Image decoding method, image encoding method, and data transmission method

Abstract

The invention relates to an image decoding method, an image encoding method, and a data transmission method. An image decoding method according to the present invention allows: acquiring image information including prediction mode information and adaptive loop filter (ALF) information from a bitstream, the ALF information including alternative filter information for a chroma component of a current block; deriving a prediction sample of the current block based on the prediction mode information; generating a reconstructed sample based on the prediction sample; and generating a modified reconstructed sample of the chroma component of the current block based on the alternative filter information.

Description

[0001] This application is a divisional application of the invention patent application with the original application number 202080063057.X (International Application No.: PCT / KR2020 / 008933, application date: July 8, 2020, invention title: Video or Image Coding Based on Adaptive Loop Filter). Technical Field

[0002] The present disclosure relates to video or image coding based on an adaptive loop filter. Background Art

[0003] Recently, the demand for high-resolution and high-quality images / videos such as 4K or 8K or higher ultra-high definition (UHD) images / videos has increased in various fields. As image / video data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to existing image / video data. Therefore, transmitting image data using media such as existing wired / wireless broadband lines or existing storage media or storing image / video data using existing storage media increases the transmission cost and storage cost.

[0004] In addition, the interest and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content or holograms have recently increased, and the broadcasting of images / videos (e.g., game images) having characteristics different from real images has increased.

[0005] Therefore, very efficient image / video compression techniques are needed to effectively compress, transmit, store, and reproduce the information of high-resolution and high-quality images / videos having various characteristics as described above.

[0006] In addition, filtering techniques using adaptive loop filtering (ALF) to improve compression efficiency and increase subjective / objective visual quality have been discussed. To efficiently apply these techniques, a method for efficiently signaling relevant information is needed. Summary of the Invention

[0007] Technical Solution

[0008] According to an embodiment of the present disclosure, an image decoding method performed by a decoding device is provided. The method includes the steps of: obtaining image information including adaptive loop filter (ALF) information and prediction mode information from a bitstream; deriving a prediction sample of a current block based on the prediction mode information; and generating a reconstructed sample based on the prediction sample, wherein the ALF information includes alternative filter information for a chrominance component of the current block, and a modified reconstructed sample of the chrominance component of the current block is generated based on the alternative filter information.

[0009] According to another embodiment of the present disclosure, there is provided a video encoding method performed by an encoding device. The method includes the following steps: determining a prediction mode of a current block, and deriving prediction samples based on the prediction mode; generating reconstructed samples based on the prediction samples; generating adaptive loop filter (ALF) information regarding the reconstructed samples; and encoding image information including the ALF information and the prediction mode information, wherein the ALF information includes alternative filter information for a chrominance component of the current block.

[0010] According to another embodiment of the present disclosure, there is provided a computer-readable digital storage medium storing a bitstream including image information that causes a decoding device to perform an image decoding method. The image decoding method includes the following steps: obtaining, from the bitstream, image information including adaptive loop filter (ALF) information and prediction mode information; and generating a reconstructed sample of a current block based on the prediction mode information, wherein the ALF information includes alternative filter information regarding a chrominance component of the current block, and generating a modified reconstructed sample of the chrominance component of the current block based on the alternative filter information.

[0011] Advantageous Effects

[0012] According to an embodiment of the present disclosure, the overall image / video compression efficiency can be increased.

[0013] According to an embodiment of the present disclosure, subjective / objective visual quality can be increased through efficient filtering.

[0014] According to an embodiment of the present disclosure, ALF-related information can be signaled efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of a video / image encoding system to which embodiments of the present disclosure can be applied is shown.

[0016] Figure 2 FIG. schematically shows a configuration of a video / image encoding device to which embodiments of the present disclosure can be applied.

[0017] Figure 3 FIG. schematically shows a configuration of a video / image decoding device to which embodiments of the present disclosure can be applied.

[0018] Figure 4 An entropy encoding method of an encoding device is shown.

[0019] Figure 5 An entropy encoding method of a decoding device is shown.

[0020] Figure 6 A hierarchical structure for encoding an image / video is shown exemplarily.

[0021] Figure 7 is a flowchart schematically showing an example of ALF processing.

[0022] Figure 8 shows an example of the shape of an ALF filter.

[0023] Figure 9 shows an example of the hierarchical structure of ALF data.

[0024] Figure 10 shows another example of the hierarchical structure of ALF data.

[0025] Figure 11 shows a fixed order corresponding to position-related filter coefficients.

[0026] Figure 12 and Figure 13 schematically shows an example of a video / image encoding method and related components according to an embodiment of the present disclosure.

[0027] Figure 14 and Figure 15 schematically shows an example of an image / video decoding method and related components according to an embodiment of the present disclosure.

[0028] Figure 16 shows an example of a content stream system to which the embodiments disclosed in the present disclosure can be applied. Detailed Description

[0029] Although the present disclosure may have various modifications and configurations, certain embodiments have been shown in the drawings and described in detail herein. However, this should not be construed as limiting the present disclosure to any specific embodiment. The terms used herein are presented for the purpose of describing specific embodiments and are not intended to limit the technical idea of the present disclosure. Unless otherwise specified, terms in the singular form may include the plural form. It will be understood that the terms "comprising" or "having" when used herein specify the presence of the stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

[0030] Each component in the drawings described in the present disclosure is shown independently for convenience of describing different characteristic functions and is not meant that the components are implemented in separate hardware or separate software. For example, two or more configurations may be combined to form one configuration, or one configuration may be divided into multiple configurations. Embodiments in which the respective configurations are integrated and / or separated without departing from the spirit of the present disclosure are also included within the scope of the present disclosure.

[0031] In this specification, "A or B" may mean "only A", "only B", or "both A and B". In other words, in this specification, "A or B" may be interpreted as "A and / or B". For example, in this specification, "A, B, or C" may mean "only A", "only B", "only C", or "any combination of A, B, and C".

[0032] The slashes ( / ) or commas used in this specification may mean "and / or". For example, "A / B" may mean "A and / or B". Therefore, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B, or C".

[0033] 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 expressions "at least one of A or B" or "at least one of A and / or B" may be interpreted as "at least one of A and B".

[0034] Furthermore, 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".

[0035] In addition, the parentheses used in this specification may mean "for example". Specifically, when it is indicated as "prediction (intra prediction)", it may mean that "intra prediction" is presented as an example of "prediction". In other words, "prediction" in this specification is not limited to "intra prediction", and "intra prediction" may be presented as an example of "prediction". Additionally, when it is indicated as "prediction (i.e., intra prediction)", it may also mean that "intra prediction" is presented as an example of "prediction".

[0036] The technical features described separately in a figure in this specification may be implemented separately or simultaneously.

[0037] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components may be omitted.

[0038] Figure 1 An example of a video / image encoding system to which embodiments of the present disclosure can be applied is shown.

[0039] Referring to Figure 1 , the video / image encoding system may include a first device (source device) and a second device (receiving device). The source device may send the encoded video / image information or data in the form of a file or a stream to the receiving device via a digital storage medium or a network.

[0040] 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.

[0041] 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 generate video / images (electronically). 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.

[0042] The encoding device may encode the input video / images. For compression and encoding 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.

[0043] 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 through a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include elements for generating a media file in a predetermined file format and may include elements for transmitting through a broadcast / communication network. The receiver may receive / extract the bitstream and send the received bitstream to the decoding device.

[0044] The decoding device may decode the video / images by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding device.

[0045] The renderer may render the decoded video / images. The rendered video / images may be displayed through the display.

[0046] This disclosure relates to video / image encoding. For example, the methods / embodiments disclosed in this disclosure may be applied to the methods disclosed in the Versatile Video Coding (VVC) standard, the Essential Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the Second Generation Audio Video Coding Standard (AVS2), or the next-generation video / image coding standards (e.g., H.267, H.268, etc.).

[0047] The present disclosure presents various embodiments of video / image coding, and unless otherwise specified, the above embodiments can also be executed in combination with each other.

[0048] In the present disclosure, video may refer to a series of images over time. A picture generally refers to a unit of an image representing a specific time range, and a slice / tile refers to a unit that constitutes a part of a picture in terms of coding. A slice / tile may include one or more coding tree units (CTUs). A picture may be composed of one or more slices / titles.

[0049] A tile is a rectangular region of CTUs within a specific tile column and a specific tile row in a picture. A tile column is a rectangular region of CTUs with a height equal to the height of the picture and a width specified by a syntax element in the picture parameter set. A tile row is a rectangular region of CTUs with a height specified by a syntax element in the picture parameter set and a width equal to the width of the picture. A tile scan is a specific sequential ordering of CTUs that divides a picture, where CTUs are sequentially ordered in the raster scan of the CTUs of a tile, and tiles in the picture are sequentially ordered in the raster scan of the tiles of the picture. A slice may include multiple complete tiles of a picture or multiple consecutive CTU rows in a tile, which may be included in one NAL unit. In the present disclosure, tile groups and slices may be used interchangeably. For example, in the present disclosure, a tile group / tile group header may be referred to as a slice / slice header.

[0050] In addition, a picture may be divided into two or more sub - pictures. A sub - picture may be a rectangular region of one or more slices within a picture.

[0051] A pixel or pel may mean the smallest unit that constitutes a picture (or image). Additionally, "sample" may be used as a term corresponding to a pixel. A sample generally may represent a pixel or a pixel value, and may represent only the pixel / pixel value of the luminance component or only the pixel / pixel value of the chrominance component.

[0052] A unit may represent the basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to that region. A unit may include one luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a unit may be used interchangeably with terms such as a block or a region. Generally, an M×N block may include a set (or array) of samples (or a sample array) or transform coefficients in M columns and N rows. Alternatively, a sample may mean a pixel value in the spatial domain, and when such a pixel value is transformed to the frequency domain, it may mean a transform coefficient in the frequency domain.

[0053] Figure 2 FIG. schematically shows the configuration of a video / image coding device to which embodiments of the present disclosure can be applied. Hereinafter, a video coding device may include an image coding device.

[0054] Reference Figure 2 As shown in 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, a dequantizer 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 reconstruction 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 further include the memory 270 as an internal / external component.

[0055] The image splitter 210 may split an input image (or a picture or a frame) input to the encoding device 200 into one or more processors. For example, the processor may be referred to as a coding unit (CU). In this case, the coding unit may be recursively 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, one coding unit may be split into multiple coding units with a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. In this case, for example, the quadtree structure may be applied first, and then the binary tree structure and / or the ternary structure may be applied later. Alternatively, the binary tree structure may be applied first. The encoding process according to the present disclosure may be performed based on the final coding unit that is 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 if necessary, the coding unit may be recursively split into coding units with a deeper depth and the coding unit with an optimal size may be used as the final coding unit. Here, the encoding process may include processes of prediction, transformation, and reconstruction (which will be 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 split or separated from the above-mentioned 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.

[0056] In some cases, the term unit may be used interchangeably with terms such as block or region. In general, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. Samples typically may represent pixels or pixel values, which may be pixels / pixel values representing only the luminance component or pixels / pixel values representing only the chrominance component. The term sample may be used as a term corresponding to a frame (or image) of pixels or picture elements.

