Image encoding / decoding method and method for transmitting bit stream

Abstract

The invention relates to an image encoding / decoding method and a method for transmitting a bitstream. An image decoding method performed by an image decoding device according to the present disclosure may comprise the steps of: determining the number of tiles in a current picture on the basis that segmentation of the current picture is not limited; acquiring, from the bitstream, a first flag indicating whether tile boundary filtering is available, based on the number of tiles in the current picture being a plurality; and determining whether to perform filtering on the boundary of the tile belonging to the current picture based on the value of the first flag.

Description

[0001] This application is a divisional application of the original invention patent application with application number 202180014308.X (International application number: PCT / KR2021 / 001856, application date: February 15, 2021, invention name: Image encoding / decoding method and device for selectively signaling filtering available information and method for sending bit stream). Technical Field

[0002] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to an image encoding / decoding method and apparatus for selectively signaling filtering available information and a method for transmitting a bitstream generated by the image encoding method / apparatus of the present disclosure. Background Art

[0003] Recently, demand for high-resolution and high-quality images, such as high-definition (HD) and ultra-high-definition (UHD) images, is increasing across various fields. As the resolution and quality of image data improve, the amount of information or bits transmitted increases relative to existing image data. This increase in the amount of information or bits transmitted leads to increased transmission and storage costs.

[0004] Therefore, efficient image compression technology is needed to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the Invention

[0005] Technical issues

[0006] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0007] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus capable of improving encoding / decoding efficiency by selectively signaling filtering available information.

[0008] Another object of the present disclosure is to provide a method for transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure.

[0009] Another object of the present disclosure is to provide a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0010] Another object of the present disclosure is to provide a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0011] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and those skilled in the art will understand other technical problems not described herein through the following description.

[0012] Technical Solution

[0013] According to aspects of the present disclosure, an image decoding method performed by an image decoding device may include the following steps: based on the fact that the segmentation of the current picture is not restricted, determining the number of patches in the current picture; based on the fact that the number of patches in the current picture is multiple, obtaining a first flag from a bitstream indicating whether filtering of the boundaries of the patches is available; and based on the value of the first flag, determining whether filtering is performed on the boundaries of the patches belonging to the current picture.

[0014] An image decoding device according to aspects of the present disclosure may include a memory and at least one processor. The at least one processor may: determine the number of patches in the current picture based on unrestricted segmentation of the current picture; obtain a first flag from a bitstream indicating whether filtering of patch boundaries is applicable based on the number of patches in the current picture; and determine whether filtering of the patches belonging to the current picture is performed based on a value of the first flag.

[0015] According to aspects of the present disclosure, an image encoding method performed by an image encoding device may include the following steps: determining the number of patches in the current picture based on that the segmentation of the current picture is not restricted; determining the value of a first flag indicating whether filtering of the boundaries of the patches is available based on that the number of patches in the current picture is multiple; and generating a bit stream including the first flag.

[0016] In addition, the transmission method according to aspects of the present disclosure may transmit a bitstream generated by the image encoding apparatus or method of the present disclosure.

[0017] In addition, a computer-readable recording medium according to aspects of the present disclosure may store a bit stream generated by the image encoding apparatus or the image encoding method of the present disclosure.

[0018] The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the following detailed description of the present disclosure and do not limit the scope of the present disclosure.

[0019] Beneficial effects

[0020] According to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0021] Furthermore, according to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus capable of improving encoding / decoding efficiency by selectively signaling filtering available information.

[0022] Furthermore, according to the present disclosure, a method of transmitting a bitstream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0023] Furthermore, according to the present disclosure, a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure can be provided.

[0024] Furthermore, according to the present disclosure, there can be provided a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0025] Those skilled in the art will understand that the effects that can be achieved through the present disclosure are not limited to the contents that have been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a diagram schematically illustrating a video encoding system to which the present disclosure is applicable.

[0027] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0028] Figure 3 FIG. 1 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0029] Figure 4 is a diagram illustrating a segmentation structure of an image according to an embodiment.

[0030] Figure 5 is a view showing an embodiment of a partition type of a block according to a multi-type tree structure.

[0031] Figure 6 is a diagram illustrating a signaling mechanism of block partitioning information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0032] Figure 7 FIG. 4 is a diagram illustrating an embodiment of dividing a CTU into a plurality of CUs.

[0033] Figure 8 is a diagram illustrating neighboring reference samples according to an embodiment.

[0034] Figures 9 and 10 is a view illustrating intra prediction according to an embodiment.

[0035] Figure 11 is a view illustrating an encoding method using inter-frame prediction according to an embodiment.

[0036] Figure 12 is a view illustrating a decoding method using inter-frame prediction according to an embodiment.

[0037] Figure 13is a block diagram of CABAC according to an embodiment for encoding one syntax element.

[0038] Figures 14 to 17 is a view illustrating entropy encoding and entropy decoding according to an embodiment.

[0039] Figure 18 and Figure 19 is a view illustrating an example of picture decoding and encoding processes according to an embodiment.

[0040] Figure 20 is a diagram showing the layer structure of a coded image.

[0041] Figures 21 to 24 is a diagram illustrating an embodiment of dividing a screen using tiles, slices, and sub-pictures.

[0042] Figures 25 to 28 is a diagram showing individual implementations of syntax for a picture parameter set.

[0043] Figure 29 and Figure 30 It is a view showing an embodiment of a decoding method and an encoding method.

[0044] Figure 31 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0045] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, the present disclosure can be implemented in various forms and is not limited to the embodiments described herein.

[0046] When describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, its detailed description will be omitted. In the drawings, parts not related to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0047] In the present disclosure, when a component is “connected,” “coupled,” or “linked” to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component “includes” or “has” other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0048] In the present disclosure, the terms first, second, etc. may be used only to distinguish one component from other components and do not limit the order or importance of the components unless otherwise specified. Accordingly, within the scope of the present disclosure, the first component in one embodiment may be referred to as the second component in another embodiment, and similarly, the second component in one embodiment may be referred to as the first component in another embodiment.

[0049] In this disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not necessarily mean that the components must be separated. That is, multiple components can be integrated and implemented in a single hardware or software unit, or a single component can be distributed and implemented in multiple hardware or software units. Therefore, even if not otherwise specified, embodiments in which components are integrated or distributed are also included in the scope of this disclosure.

[0050] In the present disclosure, the components described in the various embodiments are not necessarily essential components, and some components may be optional components. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, embodiments that include other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0051] The present disclosure relates to encoding and decoding of images. Unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0052] In the present disclosure, "video" may mean a collection of a series of images over time. A "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit that constitutes a part of a picture when encoded. A picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs). A CTU may be divided into one or more CUs. A picture may be composed of one or more slices / tiles. A tile is a rectangular area that exists in a specific tile row and a specific tile column in a picture and may be composed of multiple CTUs. A tile column may be defined as a rectangular area of a CTU, may have the same height as the picture, and may have a width specified by a syntax element signaled from a bitstream portion such as a picture parameter set. A tile row may be defined as a rectangular area of a CTU, may have the same width as the picture, and may have a height specified by a syntax element signaled from a bitstream portion such as a picture parameter set. Tile scanning is a method of sequentially sorting the CTUs that partition a picture. Here, CTUs can be ordered sequentially according to the raster scan order of CTUs within a tile, and tiles within a picture can be ordered sequentially according to the raster scan order of tiles within the picture. A slice can contain an integer number of complete tiles, or an integer number of consecutive complete CTU rows within a tile of a picture. A slice can be included in only a single NAL unit.

[0053] A picture may consist of one or more tile groups. A tile group may include one or more tiles. A brick may indicate a rectangular area of a CTU row within a tile in a picture. A tile may include one or more tiles. A tile may represent a rectangular area of a CTU row in a tile. A tile may be divided into multiple tiles, and each tile may include one or more CTU rows belonging to the tile. A tile that is not divided into multiple tiles may also be considered a tile.

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

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

[0056] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of a picture and information related to the area. A unit may include a luma block and two chroma (e.g., Cb and Cr) blocks. In some cases, the unit may be used interchangeably with terms such as "sample array," "block," or "area." In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0057] In the present disclosure, the term "current block" may refer to one of the following: "current coding block," "current coding unit," "encoding target block," "decoding target block," or "processing target block." When prediction is performed, the term "current block" may refer to either the "current prediction block" or the "prediction target block." When transform (inverse transform) / quantization (dequantization) is performed, the term "current block" may refer to either the "current transform block" or the "transform target block." When filtering is performed, the term "current block" may refer to the "filtering target block."

[0058] In addition, in the present disclosure, unless explicitly stated as a chroma block, "current block" may mean "luminance block of the current block." "Chroma block of the current block" may be expressed by including an explicit description of the chroma block such as "chroma block" or "current chroma block."

[0059] In this disclosure, the slash " / " or "," should be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A / B / C" may mean "at least one of A, B, and / or C".

[0060] In the present disclosure, the term "or" should be interpreted as meaning "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", and / or 3) both "A and B". In other words, in the present disclosure, the term "or" should be interpreted as meaning "additionally or alternatively".

[0061] Overview of Video Coding Systems

[0062] Figure 1 is a diagram illustrating a video encoding system according to the present disclosure.

[0063] The video encoding system according to an embodiment may include a source device 10 and a receiving device 20. The source device 10 may deliver encoded video and / or image information or data to the receiving device 20 via a digital storage medium or a network in the form of a file or a stream.

[0064] The source device 10 according to an embodiment may include a video source generator 11, an encoding device 12, and a transmitter 13. The receiving device 20 according to an embodiment may include a receiver 21, a decoding device 22, and a renderer 23. The encoding device 12 may be referred to as a video / image encoding device, and the decoding device 22 may be referred to as a video / image decoding device. The transmitter 13 may be included in the encoding device 12. The receiver 21 may be included in the decoding device 22. The renderer 23 may include a display, and the display may be configured as a separate device or an external component.

[0065] The video source generator 11 can obtain video / images by capturing, synthesizing, or generating video / images. The video source generator 11 may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generation device may include, for example, a computer, a tablet computer, and a smartphone, and may generate videos / images (electronically). For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capture process may be replaced by a process for generating relevant data.

[0066] The encoding device 12 can encode the input video / image. For compression and coding efficiency, the encoding device 12 can perform a series of processes such as prediction, transformation, and quantization. The encoding device 12 can output the encoded data (encoded video / image information) in the form of a bitstream.

[0067] The transmitter 13 can transmit the encoded video / image information or data output in the form of a bitstream to the receiver 21 of the receiving device 20 in the form of a file or stream via a digital storage medium or a network. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include components for generating a media file in a predetermined file format and may also include components for transmitting via a broadcast / communication network. The receiver 21 may extract / receive the bitstream from the storage medium or network and transmit the bitstream to the decoding device 22.

[0068] The decoding device 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding device 12 , such as dequantization, inverse transformation, and prediction.

[0069] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed on a display.

[0070] Overview of Image Coding Devices

[0071] Figure 2is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0072] like Figure 2 As shown, the image encoding apparatus 100 may include an image splitter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame prediction unit 180, an intra-frame prediction unit 185, and an entropy encoder 190. The inter-frame prediction unit 180 and the intra-frame prediction unit 185 may be collectively referred to as a "prediction unit." The transformer 120, the quantizer 130, the dequantizer 140, and the inverse transformer 150 may be included in a residual processor. The residual processor may further include a subtractor 115.

[0073] In some embodiments, all or at least some of the components configuring the image encoding apparatus 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0074] The image splitter 110 can split the input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, a processing unit can be called a coding unit (CU). A coding unit can be obtained by recursively splitting a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree, binary tree, and ternary tree (QT / BT / TT) structure. For example, a coding unit can be split into multiple coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the splitting of the coding unit, the quadtree structure can be applied first, and the binary tree structure and / or the ternary tree structure can be applied later. The encoding process according to the present disclosure can be performed based on the final coding unit that is no longer split. The maximum coding unit can be used as the final coding unit, and the coding unit of a deeper depth obtained by splitting the maximum coding unit can also be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process can be a prediction unit (PU) or a transform unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0075] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information on the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0076] The intra-frame prediction unit 185 can predict the current block by referring to samples in the current picture. Depending on the intra-frame prediction mode and / or intra-frame prediction technology, the reference samples can be located in the neighborhood of the current block or can be placed separately. The intra-frame prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a planar mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is merely an example, and more or fewer directional prediction modes may be used depending on the settings. The intra-frame prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0077] The inter-frame prediction unit 180 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can also include information about the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in the reference picture. The reference picture including the reference block and the reference picture including the temporally neighboring block can be the same or different. Temporally neighboring blocks can be referred to as collocated reference blocks, collocated CUs (colCUs), etc. A reference picture including temporally neighboring blocks can be referred to as collocated pictures (colPics). For example, the inter-frame prediction unit 180 can configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate to use to derive the motion vector and / or reference picture index for the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter-frame prediction unit 180 can use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be signaled by encoding a motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0078] The prediction unit can generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit can apply not only intra-frame prediction or inter-frame prediction, but also both intra-frame prediction and inter-frame prediction simultaneously to predict the current block. The prediction method that simultaneously applies both intra-frame prediction and inter-frame prediction to predict the current block is referred to as combined inter-frame and intra-frame prediction (CIIP). In addition, the prediction unit can perform intra-frame block copying (IBC) to predict the current block. Intra-frame block copying can be used for content image / video encoding such as games, such as screen content coding (SCC). IBC is a method that uses a previously reconstructed reference block in the current picture at a predetermined distance from the current block to predict the current picture. When IBC is applied, the position of the reference block in the current picture can be encoded as a vector (block vector) corresponding to the predetermined distance. IBC essentially performs prediction in the current picture, but can be performed similarly to inter-frame prediction because the reference block is derived within the current picture. That is, IBC can use at least one of the inter-frame prediction techniques described in this disclosure.

[0079] The prediction signal generated by the prediction unit can be used to generate a reconstructed signal or a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be sent to the transformer 120.

