Image encoding and decoding method and apparatus for limiting segmentation condition of chroma block, and method for transmitting bit stream

Abstract

The present disclosure relates to an image encoding and decoding method and apparatus for limiting a segmentation condition of a chroma block, and a method for transmitting a bitstream. An image encoding / decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus includes determining a division type of a current block, dividing the current block into a plurality of lower layer blocks based on the division type, and decoding the lower layer blocks. In this case, the current block may be a chroma block, and determination of a partition type of the current block may be performed by not allowing a predetermined partition type in which a width or height of a lower block among the plurality of partition types is a predetermined value.

Description

[0001] This application is a divisional application of the patent application with application number 202080052292.7 (PCT / KR2020 / 007999) filed with the China Patent Office on January 19, 2022, with an international application date of June 19, 2020, and the invention name being “Image encoding and decoding method and device for limiting the segmentation conditions of chroma blocks and method for transmitting bit streams”. Technical Field

[0002] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to a method and apparatus for encoding / decoding an image by restricting a segmentation condition of a chroma block, 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), 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 transmitted information or bits leads to increased transmission and storage costs.

[0004] Therefore, efficient image compression techniques are 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 a method and apparatus for encoding / decoding an image using segmentation condition restrictions of chroma blocks.

[0008] Another object of the present disclosure is to provide an image encoding / decoding method and apparatus that does not signal segmentation information when a chroma block cannot be segmented.

[0009] Another object of the present disclosure is to provide a method for transmitting 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 generated by the image encoding method or apparatus according to the present disclosure.

[0011] Another object of the present disclosure is to provide a recording medium that stores a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0012] 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.

[0013] Technical Solution

[0014] According to one aspect of the present disclosure, an image decoding method performed by an image decoding device includes: determining a current block by dividing an image; obtaining prediction information of the current block; and decoding the current block by performing intra-frame prediction based on the prediction information of a specified intra-frame prediction mode.

[0015] The current block may be a chroma block, and determining the current block may be performed by segmenting a portion of the image into a segmentation type determined based on segmentation information, the segmentation information may be determined based on available segmentation types that can be used to segment the portion of the image, and the available segmentation type may be determined based on a width of the portion of the image.

[0016] Based on the prediction information of the intra prediction mode determined based on the intra prediction mode of the designated reference luminance block, the intra prediction mode of the current block may be determined based on the intra prediction information of the luminance block corresponding to the current block.

[0017] Based on the number of samples of the current block being equal to or less than 16, the prediction mode for determining the sample values ​​of the current block based on the sample values ​​of the luminance block may not be determined as the prediction mode of the current block.

[0018] Based on the width of the portion of the image being 4, a quadtree partition type and a vertical binary partition type may be excluded from the available partition types.

[0019] Based on the tree structure of the portion of the image being a dual-tree structure and the width of the portion of the image being 4, a quadtree partition type and a vertical binary partition type may be excluded from the available partition types.

[0020] Based on the width of the portion of the image being 8, a vertical trifurcated segmentation type may be excluded from the available segmentation types.

[0021] Based on the tree structure of the portion of the image being a dual-tree structure and the width of the portion of the image being 8, a vertical trifurcated segmentation type may be excluded from the available segmentation types.

[0022] Based on the image decoding apparatus performing decoding on a pixel set consisting of a 1×4 matrix per processing unit and the height of the portion of the image being 4, the quadtree partition type and the horizontal binary partition type may be excluded from the available partition types.

[0023] Based on the image decoding device performing decoding on a pixel set consisting of a 1×4 matrix per processing unit and the height of the portion of the image being 4, the horizontal trifurcated partition type may be excluded from the available partition types.

[0024] The width of the portion of the image may be determined based on a width of a luminance portion corresponding to the portion of the image and a color format.

[0025] The width of the portion of the image may be determined as a value obtained by dividing a width of a luma portion corresponding to the portion of the image by a component ratio of chroma samples and luma samples derived based on the color format.

[0026] According to one aspect of the present disclosure, an image decoding apparatus may include a memory and at least one processor. The at least one processor may determine a current block by segmenting an image; obtain prediction information for the current block; and decode the current block by performing intra-frame prediction based on the prediction information specifying an intra-frame prediction mode. The current block may be a chroma block, a portion of the image may be segmented into a segmentation type determined based on segmentation information, the segmentation information may be determined based on available segmentation types that can be used to segment the portion of the image, and the available segmentation types may be determined based on the width of the portion of the image.

[0027] According to an aspect of the present disclosure, an image encoding method performed by an image encoding device may include: determining a current block by dividing an image; determining a prediction mode of the current block; and encoding prediction information specifying the intra-frame prediction mode based on the determined prediction mode being an intra-frame prediction mode.

[0028] The current block may be a chroma block, and determining the current block may be performed by partitioning a portion of the image into a partitioning type determined based on available partitioning types that can be used to partition the portion of the image, and the available partitioning type may be determined based on a width of the portion of the image.

[0029] The available segmentation types may be determined by limiting the use of segmentation types having a width less than 4 as a result of the width of the portion dividing the image.

[0030] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding apparatus or the image encoding method of the present disclosure.

[0031] In addition, a computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0032] The features described above with respect to a brief summary of 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.

[0033] Beneficial effects

[0034] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0035] According to the present disclosure, an image encoding / decoding method and apparatus can be provided that reduces bit rate by not signaling segmentation information of a chroma block when a predetermined segmentation condition of a chroma block is restricted and a predetermined segmentation type is accordingly restricted.

[0036] 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.

[0037] 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.

[0038] Furthermore, according to the present disclosure, a recording medium can be provided that stores a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0039] Those skilled in the art will appreciate that the effects that can be achieved by the present disclosure are not limited to what has 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

[0040] Figure 1 FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment of the present disclosure is applicable.

[0041] Figure 2 FIG2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0042] Figure 3 FIG. 1 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure is applicable.

[0043] Figure 4 is a diagram of a segmentation structure of an image according to an embodiment.

[0044] Figure 5 is a view illustrating an embodiment of partition types of blocks according to a multi-type tree structure.

[0045] Figure 6 is a schematic diagram illustrating a signaling mechanism of block partitioning information in a quadtree with a nested multi-type tree structure according to the present invention.

[0046] Figure 7 is a diagram illustrating an embodiment in which a CTU is partitioned into a plurality of CUs.

[0047] Figure 8 is a view illustrating an embodiment of a redundant partition pattern.

[0048] Figure 9 is a flowchart illustrating a video / image encoding method based on inter-frame prediction.

[0049] Figure 10 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0050] Figure 11 is a flowchart illustrating a video / image decoding method based on inter-frame prediction.

[0051] Figure 12 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0052] Figure 13 is a view illustrating neighboring blocks that may be used as spatial merging candidates according to an embodiment.

[0053] Figure 14 is a view schematically illustrating a merge candidate list construction method according to an embodiment.

[0054] Figure 15 is a view schematically illustrating a motion vector predictor candidate list construction method according to an embodiment.

[0055] Figure 16 is a view illustrating a syntax structure for transmitting an MVD from an image encoding device to an image decoding device according to an embodiment.

[0056] Figure 17 is a flowchart illustrating an IBC-based video / image encoding method according to an embodiment.

[0057] Figure 18 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image encoding method according to an embodiment.

[0058] Figure 19 is a flowchart illustrating an IBC-based video / image decoding method according to an embodiment.

[0059] Figure 20 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image decoding method according to an embodiment.

[0060] Figure 21 is a diagram illustrating a pipeline delay problem according to an embodiment.

[0061] Figure 22 is a view illustrating experimental data measured in a case where splitting of a chroma block into 2×N chroma blocks is restricted when a current block has a dual-tree structure.

[0062] Figure 23 is a view illustrating a method of determining whether vertical trifurcated splitting (SPLIT_TT_VER) is allowed for a current block by a decoding apparatus according to an embodiment.

[0063] Figure 24 is a view illustrating a method of determining whether horizontal trifurcated splitting (SPLIT_TT_HOR) is allowed for a current block by a decoding apparatus according to an embodiment.

[0064] Figure 25 is a view illustrating a method of determining whether horizontal binary splitting (SPLIT_BT_HOR) is allowed for a current block by a decoding apparatus according to an embodiment.

[0065] Figure 26 is a view illustrating a method of determining whether vertical binary splitting (SPLIT_BT_VER) is allowed for a current block by a decoding apparatus according to an embodiment.

[0066] Figure 27 is a view illustrating a method of determining whether quadtree partitioning is allowed for a current block by a decoding apparatus according to an embodiment.

[0067] Figure 28 is a diagram illustrating experimental results obtained in the case where only the first restriction condition is applied.

[0068] Figure 29 is a diagram illustrating experimental results obtained in the case where all of the first, second, and third restriction conditions are applied.

[0069] Figure 30 is a flowchart illustrating a method of encoding an image by an encoding apparatus according to an embodiment.

[0070] Figure 31 is a view illustrating a syntax for bitstream signaling information about partitioning of a current block according to an embodiment.

[0071] Figure 32 is a flowchart illustrating a method of decoding an image by a decoding apparatus according to an embodiment.

[0072] Figure 33 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0073] 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.

[0074] 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.

[0075] In this 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.

[0076] In the present disclosure, the terms first, second, etc. are 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.

[0077] 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 specifically stated, embodiments in which these components are integrated or distributed are also included in the scope of this disclosure.

[0078] 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.

[0079] 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.

[0080] In this disclosure, a "picture" generally refers to a unit representing an image within a specific time period. A slice or tile is a coding unit that constitutes a portion of a picture. A picture can be composed of one or more slices or tiles. In addition, a slice or tile can include one or more coding tree units (CTUs).

[0081] In this disclosure, "pixel" or "picture element (pel)" may refer to the smallest unit constituting a picture (or image). Furthermore, "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 luma component or only a pixel / pixel value of a chroma component.

[0082] In this disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific region of an image and information related to the region. In some cases, the unit may be used interchangeably with terms such as "sample array," "block," or "region." In general, an M×N block may include M columns and N rows of samples (or a sample array) or a set (or array) of transform coefficients.

[0083] In the present disclosure, the term "current block" may refer to one of the following: "current coding block," "current coding unit," "coding 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."

[0084] 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."

[0085] In the present disclosure, the slash " / " or "," may be interpreted as indicating "and / or". For example, "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".

[0086] In this disclosure, the term "or" should be interpreted to mean "and / or." For example, the expression "A or B" may include 1) only "A," 2) only "B," or 3) both "A and B." In other words, in this disclosure, "or" should be interpreted to mean "additionally or alternatively."

[0087] Video Compilation System Overview

[0088] Figure 1 is a diagram schematically illustrating a video coding system according to the present disclosure.

[0089] The video coding system according to an embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or stream.

[0090] The encoding device 10 according to an embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to an embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be referred to as a video / image encoding unit, and the decoding unit 22 may be referred to as a video / image decoding unit. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display, and the display may be configured as a separate device or an external component.

[0091] The video source generator 11 can obtain videos / images by capturing, synthesizing, or generating videos / 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 containing previously captured videos / images, etc. The video / image generation device may include, for example, a computer, a tablet computer, or a smartphone, and may (electronically) generate videos / images. 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.

[0092] The encoding unit 12 can encode the input video / image. For compression and coding efficiency, the encoding unit 12 can perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 can output the encoded data (encoded video / image information) in the form of a bitstream.

[0093] Transmitter 13 can transmit the encoded video / image information or data output in the form of a bitstream to receiver 21 of decoding device 20 via a digital storage medium or network in the form of a file or stream. Digital storage media can include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. Transmitter 13 can include components for generating media files in a predetermined file format and can also include components for transmission via a broadcast / communication network. Receiver 21 can extract / receive the bitstream from the storage medium or network and transmit the bitstream to decoding unit 22.

[0094] The decoding unit 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoding unit 12 , such as dequantization, inverse transformation, and prediction.

[0095] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed on a display.

[0096] Overview of Image Coding Device

[0097] Figure 2 FIG. 1 is a diagram schematically illustrating an image encoding device to which an embodiment of the present disclosure is applicable.

[0098] like Figure 2 As shown, the image encoding device 100 may include an image partitioner 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.

[0099] 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.

[0100] The image partitioner 110 may partition 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 may be referred to as a coding unit (CU). A coding unit may be obtained by recursively partitioning a coding tree unit (CTU) or a largest coding unit (LCU) according to a quadtree, binary tree, or ternary tree (QT / BT / TT) structure. For example, a coding unit may be partitioned into multiple coding units of a greater depth based on a quadtree, binary tree, and / or ternary tree structure. The quadtree structure may be applied first, followed by a binary tree and / or ternary tree structure. The coding process according to the present disclosure may be performed based on a final coding unit that is no longer partitioned. The largest coding unit may be used as the final coding unit, or a coding unit of a greater depth obtained by partitioning the largest coding unit may be used as the final coding unit. The coding process may include prediction, transform, and reconstruction processes, which will be described later. As another example, the processing unit of the coding process may be a prediction unit (PU) or a transform unit (TU). The prediction unit and the transform unit may be split 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.

[0101] The prediction unit (inter-frame prediction unit 180 or intra-frame prediction unit 185) can 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 can determine whether to apply intra-frame prediction or inter-frame prediction based on the current block or CU. The prediction unit can generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information about the prediction can be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0102] 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.

[0103] 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 in a reference picture. To reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation of motion information between neighboring blocks and the current block. Motion information can include a motion vector and a reference picture index. It can also include information about the inter-frame prediction direction (e.g., L0 prediction, L1 prediction, or Bi prediction). In inter-frame prediction, neighboring blocks can include spatially neighboring blocks in the current picture and temporally neighboring blocks in a reference picture. The reference picture containing the reference block and the reference picture containing 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 containing temporally neighboring blocks can be referred to as a collocated picture (colPic). For example, the inter-frame prediction unit 180 can configure a motion information candidate list based on the neighboring blocks and generate information specifying 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 skip mode and merge mode, the inter-frame prediction unit 180 can use the motion information of the neighboring blocks as the motion information of the current block. In skip mode, unlike merge mode, a residual signal may not be transmitted. In motion vector prediction (MVP) mode, the motion vector of the neighboring blocks may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding a motion vector difference and an indicator of the motion vector predictor. The motion vector difference may refer to the difference between the motion vector of the current block and the motion vector predictor.