[0057] In the encoding device 200, a prediction signal (prediction block, prediction sample array) output from the inter-frame predictor 221 or the intra-frame predictor 222 is subtracted from the input image signal (original block, original sample array) to generate a residual signal (residual block, residual sample array), and the generated residual signal is sent to the transformer 232. In this case, as shown, the unit that subtracts the prediction signal (prediction block, prediction sample array) from the input image signal (original block, original sample array) in the encoding device 200 may be referred to as the subtractor 231. The predictor may perform prediction on a block to be processed (hereinafter, referred to as the current block) and generate a prediction block including the prediction samples of the current block. The predictor may determine whether to apply intra-frame prediction or inter-frame prediction based on the current block or CU. As will be described later in the description of each prediction mode, the predictor may generate various information related to the prediction (e.g., prediction mode information) and send the generated information to the entropy encoder 240. Information about the prediction may be encoded in the entropy encoder 240 and output in the form of a bitstream.

[0058] The intra-frame predictor 222 may 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-frame 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 depending on the settings. The intra-frame predictor 222 may use the prediction mode applied to the neighboring block to determine the prediction mode applied to the current block.

[0059] The inter-frame predictor 221 may derive a predicted block of a current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. Here, in order to reduce the amount of motion information transmitted in the inter-frame prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter-frame prediction direction (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 blocks may be the same or different. The temporal neighboring blocks may be referred to as collocated reference blocks, collocated CUs (colCUs), etc., and the reference picture including the temporal neighboring blocks may be referred to as a collocated picture (colPic). For example, the inter-frame predictor 221 may configure a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter-frame prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter-frame predictor 221 may 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 transmitted. In the case of the motion vector prediction (MVP) mode, the motion vector of a neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling a motion vector difference.

[0060] The predictor 220 may generate a prediction signal based on various prediction methods described below. For example, the predictor may apply not only intra-frame prediction or inter-frame prediction to predict a block, but also both intra-frame prediction and inter-frame prediction at the same time. This may be referred to as combined intra and inter prediction (CIIP). Additionally, the predictor may predict a block based on the intra-block copy (IBC) prediction mode or the palette mode. The IBC prediction mode or the palette mode may be used for content image / video coding such as games, e.g., screen content coding (SCC). IBC basically performs prediction in the current picture, but may be performed similarly to inter-frame prediction such that a reference block is derived in the current picture. That is, IBC may use at least one inter-frame prediction technique described in the present disclosure. The palette mode may be regarded as an example of intra-frame coding or intra-frame prediction. When the palette mode is applied, the sample values within the picture may be signaled based on information about the palette table and the palette index.

[0061] The prediction signal generated by a predictor (including the inter-frame predictor 221 and / or the intra-frame predictor 222) can be used to generate a reconstructed signal or generate a residual signal. The transformer 232 can generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique can include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen - Loève transform (KLT), a graph-based transform (GBT), or a conditional non-linear transform (CNT). Here, when the relationship information between pixels is represented by a graph, GBT means a transform obtained from the graph. CNT refers to a transform generated based on a prediction signal generated using all previously reconstructed pixels. Additionally, the transform process can be applied to square pixel blocks of the same size or can be applied to blocks of variable size other than squares.

[0062] The quantizer 233 can quantize the transform coefficients and send them to the entropy encoder 240, and the 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 can be referred to as residual information. The quantizer 233 can rearrange the block-type 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. Information about the transform coefficients can be generated. The entropy encoder 240 can perform various coding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 240 can encode together or separately the information required for video / image reconstruction other than the quantized transform coefficients (e.g., the values of syntax elements, etc.). The encoded information (e.g., the 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 can also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). Additionally, the video / image information can also include general constraint information. In the present disclosure, the information and / or syntax elements sent / signaled from the encoding device to the decoding device can be included in the video / picture information. The video / image information can be encoded through the above encoding process and included in the bitstream. The bitstream can be sent via a network or can be stored in a digital storage medium. The network can include a broadcast network and / or a communication network, and the digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for sending the signal output from the entropy encoder 240 and / or a storage unit (not shown) for storing the signal can be included as internal / external elements of the encoding device 200, and alternatively, the transmitter can be included in the entropy encoder 240.

[0063] The quantized transform coefficients output from the quantizer 233 can be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transformation to the quantized transform coefficients via the dequantizer 234 and the inverse transform unit 235. The adder 250 adds the reconstructed residual signal and the prediction signal output from the inter-frame predictor 221 or the intra-frame predictor 222 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If there is no residual in the block to be processed (e.g., in the case of applying the skip mode), the predicted block can be used as the reconstructed block. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. As described below, the generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture and can be used for inter-frame prediction of the next picture through filtering.

[0064] In addition, luminance mapping with chroma scaling (LMCS) can be applied during picture encoding and / or reconstruction.

[0065] The filter 260 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 260 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture and store the modified reconstructed picture in the memory 270 (specifically, the DPB of the memory 270). For example, various filtering methods may include deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 260 can generate various information related to filtering and send the generated information to the entropy encoder 240, as will be described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 240 and output in the form of a bitstream.

[0066] The modified reconstructed picture sent to the memory 270 can be used as a reference picture in the inter-frame predictor 221. When inter-frame prediction is applied by the encoding device, prediction mismatch between the encoding device 200 and the decoding device 300 can be avoided and the encoding efficiency can be improved.

[0067] The DPB of the memory 270 can store the modified reconstructed picture used as a reference picture in the inter-frame predictor 221. The memory 270 can store the motion information of the block that derives (or encodes) the motion information in the current picture and / or the motion information of the block that has been reconstructed in the picture. The stored motion information can be sent to the inter-frame predictor 221 and used as the motion information of spatially neighboring blocks or temporally neighboring blocks. The memory 270 can store the reconstructed samples of the reconstructed blocks in the current picture and can transfer the reconstructed samples to the intra-frame predictor 222.

[0068] In the present disclosure, 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 consistency of expression, may still be referred to as transform coefficients.

[0069] Furthermore, in the present disclosure, the quantized transform coefficients and the transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In such a case, the residual information may include information about the transform coefficients, and the information about the transform coefficients may be signaled by a 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 an inverse transform (scaling) of the transform coefficients. The residual samples may be derived based on an inverse transform (transform) of the scaled transform coefficients. These details may also be applied / expressed in other parts of the present disclosure.

[0070] Figure 3 is a diagram schematically showing the configuration of a video / image decoding device to which embodiments of the present disclosure may be applied.

[0071] Referring to Figure 3 , the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an intra predictor 331 and an inter predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. According to an embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured by hardware components (e.g., a decoder chipset or a processor). Additionally, the memory 360 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may also include the memory 360 as an internal / external component.

[0072] When receiving a bitstream including 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 block partitioning related information obtained from the bitstream. The decoding device 300 may perform decoding using a processor applied in the encoding device. Thus, for example, the decoding processor may be an encoding unit, and the encoding unit may be partitioned from a coding tree unit or a largest coding 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 coding unit. The reconstructed image signal decoded and output by the decoding device 300 may be reproduced by a reproduction device.

[0073] The decoding device 300 may receive from Figure 2The signal output by the encoding device in the form of a bitstream, and the received signal can be decoded by the entropy decoder 310. For example, the entropy decoder 310 can parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an Adaptive Parameter Set (APS), a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), or a Video Parameter Set (VPS). Additionally, the video / image information may also include general constraint information. The decoding device can also decode the picture based on the information about the parameter set and / or the general constraint information. The signaled / received information and / or syntax elements described later in this disclosure can be decoded through the decoding process and obtained from the bitstream. For example, the entropy decoder 310 decodes the information in the bitstream based on an encoding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the syntax elements required for image reconstruction and the quantization values of the transform coefficients of the residuals. More specifically, the CABAC entropy decoding method can receive bins corresponding to the respective syntax elements in the bitstream, use the information of the syntax element to be decoded, the decoding information of the block to be decoded, or the information of the symbols / bins decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bin by predicting the probability of the bin occurrence according to the determined context model, and generate symbols corresponding to the values of the respective syntax elements. In this case, after determining the context model, 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. Among the information decoded by the entropy decoder 310, the information related to prediction can be provided to the predictors (inter-frame predictor 332 and intra-frame predictor 331), and the residual values (i.e., the quantized transform coefficients and the related parameter information) for which entropy decoding has been performed in the entropy decoder 310 can be input to the residual processor 320. The residual processor 320 can derive a residual signal (residual block, residual sample, residual sample array). Additionally, the information about filtering among the information decoded by the entropy decoder 310 can be provided to the filter 350. Furthermore, a receiver (not shown) for receiving the signal output by the encoding device can also be configured as an internal / external component of the decoding device 300, or the receiver can be a component of the entropy decoder 310. Additionally, the decoding device according to the present disclosure 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 may include the entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverse transformer 322, an adder 340, a filter 350, a memory 360, an inter-frame predictor 332, and an intra-frame predictor 331.

[0074] The dequantizer 321 can dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 321 can rearrange the quantized transform coefficients in a two-dimensional block form. In this case, the rearrangement can be performed based on the coefficient scan order executed in the encoding device. The dequantizer 321 can dequantize the quantized transform coefficients using quantization parameters (e.g., quantization step information) and obtain the transform coefficients.

[0075] The inverse transformer 322 inversely transforms the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0076] The predictor can perform prediction on the current block and generate a prediction block including the prediction samples of 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.

[0077] The predictor 330 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). Additionally, the predictor can predict a block based on the intra block copy (IBC) prediction mode or the palette mode. The IBC prediction mode or the palette mode can be used for content image / video coding such as games, e.g., screen content coding (SCC). IBC basically performs prediction in the current picture, but can be performed similarly to inter prediction so that 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 disclosure. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, the sample values within the picture can be signaled based on the information about the palette table and the palette index.

[0078] The intra predictor 331 can predict the current block by referring to the samples in the current picture. Depending on the prediction mode, the samples referred to can be located near the current block or can be separated. 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 use the prediction mode applied to the neighboring blocks to determine the prediction mode applied to the current block.

[0079] The inter-frame predictor 332 may derive a prediction block of a 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 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 further include inter-frame prediction direction (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. For example, the inter-frame predictor 332 may configure a motion information candidate list based on neighboring blocks and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. The inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0080] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to a prediction signal (prediction block, prediction sample array) output from a predictor (including the inter-frame predictor 332 and / or the intra-frame predictor 331). If there is no residual for the block to be processed, for example, when the skip mode is applied, the prediction block may be used as the reconstructed block.

[0081] The adder 340 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra-frame prediction of the next block to be processed in the current picture, may be output through filtering as described below, or may be used for inter-frame prediction of the next picture.

[0082] In addition, luminance mapping with chroma scaling (LMCS) may be applied in the picture decoding process.

[0083] The filter 350 may improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 350 may 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). For example, various filtering methods may include deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0084] 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 that derive (or decode) the motion information in the current picture and / or the motion information of the blocks that have been reconstructed in the picture. The stored motion information can be sent to the inter-frame predictor 332 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 transmit the reconstructed samples to the intra-frame predictor 331.

[0085] In the present disclosure, the embodiments described in the filter 260, the inter-frame predictor 221, and the intra-frame predictor 222 of the encoding device 200 can be the same as or respectively correspond to the filter 350, the inter-frame predictor 332, and the intra-frame predictor 331 of the decoding device 300 and be applied accordingly. This also applies to the inter-frame predictor 332 and the intra-frame predictor 331.

