Method and apparatus for signaling image information applied at picture or slice level

Abstract

To provide a method for decoding an image.SOLUTION: The method for decoding an image performed by a decoder according to the present disclosure includes the steps of: acquiring instruction information related to whether deblocking filter information is in a picture header or in a slice header; determining which of the picture header and the slice header the deblocking filter information is in on the basis of the instruction information; and parsing the deblocking filter information from one of the picture header and the slice header on the basis of the determination.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to image coding techniques and to methods and apparatus for signaling image information applied at the picture or slice level in an image coding system. [Background technology]

[0002] In recent years, demand for high-resolution, high-quality images such as HD (High Definition) images and UHD (Ultra High Definition) images has been increasing in various fields. As image data has higher resolution and quality, the amount of information or bits to be transmitted increases relatively compared to existing image data. Therefore, when image data is transmitted using a medium such as an existing wired or wireless broadband line or when image data is stored using an existing storage medium, transmission costs and storage costs increase.

[0003] This calls for highly efficient image compression techniques to effectively transmit, store, and reproduce high-resolution, high-quality image information. Summary of the Invention [Problem to be solved by the invention]

[0004] A technical problem of the present disclosure is to provide a method and apparatus for increasing image coding efficiency.

[0005] Another technical problem of the present disclosure is to provide a method and apparatus for signaling image information applied at the picture level or slice level.

[0006] Yet another technical object of the present disclosure is to provide a method and apparatus for decoding a current block based on image information applied at a picture level or a slice level. [Means for solving the problem]

[0007] According to an embodiment of the present disclosure, there is provided an image decoding method performed by a decoding device, the method including the steps of: obtaining indication information indicating whether at least one tool for a current block is applied at a picture level or a slice level; determining whether information related to the at least one tool is present in a picture header or a slice header based on the indication information; parsing the information related to the at least one tool from the picture header or the slice header based on the determination result; and decoding the current block based on the information related to the at least one tool.

[0008] According to another embodiment of the present disclosure, there is provided an image encoding method performed by an encoding device, the method including the steps of generating indication information indicating whether at least one tool applied to a current block is applied at a picture level or a slice level, generating information related to the at least one tool, and encoding image information including the indication information and the information related to the at least one tool, wherein the indication information indicates in which header, a picture header or a slice header, the information related to the at least one tool is present.

[0009] According to yet another embodiment of the present disclosure, there is provided a computer-readable digital storage medium storing encoded image information for causing a decoding device to perform an image decoding method, the decoding method including the steps of: obtaining indication information indicating whether at least one tool to be applied to a current block is applied at a picture level or a slice level; determining whether information related to the at least one tool is present in a picture header or a slice header based on the indication information; parsing the information related to the at least one tool from the picture header or the slice header based on the determination result; and decoding the current block based on the information related to the at least one tool. [Effects of the Invention]

[0010] According to this specification, the overall image / video compression efficiency can be improved.

[0011] According to this specification, the efficiency of image decoding can be improved based on indication information indicating whether at least one tool for a current block is applied at the picture level or the slice level. [Brief explanation of the drawings]

[0012] [Figure 1] 1 illustrates schematically an example of a video / image coding system to which the present disclosure may be applied. [Figure 2] 1 is a diagram illustrating the configuration of a video / image encoding device to which the present disclosure can be applied. [Figure 3] 1 is a diagram illustrating the configuration of a video / image decoding device to which the present disclosure can be applied. [Figure 4] 10 shows an exemplary hierarchical structure for coded data. [Figure 5] 1 is a flow chart illustrating one embodiment of a method for performing deblocking filtering. [Figure 6] 1 is a flow chart illustrating an example of an ALF procedure. [Figure 7] 1 shows examples of filter shapes for ALF. [Figure 8] 10 is a flowchart illustrating an operation of an encoding device according to an embodiment. [Figure 9] FIG. 1 is a block diagram showing a configuration of an encoding device according to an embodiment. [Figure 10] 10 is a flowchart illustrating an operation of a decoding device according to an embodiment. [Figure 11] 1 is a block diagram showing a configuration of a decoding device according to an embodiment. [Figure 12] 1 illustrates an example of a content streaming system to which the disclosure of this document may be applied. DETAILED DESCRIPTION OF THE INVENTION

[0013] This document may be modified in various ways and may have various embodiments. Specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit this document to the specific embodiment. Common terms used in this document are used merely to describe specific embodiments and are not intended to limit the technical ideas of this document. A singular expression includes a plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0014] Meanwhile, each component in the drawings described in this document is illustrated independently for the convenience of explaining the different characteristic functions, and does not mean that each component is realized by separate hardware or software. For example, two or more components may be combined to form a single component, or a single component may be divided into multiple components. Embodiments in which each component is integrated and / or separated are also included within the scope of this document as long as they do not deviate from the essence of this document.

[0015] As used herein, "A or B" can mean "only A," "only B," or "both A and B." In other words, as used herein, "A or B" can be interpreted as "A and / or B." For example, as used herein, "A, B, or C" can mean "only A," "only B," "only C," or "any combination of A, B, and C."

[0016] As used herein, a slash ( / ) or a comma can mean "and / or." For example, "A / B" can mean "A and / or B." Thus, "A / B" can mean "only A," "only B," or "both A and B." For example, "A, B, C" can mean "A, B, or C."

[0017] As used herein, "at least one of A and B" can mean "only A," "only B," or "both A and B." Furthermore, as used herein, the expressions "at least one of A or B" and "at least one of A and / or B" can be interpreted as "at least one of A and B."

[0018] Furthermore, in this specification, "at least one of A, B, and C" can mean "only A," "only B," "only C," or "any combination of A, B, and C." Furthermore, "at least one of A, B, or C" or "at least one of A, B, and / or C" can mean "at least one of A, B, and C."

[0019] Furthermore, parentheses used herein may mean "for example." Specifically, when "prediction (intra prediction)" is used, "intra prediction" is proposed as an example of "prediction." In other words, "prediction" in this specification is not limited to "intra prediction," and "intra prediction" is proposed as an example of "prediction." Furthermore, when "prediction (i.e., intra prediction)" is used, "intra prediction" is proposed as an example of "prediction."

[0020] In this specification, technical features individually described in one drawing may be realized individually or simultaneously.

[0021] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used to refer to the same components in the drawings, and redundant descriptions of the same components may be omitted.

[0022] FIG. 1 illustrates schematically an example of a video / image coding system to which the present disclosure may be applied.

[0023] As shown in Figure 1, a video / image coding system may include a first device (source device) and a second device (receiving device). The source device may transmit encoded video / image information or data to the receiving device in file or streaming form via a digital storage medium or a network.

[0024] The source device may include a video source, an encoding device, and a transmitting unit. The receiving device may include a receiving unit, a decoding device, and a renderer. The encoding device may be referred to as a video / image encoding device, and the decoding device may be referred to as a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may include a display unit, which may be a separate device or an external component.

[0025] A video source can acquire video / images through a video / image capture, synthesis, or generation process. A video source can include a video / image capture device and / or a video / image generation device. A video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. A video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, a virtual video / image can be generated via a computer, etc., in which case the video / image capture process can be replaced with a process in which related data is generated.

