Image encoding / decoding method and apparatus based on ISP mode, and recording medium storing bit stream

Abstract

Provided are an image encoding / decoding method and apparatus. An image decoding method according to the present disclosure may comprise the steps of: dividing a current block into a plurality of sub-blocks based on an intra sub-partition (ISP) prediction being applied to the current block; determining an intra prediction mode of each of the plurality of sub-blocks; and generating a prediction block for each of a plurality of sub-blocks based on the determined intra prediction mode, the plurality of sub-blocks including a first sub-block and a second sub-block, the intra prediction mode of the first sub-block being determined based on prediction mode information of the first sub-block or a first neighboring reference sample of the first sub-block, and the intra prediction mode of the second sub-block being determined based on prediction mode information of the second sub-block. And the intra prediction mode of the second sub-block is determined based on a second neighboring reference sample of the second sub-block.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method and apparatus and a recording medium for storing a bit stream, and more specifically, to an image encoding / decoding method and apparatus based on an ISP mode, and a recording medium for storing 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 bit volume transmitted is relatively increased compared to existing image data. The increase in the amount of information or bit volume 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] In addition, an object of the present disclosure is to provide an image encoding / decoding method and device based on the ISP mode.

[0007] In addition, an object of the present disclosure is to provide an image encoding / decoding method and apparatus for performing intra-frame prediction based on a prediction mode determined for each sub-block in an ISP mode.

[0008] In addition, an object of the present disclosure is to provide a non-transitory computer-readable recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0009] In addition, an object of the present disclosure is to provide a non-transitory computer-readable 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] In addition, an object of the present disclosure is to provide a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0011] 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.

[0012] Technical Solution

[0013] According to an aspect of the present disclosure, an image decoding method may include the following steps: dividing a current block into a plurality of sub-blocks based on an intra sub-partitioning (ISP) prediction applied to the current block; determining an intra prediction mode for each of the plurality of sub-blocks; and generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode. The plurality of sub-blocks may include a first sub-block and a second sub-block, the intra prediction mode of the first sub-block may be determined based on prediction mode information of the first sub-block or a first neighboring reference sample of the first sub-block, and the intra prediction mode of the second sub-block may be determined based on a second neighboring reference sample of the second sub-block.

[0014] According to another aspect of the present disclosure, an image decoding device may include a memory and at least one processor. The at least one processor may be applied to the current block based on intra sub-partitioning (ISP) prediction to divide the current block into a plurality of sub-blocks; determine an intra prediction mode for each of the plurality of sub-blocks; and generate a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode. The plurality of sub-blocks may include a first sub-block and a second sub-block, the intra prediction mode of the first sub-block may be determined based on prediction mode information of the first sub-block or a first neighboring reference sample of the first sub-block, and the intra prediction mode of the second sub-block may be determined based on a second neighboring reference sample of the second sub-block.

[0015] According to another aspect of the present disclosure, an image encoding method may include the following steps: dividing the current block into a plurality of sub-blocks based on intra sub-partitioning (ISP) prediction applied to the current block; determining an intra prediction mode for each of the plurality of sub-blocks; and generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode. The plurality of sub-blocks may include a first sub-block and a second sub-block, and only information about the intra prediction mode of the first sub-block among the first sub-block and the second sub-block may be encoded in a bitstream.

[0016] A computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding method or the image encoding apparatus of the present disclosure.

[0017] A transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding method or the image encoding device of the present disclosure.

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

[0019] Beneficial Effects

[0020] According to the present disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0021] In addition, according to the present disclosure, an image encoding / decoding method and apparatus based on the ISP mode may be provided.

[0022] In addition, according to the present disclosure, an image encoding / decoding method and apparatus for performing intra prediction based on a prediction mode determined for each subblock in an ISP mode may be provided.

[0023] Furthermore, according to the present disclosure, a non-transitory computer-readable recording medium storing a bit stream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0024] Furthermore, according to the present disclosure, a non-transitory computer-readable 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 can be provided.

[0025] Furthermore, according to the present disclosure, a method of transmitting a bit stream generated by the image encoding method or apparatus according to the present disclosure may be provided.

[0026] Those skilled in the art will understand that the effects that can be achieved through 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

[0027] Figure 1 FIG. 4 is a diagram schematically showing a video encoding system to which an embodiment of the present disclosure is applicable.

[0028] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0029] Figure 3 is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0030] Figure 4 An example of screen division is shown.

[0031] Figure 5a and Figure 5b An example of sub-block partitioning in ISP mode is shown.