[0080] The transformer 120 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-Loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or to blocks of variable size other than square.

[0081] The quantizer 130 may quantize the transform coefficients and transmit them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0082] The entropy encoder 190 can perform various encoding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 can encode information required for video / image reconstruction (e.g., values of syntax elements, etc.) other than quantized transform coefficients together or separately. The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream in units of a network abstraction layer (NAL). The video / image information may also include information about various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in the present disclosure may be encoded through the above-mentioned encoding process and included in the bitstream.

[0083] The bitstream may be transmitted via a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image encoding apparatus 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0084] The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transform to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0085] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as when skip mode is applied, the prediction block can be used as the reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture through filtering as described below.

[0086] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and send the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bitstream.

[0087] The modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image encoding apparatus 100, prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus may be avoided and encoding efficiency may be improved.

[0088] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame prediction unit 180. The memory 170 may store motion information of a block for deriving (or encoding) motion information in the current picture and / or motion information of a reconstructed block in the picture. The stored motion information may be sent to the inter-frame prediction unit 180 and used as motion information of a spatially adjacent block or motion information of a temporally adjacent block. The memory 170 may store reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0089] Overview of Image Decoding Equipment

[0090] Figure 3 FIG. 1 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0091] like Figure 3 As shown, the image decoding apparatus 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, and an intra-frame prediction unit 265. The inter-frame prediction unit 260 and the intra-frame prediction unit 265 may be collectively referred to as a "prediction unit." The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0092] According to an embodiment, all or at least some of the components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0093] The image decoding apparatus 200 having received a bit stream including video / image information may decode the image by performing the same operation as that performed by Figure 2 The image is reconstructed by processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 can perform decoding using the processing unit applied in the image encoding device. Therefore, the processing unit of decoding can be, for example, a coding unit. The coding unit can be obtained by dividing the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 can be reproduced by a reproduction device (not shown).

[0094] The image decoding device 200 can receive the image in the form of a bit stream from Figure 2The received signal can be decoded by the entropy decoder 210. For example, the entropy decoder 210 can parse the bitstream to derive the information required for image reconstruction (or picture reconstruction) (for example, video / image information). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the information about the parameter set and / or the general constraint information. The signaled / received information and / or syntax elements described in the present disclosure can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values of the syntax elements required for image reconstruction and the quantized values of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring blocks and the decoding target block, or the information of the symbol / bin decoded at the previous stage to determine the context model, perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, after determining the context model, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin. The information related to prediction among the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value (i.e., quantized transform coefficient and related parameter information) on which entropy decoding is performed in the entropy decoder 210 can be input to the dequantizer 220. In addition, the information about filtering among the information decoded by the entropy decoder 210 can be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal / external element of the image decoding apparatus 200 , or the receiver may be a component of the entropy decoder 210 .

[0095] In addition, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image 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 an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or at least one of an intra-frame prediction unit 265.

[0096] The dequantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may dequantize the quantized transform coefficients using quantization parameters (e.g., quantization step size information) and obtain the transform coefficients.

[0097] The inverse transformer 230 may perform inverse transformation on the transformation coefficients to obtain a residual signal (residual block, residual sample array).

[0098] The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0099] As described in the prediction unit of the image encoding device 100 , the prediction unit can generate a prediction signal based on various prediction methods (techniques) to be described later.

[0100] The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 is also applicable to the intra prediction unit 265.

[0101] The inter-frame prediction unit 260 can derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. Motion information may include a motion vector and a reference picture index. Motion information may also include information on the inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter-frame prediction, neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. For example, the inter-frame prediction unit 260 may configure a motion information candidate list based on neighboring blocks and derive a motion vector and / or reference picture index for the current block based on received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0102] The adder 235 can generate a reconstruction signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 also applies to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture through filtering as described below.

[0103] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0104] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter-frame prediction unit 260. The memory 250 can store motion information of blocks for deriving (or decoding) motion information in the current picture and / or motion information of reconstructed blocks in the picture. The stored motion information can be sent to the inter-frame prediction unit 260 to be used as motion information of spatially adjacent blocks or motion information of temporally adjacent blocks. The memory 250 can store reconstructed samples of the reconstructed blocks in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0105] In the present disclosure, the embodiments described in the filter 160, the inter-frame prediction unit 180 and the intra-frame prediction unit 185 of the image encoding device 100 can be applied equally or correspondingly to the filter 240, the inter-frame prediction unit 260 and the intra-frame prediction unit 265 of the image decoding device 200.

[0106] Overview of Image Segmentation

[0107] The video / image encoding method according to the present disclosure can be performed based on the following image segmentation structure. Specifically, the prediction, residual processing ((inverse) transform, (de)quantization, etc.), syntax element encoding and filtering processes described later can be performed based on the CTU, CU (and / or TU, PU) derived according to the image segmentation structure. The image can be segmented in block units and the block segmentation process can be performed in the image segmentor 110 of the encoding device. The segmentation related information can be encoded by the entropy encoder 190 and sent to the decoding device in the form of a bit stream. The entropy decoder 210 of the decoding device can derive the block segmentation structure of the current picture based on the segmentation related information obtained from the bit stream, and based on this, a series of processes (for example, prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) can be performed to perform image decoding.

[0108] A picture may be partitioned into a sequence of coding tree units (CTUs). Figure 4 An example of a picture being partitioned into CTUs is shown. A CTU may correspond to a coding tree block (CTB). Alternatively, a CTU may include a coding tree block of luma samples and two coding tree blocks of corresponding chroma samples. For example, for a picture containing three sample arrays, a CTU may include an N×N block of luma samples and two corresponding blocks of chroma samples. The maximum allowed size of a CTU for encoding and prediction may be different from the maximum allowed size of a CTU for transform. For example, even if the maximum size of a luma transform block is 64×64, the maximum allowed size of a luma block in a CTU may be 128×128.

[0109] Overview of CTU Segmentation

[0110] As described above, a coding unit (CTU) or a largest coding unit (LCU) may be obtained by recursively partitioning the coding tree unit (CTU) or the largest coding unit (LCU) according to a quadtree / binarytree / ternarytree (QT / BT / TT) structure. For example, the CTU may be first partitioned into a quadtree structure. Thereafter, the leaf nodes of the quadtree structure may be further partitioned using a multi-type tree structure.

[0111] Splitting according to the quadtree means that the current CU (or CTU) is equally split into four. By splitting according to the quadtree, the current CU can be split into four CUs with the same width and the same height. When the current CU is no longer split into the quadtree structure, the current CU corresponds to the leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure can no longer be split and can be used as the final coding unit mentioned above. Alternatively, the CU corresponding to the leaf node of the quadtree structure can be further split by a multi-type tree structure.

[0112] Figure 51 is a diagram illustrating an embodiment of a partition type of a block according to a multi-type tree structure. The partition according to the multi-type tree structure may include two types of partitions according to a binary tree structure and two types of partitions according to a ternary tree structure.

[0113] The two types of splits according to the binary tree structure may include vertical binary split (SPLIT_BT_VER) and horizontal binary split (SPLIT_BT_HOR). Vertical binary split (SPLIT_BT_VER) means that the current CU is equally split into two in the vertical direction. Figure 4 As shown in FIG, by vertical binary splitting, two CUs with the same height as the current CU and half the width of the current CU can be generated. Horizontal binary splitting (SPLIT_BT_HOR) means that the current CU is equally split into two in the horizontal direction. Figure 5 As shown, through horizontal binary partitioning, two CUs with a height half of the height of the current CU and the same width as the current CU can be generated.

[0114] The two types of splits according to the ternary tree structure may include vertical ternary split (SPLIT_TT_VER) and horizontal ternary split (SPLIT_TT_HOR). In vertical ternary split (SPLIT_TT_VER), the current CU is split in a vertical direction at a ratio of 1:2:1. Figure 5 As shown, through vertical trifurcated partitioning, two CUs with the same height as the current CU and a width of 1 / 4 of the current CU width and one CU with the same height as the current CU and a width of half the current CU width can be generated. In horizontal trifurcated partitioning (SPLIT_TT_HOR), the current CU is split in the horizontal direction at a ratio of 1:2:1. Figure 5 As shown, through horizontal trifurcated partitioning, two CUs with a height of 1 / 4 of the current CU and the same width as the current CU and one CU with a height of half the current CU and the same width as the current CU can be generated.

[0115] Figure 6 is a diagram illustrating a signaling mechanism of block partitioning information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0116] Here, the CTU is regarded as the root node of the quadtree and is first split into a quadtree structure. Information (e.g., qt_split_flag) indicating whether quadtree partitioning is performed on the current CU (CTU or node (QT_node) of the quadtree) can be signaled. For example, when qt_split_flag has a first value (e.g., "1"), the current CU can be quadtree split. In addition, when qt_split_flag has a second value (e.g., "0"), the current CU is not quadtree split, but becomes a leaf node (QT_leaf_node) of the quadtree. Each quadtree leaf node can then be further split into a multi-type tree structure. That is, the leaf node of the quadtree can become a node (MTT_node) of a multi-type tree. In the multi-type tree structure, a first flag (e.g., Mtt_split_cu_flag) can be signaled to indicate whether the current node is additionally split. If the corresponding node is additionally split (for example, if the first flag is 1), the second flag (for example, Mtt_split_cu_vertical_flag) can be signaled to indicate the split direction. For example, the split direction can be a vertical direction when the second flag is 1, and a horizontal direction when the second flag is 0. Then, a third flag (for example, Mtt_split_cu_binary_flag) can be signaled to indicate whether the split type is a binary split type or a ternary split type. For example, the split type can be a binary split type when the third flag is 1, and a ternary split type when the third flag is 0. The nodes of the multi-type tree obtained by binary splitting or ternary splitting can be further split into a multi-type tree structure. However, the nodes of the multi-type tree may not be split into a quadtree structure. If the first flag is 0, the corresponding node of the multi-type tree is no longer split, but becomes a leaf node (MTT_leaf_node) of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree can be used as the above-mentioned final coding unit.

[0117] Based on mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree partition mode (MttSplitMode) of a CU may be derived as shown in the following Table 1. In the following description, a multi-type tree partition mode may be referred to as a multi-tree partition type or a partition type.

[0118] [Table 1]

[0119] MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flag SPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

[0120] Figure 7 is a diagram showing an example of partitioning a CTU into a plurality of CUs by applying a multi-type tree after applying a quadtree. Figure 7 , the bold block edge 710 represents quadtree partitioning, while the remaining edges 720 represent multi-type tree partitioning. The CU may correspond to a coding block (CB). In an embodiment, the CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples. The chroma component (sample) CB or TB size may be derived based on the luma component (sample) CB or TB size based on the component ratio according to the color format (chroma format, for example, 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image. In the case of a 4:4:4 color format, the chroma component CB / TB size may be set to be equal to the luma component CB / TB size. In the case of a 4:2:2 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to the height of the luma component CB / TB. In the case of a 4:2:0 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to half the height of the luma component CB / TB.

[0121] In an embodiment, when the size of the CTU is based on a luma sample unit of 128, the size of the CU may be from 128×128 to 4×4, which is the same size as the CTU. In an embodiment, in the case of a 4:2:0 color format (or chroma format), the chroma CB size may be from 64×64 to 2×2.

[0122] Furthermore, in an embodiment, the CU size and the TU size may be the same. Alternatively, there may be multiple TUs in a CU region. The TU size may generally represent the luma component (sample) transform block (TB) size.

[0123] The TU size can be derived based on the maximum allowed TB size maxTbSize as a predetermined value. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) with maxTbSize can be derived from the CU, and transformation / inverse transformation can be performed in units of TUs (TBs). For example, the maximum allowed luma TB size can be 64×64 and the maximum allowed chroma TB size can be 32×32. If the width or height of the CB split according to the tree structure is larger than the maximum transform width or height, the CB can be automatically (or implicitly) split until the TB size limits in the horizontal and vertical directions are met.

[0124] In addition, for example, when intra prediction is applied, the intra prediction mode / type can be derived in units of CU (or CB), and the neighboring reference sample derivation and prediction sample generation process can be performed in units of TU (or TB). In this case, there can be one or more TUs (or TBs) in a CU (or CB) area, and in this case, multiple TUs or (TBs) can share the same intra prediction mode / type.

[0125] In addition, for a quadtree coding tree scheme with nested multi-type trees, the following parameters may be signaled from the encoding device to the decoding device as SPS syntax elements. For example, at least one of the following parameters may be signaled: a CTU size representing the size of the root node of the quadtree, a MinQTSize representing the minimum allowed quadtree leaf node size, a MaxBtSize representing the maximum allowed binary tree root node size, a MaxTtSize representing the maximum allowed ternary tree root node size, a MaxMttDepth representing the maximum allowed hierarchical depth of multi-type tree partitioning from a quadtree leaf node, a MinBtSize representing the minimum allowed binary tree leaf node size, or a MinTtSize representing the minimum allowed ternary leaf node size.

[0126] As an embodiment using a 4:2:0 chroma format, the CTU size can be set to 128×128 luminance blocks and two 64×64 chroma blocks corresponding to these luminance blocks. In this case, MinOTSize can be set to 16×16, MaxBtSize can be set to 128×128, MaxTtSzie can be set to 64×64, MinBtSize and MinTtSize can be set to 4×4, and MaxMttDepth can be set to 4. Quadtree partitioning can be applied to the CTU to generate quadtree leaf nodes. Quadtree leaf nodes can be referred to as leaf QT nodes. The size of the quadtree leaf node can range from 16×16 size (e.g., MinOTSize) to 128×128 size (e.g., CTU size). If the leaf QT node is 128×128, it may not be additionally partitioned into a binary tree / ternary tree. This is because, in this case, even if partitioned, it exceeds MaxBtsize and MaxTtszie (e.g., 64×64). In other cases, the leaf QT node may be further split into a multi-type tree. Therefore, the leaf QT node is the root node of the multi-type tree, and the leaf QT node may have a multi-type tree depth (mttDepth) value of 0. If the multi-type tree depth reaches MaxMttdepth (for example, 4), further splitting may not be considered. If the width of the multi-type tree node is equal to MinBtSize and is less than or equal to 2×MinTtSize, further horizontal splitting may not be considered. If the height of the multi-type tree node is equal to MinBtSize and is less than or equal to 2×MinTtSize, further vertical splitting may not be considered. When splitting is not considered, the encoding device may skip signaling of the splitting information. In this case, the decoding device may derive splitting information with a predetermined value.