[0026] An encoding device can encode input video / images. The encoding device can perform a series of steps such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0027] The transmitter may transmit the encoded video / image information or data output in the form of a bitstream to a receiver of a receiving device via a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, and SSD. The transmitter may include elements for generating a media file in a predetermined file format and elements for transmission via a broadcasting / communication network. The receiver may receive / extract the bitstream and transmit it to a decoding device.

[0028] The decoding device can decode the video / image by performing a series of steps such as inverse quantization, inverse transform, prediction, etc., which correspond to the operations of the encoding device.

[0029] The renderer can render the decoded video / image, and the rendered video / image can be displayed via the display unit.

[0030] This document relates to video / image coding. For example, the methods / embodiments disclosed in this document can be applied to 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 next generation video / image coding standards (e.g., H.267 or H.268).

[0031] This document presents various embodiments relating to video / image coding, which may be combined with one another unless otherwise stated.

[0032] In this document, video can refer to a collection of a series of images over time. A picture generally refers to a unit representing one image at a specific time, and a slice / tile is a unit that constitutes part of a picture in coding. A slice / tile can include one or more coding tree units (CTUs). One picture can be composed of one or more slices / tiles.

[0033] A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set. The tile row is a rectangular region of CTUs having a width specified by syntax elements in the picture parameter set and a height equal to the height of the picture.A tile scan may represent a specific sequential ordering of CTUs partitioning a picture, where the CTUs are ordered consecutively in a CTU raster scan in a tile, whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture. A slice may include multiple complete tiles or multiple consecutive CTU rows in one tile of a picture, which may be included in one NAL unit. In this document, the terms tile group and slice may be used interchangeably. For example, in this document, tile group / tile group header may be referred to as slice / slice header.

[0034] On the other hand, a picture can be divided into two or more sub-pictures, each of which can be a rectangular region of one or more slices within a picture.

[0035] A pixel or a pel can refer to the smallest unit that constitutes one picture (or image). A term corresponding to a pixel can also be used: "sample." A sample can generally represent a pixel or a pixel value, and can represent only a pixel / pixel value of a luma component, or can represent only a pixel / pixel value of a chroma component.

[0036] A unit may refer to a 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. One unit may include one luma block and two chroma (e.g., cb, cr) blocks. The term unit may be used interchangeably with terms such as block or area. In general, an M×N block may include samples (or a sample array) consisting of M columns and N rows, or a set (or an array) of transform coefficients.

[0037] 2 is a diagram for explaining the configuration of a video / image encoding device to which this document can be applied. Hereinafter, the term "video encoding device" may include an image encoding device.

[0038] As shown in FIG. 2, the encoding device 200 may include an image partitioner 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 predictor 221 and an intra 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 reconstructed block generator. The image dividing unit 210, the predicting unit 220, the residual processing unit 230, the entropy encoding unit 240, the adding unit 250, and the filtering unit 260 may be configured by one or more hardware components (e.g., an encoder chipset or a processor) depending on the embodiment. Also, the memory 270 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may further include the memory 270 as an internal / external component.

[0039] The image division unit 210 may divide an input image (or picture, frame) input to the encoding device 200 into one or more processing units. For example, the processing units may be called coding units (CUs). In this case, the coding units may be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) using a quad-tree, binary-tree, ternary-tree (QTBTTT) structure. For example, one coding unit may be divided into multiple coding units of deeper depths based on a quad-tree structure, a binary tree structure, and / or a ternary structure. In this case, for example, the quad-tree structure may be applied first, and then the binary tree structure and / or the ternary structure may be applied. Alternatively, the binary tree structure may be applied first. The coding procedure according to the present disclosure may be performed based on a final coding unit that is not further divided. In this case, the largest coding unit may be used as the final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units of lower depths as needed, and a coding unit of an optimal size may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and restoration, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may each be divided or partitioned from the final coding unit.The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0040] The term "unit" may be used interchangeably with terms such as "block" or "area." In general, an MxN block can refer to a set of samples or transform coefficients consisting of M columns and N rows. A sample generally refers to a pixel or pixel value, and can refer to only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component. A sample can also be used as a term corresponding to one pixel or pel of a picture (or image).

[0041] The encoding apparatus 200 may generate a residual signal (residual block, residual sample array) by subtracting a prediction signal (predicted block, prediction sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from an input image signal (original block, original sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, as shown in the figure, a unit in the encoding apparatus 200 that subtracts a prediction signal (predicted block, prediction sample array) from an input image signal (original block, original sample array) may be referred to as a subtraction unit 231. The prediction unit may perform prediction on a current block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied on a current block or CU basis. The prediction unit may generate various information related to prediction, such as prediction mode information, and transmit the information to the entropy encoding unit 240, as will be described later in the description of each prediction mode. The prediction information can be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0042] The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located adjacent to or distant from the current block depending on the prediction mode. Prediction modes in intra prediction may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, DC mode and planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the granularity of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the settings. The intra prediction unit 222 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0043] The inter prediction unit 221 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (such as L0 prediction, L1 prediction, or Bi prediction). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a collocated CU (col CU), or the like, and the reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter predictor 221 may construct a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive a motion vector and / or a reference picture index for the current block. Inter prediction may be performed based on various prediction modes, and for example, in the case of a skip mode or a merge mode, the inter predictor 221 may use motion information of neighboring blocks as motion information of the current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted.In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0044] The predictor 220 may generate a prediction signal based on various prediction methods, which will be described later. For example, the predictor may not only apply intra prediction or inter prediction for predicting a block, but also apply both intra prediction and inter prediction simultaneously. This may be referred to as combined inter and intra prediction (CIIP). The predictor may also use intra block copy (IBC) prediction mode or palette mode for predicting a block. The IBC prediction mode or palette mode may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be similar to inter prediction in that it derives a reference block within the current picture. That is, IBC may utilize at least one of the inter prediction techniques described herein. Palette mode may be considered an example of intra coding or intra prediction. When palette mode is applied, sample values ​​within a picture may be signaled based on information related to a palette table and a palette index.

[0045] The prediction signal generated by the prediction unit (including the inter prediction unit 221 and / or the intra prediction unit 222) may be used to generate a reconstructed signal or a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loeve transform (KLT), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). Here, GBT refers to a transform obtained from a graph representing inter-pixel relationship information. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. The transform process may be applied to pixel blocks having the same square size, or to non-square blocks of variable size.

[0046] The quantizer 233 quantizes the transform coefficients and transmits the quantized signal to the entropy encoder 240. The entropy encoder 240 encodes the quantized signal (information about the quantized transform coefficients) and outputs it as a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 233 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and may generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoder 240 may perform various encoding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). In addition to the quantized transform coefficients, the entropy encoder 240 may also encode information required for video / image restoration (e.g., values ​​of syntax elements) together with or separately from the quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in the form of a bitstream in units of network abstraction layer (NAL) units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. Information and / or syntax elements transmitted / signaled from an encoding device to a decoding device in this document may be included in the video / image information. The video / image information may be encoded through the above-described encoding procedure and included in the bitstream.The bitstream can be transmitted via a network or stored in a digital storage medium. Here, the network can include a broadcasting 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 transmitting the signal output from the entropy encoding unit 240 and / or a storage unit (not shown) for storing the signal can be configured as internal / external elements of the encoding device 200, or the transmitter can be included in the entropy encoding unit 240.