[0032] Figure 6 An example of a HoG construction is shown.

[0033] Figure 7 is a view used to explain the HoG-based hybrid mode.

[0034] Figures 8 to 10is a view showing an example of the ISP split mode.

[0035] Fig.11 and Fig.12 is a view for explaining an ISP mode according to one embodiment of the present disclosure.

[0036] Fig.13 is a view for explaining an ISP mode according to one embodiment of the present disclosure.

[0037] Fig.14 is a view showing a reference area that can be used in an ISP mode according to one embodiment of the present disclosure.

[0038] Fig.15 is a view for explaining an ISP mode according to one embodiment of the present disclosure.

[0039] Fig.16 is a flowchart illustrating an image encoding method according to one embodiment of the present disclosure.

[0040] Fig.17 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure.

[0041] Fig.18 is a diagram showing a content streaming system to which one embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0042] 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 may be implemented in various forms and is not limited to the embodiments described herein.

[0043] 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.

[0044] 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.

[0045] In the present disclosure, the terms first, second, etc. may be 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, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0046] 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 otherwise specified, these embodiments in which the components are integrated or the components are distributed are also included in the scope of the present disclosure.

[0047] In the present disclosure, the components described in each embodiment are not necessarily indispensable components, and some components may be optional components. Therefore, the embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, the embodiments including other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0048] 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.

[0049] In this disclosure, "video" may mean a set of images over time.

[0050] In the present disclosure, "picture" generally means the basis of 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).

[0051] In the present disclosure, "pixel" or "pel" may refer to the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, or may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0052] 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 ​​the picture and information related to the area. A unit may include a luminance block and two chrominance (e.g., Cb, Cr) blocks. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0053] 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".

[0054] In addition, in the present disclosure, unless explicitly stated as a chroma block, "current block" may mean a block including a luma component block and a chroma component block or a "luminance block of the current block". The luma component block of the current block may be expressed by an explicit description including a luma component block such as "luminance block" or "current luma block". In addition, "chroma component block of the current block" may be expressed by an explicit description including a chroma component block such as "chroma block" or "current chroma block".

[0055] In the present disclosure, the slash " / " or "," should be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A, B, C" may mean "at least one of A, B and / or C".

[0056] In the present disclosure, the term "or" should be interpreted as indicating "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", and / or 3) both "A and B". In other words, in the present disclosure, the term "or" should be interpreted as indicating "additionally or alternatively".

[0057] In the present disclosure, "at least one of A, B, and C" may mean "only A", "only B", "only C", or "any and all combinations of A, B, and C". In addition, "at least one of A, B, or C" or "at least one of A, B and / or C" may mean "at least one of A, B, and C".

[0058] The brackets used in the present disclosure may mean "for example". For example, if "prediction (intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction". In other words, "prediction" in the present disclosure is not limited to "intra-frame prediction", and "intra-frame prediction" may be proposed as an example of "prediction". In addition, even when "prediction (i.e., intra-frame prediction)" is indicated, "intra-frame prediction" may be proposed as an example of "prediction".

[0059] Overview of Video Coding Systems

[0060] Figure 1 is a diagram schematically showing a video encoding system to which an embodiment of the present disclosure is applicable.

[0061] The video encoding system according to the embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver the 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.

[0062] The encoding device 10 according to the embodiment may include a video source generator 11, an encoder 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoder 22, and a renderer 23. The encoder 12 may be referred to as a video / image encoding device, and the decoder 22 may be referred to as a video / image decoding device. The transmitter 13 may be included in the encoder 12. The receiver 21 may be included in the decoder 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0063] 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 generate the video / image (electronically). 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.

[0064] The encoder 12 may encode the input video / image. For compression and coding efficiency, the encoder 12 may perform a series of processes such as prediction, transformation, and quantization. The encoder 12 may output the encoded data (encoded video / image information) in the form of a bitstream.

[0065] The transmitter 13 may transmit the encoded video / image information or 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 transmitter 13 may be provided as a transmitting device separated from the encoder 12. In this case, the transmitting device includes: at least one processor that obtains the encoded video / image information or data output in the form of a bit stream; and a transmitter that delivers the encoded video / image information or data in the form of a file or stream. The receiver 21 may extract / receive a bit stream from a storage medium or a network and transmit the bit stream to the decoder 22.

[0066] The decoder 22 may decode a video / image by performing a series of processes corresponding to the operations of the encoder 12, such as dequantization, inverse transformation, and prediction.