[0127] In addition, one CTU may include a coding block of luma samples (hereinafter referred to as "luminance block") and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as "chroma blocks"). The above-mentioned coding tree scheme may be applied equally or separately to the luma blocks and chroma blocks of the current CU. Specifically, the luma blocks and chroma blocks in one CTU may be partitioned into the same block tree structure, and in this case, the tree structure may be represented as SINGLE_TREE. Alternatively, the luma blocks and chroma blocks in one CTU may be partitioned into separate block tree structures, and in this case, the tree structure may be represented as DUAL_TREE. That is, when the CTU is partitioned into dual trees, the block tree structure for the luma block and the block tree structure for the chroma block may exist separately. In this case, the block tree structure for the luma block may be referred to as DUAL_TREE_LUMA, and the block tree structure for the chroma component may be referred to as DUAL_TREE_CHROMA. For P and B slices / tile groups, the luma blocks and chroma blocks in one CTU may be restricted to have the same coding tree structure. However, for I slices / patch groups, luma blocks and chroma blocks can have separate block tree structures. If a separate block tree structure is applied, luma CTBs can be split into CUs based on a specific coding tree structure, and chroma CTBs can be split into chroma CUs based on another coding tree structure. That is, this means that a CU in an I slice / patch group to which a separate block tree structure is applied can include coding blocks for the luma component or coding blocks for two chroma components, and a CU in a P or B slice / patch group can include blocks for three color components (one luma component and two chroma components).

[0128] Although a quadtree coding tree structure with nested multi-type trees has been described, the structure for partitioning a CU is not limited thereto. For example, the BT structure and the TT structure may be interpreted as concepts included in a multi-partition tree (MPT) structure, and the CU may be interpreted as being partitioned using the QT structure and the MPT structure. In an example where a CU is partitioned using the QT structure and the MPT structure, a syntax element (e.g., MPT_split_type) including information about how many blocks a leaf node of the QT structure is partitioned into and a syntax element (e.g., MPT_split_mode) including information about which direction a leaf node of the QT structure is partitioned into, may be signaled to determine the partition structure.

[0129] In another example, the CU may be split in a manner different from the QT structure, the BT structure, or the TT structure. That is, instead of splitting a CU of a lower depth into 1 / 4 of a CU of a higher depth according to the QT structure, splitting a CU of a lower depth into 1 / 2 of a CU of a higher depth according to the BT structure, or splitting a CU of a lower depth into 1 / 4 or 1 / 2 of a CU of a higher depth according to the TT structure, in some cases the CU of a lower depth may be split into 1 / 5, 1 / 3, 3 / 8, 3 / 5, 2 / 3, or 5 / 8 of a CU of a higher depth, and the method of splitting the CU is not limited thereto.

[0130] A quadtree coding block structure with multiple tree types can provide a very flexible block segmentation structure. Due to the supported segmentation types in the multi-type tree, different segmentation patterns can potentially produce the same coding block structure in some cases. By limiting the occurrence of such redundant segmentation patterns in encoding and decoding devices, the amount of segmentation information data can be reduced.

[0131] In addition, in the video / image encoding and decoding according to the present disclosure, the image processing unit may have a hierarchical structure. A picture may be divided into one or more tiles, tiles, slices and / or tile groups. A slice may include one or more tiles. A tile may include one or more CTU rows in a tile. A slice may include an integer number of tiles in a picture. A tile group may include one or more tiles. A tile may include one or more CTUs. A CTU may be divided into one or more CUs. A tile may be a rectangular area consisting of a plurality of CTUs in a picture, including a specific tile row and a specific tile column. According to the tile raster scan in the picture, a tile group may include an integer number of tiles. The slice header may carry information / parameters applicable to the slice (tile in the slice). When the encoding device or decoding device has a multi-core processor, the encoding / decoding process of the tiles, slices, tiles and / or tile groups may be performed in parallel.

[0132] In the present disclosure, the names or concepts of slices or patch groups may be mixed. That is, a patch group header may be referred to as a slice header. Here, a slice may have one of slice types including intra (I) slices, predicted (P) slices, and bi-predicted (B) slices. For blocks in an I slice, inter prediction is not used for prediction, and only intra prediction may be used. Of course, even in this case, the original sample values may be encoded and signaled without prediction. For blocks in a P slice, intra prediction or inter prediction may be used, and when inter prediction is used, only uni-prediction may be used. In addition, for blocks in a B slice, intra prediction or inter prediction may be used, and when inter prediction is used, up to maximum bi-prediction may be used.

[0133] Based on the characteristics of the video image (e.g., resolution) or considering coding efficiency and parallel processing, the encoding device can determine the size of the tile / tile group, tile, slice, and maximum and minimum coding units. In addition, information about this or information for deriving it can be included in the bitstream.

[0134] The decoding device can obtain information indicating whether the patch / patch group, tile, and slice of the current picture, as well as the CTU in the patch, are divided into multiple coding units. The encoding device and the decoding device can improve coding efficiency by signaling this information only under specific conditions.

[0135] The slice header (slice header syntax) may include information / parameters that are commonly applied to slices. The APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are commonly applied to one or more pictures. The SPS (SPS syntax) may include information / parameters that are commonly applied to one or more sequences. The VPS (VPS syntax) may include information / parameters that are commonly applied to multiple layers. The DPS (DPS syntax) may include information / parameters that are commonly applied to the entire video. The DPS may include information / parameters related to the combination of coded video sequences (CVSs).

[0136] In addition, for example, information on the partitioning and configuration of tiles / tile groups / tiles / slices may be configured at the encoding end through a higher-level syntax and sent to the decoding device in the form of a bitstream.

[0137] Overview of Intra Prediction

[0138] Hereinafter, the intra prediction performed by the above encoding apparatus and decoding device will be described in more detail. Intra prediction may refer to prediction of generating prediction samples of the current block based on reference samples in a picture to which the current block belongs (hereinafter referred to as the current picture).

[0139] Will refer to Figure 8 . When intra prediction is applied to the current block 801, neighboring reference samples to be used for intra prediction of the current block 801 may be derived. The neighboring reference samples of the current block may include: a total of 2×nh samples including a sample 811 of size nW×nH adjacent to the left boundary of the current block and a sample 812 adjacent to the lower left, a total of 2×nW samples including a sample 821 adjacent to the upper boundary of the current block and a sample 822 adjacent to the upper right, and one sample 831 adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples.

[0140] In addition, the neighboring reference samples of the current block may include: a total of nH samples 841 of size nW×nH adjacent to the right boundary of the current block, a total of nW samples 851 adjacent to the bottom boundary of the current block, and one sample 842 adjacent to the bottom right of the current block.

[0141] However, some neighboring reference samples of the current block have not yet been decoded or may be unavailable. In this case, the decoding device can construct neighboring reference samples to be used for prediction by replacing unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction can be constructed by interpolation of available samples.

[0142] When deriving neighboring reference samples, (i) the prediction sample can be derived based on an average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction sample can be derived based on reference samples located in a specific (prediction) direction for the prediction sample among the neighboring reference samples of the current block. Case (i) can be referred to as a non-directional mode or a non-angular mode, and case (ii) can be referred to as a directional mode or an angular mode. Alternatively, the prediction sample can be generated by interpolating first and second neighboring samples located in a direction opposite to the prediction direction of the intra-frame prediction mode of the current block based on the prediction sample of the current block among the neighboring reference samples. This case can be referred to as linear interpolation intra-frame prediction (LIP). Alternatively, a linear model can be used to generate chroma prediction samples based on luma samples. This case can be referred to as LM mode. Alternatively, the temporary prediction sample of the current block can be derived based on filtered neighboring reference samples, and the prediction sample of the current block can be derived by weighted summing at least one reference sample derived according to the intra-frame prediction mode and the temporary prediction sample among the existing neighboring reference samples (i.e., unfiltered neighboring reference samples). This case can be referred to as position-dependent intra-frame prediction (PDPC). In addition, a reference sample row with the highest prediction accuracy is selected from multiple neighboring reference sample rows of the current block to derive prediction samples using reference samples on the corresponding row located in the prediction direction. In this case, intra-frame prediction encoding can be performed by indicating (signaling) the reference sample row to be used to the decoding device. This situation can be referred to as multiple reference line (MRL) intra-frame prediction or MRL-based intra-frame prediction. Furthermore, the current block is partitioned into vertical or horizontal subpartitions to perform intra-frame prediction based on the same intra-frame prediction mode, but neighboring reference samples can be derived and used on a subpartition basis. That is, in this case, the intra-frame prediction mode of the current block is also applied to the subpartitions, but in some cases, intra-frame prediction performance can be improved by deriving and using neighboring reference samples on a subpartition basis. This prediction method can be referred to as intra subpartition (ISP) or ISP-based intra-frame prediction. These intra-frame prediction methods can be referred to as intra-frame prediction types to distinguish them from intra-frame prediction modes (e.g., DC mode, planar mode, or directional mode). Intra-frame prediction types can be referred to by various terms such as intra-frame prediction techniques or additional intra-frame prediction modes. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the above-mentioned LIP, PDPC, MRL, and ISP. A general intra prediction method other than the specific intra prediction types such as LIP, PDPC, MRL, and ISP may be referred to as a normal intra prediction type. The normal intra prediction type may refer to a case where the above-mentioned specific intra prediction type is not applied, and prediction may be performed based on the above-mentioned intra prediction mode. In addition, post-filtering may be performed on the derived prediction sample if necessary.

[0143] Specifically, the intra prediction process may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and a prediction sample derivation step based on the intra prediction mode / type. In addition, if necessary, a post-filtering step may be performed on the derived prediction samples.

[0144] In addition to the above-mentioned intra prediction types, affine linear weighted intra prediction (ALWIP) can also be used. ALWIP can be referred to as linear weighted intra prediction (LWIP) or matrix weighted intra prediction or matrix-based intra prediction (MIP). When MIP is applied to the current block, i) neighboring reference samples that have been subjected to an averaging process can be used, ii) a matrix-vector multiplication process can be performed, and iii) if necessary, a horizontal / vertical interpolation process can be further performed to derive the prediction samples of the current block. The intra prediction mode used for MIP can be configured differently from the intra prediction mode used in the above-mentioned LIP, PDPC, MRL and ISP intra prediction or normal intra prediction. The intra prediction mode used for MIP can be referred to as MIP intra prediction mode, MIP prediction mode or MIP mode. For example, the matrix and offset used in the matrix-vector multiplication can be set differently depending on the intra prediction mode used for MIP. Here, the matrix can be referred to as a (MIP) weighting matrix, and the offset can be referred to as a (MIP) offset vector or a (MIP) bias vector. Later, a specific MIP method will be described.

[0145] The block reconstruction process based on intra-frame prediction and intra-frame prediction units in an encoding device may illustratively include, for example, the following. S910 may be performed by the intra-frame prediction unit 185 of the encoding device, and S920 may be performed by a residual processor including at least one of the subtractor 115, transformer 120, quantizer 130, dequantizer 140, and inverse transformer 150 of the encoding device. Specifically, S920 may be performed by the subtractor 115 of the encoding device. In S930, prediction information may be derived by the intra-frame prediction unit 185 and encoded by the entropy encoder 190. In S930, residual information may be derived by the residual processor and encoded by the entropy encoder 190. Residual information is information about residual samples. The residual information may include information about quantized transform coefficients of the residual samples. As described above, the residual samples may be derived into transform coefficients by the transformer 120 of the encoding device, and the transform coefficients may be derived into quantized transform coefficients by the quantizer 130. Information about the quantized transform coefficients may be encoded by the entropy encoder 190 through a residual encoding process.

[0146] The encoding device may perform intra prediction for the current block (S910). The encoding device may derive an intra prediction mode / type for the current block, derive neighboring reference samples for the current block, and generate prediction samples in the current block based on the intra prediction mode / type and the neighboring reference samples. Here, the process for determining the intra prediction mode / type, the process for deriving neighboring reference samples, and the process for generating prediction samples may be performed simultaneously, or any one process may be performed before the other. For example, although not shown, the intra prediction unit 185 of the encoding device may include an intra prediction mode / type determination unit, a reference sample derivation unit, and a prediction sample derivation unit. The intra prediction mode / type determination unit may determine the intra prediction mode / type for the current block, the reference sample derivation unit may derive neighboring reference samples for the current block, and the prediction sample derivation unit may derive prediction samples for the current block. In addition, when performing the prediction sample filtering process described below, the intra prediction unit 185 may further include a prediction sample filter. The encoding device may determine the mode / type to be applied to the current block from among a plurality of intra prediction modes / types. The encoding device may compare RD costs of intra prediction modes / types and determine an optimal intra prediction mode / type for the current block.

[0147] In addition, the encoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0148] The encoding apparatus may generate residual samples of the current block based on the (filtered) prediction samples (S920).The encoding apparatus may compare the prediction samples with the original samples of the current block based on the phase and derive the residual samples.

[0149] The encoding device may encode image information including information about intra-frame prediction (prediction information) and residual information of residual samples (S930). The prediction information may include intra-frame prediction mode information and intra-frame prediction type information. The encoding device may output the encoded image information in the form of a bitstream. The output bitstream may be sent to a decoding device via a storage medium or a network.

[0150] The residual information may include the following residual coding syntax. The encoding device may transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information about the quantized transform coefficients.