[0086] As described above, in video coding, prediction is performed to increase the compression efficiency. Thus, a prediction block including prediction samples of a current block (a block to be encoded) can be generated. Here, the prediction block includes prediction samples in the spatial domain (or pixel domain). The prediction block is derived identically in the encoding device and the decoding device, and the encoding device decodes information about the residual between the original block and the prediction block (residual information) rather than the original sample values of the original block itself. By signaling the device, the image coding efficiency can be increased. The decoding device can derive a residual block including residual samples based on the residual information, and generate a reconstructed block including reconstructed samples by summing the residual block and the prediction block, and generate a reconstructed picture including the reconstructed block.

[0087] The residual information can be generated through transform processing and quantization processing. For example, the encoding device can derive a residual block between the original block and the prediction block, and perform transform processing on the residual samples (residual sample array) included in the residual block to derive transform coefficients, and then, by performing quantization processing on the transform coefficients, derive quantized transform coefficients to signal the residual-related information (via the bitstream) to the decoding device. Here, the residual information can include position information, transform technology, transform kernel, quantization parameters, value information of the quantized transform coefficients, etc. The decoding device can perform dequantization / inverse transform 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 dequantize / inverse transform the quantized transform coefficients for inter-frame prediction reference of a later picture to derive a residual block, and generate a reconstructed picture based on it.

[0088] In the present disclosure, 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 consistency of expression, may still be referred to as transform coefficients.

[0089] In the present disclosure, 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 a 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-transforming (transforming) of the scaled transform coefficients. This may also be applied / expressed in other parts of the present disclosure.

[0090] Intra prediction may refer to prediction for generating prediction samples of a current block based on reference samples in a 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 of size 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. Additionally, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size 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.

[0091] However, some of the neighboring reference samples of the current block may not have been decoded or may not be available yet. 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.

[0092] When deriving the neighboring reference samples, (i) the prediction samples may be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction samples may be derived based on the reference samples among the peripheral reference samples of the current block that exist in a specific (prediction) direction of the prediction samples. The case of (i) may be referred to as a non-directional mode or a non-angular mode, and the case of (ii) may be referred to as a directional mode or an angular mode.

[0093] In addition, a predicted sample can also be generated by interpolating between a second neighboring sample and a first neighboring sample among neighboring reference samples where the predicted sample based on the current block is in a direction opposite to the prediction direction of the intra prediction mode of the current block. The above situation 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 situation can be referred to as the LM mode.

[0094] Furthermore, a temporary predicted sample of the current block can be derived based on filtered neighboring reference samples, and at least one reference sample (i.e., unfiltered neighboring reference sample) derived according to the intra prediction mode among the existing neighboring reference samples and the temporary predicted sample can be weighted and summed to derive the predicted sample of the current block. The above situation can be referred to as position-dependent intra prediction (PDPC).

[0095] Moreover, the reference sample row with the highest prediction accuracy among the neighboring multi-reference sample rows of the current block can be selected to derive the predicted sample using the reference samples located in the prediction direction on the corresponding row, and then the reference sample row used herein can be indicated (signaled) to the decoding device to perform intra prediction coding. The above situation can be referred to as multi-reference row (MRL) intra prediction or MRL-based intra prediction.

[0096] In addition, intra prediction can be performed by dividing the current block into vertical or horizontal sub-partitions based on the same intra prediction mode, and the neighboring reference samples can be derived and used on a sub-partition basis. That is, in this case, the intra prediction mode of the current block also applies to the sub-partitions, and in some cases, the intra prediction performance can be improved by deriving and using the neighboring reference samples on a sub-partition basis. This prediction method can be referred to as intra-sub-partition (ISP) or ISP-based intra prediction.

[0097] The above intra prediction methods can be referred to as intra prediction types separately from the intra prediction mode. Intra prediction types can be called 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 above 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. The normal intra prediction type can generally be applied when a specific intra prediction type is not applied, and prediction can be performed based on the above intra prediction mode. Additionally, post-filtering can be performed on the derived predicted samples as needed.

[0098] Specifically, the intra prediction process can 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 can be performed on the derived predicted samples as needed.

[0099] When intra prediction is applied, the intra prediction mode applied to a current block may be determined using the intra prediction modes of neighboring blocks. For example, the decoding device may select one of the mpm candidates of the mpm list derived from the intra prediction modes of neighboring blocks (e.g., left and / or upper neighboring blocks) of the current block based on the received most probable mode (mpm) index, and select one of the other remaining intra prediction modes not included in the mpm candidates (and the planar mode) based on the remaining intra prediction mode information. The mpm list may be configured to include or not include the planar mode as a candidate. For example, if the mpm list includes the planar mode as a candidate, the mpm list may have six candidates. If the mpm list does not include the planar mode as a candidate, the mpm list may have three candidates. When the mpm list does not include the planar mode as a candidate, a non-planar flag (e.g., intra_luma_not_planar_flag) indicating whether the intra prediction mode of the current block is not the planar mode may be signaled. For example, the mpm flag may be signaled first, and when the value of the mpm flag is 1, the mpm index and the non-planar flag may be signaled. Additionally, when the value of the non-planar flag is 1, the mpm index may be signaled. Here, the mpm list is configured not to include the planar mode as a candidate, and the non-planar flag is not signaled first to check whether it is the planar mode because the planar mode is always considered as an mpm.

[0100] For example, whether the intra prediction mode applied to the current block is among the MPM candidates (and the planar mode) or among the residual modes can be indicated based on an MPM flag (e.g., Intra_luma_mpm_flag). A value of 1 for the MPM flag can indicate that the intra prediction mode of the current block is within the MPM candidates (and the planar mode), and a value of 0 for the MPM flag can indicate that the intra prediction mode of the current block is not among the MPM candidates (and the planar mode). A value of 0 for the non-planar flag (e.g., Intra_luma_not_planar_flag) can indicate that the intra prediction mode of the current block is the planar mode, and a value of 1 for the non-planar flag can indicate that the intra prediction mode of the current block is not the planar mode. The MPM index can be signaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element, and the residual intra prediction mode information can be signaled in the form of a rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element. For example, the residual intra prediction mode information can index the residual intra prediction modes not included in the MPM candidates (and the planar mode) among all the intra prediction modes in the order of the prediction mode numbers to indicate one of them. The intra prediction mode can be the intra prediction mode of the luminance component (samples). Hereinafter, the intra prediction mode information can include at least one of an MPM flag (e.g., Intra_luma_mpm_flag), a non-planar flag (e.g., Intra_luma_not_planar_flag), an MPM index (e.g., mpm_idx or intra_luma_mpm_idx), and residual intra prediction mode information (rem_intra_luma_pred_mode or intra_luma_mpm_remainder). In the present disclosure, the MPM list can be referred to by various terms such as an MPM candidate list and a candModeList. When MIP is applied to the current block, a separate MPM flag (e.g., intra_mip_mpm_flag), an MPM index (e.g., intra_mip_mpm_idx), and residual intra prediction mode information (e.g., intra_mip_mpm_remainder) for MIP can be signaled, and the non-planar flag is not signaled.

[0101] In other words, generally, when performing block splitting on an image, the current block to be encoded and neighboring blocks have similar image characteristics. Therefore, there is a relatively high probability that the current block and neighboring blocks have the same or similar intra prediction modes. Thus, the encoder can use the intra prediction mode of a neighboring block to encode the intra prediction mode of the current block.

[0102] For example, an encoder / decoder may configure a list of the most probable modes (MPMs) for a current block. The MPM list may also be referred to as an MPM candidate list. In this document, an MPM may refer to a mode that improves coding efficiency by considering the similarity between a current block and neighboring blocks in intra prediction mode coding. As described above, the MPM list may be configured to include the planar mode, or may be configured not to include the planar mode. For example, when the MPM list includes the planar mode, the number of candidates in the MPM list may be 6. And, if the MPM list does not include the planar mode, the number of candidates in the MPM list may be 5.

[0103] The encoder / decoder may configure an MPM list including 5 or 6 MPMs.

[0104] To configure the MPM list, three types of modes may be considered: a default intra mode, a neighbor intra mode, and a derived intra mode.

[0105] For the neighbor intra mode, two neighboring blocks may be considered, i.e., a left neighboring block and an upper neighboring block.

[0106] As described above, if the MPM list is configured not to include the planar mode, the planar mode is excluded from the list, and the number of MPM list candidates may be set to 5.

[0107] In addition, non - directional modes (or non - angular modes) among intra prediction modes may include a DC mode based on the average of neighboring reference samples of a current block or an interpolated planar mode.

[0108] When performing inter-frame prediction, the predictor of an encoding device / decoding device may derive predicted samples 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 predicted block (predicted sample array) of 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 further include inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks present in the current picture and temporally neighboring blocks present in a reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring blocks may be the same or different. The temporally neighboring blocks may be referred to as co-located reference blocks, co-located CUs (colCUs), etc., and the reference picture including the temporally neighboring blocks may be referred to as a co-located 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 neighboring blocks. 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 a 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.

[0109] Depending on 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 bi - 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 output order as reference pictures, and the reference picture list L1 may include pictures later than the current picture in output order. The previous picture may be referred to as the forward (reference) picture, and the subsequent picture may be referred to as the backward (reference) picture. The reference picture list L0 may also include pictures later than the current picture in output order as reference pictures. In this case, the previous picture may be indexed first in the reference picture list L0, and the subsequent picture may be indexed later. The reference picture list L1 may also include previous pictures earlier than the current picture in output order as reference pictures. In this case, the subsequent picture may be indexed first in the reference picture list 1, and the previous picture may be indexed later. The output order may correspond to the picture order count (POC) order.

[0110] Figure 4 Shows the entropy encoding method of the encoding device. Figure 4 The method may be performed by Figure 2 The entropy encoder 240.

[0111] The encoding device performs binarization on the target syntax element (S400). Here, the binarization may be based on various binarization methods such as truncated Rice binarization processing and fixed - length binarization processing, and the binarization method for the target syntax element may be predefined.

[0112] The encoding device performs entropy encoding on the target syntax element (S410). The encoding device may encode the bit string of the target syntax element based on entropy encoding techniques such as context - adaptive arithmetic coding (CABAC) or context - adaptive variable - length coding (CAVLC) based on regular coding (context - based) or bypass coding, and the output may be included in the bitstream. As described above, the bitstream may be sent to the decoding device through a (digital) storage medium or a network.

[0113] Figure 5 Shows the entropy encoding method of the decoding device. Figure 5 The method may be performed by Figure 3 The entropy decoder 310.

[0114] The decoding device performs binarization on a target syntax element (S500). Here, the binarization can be based on various binarization methods such as truncated Rice binarization processing and fixed-length binarization processing, and the binarization method used for the target syntax element can be predefined. The decoding device can derive an available cell string (cell string candidate) of available values of the target syntax element through the binarization process.

[0115] The decoding device performs entropy decoding on the target syntax element (S510). The decoding device sequentially decodes and parses each cell of the target syntax element from the input bits (S) in the bitstream, and compares the derived cell string with the available cell strings of the corresponding syntax element. If the derived cell string is the same as one of the available cell strings, the value corresponding to the cell string is derived as the value of the corresponding syntax element. If not, the above process is performed again after further parsing the next bit in the bitstream. Through this process, the corresponding information can be signaled using variable-length bits without using the start bit or end bit of specific information (specific syntax element) in the bitstream. Thus, relatively fewer bits can be assigned to low values, and the overall coding efficiency can be increased.