[0067] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0068] Overview of Image Coding Equipment

[0069] Figure 2 is a view schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0070] like Figure 2 As shown, the image encoding device 100 may include an image segmenter 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.

[0071] 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.

[0072] The image segmenter 110 may segment the input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, the processing unit may be referred to as a coding unit (CU). The coding unit may be obtained by recursively segmenting 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 segmented into a plurality of coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the segmentation of the coding unit, the quadtree structure may be applied first, and the binary tree structure and / or the ternary tree structure may be applied later. The encoding process according to the present disclosure may be performed based on the final coding unit that is no longer segmented. The maximum coding unit may be used as the final coding unit, and the coding unit of a deeper depth obtained by segmenting the maximum coding unit may also be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0073] 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 send 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.

[0074] 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.

[0075] 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 sent 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 co-located 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 indicating 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, a residual signal may not be sent. 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.

[0076] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may apply not only intra prediction or inter prediction, but also both intra prediction and inter prediction at the same time to predict the current block. The prediction method of applying both intra prediction and inter prediction 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 copying (IBC) to predict the current block. Intra block copying may be used for content image / video encoding 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.

[0077] 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 sent to the transformer 120.

[0078] 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.

[0079] The quantizer 130 may quantize the transform coefficients and send them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0080] The entropy encoder 190 may perform various encoding methods, such as, for example, 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 other than quantized transform coefficients together or separately (e.g., values ​​of syntax elements, etc.). 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.

[0081] The bit stream may be transmitted through 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.

[0082] 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.

[0083] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as the case where 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.

[0084] In addition, as described below, chroma scaling and luminance mapping (LMCS) is applied to the picture coding process.

[0085] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filtering, bilateral filtering, etc. The filter 160 can generate various information related to filtering and send the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0086] The modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image encoding apparatus 100, prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus may be avoided and encoding efficiency may be improved.

[0087] 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 for deriving (or encoding) the motion information in the current picture and / or the motion information of the reconstructed block in the picture. The stored motion information may be sent 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 blocks in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0088] Overview of Image Decoding Equipment

[0089] Figure 3 is a view schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0090] like Figure 3 As 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.

[0091] According to an embodiment, all or at least some of the multiple 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.

[0092] The image decoding device 200 having received a bit stream including video / image information may perform the same Figure 2 The image encoding device 100 may reconstruct the image by processing corresponding to the processing 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).

[0093] The image decoding device 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 information about the parameter set and / or the general constraint information. The signaled / received information and / or syntax elements described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 may decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output 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, 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 prediction among the information decoded by the entropy decoder 210 can be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value (ie, quantized transform coefficient and related parameter information) for which entropy decoding is performed in the entropy decoder 210 can be input to the dequantizer 220. In addition, the information about filtering among the information decoded by the entropy decoder 210 can be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal / external element of the image decoding apparatus 200 , or the receiver may be a component of the entropy decoder 210 .

[0094] In addition, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, or at least one of an intra-frame prediction unit 265.

[0095] The dequantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The dequantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may dequantize the quantized transform coefficients by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficients.

[0096] The inverse transformer 230 may perform an inverse transformation on the transformation coefficients to obtain a residual signal (residual block, residual sample array).

[0097] The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0098] 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) to be described later.

[0099] 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.

[0100] The inter-frame prediction unit 260 can derive the prediction block of the current block based on the reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information sent in the inter-frame prediction mode, the motion information can 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-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, the neighboring blocks may include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter-frame prediction unit 260 may configure a motion information candidate list based on the neighboring blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter-frame prediction may be performed based on various prediction modes, and information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0101] The adder 235 can generate a reconstruction signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-prediction unit 265). If the block to be processed has no residual, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 also applies to the adder 235. The adder 235 can be called a reconstructor or a reconstructed block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0102] 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.

[0103] The (modified) reconstructed picture stored in the DPB of the memory 250 can be used as a reference picture in the inter-frame prediction unit 260. The memory 250 can store the motion information of the block for deriving (or decoding) the motion information in the current picture and / or the motion information of the reconstructed block in the picture. The stored motion information can be sent 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 can store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0104] In the present disclosure, the implementations 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.