[0104] The prediction unit can generate a prediction signal based on various prediction methods and techniques described below. For example, the prediction unit can apply not only intra prediction or inter prediction, but also both intra and inter prediction simultaneously to predict the current block. This prediction method of simultaneously applying both intra and inter prediction to predict the current block is referred to as combined inter and intra prediction (CIIP). Furthermore, the prediction unit can perform intra block copying (IBC) to predict the current block. Intra block copying can be used for content image / video coding, such as screen content coding (SCC), for gaming. 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 within the current picture, but can be similar to inter prediction in that the reference block is derived within the current picture. That is, IBC can use at least one of the inter prediction techniques described in this disclosure. IBC essentially performs prediction within the current picture, but can be similar to inter prediction in that the reference block is derived within the current picture. That is, IBC may use at least one of the inter-frame prediction techniques described in this disclosure.

[0105] 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 transmitted to the transformer 120.

[0106] Transformer 120 can 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). 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. Furthermore, the transform process can be applied to square pixel blocks of uniform size or to blocks of variable size other than square.

[0107] 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 in block form into a one-dimensional vector form based on a coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0108] 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., syntax element values, etc.) in addition to quantized transform coefficients, either together or separately. The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream using a Network Abstraction Layer (NAL) as a unit. 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). Furthermore, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in this disclosure may be encoded through the above-described encoding process and included in the bitstream.

[0109] The bitstream may be transmitted over a network or 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) for transmitting the signal output from the entropy encoder 190 and / or a storage unit (not shown) for storing the signal may be included as an internal / external element of the image encoding device 100. Alternatively, the transmitter may be provided as a component of the entropy encoder 190.

[0110] 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.

[0111] Adder 155 adds the reconstructed residual signal to the prediction signal output from inter-frame prediction unit 180 or intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed image, 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. Adder 155 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can also be used for inter-frame prediction of the next picture through filtering as described below.

[0112] 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 transmit 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.

[0113] The modified reconstructed picture transferred 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 device 100, prediction mismatch between the image encoding device 100 and the image decoding device may be avoided and encoding efficiency may be improved.

[0114] 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 the motion information of the block from which the motion information in the current picture was derived (or encoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be transmitted to the inter-frame prediction unit 180 and used as the motion information of the spatially neighboring block or the motion information of the temporally neighboring block. The memory 170 may store the reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0115] Overview of Image Decoding Device

[0116] Figure 3 FIG. 1 is a diagram schematically illustrating an image decoding device to which an embodiment of the present disclosure is applicable.

[0117] like Figure 3As 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.

[0118] 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.

[0119] 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 may be reconstructed using processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using the processing unit employed in the image encoding device. Thus, the processing unit for decoding may be, for example, a coding unit. A coding unit may be obtained by partitioning the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0120] The image decoding apparatus 200 may 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 information required for image reconstruction (or picture reconstruction) (e.g., video / image information). The video / image information may also include information about various parameter sets, such as the Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), or Video Parameter Set (VPS). Furthermore, the video / image information may also include general constraint information. The image decoding device may also decode the picture based on the parameter set information and / or general constraint information. The signaled / received information and / or syntax elements described in this 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 residual transform coefficients. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, uses information about the target syntax element to be decoded, decoded information about neighboring blocks and the target block to be decoded, or information about symbols / bins decoded at a previous stage to determine a context model. Based on the determined context model, the bins are arithmetically decoded to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method updates the context model by applying the decoded symbol / bin information to the context model for the next symbol / bin. Prediction-related information from the information decoded by the entropy decoder 210 is provided to the prediction units (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual values ​​entropy-decoded by the entropy decoder 210, namely, the quantized transform coefficients and related parameter information, are input to the dequantizer 220. Furthermore, information regarding filtering from the information decoded by the entropy decoder 210 is provided to the filter 240. Meanwhile, a receiver (not shown) for receiving a signal output from the image encoding device may be further configured as an internal / external element of the image decoding device 200 , or the receiver may be a component of the entropy decoder 210 .

[0121] Meanwhile, 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 an intra-frame prediction unit 265.

[0122] 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.

[0123] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0124] 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 prediction information output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0125] 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) described later.

[0126] 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.

[0127] 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 in 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 can include a motion vector and a reference picture index. 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. For example, the inter-frame prediction unit 260 can configure a motion information candidate list based on the neighboring blocks and derive the 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 prediction information can include information indicating the inter-frame prediction mode for the current block.

[0128] The adder 235 can generate a reconstructed block 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-frame prediction unit 265). 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 description of the adder 155 also applies to the adder 235. The adder 235 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can also be used for inter-frame prediction of the next picture through filtering as described below.

[0129] 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 image by applying various filtering methods to the reconstructed image, and store the modified reconstructed image 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.

[0130] 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 the motion information of the block from which the motion information in the current picture was derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information can be transmitted to the inter-frame prediction unit 260 for use as the motion information of the spatially neighboring block or the motion information of the temporally neighboring block. The memory 250 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0131] 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 equally or correspondingly applied to the filter 240, the inter-frame prediction unit 260 and the intra-frame prediction unit 265 of the image decoding device 200.

[0132] Overview of Image Partitioning

[0133] The video / image coding method according to the present disclosure can be performed based on the image partition structure as follows. Specifically, the prediction, residual processing ((inverse) transform, (de)quantization, etc.), syntax element coding and filtering processes described later can be performed based on the CTU, CU (and / or TU, PU) derived from the image partition structure. The image can be partitioned in block units and the block partitioning process can be performed in the image partitioner 110 of the encoding device. The partition related information can be encoded by the entropy encoder 190 and sent to the decoding device in the form of a bitstream. The entropy decoder 210 of the decoding device can derive the block partition structure of the current picture based on the partition related information obtained from the bitstream, 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.

[0134] 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 corresponding coding tree blocks of chroma samples. For example, for a picture containing three sample arrays, a CTU may include one N×N block of luma samples and two corresponding blocks of chroma samples.

[0135] Overview of CTU Partitions

[0136] As described above, a coding unit can be obtained by recursively partitioning a coding tree unit (CTU) or a largest coding unit (LCU) according to a quadtree / binarytree / ternarytree (QT / BT / TT) structure. For example, a CTU can be first partitioned into a quadtree structure. Thereafter, the leaf nodes of the quadtree structure can be further partitioned using a multi-type tree structure.

[0137] Partitioning according to a quadtree means that the current CU (or CTU) is equally partitioned into four. Through quadtree partitioning, the current CU can be partitioned into four CUs of the same width and height. When the current CU is no longer partitioned into a quadtree structure, it corresponds to a leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure can no longer be partitioned and can be used as the final coding unit described above. Alternatively, the CU corresponding to the leaf node of the quadtree structure can be further partitioned using a multi-type tree structure.

[0138] Figure 5 is a diagram illustrating an embodiment of partition types of a block according to a multi-type tree structure. Partitioning according to the multi-type tree structure may include two types of partitioning according to a binary tree structure and two types of partitioning according to a ternary tree structure.

[0139] 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 , 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 splitting, two CUs with a height half of the current CU and the same width as the current CU can be generated.

[0140] Two types of splits according to the triad structure may include vertical triad split (SPLIT_TT_VER) and horizontal triad split (SPLIT_TT_HOR). In vertical triad split (SPLIT_TT_VER), the current CU is split in a vertical direction at a ratio of 1:2:1. Figure 5 As shown in the figure, through vertical three-pronged splitting, two CUs with the same height as the current CU and a width of 1 / 4 of the current CU width, and a CU with the same height as the current CU and a width of half the current CU width can be generated. In horizontal three-pronged splitting (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 splitting, two CUs with a height of 1 / 4 of the current CU and the same width as the current CU, and a CU with a height of half the current CU and the same width as the current CU can be generated.

[0141] Figure 6 is a diagram illustrating a signaling mechanism of block partition information in a quadtree having a nested multi-type tree structure according to the present disclosure.

[0142] Here, the CTU is considered the root node of the quadtree and is initially partitioned into a quadtree structure. Information (e.g., qt_split_flag) indicating whether quadtree splitting is performed on the current CU (CTU or node (QT_node) of the quadtree) is signaled. For example, when qt_split_flag has a first value (e.g., "1"), the current CU can be quadtree partitioned. In addition, when qt_split_flag has a second value (e.g., "0"), the current CU is not quadtree partitioned but becomes a leaf node (QT_leaf_node) of the quadtree. Each quadtree leaf node can then be further partitioned into a multi-type tree structure. That is, a 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) is signaled to specify whether the current node is additionally partitioned. If the corresponding node is additionally partitioned (for example, if the first flag is 1), a second flag (e.g., Mtt_split_cu_vertical_flag) may be signaled to specify the split direction. For example, the split direction may be vertical if the second flag is 1, or horizontal if the second flag is 0. A third flag (e.g., Mtt_split_cu_binary_flag) may then be signaled to specify whether the split type is binary or ternary. For example, the split type may be binary when the third flag is 1, or ternary when the third flag is 0. The nodes of the multi-type tree obtained through binary or ternary splitting may be further partitioned into a multi-type tree structure. However, the nodes of the multi-type tree may not be partitioned into a quadtree structure. If the first flag is 0, the corresponding node of the multi-type tree is no longer partitioned and becomes a leaf node (MTT_leaf_node) of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree may be used as the final coding unit described above.

[0143] Based on mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree split mode (MttSplitMode) of a CU may be derived as shown in the following Table 1. In the following description, the multi-type tree split mode may be referred to as a multi-tree split type or a split type.

[0144] [Table 1]

[0145]

[0146] 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 In FIG, a block edge 710 in bold represents a quadtree partition, while the remaining edges 720 represent a multi-type tree partition. A CU may correspond to a coding block (CB). In an embodiment, a CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples.

[0147] The chroma component (sample) CB or TB size can be derived based on the luma component (sample) CB or TB size based on the component ratio according to the color format of the picture / image (chroma format, such as 4:4:4, 4:2:2, 4:2:0, etc.). In the case of a 4:4:4 color format, the chroma component CB / TB size can 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 can be set to half the width of the luma component CB / TB, and the height of the chroma component CB / TB can 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 can be set to half the width of the luma component CB / TB, and the height of the chroma component CB / TB can be set to half the height of the luma component CB / TB.

[0148] 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 128x128 to 4x4, 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 64x64 to 2x2.

[0149] Meanwhile, 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 generally represents the luma component (sample) transform block (TB) size.

[0150] The TU size can be derived based on the maximum allowed TB size maxTbSize, which is 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 64x64 and the maximum allowed chroma TB size can be 32x32. If the width or height of the CB partitioned according to the tree structure is larger than the maximum transform width or height, the CB can be automatically (or implicitly) partitioned until the TB size limits in the horizontal and vertical directions are met.

[0151] 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 one CU (or CB) area, and in this case, multiple TUs or (TBs) can share the same intra prediction mode / type.

[0152] Meanwhile, for a quadtree coding tree scheme with nested multi-type trees, the following parameters may be signaled from the encoding apparatus to the decoding apparatus as SPS syntax elements: for example, at least one of the following parameters: CTU size representing the size of the root node of the quadtree, MinQTSize representing the minimum allowed size of a quadtree leaf node, MaxBtSize representing the maximum allowed size of a binary tree root node, MaxTtSize representing the maximum allowed size of a ternary tree root node, MaxMttDepth representing the maximum allowed depth of a multi-type tree partition starting from a quadtree leaf node, MinBtSize representing the minimum allowed size of a binary tree leaf node, or MinTtSize representing the minimum allowed size of a ternary tree leaf node.

[0153] As an example using a 4:2:0 chroma format, the CTU size can be set to 128x128 luma blocks and two 64x64 chroma blocks corresponding to these luma blocks. In this case, MinOTSize can be set to 16x16, MaxBtSize can be set to 128x128, MaxTtSize can be set to 64x64, MinBtSize and MinTtSize can be set to 4x4, 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. Quadtree leaf nodes can range in size from 16x16 (e.g., MinOTSize) to 128x128 (e.g., the CTU size). If the leaf QT node is 128x128, it may not be additionally partitioned into a binary / ternary tree. This is because, even if partitioned, it exceeds MaxBtSize and MaxTtSize (e.g., 64x64). In other cases, the leaf QT node may be further partitioned 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 partitioning may not be considered. If the width of the multi-type tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, further horizontal partitioning may not be considered. If the height of the multi-type tree node is equal to MinBtSize and less than or equal to 2xMinTtSize, further vertical partitioning may not be considered. When partitioning is not considered, the encoding device may skip signaling of the partition information. In this case, the decoding device may derive partition information having a predetermined value.

[0154] At the same time, a CTU may include a coding block of luma samples (hereinafter referred to as a "luminance block") and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as "chroma blocks"). The above-mentioned coding tree scheme can be applied equally or separately to the luma blocks and chroma blocks of the current CU. Specifically, the luma blocks and chroma blocks in a CTU can be partitioned into the same block tree structure, and in this case, the tree structure is represented as SINGLE_TREE. Alternatively, the luma blocks and chroma blocks in a CTU can be partitioned into separate block tree structures, and in this case, the tree structure can be represented as DUAL_TREE. That is, when a CTU is partitioned into dual trees, a block tree structure for luma blocks and a block tree structure for chroma blocks can exist separately. In this case, the block tree structure for luma blocks can be referred to as DUAL_TREE_LUMA, and the block tree structure for chroma components can be referred to as DUAL_TREE_CHROMA. For P and B slices / tile groups, the luma blocks and chroma blocks in a CTU can be restricted to have the same coding tree structure. However, for I slices / tiles, luma blocks and chroma blocks can have separate block tree structures. If a separate block tree structure is applied, luma CTBs can be partitioned into CUs based on a specific coding tree structure, and chroma CTBs can be partitioned into chroma CUs based on another coding tree structure. In other words, this means that a CU in an I slice / tile 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 / tile can include blocks for three color components (one luma component and two chroma components).

[0155] 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 can be interpreted as concepts included in the multi-partition tree (MPT) structure, and the CU can be interpreted as being partitioned using the QT structure and the MPT structure. In the example of partitioning a CU 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 whether a leaf node of the QT structure is partitioned into vertically or horizontally can be signaled to determine the partition structure.

[0156] In another example, the CU may be partitioned in a manner different from the QT structure, the BT structure, or the TT structure. That is, instead of partitioning a CU of a lower depth into 1 / 4 of a CU of a higher depth according to the QT structure, partitioning a CU of a lower depth into 1 / 2 of a CU of a higher depth according to the BT structure, or partitioning 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 partitioned 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 partitioning the CU is not limited thereto.

