-component filter coefficients for the Cb color component 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 ALF data included in the APS used to derive cross-component filter coefficients for the Cb color component 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 ALF data included in the APS used to derive cross-component filter coefficients for the Cb color component may include information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component. The cross-component filter coefficients for the Cb color component may be derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component.

[0384] In an embodiment, the information related to the number of cross-component filters for the Cb color component may be coded in zero-order exponential Golomb (0EG).

[0385] In an example, the ALF data included in the APS used to derive cross-component filter coefficients for the Cr color component may include a Cr filter signal flag related to whether to signal a cross-component filter for the Cr color component. Based on the Cr filter signal flag, the ALF data included in the APS used to derive 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. Based on the information related to the number of cross-component filters for the Cr color component, the ALF data included in the APS used to derive 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 and information about the sign of the cross-component filter coefficients for the Cr color component. The cross-component filter coefficients for the Cr color component 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.

[0386] In an embodiment, the information related to the number of cross-component filters for the Cr color component may be coded in zero-order exponential Golomb (0EG).

[0387] In an embodiment, the image information may include information about a compiled tree unit. The information about the compiled tree unit may include information about whether to apply a cross-component filter to the current block of the Cb color component and / or information about whether to apply a cross-component filter to the current block of the Cr color component.

[0388] In an embodiment, the information about the compiled tree unit may include information about the filter set index of the cross-component filter applied to the current block of the Cb color component and / or information about the filter set index of the cross-component filter applied to the current block of the Cr color component.

[0389] 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 transform coefficients for the residual samples. The decoding device may derive the residual samples (or an array of residual samples) for the current block based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector form based on the coefficient scan order. The decoding device may derive transform coefficients based on an inverse quantization process for the quantized transform coefficients. The decoding device may derive residual samples based on the transform coefficients.

[0390] The decoding device may generate reconstructed samples based on (intra) prediction samples and residual samples, and may derive a reconstructed block or a reconstructed picture based on the reconstructed samples. Specifically, the decoding device may generate reconstructed samples based on the sum of the (intra) prediction samples and the residual samples. Thereafter, as described above, if necessary, the decoding device may apply loop filter processing (e.g., deblocking filtering and / or SAO processing) to the reconstructed picture to improve the subjective / objective picture quality.

[0391] For example, the decoding device may obtain image information including all or some of the above information (or syntax elements) by decoding a bitstream or encoded information. Additionally, the bitstream or encoded information may be stored in a computer-readable storage medium, or the above decoding method may be executed.

[0392] In the above embodiments, a method is described based on a flowchart having a series of steps or boxes. The present disclosure is not limited to the order of the above steps or boxes. Some steps or boxes may occur simultaneously with other steps or boxes as described above or in an order different from other steps or boxes as described above. Additionally, those skilled in the art will understand that the steps shown in the above flowchart are not exclusive, may include additional steps, or one or more steps in the flowchart may be deleted without affecting the scope of this document.

[0393] The method according to the above embodiments of this document can be implemented in software form, and the encoding device and / or decoding device according to this document can be included, for example, in devices that perform image processing such as TVs, computers, smart phones, set-top boxes, and display devices.

[0394] When the embodiments in this document are implemented in software, the above method can be implemented as a module (processing, function, etc.) that performs 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 well-known means. The processor can include an application-specific integrated circuit (ASIC), other chip sets, logic circuits, and / or data processing devices. The memory can include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and / or other storage devices. That is, 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 drawing can be implemented and executed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information about the instructions or algorithms for the implementation can be stored in a digital storage medium.

[0395] In addition, the decoding device and encoding device applying this document can be included in a multimedia broadcast transmission / reception device, a mobile communication terminal, a home theater video device, a digital cinema 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 VoD service providing device, an over-the-top (OTT) video device, an Internet streaming service providing device, a three-dimensional (3D) video device, a video conferencing device, a transportation user device (i.e., an in-vehicle user device, an aircraft user device, a ship user device, etc.), and a medical video device, and can be used to process video signals and data signals. For example, an over-the-top (OTT) video device can include a game console, a Blu-ray player, an Internet-connected TV, a home theater system, a smart phone, a tablet, a digital video recorder (DVR), etc.

[0396] In addition, the processing method described in this document can be generated in the form of a program executable by a computer and can be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present disclosure can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices that store data readable by a computer system. For example, the computer-readable recording medium can include BD, Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage devices. In addition, the computer-readable recording medium includes a medium implemented in the form of a carrier wave (i.e., transmission via the Internet). Additionally, the bitstream generated by an encoding method can be stored in a computer-readable recording medium or can be transmitted via a wired or wireless communication network.

[0397] Furthermore, embodiments of this document can be implemented using a computer program product according to 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.

[0398] Figure 21 An example of a content streaming system to which embodiments of this document can be applied is shown.

[0399] Reference Figure 21 , a content streaming system applying embodiments of this document generally includes an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0400] The encoding server compresses the content input from a multimedia input device (e.g., a smart phone, a camera, a video camera, etc.) into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smart phone, a camera, a video camera, etc. directly generates a bitstream, the encoding server can be omitted.

[0401] A bitstream can be generated by applying an encoding method or a bitstream generation method according to embodiments of the present disclosure, and the streaming server can temporarily store the bitstream in the process of sending or receiving the bitstream.