[0105] Overview of Image Segmentation

[0106] The video / image encoding method according to the present disclosure can be performed based on the segmentation structure of the image described below. Specifically, the above-mentioned processes of prediction, residual processing ((inverse) transform, (de)quantization, etc.), syntax element encoding and filtering can be performed based on the CTU or CU (and / or TU, PU) derived from the segmentation structure of the image. The image can be divided into block units, and the block segmentation process can be performed in the image segmentor 110 of the above-mentioned image encoding device 100. The segmentation related information can be encoded in the entropy encoder 190 and transmitted to the image decoding device 200 in the form of a bitstream. The entropy decoder 210 of the image decoding device 200 can derive the block segmentation structure of the current picture based on the segmentation related information obtained from the bitstream, and perform a series of processes for image decoding (e.g., prediction, residual processing, block / picture reconstruction, in-loop filtering, etc.) based on the block segmentation structure. According to the present disclosure, the CU size and the TU size can be equal to each other. Alternatively, multiple TUs can exist in the CU area. In addition, the CU size can generally represent the luminance component (sample) CB size. The TU size can generally represent the luminance component (sample) TB size. The chroma component (sample) CB or TB size can be derived based on the luminance component (sample) CB or TB size according to the component ratio according to the color format (chroma format, for example, 4:4:4, 4:2:2, 4:2:0) of the picture / image. The TU size can be derived based on maxTbSize. For example, when the CU size is larger than maxTbSize, multiple TUs (TBs) of maxTbSize can be derived from the CU, and the transform / inverse transform can be performed in TU (TB) units. In addition, for example, when intra prediction is applied, the intra prediction mode / type can be derived in units of CU (or CB), and the process of deriving neighbor reference samples and generating prediction samples can be performed in units of TU (or TB). In this case, one TU (or TB) or multiple TUs (or TBs) may exist in one CU (or CB) area, and in this case, multiple TUs (or TBs) may share the same intra prediction mode / type.

[0107] In addition, in the video / image coding according to the present disclosure, the image processing unit may have a hierarchical structure. A picture may be divided into one or more tiles, tiles, slices and / or tile groups. A slice may include one or more tiles. A tile may include one or more CTU rows in a tile. A slice may include an integer number of tiles. A tile group may include one or more tiles. A tile may include one or more CTUs. A CTU may be divided into one or more CUs. A tile is a rectangular area of ​​a CTU within a specific tile column and a specific tile row in a picture. A tile group may include an integer number of tiles scanned according to a tile raster in a picture. A slice header may carry information / parameters applicable to a corresponding slice (a block in a slice). In the case where the image encoding device 100 / image decoding device 200 has a multi-core processor, the encoding / decoding process for tiles, slices, tiles and / or tile groups may be processed in parallel. In this document, slices or tile groups may be used interchangeably. That is, a tile group header may be referred to as a slice header. Herein, a slice may have a type of slice type, including an intra (I) slice, a predicted (P) slice, and a bidirectional predicted (B) slice. For blocks in an I slice, inter prediction is not used for prediction, and only intra prediction may be used. Of course, in this case, the original sample values ​​may be encoded and signaled without prediction. For blocks in a P slice, intra prediction or inter prediction may be used, and when inter prediction is used, only unidirectional prediction may be used. In addition, for blocks in a B slice, intra prediction or inter prediction may be used, and when inter prediction is used, bidirectional prediction may also be used.

[0108] In the encoding device, the patch / patch group, tile, slice, and maximum and minimum coding unit sizes can be determined based on the characteristics of the video (e.g., resolution) or by considering the efficiency of encoding or parallel processing, and information about them or information that can be derived can be included in the bitstream.

[0109] In the decoding device, information indicating whether a CTU, tile, slice, or tile in a tile / tile group of the current picture is divided into a plurality of coding units may be acquired. If such information is set to be acquired (sent) under certain conditions, efficiency may be improved.

[0110] The slice header (Slice Header Syntax) may include information / parameters that are generally applicable to slices. The APS (APS Syntax) or PPS (PPS Syntax) may include information / parameters that are generally applicable to one or more pictures. The SPS (SPS Syntax) may include information / parameters that are generally applicable to one or more sequences. The VPS (VPS Syntax) may include information / parameters that are generally applicable to multiple layers. The DPS (DPS Syntax) may include information / parameters that are generally applicable to the overall video. The DPS may include information / parameters related to the concatenation of a coded video sequence (CVS).

[0111] In the present disclosure, the upper layer syntax may include at least one of APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, and slice header syntax. In addition, for example, information on the partitioning and configuration of tiles / tile groups / tiles / slices may be configured in the image encoding device 100 through the upper layer syntax and delivered to the image decoding device 200 in the form of a bitstream.

[0112] Split structure

[0113] A picture may be partitioned into a sequence of coding tree units (CTUs). A CTU may correspond to a coding tree block (CTB). Alternatively, a CTU may include a coding tree block of luma samples and two coding tree blocks of chroma samples corresponding to the luma samples. For example, for a picture containing three sample arrays, a CTU may include an N×N block of luma samples and two corresponding blocks of chroma samples. Figure 4 An example is shown in which one picture is divided into a plurality of CTUs.