[0157] A quadtree coding block structure with multiple tree types can provide a very flexible block partition structure. Due to the supported partition types in the multiple tree types, different partition patterns can potentially produce the same coding block structure in some cases. By limiting the occurrence of such redundant partition patterns in encoding and decoding devices, the amount of partition information data can be reduced.

[0158] For example, Figure 8 The following shows the redundant partitioning patterns that may appear in binary tree partitioning and ternary tree partitioning. Figure 8 As shown, the consecutive binary partitions 810 and 820 for one direction of the two-step level have the same coding block structure as the binary partition for the center partition after the ternary partition. In this case, the binary tree partition for the center blocks 830 and 840 of the ternary tree partition can be prohibited. This prohibition applies to CUs of all pictures. When this particular partition is prohibited, the signaling of the corresponding syntax element can be modified by reflecting this prohibition, thereby reducing the number of bits for signaling the partition. For example, Figure 8 As shown in the example shown in , when binary tree partitioning for the center block of a CU is prohibited, the syntax element mtt_split_cu_binary_flag specifying whether the partitioning is binary or ternary is not signaled and its value may be derived as 0 by the decoding device.

[0159] Overview of Inter-frame Prediction

[0160] Hereinafter, inter prediction according to the present disclosure will be described.

[0161] The prediction unit of the image encoding / decoding device according to the present disclosure can perform inter-frame prediction on a block-by-block basis to derive prediction samples. Inter-frame prediction may refer to predictions derived in a manner that depends on data elements (e.g., sample values, motion information, etc.) from pictures other than the current picture. When inter-frame prediction is applied to the current block, the prediction block (prediction block or prediction sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector in 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 correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include information on the inter-frame prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). When inter-frame prediction is applied, neighboring blocks may include spatially neighboring blocks in the current picture and temporally neighboring blocks in reference pictures. The reference picture comprising the reference block and the reference picture comprising the temporally neighboring blocks may be the same or different. A temporally neighboring block may be referred to as a collocated reference block, a collocated CU (ColCU), or a colBlock, and a reference picture including the temporally neighboring block may be referred to as a collocated picture (colPic) or a colPicture. For example, a motion information candidate list may be constructed based on neighboring blocks of the current block, and a flag or index information specifying which candidate is selected (used) may be signaled to derive a motion vector and / or reference picture index for the current block.

[0162] Inter-frame prediction can be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the motion information of the current block can be equal to the motion information of the selected neighboring block. In the case of skip mode, unlike merge mode, a residual signal may not be sent. In the case of motion information prediction (MVP) mode, the motion vector of the selected neighboring block can be used as a motion vector predictor and the motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference. In the present disclosure, MVP mode may have the same meaning as advanced motion vector prediction (AMVP).

[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, while 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 and L1 motion vectors may be referred to as Bi prediction. Here, the L0 motion vector may specify a motion vector associated with reference picture list L0 (L0), while the L1 motion vector may specify 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, while reference picture list L1 may include pictures following the current picture in output order. The preceding picture may be referred to as a forward (reference) picture, while 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 reference picture list L0, the previous picture may be indexed first, followed by the subsequent picture. Reference picture list L1 may also include pictures preceding the current picture in output order as reference pictures. In this case, within reference picture list L1, the subsequent picture may be indexed first, followed by the previous picture. Here, the output order may correspond to the picture order count (POC) order.

[0164] Figure 9 is a flowchart illustrating a video / image encoding method based on inter-frame prediction.

[0165] Figure 10 is a view illustrating a configuration of the inter prediction unit 180 according to the present disclosure.

[0166] Figure 9 The encoding method can be Figure 2 The image encoding device may be performed. Specifically, step S610 may be performed by the inter-frame prediction unit 180, and step S620 may be performed by the residual processor. Specifically, step S620 may be performed by the subtractor 115. Step S630 may be performed by the entropy encoder 190. The prediction information of step S630 may be derived by the inter-frame prediction unit 180, and the residual information of step S630 may be derived by the residual processor. The residual information is information about the residual samples. The residual information may include information about the quantized transform coefficients for the residual samples. As described above, the residual samples may be derived as transform coefficients by the transformer 120 of the image encoding device, and the transform coefficients may be derived as quantized transform coefficients by the quantizer 130. The information about the quantized transform coefficients may be encoded by the entropy encoder 190 through the residual coding process.

[0167] The image encoding device may perform inter-frame prediction on the current block (S610). The image encoding device may derive the inter-frame prediction mode and motion information of the current block and generate prediction samples of the current block. Here, the inter-frame prediction mode determination, motion information derivation, and prediction sample generation processes may be performed simultaneously or any one of them may be performed before the other process. For example, Figure 10 As shown, the inter-frame prediction unit 180 of the image coding apparatus may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. The prediction mode determination unit 181 may determine the prediction mode for the current block, the motion information derivation unit 182 may derive the motion information for the current block, and the prediction sample derivation unit 183 may derive the prediction sample for the current block. For example, the inter-frame prediction unit 180 of the image coding apparatus may use motion estimation to search for blocks similar to the current block within a predetermined area (search area) of a reference picture and derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or minimum value. Based on this, the inter-frame prediction unit 180 may derive a reference picture index specifying the reference picture in which the reference block is located, and a motion vector may be derived based on the positional difference between the reference block and the current block. The image coding apparatus may determine a prediction mode to be applied to the current block from among various prediction modes. The image coding apparatus may compare the rate-distortion (RD) costs for the various prediction modes and determine the optimal prediction mode for the current block. However, the method by which the image coding apparatus determines the prediction mode for the current block is not limited to the above example, and various methods may be used.

[0168] For example, when skip mode or merge mode is applied to the current block, the image encoding device may derive merge candidates from neighboring blocks of the current block and construct a merge candidate list using the derived merge candidates. Furthermore, the image encoding device may derive a reference block whose difference with the current block is equal to or less than a predetermined criterion or minimum value from among the reference blocks specified 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 specifying the selected merge candidate may be generated and signaled to the image decoding device. The motion information of the selected merge candidate may be used to derive the motion information of the current block.

[0169] As another example, when MVP mode is applied to the current block, the image encoding device may derive motion vector predictor (MVP) candidates from neighboring blocks of the current block and use the derived MVP candidates to construct an MVP candidate list. Furthermore, the image encoding device may use the motion vector of an MVP candidate selected from among the MVP candidates included in the MVP candidate list as the MVP for the current block. In this case, for example, the motion vector of a reference block derived through the aforementioned motion estimation may be used as the motion vector for the current block, and the current block with the motion vector that has the smallest difference with the motion vector of the current block among the MVP candidates may be the selected MVP candidate. A motion vector difference (MVD) may be derived as the difference obtained by subtracting the MVP from the motion vector of the current block. In this case, index information specifying the selected MVP candidate and information regarding the MVD may be signaled to the image decoding device. Furthermore, when MVP mode is applied, the value of a reference picture index may be constructed as reference picture index information and separately signaled to the image decoding device.

[0170] The image encoding apparatus may derive residual samples based on the predicted samples (S620). The image encoding apparatus may derive residual samples by comparing the original samples of the current block with the predicted samples. For example, the residual samples may be derived by subtracting the corresponding predicted samples from the original samples.

[0171] The image encoding device may encode image information including prediction information and residual information (S630). The image 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) and information regarding motion information as information related to the prediction process. Among the prediction mode information, the skip flag specifies whether skip mode applies to the current block, while the merge flag specifies whether merge mode applies to the current block. Alternatively, the prediction mode information may specify one of multiple prediction modes, such as a mode index. When the skip flag and the merge flag are 0, it can be determined that MVP mode applies to the current block. The information regarding motion information may include candidate selection information (e.g., a merge index, an MVP flag, or an MVP index), which is used to derive a motion vector. Among the candidate selection information, the merge index may be signaled when the merge mode applies to the current block and may be used to select one of the merge candidates included in the merge candidate list. Among the candidate selection information, the MVP flag or MVP index may be signaled when the MVP mode applies to the current block and may be used to select one of the MVP candidates in the MVP candidate list. In addition, the information about motion information may include information about the MVD and / or reference picture index information. In addition, the information about motion information may include information specifying whether L0 prediction, L1 prediction, or Bi prediction is applied. The residual information is information about residual samples. The residual information may include information about quantized transform coefficients used for the residual samples.

[0172] The output bit stream may be stored in a (digital) storage medium and transmitted to the image decoding device or may be transmitted to the image decoding device via a network.

[0173] As described above, the image encoding device can generate a reconstructed picture (a picture including reconstructed samples and reconstructed blocks) based on reference samples and residual samples. This is to allow the image encoding device to derive the same prediction result as the prediction result performed by the image decoding device, thereby improving coding efficiency. Therefore, the image encoding device can store the reconstructed picture (or reconstructed samples and reconstructed blocks) in memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0174] Figure 11 is a flowchart illustrating a video / image decoding method based on inter-frame prediction.

[0175] Figure 12 is a view illustrating a configuration of the inter prediction unit 260 according to the present disclosure.

[0176] The image decoding device may perform an operation corresponding to the operation performed by the image encoding device. The image decoding device may perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0177] Figure 11 The decoding method can be obtained by Figure 3 The image decoding device of FIG. 8 is performed by the inter-frame prediction unit 260. Steps S810 to S830 can be performed by the inter-frame prediction unit 260, and the prediction information of step S810 and the residual information of step S840 can be obtained from the bitstream by the entropy decoder 210. The residual processor of the image decoding device can derive residual samples of the current block based on the residual information (S840). Specifically, the dequantizer 220 of the residual processor can perform dequantization based on the dequantized transform coefficients derived according to the residual information to derive transform coefficients, and the inverse transformer 230 of the residual processor can perform inverse transform on the transform coefficients to derive residual samples of the current block. Step S850 can be performed by the adder 235 or the reconstructor.

[0178] Specifically, the image decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S810).The image decoding apparatus may determine which inter prediction mode is applicable to the current block based on prediction mode information in the prediction information.

[0179] For example, whether skip mode is applicable to the current block can be determined based on a skip flag. Furthermore, whether merge mode or MVP mode is applicable to the current block can be determined based on a merge flag. Alternatively, one of various inter-prediction mode candidates can be selected based on a mode index. Inter-prediction mode candidates can include skip mode, merge mode, and / or MVP mode, or can include various inter-prediction modes described below.

[0180] The image decoding device may derive motion information for the current block based on the determined inter-frame prediction mode (S820). For example, when skip mode or merge mode is applicable to the current block, the image decoding device may construct a merge candidate list (described below) and select one of the merge candidates included in the merge candidate list. This selection may be performed based on the candidate selection information (merge index) described above. The motion information of the selected merge candidate may be used to derive motion information for the current block. For example, the motion information of the selected merge candidate may be used as the motion information for the current block.

[0181] As another example, when the MVP mode is applied to the current block, the image decoding device may construct an MVP candidate list and use the motion vector of an MVP candidate selected from the MVP candidates included in the MVP candidate list as the MVP of the current block. This selection may be performed based on the candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the MVD information, and the motion vector of the current block may be derived based on the MVP and MVD of the current block. Furthermore, 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 for inter-frame prediction of the current block.

[0182] The image decoding apparatus may generate prediction samples for the current block based on the motion information of the current block (S830). In this case, a reference picture may be derived based on the reference picture index of the current block, and the prediction samples for the current block may be derived using samples of the reference block indicated by the motion vector of the current block in the reference picture. In some cases, a prediction sample filtering process may also be performed on all or some of the prediction samples for the current block.

[0183] For example, Figure 12 As shown, the inter-frame prediction unit 260 of the image decoding apparatus may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. In the inter-frame prediction unit 260 of the image decoding apparatus, the prediction mode determination unit 261 may determine a prediction mode for a current block based on received prediction mode information, the motion information derivation unit 262 may derive motion information (such as a motion vector and / or a reference picture index) of the current block based on the received motion information, and the prediction sample derivation unit 263 may derive a prediction sample for the current block.

[0184] The image decoding apparatus may generate residual samples for the current block based on the received residual information (S840). The image decoding apparatus may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and generate a reconstructed picture based thereon (S850). Thereafter, the in-loop filtering process is applied to the reconstructed picture as described above.

[0185] As described above, the inter-frame prediction process may include determining an inter-frame prediction mode, deriving motion information based on the determined prediction mode, and performing prediction (generating prediction samples) based on the derived motion information. As described above, the inter-frame prediction process may be performed by an image encoding device and an image decoding device.

[0186] Hereinafter, the steps of deriving motion information according to the prediction mode will be described in more detail.

[0187] As described above, inter-frame prediction can be performed using the motion information of the current block. The image encoding device can derive optimal motion information for the current block through a motion estimation process. For example, the image encoding device can use the original block in the original picture of the current block in fractional pixel units to search for a similar reference block with high correlation within a predetermined search range in the reference picture, and use it to derive motion information. The similarity of the blocks can be calculated based on the sum of absolute differences (SAD) between the current block and the reference block. In this case, the motion information can be derived based on the reference block with the smallest SAD in the search area. The derived motion information can be signaled to the image decoding device according to various methods based on the inter-frame prediction mode.

[0188] When merge mode is applied to the current block, the motion information of the current block is not directly transmitted, and the motion information of the neighboring blocks is used to derive the motion information of the current block. Therefore, the motion information of the current prediction block can be indicated by transmitting flag information specifying that merge mode is used and candidate selection information (e.g., merge index) specifying which neighboring block is used as a merge candidate. In the present disclosure, since the current block is the unit of prediction performance, the current block can be used to mean the same as the current prediction block, and the neighboring block can be used to mean the same as the neighboring prediction block.

[0189] The image encoding device may search for merge candidate blocks for deriving motion information for the current block to execute merge mode. For example, up to five merge candidate blocks may be used, but this is not limited to this. The maximum number of merge candidate blocks may be sent in a slice header or tile group header, but this is not limited to this. After finding the merge candidate blocks, the image encoding device may generate a merge candidate list and select the merge candidate block with the minimum RD cost as the final merge candidate block.

[0190] The present disclosure provides various embodiments for configuring a merge candidate list of merge candidate blocks. The merge candidate list may include, for example, five merge candidate blocks. For example, four spatial merge candidates and one temporal merge candidate may be used.

[0191] Figure 13 is a view illustrating neighboring blocks that can be used as spatial merging candidates.

