Image encoding / decoding method and device, and method for transmitting bit stream

Abstract

An image encoding / decoding method and apparatus are provided. The image decoding method performed by the image decoding apparatus may include: obtaining a current block by segmenting an image, determining prediction mode characteristic information based on encoding information of the current block, determining a prediction mode type of a lower layer block segmented from the current block based on the prediction mode characteristic information, obtaining a lower layer block by segmenting the current block, and decoding the lower layer block based on the determined prediction mode type of the lower layer block. The prediction mode characteristic information may be determined based on a color format of the current block.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method and apparatus, and more particularly, to an image encoding / decoding method for determining a partitioning mode according to a color format, and a method of transmitting a bit stream generated by the image encoding method / apparatus of the present disclosure. Background Art

[0002] Recently, the demand for high-resolution and high-quality images, such as high-definition (HD) images and ultra-high-definition (UHD) images, is increasing in various fields. As the resolution and quality of image data are improved, the amount of information or bits transmitted is relatively increased compared to existing image data. The increase in the amount of information or bits transmitted leads to an increase in transmission cost and storage cost.

[0003] Therefore, efficient image compression technology is needed to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the invention

[0004] Technical issues

[0005] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] An object of the present disclosure is to provide an image encoding / decoding method and apparatus for improving encoding / decoding efficiency by determining a segmentation mode according to a color format.

[0007] 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.

[0008] 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.

[0009] Another object of the present disclosure is to provide a recording medium storing a bit stream received and decoded by the image decoding apparatus according to the present disclosure and used to reconstruct an image.

[0010] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described herein will be apparent to those skilled in the art through the following description.

[0011] Technical Solution

[0012] According to one aspect of the present disclosure, an image decoding method performed by an image decoding device may include: obtaining a current block by segmenting an image, determining prediction mode characteristic information based on encoding information of the current block, determining a prediction mode type of a lower layer block segmented from the current block based on the prediction mode characteristic information, obtaining a lower layer block by segmenting the current block, and decoding the lower layer block based on the determined prediction mode type of the lower layer block. The prediction mode characteristic information may be determined based on a color format of the current block.

[0013] In addition, obtaining the lower layer block by partitioning the current block can be performed by determining the partition structure of the lower layer block based on the prediction mode type of the lower layer block, and based on the prediction mode type of the lower layer block being an intra-frame prediction mode type, the partition structure of the lower layer block can be determined as a dual-tree partition structure.

[0014] In addition, based on the partition structure of the lower layer block being determined as a dual-tree partition structure, the partition availability of the luminance block and the chrominance block for the current block can be independently determined, and the partition availability of the chrominance block can be determined based on the color format. For example, the prediction mode characteristic information can be determined to be a first value based on the color format of the current block being a monochrome format or a 4:4:4 format. Based on the prediction mode characteristic information being a first value, the prediction mode type of the lower layer block can be determined to be the prediction mode type of the current block.

[0015] For example, based on the number of luminance samples of the current block being 64, the partition mode of the current block being a binary partition mode, and the color format of the current block being a predetermined format, the prediction mode characteristic information may be determined as a first value. Alternatively, based on the number of luminance samples of the current block being 128, the partition mode of the current block being a trifurcated partition mode, and the color format of the current block being a predetermined format, the prediction mode characteristic information may be determined as a first value. The predetermined format may be a monochrome format or a 4:4:4 format.

[0016] Alternatively, based on the color format of the current block being 4:2:0 format, the number of luminance samples of the current block being 64, and the partition mode of the current block being a binary partition mode, the prediction mode characteristic information may be determined depending on whether the slice to which the current block belongs is an I slice.

[0017] Alternatively, based on the color format of the current block being 4:2:0 format, the number of luminance samples of the current block being 128, and the partition mode of the current block being a three-pronged partition mode, the prediction mode characteristic information may be determined depending on whether the slice to which the current block belongs is an I slice.

[0018] In addition, based on the slice to which the current block belongs being an I slice, the prediction mode characteristic information may be determined as a second value, and based on the prediction mode characteristic information being the second value, the prediction mode type of the lower layer block may be determined as an intra prediction mode type.

[0019] At the same time, based on the fact that the slice to which the current block belongs is not an I slice, the prediction mode characteristic information may be determined as a third value, and based on the prediction mode characteristic information being the third value, the prediction mode type of the lower layer block may be determined based on the mode constraint information obtained from the bitstream. The mode constraint information may specify whether the inter-frame prediction mode is allowed, and based on the mode constraint information specifying that the inter-frame prediction mode is allowed, the prediction mode type of the lower layer block may be determined as an inter-frame prediction mode type.

[0020] In addition, an image decoding device according to an aspect of the present disclosure may include a memory and at least one processor. The at least one processor may: obtain a current block by segmenting an image, determine prediction mode characteristic information based on encoding information of the current block, determine a prediction mode type of a lower layer block segmented from the current block based on the prediction mode characteristic information, obtain a lower layer block by segmenting the current block, and decode the lower layer block based on the determined prediction mode type of the lower layer block. The prediction mode characteristic information may be determined based on a color format of the current block.

[0021] In addition, an image encoding method performed by an image encoding device according to an aspect of the present disclosure may include: obtaining a current block by segmenting an image, determining prediction mode characteristic information based on encoding information of the current block, determining a prediction mode type of a lower layer block segmented from the current block based on the prediction mode characteristic information, obtaining a lower layer block by segmenting the current block, and encoding the lower layer block based on the determined prediction mode type of the lower layer block. The prediction mode characteristic information may be determined based on a color format of the current block.

[0022] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding device or the image encoding method of the present disclosure.

[0023] 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.

[0024] 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.

[0025] Beneficial Effects

[0026] According to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0027] Furthermore, according to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus for improving encoding / decoding efficiency by determining a partitioning mode according to a color format.

[0028] Furthermore, according to the present disclosure, it is possible to provide a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0029] Furthermore, according to the present disclosure, it is possible to provide a recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0030] Furthermore, according to the present disclosure, it is possible to provide a recording medium that stores a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0031] 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

[0032] Figure 1 is a view schematically showing a video coding system to which an embodiment of the present disclosure is applicable.

[0033] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0034] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0035] Figure 4 is a diagram of a partition structure of an image according to an embodiment.

[0036] Figure 5 is a view showing an embodiment of partition types of blocks according to a multi-type tree structure.

[0037] 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.

[0038] Figure 7 is a diagram showing an embodiment in which a CTU is partitioned into a plurality of CUs.

[0039] Figure 8 is a view illustrating an embodiment of a redundant partition pattern.

[0040] Figures 9 to 11 is a view illustrating a positional relationship between luma samples and chroma samples determined according to a chroma format according to an embodiment.

[0041] Fig.12 is a view illustrating a syntax for chroma format signaling according to an embodiment.

[0042] Fig.13is a view illustrating a chroma format classification table according to an embodiment.

[0043] Fig.14 is a view illustrating an embodiment of a luma block and a chroma block when a color format is 4:2:0.

[0044] Figures 15 to 17 is a view illustrating one syntax for a coding tree unit (CTU) according to an embodiment.

[0045] Fig.18 is a view illustrating a luma block and a chroma block when the color format is 4:4:4.

[0046] Figure 19 to Figure 20 is a flowchart illustrating that an encoding apparatus and a decoding apparatus according to an embodiment perform encoding and decoding methods according to an embodiment.

[0047] Fig.21 is a view illustrating a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0048] 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.

[0049] 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, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

[0050] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may also be included, rather than excluding other components.

[0051] In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing 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.

[0052] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one 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 the present disclosure.

[0053] 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.

[0054] 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.

[0055] In the present disclosure, a "picture" generally refers to a unit representing an image within a specific time period, and a slice / tile is a coding unit that constitutes a part of a picture. A picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0056] In the present disclosure, "pixel" or "pel" may mean the smallest single unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0057] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0058] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0059] Furthermore, 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 a chroma block such as “chroma block” or “current chroma block.”

[0060] 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".

[0061] In the present disclosure, the term "or" should be interpreted to indicate "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 the present disclosure, "or" should be interpreted to indicate "additionally or alternatively".