[0151] In addition, as described above, the encoding device can generate a reconstructed picture (including reconstructed samples and reconstructed blocks). To this end, the encoding device can perform dequantization / inverse transformation on the quantized transform coefficients again to derive (modified) residual samples. The residual samples are transformed / quantized and then dequantized / inverse transformed to derive residual samples that are the same as the residual samples derived in the decoding device as described above. The encoding device can generate a reconstructed block including reconstructed samples of the current block based on the predicted samples and the (modified) residual samples. A reconstructed picture of the current picture can be generated based on the reconstructed block. As described above, the in-loop filtering process is further applied to the reconstructed picture.

[0152] The video / image decoding process based on intra prediction and intra prediction units in the decoding device may illustratively include, for example, the following: The decoding device may perform operations corresponding to those performed by the encoding device.

[0153] S1010 to S1030 may be performed by the intra-frame prediction unit 265 of the decoding device, and the prediction information of S1010 and the residual information of S1040 may be obtained from the bitstream by the entropy decoder 210 of the decoding device. A residual processor including the dequantizer 220 or the inverse transformer 230 of the decoding device may derive residual samples of the current block based on the residual information. Specifically, the dequantizer 220 of the residual processor may perform dequantization based on the quantized transform coefficients derived from the residual information to derive transform coefficients, and the dequantizer 220 of the residual processor may perform inverse transform on the transform coefficients to derive residual samples of the current block. S1050 may be performed by the adder 235 or the reconstructor of the decoding device.

[0154] Specifically, the decoding device may derive the intra prediction mode / type of the current block based on the received prediction information (intra prediction mode / type information) (S1010). The decoding device may derive neighboring reference samples of the current block (S1020). The decoding device may generate prediction samples in the current block based on the intra prediction mode / type and the neighboring reference samples (S1030). In this case, the decoding device may perform a prediction sample filtering process. Prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered through the prediction sample filtering process. In some cases, the prediction sample filtering process may be omitted.

[0155] The decoding device generates residual samples of the current block based on the received residual information. The decoding device can generate reconstructed samples of the current block based on the predicted samples and the residual samples, and derive a reconstructed block including the reconstructed samples (S1040). A reconstructed picture of the current picture can be generated based on the reconstructed block. As described above, the in-loop filtering process is further applicable to the reconstructed picture.

[0156] Here, the intra-frame prediction unit 265 of the decoding device may include an intra-frame prediction mode / type determination unit, a reference sample derivation unit, and a prediction sample derivation unit. The intra-frame prediction mode / type determination unit may determine the intra-frame prediction mode / type of the current block based on the intra-frame prediction mode / type information obtained by the entropy decoder 210. The reference sample derivation unit may derive neighboring reference samples of the current block, and the prediction sample derivation unit may derive the prediction sample of the current block. In addition, although not shown, when performing the above-mentioned prediction sample filtering process, the intra-frame prediction unit 265 may further include a prediction sample filter.

[0157] The intra-frame prediction mode information may include flag information (e.g., intra_luma_mpm_flag) specifying whether the most probable mode (MPM) or the residual mode is applied to the current block, and when MPM is applied to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) specifying one of the intra-frame prediction mode candidates (MPM candidates). The intra-frame prediction mode candidates (MPM candidates) may be configured as an MPM candidate list or an MPM list. In addition, when MPM is not applied to the current block, the intra-frame prediction mode information may further include residual mode information (e.g., intra_luma_mpm_remainder) specifying one of the remaining intra-frame prediction modes other than the intra-frame prediction mode candidates (MPM candidates). The decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction mode information. For the above-mentioned MIP, a separate MPL list may be constructed.

[0158] In addition, the intra-frame prediction type information can be implemented in various forms. For example, the intra-frame prediction type information may include intra-frame prediction type index information specifying one of the intra-frame prediction types. As another example, the intra-frame prediction type information may include reference sample row information (e.g., intra_luma_ref_idx) specifying whether MRL is applied to the current block and which reference sample row to use if applied, ISP flag information (e.g., intra_subpartitions_mode_flag) specifying whether ISP is applied to the current block, ISP type information (e.g., intra_subpartitions_split_flag) specifying the split type of the sub-partition when ISP is applied, flag information specifying whether PDCP is applied, or flag information specifying whether LIP is applied. In addition, the intra-frame prediction type information may include at least one of a MIP flag specifying whether MIP is applied to the current block.

[0159] The intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by the encoding method described in the present disclosure. For example, the intra-frame prediction mode information and / or the intra-frame prediction type information may be encoded / decoded by entropy coding (e.g., CABAC or CAVLC) based on a truncated (Rice) binary code.

[0160] Overview of Inter-frame Prediction

[0161] Hereinafter, reference will be described Figure 2 and Figure 3 Detailed techniques for inter-frame prediction methods are provided in the description of encoding and decoding. In the case of a decoding device, the video / image decoding method based on inter-frame prediction and the inter-frame prediction unit in the decoding device can operate according to the following description. In the case of an encoding device, the video / image encoding method based on inter-frame prediction and the inter-frame prediction unit in the encoding device can operate according to the following description. In addition, the data encoded according to the following description can be stored in the form of a bitstream.

[0162] The prediction units of the encoding and decoding devices can perform inter-frame prediction on a block-by-block basis to derive prediction samples. Inter-frame prediction may refer to prediction derived in a manner that depends on data elements (e.g., sample values, motion information, etc.) of a picture other than the current picture. When inter-frame prediction is applied to the current block, the prediction block (prediction sample array) of the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, the motion information of the current block can be predicted on a block, sub-block, or sample basis based on the motion information correlation between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include information on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). When inter-frame prediction is applied, 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 blocks may be the same or different. Temporally neighboring blocks may be referred to as collocated reference blocks, collocated CUs (ColCUs), and reference pictures including temporally neighboring blocks may be referred to as collocated pictures (colPic). For example, a motion information candidate list may be constructed based on neighboring blocks of the current block, and in order to derive the motion vector and / or reference picture index of the current block, a flag or index information indicating which candidate is selected (used) may be signaled. Inter-frame prediction may be performed based on various prediction modes. For example, in skip mode and merge mode, the motion information of the current block may be equal to the motion information of the selected neighboring block. In skip mode, a residual signal may not be sent as in merge mode. In motion vector prediction (MVP) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor, and the motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0163] Depending on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.), the motion information may include L0 motion information and / or L1 motion information. A motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and a motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on the L0 motion vector may be referred to as L0 prediction, prediction based on the L1 motion vector may be referred to as L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bi-prediction. Here, the L0 motion vector may indicate a motion vector associated with reference picture list L0 (L0), and the L1 motion vector may indicate a motion vector associated with reference picture list L1 (L1). Reference picture list L0 may include pictures preceding the current picture in output order as reference pictures, and reference picture list L1 may include pictures following the current picture in output order. The previous picture may be referred to as a forward (reference) picture, and the subsequent picture may be referred to as a backward (reference) picture. Reference picture list L0 may also include pictures following the current picture in output order as reference pictures. In this case, within the reference picture list L0, the previous picture may be indexed first, and then the subsequent picture may be indexed. The reference picture list L1 may also include pictures preceding the current picture in the output order as reference pictures. In this case, within the reference picture list L1, the subsequent picture may be indexed first, and then the previous picture may be indexed. Here, the output order may correspond to the picture order count (POC) order.

[0164] The video / image encoding process based on inter-frame prediction and inter-frame prediction unit in the encoding device can schematically include, for example, the following. Figure 11This is described. The encoding device performs inter-frame prediction for the current block (S1100). The image encoding device can derive the inter-frame prediction mode and motion information of the current block and generate prediction samples for the current block. Here, the inter-frame prediction mode determination, motion information derivation and prediction sample generation processes can be performed simultaneously, or any one of them can be performed before the other process. For example, the inter-frame prediction unit of the encoding device may include a prediction mode determination unit, a motion information derivation unit and a prediction sample derivation unit, and the prediction mode determination unit can determine the prediction mode of the current block, the motion information derivation unit can derive the motion information of the current block, and the prediction sample derivation unit can derive the prediction samples of the current block. For example, the inter-frame predictor of the encoding device can search for a block similar to the current block in a predetermined area (search area) of a reference picture through motion estimation, and derive a reference block whose difference with the current block is equal to or less than a predetermined standard or minimum value. Based on this, a reference picture index indicating the reference picture where the reference block is located can be derived, and a motion vector can be derived based on the position difference between the reference block and the current block. The encoding device can determine a mode to be applied to the current block from among various prediction modes. The encoding device may compare RD costs of various prediction modes and determine an optimal prediction mode for the current block.

[0165] For example, when skip mode or merge mode is applied to the current block, the encoding device may construct a merge candidate list and derive a reference block whose difference with the current block is equal to or less than a predetermined standard or minimum value among the reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. The motion information of the selected merge candidate may be used to derive the motion information of the current block.

[0166] As another example, when the (A)MVP mode is applied to the current block, the encoding device may construct an (A)MVP candidate list and derive a motion vector of an MVP candidate selected from among the MVP candidates included in the (A)MVP candidate list. In this case, for example, the motion vector indicating the reference block derived by the above-mentioned motion estimation may be used as the motion vector of the current block, and the MVP candidate having the smallest motion vector difference with the motion vector of the current block among the MVP candidates may be the selected MVP candidate. A motion vector difference (MVD) as the difference obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, information about the MVD may be signaled to the decoding device. In addition, when the (A)MVP mode is applied, the value of the reference picture index may be constructed as reference picture index information and separately signaled to the decoding device.

[0167] The encoding apparatus may derive residual samples based on the predicted samples (S1120). The encoding apparatus may derive residual samples by comparing the original samples of the current block with the predicted samples.

[0168] The encoding device may encode image information including prediction information and residual information (S1130). The encoding device may output the encoded image information in the form of a bitstream. The prediction information may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index, etc.) and information about motion information as information related to the prediction process. The information about the motion information may include candidate selection information (e.g., a merge index, an mvp flag, or an mvp index) as information for deriving a motion vector. In addition, the information about the motion information may include information about the above-mentioned MVD and / or reference picture index information. In addition, the information about the motion information may include information indicating whether L0 prediction, L1 prediction, or dual prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients for the residual sample.

[0169] The output bitstream may be stored in a (digital) storage medium and sent to the decoding device, or may be sent to the decoding device via a network.

[0170] As described above, the encoding device can generate a reconstructed picture (including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This allows the encoding device to derive the same prediction result as the prediction result performed by the decoding device, thereby improving encoding efficiency. Therefore, the encoding device can store the reconstructed picture (or reconstructed samples and reconstructed blocks) in a memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is further applied to the reconstructed picture.

[0171] The video / image decoding process based on inter-frame prediction and inter-frame prediction units in the decoding device may illustratively include, for example, the following contents.

[0172] The decoding device may perform an operation corresponding to the operation performed by the encoding device. The decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0173] Specifically, the decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S1210).The image decoding apparatus may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

[0174] For example, whether merge mode or (A)MVP mode is applied to the current block can be determined based on the merge flag. Alternatively, one of various inter-frame prediction mode candidates can be selected based on the mode index. Inter-frame prediction mode candidates can include skip mode, merge mode and / or (A)MVP mode, or can include various inter-frame prediction modes described below.

[0175] The decoding device may derive motion information of the current block based on the determined inter-frame prediction mode (S1220). For example, when skip mode or merge mode is applied to the current block, the decoding device may construct a merge candidate list to be described below and select one of the merge candidates included in the merge candidate list. The selection may be performed based on the above-mentioned candidate selection information (merge index). The motion information of the selected merge candidate may be used to derive the motion information of the current block. The motion information of the selected merge candidate may be used as the motion information of the current block.

[0176] As another example, when the (A)MVP mode is applied to the current block, the decoding device may construct an (A)MVP candidate list and use the motion vector of the MVP candidate selected as the MVP of the current block from among the MVP candidates included in the (A)MVP candidate list. The selection may be performed based on the above-mentioned candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the information about the MVD, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. In addition, the reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list of the current block may be derived as the reference picture referenced by the inter-frame prediction of the current block.

[0177] In addition, as described below, the motion information of the current block can be derived without the candidate list construction, and in this case, the motion information of the current block can be derived according to the process disclosed in the prediction mode described below. In this case, the above-mentioned candidate list construction can be omitted.

[0178] The image decoding apparatus may generate prediction samples of the current block based on the motion information of the current block (S1230). In this case, a reference picture may be derived based on a reference picture index of the current block, and the prediction samples of the current block may be derived using samples of the reference block indicated by the motion vector of the current block on the reference picture. In this case, as described below, in some cases, a prediction sample filtering process may be further performed on all or some of the prediction samples of the current block.

[0179] For example, the inter-frame prediction unit of the decoding device may include a prediction mode determination unit, a motion information derivation unit and a prediction sample derivation unit, and the prediction mode determination unit can determine the prediction mode of the current block based on the received prediction mode information, the motion information derivation unit can derive the motion information (motion vector and / or reference picture index, etc.) of the current block based on the received motion information, and the prediction sample derivation unit can derive the prediction sample of the current block.

[0180] The decoding device may generate residual samples of the current block based on the received residual information (S1240). The decoding device may generate reconstructed samples of the current block based on the predicted samples and the residual samples, and generate a reconstructed picture based thereon (S1250). Thereafter, the in-loop filtering process is applied to the reconstructed picture, as described above.

[0181] As described above, the inter-frame prediction process may include the steps of determining an inter-frame prediction mode, deriving motion information according to the determined prediction mode, and performing prediction (generating prediction samples) based on the derived motion information. The inter-frame prediction process may be performed by an encoding device and a decoding device, as described above.

[0182] Quantization / Dequantization

[0183] As described above, the quantizer of the encoding device may derive quantized transform coefficients by applying quantization to the transform coefficients, and the dequantizer of the encoding device or the dequantizer of the decoding device may derive transform coefficients by applying dequantization to the quantized transform coefficients.