[0192] Figure 14 is a view schematically illustrating a method for constructing a merge candidate list according to an example of the present disclosure.

[0193] The image encoding / decoding apparatus may insert a spatial merging candidate derived by searching for spatially adjacent blocks of the current block into the merging candidate list (S1110). Figure 13As shown, the spatial neighboring blocks may include the left bottom corner neighboring block A0, the left neighboring block A1, the right top corner neighboring block B0, the top neighboring block B1, and the left top corner neighboring block B2 of the current block. However, this is an example, and in addition to the above-mentioned spatial neighboring blocks, additional neighboring blocks such as the right neighboring block, the bottom neighboring block, and the right bottom neighboring block may be further used as spatial neighboring blocks. The image encoding / decoding device may detect available blocks by searching the spatial neighboring blocks based on priority, and derive motion information of the detected blocks as spatial merging candidates. For example, the image encoding / decoding device may detect available blocks by searching in the order of A1, B1, B0, A0, and B2. Figure 13 The five blocks shown are used and the available candidates are sequentially indexed to build a merge candidate list.

[0194] The image encoding / decoding apparatus may insert temporal merge candidates derived by searching temporally neighboring blocks of the current block into a merge candidate list (S1120). The temporally neighboring blocks may be located in a reference picture different from the current picture in which the current block is located. The reference picture in which the temporally neighboring blocks are located may be referred to as a collocated picture or col picture. The temporally neighboring blocks may be searched in the col picture in the order of the right bottom corner neighboring block and the right bottom center block of the collocated block of the current block. Furthermore, when motion data compression is applied to reduce memory load, specific motion information may be stored as representative motion information for each predetermined storage unit of the col picture. In this case, it is not necessary to store motion information for all blocks in the predetermined storage unit, thereby achieving motion data compression. In this case, the predetermined storage unit may be predetermined, for example, as a 16×16 sample unit or an 8×8 sample unit, or the size of the predetermined storage unit may be signaled from the image encoding apparatus to the image decoding apparatus. When motion data compression is applied, the motion information of the temporally neighboring blocks may be replaced with the representative motion information of the predetermined storage unit in which the temporally neighboring blocks are located. That is, in this case, from the perspective of implementation, a temporal merging candidate can be derived based on the motion information of a prediction block covering the arithmetically left-shifted position after being arithmetically right-shifted by a predetermined value based on the coordinates (top left sample position) of the temporally adjacent block (instead of the prediction block located on the coordinates of the temporally adjacent block). For example, when the predetermined storage unit is 2 n x2 nWhen the coordinates of the sample unit and the temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb>>n)<<n), (yTnb>>n)<<n)) can be used for temporal merge candidates. Specifically, for example, when the predetermined storage unit is a 16x16 sample unit and the coordinates of the temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb>>4)<<4), (yTnb>>4)<<4)) can be used for temporal merge candidates. Alternatively, for example, when the predetermined storage unit is an 8x8 sample unit and the coordinates of the temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the modified position ((xTnb>>3)<<3), (yTnb>>3)<<3)) can be used for temporal merge candidates.

[0195] Referring again to Figure 14 , the image encoding / decoding device may check whether the number of current merge candidates is less than the maximum number of merge candidates (S1130). The maximum number of merge candidates may be predefined or signaled from the image encoding device to the image decoding device. For example, the image encoding device may generate and encode information regarding the maximum number of merge candidates, and send the encoded information to the image decoding device in the form of a bitstream. When the maximum number of merge candidates is satisfied, the subsequent candidate addition process S1140 may not be performed.

[0196] When, as a result of the check in step S1130, the number of current merge candidates is less than the maximum number of merge candidates, the image encoding / decoding device may derive additional merge candidates according to a predetermined method, and then insert the additional merge candidates into the merge candidate list (S1140).

[0197] When, as a result of the check in step S1130, the number of current merge candidates is not less than the maximum number of merge candidates, the image encoding / decoding device may end the construction of the merge candidate list. In this case, the image encoding device may select the best merge candidate from the merge candidates configuring the merge candidate list, and signal candidate selection information (e.g., merge index) specifying the selected merge candidate to the image decoding device. The image decoding device may select the best merge candidate based on the merge candidate list and the candidate selection information.

[0198] As described above, the motion information of the selected merge candidate may be used as the motion information of the current block, and the prediction samples of the current block may be derived based on the motion information of the current block. The image encoding device may derive residual samples of the current block based on the prediction samples, and signal the residual information of the residual samples to the image decoding device. As described above, the image decoding device may generate reconstructed samples based on the residual samples derived from the residual information and the prediction samples, and generate a reconstructed picture based on the reconstructed samples.

[0199] When skip mode is applied to the current block, the motion information of the current block can be derived using the same method as when merge mode is applied. However, when skip mode is applied, the residual signal of the corresponding block is omitted, and thus the prediction sample can be directly used as the reconstructed sample.

[0200] When the MVP mode is applied to the current block, the reconstructed spatial neighboring blocks (e.g. Figure 13 A motion vector predictor (MVP) candidate list is generated based on the motion vectors of the reconstructed spatially neighboring blocks (as shown) and / or the motion vectors corresponding to the temporally neighboring blocks (or Col blocks). That is, the motion vectors of the reconstructed spatially neighboring blocks and the motion vectors corresponding to the temporally neighboring blocks can be used as motion vector predictor candidates for the current block. When BI prediction is applied, an MVP candidate list for L0 motion information derivation and an MVP candidate list for L1 motion information derivation are separately generated and used. The prediction information (or information about prediction) for the current block may include candidate selection information (e.g., an MVP flag or MVP index) specifying the best motion vector predictor candidate selected from the motion vector predictor candidates included in the MVP candidate list. In this case, the prediction unit can use the candidate selection information to select the motion vector predictor for the current block from the motion vector predictor candidates included in the MVP candidate list. The prediction unit of the image encoding device can obtain and encode the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and output the encoded MVD in the form of a bitstream. That is, the MVD can be obtained by subtracting the motion vector predictor from the motion vector of the current block. The prediction unit of the image decoding device can obtain the motion vector difference included in the prediction information and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit of the image encoding device can obtain or derive the reference picture index of the specified reference picture from the prediction information.

[0201] Figure 15 is a diagram schematically illustrating a method for constructing a motion vector predictor candidate list according to an example of the present disclosure.

[0202] First, the spatial candidate blocks of the current block can be searched and the available candidate blocks can be inserted into the MVP candidate list (S1210). Thereafter, it is determined whether the number of MVP candidates included in the MVP candidate list is less than 2 (S1220), and when the number of MVP candidates is 2, the construction of the MVP candidate list can be completed.

[0203] In step S1220, when the number of available spatial candidate blocks is less than 2, a temporal candidate block of the current block may be searched and the available candidate blocks may be inserted into the MVP candidate list (S1230). When a temporal candidate block is not available, a zero motion vector may be inserted into the MVP candidate list, thereby completing the construction of the MVP candidate list.

[0204] Meanwhile, when MVP mode is applied, reference picture indexes can be explicitly signaled. In this case, the reference picture index refidxL0 for L0 prediction and the reference picture index refidxL1 for L1 prediction can be signaled separately. For example, when MVP mode is applied and Bi prediction is applied, information about refidxL0 and information about refidxL1 can be signaled.

[0205] As described above, when the MVP mode is applied, information regarding the MVP derived by the image encoding device can be signaled to the image decoding device. For example, the MVD information can include information specifying the x and y components of the absolute value (MVD absolute value) and the sign of the MVD. In this case, when the MVD absolute value is greater than 0, information specifying whether the MVD absolute value is greater than 1 and the MVD remainder can be signaled in a step-by-step manner. For example, information specifying whether the MVD absolute value is greater than 1 can be signaled only when the value of the flag information specifying whether the MVD absolute value is greater than 0 is 1.

[0206] Figure 16 is a diagram illustrating a syntax structure for transmitting an MVD from an image encoding device to an image decoding device according to an embodiment of the present disclosure.

[0207] exist Figure 16 In , abs_mvd_greater0_flag[0] specifies whether the absolute value of the x component of the MVD is greater than 0, and abs_mvd_greater0_flag[1] specifies whether the absolute value of the y component of the MVD is greater than 0. Similarly, abs_mvd_greater1_flag[0] specifies whether the absolute value of the x component of the MVD is greater than 1, and abs_mvd_greater1_flag[1] specifies whether the absolute value of the y component of the MVD is greater than 1. Figure 16As shown in Figure 1, abs_mvd_greater1_flag can be sent only when abs_mvd_greater0_flag is 1. Figure 16 In , abs_mvd_minus2 can specify the value obtained by subtracting 2 from the absolute value of MVD, and mvd_sign_flag specifies whether the sign of MVD is positive or negative. Figure 16 The grammatical structure shown, the MVD can be derived as shown in the following equation 1.

[0208] [Equation 1]

[0209]

[0210] Meanwhile, the MVD for L0 prediction (MVDL0) and the MVD for L1 prediction (MVDL1) may be signaled separately, and the MVD information may include information about MVDL0 and / or information about MVDL1. For example, when the MVP mode and BI prediction are applied to the current block, information about MVDL0 and information about MVDL1 may be signaled.

[0211] Overview of Intra Block Copy (IBC) Prediction

[0212] Hereinafter, IBC prediction according to the present disclosure will be described.

[0213] IBC prediction can be performed by a prediction unit of an image encoding / decoding device. IBC prediction can be simply referred to as IBC. IBC can be used for content image / motion image coding such as screen content coding (SCC). IBC prediction can basically perform IBC 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. For example, IBC can use at least one of the above-mentioned motion information (motion vector) derivation methods. It is considered that IBC prediction can partially modify and use at least one of the inter-frame prediction techniques. IBC can refer to the current picture and can therefore be called current picture reference (CPR).

[0214] For IBC, the image encoding device may perform block matching (BM) and derive an optimal block vector (or motion vector) for the current block (e.g., a CU). This derived block vector (or motion vector) may be signaled to the image decoding device via the bitstream using a method similar to the signaling of motion information (motion vectors) in inter-frame prediction described above. The image decoding device may use the signaled block vector (motion vector) to derive a reference block for the current block in the current picture, and thereby derive a prediction signal (prediction block or prediction sample) for the current block. Here, a block vector (or motion vector) may specify the displacement from the current block to a reference block located in a reconstructed region of the current picture. Therefore, a block vector (or motion vector) may be referred to as a displacement vector. Hereinafter, in IBC, a motion vector may correspond to a block vector or a displacement vector. The motion vector of the current block may include the motion vector of the luma component (luminance motion vector) or the motion vector of the chroma component (chroma motion vector). For example, the luma motion vector of an IBC-coded CU may be in integer sample units (i.e., integer precision). Chroma motion vectors may be pruned in integer sample units. As described above, IBC may use at least one of the inter-frame prediction techniques, and for example, may use the above-described merge mode or MVP mode to encode / decode the luma motion vector.

[0215] When applying the merge mode to the luma IBC block, it can be similar to the reference Figure 14 The merging candidate list in the inter mode described above constructs the merging candidate list for the luma IBC block. However, in the case of a luma IBC block, temporally neighboring blocks may not be used as merging candidates.

[0216] When MVP mode is applied to the luma IBC block, it can be similar to the reference Figure 15 The MVP candidate list in the inter mode described above constructs the MVP candidate list for the luma IBC block. However, in the case of the luma IBC block, the temporal candidate block may not be used as the MVP candidate.

[0217] In IBC, reference blocks are derived from reconstructed regions within the current picture. To reduce memory consumption and complexity in the image decoding device, a predefined region within the reconstructed region within the current picture can be used for reference. This predefined region can include the current CTU in which the current block is included. By limiting the reconstructed region that can be referenced to the predefined region, IBC mode can be implemented in hardware using local on-chip memory.

[0218] An image encoding apparatus for performing IBC may search a predefined area to determine a reference block having a minimum RD cost and derive a motion vector (block vector) based on positions of the reference block and a current block.

[0219] Whether IBC is applied to the current block can be signaled as IBC performance information at the CU level. Information regarding the signaling method for the current block's motion vector (IBC MVP mode or IBC skip / merge mode) can also be signaled. This IBC performance information can be used to determine the prediction mode for the current block. Therefore, the IBC performance information can be included in the prediction mode information for the current block.

[0220] In the case of IBC skip / merge mode, a merge candidate index can be signaled to specify a block vector to be used for prediction of the current luma block among the block vectors included in the merge candidate list. In this case, the merge candidate list can include IBC-encoded neighboring blocks. The merge candidate list can be configured to include spatial merge candidates but not temporal merge candidates. In addition, the merge candidate list can also include history-based motion vector predictor (HMVP) candidates and / or paired candidates.

[0221] In the case of the IBC MVP mode, the block vector difference can be encoded using the same method as the motion vector difference of the inter-frame mode described above. The block vector prediction method can be constructed similarly to the MVP mode of the inter-frame mode and use an MVP candidate list including two candidates as predictors. One of the two candidates can be derived from the left neighboring block, and the other candidate can be derived from the top neighboring block. In this case, the candidate can only be derived from the corresponding neighboring block when the left or top neighboring block is IBC encoded. If the left or top neighboring block is not available, for example, it is not IBC encoded, the default block vector can be included in the MVP candidate list as a predictor. In addition, information specifying one of the two block vector predictors (e.g., a flag) is signaled similarly to the MVP mode of the inter-frame mode and used as candidate selection information. The MVP candidate list may include an HMVP candidate and / or a zero motion vector as the default block vector.

[0222] The HMVP candidate may be referred to as a history-based MVP candidate, and the MVP candidate, merge candidate, or block vector candidate used before encoding / decoding of the current block may be stored in the HMVP list as an HMVP candidate. Thereafter, when the merge candidate list or MVP candidate list of the current block does not include the maximum number of candidates, the candidate stored in the HMVP list may be added as an HMVP candidate to the merge candidate list or MVP candidate list of the current block.

[0223] The pair of candidates means candidates derived by selecting two candidates from among candidates already included in the merge candidate list of the current block according to a predetermined order and calculating an average of the selected two candidates.

[0224] Figure 17 is a flowchart illustrating a video / image encoding method based on IBC.

[0225] Figure 18 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image encoding method according to the present disclosure.