[0047] The quantized transform coefficients output from the quantizer 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) may be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients via the inverse quantizer 234 and the inverse transformer 235. The adder 155 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the inter predictor 221 or the intra predictor 222. When there is no residual for the current block, such as when skip mode is applied, a predicted block may be used as the reconstructed block. The adder 250 may be referred to as a reconstruction unit or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, or may be used for inter prediction of the next picture after filtering, as described below.

[0048] Meanwhile, luma mapping with chrominance scaling (LMCS) can be applied during picture encoding and / or restoration.

[0049] The filtering unit 260 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 260 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture and store the modified reconstructed picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset (SAO), an adaptive loop filter, a bilateral filter, etc. The filtering unit 260 may generate various information related to filtering and transmit it to the entropy encoding unit 290, as will be described later in the description of each filtering method. The filtering information may be encoded by the entropy encoding unit 290 and output in the form of a bitstream.

[0050] The modified reconstructed picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 280. When inter prediction is applied through this, the encoding device can avoid prediction mismatch between the encoding device 200 and the decoding device, and can also improve coding efficiency.

[0051] The DPB of the memory 270 may store a modified reconstructed picture to be used as a reference picture in the inter predictor 221. The memory 270 may store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of a block in an already reconstructed picture. The stored motion information may be transmitted to the inter predictor 221 to be used as motion information of a spatially neighboring block or a temporally neighboring block. The memory 270 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 222.

[0052] FIG. 3 is a diagram illustrating the configuration of a video / image decoding device to which this document can be applied.

[0053] As shown in FIG. 3, the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter predictor 331 and an intra predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 321. Depending on the embodiment, the entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 may be configured as a single hardware component (e.g., a decoder chipset or processor). In addition, the memory 360 may include a decoded picture buffer (DPB) or may be configured as a digital storage medium. The hardware components may further include a memory 360 as an internal / external component.

[0054] When a bitstream including video / image information is input, the decoding device 300 can reconstruct an image corresponding to the process in which the video / image information was processed by the encoding device of FIG. 3. For example, the decoding device 300 can derive units / blocks based on block division-related information obtained from the bitstream. The decoding device 300 can perform decoding using a processing unit applied by the encoding device. Therefore, the processing unit for decoding can be, for example, a coding unit, and the coding unit can be divided from a coding tree unit or a maximal coding unit according to a quad tree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a playback device.

[0055] The decoding device 300 may receive a signal output from the encoding device of FIG. 3 in the form of a bitstream, and the received signal may be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (e.g., video / image information) necessary for image restoration (or picture restoration). The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The decoding device may further decode pictures based on the information on the parameter sets and / or the general constraint information. Signaling / received information and / or syntax elements, which will be described later in this document, may be decoded via the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 may decode information in a bitstream based on a coding method such as Exponential-Golomb coding, CAVLC, or CABAC, and output values ​​of syntax elements required for image restoration, quantized values ​​of transform coefficients related to residuals, etc. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, determines a context model using information on the syntax element to be decoded and decode information on neighboring and current blocks, or information on symbols / bins decoded in previous steps, predicts the occurrence probability of the bins based on the determined context model, and performs arithmetic decoding of the bins to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method may update the context model using information on the decoded symbols / bins for the context model of the next symbol / bin.Among the information decoded by the entropy decoding unit 310, information related to prediction is provided to a prediction unit (inter prediction unit 332 and intra prediction unit 331), and residual values ​​entropy decoded by the entropy decoding unit 310, i.e., quantized transform coefficients and related parameter information, may be input to the residual processing unit 320. The residual processing unit 320 may derive a residual signal (residual block, residual sample, residual sample array). In addition, among the information decoded by the entropy decoding unit 310, information related to filtering may be provided to the filtering unit 350. Meanwhile, a receiving unit (not shown) that receives a signal output from the encoding device may be further configured as an internal / external element of the decoding device 300, or the receiving unit may be a component of the entropy decoding unit 310. Meanwhile, the decoding device according to this document may be called a video / image / picture decoding device, and the decoding device may be divided 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 decoding unit 310, and the sample decoder may include at least one of the inverse quantization unit 321, the inverse transform unit 322, the addition unit 340, the filtering unit 350, the memory 360, the inter prediction unit 332, and the intra prediction unit 331.

[0056] The inverse quantization unit 321 may inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The inverse quantization unit 321 may inverse quantize the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) to obtain transform coefficients.

[0057] The inverse transform unit 322 performs inverse transform on the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0058] The prediction unit may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 310, and may determine a specific intra / inter prediction mode.

[0059] The predictor 330 may generate a prediction signal based on various prediction methods, which will be described later. For example, the predictor may not only apply intra prediction or inter prediction for predicting a block, but also simultaneously apply intra prediction and inter prediction. This may be referred to as combined inter and intra prediction (CIIP). The predictor may also use an intra block copy (IBC) prediction mode or a palette mode for predicting a block. The IBC prediction mode or palette mode may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be similar to inter prediction in that a reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described herein. The palette mode may be considered an example of intra coding or intra prediction. When the palette mode is applied, information regarding a palette table and a palette index may be included in the video / image information and signaled.

[0060] The intra prediction unit 332 may predict the current block by referring to samples in the current picture. The referenced samples may be located adjacent to the current block or may be located far away depending on the prediction mode. In intra prediction, prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 332 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0061] The inter prediction unit 331 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. For example, the inter prediction unit 331 may construct a motion information candidate list based on the neighboring blocks and derive a motion vector and / or a reference picture index for the current block based on received candidate selection information. Inter prediction may be performed based on various prediction modes, and the prediction information may include information indicating the inter prediction mode for the current block.

[0062] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the acquired residual signal to the predicted signal (predicted block, predicted sample array) output from the predictor 330. When there is no residual for the current block, such as when a skip mode is applied, the predicted block may be used as the reconstructed block.

[0063] The adder 340 may be referred to as a reconstruction unit or a reconstruction block generator. The generated reconstruction signal may be used for intra prediction of a next block to be processed in the current picture, may be output after filtering as described below, or may be used for inter prediction of a next picture.

[0064] Meanwhile, LMCS (luma mapping with chroma scaling) can be applied during the picture decoding process.

[0065] The filtering unit 350 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 350 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may transmit the modified reconstructed picture to the memory 60, specifically, to the DPB of the memory 360. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0066] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter predictor 331. The memory 360 can store motion information of a block from which motion information in the current picture is derived (or decoded) and / or motion information of a block in an already reconstructed picture. The stored motion information can be transmitted to the inter predictor 331 to be used as motion information of a spatially neighboring block or a temporally neighboring block. The memory 360 can store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 332.

[0067] In this specification, the embodiments described for the filtering unit 260, inter prediction unit 221, and intra prediction unit 222 of the encoding device 100 can also be applied identically or correspondingly to the filtering unit 350, inter prediction unit 332, and intra prediction unit 331 of the decoding device 300, respectively.