[0116] Figure 6 An exemplary hierarchical structure for encoding an image / video is shown.

[0117] Refer to Figure 6 , the encoded 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 encoded information, and a NAL (network abstraction layer) that is responsible for functions and exists between the VCL and the subsystem.

[0118] In the VCL, VCL data including compressed image data (slice data) is generated, or a parameter set including a picture parameter set (PSP), a sequence parameter set (SPS), and a video parameter set (VPS) or a supplementary enhancement information (SEI) message that is additionally required for image decoding processing can be generated.

[0119] 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.

[0120] As shown in the figure, NAL units can be classified 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).

[0121] The above VCL NAL units and non-VCL NAL units can be sent over a network by attaching header information according to the data standard of the subsystem. For example, 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.

[0122] As described above, NAL units can be specified by 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 in the NAL unit header and signaled.

[0123] 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 type can be classified according to the nature and type of the pictures included in the VCL NAL unit, and the non-VCL NAL unit type can be classified according to the type of the parameter set.

[0124] The following are examples of NAL unit types specified according to the type of the parameter set included in the non-VCL NAL unit type.

[0125] - APS (Adaptive Parameter Set) NAL unit: The type of NAL unit including APS

[0126] - DPS (Decoding Parameter Set) NAL unit: The type of NAL unit including DPS

[0127] - VPS (Video Parameter Set) NAL unit: The type of NAL unit including VPS

[0128] - SPS (Sequence Parameter Set) NAL unit: The type of NAL unit including SPS

[0129] - PPS (Picture Parameter Set) NAL unit: The type of NAL unit including PPS

[0130] - PH (Picture Header) NAL unit: The type of NAL unit including PH

[0131] The above NAL unit type may have syntax information of the NAL unit type, and the syntax information may be stored in and signaled by 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.

[0132] In addition, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to the multiple slices (slice header and slice data sets) in a picture. The picture header (picture header syntax) may include information / parameters generally applicable to the picture. In the present disclosure, a tile group may be mixed with or replaced by slices or a picture. Additionally, in the present disclosure, a tile group header may be mixed with or replaced by a slice header or a picture header.

[0133] The slice header (slice header syntax) may include information / parameters generally applicable to the slice. APS (APS syntax) or PPS (PPS syntax) may include information / parameters generally applicable to one or more slices or pictures. SPS (SPS syntax) may include information / parameters generally applicable to one or more sequences. VPS (VPS syntax) may include information / parameters generally applicable to multiple layers. DPS (DPS syntax) may include information / parameters generally applicable to the total video. DPS may include information / parameters related to the concatenation of coded video sequences (CVS). The high-level syntax (HLS) in the present disclosure may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax.

[0134] In the present disclosure, the image / image information encoded by the encoding device and signaled in the form of a bitstream to the decoding device includes not only information related to segmentation in the picture, intra / inter prediction information, residual information, loop filter 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.

[0135] In addition, in order to compensate for the difference between the original image and the reconstructed image caused by errors occurring in compression encoding processes such as quantization, loop filter processing may be performed on the reconstructed samples or the reconstructed picture as described above. As described above, the loop filter 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.

[0136] Figure 7It is a flowchart schematically showing an example of ALF processing. Figure 7 The ALF processing disclosed in [reference] can be executed in an encoding device and a decoding device. In the present disclosure, the encoding device may include an encoding device and / or a decoding device.

[0137] Refer to Figure 7 , the encoding device derives a filter for ALF (S700). The filter may include filter coefficients. The encoding device may determine whether to apply ALF, and when it is determined to apply ALF, it may derive a filter including filter coefficients for ALF. Information for deriving a filter (coefficients) for ALF or a filter (coefficients) for ALF may be referred to as ALF parameters. Information on whether to apply ALF (i.e., an ALF enable flag) and ALF data for deriving a filter may be signaled from the encoding device to the decoding device. The ALF data may include information for deriving a filter for ALF. Additionally, for example, for hierarchical control of ALF, the ALF enable flag may be signaled at the SPS, picture header, slice header, and / or CTB levels, respectively.

[0138] To derive a filter for ALF, the activity and / or directionality of the current block (or ALF target block) is derived, and the filter may be derived based on the activity and / or directionality. For example, ALF processing may be applied in units of 4×4 blocks (based on the luminance component). The current block or ALF target block may be, for example, a CU, or may be a 4×4 block within a CU. Specifically, for example, a filter for ALF may be derived based on a first filter derived from information included in the ALF data and a predefined second filter, and the encoding device may select one of the filters based on the activity and / or directionality. The encoding device may perform ALF using the filter coefficients included in the selected filter.

[0139] The encoding device performs filtering based on the filter (S710). Modified reconstructed samples may be derived based on the filtering. For example, the filter coefficients in the filter may be arranged or assigned according to the filter shape, and filtering may be performed on the reconstructed samples in the current block. Here, the reconstructed samples in the current block may be the reconstructed samples after deblocking processing and SAO processing are completed. For example, one filter shape may be used, or one filter shape may be selected and used from among multiple predetermined filter shapes. For example, the filter shape applied to the luminance component and the filter shape applied to the chrominance component may be different. For example, a 7×7 diamond filter shape may be used for the luminance component, and a 5×5 diamond filter shape may be used for the chrominance component.

[0140] Figure 8 Shows an example of the shape of the ALF filter. Figure 8 C0 to C11 in (a) of Figure 8C0 to C5 in (b) can be filter coefficients depending on the position within each filter shape.

[0141] Figure 8 (a) shows the shape of a 7×7 diamond filter, Figure 8 (b) shows the shape of a 5×5 diamond filter. In Figure 8 , Cn in the filter shape represents a filter coefficient. When n in Cn is the same, this indicates that the same filter coefficient can be assigned. In the present disclosure, the position and / or cell where a filter coefficient is assigned according to the filter shape of the ALF may be referred to as a filter tap. In this case, one filter coefficient can be assigned to each filter tap, and the arrangement of the filter taps can correspond to the filter shape. The filter tap located at the center of the filter shape may be referred to as the central filter tap. The same filter coefficient can be assigned to two filter taps with the same n value that exist at corresponding positions with respect to the central filter tap. For example, in the case of a 7×7 diamond filter shape, there are 25 filter taps, and since the filter coefficients C0 to C11 are assigned in a centrosymmetric form, only 13 filter coefficients can be used to assign filter coefficients to 25 filter taps. Additionally, for example, in the case of a 5×5 diamond filter shape, there are 13 filter taps, and since the filter coefficients C0 to C5 are assigned in a centrosymmetric form, only 7 filter coefficients can be used to assign filter coefficients to 13 filter taps. For example, in order to reduce the amount of data for signaling information about the filter coefficients, 12 out of the 13 filter coefficients of the 7×7 diamond filter shape can be (explicitly) signaled, and one filter coefficient can be (implicitly) derived. Additionally, for example, 6 out of the 7 filter coefficients of the 5×5 diamond filter shape can be (explicitly) signaled, and one filter coefficient can be (implicitly) derived.

[0142] According to an embodiment of the present disclosure, the ALF parameters for ALF processing can be signaled by an Adaptive Parameter Set (APS). The ALF parameters can be derived from the filter information or ALF data for the ALF.

[0143] 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 high-level design of the ALF tool can include syntax elements that can be accessed from the SPS and / or slice header (or tile group header).

[0144] Figure 9 Shows an example of the hierarchical structure of the ALF data.

[0145] Reference Figure 9 , the coded video sequence (CVS) 900 may include an SPS, one or more PPSs, and one or more subsequent coded pictures. Each coded picture may be divided into rectangular regions. The rectangular regions may be referred to as tiles. One or more tiles may be aggregated to form a tile group or a slice. In this case, the tile group header may be linked to the PPS, and the PPS may be linked to the SPS. According to the existing method, ALF data (ALF parameters) are included in the tile group header. Considering that a video consists of multiple pictures and a picture includes multiple tiles, the frequent ALF data (ALF parameters) signaling in units of tile groups reduces the coding efficiency.

[0146] According to the embodiments proposed in the present disclosure, the ALF parameters may be included in the APS and signaled as follows.

[0147] Figure 10 Another example showing the hierarchical structure of ALF data.

[0148] Reference Figure 10 , the CVS 1000 may include an SPS, one or more PPSs, one or more APSs, and one or more subsequent coded pictures. That is, the APS is defined, and the APS may carry the necessary ALF data (ALF parameters). In addition, the APS may have self-identification parameters and ALF data. The self-identification parameters of the APS may include the APS ID. That is, in addition to the ALF data field, the APS may include information indicating the APS ID. The tile group header or the slice header may use the APS index information to refer to the APS. In other words, the tile group header or the slice header may include the APS index information and may perform ALF processing on the target block based on the ALF data (ALF parameters) included in the APS having the APS ID indicated by the APS index information. Here, the APS index information may be referred to as APS ID information.

[0149] In addition, the SPS may include a flag allowing the use of ALF. For example, when the CVS starts, the SPS may be checked, and the flag may be checked in the SPS. For example, the SPS may include the syntax of Table 1 below. The syntax of Table 1 may be part of the SPS.

[0150] [Table 1]

[0151]

[0152] For example, the semantics of the syntax elements included in the syntax of Table 1 may be represented as shown in Table 2 below.

[0153] [Table 2]

[0154]

[0155] That is, the syntax element sps_alf_enabled_flag can indicate whether ALF is enabled. When the value of the ALF enable flag sps_alf_enabled_flag signaled by SPS (or SPS level) is 1, it can be determined that ALF is enabled for the pictures in the CVS of the reference SPS. Additionally, when the value of sps_alf_enabled_flag is 0, it can be determined that ALF is not enabled for the pictures in the CVS of the reference SPS.

[0156] In addition, as described above, ALF can be individually turned on / off by signaling an additional enable flag at a level lower than SPS. For example, when the ALF tool is enabled for the CVS, slice_alf_enabled_flag can be signaled in the tile group header or slice header. For example, the slice header can include the syntax in Table 3 below.

[0157] [Table 3]

[0158]

[0159] For example, the semantics of the syntax elements included in the syntax of Table 3 can be represented as shown in the table below.

[0160] [Table 4]

[0161]

[0162] For example, when ALF is enabled at the SPS level, slice_alf_enabled_flag can be parsed / signaled. Each tile group composed of one or more tiles can determine whether ALF is enabled based on slice_alf_enabled_flag.

[0163] When the value of the ALF enable flag sps_alf_enabled_flag signaled in the tile group header or slice header is 1, the ALF data can be parsed through the slice header. For example, slice_alf_enabled_flag can specify the ALF enable conditions for the luminance and chrominance components.

[0164] The ALF data can be accessed through the APS ID information (i.e., slice_alf_aps_id). The APS referred to by the corresponding tile group or corresponding slice can be identified based on the APS ID information. The APS can include the ALF data.

[0165] In addition, the structure of the APS including the ALF data can be described based on the syntax in Table 5 below, for example. The syntax of Table 5 can be part of the APS.

[0166] [Table 5]

[0167]

[0168] For example, the semantics of the syntax elements included in the syntax of Table 5 can be represented as shown in Table 6 below.