[0226] Figure 17 The encoding method can be Figure 2 The image encoding device of is performed. Specifically, step S1410 can be performed by the prediction unit and step S1420 can be performed by the residual processor. Specifically, step S1420 can be performed by the subtractor 115. Step S1430 can be performed by the entropy encoder 190. The prediction information of step S1430 can be derived by the prediction unit and the residual information of step S1430 can be derived by the residual processor. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficient for the residual sample. As described above, the residual sample can be derived through the transform coefficient via the transformer 120 of the image encoding device, and the transform coefficient can be derived through the transform coefficient quantized by the quantizer 130. The information about the quantized transform coefficient can be encoded by the entropy encoder 190 through the residual coding process.

[0227] The image encoding device may perform IBC prediction (IBC-based prediction) for the current block (S1410). The image encoding device may derive a prediction mode and a motion vector (block vector) of the current block and generate a prediction sample of the current block. The prediction mode may include at least one of the above-mentioned inter-frame prediction modes. Here, the prediction mode determination, motion vector derivation, and prediction sample generation processes may be performed simultaneously, or any one process may be performed before the other process. For example, Figure 18 As shown, the prediction unit of an image coding device for performing an IBC-based video / image coding method may include a prediction mode determination unit, a motion vector derivation unit, and a prediction sample derivation unit. The prediction mode determination unit may determine a prediction mode for a current block, the motion vector derivation unit may derive a motion vector for the current block, and the prediction sample derivation unit may derive prediction samples for the current block. For example, the prediction unit of the image coding device may search for a block similar to the current block in a reconstructed area (or a certain area (search area) of the reconstructed area) of the current picture and derive a reference block whose difference with the current block is equal to or less than a certain criterion or minimum value. The image coding device may derive a motion vector based on the displacement difference between the reference block and the current block. The image coding device may determine a mode to be applied to the current block from among various prediction modes. The image coding device may compare the RD costs for the various prediction modes and determine the optimal prediction mode for the current block. However, the method by which the image coding device determines the prediction mode for the current block is not limited to the above example, and various methods may be used.

[0228] For example, when skip mode or merge mode is applied to the current block, the image encoding device can derive merge candidates from neighboring blocks of the current block and use the derived merge candidates to construct a merge candidate list. In addition, the image encoding device can derive a reference block whose difference with the current block is equal to or less than a specific criterion or minimum value from 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 can be selected, and merge index information specifying the selected merge candidate can be generated and signaled to the image decoding device. Using the motion vector of the selected merge candidate, the motion vector of the current block can be derived.

[0229] As another example, when MVP mode is applied to the current block, the image encoding device may derive motion vector predictor (MVP) candidates from neighboring blocks of the current block and use the derived MVP candidates to construct an MVP candidate list. Furthermore, the image encoding device may use the motion vector of an MVP candidate selected from among the MVP candidates included in the MVP candidate list as the MVP for the current block. In this case, for example, the motion vector of a reference block derived through the aforementioned motion estimation may be used as the motion vector of the current block, and the MVP candidate with the smallest difference from the motion vector of the current block among the MVP candidates may be selected as the MVP candidate. A motion vector difference (MVD) obtained by subtracting the MVP from the motion vector of the current block may be derived. In this case, index information specifying the selected MVP candidate and information regarding the MVD may be signaled to the image decoding device.

[0230] The image encoding apparatus may derive residual samples based on the predicted samples (S1420). The image encoding apparatus may derive residual samples by comparing the original samples of the current block with the predicted samples. For example, the residual samples may be derived by subtracting the corresponding predicted samples from the original samples.

[0231] The image encoding device may encode image information including prediction information and residual information (S1430). The image 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) and information about motion vectors as information related to the prediction process. Among the prediction mode information, the skip flag specifies whether skip mode is applied to the current block, while the merge flag specifies whether merge mode is applied to the current block. Alternatively, the prediction mode information may specify one of multiple prediction modes, such as a mode index. When the skip flag and the merge flag are 0, it can be determined that MVP mode is applicable to the current block. The information about the motion vector may include candidate selection information (e.g., a merge index, an MVP flag, or an MVP index) as information used to derive the motion vector. Among the candidate selection information, the merge index may be signaled when the merge mode is applied to the current block and may be information used to select one of the merge candidates included in the merge candidate list. Among the candidate selection information, an MVP flag or an MVP index may be signaled when applying the MVP mode to the current block, and may be information for selecting one of the MVP candidates included in the MVP candidate list. In addition, the information about the motion vector may include information about the above-mentioned MVD. In addition, the information about the motion vector may include information specifying whether L0 prediction, L1 prediction, or bi prediction is applied. The residual information is information about the residual sample. The residual information may include information about the quantized transform coefficients used for the residual sample.

[0232] The output bit stream may be stored in a (digital) storage medium and transmitted to the image decoding device or may be transmitted to the image decoding device via a network.

[0233] At the same time, as described above, the image encoding device can generate a reconstructed picture (a picture including reconstructed samples and reconstructed blocks) based on the reference samples and residual samples. This is to allow the image encoding device to derive the same prediction result as the prediction result performed by the image decoding device, thereby improving coding efficiency. Therefore, the image encoding device can store the reconstructed picture (or reconstructed samples and reconstructed blocks) in memory and use it as a reference picture for inter-frame prediction. As described above, the in-loop filtering process is also applicable to the reconstructed picture.

[0234] Figure 19 is a flowchart illustrating a video / image decoding method based on IBC.

[0235] Figure 20 is a view illustrating a configuration of a prediction unit for performing an IBC-based video / image decoding method according to the present disclosure.

[0236] The image decoding apparatus may perform an operation corresponding to the operation performed by the image encoding apparatus.The image decoding apparatus may perform IBC prediction on the current block based on the received prediction information to derive a prediction sample.

[0237] Figure 19 The decoding method can be obtained by Figure 3 The image decoding device of FIG. 16 is executed by the image decoding device. Steps S1610 to S1630 may be performed by the prediction unit, and the prediction information of step S1610 and the residual information of step S1640 may be obtained from the bitstream by the entropy decoder 210. The residual processor of the image decoding device may derive residual samples of the current block based on the residual information (S1640). 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 inverse transformer 230 of the residual processor may perform inverse transform on the transform coefficients to derive residual samples of the current block. Step S1650 may be performed by the adder 235 or the reconstructor.

[0238] Specifically, the image decoding apparatus may determine a prediction mode of the current block based on the received prediction information (S1610).The image decoding apparatus may determine which prediction mode is applicable to the current block based on prediction mode information in the prediction information.

[0239] For example, whether to apply skip mode to the current block can be determined based on a skip flag. Alternatively, whether to apply merge node or MVP mode to the current block can be determined based on a merge flag. Alternatively, one of various prediction mode candidates can be selected based on a mode index. Prediction mode candidates can include skip mode, merge mode, and / or MVP mode, or can include the various inter-frame prediction modes described above.

[0240] The image encoding device may derive a motion vector for the current block based on the determined prediction mode (S1620). For example, when skip mode or merge mode is applied to the current block, the image decoding device may construct the merge candidate list and select one of the merge modes included in the merge candidate list. This selection may be performed based on the candidate selection information (merge index). The motion vector of the selected merge candidate may be used to derive the motion vector for the current block. For example, the motion vector of the selected merge candidate may be used as the motion vector for the current block.

[0241] As another example, when the MVP mode is applied to the current block, the image decoding device may construct an MVP candidate list and use the motion vector of an MVP candidate selected from the MVP candidate list as the MVP of the current block. The selection may be performed based on the candidate selection information (MVP flag or MVP index). In this case, the MVD of the current block may be derived based on the MVD information, and the motion vector of the current block may be derived based on the MVP and MVD of the current block.

[0242] The image decoding apparatus may generate prediction samples for the current block based on the motion vector of the current block (S1630). The prediction samples for the current block may be derived using samples of a reference block indicated by the motion vector of the current block in the current picture. In some cases, a prediction sample filtering process may be further performed on all or some of the prediction samples for the current block.

[0243] For example, Figure 20 As shown, the prediction unit of an image decoding device for performing an IBC-based video / image decoding method may include a prediction mode determination unit, a motion vector derivation unit, and a prediction sample derivation unit. The prediction unit of the image decoding device may determine a prediction mode for a current block based on received prediction mode information in the prediction mode determination unit, derive a motion vector for the current block based on received information about the motion vector in the motion vector derivation unit, and derive a prediction sample for the current block in the prediction sample derivation unit.

[0244] The image decoding apparatus may generate residual samples for the current block based on the received residual information (S1640). The image decoding apparatus may generate reconstructed samples for the current block based on the predicted samples and the residual samples, and generate a reconstructed picture based on the samples (S1650). Thereafter, as described above, the in-loop filtering process is also applied to the reconstructed picture.

[0245] As described above, a unit (e.g., a coding unit (CU)) may include a luma block (luma coding block (CB)) and a chroma block (chroma CB). In this case, the luma block and the corresponding chroma block may have the same motion information (e.g., motion vector) or different motion information. For example, the motion information of the chroma block may be derived based on the motion information of the luma block, so that the luma block and the corresponding chroma block have the same motion information.

[0246] Intra prediction on chroma blocks

[0247] When intra prediction is performed on the current block, prediction of the luminance component block (luminance block) and prediction of the chrominance component block (chrominance block) of the current block can be performed. In this case, the intra prediction mode of the chrominance block can be set separately from the intra prediction mode of the luminance block.

[0248] For example, the intra prediction mode for the chroma block can be specified based on the intra chroma prediction mode information, and the intra chroma prediction mode information can be signaled in the form of the intra_chroma_pred_mode syntax element. For example, the intra chroma prediction mode information can indicate one of the planar mode, DC mode, vertical mode, horizontal mode, derived mode (DM), and cross-component linear model (CCLM) mode. Here, the planar mode can specify intra prediction mode #0, the DC mode can specify intra prediction mode #1, the vertical mode can specify intra prediction mode #26, and the horizontal mode can specify intra prediction mode #10. DM can also be called a direct mode. CCLM can also be called a linear model (LM).

[0249] Meanwhile, DM and CCLM are related intra-prediction modes for predicting chroma blocks using information about luma blocks. DM may indicate a mode in which the same intra-prediction mode as the luma component is applied as the intra-prediction mode for the chroma components. Alternatively, CCLM may indicate an intra-prediction mode in which samples derived by subsampling reconstructed samples of the luma block and then applying α and β, which are CCLM parameters, to the subsampled samples in generating prediction blocks for the chroma blocks are used as prediction samples for the chroma blocks.

[0250] [Equation 2]

[0251]

[0252] Among them, pred c (i, j) can represent the predicted sample of the (i, j) coordinate of the current chroma block in the current CU. L '(i, j) can represent the reconstructed sample of the (i, j) coordinate of the current luminance block in the CU. For example, rec L '(i,j) may represent the downsampled reconstructed sample of the current luma block. The linear model coefficients α and β may be signaled or derived from neighboring samples.

[0253] Coding efficiency degradation problem of 2×N and N×2 blocks

[0254] In the case of the VVC standard, the encoding target image is a high-resolution image such as UHD or FHD. The hardware configuration for processing such a high-resolution image is becoming increasingly complex. In an embodiment, TVM, which is the VVC specification and standard software, can use a CTU of size 128×128 during intra prediction. Even in this case, as the size of the minimum CU block, a 4×4 block can be used in the case of a luminance block. In the case of a chrominance block, when the tree structure of the current block is a single tree, a 2×2 block can be used, and when the tree structure of the current block is a dual tree, a 2×8, 8×2, or 4×4 block can be used.

[0255] Therefore, when encoding a UHD image with a resolution of 3840×2160 by performing intra-frame prediction using VTM software, all luma blocks are encoded as 4×4 blocks, and all chroma blocks can be encoded as 4×4 blocks according to the dual-tree. In this case, the UHD image is divided into 518,400 4×4 luma and chroma blocks. In the hardware implementation of VTM, the corresponding hardware must be driven even at the worst-case data throughput. Therefore, when this occurs, in order to prepare for it, hardware manufacturing costs increase and processing delays occur during encoding and decoding.

[0256] In the case of a technique using association between luminance blocks and chrominance blocks (eg, CCLM), since encoding of chrominance blocks should be performed after encoding of all luminance blocks is completed, as shown in FIG. Figure 21 As shown, pipeline delay issues occur in hardware implementation.

[0257] In addition, unlike a single tree, in the case of a dual tree, the encoding of the chroma block should be performed after the encoding of all the luma blocks is completed. Therefore, by delaying the encoding of the chroma block until the encoding of the luma block is completed, a pipeline delay problem occurs in the hardware implementation. Specifically, since 2×8, 2×16, and 2×32 structures are generated in the chroma block of the dual tree, the existing hardware structure that performs encoding and decoding in units of 4×1 per clock can be eliminated. Therefore, a new hardware structure for performing the process in units of 2×2 or 1 / 4 per clock is required.

[0258] The present disclosure proposes a method for adaptively limiting the size of chroma blocks or limiting or adjusting the size of CCLM prediction blocks to solve the above-mentioned problems in hardware implementation. Therefore, the complexity of hardware implementation can be significantly reduced while minimizing the loss of coding efficiency.

[0259] In the following description, limiting a specific block size may indicate that segmentation into blocks of a specific size is not permitted. To disallow segmentation into blocks of a specific size, segmentation under specific conditions may be limited. This may indicate that segmentation under specific conditions is set to be unavailable. In this case, the upper layer block may be segmented into block sizes different from the specific block size, and the segmented blocks may then be used as current blocks to perform a series of coding processes (prediction, residual processing, block reconstruction, image / video information encoding / decoding, etc.). The image / video information may include segmentation information, and the segmentation information may include information specifying segmentation into block sizes other than the limited segmentation size.

[0260] Improved performance based on block split limits

[0261] The encoding apparatus and the decoding apparatus according to an embodiment may resolve the complexity of hardware implementation by adaptively limiting the size of a block partitioned from a CTU depending on whether the CTU of the current image is partitioned according to a single-tree or dual-tree structure.

[0262] As described above, in the case of dual-tree, after encoding or decoding all luminance blocks of a certain size, encoding of the chrominance blocks corresponding to the luminance blocks can be performed. Therefore, it is necessary to use a pipeline method different from the single-tree hardware used in H.264 and HEVC.

[0263] In the case of using the VVC standard, when dual-tree is applied, in the case of a 4:2:0 color format, after encoding the 64×64 luminance block, encoding of the 32×32 chrominance block is performed. Therefore, encoding and decoding of the luminance block and the chrominance block are performed sequentially. In the case of the luminance block, the method of processing 4×1 pixels per clock used in the existing hardware can be used without change. However, since a 2x8, 2x16, or 2x32 structure is generated in the chrominance block, the existing hardware structure for encoding and decoding in units of 4x1 can be used.