[0184] In the encoding and decoding of moving images / still images, the quantization rate can be changed and the compression rate can be adjusted using the changed quantization rate. From an implementation perspective, taking into account complexity, instead of directly using the quantization rate, a quantization parameter (QP) can be used. For example, a quantization parameter having an integer value from 0 to 63 can be used, and each quantization parameter value can correspond to the actual quantization rate. In addition, the quantization parameter QP of the luminance component (luminance sample) can be set differently. Y and the quantization parameter QP of the chroma component (chroma samples) C .

[0185] In the quantization process, a transform coefficient C can be received and divided by a quantization rate Qstep to obtain a quantized transform. In this case, considering computational complexity, the quantization rate can be multiplied by a scale to form an integer, and a shift operation can be performed according to a value corresponding to the scale value. The quantization scale can be derived based on the product of the quantization rate and the scale value. In other words, the quantization scale can be derived based on the QP. By applying the quantization scale to the transform coefficient C, the quantized transform coefficient C' can be derived.

[0186] The dequantization process is the inverse of the quantization process. The reconstructed transform coefficient C" is obtained by multiplying the quantized transform coefficient C' by the quantization rate Qstep. In addition, the level scale can be derived from the quantization parameter, and the level scale can be applied to the quantized transform coefficient C' to derive the reconstructed transform coefficient C". Due to the loss of the transformation and / or quantization process, the reconstructed transform coefficient C" may be slightly different from the initial transform coefficient C. Therefore, dequantization can be performed even in the encoding device in the same manner as in the decoding device.

[0187] In addition, an adaptive frequency-weighted quantization technique that adjusts the quantization strength according to frequency can be applied. Adaptive frequency-weighted quantization refers to a method that applies quantization strength differently according to frequency. In adaptive frequency-weighted quantization, a predefined quantization scaling matrix can be used to apply quantization strength differently according to frequency. That is, the above-mentioned quantization / dequantization processing can be performed based on the quantization scaling matrix. For example, different quantization scaling matrices can be used depending on the size of the current block and / or whether the prediction mode applied to the current block to generate the residual signal of the current block is inter-frame prediction or intra-frame prediction. The quantization scaling matrix can be referred to as a quantization matrix or a scaling matrix. The quantization scaling matrix can be predefined. In addition, for frequency-adaptive scaling, frequency quantization scale information of the quantization scaling matrix can be constructed / encoded in the encoding device and signaled to the decoding device. The frequency quantization scaling information can be referred to as quantization scaling information. The frequency quantization scaling information can include scaling list data scaling_list_data. The quantization scaling matrix can be derived (modified) based on the scaling list data. In addition, the frequency quantization scaling information can include a presence flag indicating whether the scaling list data exists. Alternatively, when the scaling list data is signaled at a higher level (eg, SPS), information indicating whether the scaling list data is modified at a lower level (eg, PPS or patch group header, etc.) may be further included.

[0188] Transformation / Inverse Transformation

[0189] As described above, the encoding device may derive a residual block (residual samples) based on a block predicted by intra / inter / IBC prediction (prediction block), and derive quantized transform coefficients by applying transform and quantization to the derived residual samples. Information regarding the quantized transform coefficients (residual information) may be included and encoded in the residual coding syntax and output in the form of a bitstream. The decoding device may obtain and decode the information regarding the quantized transform coefficients (residual information) from the bitstream to derive the quantized transform coefficients. The decoding device may derive residual samples based on the quantized transform coefficients by dequantization / inverse transform. As described above, at least one of quantization / dequantization and / or transform / inverse transform may be skipped. When the transform / inverse transform is skipped, the transform coefficient may be referred to as a coefficient or a residual coefficient, or, for uniformity of expression, may still be referred to as a transform coefficient. Whether the transform / inverse transform is skipped may be signaled based on a transform skip flag (e.g., transform_skip_flag).

[0190] Transformation / inverse transformation can be performed based on a transform kernel. For example, a multi-transform selection (MTS) scheme for performing transform / inverse transformation is applicable. In this case, some of a plurality of transform kernel sets can be selected and applied to the current block. The transform kernel can be referred to by various terms such as a transform matrix or a transform type. For example, a transform kernel set can indicate a combination of a vertical transform kernel (vertical transform kernel) and a horizontal transform kernel (horizontal transform kernel).

[0191] The transform / inverse transform can be performed in units of CU or TU. That is, the transform / inverse transform is applied to the residual samples in the CU or the residual samples in the TU. The CU size can be equal to the TU size, or there can be multiple TUs in the CU area. In addition, the CU size can generally indicate the luminance component (sample) CB size. The TU size can generally indicate the luminance component (sample) TB size. The chrominance component (sample) CB or TB size can be derived based on the luminance component (sample) CB or TB size according to the component ratio according to the color format (chrominance format) (for example, 4:4:4, 4:2:2, 4:2:0, etc.). The TU size can be derived based on maxTbSize. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) of maxTbSize can be derived from the CU, and the transform / inverse transform can be performed in units of TU (TB). The maxTbSize can be considered to determine whether to apply various intra-frame prediction types such as ISP. Information about maxTbSize can be predetermined or can be generated and encoded in the encoding device and notified to the encoding device using a signal.

[0192] Entropy Coding

[0193] All or some of the video / image information can be obtained by referring to the above Figure 2 The entropy encoder 190 described entropy encoding, refer to Figure 3 All or some of the described video / image information may be entropy decoded by the entropy decoder 310. In this case, the video / image information may be encoded / decoded in units of syntax elements. In the present disclosure, the encoding / decoding information may include encoding / decoding performed by the method described in this paragraph.

[0194] Figure 13 This is a block diagram of CABAC for encoding a syntax element. In the CABAC encoding process, first, when the input signal is a syntax element other than a binary value, the input signal can be converted to a binary value through binarization. When the input signal already has a binary value, the binarization can be bypassed. Here, the binary number 0 or 1 that configures the binary value can be called a bin. For example, when the binary string (bin string) after binarization is 110, each of 1, 1, and 0 can be called a bin. The bin of a syntax element can represent the value of the corresponding syntax element.

[0195] The binarized bins can be input to a conventional coding engine or a bypass coding engine. The conventional coding engine can assign a context model reflecting the probability value to the corresponding bin and encode the corresponding bit based on the assigned context model. The conventional coding engine can encode each bin and then update the probability model of the corresponding bin. The bin encoded in this way can be called a context coding bin. The bypass coding engine can bypass the process of estimating the probability for the input bin and the process for updating the probability model applied to the corresponding bin after encoding. Instead of assigning context, the bypass coding engine can encode the input bin by applying a uniform probability distribution (e.g., 50:50), thereby improving the coding speed. The bin encoded in this way can be called a bypass bin. The context model can be assigned and updated for each context coding (conventional coding) bin, and the context model can be indicated based on ctxidx or ctxInc. ctxidx can be derived based on ctxInc. Specifically, for example, the context index ctxidx indicating the context model for each conventionally coded bin can be derived as the sum of the context index increment ctxInc and the context index offset ctxIdxOffset. Here, ctxInc can be derived differently for each bin. ctxIdxOffset can be represented by the lowest value of ctxIdx. The lowest value of ctxIdx can be called the initial value initValue of ctxIdx. ctxIdxOffset is generally a value used to distinguish from the context model of other syntax elements, and the context model of a syntax element can be distinguished / derived based on ctxInc.

[0196] During the entropy encoding process, it can be determined whether encoding is performed by a normal encoding engine or a bypass encoding engine, and the encoding path can be switched. Entropy decoding can be performed in the reverse order of the same process as entropy encoding.

[0197] For example, Figure 14 and Figure 15 As shown, the above entropy coding can be performed. Figure 14 and Figure 15 The encoding device (entropy encoder) may perform an entropy encoding process on the image / video information. The image / video information may include segmentation-related information, prediction-related information (e.g., inter-frame / intra-frame prediction distinction information, intra-frame prediction mode information, inter-frame prediction mode information, etc.), residual information, in-loop filtering-related information, etc., or may include various syntax elements related thereto. Entropy encoding may be performed in units of syntax elements. Figure 14 Steps S1410 to S1420 can be performed by Figure 2 The encoding is performed by the entropy encoder 190 of the encoding device.

[0198] The encoding device may perform binarization on the target syntax element (S1410). Here, the binarization may be based on various binarization methods such as truncated Rice binarization, fixed-length binarization, etc., and the binarization method used for the target syntax element may be predefined. The binarization process may be performed by the binarization unit 191 in the entropy encoder 190.

[0199] The encoding device may perform entropy encoding for the target syntax element (S1420). The encoding device may perform encoding based on conventional encoding (context-based) or bypass encoding for the bin string of the target syntax element based on an entropy encoding technique such as CABAC (context adaptive arithmetic coding) or CAVLC (context adaptive variable length coding), and its output may be included in the bitstream. The entropy encoding process may be performed by the entropy encoding processor 192 in the entropy encoder 190. As described above, the bitstream may be sent to the decoding device via a (digital) storage medium or a network.

[0200] refer to Figure 16 and Figure 17 , a decoding device (entropy decoder) can decode the encoded image / video information. The image / video information may include segmentation-related information, prediction-related information (e.g., inter-frame / intra-frame prediction distinction information, intra-frame prediction mode information, inter-frame prediction mode information, etc.), residual information, in-loop filtering-related information, etc., or may include various syntax elements related thereto. Entropy coding can be performed in units of syntax elements. Figure 16 Steps S1610 to S1620 can be performed by Figure 3 The entropy decoder 210 of the decoding device is executed.

[0201] The decoding device may perform binarization on the target syntax element (S1610). Here, the binarization may be based on various binarization methods such as truncated Rice binarization, fixed-length binarization, etc., and the binarization method used for the target syntax element may be predefined. The decoding device may derive available bin strings (bin string candidates) for available values of the target syntax element through the binarization process. The binarization process may be performed by the binarization unit 211 in the entropy decoder 210.

[0202] The decoding device can perform entropy decoding (S1620) for the target syntax element. The decoding device can compare the derived bin string with the available bin string of the corresponding syntax element, and decode and parse the bin of the target syntax element in sequence from the input bits in the bitstream. If the derived bin string is equal to one of the available bin strings, the value corresponding to the corresponding bin string can be derived as the value of the corresponding syntax element. If not, the above process can be performed again after further parsing the next bit in the bitstream. Through this processing, variable length bits can be used to signal the corresponding information without using the start bit or end bit of specific information (specific syntax element) in the bitstream. Thus, relatively few bits can be allocated to low values, and the overall coding efficiency can be improved.

[0203] The decoding device can perform context-based or bypass-based decoding on a bin in a bin string from a bitstream based on an entropy coding technique such as CABAC or CAVLC. The entropy decoding process can be performed by an entropy decoding processor 212 in the entropy decoder 210. The bitstream can include various information for image / video decoding as described above. As described above, the bitstream can be sent to the decoding device via a (digital) storage medium or a network.

[0204] In the present disclosure, a table including syntax elements (syntax table) can be used to indicate information signaling from an encoding device to a decoding device. The order of syntax elements in the table including syntax elements used in the present disclosure can indicate the parsing order of syntax elements from a bitstream. The encoding device can construct and encode syntax elements so that the decoding device parses the syntax elements in the parsing order, and the decoding device can parse and decode the syntax elements of the corresponding syntax table from the bitstream according to the parsing order and obtain the values of the syntax elements.

[0205] General image / video encoding process

[0206] In image / video encoding, the pictures constituting the image / video can be encoded / decoded according to the decoding order. The picture order corresponding to the output order of the decoded pictures can be set differently from the decoding order, and based on this, not only forward prediction but also backward prediction can be performed during inter-frame prediction.

[0207] Figure 18 An example of a schematic picture decoding process to which the embodiments of the present disclosure are applicable is shown. Figure 18 In the embodiment of the present invention, S1810 may be performed in the entropy decoder 210 of the decoding device, S1820 may be performed in the prediction unit including the intra prediction unit 265 and the inter prediction unit 260, S1830 may be performed in the residual processor including the dequantizer 220 and the inverse transformer 230, S1840 may be performed in the adder 235, and S1850 may be performed in the filter 240. S1810 may include the information decoding process described in the present disclosure, S1820 may include the inter / intra prediction process described in the present disclosure, S1830 may include the residual processing process described in the present disclosure, S1840 may include the block / picture reconstruction process described in the present disclosure, and S1850 may include the in-loop filtering process described in the present disclosure.

[0208] refer to Figure 18 , the picture decoding process can illustratively include a process for obtaining image / video information (by decoding) from a bitstream (S1810), a picture reconstruction process (S1820 to S1840), and an in-loop filtering process (S1850) of the reconstructed picture. The picture reconstruction process can be performed based on the prediction samples and residual samples obtained by the inter / intra prediction (S1820) and residual processing (S1830) (dequantization and inverse transformation of quantized transform coefficients) described in the present disclosure. A modified reconstructed picture can be generated by an in-loop filtering process of the reconstructed picture generated by the picture reconstruction process, and the modified reconstructed picture can be output as a decoded picture, stored in a decoded picture buffer or memory 250 of a decoding device, and used as a reference picture in an inter-frame prediction process when the picture is later decoded. In some cases, the in-loop filtering process can be omitted. In this case, the reconstructed picture can be output as a decoded picture, stored in a decoded picture buffer or memory 250 of a decoding device, and used as a reference picture in an inter-frame prediction process when the picture is later decoded. The in-loop filtering process (S1850) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filtering (ALF) process, and / or a bilateral filtering process, some or all of which may be omitted as described above. In addition, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filtering (ALF) process, and / or the bilateral filtering process may be applied sequentially, or all of them may be applied sequentially. For example, after the deblocking filtering process is applied to the reconstructed picture, the SAO process may be performed. Alternatively, for example, after the deblocking filtering process is applied to the reconstructed picture, the ALF process may be performed. This may even be performed similarly in the encoding device.