[0169] [Table 6]

[0170]

[0171] As described above, the syntax element adaptation_parameter_set_id can indicate the identifier of the corresponding APS. That is, the APS can be identified based on the syntax element adaptation_parameter_set_id. The syntax element adaptation_parameter_set_id can be referred to as APS ID information. In addition, the APS can include an ALF data field. The ALF data field alf_data() can be parsed / signaled after the syntax element adaptation_parameter_set_id.

[0172] The core processing / manipulation of the ALF information can be performed in the slice header or the tile group header. The above ALF data field can include information about the processing of the ALF filter. For example, the information that can be extracted from the ALF data field includes information about the number of filters used, information indicating whether ALF is applied only to the luminance component, information about the color component, information about the Exponential Golomb (EG) parameter, and / or the incremental value of the filter coefficient, etc.

[0173] In addition, for example, the ALF data field can include the following ALF data syntax.

[0174] [Table 7]

[0175]

[0176]

[0177]

[0178] For example, the semantics of the syntax elements included in the syntax of Table 7 can be represented as shown in the following table.

[0179] [Table 8]

[0180]

[0181]

[0182]

[0183]

[0184]

[0185]

[0186]

[0187]

[0188] Parsing of the ALF data in the slice header is started by first parsing / signaling the syntax element alf_luma_filter_signal_flag that signals whether a set of luma filters is signaled. Similarly, the syntax element alf_chroma_filter_signal_flag that signals whether chroma filters are signaled can be parsed / signaled.

[0189] When alf_luma_filter_signal_flag is enabled, alf_luma_clip_flag can be parsed.

[0190] When the flag is disabled, linear adaptive loop filtering can be specified to be applied to the luma component. When the flag is enabled, non-linear adaptive loop filtering can be specified to be applied to the luma component.

[0191] In addition, information about the number of luma filters used can be parsed.

[0192] As an example, the maximum number of filters that can be used can be set to 25. When the number of signaled luma filters is at least one, for each filter in the range from 0 to the maximum number of filters (i.e., 25, which can alternatively be referred to as classes), the index information of the filter can be parsed / signaled. This can mean that each class (i.e., from 0 to the maximum number of filters) is associated with a filter index.

[0193] Next, the alf_luma_use_fixed_filter_flag can be parsed / signalled, which is a flag indicating whether a fixed filter is used in the current slice. When the alf_luma_use_fixed_filter_flag is enabled, the alf_luma_fixed_filter_set_idx parameter can be used to signal the index of the fixed filter set. This parameter can have a value in the range of 0 to 15. Additionally, the alf_luma_fixed_filter_pred_present_flag can be parsed / signalled. This flag can specify whether a fixed filter is used to predict the i-th filter coefficient. Then, for each filter, the flag indicating whether the fixed filter is used for the corresponding filter can be decoded.

[0194] When the filters to be used for various types are marked based on the filter index, the alf_luma_coeff_delta_flag can be parsed / signalled. This flag can be used to interpret whether there is a flag alf_luma_coeff_delta_prediction_flag related to the prediction of the ALF luma filter coefficient increment value in the slice header.

[0195] If the number of luma filters signalled by the syntax element alf_luma_num_filters_signalled_minus1 is greater than 0 and the value of the syntax element alf_luma_coeff_delta_flag is 0, it means that there is a syntax element alf_luma_coeff_delta_prediction_flag in the slice header and its status is evaluated. If the status of the syntax element alf_luma_coeff_delta_prediction_flag indicates 1, this can mean that the luma filter coefficient is predicted from the previous luma (filter) coefficient. If the status of the syntax element alf_luma_coeff_delta_prediction_flag indicates 0, this can mean that the luma filter coefficient is not predicted from the increment of the previous luma (filter) coefficient.

[0196] Additionally, when the incremental filter coefficient (i.e., alf_luma_coeff_delta_abs) is encoded based on the Exp-Golomb code, the order k (order k) of the Exp-Golomb (EG) code can be determined to decode the incremental luma filter coefficient (i.e., alf_luma_coeff_delta_abs). For example, the filter coefficient can be decoded using order k based on the Exp-Golomb coding. The order of the Exp-Golomb code can be represented as EG(k).

[0197] To determine EG(k), the syntax element alf_luma_min_eg_order_minus1 may be parsed / signaled. The syntax element alf_luma_min_eg_order_minus1 may be an entropy-coded syntax element. The syntax element alf_luma_min_eg_order_minus1 may indicate the minimum order of the EG used for decoding of the incremental luminance filter coefficients. For example, the value of the syntax element alf_luma_min_eg_order_minus1 may be in the range from 0 to 6.

[0198] After parsing / signaling the syntax element alf_luma_min_eg_order_minus1, the syntax element alf_luma_eg_order_increase_flag may be parsed / signaled. If the value of the syntax element alf_luma_eg_order_increase_flag is 1, this indicates that the order of the EG indicated by the syntax element alf_luma_min_eg_order_minus1 is increased by 1. If the value of the syntax element alf_luma_eg_order_increase_flag is 0, this indicates that the order of the EG indicated by the syntax element alf_luma_min_eg_order_minus1 is not increased. The order of the EG may be represented by the index of the EG. For example, the EG order (or EG index) related to the luminance component may be determined as follows based on the syntax element alf_luma_min_eg_order_minus1 and the syntax element alf_luma_eg_order_increase_flag.

[0199] [Table 9]

[0200]

[0201] Based on the determination process, expGoOrderY may be derived as expGoOrderY = KminTab. Thus, an array including the EG order may be derived, which may be used by the decoding device. expGoOrderY may indicate the EG order (or EG index).

[0202] The following table may represent a method for deriving the Golomb order based on the above algorithm. That is, the above algorithm may be based on the following table. In the following table, the Golomb index may be the input and the k-th order to be used may be the corresponding output.

[0203] [Table 10]

[0204] Columbus index = 0 Columbus index = 1 Columbus index = 2 Kmin = 1 1 1 2 alf_luma_eg_order_increase_flag[i] 0 1 1 Columbus order k 1 2 3

[0205] Referring to Table 10, the (minimum) Columbus order and / or the (minimum) Columbus index can be increased based on alf_eg_order_increase_flag[i]. For example, if alf_luma_min_eg_order_minus1 = 0, then Kmin can be set to = 0 + 1. When the Columbus index is 0, alf_luma_eg_order_increase_flag[i] can be parsed. When this flag is enabled (if available), the Columbus order corresponding to the Columbus index = 0 can be increased by 1 from the initial Kmin value. As shown in Table 11, when this flag is disabled (not available), when the Columbus index = 0, the Columbus order may not increase. Kmin can be updated using the Columbus order. For example, the Columbus index can be regarded as (updated to) 1. Here, the value of alf_luma_eg_order_increase_flag[1] can be 1. Therefore, the Kmin Columbus order can be increased to 2. Similarly, alf_luma_eg_order_increase_flag[2] is enabled (available), which can indicate an increase of Kmin by 1 so that the final Columbus order is 3.

[0206] Figure 11 Exemplarily shown is the Columbus index of the filter coefficients according to the filter type. Figure 11 of (a) can represent a 5×5 filter, Figure 11 of (b) can represent a 7×7 filter. Here, only a part of the symmetric filter can be shown. In Figure 11 , the numbers at each position can represent the pre-assigned Columbus index of the ALF filter coefficients corresponding to each position.

[0207] In one example, the k-th order Columbus order of a given filter coefficient can be determined by indexing the Columbus index of the given coefficient position into Table 11 above. Each ALF filter coefficient can be decoded using the k-th order.

[0208] In one example, there can be a predefined Columbus order index (i.e., golombOrderIdxY). The predefined Columbus order can be used to determine the final Columbus order for encoding the coefficients.

[0209] For example, the predefined Columbus order can be configured as follows, for example.

[0210] [Equation 1]

[0211] golombOrderIdxY[] = {0, 0, 1, 0, 1, 2, 1, 0, 0, 1, 2}

[0212] Here, the order k = expGoOrderY[golombOrderIdxY[j]], and j may represent the j-th signaled filter coefficient. For example, if j = 2 (i.e., the third filter coefficient), then golomborderIdxY[2] = 1, and thus k = expGoOrderY[1].

[0213] In this case, for example, if the value of the syntax element alf_luma_coeff_delta_flag represents true (i.e., 1), then the syntax element alf_luma_coeff_flag may be signaled for each signaled filter. The syntax element alf_luma_coeff_flag indicates whether the luma filter coefficients are (explicitly) signaled.

[0214] When determining the EG order and the status of the above-mentioned related flags (i.e., alf_luma_coeff_delta_flag, alf_luma_coeff_flag, etc.), the difference information and sign information of the luma filter coefficients (i.e., when alf_luma_coeff_flag is true) may be parsed / signaled (if indicated). The absolute value information of the increment of each of the 12 filter coefficients (alf_luma_coeff_delata_abs syntax element) may be parsed / signaled. Additionally, if the syntax element alf_luma_coeff_delta_abs has a value, the sign information (syntax element alf_luma_coeff_delta_sign) may be parsed / signaled. The information including the difference information and sign information of the luma filter coefficients may be referred to as information about the luma filter coefficients.

[0215] The increment of the filter coefficients may be determined and stored together with the sign. In this case, the increment of the signed filter coefficients may be stored in the form of an array, which may be represented as filterCoefficients. The increment of the filter coefficients may be referred to as the incremental luma coefficients, and the increment of the signed filter coefficients may be referred to as the signed incremental luma coefficients.

[0216] To determine the final filter coefficients from the signed incremental luma coefficients, the (luma) filter coefficients may be updated as follows.

[0217] [Equation 2]

[0218] filterCoefficients[sigFiltIdx][j]+=filterCoefficients[sigFiltIdx][j]

[0219] Here, j may indicate the filter coefficient index, and sigFiltIdx may indicate the filter index signaled by the signal. j = {0, …, 11}, and sigFiltIdx = {0, …, alf_luma_filters_signaled_minus1}.

[0220] The coefficients may be copied into the final AlfCoeffL[filtIdx][j]. In this case, filtidx = 0, …, 24, and j = 0, …, 11.

[0221] The signed incremental luminance coefficients for a given filter index may be used to determine the first 12 filter coefficients. For example, the thirteenth filter coefficient of a 7×7 filter may be determined based on the following formula. The thirteenth filter coefficient may indicate the above-mentioned center tap filter coefficient.

[0222] [Equation 3]

[0223] AlfCoeffL[filtIdx]p12] = 128 - ∑ k AlfCoeff C [filtIdx[k] << 1

[0224] Here, the filter coefficient index 12 may indicate the thirteenth filter coefficient.

[0225] For example, to ensure bitstream consistency, the values of the final filter coefficients AlfCoeffL[filtIdx][k] range from 0, …, 11, may be in the range of -2 7 to 2 7 -1, and when k is 12, may be in the range of 0 to 2 8 -1. Here, k may be replaced by j.

[0226] When processing the luminance component, the processing of the chrominance component may be performed based on the syntax element alf_chroma_idc. If the value of the syntax element alf_chroma_idc is greater than 0, the minimum EG order information of the chrominance component (i.e., the syntax element alf_chroma_min_eg_order_minus1) may be parsed / signaled. According to the above embodiments of the present disclosure, a 5×5 diamond filter shape may be used for the chrominance component. In this case, the maximum Columbus index may be 2. In this case, for example, the EG order (or EG index) of the chrominance component may be determined as follows.