[0264] To use existing hardware structures without changes, the size of the chroma block can be limited to the existing encoding and decoding units. For example, when the process is performed with A×1 units per clock as the encoding and decoding unit, the chroma block size can be limited to B×N so that the chroma block can be encoded / decoded in this structure. Here, A can be an integer greater than 0 and less than or equal to the maximum width of the block, B can be an integer greater than 0 and less than A, and N can be a value represented by a power of 2 greater than 1 (for example, 2, 4, 8, 16, 32, 64, 128, 256...). Here, limiting the block size can mean prohibiting division into corresponding block sizes. Therefore, the chroma block can be divided into block sizes up to the block size immediately before it is divided into the corresponding block size.

[0265] For example, when the process is performed with 4×1 units per clock as encoding and decoding units, the chroma block size can be limited to 2×N so that the chroma block can be encoded / decoded in this structure. Here, N can be a value represented by a power of 2 greater than 1.

[0266] For example, the chroma block may be prohibited from being split into 2xN blocks. In an embodiment, in order to prohibit the chroma block from being split into this size, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trisection splitting, or vertical trisection splitting for generating a chroma block having a size of 2×N by splitting the current block may be restricted.

[0267] Limiting this partitioning applies only when the current block has a dual-tree structure, only when the current block has a single-tree structure, or when the current block has either a dual-tree structure or a single-tree structure.

[0268] Meanwhile, when the current block is a luma block, the tree structure of the current block is a single tree, and the color format of the current block is 4:2:2 or 4:2:0, in order to limit the generation of 2×N chroma blocks, splitting the current block to generate a 4×N luma block may be limited. For example, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trisection splitting, or vertical trisection splitting for generating a 4×N luma block by splitting the current block may be limited.

[0269] Figure 22 is a diagram illustrating a coding rate measured in the case of limiting the division of the chroma block into 2xN chroma blocks when the current block has a dual-tree structure. Figure 22 As shown in the experimental results, coding losses of 0.02% for Y, 0.34% for Cb, and 0.38% for Cr were observed in all intra-frame experiments. By limiting the processing to 2×N blocks, the 4×1 pixel processing of existing hardware can be applied unchanged to chroma blocks, and the coding loss can also be minimized.

[0270] At the same time, the embodiments described above can be applied to situations where the encoding / decoding process is performed in units of 1×A per clock. For example, the N×B block size of the chroma block can be limited so that the chroma block is encoded / decoded in an encoding / decoding structure that performs the encoding / decoding process in units of 1×A per clock. Here, A can be an integer greater than 0 and less than or equal to the maximum width of the block, B can be an integer greater than 0 and less than A, and N can be a value represented by a power of 2 greater than 1 (for example, 2, 4, 8, 16, 32, 64, 128, 256...). Here, limiting the block size can mean prohibiting segmentation into corresponding block sizes. Therefore, the chroma block can be segmented into block sizes up to the block size immediately before being segmented into the corresponding block size.

[0271] For example, when the process is performed with 1×4 units per clock as encoding and decoding units, the N×2 block size of the chroma block can be limited so that the chroma block is encoded / decoded in this structure. Here, N can be a value represented by a power of 2 greater than 1.

[0272] For example, splitting a chroma block into N×2 blocks may be prohibited. In an embodiment, to prohibit splitting a chroma block into such a size, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trisection splitting, or vertical trisection splitting for generating a chroma block having an N×2 size by splitting the current block may be restricted.

[0273] Limiting this partitioning applies only when the current block has a dual-tree structure, only when the current block has a single-tree structure, or when the current block has either a dual-tree structure or a single-tree structure.

[0274] Meanwhile, when the current block is a luma block, the tree structure of the current block is a single tree and the color format of the current block is 4:2:2 or 4:2:0, in order to limit the generation of N×2 chroma blocks, splitting the current block to generate an N×4 luma block may be limited. For example, quadtree splitting, horizontal binary tree splitting, vertical binary tree splitting, horizontal trifurcating splitting, or vertical trifurcating splitting for generating a luma block having an N×4 size by splitting the current block may be limited.

[0275] Example 1

[0276] As described above, the encoding device and the decoding device can limit the division of the chroma block to a size of 2×N. For example, the encoding / decoding device can limit the minimum width of the chroma block to a length of 4 samples. To this end, the encoding / decoding device according to the embodiment can determine whether a predetermined division mode is allowed for the current block based on whether the current block is a chroma block or the width of the current block. In the following, the decoding device will be described, but the following description applies accordingly to the encoding device.

[0277] Figure 23 23 is a view illustrating a method for determining, by a decoding device, whether vertical three-pronged splitting (SPLIT_TT_VER) is allowed for a current block. According to an embodiment, a decoding device may determine whether a current block is a chroma block (S2310). The decoding device may check the value of a cIdx parameter specifying a color component of the current block to determine whether the current block is a chroma block. When the value of cIdx is 0, the decoding device may determine that the current block is a luma block. When the value of cIdx is greater than 0, the decoding device may determine that the current block is a chroma block. More specifically, when the value of cIdx is 1 or 2, the decoding device may determine that the current block is a chroma cb block. When the value of cIdx is 2, the decoding device may determine that the current block is a chroma cr block.

[0278] In addition, the decoding apparatus according to the embodiment may further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., dual_tree_chroma) for chroma components, the decoding apparatus may determine that the current block is a chroma block and the tree type is a dual tree type.

[0279] Next, the decoding apparatus may determine whether the width of the current block is equal to or less than 8 samples (S2320). When the value of the parameter specifying the width of the current block is equal to or less than 8, the decoding apparatus may determine that the width of the current block is equal to or less than 8.

[0280] Meanwhile, in the case of a chroma block, the width of the chroma block can be determined based on the width of the corresponding luminance block. In this case, the width of the current chroma block can be determined based on the width of the luminance block and the color format of the current image. For example, when the color format is 4:4:4, the width and height of the chroma block can be set to the width and height of the luminance block, respectively. When the color format is 4:2:2, the width of the chroma block can be set to half the width of the luminance block, and the height of the chroma block can be set to the height of the luminance block. When the color format is 4:2:0, the width of the chroma block can be set to half the width of the luminance block, and the height of the chroma block can be set to half the height of the luminance block.

[0281] Therefore, when the color format of the current block is 4:4:4, the decoding apparatus may perform step S2320 by determining whether the width of the luma block is equal to or less than 8. Similarly, when the color format of the current block is 4:2:2 or 4:2:0, the decoding apparatus may perform step S2320 by determining whether the width of the luma block is equal to or less than 16.

[0282] Finally, when all the above conditions are met, the decoding apparatus may determine that the current block does not allow vertical trisection splitting (S2330). For example, when the current block is a chroma block and the width is equal to or less than 8, the decoding apparatus may determine that the current block does not allow vertical trisection splitting. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual-tree type, and the width is equal to or less than 8, the decoding apparatus may determine that the current block does not allow vertical trisection splitting.

[0283] Meanwhile, when the above conditions are not met, the decoding device may determine that vertical trifurcated splitting is permitted for the current block. In this case, the decoding device may determine whether vertical trifurcated splitting is permitted for the current block by determining an additional condition that the current block cannot be split by vertical trifurcated splitting (S2340). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowable hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that vertical trifurcated splitting is not permitted for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that vertical trifurcated splitting is permitted for the current block.

[0284] Example 2

[0285] As mentioned above, it is necessary to limit the minimum height of the chroma block to a length of four samples. Figure 24 A method of limiting horizontal trifurcating division for a current block by an encoding / decoding apparatus according to an embodiment in order to limit the minimum height of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applied to an encoding apparatus.

[0286] Figure 24 This figure illustrates a method for a decoding device to determine whether horizontal three-way splitting (SPLIT_TT_HOR) is permitted for a current block. According to an embodiment, a decoding device may determine whether a current block is a chroma block (S2410). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0287] In addition, the decoding apparatus according to an embodiment may further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., dual_tree_chroma) for chroma components, the decoding apparatus may determine that the current block is a chroma block and the tree type is a dual tree type.

[0288] Next, the decoding apparatus according to an embodiment may determine whether the height of the current block is equal to or less than a length of 8 samples (S2420). When the value of the parameter specifying the height of the current block is equal to or less than 8, the decoding apparatus may determine that the height of the current block is equal to or less than 8. Alternatively, as described above, the decoding apparatus may perform step S2420 based on whether the height of the luma block is equal to or less than 8 or 16, depending on the color format of the current block.

[0289] As described above, in the case of a chroma block, the height of the chroma block can be determined based on the height of the corresponding luma block. For example, when the color format of the current block is 4:4:4 or 4:2:2, the decoding device can perform step S2420 by determining whether the height of the luma block is equal to or less than 8. Similarly, when the color format of the current block is 4:2:2, the decoding device can perform step S2420 by determining whether the height of the luma block is equal to or less than 16.

[0290] Finally, when all the above conditions are met, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block (S2430). For example, when the current block is a chroma block and the height is equal to or less than 8, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual-tree type, and the height is equal to or less than 8, the decoding device may determine that horizontal trifurcated splitting is not allowed for the current block.

[0291] Meanwhile, when the above conditions are not met, the decoding device may determine that horizontal trifurcated splitting is permitted for the current block. In this case, as described above, the decoding device may determine whether horizontal trifurcated splitting is permitted for the current block by determining an additional condition that prohibits horizontal trifurcated splitting for the current block (S2440). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum permissible hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that horizontal trifurcated splitting is not permitted for the current block, whereas when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that horizontal trifurcated splitting is permitted for the current block.

[0292] Example 3

[0293] As mentioned above, it is necessary to limit the minimum height of the chroma block to a length of four samples. Figure 25 A method of limiting horizontal binary splitting of a current block by an encoding / decoding apparatus according to an embodiment in order to limit the minimum height of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applied to an encoding apparatus.

[0294] Figure 25 This figure illustrates a method for a decoding device to determine whether horizontal binary split (SPLIT_BT_HOR) is permitted for a current block. According to an embodiment, a decoding device may determine whether a current block is a chroma block (S2510). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0295] In addition, the decoding apparatus according to an embodiment may further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., dual_tree_chroma) of the chroma component, the decoding apparatus may determine that the current block is a chroma block and the tree type is a dual tree type.

[0296] Next, the decoding device according to the embodiment may determine whether the height of the current block is equal to or less than the length of 4 samples (S2520). When the value of the parameter specifying the height of the current block is equal to or less than 4, the decoding device may determine that the height of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2520 based on whether the height of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4 or 4:2:2, the decoding device may perform step S2520 by determining whether the height of the luminance block is equal to or less than 4. Similarly, when the color format of the current block is 4:2:2, the decoding device may perform step S2520 by determining whether the height of the luminance block is equal to or less than 8.

[0297] Finally, when all the above conditions are met, the decoding device may determine that horizontal binary splitting is not allowed for the current block (S2530). For example, when the current block is a chroma block and the height is equal to or less than 4, the decoding device may determine that horizontal binary splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual-tree type, and the height is equal to or less than 4, the decoding device may determine that horizontal binary splitting is not allowed for the current block.

[0298] Meanwhile, when the above conditions are not met, the decoding device may determine that horizontal binary splitting is permitted for the current block. In this case, as described above, the decoding device may determine whether horizontal binary splitting is permitted for the current block by determining an additional condition that prohibits horizontal binary splitting for the current block (S2540). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum allowable hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that horizontal binary splitting is not permitted for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that horizontal binary splitting is permitted for the current block.

[0299] Example 4

[0300] As mentioned above, it is necessary to limit the minimum width of the chrominance block to a length of four pixels. Figure 26A method of limiting vertical binary splitting of a current block by an encoding / decoding apparatus according to an embodiment in order to limit the minimum width of a chroma block is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applied to an encoding apparatus.

[0301] Figure 26 26 is a diagram illustrating a method by which a decoding device determines whether vertical binary split (SPLIT_BT_VER) is permitted for a current block. According to an embodiment, a decoding device may determine whether a current block is a chroma block (S2610). As described above, the decoding device may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0302] In addition, the decoding apparatus according to an embodiment may further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., dual_tree_chroma) of the chroma component, the decoding apparatus may determine that the current block is a chroma block and the tree type is a dual tree type.

[0303] Next, the decoding device according to the embodiment may determine whether the width of the current block is equal to or less than the length of 4 samples (S2620). When the value of the parameter specifying the width of the current block is equal to or less than 4, the decoding device may determine that the width of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2620 based on whether the width of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4, the decoding device may perform step S2620 by determining whether the width of the luminance block is equal to or less than 4. Similarly, when the color format of the current block is 4:2:2 or 4:2:0, the decoding device may perform step S2620 by determining whether the width of the luminance block is equal to or less than 8.

[0304] Finally, when all the above conditions are met, the decoding device may determine that vertical binary splitting is not allowed for the current block (S2630). For example, when the current block is a chroma block and the width is equal to or less than 4, the decoding device may determine that vertical binary splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual-tree type, and the width is equal to or less than 4, the decoding device may determine that vertical binary splitting is not allowed for the current block.

[0305] Meanwhile, when the above conditions are not met, the decoding device may determine that vertical binary splitting is permitted for the current block. In this case, as described above, the decoding device may determine whether vertical binary splitting is permitted for the current block by determining an additional condition that vertical binary splitting is not permitted for the current block (S2640). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum permissible hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that vertical binary splitting is not permitted for the current block, whereas when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that vertical binary splitting is permitted for the current block.

[0306] Example 5

[0307] As mentioned above, it is necessary to limit the minimum width or height of the chroma block to a unit of 4 pixels. In the following, in order to limit the minimum width and height of the chroma block, reference will be made to Figure 27 A method of limiting quadtree partitioning of a current block by an encoding / decoding apparatus according to an embodiment is described. Hereinafter, a decoding apparatus will be described, but the following description may also be applied to an encoding apparatus.

[0308] Figure 27 27 is a diagram illustrating a method for a decoding apparatus according to an embodiment to determine whether quadtree splitting is permitted for a current block. The decoding apparatus according to an embodiment may determine whether the current block is a chroma block (S2710). The decoding apparatus may check the value of the cIdx parameter specifying the color component of the current block to determine whether the current block is a chroma block.