[0068] Meanwhile, as described above, prediction is performed to improve compression efficiency during video coding. Accordingly, a predicted block including predicted samples for a current block, which is a block to be coded, can be generated. Here, the predicted block includes predicted samples in the spatial domain (or pixel domain). The predicted block is derived in the same way by an encoding device and a decoding device. The encoding device can improve image coding efficiency by signaling to a decoding device information (residual information) regarding the residual between the original block and the predicted block, rather than the original sample values ​​of the original block themselves. The decoding device can derive a residual block including residual samples based on the residual information, add the residual block and the predicted block to generate a reconstructed block including reconstructed samples, and generate a reconstructed picture including the reconstructed block.

[0069] The residual information may be generated through a transform and quantization procedure. For example, an encoding device may derive a residual block between the original block and the predicted block, perform a transform procedure on residual samples (residual sample array) included in the residual block to derive transform coefficients, and perform a quantization procedure on the transform coefficients to derive quantized transform coefficients, and then signal the related residual information (via a bitstream) to a decoding device. Here, the residual information may include information such as value information, position information, transform technique, transform kernel, and quantization parameter of the quantized transform coefficients. The decoding device may derive residual samples (or residual blocks) by performing an inverse quantization / inverse transform procedure based on the residual information. The decoding device may generate a reconstructed picture based on the predicted block and the residual block. The encoding device may also derive a residual block by inverse quantizing / inverse transforming the quantized transform coefficients for reference for inter-prediction of a future picture, and generate a reconstructed picture based on the residual block.

[0070] FIG. 4 shows an example of a hierarchical structure for coded data.

[0071] As shown in Figure 4, the coded data can be divided into a VCL (video coding layer) that handles the video / image coding process and itself, and a NAL (Network abstraction layer) that is located between the lower system that stores and transmits the coded video / image data.

[0072] The VCL can generate parameter sets (picture parameter set (PPS), sequence parameter set (SPS), video parameter set (VPS), etc.) corresponding to headers of sequences and pictures, and supplemental enhancement information (SEI) messages additionally required for the video / image coding process. The SEI message is separated from information about the video / image (slice data). The VCL containing information about the video / image consists of slice data and a slice header. Meanwhile, the slice header can be called a tile group header, and the slice data can be called tile group data.

[0073] In NAL, NAL units can be generated by adding header information (NAL unit header) to RBSP (Raw Byte Sequence Payload) generated by VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated by VCL. The NAL unit header can include NAL unit type information identified by the RBSP data included in the NAL unit.

[0074] The NAL unit, which is the basic unit of NAL, maps coded images to bitstreams of lower systems such as file formats according to a predetermined standard, Real-time Transport Protocol (RTP), Transport Stream (TS), etc.

[0075] As shown in the figure, NAL units can be divided into VCL NAL units and non-VCL NAL units according to the RBSP generated by the VCL. A VCL NAL unit can refer to a NAL unit containing information about an image (slice data), and a non-VCL NAL unit can refer to a NAL unit containing information necessary for decoding an image (parameter set or SEI message).

[0076] The VCL NAL unit and non-VCL NAL unit described above can be transmitted over a network with header information according to the data standard of the lower system. For example, the NAL unit can be transformed into a data format of a predetermined standard such as H.266 / VVC file format, RTP (Real-time Transport Protocol), TS (Transport Stream), etc., and transmitted over various networks.

[0077] As described above, the NAL unit type of an NAL unit can be identified by the RBSP data structure included in the NAL unit, and information about such NAL unit type can be stored and signaled in the NAL unit header.

[0078] For example, NAL units can be broadly classified into VCL NAL unit types and non-VCL NAL unit types depending on whether they contain information about an image (slice data). VCL NAL unit types can be classified according to the nature and type of pictures contained in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0079] The following is an example of a NAL unit type identified by the type of parameter set included in the non-VCL NAL unit type. The NAL unit type can be identified by the type of parameter set included. For example, the NAL unit type can be identified as any one of an APS (Adaptation Parameter Set) NAL unit, which is a type for a NAL unit including an APS, a DPS (Decoding Parameter Set) NAL unit, which is a type for a NAL unit including a DPS, a VPS (Video Parameter Set) NAL unit, which is a type for a NAL unit including a VPS, an SPS (Sequence Parameter Set) NAL unit, which is a type for a NAL unit including an SPS, and a PPS (Picture Parameter Set) NAL unit, which is a type for a NAL unit including a PPS.

[0080] The above-mentioned NAL unit type has syntax information for the NAL unit type, and the syntax information can be stored in a NAL unit header and signaled. For example, the syntax information can be nal_unit_type, and the NAL unit type can be specified by the nal_unit_type value.

[0081] Meanwhile, as described above, one picture may include multiple slices, and one slice may include a slice header and slice data. In this case, one picture header may be added to multiple slices (slice header and slice data set) in one picture. The picture header (picture header syntax) may include information / parameters commonly applicable to the picture. The slice header (slice header syntax) may include information / parameters commonly applicable to the slices. The APS (APS syntax) or PPS (PPS syntax) may include information / parameters commonly applicable to one or more slices or pictures. The SPS (SPS syntax) may include information / parameters commonly applicable to one or more sequences. The VPS (VPS syntax) may include information / parameters commonly applicable to multiple layers. The DPS (DPS syntax) may include information / parameters commonly applicable to the entire video. The DPS may include information / parameters related to concatenation of a coded video sequence (CVS). In this document, a high level syntax (HLS) may include at least one of the APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, a picture header syntax, and a slice header syntax.

[0082] In this document, image / video information encoded from an encoding device to a decoding device and signaled in the form of a bitstream may include not only partitioning-related information within a picture, intra / inter prediction information, residual information, in-loop filtering information, etc., but also information included in the slice header, information included in the picture header, information included in the APS, information included in the PPS, information included in the SPS, information included in the VPS, and / or information included in the DPS. In addition, the image / video information may further include information of a NAL unit header.

[0083] Meanwhile, as described above, the encoding device / decoding device may perform an in-loop filtering procedure on a reconstructed picture to improve subjective / objective image quality. A modified reconstructed picture may be generated through the in-loop filtering procedure, and the modified reconstructed picture may be output as a decoded picture by the decoding device or stored in a decoded picture buffer or memory of the encoding device / decoding device. Furthermore, the modified reconstructed picture may later be used as a reference picture in an inter-prediction procedure during encoding / decoding. The in-loop filtering procedure may include a deblocking filtering procedure, a sample adaptive offset (SAO) procedure, and / or an adaptive loop filter (ALF) procedure, as described above. In this case, one or some of the deblocking filtering procedure, the sample adaptive offset (SAO) procedure, and the adaptive loop filter (ALF) procedure may be applied sequentially, or all of them may be applied sequentially. For example, the SAO procedure may be performed after the deblocking filtering procedure is applied to the reconstructed picture. Alternatively, the ALF procedure may be performed after the deblocking filtering procedure is applied to the reconstructed picture. This can be done in the encoding device as well.

[0084] The deblocking filtering procedure is a procedure for removing distortions occurring at boundaries between blocks in a reconstructed picture. The deblocking filtering procedure may, for example, derive a target boundary in the reconstructed picture, determine a boundary strength (bS) for the target boundary, and perform deblocking filtering on the target boundary based on bS. bS may be determined based on the prediction modes of two blocks adjacent to the target boundary, the motion vector difference, whether the reference pictures are the same, whether there are significant coefficients other than zero, etc.