[0114] The maximum allowable size of a CTU for coding and prediction may be different from the maximum allowable size of a CTU for transform. For example, even if the maximum allowable size of a CTU for transform is 64×64, the maximum allowable size of a luma block in a CTU for coding and prediction may be 128×128.

[0115] In addition, the picture may be partitioned into one or more tile rows and one or more tile columns. A tile may be a sequence of CTUs covering a rectangular area of ​​the picture. The CTUs of a tile may be scanned in a raster scan order within the tile.

[0116] A slice may consist of an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile of a picture. Two modes of slicing may be supported: one is a raster scan slicing mode, and the other is a rectangular slicing mode.

[0117] In raster scan slice mode, a slice may include a sequence of complete tiles in a tile raster scan of the picture. In the present disclosure, a slice according to the raster scan slice mode may be referred to as a raster scan slice.

[0118] In the rectangular slice mode, a slice may include a plurality of complete tiles that together form a rectangular area of ​​a picture or a plurality of continuous complete CTU rows that together form a tile of a rectangular area of ​​a picture. In the present disclosure, a slice according to the rectangular slice mode may be referred to as a rectangular slice. Tiles included in a rectangular slice may be scanned in a tile raster scan order within a rectangular area corresponding to the slice.

[0119] Furthermore, one or more slices may constitute a sub-picture. That is, a sub-picture may include one or more slices that together cover a rectangular area of ​​the picture.

[0120] Overview of intra prediction

[0121] Intra-frame prediction may refer to a prediction for generating a prediction sample of a current block based on a reference sample in a picture (current picture) to which the current block belongs. When intra-frame prediction is applied to the current block, neighboring reference samples to be used for intra-frame prediction of the current block may be derived. The neighboring reference samples of the current block may include: a total of 2×nh samples including samples adjacent to the left boundary of the current block of size nW×nH and samples adjacent to the lower left, a total of 2×nW samples including samples adjacent to the upper boundary of the current block and samples adjacent to the upper right, and one sample adjacent to the upper left of the current block. Alternatively, the neighboring reference samples of the current block may include multiple columns of upper neighboring samples and multiple rows of left neighboring samples. In addition, the neighboring reference samples of the current block may include: a total of nH samples of size nW×nH adjacent to the right boundary of the current block, a total of nW samples adjacent to the lower boundary of the current block, and one sample adjacent to the lower right of the current block.

[0122] However, some neighboring reference samples of the current block have not been decoded or may not be available. In this case, the image decoding device 200 can construct neighboring reference samples to be used for prediction by replacing unavailable samples with available samples. Alternatively, the neighboring reference samples to be used for prediction can be constructed by interpolation of available samples.

[0123] When deriving neighboring reference samples, (i) the prediction samples may be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the prediction samples may be derived based on the reference samples existing in a specific (prediction) direction relative to the prediction samples among the neighboring reference samples of the current block. The case of (i) may be referred to as a non-directional mode or a non-angle mode, and the case of (ii) may be referred to as a directional mode or an angle mode. In addition, the prediction samples may be generated by interpolating the first neighboring samples and the second neighboring samples set in the opposite direction of the prediction direction of the intra prediction mode of the current block based on the prediction samples of the current block among the neighboring reference samples. The above case may be referred to as linear interpolation intra prediction (LIP). In addition, the chroma prediction samples may be generated based on the luminance samples using a linear model. This case may be referred to as an LM mode. In addition, the temporary prediction samples of the current block may be derived based on the filtered neighboring reference samples, and the prediction samples of the current block may be derived by the weighted sum of at least one reference sample derived according to the intra prediction mode among the temporary prediction samples and the existing neighboring reference samples (that is, the unfiltered neighboring reference samples). The above case may be referred to as position-dependent intra prediction (PDPC). In addition, a reference sample line with the highest prediction accuracy is selected from a plurality of adjacent reference sample lines of the current block to derive a prediction sample using a reference sample located in the prediction direction in the corresponding line, and at this time, intra-frame prediction encoding can be performed by indicating (signaling) the reference sample line used to the image decoding device 200. The above situation may be referred to as multi-reference line (MRL) intra-frame prediction or MRL-based intra-frame prediction. In addition, by partitioning the current block into vertical or horizontal sub-partitions, intra-frame prediction is performed based on the same intra-frame prediction mode, and adjacent reference samples may be derived and used in units of sub-partitions. That is, in this case, the intra-frame prediction mode for the current block is equally applied to the sub-partitions, but in some cases, the intra-frame prediction performance may be improved by deriving and using adjacent reference samples in units of sub-partitions. The prediction method may be referred to as intra-frame sub-partitioning (ISP) or intra-frame prediction based on ISP. The above intra-frame prediction method may be referred to as an intra-frame prediction type. The intra-frame prediction type may be referred to as various terms such as an intra-frame prediction technique or an additional intra-frame prediction mode. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the above-mentioned LIP, PDPC, MRL or ISP. Common intra prediction methods other than specific intra prediction types such as LIP, LM, PDPC, MRL and ISP may be referred to as normal intra prediction types. The normal intra prediction type may generally be applied when the above specific intra prediction type is not applied, and prediction may be performed based on the above intra prediction mode. In addition, post-processing filtering may be performed on the derived prediction samples, if necessary.