[0309] In addition, the decoding apparatus according to an embodiment may further determine whether the tree structure of the current block is a dual tree. When the tree information (e.g., treeType) specifying the tree structure of the current block is a dual tree type (e.g., dual_tree_chroma) for chroma components, the decoding apparatus may determine that the current block is a chroma block and the tree type is a dual tree type.

[0310] Next, the decoding device according to the embodiment may determine whether the width or height of the current block is equal to or less than the length of 4 samples (S2720). When the value of the parameter specifying the width of the current block is equal to or less than 4, the decoding device may determine that the width of the current block is equal to or less than 4. Alternatively, as described above, the decoding device may perform step S2720 based on whether the width of the luminance block is equal to or less than 4 or 8 according to the color format of the current block. For example, when the color format of the current block is 4:4:4, the decoding device may perform step S2720 by determining whether the width of the luminance block is equal to or less than 4. In a similar manner, when the color format is 4:4:2 or 4:2:0, the decoding device may perform step S2720 by determining whether the width of the luminance block is equal to or less than 8.

[0311] Finally, when all the above conditions are met, the decoding device may determine that quadtree splitting is not allowed for the current block (S2730). For example, when the current block is a chroma block and the width or height is equal to or less than 4, the decoding device may determine that quadtree splitting is not allowed for the current block. Alternatively, when the current block is a chroma block, the tree type of the current block is a dual-tree type, and the width or height is equal to or less than 4, the decoding device may determine that quadtree splitting is not allowed for the current block.

[0312] Meanwhile, when the above conditions are not met, the decoding device may determine that quadtree splitting is permitted for the current block. In this case, as described above, the decoding device may determine whether quadtree splitting is permitted for the current block by determining an additional condition that quadtree splitting is not permitted for the current block (S2740). For example, when the number of times the current block is split from a quadtree leaf node is equal to or greater than the value of MaxMttDepth, which is a parameter specifying the maximum permissible hierarchical depth of a multi-type tree split from a quadtree leaf node, the decoding device may determine that quadtree splitting is not permitted for the current block, and when the number of times the current block is split is less than the value of MaxMttDepth, the decoding device may determine that quadtree splitting is permitted.

[0313] Implementing performance improvements based on CCLM application restrictions

[0314] The encoding and decoding devices according to the embodiments can adaptively perform CCLM prediction based on the size of the chroma block. As described above, since CCLM prediction generates chroma block sample values ​​based on luma block sample values, it is necessary to refer to corresponding (e.g., co-located) luma samples. Since CCLM prediction can be performed after encoding / decoding all luma samples, delays in the hardware pipeline are unavoidable.

[0315] In addition, unlike a single-tree block in which encoding / decoding of a co-located chroma block is performed after encoding / decoding of a luminance block, CCLM prediction in a dual-tree in which luminance blocks and chroma blocks of a certain size or larger are independently encoded further exacerbates the hardware pipeline latency problem. In the worst case, CCLM prediction is performed in 256 CUs in a dual-tree CTU, which significantly affects throughput (e.g., data throughput) in hardware implementation.

[0316] Therefore, in order to reduce the data throughput of CCLM prediction, the encoding device and decoding device according to the embodiment can determine whether to perform CCLM prediction based on the size of the chroma block when performing CCLM prediction. In addition, the encoding device and decoding device can determine whether to perform CCLM prediction based on whether the tree structure of the chroma block is a single tree or a dual tree and the size of the chroma block.

[0317] More specifically, when the number of pixels (samples) in a chroma block is equal to or less than 16 when CCLM prediction is performed (a first restriction condition), the encoding and decoding devices according to the present embodiment can restrict (e.g., prohibit) CCLM prediction. For example, the encoding and decoding devices can not perform CCLM prediction for chroma blocks of sizes 2×2, 2×4, 2×8, 4×2, 4×4, or 8×2. Experiments have confirmed that by performing CCLM prediction in this manner, data throughput can be halved compared to a case where CCLM is performed on all chroma blocks without restricting the size of the chroma blocks.

[0318] Alternatively, when performing CCLM prediction, the encoding device and the decoding device may limit CCLM prediction when the width of the chroma block is 2 samples in length (e.g., 2×N chroma block) (second restriction condition), and limit CCLM prediction when the height of the chroma block is 2 samples in length (e.g., N×2 chroma block) (third restriction condition).

[0319] In an embodiment, the encoding device and the decoding device may use a selective combination of the first constraint, the second constraint, and the third constraint. For example, the encoding device may use a combination of the first constraint and the second constraint, a combination of the first constraint and the third constraint, a combination of the second constraint and the third constraint, or a combination of the first constraint, the second constraint, and the third constraint.

[0320] An example of coding loss rate according to the above combination is Figure 28 and Figure 29 Shown in. Figure 28 is a diagram illustrating experimental results obtained in the case where only the first restriction condition is applied. Figure 29is a diagram illustrating experimental results obtained when all the first, second and third constraints are applied. The experiment was performed on VTM5 software and for all frames based on the dual tree. Figure 28 As shown in the experimental results, coding losses of Y0.03%, Cb 0.53% and Cr 0.60% are observed in all intra-frame experiments when only the first restriction condition is applied.

[0321] In addition, if Figure 29 As shown in the experimental results, coding losses of Y 0.05%, Cb 0.75% and Cr 0.83% were observed in all intra-frame experiments when only the first to third constraints were applied. Figure 29 In the experimental results of , the chroma blocks for which CCLM prediction is not performed are 2xN, Nx2, and 4x4 chroma blocks. Figure 28 and Figure 29 In the experimental example of , by limiting CCLM prediction in chroma blocks with a predetermined size, the data throughput for encoding chroma blocks can be reduced and the coding loss can be minimized.

[0322] Encoding method

[0323] Figure 30 is a flowchart illustrating a method for encoding an image by a decoding device according to an embodiment. The encoding device according to the embodiment may include a memory and at least one processor, and the encoding device may perform the following encoding method using at least one processor. Figure 30 The encoding method for executing the above-mentioned embodiment will be described.

[0324] According to an embodiment, the encoding apparatus may determine a current block by segmenting an image (S3010). Here, the current block may be a chroma block. The encoding apparatus may determine the current block by segmenting a portion of the image according to a segmentation type, where the segmentation type is determined based on available segmentation types that can be used to segment the portion of the image. Here, the available segmentation types may be determined based on the width of the portion of the image. In the following description, the portion of the image segmented to determine the current block may be referred to as an upper layer block.

[0325] More specifically, the encoding device may partition the upper layer block by applying the permitted available partition types among the aforementioned quadtree and multitree partition types, and calculate the RD cost based on each partition type. The encoding device may determine the partition type to be applied to the upper layer block based on the RD cost determined for each partition type. For example, if horizontal trifurcated partitioning is permitted for the upper layer block, the encoding device may determine to apply the horizontal trifurcated partitioning type as the partition type of the upper layer block, and calculate the optimal RD cost when performing encoding by partitioning the upper layer block into the corresponding types.

[0326] In conjunction with the selection of an available partition type, the encoding device may not allow a predetermined partition type, among multiple partition types, in which the width or height of the upper layer block is a predetermined value, to be an available partition type that can partition the upper layer block. Therefore, the encoding device may determine the partition type of the upper layer block to be an available partition type other than the predetermined partition type among the multiple partition types. The predetermined value may be greater than 0 and less than the block size processed per processing unit (e.g., clock) of the image encoding device. In this case, the encoding device may determine whether to allow the predetermined partition type as an available partition type by further considering whether the tree structure of the upper layer block is a dual-tree structure.

[0327] The width of the upper layer block may be determined based on the color format and width of the luminance block corresponding to the upper layer block. For example, the width of the upper layer block may be determined as a value obtained by dividing the width of the luminance block corresponding to the upper layer block by a component ratio of chrominance samples to luminance samples derived based on the color format. The width of the upper layer block may be determined by dividing the width of the upper layer block according to the partition type of the upper layer block.

[0328] For example, when the size of a block processed by each processing unit (e.g., a clock) of an image encoding device is 4×1, when the width of the current block is 4, the encoding device may not allow a quadtree partition type and a vertical binary partition type as the partition type of the upper layer block, and when the width of the upper layer block is 8, the encoding device may not allow a vertical trifurcated partition type as the partition type of the upper layer block.

[0329] More specifically, when the tree structure of the upper layer block is a dual tree structure and the width of the upper layer block is 4, the encoding apparatus may not allow a quadtree partition type and a vertical binary partition type as the partition type of the upper layer block.

[0330] In addition, when the tree structure of the upper layer block is a dual tree structure and the width of the upper layer block is 8, the encoding apparatus may not allow a vertical three-way partition type as a partition type of the upper layer block.

[0331] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the upper layer block is 4, the encoding device may not allow the quadtree partition type and the horizontal binary partition type as the partition type of the upper layer block. In this case, the encoding device may determine whether to allow the partition type by further considering whether the tree structure of the upper layer block is a dual tree structure.

[0332] In addition, when the size of the processing block per clock of the image decoding device is 1×4 and the height of the upper layer block is 8, the encoding device may not allow the horizontal three-branch partition type as the partition type of the upper layer block. In this case, the encoding device may determine whether to allow the partition type by further considering whether the tree structure of the higher layer block is a dual tree structure.

[0333] Next, the encoding device may determine a prediction mode for the current block (S3020). For example, the decoding device may generate prediction information for the current block based on various prediction modes, such as intra, inter, and IBC modes. In the case of intra prediction mode, prediction information for the current block may be generated based on multiple prediction modes, such as directional mode or CCLM. Furthermore, if the number of samples in the current block is equal to or less than 16, CCLM mode may not be selected as the prediction mode for the current block.

[0334] The encoding device may determine the prediction mode with the highest encoding efficiency (e.g., high RD cost) as the prediction mode of the current block. In addition, the encoding device may generate residual information based on the prediction result according to the determined prediction mode, and encode the prediction information and the residual information to encode the current block.

[0335] Next, when the determined prediction mode is an intra prediction mode, the encoding device may encode prediction information specifying the intra prediction mode (S3030). For example, when the intra prediction information of the luminance block corresponding to the current block is the same as the intra prediction information of the current block, the encoding device may encode the prediction information specifying the intra prediction mode of the current block to specify that the DM mode is set as the intra prediction mode of the current block.

[0336] Furthermore, as described above, by partitioning the upper layer block, the encoding device may encode information used to partition the upper layer block, thereby indicating the partition type used to determine the current block. In an embodiment, as described above, the encoding device may use qt_split_flag to specify whether the upper layer block is partitioned into a quadtree structure. If the upper layer block is partitioned into a quadtree, the encoding device may set qt_split_flag to a first value (e.g., 1) and perform encoding. If the upper layer block is not partitioned into a quadtree, the encoding device may set qt_split_flag to a second value (e.g., 0) and perform encoding.

[0337] In this embodiment, when the upper layer block is not partitioned into quadtrees but partitioned into multitrees, the encoding apparatus may specify whether the current block is partitioned into multitrees using mtt_split_cu_flag which is multitree partitioning information.

[0338] When the upper layer block is partitioned into multiple trees, the encoding apparatus may set mtt_split_cu_flag to a first value (eg, 1) and perform encoding. When the upper layer block is not partitioned into multiple trees, the encoding apparatus may set mtt_split_cu_flag to a second value (eg, 0) and perform encoding.

[0339] In addition, the encoding device may encode mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag to specify the multi-tree partition type and multi-tree partition direction of the upper layer block. For example, mtt_split_cu_vertical_flag may be set to a first value (e.g., 0) when the upper layer block is partitioned in the horizontal direction, and may be set to a second value (e.g., 1) when the upper layer block is partitioned in the vertical direction. mtt_split_cu_binary_flag may be set to a first value (e.g., 0) when the upper layer block is partitioned into a ternary tree, and may be set to a second value (e.g., 1) when the upper layer block is partitioned into a binary tree.

[0340] At the same time, if Figure 31 As shown, the encoding device can encode information about the partitioning of the upper layer block by encoding split_cu_flag (3110) as partitioning information specifying whether the upper layer block is partitioned, split_cu_flag (3120) as quadtree partitioning information specifying whether quadtree partitioning of the upper layer block is performed, mtt_split_cu_vertical_flag (3130) as partitioning direction information specifying the partitioning direction of the upper layer block in the multi-tree structure, and mtt_split_cu_binary_flag (3140) as partitioning type information specifying whether the partitioning type of the upper layer block is a binary partitioning type or a ternary partitioning type in the multi-tree structure.

[0341] As described above, split_cu_flag (3110) can be set to a first value (e.g., 0) when the upper layer block is not split, and can be set to a second value (e.g., 1) when the upper layer block is split into the current block. split_qt_flag (3120) can be set to a first value (e.g., 0) when the upper layer block is split into a quadtree, and can be set to a second value (e.g., 1) when the upper layer block is not split into a quadtree but is split into a multitree. mtt_split_cu_vertical_flag (3130) can be set to a first value (e.g., 0) when the upper layer block is split in the horizontal direction, and can be set to a second value (e.g., 1) when the upper layer block is split in the vertical direction. mtt_split_cu_binary_flag (3140) can be set to a first value (e.g., 0) when the upper layer block is split into a ternary tree, and can be set to a second value (e.g., 1) when the upper layer block is split into a binary tree.

[0342] The encoding device may encode information about the partitioning of the upper layer block based on whether the predetermined partitioning is allowed for the upper layer block. For example, when both quadtree partitioning and multitree partitioning are allowed for the upper layer block, the encoding device may not encode split_cu_flag. In this case, the decoding device may derive split_cu_flag as a predetermined value.

[0343] In addition, when quadtree partitioning is allowed for the upper layer block but multitree partitioning is not allowed, the encoding device may not encode qt_split_flag. In this case, the decoding device may derive qt_split_flag as a predetermined value.

[0344] In addition, when qt_split_flag specifies to perform quadtree splitting, horizontal binary splitting and horizontal ternary splitting are not allowed for the upper layer block, or vertical binary splitting and vertical ternary splitting are not allowed, the encoding device may not encode mtt_split_cu_vertical_flag. In this case, the decoding device may derive mtt_split_cu_vertical_flag as a predetermined value.