[0085] SAO is a method for compensating for an offset difference between a reconstructed picture and an original picture on a sample-by-sample basis. For example, SAO can be applied according to a type such as band offset or edge offset. According to SAO, samples can be classified into different categories according to the SAO type, and an offset value can be added to each sample according to the category. Filtering information for SAO can include whether SAO is applicable, SAO type information, and SAO offset value information. For example, SAO can be applied to a reconstructed picture after deblocking filtering has been applied.

[0086] An adaptive loop filter (ALF) procedure is a procedure for filtering a reconstructed picture on a sample-by-sample basis based on filter coefficients according to a filter shape. An encoding apparatus can compare a reconstructed picture with an original picture to determine whether to apply an ALF, the ALF shape and / or ALF filtering coefficients, etc., and signal the result to a decoding apparatus. That is, filtering information for the ALF can include whether to apply an ALF, ALF filter shape information, ALF filtering coefficient information, etc. The ALF procedure can be applied to a reconstructed picture after deblocking filtering is applied.

[0087] FIG. 5 is a flow chart illustrating one embodiment of a method for performing deblocking filtering.

[0088] As described above, the encoding device / decoding device can reconstruct a picture in units of blocks. When such block-based image reconstruction is performed, block artifacts may occur at boundaries between blocks in the reconstructed picture. Therefore, the encoding device and the decoding device can use a deblocking filter to remove block artifacts that occur at boundaries between blocks in the reconstructed picture.

[0089] Therefore, the encoding device / decoding device can derive inter-block boundaries in the reconstructed picture where deblocking filtering is performed. Meanwhile, the boundaries where deblocking filtering is performed may be called edges. The boundaries where deblocking filtering is performed may include two types, which may be vertical boundaries and horizontal boundaries. The vertical boundaries may be called vertical edges, and the horizontal boundaries may be called horizontal edges. The encoding device / decoding device can perform deblocking filtering on vertical edges and can perform deblocking filtering on horizontal edges.

[0090] For example, the encoding / decoding device can derive a target boundary for filtering in the reconstructed picture (S510).

[0091] The encoding / decoding device may also determine a boundary strength (bS) for the boundary where deblocking filtering is performed (S520). bS may also be expressed as boundary filtering strength. For example, a case may be assumed in which a bS value for the boundary (block edge) between block P and block Q is to be determined. In this case, the encoding / decoding device may determine a bS value for the boundary (block edge) between block P and block Q based on the block P and the block Q. For example, bS may be determined according to the following table:

[0092] [Table 1-1]

[0093] [Table 1-2]

[0094] Here, p may represent a sample of a block P adjacent to the boundary to be deblocking filtered, and q may represent a sample of a block Q adjacent to the boundary to be deblocking filtered.

[0095] Furthermore, for example, p0 may represent a sample of a block adjacent to the left or above the deblocking filtering target boundary, and q0 may represent a sample of a block adjacent to the right or below the deblocking filtering target boundary. For example, if the target boundary is oriented vertically (i.e., the target boundary is a vertical boundary), p0 may represent a sample of a block adjacent to the left of the deblocking filtering target boundary, and q0 may represent a sample of a block adjacent to the right of the deblocking filtering target boundary. Alternatively, if the target boundary is oriented horizontally (i.e., the target boundary is a horizontal boundary), p0 may represent a sample of a block adjacent to the above of the deblocking filtering target boundary, and q0 may represent a sample of a block adjacent to the below of the deblocking filtering target boundary.

[0096] Referring again to FIG. 5, the encoding / decoding apparatus may perform deblocking filtering based on the bS (S530). For example, if the bS value is 0, filtering is not applied to the target boundary. Meanwhile, a filter to be applied to the boundary between blocks may be determined based on the determined bS value. The filters may be classified into strong filters and weak filters. The encoding / decoding apparatus may improve coding efficiency by filtering different filters for boundaries at positions where blocking artifacts are likely to occur in the reconstructed picture and boundaries at positions where blocking artifacts are unlikely to occur.

[0097] 6 is a flow chart illustrating an example of an ALF procedure. The ALF procedure disclosed in FIG. 6 can be performed in an encoding device and a decoding device. In this document, a coding device may include the encoding device and / or the decoding device.

[0098] As shown in FIG. 6, a coding apparatus derives a filter for ALF (S610). The filter may include filter coefficients. The coding apparatus may determine whether to apply ALF, and if it determines to apply the ALF, may derive a filter including filter coefficients for the ALF. A filter (coefficients) for ALF or information for deriving a filter (coefficients) for ALF may be referred to as ALF parameters. Information regarding whether ALF is applicable (e.g., an ALF availability flag) and ALF data for deriving the filter may be signaled from an encoding apparatus to a decoding apparatus. The ALF data may include information for deriving the filter for ALF. Also, for example, for hierarchical control of ALF, an ALF availability flag may be signaled at the SPS, picture header, slice header, and / or CTB level, respectively.

[0099] To derive a filter for the ALF, activity and / or directionality of a current block (or an ALF target block) may be derived, and the filter may be derived based on the activity and / or directionality. For example, the ALF procedure may be applied in units of 4x4 blocks (based on the luma component). The current block or the ALF target block may be, for example, a CU, or a 4x4 block within a CU. Specifically, for example, a filter for the ALF may be derived based on a first filter derived from information included in the ALF data and a predefined second filter, and a coding device may select one of the filters based on the activity and / or directionality. The coding device may use filter coefficients included in the selected filter for the ALF.

[0100] The coding apparatus performs filtering based on the filter (S620). Modified reconstruction samples may be derived based on the filtering. For example, the filter coefficients in the filter may be arranged or assigned according to a filter shape, and the filtering may be performed on reconstruction samples in the current block. Here, the reconstruction samples in the current block may be reconstruction samples after the deblocking filter procedure and the SAO procedure are completed. For example, one filter shape may be used, or one filter shape may be selected from a plurality of predetermined filter shapes. For example, the filter shape applied to the luma component may be different from the filter shape applied to the chroma component. For example, a 7x7 diamond filter shape may be used for the luma component, and a 5x5 diamond filter shape may be used for the chroma component.

[0101] 7 shows examples of filter shapes for ALF, where C0 to C11 in (a) and C0 to C5 in (b) can be filter coefficients that depend on the position within each filter shape.

[0102] FIG. 7(a) shows a 7×7 diamond filter shape, and FIG. 7(b) shows a 5×5 diamond filter shape. In FIG. 7, Cn in the filter shape indicates a filter coefficient. When n is the same in Cn, this indicates that the same filter coefficient may be assigned. In this document, the position and / or unit to which filter coefficients are assigned according to the ALF filter shape may be referred to as a filter tab. In this case, one filter coefficient may be assigned to each filter tab, and the arrangement of the filter tabs may correspond to the filter shape. A filter tab located at the center of the filter shape may be referred to as a center filter tab. Two filter tabs with the same n value that are located at corresponding positions based on the center filter tab may be assigned the same filter coefficient. For example, a 7×7 diamond filter shape includes 25 filter tabs, and filter coefficients C0 to C11 are assigned in a centrally symmetrical manner, so that filter coefficients can be assigned to the 25 filter tabs using only 13 filter coefficients. For example, a 5×5 diamond filter shape includes 13 filter tabs, and filter coefficients C0 to C5 are assigned in a centrally symmetric manner, so that filter coefficients can be assigned to the 13 filter tabs using only seven filter coefficients. For example, to reduce the amount of data related to signaled filter coefficients, 12 of the 13 filter coefficients for a 7×7 diamond filter shape can be signaled (explicitly) and one filter coefficient can be derived (implicitly). For example, for a 5×5 diamond filter shape, 6 of the 7 filter coefficients can be signaled (explicitly) and one filter coefficient can be derived (implicitly).