[0124] Specifically, the intra prediction process may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and a prediction sample derivation step based on the intra prediction mode / type. In addition, if necessary, a post-filtering step may be performed on the derived prediction samples.

[0125] In addition, in addition to the above-mentioned intra prediction types, affine linear weighted intra prediction (ALWIP) can also be used. ALWIP can also be called linear weighted intra prediction (LWIP) or matrix weighted intra prediction (MWIP) or matrix-based intra prediction (MIP). If MIP is applied to the current block, i) use the neighboring reference samples for which the averaging process has been performed, ii) perform the matrix vector multiplication process, and iii) further perform the horizontal / vertical interpolation process when necessary to derive the prediction sample for the current block. The intra prediction mode for MIP can be configured to be different from the intra prediction mode used in LIP, PDPC, MRL, ISP intra prediction or normal intra prediction. The intra prediction mode for MIP can be called MIP intra prediction mode, MIP prediction mode or MIP mode. For example, the matrix and offset used in the matrix vector multiplication can be set differently according to the intra prediction mode for MIP. Here, the matrix can be called a (MIP) weighting matrix, and the offset can be called a (MIP) offset vector or a (MIP) offset vector.

[0126] Overview of the MPM Model

[0127] Typically, when an image is divided into blocks, the current block to be encoded and the neighboring blocks have similar image characteristics. Therefore, the current block and the neighboring blocks have a high probability of having the same or similar intra prediction modes. Therefore, the encoder can use the intra prediction mode of the neighboring blocks to encode the intra prediction mode of the current block.

[0128] For example, the encoder / decoder may construct an MPM (most probable mode) list for the current block. The MPM list may also be expressed as an MPM candidate list. Here, MPM may mean a mode for improving coding efficiency by considering the similarity between the current block and the neighboring blocks during intra-frame prediction mode encoding. As described above, the MPM list may be constructed to include a plane mode, or may be constructed to exclude a plane mode. For example, if the MPM list includes a plane mode, the number of candidates in the MPM list may be 6. In addition, if the MPM list does not include a plane mode, the number of candidates in the MPM list may be 5.

[0129] The encoder / decoder can build an MPM list containing 6 MPMs.

[0130] The following types of patterns can be considered to build the MPM list.

[0131] -Default intra mode

[0132] -Neighborhood Intra Mode

[0133] - Intra mode derived from neighboring inter modes

[0134] -Decoder-side intra mode derivation (DIMD) mode

[0135] -Derived intra mode

[0136] For the neighbor intra mode, the neighbor blocks (i.e., the left neighbor block, the upper neighbor block, the lower left neighbor block, the upper right neighbor block, the upper left neighbor block, etc.) can be considered. When the neighbor intra mode is used as the MPM, the input order can be changed according to the size information of the current block. For example, when the height of the block is greater than or equal to the width of the block, the intra mode of the upper neighbor block can be considered first, and then the intra mode of the left neighbor block can be considered.

[0137] Even when the neighboring block is encoded in inter mode instead of intra mode, intra mode information can be obtained through the IPM buffer. If the position pointed by the motion vector of the neighboring inter block is intra mode, the intra mode can be stored in the IPM buffer. The intra mode stored in the IPM buffer can be used as the MPM mode of the neighboring block.

[0138] The MPM candidate may be constructed according to DIMD described in 1.4.10. If the current block is not in DIMD mode, the intra mode derived from DIMD may be used as the MPM candidate.

[0139] As described above, if the MPM list is constructed to not include the planar mode, the planar mode is excluded from the list and the number of MPM list candidates may be set to five.