[0062] Video compilation system overview

[0063] Figure 1 is a view schematically illustrating a video coding system according to the present disclosure.

[0064] 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 a stream.

[0065] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit 22, and a renderer 23. The encoding unit 12 may be called a video / image encoding unit, and the decoding unit 22 may be called 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.

[0066] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0067] The encoding unit 12 may encode the input video / image. For compression and coding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output encoded data (encoded video / image information) in the form of a bitstream.

[0068] The transmitter 13 may transmit the encoded video / image information or the data output in the form of a bit stream to the receiver 21 of the decoding device 20 in the form of a file or stream through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmitting through a broadcast / communication network. The receiver 21 may extract / receive a bit stream from a storage medium or a network and transmit the bit stream to the decoding unit 22.

[0069] 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.

[0070] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0071] Overview of Image Coding Device

[0072] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0073] like Figure 2As 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 also include a subtractor 115.

[0074] 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.

[0075] The image partitioner 110 may partition an 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 maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QT / BT / TT) structure. For example, a coding unit may be partitioned into multiple coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary structure. For the partitioning of the coding unit, a quadtree structure may be applied first, and then a binary tree structure and / or a ternary structure may be applied. The coding process according to the present disclosure may be performed based on a final coding unit that is no longer partitioned. The maximum coding unit may be used as the final coding unit, or a coding unit of a deeper depth obtained by partitioning the maximum coding unit may be used as the final coding unit. Here, the coding process may include a prediction, transformation, and reconstruction process to be described later. As another example, the processing unit of the coding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transformation 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 a transform coefficient.

[0076] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and transmit the generated information to the entropy encoder 190. The information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0077] The intra prediction unit 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or the intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra 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 plane 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 only an example, and more or fewer directional prediction modes may be used according to the settings. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0078] The inter prediction unit 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on the neighboring blocks and generate information specifying which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter prediction unit 180 may use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding the motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0079] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may not only apply intra prediction or inter prediction, but may also apply intra prediction and inter prediction simultaneously to predict the current block. The prediction method of applying both intra prediction and inter prediction simultaneously to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copy (IBC) to predict the current block. Intra block copy may be used for content image / video coding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because 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.

[0080] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate 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.

[0081] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT refers to a transform obtained from a graph when relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size rather than square.

[0082] 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 the block form into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0083] The entropy encoder 190 may 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 may encode information required for video / image reconstruction (e.g., values ​​of syntax elements, etc.) together or separately in addition to quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may also include general constraint information. The signaled information, transmitted information, and / or syntax elements described in the present disclosure may be encoded and included in a bitstream through the above-described encoding process.

[0084] The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0085] 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 transformation to the quantized transform coefficients through the dequantizer 140 and the inverse transformer 150.

[0086] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed image, reconstructed block, reconstructed sample array). If there is no residual in the block to be processed, such as when the skip mode is applied, the prediction block can be used as a reconstructed block. The adder 155 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0087] 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 bit stream.

[0088] 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.

[0089] 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 is 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 spatial neighboring block or the motion information of the temporal 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.

[0090] Overview of image decoding device

[0091] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0092] like Figure 3As shown, the image decoding device 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.

[0093] According to an embodiment, all or at least some of the plurality of 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.

[0094] The image decoding apparatus 200 having received a bit stream including video / image information may perform the same operation as that performed by Figure 2 The image may be reconstructed by a process corresponding to the process performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The 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).

[0095] The image decoding apparatus 200 may receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, 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 the general constraint information. The information and / or syntax elements signaled / received described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residual. More specifically, the CABAC entropy decoding method can receive a bin corresponding to each syntax element in the bitstream, use the decoding target syntax element information, the decoding information of the neighboring block and the decoding target block, or the information of the symbol / bin decoded in the previous stage to determine the context model, and perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. The information related to the prediction in the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value on which entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information can be input to the dequantizer 220. In addition, information about filtering among the information decoded by the entropy decoder 210 can be 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 .

[0096] 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, at least one of an inter-frame prediction unit 160 or an intra-frame prediction unit 265.

[0097] The dequantizer 220 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 220 may rearrange the quantized transform coefficient in the form of a two-dimensional block. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may perform dequantization on the quantized transform coefficient by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0098] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0099] The prediction unit may perform prediction on the current block and generate a prediction block including a prediction sample of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about the prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0100] The same 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.

[0101] 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.

[0102] The inter prediction unit 260 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter prediction unit 260 may configure a motion information candidate list based on the neighboring blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and information about the prediction may include information indicating an inter prediction mode of the current block.

[0103] 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-prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 is also applicable to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0104] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc.

[0105] The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter-frame prediction unit 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) 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 260 to be used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0106] 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.

[0107] Overview of Image Partitioning

[0108] 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 (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) can be performed to perform image decoding.

[0109] 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.

[0110] Overview of CTU Partitions

[0111] As described above, the coding unit may be obtained by recursively partitioning the coding tree unit (CTU) or the largest coding unit (LCU) according to the quadtree / binary tree / ternary tree (QT / BT / TT) structure. For example, the CTU may be first partitioned into a quadtree structure. Thereafter, the leaf nodes of the quadtree structure may be further partitioned by a multi-type tree structure.

[0112] Partitioning according to the quadtree means that the current CU (or CTU) is equally partitioned into four. By partitioning according to the quadtree, the current CU can be partitioned into four CUs with the same width and the same height. When the current CU is no longer partitioned into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. The CU corresponding to the leaf node of the quadtree structure may no longer be partitioned and may be used as the above-mentioned final coding unit. Alternatively, the CU corresponding to the leaf node of the quadtree structure may be further partitioned by a multi-type tree structure.

[0113] Figure 5 is a view showing an embodiment of partition types of a block according to a multi-type tree structure. The partition according to the multi-type tree structure may include two types of partitions according to a binary tree structure and two types of partitions according to a ternary tree structure.

[0114] The two types of splits according to the binary tree structure may include vertical binary split (SPLIT_BT_VER) and horizontal binary split (SPLIT_BT_HOR). Vertical binary split (SPLIT_BT_VER) means that the current CU is equally split into two in the vertical direction. Figure 4 As shown in FIG, by vertical binary splitting, two CUs with the same height as the current CU and half the width of the current CU can be generated. Horizontal binary splitting (SPLIT_BT_HOR) means that the current CU is equally split into two in the horizontal direction. Figure 5 As shown, through horizontal binary splitting, two CUs with a height half of the height of the current CU and the same width as the current CU can be generated.

[0115] The two types of splits according to the ternary tree structure may include vertical ternary split (SPLIT_TT_VER) and horizontal ternary split (SPLIT_TT_HOR). In vertical ternary split (SPLIT_TT_VER), the current CU is split in a vertical direction at a ratio of 1:2:1. Figure 5 As shown, through vertical three-pronged splitting, two CUs with the same height as the current CU and a width of 1 / 4 of the width of the current CU, and a CU with the same height as the current CU and a width of half the width of the current CU 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 whose height is 1 / 4 of the height of the current CU and whose width is the same as the current CU, and a CU whose height is half of the height of the current CU and whose width is the same as the current CU can be generated.

[0116] 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.

[0117] Here, the CTU is regarded as the root node of the quadtree and is partitioned into a quadtree structure for the first time. Information (e.g., qt_split_flag) specifying whether to perform quadtree segmentation 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 partitioned by the quadtree. 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, the leaf node of the quadtree can become a node (MTT_node) of a multi-type tree. In the multi-type tree structure, a first flag (e.g., Mtt_split_cu_flag) is signaled to specify whether the current node is additionally partitioned. If the corresponding node is additionally partitioned (e.g., if the first flag is 1), a second flag (e.g., Mtt_split_cu_vertical_flag) may be signaled to specify the partition direction. For example, the partition direction may be a vertical direction when the second flag is 1, and a horizontal direction when the second flag is 0. Then, a third flag (e.g., Mtt_split_cu_binary_flag) may be signaled to specify whether the partition type is a binary partition type or a ternary partition type. For example, the partition type may be a binary partition type when the third flag is 1, and a ternary partition type when the third flag is 0. The nodes of the multi-type tree obtained by binary partitioning or ternary partitioning 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, but becomes a leaf node (MTT_leaf_node) of the multi-type tree. The CU corresponding to the leaf node of the multi-type tree may be used as the above-mentioned final coding unit.