[0345] In addition, when qt_split_flag specifies that quadtree splitting is performed, or vertical binary splitting or vertical ternary splitting is not allowed for the upper layer block, or mtt_split_cu_vertical_flag specifies horizontal splitting and horizontal binary splitting or horizontal ternary splitting is not allowed for the upper layer block, or mtt_split_cu_vertical_flag specifies vertical splitting, the encoding device may not encode mtt_split_cu_binary_flag. In this case, the decoding device may derive mtt_split_cu_binary_flag as a predetermined value.

[0346] BitTorrent

[0347] Will refer to Figure 31 The method for generating a bitstream by an encoding device is described in more detail. The encoding device may determine whether to split the upper layer block used to determine the current block based on the above embodiment. More specifically, the encoding device may determine the value of the parameter allowSplitTtVer, which specifies whether vertical three-pronged splitting is allowed for the upper layer block, and determine the value to be a first value (e.g., 1) when splitting is allowed, and a second value (e.g., 0) when splitting is not allowed.

[0348] In addition, the encoding device can determine the value of the parameter allowSplitTtHor that specifies whether horizontal three-pronged splitting is allowed for the upper layer block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0349] In addition, the encoding device can determine the value of the parameter allowSplitBtVer that specifies whether vertical binary splitting is allowed for the upper layer block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0350] In addition, the encoding device can determine the value of the parameter allowSplitBtHor that specifies whether horizontal binary splitting is allowed for the upper layer block, determine the value to be a first value (e.g., 1) when splitting is allowed, and determine the value to be a second value (e.g., 0) when splitting is not allowed.

[0351] According to the determination, the encoding apparatus may determine whether at least one of split_cu_flag (3110), qt_split_flag (3120), mtt_split_cu_vertical_flag (3130), or mtt_split_cu_binary_flag (3140), which is the split information of the upper layer block, is output as a bitstream, as described above with reference to Figure 31 As stated.

[0352] Decoding method

[0353] Figure 32 is a flowchart illustrating a method for decoding an image by a decoding device according to an embodiment. Figure 32 The decoding method for executing the above-mentioned embodiment is described. The decoding apparatus according to the embodiment may include a memory and at least one processor, and the decoding apparatus may execute the following decoding method using the at least one processor.

[0354] According to an embodiment, the decoding apparatus may determine a current block by segmenting an image (S3210). Here, the current block may be a chroma block. The decoding apparatus may determine the current block by segmenting a portion of the image using a segmentation type determined based on segmentation information. Here, the segmentation information may be determined based on available segmentation types that can be used to segment a higher-layer block that is the portion of the image, and the available segmentation types may be determined based on the width of the portion of the image.

[0355] In an embodiment, the decoding device may not allow a predetermined partition type, among multiple partition types, in which the width or height of the current block determined by partitioning the upper layer block is a predetermined value, as an available partition type. Therefore, the decoding device may determine the partition type of the upper layer block to be an available partition type other than the predetermined partition type among the multiple partition types. The predetermined value may be greater than 0 and less than the value of blocks processed per processing unit (e.g., clock) by the image decoding device. In this case, the encoding device may determine whether to allow the predetermined partition type as an available partition type by further considering whether the tree structure of the upper layer block is a dual-tree structure.

[0356] The width of the upper layer block may be determined based on the color format and width of the luminance block corresponding to the upper layer block. For example, the width of the upper layer block may be determined as a value obtained by dividing the width of the luminance block corresponding to the upper layer block by a component ratio of chrominance samples to luminance samples derived based on the color format. The width of the upper layer block may be determined by dividing the width of the upper layer block according to the division type of the upper layer block.

[0357] For example, when the size of the processing block per clock of the image decoding device is 4×1, in order to limit the determination of the current block with a width less than 4, when the width of the upper layer block is 4, the decoding device may not allow the quadtree partition type and the vertical binary partition type as the partition type of the upper layer block, and when the width of the upper layer block is 8, the decoding device may not allow the vertical trifurcated partition type as the partition type of the upper layer block.

[0358] More specifically, when the tree structure of the upper layer block is a dual tree structure, the width of the luminance block corresponding to the upper layer block is 4, and the decoding apparatus may not allow a quadtree partition type and a vertical binary partition type as the partition type of the upper layer block.

[0359] In addition, when the tree structure of the upper layer block is a dual tree structure and the width of the upper layer block is 8, the decoding apparatus may not allow a vertical trifurcated partition type as a partition type of the current block.

[0360] In addition, when the size of the processing block per clock of the image decoding device is 1×4, in order to limit the determination of the current block having a height less than 4, when the height of the upper layer block is 4, the decoding device may not allow the quadtree partition type and the horizontal binary partition type as the partition type of the upper layer block. In this case, the decoding device may determine whether to allow the partition type by further considering whether the tree structure of the upper layer block is a dual tree structure.

[0361] In addition, when the size of the processing block per clock of the image decoding device is 1×4, in order to limit the determination of the current block having a height less than 4, the decoding device may not allow the horizontal three-branch partition type as the partition type of the upper layer block when the height of the upper layer block is 8. In this case, the decoding device may determine whether to allow the partition type by further considering whether the tree structure of the upper layer block is a dual-tree structure.

[0362] According to the above determination, the decoding device can determine the partition type of the upper layer block by determining the available partition types other than the predetermined partition type among the multiple partition types. For example, the decoding device can obtain or derive information about the partition of the upper layer block from the bitstream based on whether the predetermined partition is allowed. Figure 31 When predetermined splitting is allowed, the decoding apparatus may obtain at least one of split_cu_flag (3110), split_qt_flag (3120), mtt_split_cu_vertical_flag (3130), or mtt_split_cu_binary_flag (3140), which is information about splitting of the upper layer block, from the bitstream by parsing the bitstream.

[0363] Meanwhile, when the predetermined split is not permitted, the decoding apparatus may determine the information regarding the split of the upper layer block to be a value specifying a split other than the predetermined split. For example, when the predetermined split is not permitted, the information regarding the split of the upper layer block may be derived as a predetermined value without being obtained from the bitstream. For example, the split_cu_flag specifying whether to perform split may be derived as 0.

[0364] In an embodiment, when the value of split_cu_flag is 1, and based on the above embodiment, all vertical trifurcations, horizontal trifurcations, vertical binary splits, and horizontal binary splits are not allowed for the upper layer block, split_qt_flag specifying whether to perform quadtree splitting can be exported as 1, otherwise, it can be exported as 0.

[0365] When horizontal trifurcating splitting or horizontal binary splitting is allowed for the upper layer block, mtt_split_cu_vertical_flag, which is split direction information, may be derived as 0, and otherwise, may be derived as 1.

[0366] When vertical binary splitting and horizontal binary splitting are not allowed for the upper layer block, mtt_split_cu_binary_flag as the splitting type information can be derived as 0, and when vertical trigeminal splitting and horizontal trigeminal splitting are not allowed for the upper layer block, it can be derived as 1, when horizontal binary splitting and vertical trigeminal splitting are allowed for the upper layer block, it can be derived as 1-mtt_split_cu_vertical_flag value, and when vertical binary splitting and horizontal trigeminal splitting are allowed for the upper layer block, it can be derived as mtt_split_cu_vertical_flag value.

[0367] As described above, the decoding apparatus may determine the partition type of the upper layer block to be a partition mode corresponding to any one of quadtree or multitree based on split_qt_flag ( 3120 ), mtt_split_cu_vertical_flag ( 3130 ), and mtt_split_cu_binary_flag ( 3140 ) and Table 1.

[0368] Next, the decoding apparatus according to an embodiment may obtain a prediction mode of the current block (S3220). In addition, when the prediction information specifies an intra prediction mode, the decoding apparatus may decode the current block by performing intra prediction (S3230).

[0369] For example, the prediction information may indicate one of a directional intra-frame prediction mode, a DM mode, and a CCLM mode. For example, when the prediction information specifies a DM mode determined with reference to the intra-frame prediction mode of a luma block, the decoding device may determine the intra-frame prediction mode of the current block based on the intra-frame prediction information of the luma block corresponding to the current block. Meanwhile, when the number of samples of the current block is equal to or less than 16, the decoding device may not determine the CCLM mode used to determine the sample values ​​of the current block based on the sample values ​​of the luma block as the prediction mode for the current block. In this case, the decoding device may determine the prediction mode for the current block as a predetermined intra-frame prediction mode (e.g., a directional intra-frame prediction mode or a DM mode) instead of the CCLM mode.

[0370] Application Examples

[0371] Although the exemplary method of the present disclosure is shown as a series of operations for the sake of clarity of description, it is not intended to limit the order in which the steps are performed, and these steps can be performed simultaneously or in a different order if necessary. In order to implement the method according to the present invention, 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.

[0372] In the present disclosure, an image encoding device or image decoding device that performs a predetermined operation (step) may perform an operation (step) that confirms the conditions or circumstances for executing the corresponding operation (step). For example, if a description is given of performing a predetermined operation 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.

[0373] 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 combination of two or more.

[0374] 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.

[0375] Furthermore, the image decoding apparatus and image encoding apparatus to which the embodiments of the present disclosure are applied may be included in multimedia broadcast transmission and reception equipment, mobile communication terminals, home theater video equipment, digital theater video equipment, surveillance cameras, video chat equipment, real-time communication equipment such as video communication, mobile streaming equipment, storage media, cameras, video on demand (VoD) service provision equipment, over-the-top (OTT) video equipment, internet streaming service provision equipment, three-dimensional (3D) video equipment, video phone video equipment, medical video equipment, and the like, and may be used to process video signals or data signals. For example, OTT video equipment may include game consoles, Blu-ray players, internet-connected televisions, home theater systems, smartphones, tablet PCs, digital video recorders (DVRs), and the like.

[0376] Figure 33 is a diagram illustrating a content streaming system to which an embodiment of the present disclosure can be applied.

[0377] like Figure 33 As shown in , a content streaming system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming server, a network server, a media storage, a user device, and a multimedia input device.

[0378] The encoding server compresses the content input from multimedia input devices such as smartphones, cameras, and camcorders into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when multimedia input devices such as smartphones, cameras, and camcorders directly generate the bitstream, the encoding server can be omitted.

[0379] 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.

[0380] The streaming server transmits multimedia data to user devices based on user requests via a network server, and the network server serves as an intermediary for notifying 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 serves to control the command and response between devices in the content streaming system.

[0381] The streaming server can receive content from a media storage and / or encoding server. For example, when receiving content from an encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined time.

[0382] 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 PCs, tablet computers, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0383] Each server in the content streaming system may operate as a distributed server, in which case the data received from each server may be distributed.

[0384] The scope of the present disclosure includes software or 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 a non-transitory computer-readable medium having such software or commands stored thereon and executable on a device or computer.

[0385] Industrial Applicability

[0386] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. A device for image decoding, the device comprising: Memory; as well as at least one processor connected to the memory, the at least one processor being configured to: determining whether a predetermined partition type is allowed for the current block; determining a partition type of the current block based on whether the predetermined partition type is allowed for the current block; Based on the determined segmentation type of the current block, segment the current block into a plurality of lower-layer blocks; as well as decoding the lower layer block, wherein the predetermined segmentation type is not allowed to be used for the current block based on the width of the chroma block derived from the current block by the predetermined segmentation type being 2 or the number of times the current block is segmented from a quad leaf node is equal to or greater than a predetermined threshold, and Wherein, based on the fact that the height of the chroma block derived from the current block by the predetermined partition type is 2 and the number of times the current block is partitioned from a quad leaf node is less than a predetermined threshold, the predetermined partition type is allowed to be used for the current block.

2. The image decoding device according to claim 1, wherein: The predetermined segmentation type includes at least one of a vertical binary segmentation type and a vertical trifurcated segmentation type.

3. The image decoding device according to claim 1, wherein: Based on the predetermined partition type being allowed for the current block, a width of the current block is greater than a predetermined first value.

4. The image decoding device according to claim 3, wherein: The predetermined first value is determined differently based on the predetermined segmentation type.

5. The image decoding device according to claim 1, wherein: Based on the predetermined partition type being determined as the partition type of the current block, a width of each of the lower layer blocks is equal to or greater than 4.

6. The image decoding device according to claim 1, wherein: The tree structure of the current block is a dual tree structure.

7. A device for image encoding, the device comprising: Memory; as well as at least one processor connected to the memory, the at least one processor being configured to: determining whether a predetermined partition type is allowed for the current block; determining a partition type of the current block based on whether the predetermined partition type is allowed for the current block; Based on the determined segmentation type of the current block, segment the current block into a plurality of lower-layer blocks; and encoding the lower layer block, wherein the predetermined segmentation type is not allowed to be used for the current block based on the width of the chroma block derived from the current block by the predetermined segmentation type being 2 or the number of times the current block is segmented from a quad leaf node is equal to or greater than a predetermined threshold, and Wherein, based on the fact that the height of the chroma block derived from the current block by the predetermined partition type is 2 and the number of times the current block is partitioned from a quad leaf node is less than a predetermined threshold, the predetermined partition type is allowed to be used for the current block.

8. The image encoding device according to claim 7, wherein: The predetermined segmentation type includes at least one of a vertical binary segmentation type and a vertical trifurcated segmentation type.

9. The image encoding device according to claim 7, wherein: Based on the predetermined partition type being allowed for the current block, a width of the current block is greater than a predetermined first value.

10. The image encoding device according to claim 9, wherein: The predetermined first value is determined differently based on the predetermined segmentation type.

11. The image encoding device according to claim 7, wherein: Based on the predetermined partition type being determined as the partition type of the current block, a width of each of the lower layer blocks is equal to or greater than 4.

12. The image encoding device according to claim 7, wherein: The tree structure of the current block is a dual tree structure.

13. A device for sending image data, the device comprising: at least one processor configured to obtain a bitstream; as well as A transmitter, the transmitter being configured to transmit the bit stream, wherein the bit stream is generated by an image encoding method, the image encoding method comprising: determining whether a predetermined partition type is allowed for the current block; determining a partition type of the current block based on whether the predetermined partition type is allowed for the current block; Based on the determined segmentation type of the current block, segment the current block into a plurality of lower-layer blocks; and encoding the lower layer block into the bitstream, wherein the predetermined segmentation type is not allowed to be used for the current block based on the width of the chroma block derived from the current block by the predetermined segmentation type being 2 or the number of times the current block is segmented from a quad leaf node is equal to or greater than a predetermined threshold, and Wherein, based on the fact that the height of the chroma block derived from the current block by the predetermined partition type is 2 and the number of times the current block is partitioned from a quad leaf node is less than a predetermined threshold, the predetermined partition type is allowed to be used for the current block.

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