[0402] The streaming server sends multimedia data to the user device via the web server based on the user's request. The web server serves as a medium for notifying the user of the service. When the user requests a 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 can include a separate control server. In this case, the control server is used to control the commands / responses between the devices in the content streaming system.

[0403] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from the 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.

[0404] Examples of user equipment can include mobile phones, smartphones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage, etc. Each server in the content streaming system can be operated as a distributed server, and in this case, the data received from each server can be distributed.

[0405] Each server in the content streaming system can be operated as a distributed server, and in this case, the data received from each server can be processed in a distributed manner.

[0406] The claims described herein can be combined in various ways. For example, the technical features of the method claims in this document can be combined and implemented as a device, and the technical features of the device claims in this document can also be combined and implemented as a method. Additionally, the technical features of the method claims in this document and the technical features of the device claims in this document can be combined to be implemented as a device, and the technical features of the method claims in this document and the technical features of the device claims in this document can be combined and implemented as a method.

Claims

1. An image decoding method performed by a decoding device, comprising: Obtain image information including residual information from a bitstream; Derive quantization transform coefficients based on the residual information; Derive transform coefficients based on an inverse quantization process for the quantization transform coefficients; Derive residual samples based on an inverse transform process for the transform coefficients; Generate reconstructed samples based on the residual samples, the reconstructed samples including reconstructed luminance samples and reconstructed chrominance samples; Derive ALF filter coefficients for an adaptive loop filter (ALF) process for the reconstructed chrominance samples; Generate filtered reconstructed chrominance samples based on the reconstructed chrominance samples and the ALF filter coefficients; Derive cross-component filter coefficients for cross-component filtering; and Generate modified filtered reconstructed chrominance samples based on the reconstructed luminance samples, the filtered reconstructed chrominance samples, and the cross-component filter coefficients, wherein the image information includes header information and an adaptive parameter set (APS) including ALF data, wherein the cross-component filter coefficients are derived based on the ALF data, wherein the header information includes information related to an identifier of the APS and a first flag related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chrominance samples, wherein based on determining that the value of the first flag is 1, the header information includes information related to the identifier of the APS for deriving the cross-component filter coefficients for the Cb color component, wherein the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes a Cb filter signal flag related to whether to signal the cross-component filter for the Cb color component, wherein based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes information related to the number of cross-component filters for the Cb color component, wherein based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component, and wherein the cross-component filter coefficients for the Cb color component are derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component.

2. An image encoding method performed by an encoding device, comprising: Generate residual samples for a current block; Derive transform coefficients based on a transform process for the residual samples; Derive quantization transform coefficients based on a quantization process for the transform coefficients; Generate residual information indicating the quantization transform coefficients; Generate reconstructed samples based on the residual information; Generate adaptive loop filter (ALF) related information and cross-component ALF (CCALF) related information for the reconstructed sample; and Encode the image information including the residual information, the ALF related information, and the CCALF related information, wherein the image information includes header information and an adaptive parameter set (APS), wherein the header information includes a first flag related to whether CCALF is enabled for the Cb color component of the filtered reconstructed chrominance samples and information related to the identifier of the APS including the ALF data, and Based on the ALF data, represent the cross-component filter coefficients, wherein, based on determining that the value of the first flag is 1, the header information includes information related to the identifier of the APS for deriving the cross-component filter coefficients of the Cb color component, wherein the ALF data included in the APS for deriving the cross-component filter coefficients of the Cb color component includes a Cb filter signal flag related to whether to signal the cross-component filter of the Cb color component, wherein, based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients of the Cb color component includes information related to the number of cross-component filters for the Cb color component, wherein, based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients of the Cb color component includes information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component, and wherein the cross-component filter coefficients for the Cb color component are derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component.

3. A method for transmitting data of an image, the method comprising: Obtain a bitstream for the image, wherein the bitstream is generated based on the following steps: generate residual samples for a current block; Derive transform coefficients based on a transform process for the residual samples; derive quantized transform coefficients based on a quantization process for the transform coefficients; generate residual information indicating the quantized transform coefficients; generate reconstructed samples based on the residual information; generate adaptive loop filter (ALF) related information and cross-component ALF (CCALF) related information for the reconstructed samples; and encode the image information including the residual information, the ALF related information, and the CCALF related information; and Transmit the data including the bitstream, wherein the image information includes header information and an adaptive parameter set (APS), Among them, the header information includes a first flag related to whether CCALF is enabled for the Cb color component of the reconstructed chrominance samples for the filtering and information related to the identifier of the APS. Among them, based on the ALF data, the cross-component filter coefficients are represented. Among them, based on determining that the value of the first flag is 1, the header information includes information related to the identifier of the APS for deriving the cross-component filter coefficients for the Cb color component. Among them, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes a Cb filter signal flag related to whether to signal the cross-component filter for the Cb color component. Among them, based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes information related to the number of cross-component filters for the Cb color component. Among them, based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component includes information about the absolute value of the cross-component filter coefficients for the Cb color component and information about the sign of the cross-component filter coefficients for the Cb color component, and Among them, the cross-component filter coefficients for the Cb color component are derived based on the information about the absolute value of the cross-component filter coefficients for the Cb color component and the information about the sign of the cross-component filter coefficients for the Cb color component.

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