[0118] Based on mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, a multi-type tree partition mode (MttSplitMode) of a CU may be derived as shown in the following Table 1. In the following description, a multi-type tree partition mode may be referred to as a multi-tree partition type or a partition type.

[0119] [Table 1]

[0120] MttSplitMode mtt_split_cu_vertical_flag mtt_split_cu_binary_flag SPLIT_TT_HOR 0 0 SPLIT_BT_HOR 0 1 SPLIT_TT_VER 1 0 SPLIT_BT_VER 1 1

[0121] Figure 7 is a view showing an example of partitioning a CTU into a plurality of CUs by applying a multi-type tree after applying a quadtree. Figure 7 , the bold block edge 710 represents a quadtree partition, and the remaining edge 720 represents a multi-type tree partition. The CU may correspond to a coding block (CB). In an embodiment, the CU may include a coding block of luma samples and two coding blocks of chroma samples corresponding to the luma samples. The chroma component (sample) CB or TB size may be derived based on the luma component (sample) CB or TB size based on the component ratio according to the color format (chroma format, for example, 4:4:4, 4:2:2, 4:2:0, etc.) of the picture / image. In the case of a 4:4:4 color format, the chroma component CB / TB size may be set to be equal to the luma component CB / TB size. In the case of a 4:2:2 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to the height of the luma component CB / TB. In the case of a 4:2:0 color format, the width of the chroma component CB / TB may be set to half the width of the luma component CB / TB and the height of the chroma component CB / TB may be set to half the height of the luma component CB / TB.

[0122] In an embodiment, when the size of the CTU is 128 based on the luma sample unit, the size of the CU may have a size 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 have a size from 64x64 to 2x2.

[0123] 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 indicates the luma component (sample) transform block (TB) size.

[0124] The TU size can be derived based on the maximum allowed TB size maxTbSize as a predetermined value. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) with maxTbSize can be derived from the CU, and transform / inverse transform can be performed in units of TU (TB). 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.

[0125] In addition, for example, when intra prediction is applied, the intra prediction mode / type may be derived in units of CU (or CB), and the neighboring reference sample derivation and prediction sample generation process may be performed in units of TU (or TB). In this case, there may be one or more TUs (or TBs) in a CU (or CB) region, and in this case, multiple TUs or (TBs) may share the same intra prediction mode / type.

[0126] Meanwhile, for a quadtree coding tree scheme with nested multi-type trees, the following parameters may be signaled from an encoding device to a decoding device as SPS syntax elements. For example, at least one of a CTU size as a parameter indicating a root node size of a quadtree, a MinQTSize as a parameter indicating a minimum allowed quadtree leaf node size, a MaxBtSize as a parameter indicating a maximum allowed binary tree root node size, a MaxTtSize as a parameter indicating a maximum allowed ternary tree root node size, a MaxMttDepth as a parameter indicating a maximum allowed hierarchical depth of multi-type tree partitioning from a quadtree leaf node, a MinBtSize as a parameter indicating a minimum allowed binary tree leaf node size, or a MinTtSize as a parameter indicating a minimum allowed ternary tree leaf node size is signaled.

[0127] As an embodiment using a 4:2:0 chroma format, the CTU size may be set to 128x128 luminance blocks and two 64x64 chrominance blocks corresponding to these luminance blocks. In this case, MinOTSize may be set to 16x16, MaxBtSize may be set to 128x128, MaxTtSzie may be set to 64x64, MinBtSize and MinTtSize may be set to 4x4, and MaxMttDepth may be set to 4. Quadtree partitioning may be applied to a CTU to generate a quadtree leaf node. A quadtree leaf node may be referred to as a leaf QT node. The size of a quadtree leaf node may be from 16x16 size (e.g., MinOTSize) to 128x128 size (e.g., CTU size). If the leaf QT node is 128x128, it may not be additionally partitioned into a binary tree / ternary tree. This is because, in this case, even if partitioned, it exceeds MaxBtsize and MaxTtszie (e.g., 64x64). In other cases, the leaf QT node can 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 can 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 is 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 is less than or equal to 2xMinTtSize, further vertical partitioning may not be considered. When partitioning is not considered, the encoding device may skip the signaling of the partition information. In this case, the decoding device may derive partition information having a predetermined value.

[0128] At the same time, one CTU may include a coding block of luma samples (hereinafter referred to as "luminance block") and two coding blocks of chroma samples corresponding thereto (hereinafter referred to as "chroma blocks"). The above coding tree scheme may be applied equally or individually to the luma block and chroma block of the current CU. Specifically, the luma block and chroma block in one CTU may be partitioned into the same block tree structure, and in this case, the tree structure is represented as SINGLE_TREE. Alternatively, the luma block and chroma block in one CTU may be partitioned into separate block tree structures, and in this case, the tree structure may be represented as DUAL_TREE. That is, when the CTU is partitioned into dual trees, the block tree structure for the luma block and the block tree structure for the chroma block may exist separately. In this case, the block tree structure for the luma block may be referred to as DUAL_TREE_LUMA, and the block tree structure for the chroma component may be referred to as DUAL_TREE_CHROMA. For P and B slices / block groups, the luma block and the chroma block in one CTU may be restricted to have the same coding tree structure. However, for I slices / patch groups, luma blocks and chroma blocks may have separate block tree structures from each other. If a separate block tree structure is applied, luma CTBs may be partitioned into CUs based on a specific coding tree structure, and chroma CTBs may be partitioned into chroma CUs based on another coding tree structure. That is, this means that a CU in an I slice / patch group to which a separate block tree structure is applied may include a coding block of a luma component or a coding block of two chroma components, and a CU of a P or B slice / patch group may include blocks of three color components (one luma component and two chroma components).

[0129] Although a quadtree coding tree structure with nested multi-type trees has been described, the structure for partitioning a CU is not limited thereto. For example, the BT structure and the TT structure may be interpreted as concepts included in a multi-partition tree (MPT) structure, and the CU may be interpreted as being partitioned by the QT structure and the MPT structure. In an example where a CU is partitioned by the QT structure and the MPT structure, a syntax element (e.g., MPT_split_type) including information about how many blocks a leaf node of the QT structure is partitioned into and a syntax element (e.g., MPT_split_mode) including information about which of the vertical and horizontal directions a leaf node of the QT structure is partitioned into may be signaled to determine the partition structure.

[0130] 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.

[0131] The quadtree coding block structure with multi-type trees can provide a very flexible block partition structure. Due to the partition types supported in the multi-type trees, different partition patterns can potentially produce the same coding block structure in some cases. In the encoding device and the decoding device, by limiting the occurrence of such redundant partition patterns, the amount of data of the partition information can be reduced.

[0132] For example, Figure 8 The following figure 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, as 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 partitioning or ternary partitioning is not signaled and its value may be derived as 0 by the decoding device.

[0133] Chroma Format Overview

[0134] Hereinafter, the chroma format will be described. An image may be encoded into encoded data including a luma component (e.g., Y) array and two chroma component (e.g., Cb and Cr) arrays. For example, one pixel of an encoded image may include a luma sample and a chroma sample. A chroma format may be used to represent the configuration format of luma samples and chroma samples, and a chroma format may be referred to as a color format.

[0135] In an embodiment, an image may be encoded into various chroma formats, such as monochrome, 4:2:0, 4:2:2, or 4:4:4. In monochrome sampling, there may be one sample array, and the sample array may be a luma array. In 4:2:0 sampling, there may be one luma sample array and two chroma sample arrays, and each of the two chroma arrays may have a height equal to half the height of the luma array, and a width equal to half the width of the luma array. In 4:2:2 sampling, there may be one luma sample array and two chroma sample arrays, and each of the two chroma arrays may have a height equal to the height of the luma array and a width equal to half the width of the luma array. In 4:4:4 sampling, there may be one luma sample array and two chroma sample arrays, and each of the two chroma arrays may have a height and width equal to the height and width of the luma array.