[0227] [Table 11]

[0228]

[0229] Based on the determination process, expGoOrderC can be derived as expGoOrderC = KminTab. Thus, an array including the EG order can be derived, which can be used by the decoding device. expGoOrderC can indicate the EG order (or EG index) of the chrominance component.

[0230] If alf_luma_clip_flag is enabled (if available), the minimum exponent Golomb order for clipping can be parsed. Similar to the ALF coefficient signaling, alf_luma_clip_eg_order_increase_flag can be parsed. Then, for each filter index, alf_luma_doeff_flag is enabled (available), and if there are filter coefficients (i.e., j = 0..1), the clipping index can be parsed.

[0231] Once the luma filter coefficients are reconstructed, the chroma coefficients can also be parsed. Additionally, there can be a predefined Golomb order index (golombOrderIdxC). The predefined Golomb order can be used to determine the final Golomb order for encoding the coefficients.

[0232] For example, the predefined Golomb order can be configured as follows, for example.

[0233] [Equation 4]

[0234] golombOrderIdxC[] = {0, 0, 1, 0, 0, 1}

[0235] Here, the order k = expGoOrderC[golombOrderIdxC[j]], and j can represent the j-th signaled filter coefficient. For example, if j = 2, it indicates the third filter coefficient, golomborderIdxY[2] = 1, so k = expGoOrderC[1].

[0236] Based on this, the absolute value information and sign information of the chroma filter coefficients can be parsed / signaled. The information including the absolute value information and sign information of the chroma filter coefficients can be referred to as information about the chroma filter coefficients. For example, a 5×5 diamond filter shape can be applied to the chroma component. In this case, the absolute increment information (syntax element alf_chroma_coeff_abs) of each of the six (chroma component) filter coefficients can be parsed / signaled. Additionally, if the value of the syntax element alf_chroma_coeff_abs is greater than 0, the sign information (syntax element alf_chroma_coeff_sign) can be parsed / signaled. For example, the six chroma filter coefficients can be derived based on the information about the chroma filter coefficients. In this case, for example, the seventh chroma filter coefficient can be determined based on the following formula. The seventh filter coefficient can represent the above-mentioned center tap filter coefficient.

[0237] [Equation 5]

[0238] AlfCoeffC[6] = 128 - ∑ k AlfCoeff C [filtIdx][k] << 1

[0239] Here, the filter coefficient index 6 can indicate the seventh filter coefficient. For reference, since the filter coefficient index starts from 0, the value 6 can indicate the seventh filter coefficient.

[0240] For example, to ensure bitstream consistency, when k is 0, …, 5, the value range of the final filter coefficient AlfCoeffC[filtIdx][k] can be from -2 7 to 2 7 - 1, and when k is 6, the value range of the final filter coefficient AlfCoeffC[filtIdx][k] can be from -2 8 to 2 8 - 1. Here, k can be replaced by j.

[0241] Then, similar to the case of luma, when determining the chroma clipping index, alf_luma_clip_flag can be checked. If this flag is enabled (if available), the minimum Golomb order of the clipping can be parsed. Then, if there are filter coefficients, alf_chroma_clip_index can be parsed.

[0242] As described above, when deriving (luminance / chrominance) filter coefficients, ALF-based filtering may be performed based on the filter coefficients or a filter including the filter coefficients. Thus, as described above, modified reconstructed samples may be derived. Additionally, multiple filters may be derived, and the filter coefficients of one of the multiple filters may be used for ALF processing. For example, one of the multiple filters may be indicated based on signaling filter selection information. Or, for example, one of the multiple filters may be selected based on the activity and / or directionality of the current block or the ALF target block, and the filter coefficients of the selected filter may be used for ALF processing.

[0243] Once the layer information from the APS and the slice header is decoded, the coding tree unit (CTU) is decoded. A network abstraction layer (NAL) unit may include a slice header and slice data. The slice data may facilitate the decoding of the coding tree unit.

[0244] The following table exemplarily represents the syntax of the coding tree unit.

[0245] [Table 12]

[0246]

[0247] For example, the semantics of the syntax elements included in the syntax of Table 12 may be represented as shown in the following table.

[0248] [Table 13]

[0249]

[0250] In CTU-level processing, when ALF is enabled for a slice, the syntax element alf_ctb_flag may be parsed / signaled. The alf_ctb_flag may specify the application of ALF to the coding tree block (CTB). When ALF is applied to the CTB and the number of transmitted APS IDs is greater than 0, another flag alf_use_aps_flag may be parsed / signaled. When alf_use_aps_flag is 1, the filter information of the APS for the luminance CTB may be specified. However, when alf_use_aps_flag is disabled, one of the fixed filter sets may be applied to the CTB.

[0251] In an embodiment of the present disclosure, a coding process for efficiently applying the above ALF is proposed. According to an embodiment of the present disclosure, an example of the binarization process of the above syntax element alf_luma_fixed_filter_idx is proposed. Here, the alf_luma_fixed_filter_idx may specify the fixed filter applied to the (luminance) CTB (reconstructed samples).

[0252] In one example, if alf_use_aps_flag is true (value 1), a set of filters from APS can be applied to the (luma) CTB (reconstructed samples), and filter coefficients can be derived based on information about the previous filter (e.g., alf_luma_prev_filter_idx_minus1). When alf_use_aps_flag is false (value 0), a fixed filter can be applied to the (luma) CTB (reconstructed samples). For example, the value of alf_luma_fixed_filter_idx can be in the range of 0 to 15.

[0253] The following table shows an example of the binarization process of syntax elements related to ALF.

[0254] [Table 14]

[0255]

[0256] In Table 14, the syntax element alf_luma_fixed_filter_idx can be encoded based on truncated binary (TB) binarization. For example, the maximum value related to the syntax element (e.g., cMax) can be 15. According to the TB binarization, only the complexity will increase unnecessarily without any additional benefit. For this reason, the following example based on fixed-length (FL) binarization is proposed.

[0257] The following table shows another example of the binarization information of syntax elements related to the ALF process.

[0258] [Table 15]

[0259]

[0260] Table 15 is described focusing on the differences from Table 14. In Table 15, the syntax element alf_luma_fixed_filter_idx can be encoded based on FL binarization. For example, the maximum value related to the syntax element (e.g., cMax) can be represented using 4 bits.

[0261] The following table shows an example of assigning ctxInc to a context-coded cell as a syntax element of the context-coded cell according to Table 15 above. In Table 15, for example, cells with binIdx greater than or equal to 5 may not exist (or may not be available) for the syntax element alf_luma_fixed_filter_idx.

[0262] [Table 16]

[0263]

[0264] According to an embodiment of the present disclosure, an example of the binarization process of the above-mentioned syntactic element alf_luma_fixed_filter_set_idx is presented. Here, alf_luma_fixed_filter_set_idx can specify the index of a fixed filter set.

[0265] For example, a fixed-length (FL) binarization process can be applied to the signaling of alf_luma_fixed_filter_set_idx.

[0266] The following table illustrates the ALF data syntax by way of example.

[0267] [Table 17]

[0268]

[0269] Referring to the above table, alf_luma_fixed_filter_set_idx can be encoded based on a fixed-length (FL) binarization process rather than a truncated binary (TB) binarization process. For example, the semantics of alf_luma_fixed_filter_set_idx included in the table can be represented as shown in the following table.

[0270] [Table 18]

[0271]

[0272] In an embodiment of the present disclosure, a signaling method related to ALF coefficients for simplifying the signaling derivation process of the Columbus order is proposed. For example, in an embodiment of the present disclosure, the proposed method can be implemented by fixed signaling. In one example, the k-th order of the exponential Golomb code can be fixed to 2 for luminance and 3 for chrominance. However, the embodiments of the present disclosure are not necessarily limited to such examples, and the k-th order can be fixed to another appropriate value.

[0273] The following table shows the syntax of the ALF data field to which the above simplification is applied.

[0274] [Table 19]

[0275]

[0276]

[0277] For example, the semantics of the syntactic elements included in the syntax of Table 19 can be represented as shown in the following table.

[0278] [Table 20]

[0279]

[0280] In an embodiment of the present disclosure, a method of using a predetermined Golomb order for each ALF filter coefficient is proposed.

[0281] The following table exemplarily shows the Golomb order (the k-th order) for decoding ALF luminance coefficients. C0 to C11 represent ALF luminance coefficient indices (or, for example, filter coefficients depending on the position in the filter shape for ALF), where, for example, the k-th order can be 2 or 3. Figure 6 For example, the k-th order can be 2 or 3.

[0282] [Table 21]

[0283] Coefficient index k-th order <![CDATA[C0]]> 2 <![CDATA[C1]]> 2 <![CDATA[C2]]> 2 <![CDATA[C3]]> 2 <![CDATA[C4]]> 2 <![CDATA[C5]]> 3 <![CDATA[C6]]> 3 <![CDATA[C7]]> 3 <![CDATA[C8]]> 2 <![CDATA[C9]]> 2 <![CDATA[C 10 > 2 <![CDATA[C 11 > 3

[0284] The following table exemplarily illustrates the coding-based semantics according to this embodiment. For example, the following table can be the semantics for modifying the Golomb order of luminance coefficients or chrominance coefficients.

[0285] [Table 22]

[0286]

[0287]

[0288]

[0289] In an embodiment of the present disclosure, a method of signaling a fixed Golomb order only for the chrominance component is proposed. That is, an example of signaling for fixing the Golomb order of the chrominance component is implemented according to this embodiment.

[0290] The following table exemplarily shows the syntax of the coding-based ALF data field according to an embodiment of the present disclosure.

[0291] [Table 23]

[0292]

[0293]

[0294]

[0295] For example, the semantics of the syntax elements included in the syntax of Table 23 can be represented as shown in the following table.

[0296] [Table 24]

[0297]

[0298] In an embodiment of the present disclosure, fixed signaling for encoding information regarding ALF clipping (e.g., alf_luma_clip_idx[sfIdx][j], alf_chroma_clip_idx[j], etc.) is proposed. For example, the k-th order Golomb can be predefined or pre-fixed and used as in the above embodiments.

[0299] The following table illustrates an example of the syntax of an encoded ALF data field according to this embodiment.

[0300] [Table 25]

[0301]

[0302]

[0303] For example, the semantics of the syntax elements included in the syntax of Table 25 can be represented as shown in the following table.

[0304] [Table 26]

[0305]

[0306]

[0307] In an embodiment of the present disclosure, a signaling combination from various perspectives of an ALF data field based on (or dependent on) exponential Golomb coding is proposed. That is, an example of signaling that combines at least one of the above embodiments can be achieved through this embodiment.

[0308] The following table illustratively shows the syntax of an encoded ALF data field according to this embodiment.

[0309] [Table 27]

[0310]

[0311]

[0312] For example, the semantics of the syntax elements included in the syntax of Table 27 can be represented as shown in the following table.

[0313] [Table 28]

[0314]

[0315]

[0316] In an embodiment of the present disclosure, a method for preventing the APS ID of chrominance from being signaled and inferred is proposed. The following table illustrates an example of the syntax of an encoded slice header according to this embodiment.