[0103] According to one embodiment of this document, ALF parameters used for the ALF procedure can be signaled via an adaptation parameter set (APS), and the ALF parameters can be derived from filter information or ALF data for the ALF.

[0104] As described above, ALF is a type of in-loop filtering technique that can be applied in video / image coding. ALF can be performed using a Wiener-based adaptive filter. This can be done to minimize the mean square error (MSE) between the original samples and the decoded samples (or reconstructed samples). A high-level design for an ALF tool can incorporate syntax elements that can be accessed in the SPS and / or slice header (or tile group header).

[0105] Meanwhile, a picture header includes syntax elements that are applied to the picture header, and the syntax elements can be applied to all slices of a picture associated with the picture header. If a particular syntax element is applied only to a particular slice, the particular syntax element must be signaled in a slice header, not a picture header.

[0106] Conventionally, signaling of control flags and parameters for enabling or disabling various tools for picture encoding or decoding could be present in the picture header and could be overridden in the slice header. This method provides flexibility by allowing tool control to be performed at both the picture level and the slice level. However, this method can impose a burden on the decoder because it must check the slice header after checking the picture header.

[0107] Accordingly, an embodiment of the present invention proposes indication information indicating whether at least one tool is applied at the picture level or the slice level. In this case, the indication information may be included in either a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS). That is, when a specific tool is activated in a CLVS, an indication or flag indicating whether the specific tool is applied at the picture level or the slice level may be signaled in a parameter set such as an SPS or a PPS. The indication or flag may be for one tool, but is not limited thereto. For example, an indication or flag indicating whether all tools other than a specific tool are applied at the picture level or the slice level may be signaled in a parameter set such as an SPS or a PPS.

[0108] Control flags and parameters for activating or deactivating a tool can be signaled at the picture level or the slice level, but not at both the picture level and the slice level. For example, when obtaining indication information indicating whether a particular tool is applied at the picture level, control flags and parameters for activating or deactivating the tool can be signaled only in the picture header. Similarly, when obtaining indication information indicating whether a particular tool is applied at the slice level, control flags and parameters for activating or deactivating the tool can be signaled only in the slice header.

[0109] Also, for example, a tool that is specified to be applied at the picture level in a particular parameter set can be specified to be applied at the slice level in another parameter set of the same type.

[0110] For example, the PPS syntax including the indication information may be as follows:

[0111] [Table 2]

[0112] The semantics of the syntax elements included in the syntax of Table 2 can be expressed, for example, as shown in Table 3 below.

[0113] [Table 3]

[0114] Referring to the table, the indication information may include a flag indicating whether reference picture list signaling is applied at the picture level or the slice level. For example, the indication information may specify whether information related to reference picture list signaling is present in a picture header or a slice header. For example, the flag may be referred to as rpl_present_in_ph_flag. If the value of the flag is equal to 1, information related to reference picture list signaling may be present in a picture header, and if the value of the flag is equal to 0, information related to reference picture list signaling may be present in a slice header.

[0115] The indication information may also include a flag indicating whether a Sample Adaptive Offset (SAO) procedure is applied at the picture level or the slice level. For example, the indication information may specify whether information related to the SAO procedure is present in a picture header or a slice header. For example, the flag may be referred to as sao_present_in_ph_flag. If the value of the flag is equal to 1, information related to the SAO procedure may be present in a picture header, and if the value of the flag is equal to 0, information related to the SAO procedure may be present in a slice header.

[0116] The indication information may also include a flag indicating whether an Adaptive Loop Filter (ALF) procedure is applied at the picture level or the slice level. For example, the indication information may specify whether information related to the ALF procedure is present in a picture header or a slice header. For example, the flag may be referred to as alf_present_in_ph_flag. If the value of the flag is equal to 1, information related to the ALF procedure may be present in a picture header, and if the value of the flag is equal to 0, information related to the ALF procedure may be present in a slice header.

[0117] The indication information may also include at least one flag indicating whether a deblocking procedure is applied at a picture level or a slice level. For example, based on the at least one flag, information related to the deblocking procedure may be present in one of a picture header and a slice header. For example, the at least one flag may be referred to as a deblocking_filter_ph_override_enabled_flag or a deblocking_filter_sh_override_enabled_flag. For example, if the value of the at least one flag is equal to 1, a flag indicating whether parameters related to the deblocking procedure are present in the picture header may be present in the picture header, and if the value of the at least one flag is equal to 0, a flag indicating whether parameters related to the deblocking procedure are present in the picture header may not be present in the picture header.

[0118] Alternatively, a flag indicating whether parameters related to the deblocking procedure are present in the slice header may be present in the slice header when the value of the at least one flag is equal to 1, and a flag indicating whether parameters related to the deblocking procedure are present in the slice header may not be present in the slice header when the value of the at least one flag is equal to 0. In this case, the values ​​of deblocking_filter_ph_override_enabled_flag and deblocking_filter_sh_override_enabled_flag may not both be equal to 1.

[0119] Meanwhile, the picture header syntax may be as follows:

[0120] [Table 4-1]

[0121] [Table 4-2]

[0122] The semantics of the syntax elements included in the syntax of Table 4 can be expressed, for example, as shown in Table 5 below.

[0123] [Table 5]

[0124] Referring to the table, pic_deblocking_filter_override_present_flag may be signaled when the value of deblocking_filter_ph_override_enabled_flag, which corresponds to a flag indicating whether a deblocking procedure is applied at the picture level, is 1. When the value of pic_deblocking_filter_override_present_flag is 1, pic_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure are present in the picture header, may be present in the picture header. Alternatively, when the value of pic_deblocking_filter_override_present_flag is 0, pic_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure are present in the picture header, may not be present in the picture header.

[0125] In addition, if the value of pic_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure exist in the picture header, is equal to 1, the deblocking parameters may exist in the picture header. If the value of pic_deblocking_filter_override_flag is equal to 0, the deblocking parameters may not exist in the picture header.

[0126] Also, if the value of pic_deblocking_filter_disabled_flag is equal to 1, a deblocking filter may not be applied to a slice associated with the picture header. If the value of pic_deblocking_filter_disabled_flag is equal to 0, a deblocking filter may be applied to a slice associated with the picture header.

[0127] Additionally, pic_beta_offset_div2 and pic_tc_offset_div2 can specify deblocking parameter offsets for β and tC (divided by 2) for the slice associated with the picture header. The values ​​of pic_beta_offset_div2 and pic_tc_offset_div2 are both in the range of -6 to 6.

[0128] Meanwhile, the slice header syntax may be as shown in the following table.

[0129] [Table 6-1]

[0130] [Table 6-2]

[0131] The semantics of the syntax elements included in the syntax of Table 6 can be expressed, for example, as shown in Table 7 below.