[0136] Fig. 9 is a diagram illustrating relative positions of luma samples and chroma samples according to an embodiment according to 4:2:0 sampling. Fig.10 is a diagram illustrating relative positions of luma samples and chroma samples according to an embodiment according to 4:2:2 sampling. Fig.11 2 is a diagram illustrating relative positions of luma samples and chroma samples according to an embodiment of 4:4:4 sampling. Fig. 9 As shown in , in 4:2:0 sampling, chroma samples can be located below their corresponding luma samples. Fig.10 As shown in , in 4:2:2 sampling, chroma samples can be located so as to overlap with their corresponding luma samples. Fig.11 As shown in , in 4:4:4 sampling, both luma samples and chroma samples can be located at overlapping positions.

[0137] The chroma format used in the encoding device and the decoding device may be predetermined. Alternatively, the chroma format may be signaled from the encoding device to the decoding device to be adaptively used in the encoding device and the decoding device. In an embodiment, the chroma format may be signaled based on at least one of chroma_format_idc or separate_colour_plane_flag. At least one of chroma_format_idc or separate_colour_plane_flag may be signaled via a higher level syntax such as DPS, VPS, SPS, or PPS. For example, chroma_format_idc and separate_colour_plane_flag may be included in Fig.12 In the SPS syntax shown in .

[0138] at the same time, Fig.13 An embodiment of chroma format classification using signaling of chroma_format_idc and separate_colour_plane_flag is shown. chroma_format_idc can be information specifying the chroma format applied to the encoded image. separate_colour_plane_flag can specify whether the color array is processed separately in a specific chroma format. For example, a first value (e.g., 0) of chroma_format_idc can specify monochrome sampling. A second value (e.g., 1) of chroma_format_idc can specify 4:2:0 sampling. A third value (e.g., 2) of chroma_format_idc can specify 4:2:2 sampling. A fourth value (e.g., 3) of chroma_format_idc can specify 4:4:4 sampling.

[0139] In 4:4:4, the following may apply based on the value of separate_colour_plane_flag. If the value of separate_colour_plane_flag is a first value (e.g., 0), each of the two chroma arrays may have the same height and width as the luma array. In this case, the value of ChromaArrayType, which specifies the type of the chroma sample array, may be set equal to chroma_format_idc. If the value of separate_colour_plane_flag is a second value (e.g., 1), the luma, Cb, and Cr sample arrays may be processed separately and together with a monochrome sampled picture. In this case, ChromaArrayType may be set to 0.

[0140] Intra prediction on chroma blocks

[0141] When intra prediction is performed on the current block, prediction of the luminance component block (luminance block) of the current block and prediction of the chrominance component block (chrominance block) can be performed. In this case, the intra prediction mode for the chrominance block can be set separately from the intra prediction mode for the luminance block.

[0142] For example, an intra prediction mode for a chroma block may be specified based on the intra chroma prediction mode information, and the intra chroma prediction mode information may be signaled in the form of an intra_chroma_pred_mode syntax element. For example, the intra chroma prediction mode information may represent one of a plane mode, a DC mode, a vertical mode, a horizontal mode, a derived mode (DM), and a cross-component linear model (CCLM) mode. Here, the plane mode may specify intra prediction mode #0, the DC mode may specify intra prediction mode #1, the vertical mode may specify intra prediction mode #26, and the horizontal mode may specify intra prediction mode #10. DM may also be referred to as a direct mode. CCLM may also be referred to as a linear model (LM). The CCLM mode may include at least one of L_CCLM, T_CCLM, and LT_CCLM.

[0143] Meanwhile, DM and CCLM are related intra prediction modes for predicting chrominance blocks using information about luma blocks. DM may represent a mode in which the same intra prediction mode as the intra prediction mode of the luma component is applied as the intra prediction mode for the chroma component. In addition, CCLM may represent an intra prediction mode in which, in generating a prediction block for a chroma block, samples derived by subsampling a reconstructed sample of a luma block and then applying α and β as CCLM parameters to the subsampled samples are used as prediction samples for the chroma block.

[0144] CCLM (Cross-Component Linear Model) mode

[0145] As described above, the CCLM mode can be applied to the chroma block. The CCLM mode is an intra-frame prediction mode using the correlation between the luminance block and the chroma block corresponding to the luminance block, and is performed by deriving a linear model based on the neighboring samples of the luminance block and the neighboring samples of the chroma block. In addition, the prediction sample of the chroma block can be derived based on the derived linear model and the reconstructed sample of the luminance block.

[0146] Specifically, when the CCLM mode is applied to the current chrominance block, the parameters of the linear model can be derived based on the neighboring samples for intra-frame prediction of the current chrominance block and the neighboring samples for intra-frame prediction of the current luminance block. For example, the linear model of CCLM can be expressed based on the following equation.

[0147] [Equation 1]

[0148] pred C (i, j) = α·rec L ′(i, j)+β

[0149] Among them, pred c(i, j) may 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 samples of the current luma block. The linear model coefficients α and β may be signaled or derived from neighboring samples.

[0150] Minimum size limit for chroma blocks

[0151] If a chroma block with a very small size is frequently generated during encoding and decoding of a high-resolution image such as VVC, the encoding and decoding process throughput may be deteriorated. In order to improve the throughput, the partitioning of the CU may be limited so that a chroma block with a specific size is not generated.

[0152] In an embodiment, in order to limit the generation of chroma blocks with a specific size, a minimum size of the chroma block may be set. In an embodiment, the encoding device and the decoding device may limit the size of the chroma block so that the chroma block includes at least 16 chroma samples. For example, the segmentation of the luminance block or the chroma block may be limited so that a chroma block with a chroma sample size of 2x2, 2x4, or 4x2 is not generated during the encoding and decoding process.

[0153] For example, in order to prevent the generation of chroma blocks (e.g., chroma sample units) having a size of 2x2, 2x4, or 4x2, in the case of a dual-tree partitioning structure, quadtree partitioning or binary tree partitioning of chroma blocks having a size of 2x8, 4x4, or 8x2 may be prohibited, and ternary partitioning of chroma blocks having a size of 2x8, 2x16, 4x4, 4x8, 8x2, or 8x4 may be prohibited.

[0154] More specifically, when any one of the following conditions is satisfied, quadtree partitioning for the current block may be limited.

[0155] (Condition 1-1) The partition structure of the current block is single-tree or dual-tree luminance, and the size of the luminance block is the minimum size that can be quadtree partitioned

[0156] (Condition 1-2) The partition structure of the current block is dual-tree chroma, and the size of the chroma block is the minimum size that can be quadtree partitioned

[0157] (Condition 1-3) The partition structure of the current block is dual-tree chroma, and the size of the chroma block is less than 4

[0158] (Condition 1-4) The partition structure of the current block is dual-tree chroma, and the prediction mode of the current block is MODE_TYPE_INTRA

[0159] Alternatively, when any one of the following conditions is satisfied, the binary tree partitioning for the current block may be limited.

[0160] (Condition 2-1) The partition structure of the current block is dual-tree chroma, and the product of the width and height of the current block is equal to or less than 16 (for example, the number of chroma samples belonging to the current block is equal to or less than 16)

[0161] (Condition 2-2) The partition structure of the current block is dual-tree chroma, and the prediction mode of the current block is MODE_TYPE_INTRA

[0162] Alternatively, when any one of the following conditions is satisfied, ternary tree splitting of the current block may be restricted.

[0163] (Condition 3-1) The partition structure of the current block is dual-tree chroma, and the product of the width and height of the current block is equal to or less than 32 (for example, the chroma samples belonging to the current block are equal to or less than 32)

[0164] (Condition 3-2) The partition structure of the current block is dual-tree chroma, and the prediction mode of the current block is MODE_TYPE_INTRA

[0165] Transformation from single-tree partition structure to dual-tree partition structure

[0166] Meanwhile, in the case of a single tree partition structure, the luminance block and the chrominance block may form one CU, and the luminance block and the chrominance block may be partitioned into the same partition structure according to the partition of the CU. In this case, when the luminance block is partitioned, the chrominance block may also be partitioned using the same method as the method of partitioning the luminance block. In this case, whether to partition the CU may be determined based on the size of the luminance block, and the size of the chrominance block corresponding thereto may be determined based on the size of the luminance block based on the color format.