[0140] When MIP is not applied to the current block, the above-mentioned MPM list construction method can be used. For example, the above-mentioned MPM list construction method can be used to derive the intra prediction mode used in LIP, PDPC, MRL, ISP intra prediction or normal intra prediction. In addition, the left neighbor block or the upper neighbor block can be encoded based on the above-mentioned MIP. That is, MIP can be applied when encoding the left neighbor block or the upper neighbor block. In this case, it is inappropriate to use the number of MIP intra prediction modes of the neighbor block (left neighbor block / upper neighbor block) to which MIP is applied as in the MPM list for the current block to which MIP is not applied. Therefore, in this case, as an example, the intra prediction mode of the neighbor block (left neighbor block / upper neighbor block) to which MIP is applied can be considered as DC or plane mode. As another example, the intra prediction mode of the neighbor block (left neighbor block / upper neighbor block) to which MIP is applied can be mapped to the normal intra prediction mode based on the mapping table and used to construct the MPM list. In this case, the mapping can be performed based on the block size type of the current block. For example, the mapping table can be expressed as follows.

[0141] [Table 1]

[0142]

[0143] Here, MIP IntraPredMode[xNbX][yNbX] represents the MIP intra prediction mode of the neighbor block (left neighbor block / upper neighbor block), and the block size type MipSizeId represents the block size type of the neighbor block or the current block. For each block size type, the number under the block size type values ​​0, 1, and 2 represents the normal intra prediction mode to which the MIP intra prediction mode is mapped.

[0144] For example, if the block size type of the current block is 0 and the MIP intra prediction mode number of the neighbor block is 10, the mapped normal intra prediction mode number may be 18.

[0145] However, the mapping relationship is an example and may be changed.

[0146] In addition, if MIP is applied to the current block, a separate MPM list may be constructed for the current block to which the MIP is applied. The MPM list may be referred to by various names such as MIP MPM list (or MPM list for MIP, candMipModeList) to distinguish it from the MPM list when the MIP is not applied to the current block. In the following, for the sake of distinction, it is expressed as a MIP MPM list, but it may be referred to as an MPM list.

[0147] The MIP MPM list may include n candidates, for example, n may be 3. The MIP MPM list may be constructed based on the left neighbor block and the upper neighbor block of the current block. Here, the left neighbor block may refer to a block located at the uppermost position among the neighbor blocks adjacent to the left boundary of the current block. In addition, the upper neighbor block may refer to a block located at the leftmost position among the neighbor blocks adjacent to the upper boundary of the current block.

[0148] For example, when MIP is applied to the left neighbor block (and the block size type of the left neighbor block is the same as the block size type of the current block), the first candidate intra prediction mode (or candMipModeA) can be set to be the same as the MIP intra prediction mode of the left neighbor block. In addition, for example, when MIP is applied to the upper neighbor block (and the block size type of the upper neighbor block is the same as the block size type of the current block), the second candidate intra prediction mode (or cand-ipModeB) can be set to be the same as the MIP intra prediction mode of the upper neighbor block. In addition, the left neighbor block or the upper neighbor block can be encoded based on intra prediction other than MIP. That is, when the left neighbor block or the upper neighbor block is encoded, the intra prediction type other than MIP can be applied. In this case, it is inappropriate to use the normal intra prediction mode number of the neighbor block (left neighbor block / upper neighbor block) to which MIP is not applied as the candidate intra mode for the current block to which MIP is applied. Therefore, in this case, as an example, the MIP intra prediction mode of the neighbor block (left neighbor block / upper neighbor block) to which MIP is not applied can be regarded as a MIP intra prediction mode of a specific value (e.g., 0, 1, or 2, etc.). As another example, the normal intra prediction mode of the neighbor block (left neighbor block / upper neighbor block) to which MIP is not applied can be mapped to the MIP intra prediction mode based on the mapping table and used to construct the MIP MPM list. In this case, the mapping can be performed based on the block size type of the current block. For example, the mapping table can be expressed as follows.

[0149] [Table 2]

[0150]

[0151] Here, IntraPredModeY[xNbX][yNbX] represents the intra prediction mode of the neighboring block (left neighboring block / upper neighboring block). Here, the intra prediction mode of the neighboring block can be an intra prediction mode for the luma component (sample) (i.e., luma intra prediction mode). The block size type MipSizeId represents the block size type of the neighboring block or the current block. For each block size type, the number under the block size type values ​​0, 1, and 2 represents the MIP intra prediction mode to which the normal intra prediction mode is mapped.