[0209] Figure 19 An example of a schematic picture encoding process to which the embodiments of the present disclosure are applicable is shown. Figure 19 In the S1910, you can refer to the above Figure 2 The described encoding device may be performed in the intra prediction unit 185 or the prediction unit of the inter prediction unit 180, S1920 may be performed in the residual processor including the transformer 120 and / or the quantizer 130, and S1930 may be performed in the entropy encoder 190. S1910 may include the inter / intra prediction process described in the present disclosure, S1920 may include the residual processing process described in the present disclosure, and S1930 may include the information encoding process described in the present disclosure.

[0210] refer to Figure 19 , the picture encoding process may illustratively include not only a process for encoding and outputting information for picture reconstruction (e.g., prediction information, residual information, segmentation information, etc.) in the form of a bit stream, but also a process for generating a reconstructed picture of the current picture and a process for applying in-loop filtering to the reconstructed picture (optional), as described in relation to Figure 2 Described. The encoding device can derive (modified) residual samples from the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150, and generate a reconstructed picture based on the predicted samples and the (modified) residual samples as the output of S1910. The reconstructed picture generated in this way can be the same as the reconstructed picture generated in the decoding device. Similar to the decoding device, the modified reconstructed picture can be generated by an in-loop filtering process for the reconstructed picture, can be stored in the decoded picture buffer or the memory 170, and can be used as a reference picture in the inter-frame prediction process when the picture is later encoded. As described above, in some cases, some or all of the in-loop filtering process can be omitted. When the in-loop filtering process is performed, the (in-loop) filtering related information (parameters) can be encoded in the entropy encoder 190 and output in the form of a bitstream, and the decoding device can perform the in-loop filtering process based on the filtering related information using the same method as the encoding device.

[0211] This in-loop filtering process can reduce noise (e.g., blocking artifacts and ringing artifacts) that occurs during image / video encoding, and improve subjective / objective visual quality. Furthermore, by performing the in-loop filtering process in both the encoding device and the decoding device, the encoding device and the decoding device can derive the same prediction result, increase picture encoding reliability, and reduce the amount of data to be transmitted for picture encoding.

[0212] As described above, the picture reconstruction process can be performed not only in a decoding device but also in an encoding device. Reconstructed blocks can be generated in units of blocks based on intra-frame prediction / inter-frame prediction, and a reconstructed picture including the reconstructed blocks can be generated. When the current picture / slice / patchwork group is an I picture / slice / patchwork group, the blocks included in the current picture / slice / patchwork group can be reconstructed based only on intra-frame prediction. In addition, when the current picture / slice / patchwork group is a P or B picture / slice / patchwork group, the blocks included in the current picture / slice / patchwork group can be reconstructed based on intra-frame prediction or inter-frame prediction. In this case, inter-frame prediction can be applied to some blocks in the current picture / slice / patchwork group, and intra-frame prediction can be applied to the remaining blocks. The color components of the picture may include luminance components and chrominance components, and unless explicitly limited in the present disclosure, the methods and embodiments of the present disclosure are applicable to luminance components and chrominance components.

[0213] Examples of coding layers and structures

[0214] For example, the encoded video / image according to the present disclosure may be processed according to the coding layers and structures to be described below.

[0215] Figure 20 This diagram shows the layer structure of a coded image. The coded image can be classified into a video coding layer (VCL) for image decoding and processing itself, a lower layer system for transmitting and storing coded information, and a network abstraction layer (NAL) that exists between the VCL and the lower layer system and is responsible for network adaptation functions.

[0216] In the VCL, VCL data including compressed image data (slice data) can be generated, or a supplemental enhancement information (SEI) message additionally required for the decoding process of the image or a parameter set including information such as a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS) can be generated.

[0217] In NAL, header information (NAL unit header) can be added to the raw byte sequence payload (RBSP) generated in the VCL to generate a NAL unit. In this case, RBSP refers to slice data, parameter sets, and SEI messages generated in the VCL. The NAL unit header can include NAL unit type information specified according to the RBSP data included in the corresponding NAL unit.

[0218] As shown in the figure, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the RBSP generated in the VCL. A VCL NAL unit may refer to a NAL unit including information about an image (slice data), and a non-VCL NAL unit may refer to a NAL unit including information required for decoding an image (parameter set or SEI message).

[0219] VCL NAL units and non-VCL NAL units can be attached with header information and sent over a network according to the data standard of the underlying system. For example, NAL units can be modified into a predetermined standard data format such as the H.266 / VVC file format, RTP (Real-time Transport Protocol), or TS (Transport Stream) and sent over various networks.

[0220] As described above, in a NAL unit, a NAL unit type may be specified according to an RBSP data structure included in a corresponding NAL unit, and information on the NAL unit type may be stored in a NAL unit header and signaled.

[0221] For example, this can be roughly classified into VCL NAL unit types and non-VCL NAL unit types according to whether the NAL unit includes information about the image (slice data). VCL NAL unit types can be classified according to the nature and type of the picture included in the VCL NAL unit, and non-VCL NAL unit types can be classified according to the type of parameter set.

[0222] Examples of NAL unit types specified according to the types of parameter sets / information included in the non-VCL NAL unit type will be listed below.

[0223] -DCI (Decoding Capability Information) NAL unit: NAL unit type that includes DCI

[0224] -VPS (Video Parameter Set) NAL unit: includes the NAL unit type of the VPS

[0225] -SPS (Sequence Parameter Set) NAL unit: NAL unit type including SPS

[0226] -PPS (Picture Parameter Set) NAL unit: NAL unit type including PPS

[0227] -APS (Adaptation Parameter Set) NAL unit: NAL unit type including APS

[0228] -PH (picture header) NAL unit: includes the NAL unit type of PH

[0229] The above-mentioned NAL unit type may have syntax information of the NAL unit type, and the syntax information may be stored in the NAL unit header and notified by signaling. For example, the syntax information may be nal_unit_type, and the NAL unit type may be specified as a nal_unit_type value.

[0230] In addition, as described above, a picture may include multiple slices, and a slice may include a slice header and slice data. In this case, a picture header may be further added to the multiple slices (slice headers and slice data sets) in a picture. The picture header (picture header syntax) may include information / parameters commonly applicable to the picture.

[0231] The slice header (slice header syntax) may include information / parameters that are commonly applicable to the slice. APS (APS syntax) or PPS (PPS syntax) may include information / parameters that are commonly applicable to one or more slices or pictures. SPS (SPS syntax) may include information / parameters that are commonly applicable to one or more sequences. VPS (VPS syntax) may include information / parameters that are commonly applicable to multiple layers. DCI (DCI syntax) may include information / parameters that are commonly applicable to the entire video. DCI may include information / parameters related to decoding capabilities. In the present disclosure, high-level syntax (HLS) may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DCI syntax, picture header syntax, or slice header syntax. In addition, in the present disclosure, low-level syntax (LLS) may include, for example, slice data syntax, CTU syntax, coding unit syntax, transform unit syntax, and the like.

[0232] In the present disclosure, the image / video information encoded in the encoding device and signaled to the decoding device in the form of a bitstream may include not only information related to intra-frame segmentation, intra-frame / inter-frame prediction information, residual information, and in-loop filtering information, but also information about slice headers, picture headers, APS, PPS, SPS, VPS, and / or DCI. In addition, the image / video information may also include general constraint information and / or information about NAL unit headers.

[0233] Split the screen using sprites, slices, and tiles

[0234] A picture can be partitioned into at least one tile row and at least one tile column. A tile can consist of a sequence of CTUs and can cover a rectangular area of a picture.

[0235] A slice can consist of an integer number of complete tiles or an integer number of consecutive complete CTU rows in a picture.

[0236] For slicing, two modes may be supported: one mode may be referred to as raster scan slicing mode, and the other mode may be referred to as rectangular slicing mode. In raster scan slicing mode, a slice may include a sequence of complete tiles that exist in a picture in tile raster scan order. In rectangular slicing mode, a slice may include multiple complete tiles assembled to form a rectangular area of the picture or multiple consecutive complete CTU rows assembled to form a tile of a rectangular area of the picture. Tiles in a rectangular slice may be scanned in tile raster scan order in the rectangular area corresponding to the slice. A sub-picture may include at least one slice assembled to cover a rectangular area of the picture.

[0237] To describe the split relationship of the screen in more detail, refer to Figures 21 to 24 Give a description. Figures 21 to 24 An embodiment of partitioning a screen using tiles, slices, and sub-pictures is shown. Figure 21 An example of a picture divided into 12 tiles and three raster scan slices is shown. Figure 22 An example of a picture partitioned into 24 tiles (six tile columns and four tile rows) and 9 rectangular slices is shown. Figure 23 An example of a picture partitioned into four tiles (two tile columns and two tile rows) and four rectangular slices is shown.

[0238] Figure 24 An example of dividing a screen into sub-screens is shown. Figure 24 In , a picture can be divided into 12 left tiles covering one slice composed of 4×4 CTUs and 6 right tiles covering two vertically assembled slices composed of 2×2 CTUs, so that one picture is divided into 24 slices and 24 sub-pictures with different areas. Figure 24 In the example of , individual slices correspond to individual sprites.

[0239] Overview of In-Loop Filtering

[0240] An in-loop filtering process can be performed on the reconstructed picture generated by the above process. A modified reconstructed picture can be generated by the in-loop filtering process, and the modified reconstructed picture can be output from the decoding device as a decoded picture, can be stored in the memory or decoded picture buffer of the encoding device / decoding device, and can be used as a reference picture in the inter-frame prediction process when encoding / decoding the picture. As described above, the in-loop filtering process may include a deblocking filtering process, a sample adaptive offset (SAO) process, and / or an adaptive loop filtering (ALF) process. In this case, one or some of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filtering (ALF) process, and the bilateral filtering process can be applied sequentially, or all of them can be applied sequentially. For example, after applying the deblocking filtering process to the reconstructed picture, the SAO process can be performed. Alternatively, for example, after applying the deblocking filtering process to the reconstructed picture, the ALF process can be performed. This can also be performed in the encoding device.

[0241] Deblocking filtering is a filtering technique that removes distortion at the boundaries between blocks in a reconstructed image. The deblocking filtering process can, for example, derive a target boundary from the reconstructed image, determine a boundary strength bS for the target boundary, and perform deblocking filtering on the target boundary based on bS. bS can be determined based on factors such as the prediction mode, motion vector difference, whether the reference picture is the same, and the presence of non-zero significant coefficients of the two blocks adjacent to the target boundary.

[0242] SAO is a method of compensating for the offset difference between the reconstructed picture and the original picture in units of samples, and can be applied based on types such as band offset and edge offset. According to SAO, samples can be classified into different categories according to each SAO type, and an offset value can be added to each sample based on the category. SAO filter information may include information on whether SAO is applied, SAO type information, SAO offset value information, etc. After applying deblocking filtering, SAO can be applied to the reconstructed picture.

[0243] Adaptive loop filtering (ALF) is a technique for filtering a reconstructed picture on a sample-by-sample basis using filter coefficients according to a filter shape. The encoding device can determine whether to apply ALF, the ALF shape, and / or ALF filter coefficients by comparing the reconstructed picture with the original picture, and can signal this to the decoding device. That is, ALF filter information can include information on whether to apply ALF, ALF filter shape information, ALF filter coefficient information, and so on. After deblocking filtering, ALF can be applied to the reconstructed picture.

[0244] Whether to apply in-loop filtering signaling

[0245] As described above, HLS can be encoded and / or signaled to perform video and / or image encoding. As described above, the video / image information in this specification can be included in HLS. In addition, image / video encoding methods can be performed based on such image / video information.

[0246] In an embodiment, a picture may be divided into division units such as sub-pictures, slices, and / or tiles. In addition, a signal may be used to notify whether filtering is applied to the boundaries of such division units. For example, a picture may be divided into multiple tiles. In this case, in-loop filtering across the boundaries of the tiles may be performed. Alternatively, a picture may be divided into multiple slices. In this case, in-loop filtering across the boundaries of the slices may be performed. In this case, whether in-loop filtering across the boundaries of the tiles and / or slices is performed may be signaled via HLS.

[0247] Figure 25 FIG. 1 is a diagram illustrating an embodiment of a syntax of a PPS for signaling whether in-loop filtering is performed at a patch boundary and / or a slice boundary. Figure 25 In the syntax of the 2510-bit 1-bit 1-bit 2 ...

[0248] In an embodiment, the syntax element no_pic_partition_flag 2510 may be used as a condition to signal information for partitioning patches and / or slices when a picture is partitioned into more than one patch and / or slice, and this may be included in the syntax as a conditional statement, such as Figure 252520. For example, the encoding device may use the no_pic_partition_flag 2510 to signal to the decoding device whether information about the partitioning of patches and / or slices is included in the bitstream. In addition, when the value of the no_pic_partition_flag 2510 is 1, the decoding device may not parse the information about the partitioning of patches and / or slices from the bitstream. When the value of the no_pic_partition_flag 2510 is 0, the decoding device may parse the information about the partitioning of patches and / or slices from the bitstream based on the additional information.

[0249] For the above implementation, when no_pic_partition_flag 2510 indicates that the picture can be partitioned into tiles or slices, the PPS syntax indicating that the following syntax elements can be obtained from the bitstream can be implemented as Figure 25 .

[0250] The syntax element pps_log2_ctu_size_minus5 may indicate the luma coding tree block size of an individual CTU. Specifically, the encoding device may determine the value of pps_log2_ctu_size_minus5 as a value obtained by subtracting 5 from the luma coding tree block size of the individual CTU. The decoding device may determine the value obtained by adding 5 to pps_log2_ctu_size_minus5 as the luma coding tree block size of the individual CTU.