[0167] Fig.14 1 is a view illustrating an embodiment of a luma block and a chroma block when the color format is 4:2:0. When the size of the luma block is 16x8, the size of the chroma block can be determined to be 8x4. When the 8x4 chroma block is split into a vertical ternary tree, a chroma block of size 2x4 is generated. Therefore, splitting of a luma block of size 16x8 can be prohibited.

[0168] Even when additional segmentation of chrominance blocks is not allowed, as in Fig.14As in the example of , additional segmentation of the luminance block can be allowed. In addition, even when segmentation of the chrominance block is not available, in order to increase the coding rate, it may be necessary to perform additional segmentation on the divisible luminance block. In this case, the luminance block and the chrominance block that have been segmented into a single-tree segmentation structure can be additionally segmented into a dual-tree structure. For example, the single-tree segmentation structure can be binary into a dual-tree segmentation structure for the luminance block and a dual-tree segmentation structure for the chrominance block. In such a dual-tree segmentation structure, the segmentation of the luminance block and the segmentation of the chrominance block can be performed independently. Therefore, the segmentation of the luminance block can be additionally performed, and the segmentation of the chrominance block may not be allowed.

[0169] Therefore, an embodiment of the syntax for changing a single-tree partition structure to a dual-tree partition structure is as follows: Figures 15 to 17 Shown in. Figures 15 to 17 is a view illustrating one syntax for a coding tree unit (CTU) according to an embodiment, which is divided into three drawings due to limitation of the drawings. Figures 15 to 17 The grammar of forms a continuous grammar. Figures 15 to 17 According to the syntax of the modeTypeCondition parameter, the decoding device of the embodiment may determine the modeType of the CTU as a predetermined prediction mode type based on the value of the modeTypeCondition parameter. Here, modeTypeCondition may be information that specifies the prediction mode characteristics of the CU belonging to the CTU. The determination of modeTypeCondition will be described later. modeType may specify an available prediction mode of the CU belonging to the CTU determined according to modeTypeCondition. In an embodiment, modeType may have any one of the values ​​of MODE_TYPE_ALL that specifies that all prediction modes such as intra prediction, IBC prediction, palette mode, and inter prediction are available, MODE_TYPE_INTRA that specifies that only intra, IBC, and palette modes are available, and MODE_TYPE_INTER that specifies that only inter prediction mode is available.

[0170] For example, when modeTypeCondition is the second value (eg, 1) (1520), the decoding apparatus may determine modeType as the intra prediction mode type (MODE_TYPE_INTRA) (1530).

[0171] Meanwhile, when modeTypeCondition is a third value (e.g., 2) (1540), the decoding device may determine modeType according to the value of mode_constraint_flag. mode_constraint_flag may be obtained from the bitstream (1550). mode_constraint_flag may be a parameter that specifies whether a CU in a CTU is encoded only in an inter-prediction mode. For example, a first value (e.g., 0) of mode_constraint_flag may specify that a CU in a CTU is encoded only in an inter-prediction mode. A second value (e.g., 1) of mode_constraint_flag may specify that a CU in a CTU cannot be encoded in an inter-prediction mode. In an embodiment, when mode_constraint_flag has a second value (e.g., 1), a CU in a CTU may be encoded in an intra-prediction mode or an IBC prediction mode.

[0172] exist Fig.15 In an embodiment, when the value of mode_constraint_flag is a first value (e.g., 0), modeType can be determined as an inter-frame prediction mode type (e.g., MODE_TYPE_INTER), and, when the value of mode_constraint_flag is a second value (e.g., 1), modeType can be determined as an intra-frame prediction mode type (e.g., MODE_TYPE_INTRA) (1560).

[0173] Meanwhile, when modeTypeCondition is a first value (e.g., 0), the decoding device may determine modeType as a value of modeTypeCurr. For example, modeTypeCurr is a CTU call input value and, when the current CTU is a root CTU, the value of modeTypeCurr may be set to MODE_TYPE_ALL. When the current CTU is split from an upper layer CTU, modeTypeCurr may be set to the modeType value of the upper layer CTU.

[0174] Next, the decoding device may determine the partition structure of the lower layer CTU partitioned from the current CTU according to modeType. For example, when modeType is MODE_TYPE_INTRA, the partition structure of the lower layer CTU may be determined to be dual tree brightness (DUAL_TREE_LUMA). Meanwhile, when modeType is not MODE_TYPE_INTRA, the partition structure of the lower layer CTU may be determined to be the partition structure of the current CTU (1580).

[0175] The partition structure of the lower layer CTU determined as described above can be stored in the parameter treeType. Fig.16 When performing the partitioning of the lower layer CTU as shown in 1610, it can be used as an input value for specifying the partitioning structure of the lower layer CTU. Therefore, when modeType is MODE_TYPE_INTRA, the lower layer CTU may be partitioned into a dual tree structure. In addition, the above modeType can be used as an input value for specifying the prediction mode type of the lower layer CTU.

[0176] More specifically, when the prediction mode type (e.g., modeType) of the block belonging to the lower layer CTU is MODE_TYPE_INTRA, Fig.16 The syntax and Fig.17 The lower layer CTU called by the syntax of 1710 may have a dual tree partition structure for the luminance block. In addition, the partition type (modeTypeCurr) of the current CTU is MODE_TYPE_ALL, and the prediction mode type (modeType) of the lower layer CTU is MODE_TYPE_INTRA, Fig.17 The lower layer CTU called by the syntax of 1730 may have a dual tree partition structure (DUAL_TREE_CHROMA) for chroma blocks. When the prediction mode type of the current CTU is MODE_TYPE_ALL or the prediction mode type of the lower layer CTU is MODE_TYPE_INTRA (1720), a CTU having a dual tree partition structure for chroma blocks may be generated (1730).

[0177] In the above description, modeTypeCondition may be determined as follows: In an embodiment, when any of the following conditions is true, modeTypeCondition may be determined as a first value (eg, 0).

[0178] (Condition 4-1) The slice to which the current CTU belongs is an I slice and the CTU belonging to the corresponding slice is quadtree-divided into 64x64 luminance sample CUs

[0179] (Condition 4-2) modeTypeCurr is not MODE_TYPE_ALL

[0180] Otherwise, when any of the following conditions is true, the value of modeTypeCondition may be determined to be a second value (eg, 1).

[0181] (Condition 5-1) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 64, and the current CTU is quadtree-partitioned.

[0182] (Condition 5-2) The product of the width of the luminance block belonging to the current CTU and the luminance block height is 64, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0183] (Condition 5-3) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 32, and the current block is subjected to binary vertical splitting or binary horizontal splitting.

[0184] Meanwhile, when all the above conditions are not satisfied and any of the following conditions is true, the value of modeTypeCondition may be determined as a second value (e.g., 1) or a third value (e.g., 2). Whether the value of modeTypeCondition is the second value (e.g., 1) or the third value (e.g., 2) may be determined depending on whether the slice to which the current CTU belongs is an I slice, and more specifically, the value of modeTypeCondition may be determined as 1+(slice_type!=I?1:0). Here, slice_type specifies the type of the slice to which the current CTU belongs, and may have a value of I when the current slice is an I slice, and may have a value other than I when the current slice is not an I slice.

[0185] (Condition 6-1) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 64, and the current block is subjected to binary horizontal splitting or binary vertical splitting.

[0186] (Condition 6-2) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 128, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0187] Meanwhile, when all of the above conditions are not met, modeTypeCondition may be set to a first value (eg, 0).

[0188] First Modified Example

[0189] Although the size of the luminance block is the same, the size of the chrominance block corresponding thereto may be different due to the different color formats. Therefore, even when the luminance block has a size of 16x8, the segmentation of the chrominance block can be allowed.