[0317] [Table 29]

[0318]

[0319] For example, the semantics of the syntactic elements included in the syntax of the above table can be represented as shown in the following table.

[0320] [Table 30]

[0321]

[0322] Referring to the above table, regardless of whether the slice type is I or whether the number of ALF APSs referred to by the slice is one, slice_alf_aps_id_chroma can be signaled.

[0323] In addition, in an embodiment of the present disclosure, a method for parsing / signaling alternative filter information for chrominance components is proposed.

[0324] The following table exemplarily shows the syntax based on the coded ALF data field according to this embodiment.

[0325] [Table 31]

[0326]

[0327] For example, the semantics of the syntactic elements included in the syntax of the above table can be represented as shown in the following table.

[0328] [Table 32]

[0329]

[0330]

[0331]

[0332]

[0333]

[0334]

[0335] Referring to the above table, the ALF data field may include alternative filter information for chrominance components.

[0336] For example, the syntax element alf_chroma_num_alts_minus1 may indicate the number of alternative filters for the chrominance component. The index altIdx of the alternative filter for the chrominance component may have a value in the range of 0 to alf_chroma_num_alts_minus1. Additionally, the syntax element alf_chroma_coeff_abs[altIdx][j] may indicate the absolute value of the i-th coefficient included in the alternative filter with index altIdx. Additionally, the syntax element alf_chroma_coeff_sign[altIdx][j] may indicate the sign of the i-th coefficient included in the alternative filter with index altIdx.

[0337] Comparing Table 32 above with Table 7, it can be understood that in the embodiments of the present disclosure, the syntax related to the exponential Golomb coding of the ALF coefficients and the clipping coefficients is simplified, and the syntax for predicting the filter coefficients is removed by using fixed filter prediction. Additionally, referring to Table 32 above, in the embodiments of the present disclosure, a method of signaling a fixed exponential Golomb order instead of signaling the order k of the exponential Golomb (EG) code is proposed.

[0338] The following table exemplifies the syntax of a coding tree unit (CTU).

[0339] [Table 33]

[0340]

[0341] For example, the semantics of the syntax elements included in the syntax of the above table can be represented as shown in the following table.

[0342] [Table 34]

[0343]

[0344] Referring to the above table, the index information of the alternative filter for the coding tree unit (CTU) or the chrominance component of the current block to which ALF is applied may be included. For example, the syntax element alf_ctb_filter_alt_idx may specify the index of the alternative filter for the chrominance component when ALF is applied to the chrominance component with chrominance index 1 or 2.

[0345] The following table exemplifies the syntax of sample adaptive offset (SAO).

[0346] [Table 35]

[0347]

[0348] The following table shows an example of the ALF process in the standard document format.

[0349] [Table 36]

[0350]

[0351] In addition, the following table shows an example of the coding tree unit filtering process for luminance samples in a standard document format.

[0352] [Table 37]

[0353]

[0354]

[0355]

[0356]

[0357] In addition, the following table shows an example of the process for deriving the ALF transpose and filter index for luminance samples in a standard document format.

[0358] [Table 38]

[0359]

[0360]

[0361]

[0362]

[0363] In addition, the following table shows an example of the coding tree unit filtering process for chrominance samples in a standard document format.

[0364] [Table 39]

[0365]

[0366]

[0367]

[0368] In addition, the following table shows examples of the initialization value (initValue) and shift index (shiftIdx) of the context index increment (ctxInc) according to the syntax element alf_ctb_filter_alt_idx.

[0369] [Table 40]

[0370]

[0371] Referring to the above table, the initialization value (initValue) of the syntax element alf_ctb_filter_alt_idx indicating the index information of the alternative filter can be determined based on the context index increment (ctxInc) or the initialization type (initType) of alf_ctb_filter_alt_idx. Additionally, the shift index (shiftIdx) of alf_ctb_filter_alt_idx can be determined based on the context index increment (ctxInc) of alf_ctb_filter_alt_idx.

[0372] Additionally, the following table shows examples of binarization related to various syntaxes including the syntax element alf_ctb_filter_alt_idx.

[0373] [Table 41]

[0374]

[0375]

[0376]

[0377] Referring to the above table, the syntax element alf_ctb_filter_alt_idx indicating the index information of the alternative filter for the coding tree unit (CTU) or the chrominance component of the current block to which ALF is applied can be coded based on the truncated Rice binarization method of the index parameter of the alternative filter. Additionally, the maximum value (cMax) of the index parameter of the alternative filter for the chrominance component can correspond to alf_chroma_num_alts_minus1. alf_chroma_num_alts_minus1 can correspond to a value that is 1 less than the number of alternative filters for the chrominance component. Additionally, the truncated Rice binarization method can be performed based on the Rice parameter (cRiceParam) value 0.

[0378] Additionally, the following table shows an example of the process for deriving the context index increment (ctxInc) of the syntax element alf_ctb_filter_alt_idx in the standard document format.

[0379] [Table 42]

[0380]

[0381] Cells in the cell string of the index information of the alternative filter can be entropy decoded based on a context model, and the context model of the cells in the cell string of the index information of the alternative filter can be determined based on the context index increment of the cells. Referring to the above table, the context model of the index information of the alternative filter can be determined based on the context index increment of the syntax element alf_ctb_filter_alt_idx indicating the index information of the alternative filter, and the context index increment of the index information of the alternative filter can be determined based on the chrominance component of the CTU or the current block to which the ALF is applied. For example, the context index increment of the index information of the alternative filter can be determined based on the index of the chrominance component. For example, the context index increment derived when the chrominance component of the current block is cb can be different from the context index increment derived when the chrominance component of the current block is cr. For example, when the index of the chrominance component is 0, the context index increment of alf_ctb_filter_alt_idx can have a value of 0, and when the index of the chrominance component is 1, the context index increment of alf_ctb_filter_alt_idx can have a value of 1. Alternatively, for example, when the index of the chrominance component is 1, the context index increment of alf_ctb_filter_alt_idx can have a value of 1, and when the index of the chrominance component is 2, the context index increment of alf_ctb_filter_alt_idx can have a value of 2.

[0382] Figure 12 and Figure 13 Schematically shows an example of a video / image coding method and related components according to an embodiment of the present disclosure. Figure 12 The method shown can be performed by Figure 2 the coding device shown. Specifically, for example, S1200 can be performed by the predictor 220 of the coding device, S1210 can be performed by the adder 250 of the coding device. S1220 can be performed by the filter 260 of the coding device, and S1230 can be performed by the entropy encoder 240 of the coding device. Figure 12 The method shown can include the embodiments described above in the present disclosure.

[0383] Referring to Figure 12 , the coding device determines the prediction mode of the current block and derives the prediction samples based on the prediction mode (S1200). The coding device can determine any one of the various prediction modes described in this document (e.g., inter prediction or intra prediction). The coding device can derive the prediction samples of the current block based on the determined prediction mode. The coding device can generate prediction mode information indicating the prediction mode applied to the current block.

[0384] The decoding device generates a reconstructed sample based on a prediction sample (S1210). First, the decoding device may derive a residual sample based on the prediction sample and the original sample. For example, the decoding device may derive a residual sample based on a comparison between the original sample and a modified reconstructed sample.

[0385] The encoding device may generate a reconstructed sample based on the sum of the prediction sample and the residual sample. The encoding device may perform intra prediction based on the reconstructed sample.

[0386] The encoding device generates ALF information for the reconstructed sample (S1220). The encoding device may generate ALF-related information. The encoding device derives ALF-related parameters applicable to filtering the reconstructed sample and generates ALF information. For example, the ALF information may include information about the ALF filter coefficients described above in the present disclosure, information about a fixed filter, information about clipping, etc. Alternatively, for example, the ALF information may include alternative filter information for the chrominance component of the current block. The replacement filter information may indicate an alternative filter for deriving a modified reconstructed sample of the chrominance component of the current block.

[0387] The encoding device encodes the image information including the ALF information and the residual information (S1230). The image / video information may include information for generating the reconstructed sample and / or information related to ALF. The information for generating the reconstructed sample may include, for example, prediction-related information, residual information, and / or quantization / transformation-related information. The prediction-related information may include information about various prediction modes (e.g., merge mode, MVP mode, etc.), MVD information, etc.

[0388] The encoded image / video information may be output in the form of a bitstream. The bitstream may be sent to the decoding device via a network or a storage medium.

[0389] According to an embodiment of the present disclosure, the image / video information may include various types of information.

[0390] In an embodiment, the alternative filter information may include information about the number of alternative filters for the chrominance component of the current block, absolute value information of the coefficients included in the alternative filters for the chrominance component of the current block, and sign information of the coefficients included in the alternative filters for the chrominance component of the current block.

[0391] In an embodiment, the alternative filter information may include index information of the alternative filters for the chrominance component of the current block. And the index information of the alternative filters may be based on truncated Rice binarization.

[0392] In an embodiment, the maximum value (cMax) of the index information of the alternative filter may be equal to a value that is 1 less than the number of alternative filters for the chrominance component of the current block, and the truncated Rice binarization may be performed based on a Rice parameter (cRiceParam) value of 0.

[0393] In an embodiment, the cells in the cell string of the index information for the alternative filter may be entropy encoded based on a context model. The context model for the cells in the cell string of the index information for the alternative filter may be determined based on the context index increment of the cell. Additionally, the context index increment may be determined based on the index of the chrominance component of the current block.

[0394] In an embodiment, the context index increment derived when the chrominance component of the current block is cb may be different from the context index increment derived when the chrominance component of the current block is cr.

[0395] In an embodiment, the image information may include information about ALF clipping, and the information about ALF clipping may include a flag indicating whether clipping is applied to the chrominance component of the current block and clipping index information indicating the clipping value.

[0396] Figure 14 and Figure 15 FIG. schematically shows an example of an image / video decoding method and related components according to an embodiment of the present disclosure. Figure 14 The method shown may be performed by Figure 3 the decoding device shown. Specifically, for example, S1400 may be performed by the entropy decoder 310 of the decoding device, S1410 may be performed by the predictor 330 of the decoding device, and S1420 may be performed by the adder 340 of the decoding device. Figure 14 The method shown may include the embodiments described above in the present disclosure.

[0397] Referring to Figure 14 , the decoding device obtains image information including adaptive loop filter (ALF) information and prediction mode information from the bitstream (S1400). The image information may include various information according to the above embodiments of the present disclosure. For example, the image information may include at least a part of prediction-related information or residual-related information.

[0398] For example, the prediction-related information may include inter-frame prediction mode information or inter-frame prediction type information. For example, the inter-frame prediction mode information may include information indicating at least a part of various inter-frame prediction modes. For example, various modes such as a merge mode, a skip mode, a motion vector prediction (MVP) mode, an affine mode, a sub-block merge mode, or a merge and MVD (MMVD) mode may be used. Additionally, in addition to or instead of the auxiliary mode, a decoder-side motion vector refinement (DMVR) mode, an adaptive motion vector resolution (AMVR) mode, a bi-prediction with CU-level weight (BCW), or a bidirectional optical flow (BDOF) may be used. For example, the inter-frame prediction type information may include an inter_pred_idc syntax element. Alternatively, the inter-frame prediction type information may include information indicating any one of L0 prediction, L1 prediction, and paired (bi-) prediction.