[0251] The syntax element num_exp_tile_columns_minus1 may indicate the numerical value of the width value of the tile column explicitly signaled. For example, the decoding device may determine the numerical value of the width value of the tile column explicitly signaled as a value obtained by adding 1 to num_exp_tile_columns_minus1. The value of num_exp_tile_columns_minus1 may have a value from 0 to PicWidthInCtbY-1. Here, PicWidthInCtbY may indicate the width of the picture expressed in units of the width of the luma coding block. In addition, when the value of no_pic_partition_flag is 1, the value of num_exp_tile_columns_minus1 may be derived as 0.

[0252] The syntax element num_exp_tile_rows_minus1 may indicate the numerical value of the height value of the tile row explicitly signaled. For example, the decoding device may determine the numerical value of the height value of the tile row explicitly signaled as a value obtained by adding 1 to num_exp_tile_rows_minus1. The value of num_exp_tile_rows_minus1 may have a value from 0 to PicHeightInCtbY-1. PicHeightInCtbY may indicate the height of the picture expressed in units of the height of the luma coding block. When the value of no_pic_partition_flag is 1, the value of num_exp_tile_rows_minus1 may be derived as 0.

[0253] The syntax element tile_column_width_minus1[i] may indicate the width of the i-th tile column of the picture referring to the PPS. For example, the decoding device may determine the value obtained by adding 1 to tile_column_width_minus1[i] as the width of the i-th tile column. The syntax element tile_column_width_minus1[i] may be obtained from the bitstream based on the value of num_exp_tile_columns_minus1, such as Figure 25 Same as in the syntax of .

[0254] The syntax element tile_row_height_minus1[i] may indicate the height of the i-th tile row of the picture referring to the PPS. For example, the decoding device may determine the value obtained by adding 1 to tile_row_height_minus1[i] as the height of the i-th tile row. The syntax element tile_row_height_minus1[i] may be obtained from the bitstream based on the value of num_exp_tile_rows_minus1, such as Figure 25 Same as in the syntax of .

[0255] Furthermore, the variable NumTilesInPic may be calculated based on the values of num_exp_tile_columns_minus1 and num_exp_tile_rows_minus1. In an embodiment, the decoding apparatus may determine the value of the variable NumTilesInPic indicating the number of tiles in a picture referring to the PPS as (num_exp_tile_columns_minus1+1)×(num_exp_tile_rows_minus1+1).

[0256] The syntax element rect_slice_flag may be obtained from the bitstream when the value of NumTilesInPic is greater than 1. For example, the syntax element rect_slice_flag may be obtained when the picture is partitioned into two or more tiles.

[0257] The syntax element rect_slice_flag can indicate whether the raster scan slice mode or the rectangular slice mode is applied to the individual pictures of the reference PPS. For example, the first value of rect_slice_flag (e.g., 0) can indicate that the raster scan slice mode is applied to the individual pictures of the reference PPS. In this case, the signaling of the layout of the slices can be omitted. The second value of rect_slice_flag (e.g., 1) can indicate that the rectangular slice mode is used for the individual pictures of the reference PPS. In this case, as described below, the layout of the slices can be signaled by the PPS. When rect_slice_flag is not signaled, the decoding device can derive the value of rect_slice_flag as 1.

[0258] The syntax element single_slice_per_subpic_flag may be signaled when the value of the syntax element rect_slice_flag is 1. The first value of single_slice_per_subpic_flag (e.g., 0) may indicate that an individual sub-picture may consist of more than one rectangular slice. The second value of single_slice_per_subpic_flag (e.g., 1) may indicate that an individual sub-picture consists of only one rectangular slice.

[0259] In addition, when the value of rect_slice_flag is 1 and the value of single_slice_per_subpic_flag is 0, the syntax element num_slices_in_pic_minus1 may be signaled. For example, when a picture is partitioned into two or more rectangular slices, the syntax element num_slices_in_pic_minus1 indicating the number of rectangular slices in an individual picture of a reference PPS may be signaled to signal the layout of the rectangular slices. For example, the decoding device may determine the number of rectangular slices in the picture as a value obtained by adding 1 to num_slices_in_pic_minus1. The value of num_slices_in_pic_minus1 may have a value from 0 to MaxSlicePerAu-1. The variable MaxSlicePerAu may indicate the maximum number of slices allowed per access unit, for example, may indicate the maximum number of slices allowed in the current picture.

[0260] Based on the value of num_slices_in_pic_minus1, it can also be Figure 25 The syntax elements tile_idx_delta_present_flag, slice_width_in_tiles_minus1, slice_height_in_tiles_minus1, num_exp_slices_in_tile, exp_slice_height_in_ctus_minus1, and tile_idx_delta are obtained from the bitstream in the same manner as the syntax element tile_idx_delta_present_flag. Here, the syntax element tile_idx_delta_present_flag may indicate whether the syntax element tile_idx_delta, used as an index for identifying a rectangular slice in a picture, is obtained from the bitstream. The value obtained by adding 1 to the syntax element slice_width_in_tiles_minus1[i] may indicate the width of the i-th rectangular slice in tile columns. The value obtained by adding 1 to the syntax element slice_height_in_tiles_minus1[i] may indicate the height of the i-th rectangular slice in tile rows.

[0261] The syntax element num_exp_slices_in_tile[i] may indicate the numerical value of the slice height explicitly provided for the slices in the tile including the i-th slice. The value obtained by adding 1 to the syntax element exp_slice_height_in_ctus_minus1[j] may indicate the height of the j-th rectangular slice in the tile including the i-th slice, and the unit may have a unit of CTU row. The syntax element tile_idx_delta[i] may indicate the difference between the index of the tile including the first CTU in the i-th rectangular slice and the index of the tile including the first CTU in the (i+1)-th rectangular slice.

[0262] The syntax element loop_filter_across_tiles_enabled_flag 2530 may indicate whether filtering operations are performed across the boundaries of tiles in a picture that references a PPS. For example, a first value (e.g., 0) of loop_filter_across_tiles_enabled_flag indicates that in-loop filtering operations are not performed across the boundaries of tiles in a picture that references the PPS that includes this syntax element. A second value (e.g., 1) of loop_filter_across_tiles_enabled_flag indicates that in-loop filtering operations may be performed across the boundaries of tiles in a picture that references the PPS that includes this syntax element.

[0263] Here, the in-loop filtering operation may include deblocking filtering, sample adaptive offset (SAO) filtering, and / or adaptive loop filtering (ALF). When the value of loop_filter_across_tiles_enabled_flag is not obtained from the bitstream (e.g., not provided), the value of the syntax element may be derived as a second value (e.g., 1). In addition, in another embodiment, when the value of loop_filter_across_tiles_enabled_flag is not obtained from the bitstream (e.g., not provided), the value of the syntax element may be derived as a first value (e.g., 0).

[0264] The syntax element loop_filter_across_slices_enabled_flag 2540 may indicate whether filtering operations are performed across the boundaries of slices in the picture referencing the PPS. For example, the first value of loop_filter_across_slices_enabled_flag (e.g., 0) may indicate that in-loop filtering operations are not performed across the boundaries of slices in the picture referencing the PPS including the syntax element.

[0265] A second value (eg, 1) of loop_filter_across_slices_enabled_flag may indicate that an in-loop filtering operation may be performed across boundaries of slices in a picture that references a PPS including the syntax element.

[0266] Here, as described above, the in-loop filtering operation may include deblocking filtering, SAO filtering, and / or ALF.When the value of loop_filter_across_slices_enabled_flag is not obtained from the bitstream (eg, not provided), the value of the syntax element may be derived as a first value (eg, 0).

[0267] In an embodiment, each picture may be partitioned in tile units. In this case, two or more tiles may exist in one picture, and whether in-loop filtering is applied to the boundary portion of each tile area may be determined by loop_filter_across_tiles_enabled_flag 2530 signaled in an individual PPS.

[0268] exist Figure 25In the example of FIG, when two or more tiles exist in one picture (for example, no_pic_partition_flag == 0), the value of loop_filter_across_tiles_enabled_flag may always be signaled to determine whether in-loop filtering is applied in the boundary area. However, considering the fact that the flag is signaled even when only a plurality of tiles exist in one picture, an improvement may be made so that the flag can be signaled while taking into account the number of existing tiles in order to reduce the amount of transmitted bits.

[0269] For example, in Figure 25 In the example of , when the value of no_pic_partition_flag is the first value (e.g., 0), this means that the current picture is partitioned into more than one patch or slice. In an embodiment, when the value of no_pic_partition_flag is the first value (e.g., 0), since two or more patches may exist in one picture, the value of loop_filter_across_tiles_enabled_flag may always be signaled to determine whether in-loop filtering is applied in the patch boundary area. However, the case where the value of no_pic_partition_flag is the first value (e.g., 0) includes the case where one picture is not partitioned into patches but only into slices. Therefore, even when there are no patches and only multiple slices in one picture, loop_filter_across_tiles_enabled_flag may be signaled. In view of this, an improvement may be made to signal the flag while taking into account the number of patches present so as to reduce the amount of bits sent.

[0270] Figure 26 FIG. 1 is a view illustrating an embodiment of signaling the syntax of the syntax element loop_filter_across_tiles_enabled_flag in consideration of the number of tiles in order to solve the above problem. Figure 26 As shown, the syntax element loop_filter_across_tiles_enabled_flag 2620 may be signaled based on the number of tiles belonging to a picture (eg, NumTilesInPic). Figure 26As shown, loop_filter_across_tiles_enabled_flag 2620 may be signaled through a bitstream only when the number of tiles belonging to a picture is greater than 1 (2610). Therefore, only when the number of tiles belonging to a picture is greater than 1 (2610), an encoding device may encode loop_filter_across_tiles_enabled_flag 2620 into a bitstream, and a decoding device may obtain loop_filter_across_tiles_enabled_flag 2620 from the bitstream.

[0271] In addition, Figure 25 In an embodiment, each picture may be divided in units of slices. In this case, two or more slices may be present in one picture, and whether in-loop filtering is applied to the boundary portion of each slice area may be determined by the loop_filter_across_slices_enabled_flag signaled in the individual PPS. More specifically, when two or more slices are present in one picture (e.g., no_pic_partition_flag == 0), the value of loop_filter_across_slices_enabled_flag may always be signaled to determine whether in-loop filtering is applied in the boundary area. However, considering the fact that the flag is signaled even when only a plurality of slices are present in one picture, an improvement may be made so that the flag may be signaled while taking into account the number of slices present in order to reduce the amount of bits transmitted.

[0272] In an embodiment, even when the value of no_pic_partition_flag is the first value (eg, 0), a picture referring to a PPS may be partitioned only into tiles and may not be partitioned into slices. Figure 25 In the example of FIG, even when the picture is partitioned into tiles and not into slices as described above, the value of loop_filter_across_slices_enabled_flag is always signaled. In this way, considering the fact that loop_filter_across_slices_enabled_flag is signaled even when there are only a plurality of tiles in one picture, Figure 25 The embodiment of the invention is improved so that the flag can be signaled taking into account the number of slices present in order to reduce the amount of bits sent.

[0273] Figure 27FIG. 1 is a view illustrating an embodiment of signaling the syntax of the syntax element loop_filter_across_slices_enabled_flag in consideration of the number of slices in order to solve the above problem. Figure 27 As shown, the syntax element loop_filter_across_slices_enabled_flag 2720 may be signaled based on the number of slices belonging to a picture (e.g., num_slices_in_pic_minus1). Figure 27 As shown, only when the number of slices belonging to a picture is greater than 1 (2710), loop_filter_across_slices_enabled_flag 2720 may be signaled through a bitstream. Therefore, only when the number of slices belonging to a picture is greater than 1 (2710), the encoding device may encode loop_filter_across_slices_enabled_flag 2720 to generate a bitstream, and the decoding device may obtain loop_filter_across_slices_enabled_flag 2720 from the bitstream.

[0274] Furthermore, num_slices_in_pic_minus1 is a syntax element that is signaled when a picture is partitioned into two or more rectangular slices to indicate the number of rectangular slices in an individual picture that references a PPS, thereby signaling the layout of the rectangular slices. When raster scan slice mode is applied to an individual picture, the individual picture may still be partitioned into multiple slices. Therefore, the syntax may be modified so that loop_filter_across_slices_enabled_flag 2720 may be signaled even when the value of rect_slice_flag indicates the first value (e.g., 0) indicating raster scan slice mode.

[0275] In addition, when the value of single_slice_per_subpic_flag is the second value (e.g., 1), since a picture can be divided into multiple sub-pictures, one picture can be composed of multiple slices. Therefore, the syntax can be modified so that the loop_filter_across_slices_enabled_flag 2720 can be signaled even when the value of single_slice_per_subpic_flag indicates the second value (e.g., 1).

[0276] In this way, when the value of num_slices_in_pic_minus1 is not obtained from the bitstream, since how many slices the current picture is partitioned into is not signaled, the syntax may be modified so that the loop_filter_across_slices_enabled_flag 2720 may be signaled even when the value of num_slices_in_pic_minus1 is not obtained from the bitstream. Figure 27 In the example of , as a condition for obtaining num_slices_in_pic_minus1 from the bitstream, the value of rect_slice_flag is required to be 1 and the value of single_slice_per_subpic_flag is required to be 0. In this regard, when the value of rect_slice_flag is 0 or the value of single_slice_per_subpic_flag is 1, the value of loop_filter_across_slices_enabled_flag can be obtained from the bitstream regardless of whether the value of num_slices_in_pic_minus1 is greater than 1. For this process, Figure 28 Modify the PPS syntax as shown in .

[0277] Figure 28 This is an example application reference Figures 25 to 27 This section describes an implementation of the syntax of the PPS for signaling loop_filter_across_tiles_enabled_flag and loop_filter_across_slices_enabled_flag. Figure 28 In the embodiment of the reference Figure 25 and Figure 28 pps_ is added to the names of some syntax elements described above. For example, the above syntax element no_pic_partition_flag is named pps_no_pic_partition_flag.