[0190] For example, Fig.18 4 is a view illustrating a luma block and a chroma block when the color format is 4:4:4. When the size of the luma block is 16x8, the size of the chroma block may be determined to be 16x8. Therefore, when the color format is 4:4:4, segmentation of a luma block of size 16x8 may be allowed.

[0191] However, in the above embodiment, because the value of modeTypeCondition is determined according to the size of the luminance block, even when the chrominance block can be additionally segmented according to the color format, segmentation into a single tree segmentation structure is no longer allowed. In this way, in order to determine whether to segment the chrominance block according to the color format, the modeTypeCondition can be determined as follows.

[0192] In an embodiment, when any one of the following conditions is true, the value of modeTypeCondition may be determined to be a first value (eg, 0).

[0193] (Condition 7-1) The slice to which the current CTU belongs is an I slice, and the CTU belonging to the corresponding slice is divided into 64x64 luminance sample CUs by quadtree.

[0194] (Condition 7-2) modeTypeCurr is not MODE_TYPE_ALL

[0195] Otherwise, when any of the following conditions is true, the value of modeTypeCondition may be determined to be a second value (eg, 1).

[0196] (Condition 8-1) The product of the chroma sample number unit width and the chroma sample number unit height of the chroma block belonging to the current CTU is 16, and the current block is quadtree-partitioned.

[0197] (Condition 8-2) The product of the chroma sample number unit width and the chroma sample number unit height of the chroma block belonging to the current CTU is 16, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0198] Here, the product of the chroma sample number unit width and the chroma sample number unit height of the chroma block can be calculated by (cbWidth / subWidthC)*(cbHeight / subHeightC). Here, cbWidth may be the luma sample unit width of the luma block belonging to the current CTU, cbHeight may be the luma sample unit height of the luma block belonging to the current CTU, and subWidthC and subHeightC may be based on Fig.10 The height and width ratios of the luminance blocks and chrominance blocks in the color format shown in .

[0199] Meanwhile, when all the above conditions are not met and any of the following conditions is true, the value of modeTypeCondition may be determined as a second value (e.g., 1) or a third value (e.g., 2). Whether the value of modeTypeCondition is a second value (e.g., 1) or a third value (e.g., 2) may be determined based on whether the slice to which the current CTU belongs is an I slice, and specifically, the value of modeTypeCondition may be determined as 1+(slice_type!=I?1:0).

[0200] (Condition 9-1) The product of the chroma sample number unit width and the chroma sample number unit height of the chroma block belonging to the current CTU is 16, and the current block is subjected to binary horizontal splitting or binary vertical splitting.

[0201] For example, according to condition 1, when the product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 64 and the current block is binary horizontally split or binary vertically split, if the color format is 4:2:0, the above condition 1 may be satisfied. However, when the color format is a monochrome format, a 4:2:2 format, or a 4:4:4 format, the above condition 1 may not be satisfied.

[0202] (Condition 9-2) The product of the chroma sample number unit width and the chroma sample number unit height of the chroma block belonging to the current CTU is 32, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0203] For example, according to condition 2, when the product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 128, and the current block is subjected to three-pronged horizontal splitting or three-pronged vertical splitting, if the color format is 4:2:0, the above condition 2 may be satisfied. However, when the color format is a monochrome format, a 4:2:2 format, or a 4:4:4 format, the above condition 2 may not be satisfied.

[0204] Meanwhile, when all the above conditions are met, the value of modeTypeCondition may be set to a first value (eg, 0).

[0205] Second Modified Example

[0206] When the color format of the current picture is a monochrome format or a 4:4:4 color format and each color plane is encoded independently (e.g., a separate color plane), the luma block and the chroma block cannot exist in one CTU at the same time. Therefore, it is not possible to perform a partition constraint of the chroma block based on the sample unit size of the luma block to limit the generation of 2x2, 2x4, or 4x2 chroma sample unit size blocks of the chroma block. Therefore, in this case, the above method of deriving modeTypeCondition can be changed as follows.

[0207] In an embodiment, when any of the following conditions is true, the value of modeTypeCondition may be determined to be a first value (eg, 0).

[0208] (Condition 10-1) The slice to which the current CTU belongs is an I slice, and the CTU belonging to the corresponding slice is quadtree-divided into 64x64 luminance sample CUs

[0209] (Condition 10-2) modeTypeCurr is not MODE_TYPE_ALL

[0210] (Condition 10-3) The color format of the image to which the current CTU belongs is 4:4:4 (for example, the value of chroma_format_idc is the fourth value (for example, 3))

[0211] Alternatively, when the color format of the picture to which the current CTU belongs is 4:4:4, and each color plane is independently encoded / decoded (eg, the value of separate_colour_plane_flag specifying this is 1), Condition 10-3 may apply.

[0212] (Condition 10-4) The color format of the image to which the current CTU belongs is a monochrome format (for example, the value of chroma_format_idc is the first value (for example, 0))

[0213] Otherwise, when any of the following conditions is true, the value of modeTypeCondition may be determined to be a second value (eg, 1).

[0214] (Condition 11-1) The product of the luminance block width and the luminance block height belonging to the current CTU is 64, and the current CTU is quadtree segmented.

[0215] (Condition 11-2) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 64, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0216] (Condition 11-3) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 32, and the current block is subjected to binary vertical splitting or binary horizontal splitting.

[0217] Meanwhile, when all of the above conditions are not satisfied and any of the following conditions is true, the value of modeTypeCondition may be determined as a second value (e.g., 1) or a third value (e.g., 2). Whether the value of modeTypeCondition is the second value (e.g., 1) or the third value (e.g., 2) may be determined depending on whether the slice to which the current CTU belongs is an I slice, and more specifically, the value of modeTypeCondition may be determined as 1+(slice_type!=I?1:0). Here, slice_type specifies the type of slice to which the current CTU belongs, and may have a value of I when the current slice is an I slice, and may have a value other than I when the current slice is not an I slice.

[0218] (Condition 12-1) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 64, and the current block is subjected to binary horizontal splitting or binary vertical splitting.

[0219] (Condition 12-2) The product of the width of the luminance block belonging to the current CTU and the height of the luminance block is 128, and the current block is subjected to three-pronged vertical splitting or three-pronged horizontal splitting.

[0220] Meanwhile, when all of the above conditions are not met, the value of modeTypeCondition may be set to a first value (eg, 0).

[0221] Encoding method

[0222] In the following, reference will be made to Fig.19 A method of performing encoding by an encoding device using the above method is described. The encoding device according to the embodiment may include a memory and at least one processor, and the following method may be performed by the at least one processor.

[0223] First, the encoding device may obtain the current block by segmenting the image (S1910). Next, the encoding device may determine the prediction mode characteristic information (e.g., modeTypeCondition) based on the encoding information of the current block (S1920). Here, the prediction mode characteristic information may be determined based on the color format of the current block. For example, when the color format of the current block is determined to be a monochrome format or a 4:4:4 format, the prediction mode characteristic information may be determined to be a first value (e.g., 0).

[0224] Alternatively, when the number of luminance samples of the current block is 64, the partition mode of the current block is a binary partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information may be determined as a first value (e.g., 0). In this case, the predetermined format may be a monochrome format or a 4:4:4 format.

[0225] Alternatively, when the number of luminance samples of the current block is 128, the partition mode of the current block is the three-pronged partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information may be determined as a first value (e.g., 0). In this case, the predetermined format may be a monochrome format or a 4:4:4 format.

[0226] Meanwhile, when the color format of the current block is 4:2:0, the number of luma samples of the current block is 64, and the partition mode of the current block is the binary partition mode, the prediction mode characteristic information may be determined based on whether the slice to which the current block belongs is an I slice. Alternatively, when the color format of the current block is 4:2:0 format, the number of luma samples of the current block is 128, and the partition mode of the current block is the ternary partition mode, the prediction mode characteristic information may be determined based on whether the slice to which the current block belongs is an I slice.

[0227] For example, when the slice to which the current block belongs is an I slice, the prediction mode characteristic information may be determined as a second value (e.g., 1). Meanwhile, when the slice to which the current block belongs is not an I slice, the prediction mode characteristic information may be determined as a third value (e.g., 2).