[0132] [Table 7]

[0133] Referring to the table, slice_deblocking_filter_override_present_flag may be signaled when the value of deblocking_filter_sh_override_enabled_flag, which corresponds to a flag indicating whether a deblocking procedure is applied at the slice level, is 1. When the value of slice_deblocking_filter_override_present_flag is 1, slice_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure are present in the slice header, may be present in the slice header. Alternatively, when the value of slice_deblocking_filter_override_present_flag is 0, slice_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure are present in the slice header, may not be present in the picture header.

[0134] In addition, if the value of slice_deblocking_filter_override_flag, which corresponds to a flag indicating whether parameters related to the deblocking procedure exist in the slice header, is equal to 1, the deblocking parameters may exist in the slice header. If the value of slice_deblocking_filter_override_flag is equal to 0, the deblocking parameters may not exist in the slice header.

[0135] Also, if the value of slice_deblocking_filter_disabled_flag is equal to 1, a deblocking filter may not be applied to a slice associated with the slice header. If the value of slice_deblocking_filter_disabled_flag is equal to 0, a deblocking filter may be applied to a slice associated with the slice header.

[0136] In addition, slice_beta_offset_div2 and slice_tc_offset_div2 can specify deblocking parameter offsets for β and tC (divided by 2) for the slice. The values ​​of slice_beta_offset_div2 and slice_tc_offset_div2 are both within the range of -6 to 6.

[0137] FIG. 8 is a flowchart showing the operation of the encoding device according to one embodiment, and FIG. 9 is a block diagram showing the configuration of the encoding device according to one embodiment.

[0138] The method disclosed in FIG. 8 may be performed by the encoding device disclosed in FIG. 2 or FIG. 9. S810 and S820 in FIG. 8 may be performed by the image prediction unit 220, the residual processing unit 230, or the filtering unit 260 disclosed in FIG. 2, and S830 may be performed by the entropy encoding unit 240 disclosed in FIG. 2. Furthermore, the operations of S810 to S830 are based on some of the content described above in FIGS. 1 to 7. Therefore, the description of specific content that overlaps with the content described above in FIGS. 1 to 7 will be omitted or simplified.

[0139] As shown in FIG. 8, an encoding apparatus according to an embodiment may generate indication information indicating whether at least one tool applied to a current block is applied at a picture level or a slice level (S810).

[0140] For example, the image prediction unit 220 of the encoding device may generate indication information including a flag indicating whether reference picture list signaling is applied at the picture level or the slice level. For example, if the value of the flag is equal to 1, information related to the reference picture list signaling may be present in a picture header, and if the value of the flag is equal to 0, information related to the reference picture list signaling may be present in a slice header.

[0141] For example, the filtering unit 260 of the encoding device may generate indication information including a flag indicating whether a Sample Adaptive Offset (SAO) procedure is applied at the picture level or the slice level. For example, if the value of the flag is equal to 1, information related to the SAO procedure may be present in a picture header, and if the value of the flag is equal to 0, information related to the SAO procedure may be present in a slice header.

[0142] For example, the filtering unit 260 of the encoding device may generate indication information including a flag indicating whether an Adaptive Loop Filter (ALF) procedure is applied at the picture level or the slice level. For example, if the value of the flag is 1, information related to the ALF procedure may be present in a picture header, and if the value of the flag is 0, information related to the ALF procedure may be present in a slice header.

[0143] Alternatively, for example, the filtering unit 260 of the encoding device may generate indication information including at least one flag indicating whether a deblocking procedure is applied at a picture level or a slice level. Based on the at least one flag, information related to the deblocking procedure may be present in one of a picture header and a slice header. For example, if the value of the at least one flag is equal to 1, a flag indicating whether parameters related to the deblocking procedure are present in the picture header may be present in the picture header, and if the value of the at least one flag is equal to 0, a flag indicating whether parameters related to the deblocking procedure are present in the picture header may not be present in the picture header.

[0144] An encoding device according to an embodiment may generate information related to at least one tool (S820). For example, the image prediction unit 220 of the encoding device may generate information related to signaling of a reference picture list. Alternatively, for example, the filtering unit 260 of the encoding device may generate at least one of information related to an SAO procedure, information related to an ALF procedure, and information related to a deblocking procedure.

[0145] An encoding device according to an embodiment may encode image information including instruction information and information related to at least one tool (S830). The image information may include prediction information for the current block. The prediction information may include information regarding an inter-prediction mode or an intra-prediction mode performed on the current block. The image information may also include residual information generated from an original sample by a residual processing unit 230 of the encoding device.

[0146] Meanwhile, the bitstream in which the image information is encoded can be transmitted to the decoding device via a network or a (digital) storage medium, where the network can include a broadcasting 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.

[0147] FIG. 10 is a flowchart showing the operation of a decoding device according to an embodiment, and FIG. 11 is a block diagram showing the configuration of a decoding device according to an embodiment.

[0148] The method disclosed in Fig. 10 may be performed by the decoding device disclosed in Fig. 3 or Fig. 11. Specifically, S1010 to S1030 may be performed by the entropy decoding unit 310 disclosed in Fig. 3. Also, S1040 may be performed by the prediction unit 330, the residual processing unit 320, the filtering unit 350, or the addition unit 340 disclosed in Fig. 3. Furthermore, the operations of S1010 and S1040 are based on some of the content described above with reference to Figs. 1 to 7. Therefore, the description of specific content that overlaps with the content described above with reference to Figs. 1 to 7 will be omitted or simplified.

[0149] A decoding apparatus according to an embodiment may acquire indication information indicating whether at least one tool for a current block is applied at a picture level or a slice level (S1010). For example, the indication information may include a flag indicating whether reference picture list signaling is applied at a picture level or a slice level. For example, the indication information may include a flag indicating whether a Sample Adaptive Offset (SAO) procedure is applied at a picture level or a slice level. For example, the indication information may include a flag indicating whether an Adaptive Loop Filter (ALF) procedure is applied at a picture level or a slice level. Or, for example, the indication information may include at least one flag indicating whether a deblocking procedure is applied at a picture level or a slice level.

[0150] A decoding apparatus according to an embodiment may determine whether information related to at least one tool is present in a picture header or a slice header based on the indication information (S1020).

[0151] For example, if the value of a flag indicating whether the reference picture list signaling is applied at the picture level or the slice level is equal to 1, it can be determined that information related to the reference picture list signaling exists in the picture header, and if the value of the flag is equal to 0, it can be determined that information related to the reference picture list signaling exists in the slice header.

[0152] For example, if the value of a flag indicating whether the SAO procedure is applied at the picture level or the slice level is equal to 1, it can be determined that information related to the SAO procedure exists in the picture header, and if the value of the flag is equal to 0, it can be determined that information related to the SAO procedure exists in the slice header.

[0153] For example, if the value of a flag indicating whether the ALF procedure is applied at the picture level or the slice level is equal to 1, it can be determined that information related to the ALF procedure exists in the picture header, and if the value of the flag is equal to 0, it can be determined that information related to the ALF procedure exists in the slice header.