[0399] In addition, the image information may include various information according to an embodiment of the present disclosure. For example, the image information may include ALF information, and the ALF information may include information described in at least one of Tables 1 to 42 above. For example, the ALF information may include information about the ALF filter coefficients described above in the present disclosure, information about a fixed filter, information about clipping, and the like. Alternatively, for example, the ALF information may include alternative filter information for a chrominance component of a current block.

[0400] The decoding device generates a reconstructed sample of a current block based on a predicted sample (S1410). The decoding device may derive a predicted sample of the current block based on the prediction-related information included in the image / video information. The decoding device may derive a residual sample based on the residual information included in the image / video information. The decoding device may generate a reconstructed sample based on the predicted sample and the residual sample. A reconstructed block and a reconstructed picture may be derived based on the reconstructed sample.

[0401] The decoding device generates a modified reconstructed sample of the current block based on the reconstructed sample and the ALF information (S1420). The decoding device may derive filter coefficients for the ALF from the ALF information and generate a reconstructed sample and a modified reconstructed sample based on the filter coefficients.

[0402] For example, the decoding device may generate a modified reconstructed sample by filtering the reconstructed sample, and may perform a filtering process of the reconstructed sample using a filter based on the filter coefficients. A picture reconstructed by the decoding device may include the reconstructed sample.

[0403] In an embodiment, the alternative filter information may include information about the number of alternative filters for a chrominance component of a current block, absolute value information of coefficients included in the alternative filters for a chrominance component of a current block, and sign information of coefficients included in the alternative filters for a chrominance component of a current block.

[0404] In an embodiment, the alternative filter information may include index information of an alternative filter for a chrominance component of a current block, and the index information of the alternative filter may be based on truncated Rice binarization.

[0405] In an embodiment, a maximum value (cMax) of the index information of the alternative filter may be equal to a value that is 1 less than the number of alternative filters for the chrominance component of the current block, and truncated Rice binarization may be performed based on a Rice parameter (cRiceParam) value of 0.

[0406] In an embodiment, cells in a cell string of the index information for the alternative filter may be entropy encoded based on a context model. The context model for a cell in the cell string of the index information for the alternative filter may be determined based on a context index increment of the cell. Additionally, the context index increment may be determined based on an index of the chrominance component of the current block.

[0407] In an embodiment, the context index increment derived when the chrominance component of the current block is cb may be different from the context index increment derived when the chrominance component of the current block is cr.

[0408] In an embodiment, the image information may include information about ALF clipping, and the information about ALF clipping may include a flag indicating whether clipping is applied to the chrominance component of the current block and clipping index information indicating a clipping value.

[0409] In the above embodiments, a method is described based on a flowchart having a series of steps or blocks. The present disclosure is not limited to the order of the above steps or blocks. Some steps or blocks may occur simultaneously or in an order different from other steps or blocks as described above. Further, 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 the present disclosure.

[0410] The method according to the above embodiments of the present disclosure may be implemented in software form, and an encoding device and / or a decoding device according to the present disclosure may be included, for example, in a device that performs image processing of a TV, a computer, a smart phone, a set-top box, a display device, etc.

[0411] When the embodiments in the present disclosure are implemented in software, the above methods can be implemented as modules (processes, functions, etc.) that execute the above functions. The modules can be stored in a memory and executed by a processor. The memory can be located 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 the present disclosure can be implemented and executed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in the respective drawings 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 implementation can be stored in a digital storage medium.

[0412] In addition, a decoding device and an encoding device to which the present disclosure is applied 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 (e.g., 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 videoconference video device, a vehicle user equipment (i.e., a vehicle user equipment, an aircraft user equipment, a ship user equipment, 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 access TV, a home theater system, a smart phone, a tablet PC, a digital video recorder (DVR), etc.

[0413] In addition, a processing method to which the present disclosure is applied can be generated in the form of a program to be executed 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. A computer-readable recording medium includes all types of storage devices that store data readable by a computer system. For example, a computer-readable recording medium can include a BD, a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. In addition, a computer-readable recording medium includes a medium implemented in the form of a carrier wave (i.e., transmission via the Internet). In addition, a bit stream generated by this encoding method can be stored in a computer-readable recording medium or can be transmitted via a wired / wireless communication network.

[0414] In addition, embodiments of the present disclosure can be implemented as a computer program product according to program code, and the program code can be executed in a computer by embodiments of the present disclosure. The program code can be stored on a computer-readable carrier.

[0415] Figure 16 An example of a content streaming system to which the embodiments disclosed in the present disclosure can be applied is shown.

[0416] Referring to Figure 16 , the content streaming system to which embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0417] The encoding server compresses the content input from the 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 the multimedia input device (e.g., a smart phone, a camera, a video camera, etc.) directly generates a bitstream, the encoding server can be omitted.

[0418] The bitstream can be generated by an encoding method or a bitstream generation method to which embodiments of the present disclosure are applied, and during the process of sending or receiving the bitstream, the streaming server can temporarily store the bitstream.

[0419] The streaming server sends multimedia data to the user device via the network server based on a user's request, and the network server serves as a medium for informing the user of the service. When the user requests a desired service from the network server, the network server transmits it to the streaming server, and the streaming server sends the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control commands / responses between devices in the content streaming system.

[0420] The streaming server can receive content from the media storage device and / or the 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.

[0421] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital TVs, desktop computers, digital signage, etc. Each server in the content streaming system can operate as a distributed server, and in this case, the data received from each server can be distributed.

[0422] Each server in the content stream system can operate as a distributed server, and in this case, the data received from each server can be distributed and processed.

[0423] The claims described herein can be combined in various ways. For example, the technical features of the method claims of the present disclosure can be combined and implemented as a device, and the technical features of the device claims of the present disclosure can be combined and implemented as a method. Additionally, the technical features of the method claims of the present disclosure and the technical features of the device claims of the present disclosure can be combined to be implemented as a device, and the technical features of the method claims of the present disclosure and the technical features of the device claims of the present disclosure can be combined and implemented as a method.

Claims

1. An image decoding method performed by a decoding device, the image decoding method comprising the following steps: Obtain image information including residual information and prediction mode information from a bitstream; Derive prediction samples for a current block based on the prediction mode information; Derive residual samples for the current block based on the residual information; And Generate reconstructed samples based on the prediction samples and the residual samples, wherein the image information includes an adaptive loop filter (ALF) adaptive parameter set (APS), header information, and information about a coding tree unit, wherein the information about the coding tree unit includes index information of an alternative filter for a chrominance component of the current block, wherein the ALF APS includes identifier information of the ALF APS and ALF information, wherein the header information includes ALF-related ID information, wherein the ALF information includes first flag information related to whether to signal a chrominance filter, wherein, based on the first flag information, the ALF information includes alternative filter information for the chrominance component of the current block and second flag information related to whether a non-linear ALF is applied to the chrominance component of the current block, wherein the alternative filter information includes information about the number of alternative filters for the chrominance component of the current block, absolute value information of coefficients included in the alternative filters for the chrominance component of the current block, and sign information of the coefficients included in the alternative filters for the chrominance component of the current block, wherein the ALF filter coefficients are derived based on the alternative filter information and the ALF-related ID information, wherein modified reconstructed samples for the chrominance component of the current block are generated based on the ALF filter coefficients, wherein the index information of the alternative filter is based on truncated Rice binarization, wherein cells in a cell string of the index information for the alternative filter are entropy decoded based on a context model, wherein the context model for the cells in the cell string related to the index information of the alternative filter is determined based on a context index increment for the cells, wherein the context index increment is determined based on the chrominance component of the current block, and wherein the context index increment derived based on the chrominance component cb of the current block is different from the context index increment derived based on the chrominance component cr of the current block.

2. An image encoding method performed by an encoding device, the image encoding method comprising the following steps: Determine a prediction mode of a current block and derive prediction samples based on the prediction mode; Generate prediction mode information; Derive residual samples of the current block based on the prediction samples; Generate residual information based on the residual samples; Generate reconstructed samples based on the prediction samples and the residual samples; Derive adaptive loop filter (ALF) filter coefficients for the reconstructed samples; Generate ALF information about the reconstructed sample; and Encode the image information including the ALF information and the prediction mode information, wherein the image information includes an ALF adaptive parameter set APS, header information, and information about coding tree units, wherein the information about the coding tree unit includes index information of an alternative filter for the chrominance component of the current block, wherein the ALF APS includes identifier information of the ALF APS and ALF information, wherein the header information includes ALF-related ID information, wherein the ALF information includes first flag information related to whether to signal a chrominance filter, wherein, based on the first flag information, the ALF information includes: Alternative filter information for the chrominance component of the current block and second flag information related to whether a non-linear ALF is applied to the chrominance component of the current block, wherein the alternative filter information includes information about the number of alternative filters for the chrominance component of the current block, absolute value information of coefficients included in the alternative filter for the chrominance component of the current block, and sign information of coefficients included in the alternative filter for the chrominance component of the current block, wherein the ALF-related ID information is configured to derive the ALF filter coefficients, wherein the index information of the alternative filter is based on truncated Rice binarization, wherein cells in the cell string of the index information for the alternative filter are entropy-coded based on a context model, wherein the context model for the cells in the cell string related to the index information of the alternative filter is determined based on a context index increment for the cells, wherein the context index increment is determined based on the chrominance component of the current block, and wherein the context index increment derived based on the chrominance component cb of the current block is different from the context index increment derived based on the chrominance component cr of the current block.

3. A method for sending data of an image, the sending method comprising the following steps: Obtain a bitstream for the image, wherein the bitstream is generated based on the following operations: determining the prediction mode of the current block and deriving prediction samples based on the prediction mode, generating prediction mode information, deriving the residual samples of the current block based on the prediction samples, generating residual information based on the residual samples, generating a reconstructed sample based on the prediction samples and the residual samples, deriving adaptive loop filter (ALF) filter coefficients for the reconstructed sample, generating ALF information about the reconstructed sample, and encoding the image information including the ALF information and the prediction mode information; and Send the data including the bitstream, wherein the image information includes an ALF adaptive parameter set APS, header information, and information about coding tree units, Among them, the information about the coding tree unit includes index information of an alternative filter for a chrominance component of the current block. Among them, the ALF APS includes identifier information of the ALF APS and ALF information. Among them, the header information includes ALF-related ID information. Among them, the ALF information includes first flag information related to whether to signal a chrominance filter. Among them, based on the first flag information, the ALF information includes: Alternative filter information for a chrominance component of the current block and second flag information related to whether a non-linear ALF is applied to the chrominance component of the current block. Among them, the alternative filter information includes information about the number of alternative filters for a chrominance component of the current block, absolute value information of coefficients included in the alternative filters for a chrominance component of the current block, and sign information of coefficients included in the alternative filters for a chrominance component of the current block. Among them, the ALF-related ID information is configured to derive the ALF filter coefficients. Among them, the index information of the alternative filter is based on truncated Rice binarization. Among them, cells in a cell string of the index information for the alternative filter are entropy-coded based on a context model. Among them, the context model of the cells in the cell string related to the index information of the alternative filter is determined based on a context index increment for the cells. Among them, the context index increment is determined based on the chrominance component of the current block, and Among them, the context index increment derived based on the chrominance component cb of the current block is different from the context index increment derived based on the chrominance component cr of the current block.

Images