[0228] Next, the encoding apparatus may determine a prediction mode type (eg, modeType) of a lower layer block partitioned from the current block based on the prediction mode characteristic information ( S1930 ).

[0229] As described above, when the prediction mode characteristic information is determined to be the first value (eg, 0), the prediction mode type of the lower layer block may be determined to be the same prediction mode type, such as the prediction mode type of the current block.

[0230] For example, when the prediction mode type of the current block is MODE_TYPE_ALL which specifies all prediction modes available such as intra prediction, IBC prediction, palette mode, and inter prediction, the prediction mode type of the lower layer block may also be determined as MODE_TYPE_ALL. Therefore, when encoding is performed, the prediction mode of the lower layer block may be determined as any one of the intra prediction mode, IBC prediction mode, palette mode, and inter prediction mode.

[0231] In addition, when the prediction mode characteristic information is the second value (eg, 1), the prediction mode type of the lower layer block may be determined as an intra prediction mode type (eg, MODE_TYPE_INTRA) in which only the intra prediction mode is available as the prediction mode.

[0232] In addition, when the prediction mode characteristic information is a third value (e.g., 2), the prediction mode type of the lower layer block can be determined as any one of an inter-frame prediction mode type (e.g., MODE_TYPE_INTER) in which only the inter-frame prediction mode is available as a prediction mode or an intra-frame prediction mode type (e.g., MODE_TYPE_INTRA) in which only the intra-frame prediction mode is available.

[0233] Next, the encoding device may obtain the lower layer block by segmenting the current block (S1940). For example, the encoding device may segment the current block to obtain the lower layer block by determining the segmentation structure of the lower layer block based on the prediction mode type of the lower layer block. For example, when the prediction mode type of the lower layer block is an intra-frame prediction mode type, the encoding device may determine that the segmentation structure of the lower layer block is a dual-tree segmentation structure. At the same time, when the prediction mode of the lower layer block is not an intra-frame prediction mode type, the encoding device may determine the segmentation structure of the lower layer block to be the same as the segmentation structure of the current block. For example, when the segmentation structure of the current block is a single-tree segmentation structure, the segmentation structure of the lower layer block may be determined to be a single-tree segmentation structure, and when the segmentation structure of the current block is a dual-tree segmentation structure, the segmentation structure of the lower layer block may be determined to be a dual-tree segmentation structure.

[0234] When the partition structure of the lower block is determined to be a dual-tree partition structure, the partition availability of the luminance block and the chrominance block of the current block may be determined independently. For example, the partition availability of the luminance block may be determined based on the size of the luminance block. In addition, the partition availability of the chrominance block may be determined based on the size of the chrominance block. In an embodiment, the partition availability of the chrominance block may be determined based on the color format. More specifically, as described above with reference to Fig.10 As described, in order to determine the size of the chrominance block, the size of the luminance block corresponding to the chrominance block and the color format of the chrominance block may be used.

[0235] Next, the encoding device may encode the lower layer block based on the determined prediction mode type of the lower layer block (S1950). For example, the encoding device may encode the current block by encoding the lower layer block based on the prediction mode type of the lower layer block according to any one of intra, inter, IBC, and palette modes. For example, when the prediction mode type of the lower layer block is MODE_TYPE_ALL, the encoding device may determine that the prediction mode of the lower layer block is any one of intra, inter, IBC, and palette modes. In addition, by encoding the pred_mode_flag parameter that specifies the prediction mode of the lower layer block, the prediction information of the lower layer block may be encoded.

[0236] Meanwhile, when the prediction mode characteristic information calculated above for the current block is a third value (e.g., 2), the mode constraint information (e.g., mode_constraint_flag) specifying the prediction mode of the lower layer block may be encoded. The mode constraint information may specify whether the inter prediction mode is applied to the lower layer block. In an embodiment, when the lower layer block is encoded in the inter prediction mode, the mode constraint information may be encoded as a first value (e.g., 0) specifying the use of the inter prediction mode. In addition, in an embodiment, when the prediction mode characteristic information calculated above is a third value (e.g., 2) and the lower layer block is not encoded in the inter prediction mode, the intra prediction mode may be forced to be used as the prediction mode for encoding the lower layer block. In this case, in order to signal that the lower layer block has been encoded in the intra prediction mode instead of the inter prediction mode, the mode constraint information may be encoded as a second value (e.g., 1) specifying that the intra prediction mode has been used instead of the inter prediction mode.

[0237] Decoding method

[0238] In the following, reference will be made to Fig. 20 A method of performing decoding using a decoding device using the above method is described. The decoding device according to the embodiment may include a memory and at least one processor, and the following method may be performed by the at least one processor.

[0239] First, the decoding device may obtain the current block by segmenting the image (S2010). Next, the decoding device may determine the prediction mode characteristic information (e.g., modeTypeCondition) based on the encoding information of the current block (S2020). Here, the prediction mode characteristic information may be determined based on the color format of the current block. For example, when the color format of the current block is a monochrome format or a 4:4:4 format, the prediction mode characteristic information may be determined as a first value (e.g., 0).

[0240] Alternatively, when the number of luminance samples of the current block is 64, the partition mode of the current block is a binary partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information may be determined as a first value (e.g., 0). In this case, the predetermined format may be a monochrome format or a 4:4:4 format.

[0241] Alternatively, when the number of luminance samples of the current block is 128, the partition mode of the current block is the three-pronged partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information may be determined as a first value (e.g., 0). In this case, the predetermined format may be a monochrome format or a 4:4:4 format.

[0242] Meanwhile, when the color format of the current block is the 4:2:0 format, the number of luminance samples of the current block is 64, and the partition mode of the current block is the binary partition mode, the prediction mode characteristic information may be determined based on whether the slice to which the current block belongs is an I slice. Alternatively, when the color format of the current block is the 4:2:0 format, the number of luminance samples of the current block is 128, and the partition mode of the current block is the ternary partition mode, the prediction mode characteristic information may be determined based on whether the slice to which the current block belongs is an I slice.

[0243] For example, when the slice to which the current block belongs is an I slice, the prediction mode characteristic information may be determined as a second value (e.g., 1). Meanwhile, when the slice to which the current block belongs is not an I slice, the prediction mode characteristic information may be determined as a third value (e.g., 2).

[0244] Next, the decoding apparatus may determine a prediction mode type (eg, modeType) of a lower layer block partitioned from the current block based on the prediction mode characteristic information ( S2030 ).

[0245] As described above, when the prediction mode characteristic information is determined to be a first value (e.g., 0), the prediction mode type of the lower layer block may be determined to be the same prediction mode type as the prediction mode type of the current block. In addition, when the prediction mode characteristic information is a second value (e.g., 1), the prediction mode type of the lower layer block may be determined to be an intra-frame prediction mode type (e.g., MODE_TYPE_INTRA).

[0246] In addition, when the prediction mode characteristic information is a third value (e.g., 2), the prediction mode type of the lower layer block can be determined based on the mode constraint information (e.g., mode_constraint_flag) obtained from the bitstream. In the following, the mode constraint information may specify whether the inter-frame prediction mode is available. In an embodiment, when the mode constraint information specifies that the inter-frame prediction mode is allowed, the prediction mode type of the lower layer block can be determined as an inter-frame prediction mode type (e.g., MODE_TYPE_INTER). At the same time, when the mode constraint information specifies that the inter-frame prediction mode is not allowed, the prediction mode type of the lower layer block can be determined as an intra-frame prediction mode type (e.g., MODE_TYPE_INTRA).

[0247] Next, the decoding device may obtain the lower layer block by partitioning the current block (S2040). For example, the decoding device may partition the current block to obtain the lower layer block by determining the partition structure of the lower layer block based on the prediction mode type of the lower layer block. For example, when the prediction mode type of the lower layer block is an intra-frame prediction mode type, the decoding device may determine that the partition structure of the lower layer block is a dual-tree partition structure. At the same time, when the prediction mode type of the lower layer block is not an intra-frame prediction mode type, the decoding device may determine the partition structure of the lower layer block to be the same partition structure as the partition structure of the current block. For example, when the partition structure of the current block is a single-tree partition structure, the partition structure of the lower layer block may be determined to be a single-tree partition structure, and when the partition structure of the current block is a dual-tree partition structure, the partition structure of the lower layer block may be determined to be a dual-tree partition structure.