[0278] refer to Figure 28If pps_no_pic_partition_flag has a value (e.g., 0) indicating that a picture can be partitioned into at least one of tiles or slices, the syntax elements pps_num_exp_tile_columns_minus1 indicating how many tile columns a picture of the reference PPS has and pps_num_exp_tile_rows_minus1 indicating how many tile rows a picture of the reference PPS has can be used to signal how many tiles the current picture is partitioned into. Then, the number of tiles included in the current picture can be calculated as (pps_num_exp_tile_columns_minus1+1)×(pps_num_exp_tile_rows_minus1+1) and recorded in the variable NumTileInPic.

[0279] As described above, the pps_loop_filter_across_tiles_enabled_flag syntax element, which indicates whether filtering can be applied across tile boundaries, and the pps_rect_slice_flag syntax element are available only when the value of NumTileInPic is greater than 1, that is, only when there is more than one tile in the current picture. In addition, when the value of pps_rect_slice_flag is 1, the pps_single_slice_per_subpic_flag is available from the bitstream. When the value of pps_rect_slice_flag is 1 and the value of pps_single_slice_per_subpic_flag is 0, the pps_num_slice_in_pic_minus1 syntax element is available from the bitstream. In addition, when the value of pps_rect_slice_flag is 0, the value of pps_single_slice_per_subpic_flag is 1, or the value of pps_num_slices_in_pic_minus1 is greater than 1, the value of pps_loop_filter_across_slices_enabled_flag can be obtained from the bitstream.

[0280] Encoding and decoding methods

[0281] Hereinafter, an image encoding and decoding method performed by the image encoding and decoding apparatus according to the embodiment will be described.

[0282] First, the operation of the decoding device will be described. The image decoding device according to the embodiment includes a memory and a processor, and the decoding device can perform decoding according to the operation of the processor. Figure 29A decoding method of a decoding device according to an embodiment is illustrated.

[0283] The decoding device according to the embodiment may determine the number of tiles in the current picture (e.g., NumTilesInPic) based on whether the partitioning of the current picture is not restricted (S2910). For example, the decoding device may obtain a partition restriction flag (e.g., no_pic_partition_flag) indicating whether the partitioning of the current picture is restricted from the bitstream, and may determine whether the partitioning of the current picture is restricted based on the partition restriction flag.

[0284] Next, the decoding device may obtain a first flag (e.g., loop_filter_across_tiles_enabled_flag) from the bitstream indicating whether filtering of the tile boundaries is available based on the number of tiles in the current picture being multiple (S2920). Here, the number of tiles in the current picture may be determined based on tile quantity information indicating the number of tiles that partition the current picture. Here, the tile quantity information may be obtained from the bitstream based on the fact that the partitioning of the current picture is not restricted. In addition, the tile quantity information may include information indicating the number of tile columns in the picture (e.g., num_exp_tile_columns_minus1) and information indicating the number of tile rows in the picture (e.g., num_exp_tile_rows_minus1).

[0285] Next, the decoding device may determine whether to perform filtering on the boundary of the patch belonging to the current picture based on the value of the first flag (S2930). Here, the type of filtering may be any of deblocking filtering, SAO filtering, and ALF filtering as described above. For example, when the first flag indicates that filtering is not available, filtering for decoding the corresponding image among deblocking filtering, SAO filtering, and ALF filtering may not be applied to the boundary of the patch.

[0286] In addition, the decoding apparatus may obtain a second flag (eg, loop_filter_across_slices_enabled_flag) indicating whether filtering of a boundary of a slice is available from a bitstream based on that partitioning of the current picture is not restricted ( S2940 ).

[0287] For example, the decoding device may obtain information about slices constituting the picture from the bitstream based on that the partitioning of the current picture is not restricted. In addition, the decoding device may obtain the second flag from the bitstream based on that the information about the slices does not indicate that the picture consists of one slice.

[0288] Alternatively, the decoding device may obtain the second flag from the bitstream based on the information about the slice indicating that the rectangular slice mode is not applied to the picture (e.g., rect_slice_flag==0). Alternatively, the decoding device may obtain the second flag from the bitstream based on the information about the slice indicating that the sub-picture of the picture consists of only one rectangular slice (e.g., rect_slice_flag==0 or pps_single_slice_per_subpic_flag==1).

[0289] Alternatively, the decoding device may obtain the second flag from the bitstream based on information about slices indicating that the number of slices in the current picture is multiple (for example, num_slices_in_pic_minus1>0). For example, based on the fact that the partitioning of the current picture is not restricted, it may be determined whether the slices constituting the picture are rectangular slices, based on the fact that the slices constituting the picture are rectangular slices, it may be determined whether a sub-picture of the picture consists of only one rectangular slice, based on the sub-picture of the picture consisting of more than one rectangular slice, information indicating the number of slices in the current picture may be obtained from the bitstream, and based on the information indicating the number of slices in the current picture, it may be determined whether the number of slices in the current picture is multiple.

[0290] Then, the decoding device may determine whether to perform filtering on the boundary of the slice belonging to the current picture based on the value of the second flag (S2950). For example, when the second flag indicates that filtering is not available, filtering for decoding the corresponding image among deblocking filtering, SAO filtering, and ALF filtering may not be applied to the boundary of the slice.

[0291] Next, the operation of the encoding device will be described. The image encoding device according to the embodiment includes a memory and a processor, and the encoding device can perform encoding in a manner corresponding to the decoding of the decoding device through the operation of the processor. For example, Figure 30 As shown, the encoding device may determine the number of tiles in the current picture (e.g., NumTilesInPic) based on the fact that the partitioning of the current picture is not restricted (S3010). Next, the encoding device may determine the value of a first flag (e.g., loop_filter_across_tiles_enabled_flag) indicating whether filtering on the boundary of the tiles is available based on the fact that the number of tiles in the current picture is multiple (S3020). In addition, the encoding device may also determine whether the current picture consists of one slice based on the fact that the partitioning of the current picture is not restricted (S3030). In addition, the encoding device may determine the value of a second flag (e.g., loop_filter_across_slices_enabled_flag) indicating whether filtering on the boundary of the slice is available based on the fact that the current picture does not consist of one slice (S3040).

[0292] Next, the encoding device may generate a bitstream including at least one of the first flag or the second flag or excluding either of them (S3050). For example, the encoding device may not determine the values of the first flag and the second flag based on the fact that the number of tiles in the picture is not multiple and the current picture consists of one slice, and may generate a bitstream that does not include the first flag and the second flag. In addition, the value of the partition restriction flag (e.g., no_pic_partition_flag) may be set according to whether the current picture partition is restricted, and the partition restriction flag may also be included in the bitstream.

[0293] As described above, since the no_pic_partition_flag is utilized in the encoding and decoding methods, whether the current picture is partitioned into tiles and / or slices is signaled in the no_pic_partition_flag. Furthermore, information regarding the partitioning of tiles and information regarding the number of slices are signaled accordingly. In this regard, if whether to signal the loop_filter_across_tiles_enabled_flag and the loop_filter_across_slices_enabled_flag is determined solely based on the value of the no_pic_partition_flag, then when the current picture is partitioned into only slices or only tiles, it is not necessary to signal the loop_filter_across_tiles_enabled_flag or the loop_filter_across_slices_enabled_flag.

[0294] In addition, in order to reduce the signaling of loop_filter_across_tiles_enabled_flag and loop_filter_across_slices_enabled_flag, signaling of a flag indicating whether the current picture is partitioned into tiles and a flag indicating whether the current picture is partitioned into slices together with no_pic_partition_flag does not help in terms of bit reduction.

[0295] However, as described in this specification, together with the no_pic_partition_flag, the configuration for determining whether to signal the loop_filter_across_tiles_enabled_flag and the loop_filter_across_slices_enabled_flag based on the number of tiles that partition a picture and the number of slices that partition a picture enables determination of whether the loop_filter_across_tiles_enabled_flag and the loop_filter_across_slices_enabled_flag are signaled from the parsed information of the tiles and slices without an additional flag. Therefore, the technical concept described in the present disclosure can reduce the frequency of generating the corresponding flag in the bitstream in an encoding / decoding environment in which the current picture can be partitioned into tiles and / or slices, thereby reducing the size of the bitstream.

[0296] Application Implementation

[0297] Although the exemplary methods of the present disclosure are shown as a series of operations for clarity of description, it is not intended to limit the order in which the steps are performed, and the steps may be performed simultaneously or in a different order if necessary. To implement the methods according to the present disclosure, the steps described may further include other steps, may include the remaining steps in addition to some steps, or may include other additional steps in addition to some steps.

[0298] In the present disclosure, an image encoding device or image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming the execution conditions or circumstances of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is satisfied, the image encoding device or image decoding device may perform the predetermined operation after determining whether the predetermined condition is satisfied.

[0299] The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and matters described in the various embodiments may be applied independently or in combinations of two or more.

[0300] Various embodiments of the present disclosure may be implemented in hardware, firmware, software, or a combination thereof. In the case of implementing the present disclosure in hardware, the present disclosure may be implemented in an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, or the like.

[0301] In addition, the image decoding device and the image encoding device to which the embodiments of the present disclosure are applied may be included in multimedia broadcast transmission and reception devices, mobile communication terminals, home theater video devices, digital theater video devices, surveillance cameras, video chat devices, real-time communication devices such as video communication, mobile streaming devices, storage media, cameras, video on demand (VoD) service providers, OTT video (over the top video) devices, Internet streaming service providers, three-dimensional (3D) video devices, video phone video devices, medical video devices, etc., and may be used to process video signals or data signals. For example, OTT video devices may include game consoles, Blu-ray players, Internet-connected TVs, home theater systems, smart phones, tablet PCs, digital video recorders (DVRs), etc.

[0302] Figure 31 is a diagram illustrating a content streaming system to which embodiments of the present disclosure can be applied.

[0303] like Figure 31 As shown, the content streaming system applying the embodiments of the present disclosure may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0304] The encoding server compresses content input from a multimedia input device such as a smartphone, a camera, or a camcorder into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, a camera, or a camcorder directly generates a bitstream, the encoding server may be omitted.

[0305] A bitstream may be generated by applying the image encoding method or the image encoding apparatus according to the embodiment of the present disclosure, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0306] A streaming server transmits multimedia data to a user device based on a user's request via a network server. The network server acts as an intermediary to inform users of services. When a user requests a desired service from the network server, the network server delivers it 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. In this case, the control server is used to control commands and responses between devices in the content streaming system.

[0307] The streaming server can receive content from a media storage device and / or an encoding server. For example, when receiving content from an encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time.

[0308] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, tablet computers, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0309] The various servers in the content streaming system may operate as distributed servers, in which case data received from the various servers may be distributed.

[0310] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations according to the methods of various embodiments to be performed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0311] Industrial Applicability

[0312] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Determining the number of tiles in the current picture based on that the segmentation of the current picture is not restricted; Based on the number of the mosaic blocks in the current picture being multiple, obtaining a first flag for filtering the boundary of the mosaic blocks from a bitstream; determining, based on a value of the first flag, to perform filtering on the boundary of the patch belonging to the current picture; Obtaining, from the bitstream, a second flag for filtering a slice boundary based on that the partitioning of the current picture is not restricted; Based on the value of the second flag, it is determined to perform filtering on the boundary of the slice belonging to the current picture.

2. The image decoding method according to claim 1, in, obtaining a partition restriction flag for partitioning of the current picture from the bitstream, and Wherein, it is determined based on the segmentation restriction flag that the segmentation of the current picture is restricted.

3. The image decoding method according to claim 1, wherein: The number of blocks in the current picture is determined based on the block number information indicating the number of blocks used to divide the current picture.

4. The image decoding method according to claim 3, wherein: The tile number information includes information on the number of tile columns in a picture and information on the number of tile rows in the picture.

5. The image decoding method according to claim 3, wherein: The patch quantity information is obtained from the bitstream based on that the partitioning of the current picture is not restricted.

6. The image decoding method according to claim 1, in, Based on the fact that the partitioning of the current picture is not restricted, information about slices constituting the picture is obtained from the bitstream, and The second flag is obtained from the bitstream based on the information about the slice not indicating that the picture is composed of one slice.

7. The image decoding method according to claim 6, wherein: The second flag is obtained from the bitstream based on the information about the slice indicating that a rectangular slice mode is not applied to the picture.

8. The image decoding method according to claim 6, wherein: The second flag is obtained from the bitstream based on the information on the slice indicating that a sub-picture of the picture consists of only one rectangular slice.

9. The image decoding method according to claim 6, wherein: The second flag is obtained from the bitstream based on the information about the slice indicating that the number of patches in the current picture is plural.

10. The image decoding method according to claim 9, in, determining whether the slices constituting the picture are rectangular slices based on that the segmentation of the current picture is not restricted, wherein, based on whether the slice constituting the picture is a rectangular slice, determining whether a sub-picture of the picture consists of only one rectangular slice, wherein, based on the sub-picture of the picture being composed of more than one rectangular slice, information on the number of slices in the current picture is obtained from the bitstream, and Wherein, based on the information about the number of slices in the current picture, it is determined whether the number of slices in the current picture is plural.

11. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: Determining the number of tiles in the current picture based on that the segmentation of the current picture is not restricted; Determining a value of a first flag for filtering a boundary of a patch based on a number of patches in the current picture being multiple; generating a bitstream including the first flag; determining, based on the fact that the current picture is not restricted in its segmentation, whether the current picture consists of one slice as first information; as well as Based on the fact that the current picture does not consist of only one slice, a value of a second flag for filtering a boundary of the slice is determined.

12. A method for transmitting a bit stream generated by an image encoding method, the image encoding method comprising the steps of: Determining the number of tiles in the current picture based on that the segmentation of the current picture is not restricted; Determining a value of a first flag for filtering a boundary of a patch based on a number of patches in the current picture being multiple; generating a bitstream including the first flag; determining, based on the fact that the current picture is not restricted in its segmentation, whether the current picture consists of one slice as first information; as well as Based on the fact that the current picture does not consist of only one slice, a value of a second flag for filtering a boundary of the slice is determined.

Images