[0154] Alternatively, information related to the deblocking procedure may be present in one of a picture header and a slice header, for example, based on at least one flag indicating whether the deblocking procedure is applied at a picture level or a slice level. For example, it may be determined that a flag indicating whether parameters related to the deblocking procedure are present in a picture header is present in a picture header when the value of the at least one flag is equal to 1, and that a flag indicating whether parameters related to the deblocking procedure are present in a picture header is absent when the value of the at least one flag is equal to 0. Alternatively, it may be determined that a flag indicating whether parameters related to the deblocking procedure are present in a slice header is present in a slice header when the value of the at least one flag is equal to 1, and that a flag indicating whether parameters related to the deblocking procedure are present in a slice header is absent when the value of the at least one flag is equal to 0.

[0155] A decoding apparatus according to an embodiment may parse information related to at least one tool from a picture header or a slice header based on the determination result (S1030).

[0156] A decoding apparatus according to an embodiment may decode a current block based on information related to at least one tool (S1040). For example, the prediction unit 330 of the decoding apparatus may perform prediction on the current block based on information related to reference picture list signaling obtained by receiving and parsing one of a picture header and a slice header. For example, the filtering unit 350 of the decoding apparatus may perform an SAO procedure on reconstructed samples based on information related to an SAO procedure obtained by receiving and parsing one of a picture header and a slice header. For example, the filtering unit 350 of the decoding apparatus may perform an ALF procedure on reconstructed samples based on information related to an ALF procedure obtained by receiving and parsing one of a picture header and a slice header. Alternatively, for example, the filtering unit 350 of the decoding apparatus may perform a deblocking procedure on reconstructed samples based on information related to a deblocking procedure obtained by receiving and parsing one of a picture header and a slice header.

[0157] In the above-described embodiments, the method is described based on a flowchart with a series of steps or blocks, but the embodiment is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps than those described above. Also, those skilled in the art will understand that the steps shown in the flowcharts are not exclusive, and other steps may be included, or one or more steps in the flowcharts may be deleted without affecting the scope of the embodiments herein.

[0158] The methods according to the embodiments of this document described above can be implemented in software form, and the encoding device and / or decoding device according to this document can be included in devices that perform image processing, such as TVs, computers, smartphones, set-top boxes, display devices, etc.

[0159] In this document, when an embodiment is implemented in software, the method described above may be implemented with modules (processes, functions, etc.) that perform the functions described above. The modules may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor in various well-known ways. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, a memory card, a storage medium, and / or other storage devices. That is, the embodiments described herein may be implemented and executed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each figure may be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, information (e.g., information on instructions) or algorithms for implementation may be stored on a digital storage medium.

[0160] In addition, the decoding device and encoding device to which the embodiments of this document are applied may be included in a multimedia broadcast transmitting / receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video interaction device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camcorder, a custom video (VoD) service providing device, an over-the-top (OTT) video (over-the-top) device, an internet streaming service providing device, a three-dimensional (3D) video device, a virtual reality (VR) device, an augmented reality (AR) device, an image telephone video device, a vehicle terminal (e.g., a vehicle terminal (including an autonomous vehicle), an airplane terminal, a ship terminal, etc.), a medical video device, etc., and may be used to process a video signal or a data signal. For example, an over-the-top (OTT) video (over-the-top) device may include a game console, a Blu-ray player, an internet-connected TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), etc.

[0161] In addition, a processing method to which an embodiment of this document is applied may be produced in the form of a computer-executable program and stored in a computer-readable recording medium. Multimedia data having a data structure according to an embodiment of this document may also be stored in a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices and distributed storage devices in which computer-readable data is stored. Examples of the computer-readable recording medium include Blu-ray Discs (BDs), Universal Serial Buses (USBs), ROMs, PROMs, EPROMs, EEPROMs, RAMs, CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer-readable recording medium also includes media implemented in the form of carrier waves (e.g., transmission via the Internet). A bitstream generated by an encoding method may be stored in a computer-readable recording medium or transmitted via a wired or wireless communication network.

[0162] Furthermore, the embodiments of the present document may be implemented in a computer program product by program code, which may be executed by a computer in accordance with the embodiments of the present document. The program code may be stored on a computer-readable carrier.

[0163] FIG. 12 illustrates an example of a content streaming system to which the disclosures of this document may be applied.

[0164] As shown in FIG. 12, a content streaming system to which the present disclosure is applied can broadly include an encoding server, a streaming server, a web server, a media repository, a user device, and a multimedia input device.

[0165] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, if a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server may be omitted.

[0166] The bitstream may be generated by an encoding method or a bitstream generation method applied to an embodiment of this document, and the streaming server may temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0167] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server acts as an intermediary to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, which then transmits the multimedia data to the user. In this case, the content streaming system may include a separate control server, which controls commands and responses between devices in the content streaming system.

[0168] The streaming server can receive content from a media repository and / or an encoding server. For example, if content is received from the encoding server, the content can be received in real time. In this case, the streaming server can store the bitstream for a certain period of time to provide a smooth streaming service.

[0169] Examples of the user devices include mobile phones, smartphones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation systems, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted displays (HMDs)), digital TVs, desktop computers, and digital signs.

[0170] Each server in the content streaming system can be operated as a distributed server, in which case data received by each server can be processed in a distributed manner.

[0171] The claims described herein may be combined in various ways. For example, the technical features of the method claims herein may be combined and realized in an apparatus, and the technical features of the apparatus claims herein may be combined and realized in a method. Furthermore, the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined and realized in an apparatus, and the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined and realized in a method.

Claims

1. An image decoding method performed by a decoding device, obtaining an indication information related to whether deblocking filter information is present in a picture header or a slice header; determining whether the deblocking filter information is present in the picture header or the slice header based on the indication information; parsing the deblocking filter information from the picture header or the slice header based on the determination; decoding the current block based on the deblocking filter information; The instruction information is included in a PPS (Picture Parameter Set), the picture header includes information that applies commonly to all slices in a picture; The PPS includes information that applies commonly to one or more pictures, The method, wherein the syntax level at which the instruction information is included is different from the syntax level at which the deblocking filter information is included.

2. An image encoding method performed by an encoding device, generating deblocking filter information; determining whether the deblocking filter information is present in a picture header or a slice header; generating an indication related to whether the deblocking filter information is present in the picture header or the slice header; encoding image information including the instruction information and the deblocking filter information; the indication information is configured to indicate whether the deblocking filter information is present in the picture header or the slice header; The instruction information is included in a PPS (Picture Parameter Set), the picture header includes information that applies commonly to all slices in a picture; The PPS includes information that applies commonly to one or more pictures, The method, wherein the syntax level at which the instruction information is included is different from the syntax level at which the deblocking filter information is included.

3. A method for transmitting data relating to an image, comprising: obtaining a bitstream relating to the image, the bitstream comprising: determining whether deblocking filter information is present in a picture header or a slice header; generating deblocking filter information; determining whether the deblocking filter information is present in a picture header or a slice header; generating an indication related to whether the deblocking filter information is present in the picture header or the slice header; encoding image information including the instruction information and the deblocking filter information; transmitting the data including the bitstream; the indication information is configured to indicate whether the deblocking filter information is present in the picture header or the slice header; The instruction information is included in a PPS (Picture Parameter Set), the picture header includes information that applies commonly to all slices in a picture; The PPS includes information that applies commonly to one or more pictures, A transmission method, wherein a syntax level including the instruction information is different from a syntax level including the deblocking filter information.

Images