[0248] When the partition structure of the lower block is determined to be a dual-tree partition structure, the partition availability of the luminance block and the chrominance block of the current block may be determined independently. For example, the partition availability of the luminance block may be determined based on the size of the luminance block. In addition, the partition availability of the chrominance block may be determined based on the size of the chrominance block. In an embodiment, the partition availability of the chrominance block may be determined based on the color format. More specifically, as described above with reference to Fig.10 As described, in order to determine the size of the chrominance block, the size of the luminance block corresponding to the chrominance block and the color format of the chrominance block may be used.

[0249] Next, the decoding device may decode the lower layer block based on the determined prediction mode type of the lower layer block (S2050). For example, the decoding device may determine the prediction mode of the lower layer block as any one of intra, inter, IBC, and palette modes based on the prediction mode information obtained from the bitstream according to the prediction mode type of the lower layer block, and decode the lower layer block based on the determined prediction mode to decode the current block. For example, only when the prediction mode type of the lower layer block is MODE_TYPE_ALL, the decoding device may obtain the pred_mode_flag parameter specifying the prediction mode of the lower layer block. In addition, the lower layer block may be predicted according to the prediction mode specified by pred_mode_flag (e.g., inter prediction mode or intra prediction mode).

[0250] Application Examples

[0251] Although for the sake of clarity of description, the exemplary method of the present disclosure described above is represented as a series of operations, it is not intended to limit the order of executing the steps, and these steps can be performed simultaneously or in different orders when 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 except some steps, or may include other additional steps except some steps.

[0252] In the present disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when a predetermined condition is met, the image encoding device or the image decoding device may perform the predetermined operation after determining whether the predetermined condition is met.

[0253] 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.

[0254] 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, etc.

[0255] In addition, the image decoding device and the image encoding device of the embodiment of the present disclosure can 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 providing equipment, OTT video (over the top video) equipment, Internet streaming service providing equipment, three-dimensional (3D) video equipment, video phone video equipment, medical video equipment, etc., and can be used to process video signals or data signals. For example, OTT video equipment can include game consoles, Blu-ray players, Internet access TVs, home theater systems, smart phones, tablet PCs, digital video recorders (DVRs), etc.

[0256] Fig.21 is a view showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0257] like Fig.21 As shown in , a content streaming transmission system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming transmission server, a network server, a media storage, a user device, and a multimedia input device.

[0258] The encoding server compresses the content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and sends the bitstream to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server can be omitted.

[0259] A bitstream may be generated by applying the image encoding method or the image encoding device 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.

[0260] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server serves as a medium to notify the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send 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 as a command / response between devices in the control content streaming system.

[0261] The streaming server may receive content from a media storage and / or encoding server. For example, when content is received from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

[0262] 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.

[0263] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0264] 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.

[0265] Industrial Applicability

[0266] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising: Obtain the current block by segmenting the image; Determining prediction mode characteristic information based on encoding information of the current block; Determining a prediction mode type of a lower layer block partitioned from the current block based on the prediction mode characteristic information; Obtaining the lower layer block by splitting the current block; as well as Decoding the lower layer block based on the determined prediction mode type of the lower layer block, wherein the prediction mode characteristic information is determined based on the color format of the current block, and Wherein, based on the color format of the current block being a monochrome format or a 4:4:4 format, the prediction mode characteristic information is determined to be a first value.

2. The image decoding method according to claim 1, in, Obtaining the lower layer block by partitioning the current block is performed by determining a partition structure of the lower layer block based on a prediction mode type of the lower layer block; and Wherein, based on the fact that the prediction mode type of the lower layer block is an intra-frame prediction mode type, the partition structure of the lower layer block is determined to be a dual-tree partition structure.

3. The image decoding method according to claim 2, in, Based on the partition structure of the lower layer block being determined as the dual-tree partition structure, partition availability of a luminance block and a chrominance block for the current block is independently determined, and Wherein, the segmentation availability of the chroma block is determined based on the color format.

4. The image decoding method according to claim 1, wherein: Based on the prediction mode characteristic information being a first value, the prediction mode type of the lower layer block is determined as the prediction mode type of the current block.

5. The image decoding method according to claim 1, wherein: Based on the fact that the number of luminance samples of the current block is 64, the partition mode of the current block is a binary partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information is determined to be a first value.

6. The image decoding method according to claim 1, wherein: Based on the fact that the number of luminance samples of the current block is 128, the partition mode of the current block is a three-pronged partition mode, and the color format of the current block is a predetermined format, the prediction mode characteristic information is determined to be a first value.

7. The image decoding method according to claim 6, wherein: The predetermined format is a monochrome format or a 4:4:4 format.

8. The image decoding method according to claim 1, wherein: Based on the fact that the color format of the current block is 4:2:0 format, the number of luminance samples of the current block is 64, and the partition mode of the current block is a binary partition mode, the prediction mode characteristic information is determined depending on whether the slice to which the current block belongs is an I slice.

9. The image decoding method according to claim 1, wherein: Based on the fact that the color format of the current block is 4:2:0 format, the number of luminance samples of the current block is 128, and the partition mode of the current block is a three-pronged partition mode, the prediction mode characteristic information is determined depending on whether the slice to which the current block belongs is an I slice.

10. The image decoding method according to claim 9, in, Based on the fact that the slice to which the current block belongs is an I slice, the prediction mode characteristic information is determined to be a second value, and Wherein, based on the prediction mode characteristic information being the second value, the prediction mode type of the lower layer block is determined to be an intra-frame prediction mode type.

11. The image decoding method according to claim 9, in, Based on the fact that the slice to which the current block belongs is not an I slice, the prediction mode characteristic information is determined to be a third value, wherein, based on the prediction mode characteristic information being the third value, the prediction mode type of the lower layer block is determined based on the mode constraint information obtained from the bitstream, The mode constraint information specifies whether the inter-frame prediction mode is allowed, and Wherein, based on the mode constraint information specifying that the inter-frame prediction mode is allowed, the prediction mode type of the lower layer block is determined to be an inter-frame prediction mode type.

12. An image decoding device, comprising: Memory; and at least one processor, Wherein, the at least one processor is configured to: Obtain the current block by segmenting the image; Determining prediction mode characteristic information based on encoding information of the current block; Determining a prediction mode type of a lower layer block partitioned from the current block based on the prediction mode characteristic information; Obtaining the lower layer block by segmenting the current block; and Decoding the lower layer block based on the determined prediction mode type of the lower layer block, wherein the prediction mode characteristic information is determined based on the color format of the current block, and Wherein, based on the color format of the current block being a monochrome format or a 4:4:4 format, the prediction mode characteristic information is determined to be a first value.

13. An image encoding method performed by an image encoding device, the image encoding method comprising: Obtain the current block by segmenting the image; Determining prediction mode characteristic information based on encoding information of the current block; Determining a prediction mode type of a lower layer block partitioned from the current block based on the prediction mode characteristic information; Obtaining the lower layer block by splitting the current block; as well as encoding the lower layer block based on the determined prediction mode type of the lower layer block, wherein the prediction mode characteristic information is determined based on the color format of the current block, and Wherein, based on the color format of the current block being a monochrome format or a 4:4:4 format, the prediction mode characteristic information is determined to be a first value.

14. A method for transmitting a bit stream, wherein the bit stream is generated by an image encoding method, the image encoding method comprising: Obtain the current block by segmenting the image; Determining prediction mode characteristic information based on encoding information of the current block; Determining a prediction mode type of a lower layer block partitioned from the current block based on the prediction mode characteristic information; Obtaining the lower layer block by splitting the current block; as well as Decoding the lower layer block based on the determined prediction mode type of the lower layer block, wherein the prediction mode characteristic information is determined based on the color format of the current block, and Wherein, based on the color format of the current block being a monochrome format or a 4:4:4 format, the prediction mode characteristic information is determined to be a first value.

Images