[0152] In addition, the above-mentioned neighbor block (e.g., the left neighbor block / upper neighbor block) may not be available (e.g., located outside the current picture, located outside the current patch / slice, etc.), or even if MIP is applied, a MIP intra-frame prediction mode that is not available for the current block may be used according to the block size type. In this case, a specific MIP intra-frame prediction mode predefined for the first candidate and / or the second candidate may be used as the first candidate intra-frame prediction mode or the second candidate intra-frame prediction mode. In addition, a specific MIP intra-frame prediction mode predefined for the third candidate may be used as the third candidate intra-frame prediction mode.

[0153] For example, the predefined specific MIP intra prediction mode may be as shown in the following table: The predefined specific MIP intra prediction mode may be referred to as a MIP default candidate mode.

[0154] [Table 3]

[0155]

[0156] The MIP MPM list may be constructed based on the first candidate intra prediction mode and the second candidate intra prediction mode. For example, when the first candidate intra prediction mode and the second candidate intra prediction mode are different from each other, the first candidate intra prediction mode may be placed as the 0th candidate of the MIP MPM list (e.g., candMipModeList[0]), and the second candidate intra prediction mode may be placed as the first candidate of the MIP MPM list (e.g., candMipModeList[1]). The second candidate of the MIP MPM list (e.g., candMipModeList[2]) may use the above-described predefined specific MIP intra prediction mode.

[0157] Alternatively, when the first candidate intra-frame prediction mode and the second candidate intra-frame prediction mode are the same, one of the first candidate intra-frame prediction mode and the second candidate intra-frame prediction mode can be placed as the 0th candidate of the MIP MPM list (e.g., candMipModeList[0]), and the first candidate of the MIP MPM list (e.g., candMipModeList[1]) and the second candidate of the MIP MPM list (e.g., candMipModeList[2]) can use the above-mentioned predefined specific MIP intra-frame prediction mode.

[0158] As described above, the MIP intra prediction mode of the current block may be derived based on the MIP MPM list. In this case, the MPM flag included in the intra prediction mode information for MIP as described above may be referred to as intra_mip_mpm_flag, the MPM index may be referred to as intra_mip_mpm_idx, and the remaining intra prediction mode information may be referred to as intra_mip_mpm_remainder.

[0159] Template-based Intra Mode Derivation (TIMD)

[0160] For the IPM intra modes of surrounding neighboring intra blocks and inter blocks, the sum of absolute transform differences (SATD) between the predicted block predicted from the template region and the actual restored samples can be calculated, and the mode with the lowest SATD can be selected as the intra mode of the current block.

[0161] Alternatively, after selecting the two modes with the lowest SATD, the prediction blocks for the two prediction modes may be mixed using a weighted sum method and used as the prediction block of the current block.

[0162] When the condition of the following formula 1 is satisfied, a method of mixing the two modes may be applied.

[0163] [Formula 1]

[0164] costMode2<2*costMode1

[0165] If the condition is met, the two modes are mixed to generate a prediction block, otherwise, only one mode with the minimum SATD value may be selected. The weight ratio when mixing two prediction blocks is shown in the following formula 2.

[0166] [Formula 2]

[0167] Weight 1 = costMode2 / (costMode1 + costMode2)

[0168] Weight 2 = 1 - Weight 1

[0169] Overview of Intra Subpartition (ISP) Prediction

[0170] In conventional intra prediction, the block to be encoded is regarded as a single coding unit and encoding is performed without partitioning. However, in the intra sub-partitioning (ISP) prediction method, the block to be encoded is partitioned in the horizontal or vertical direction and intra prediction encoding is performed. At this time, encoding / decoding is performed on the partitioned block unit to generate a reconstructed block, and the reconstructed block is used as a reference block for the next partitioned block. In the current intra sub-partitioning (ISP), partitioning is performed according to the block size as shown in Table 4.

[0171] [Table 4]

[0172] Block size (CU) Number of partitions 4×8 Unavailable 4×8，8×4 2 In all other cases 4

[0173] The ISP tool partitions the luma intra prediction block into 2 or 4 sub-partitions vertically or horizontally depending on the block size. The minimum block size for ISP can be, for example, 4×8 (or 8×4). If the block size is larger than 4×8 (or 8×4), the corresponding block is partitioned into 4 sub-partitions. M×128 (where M≤64) and 128×N (where N≤64) ISP blocks may cause potential problems in 64×64 VDPUs. For example, an M×128 CU in a single tree case has an M×128 luma TB and two corresponding M / 2×64 chroma TBs. When the CU uses ISP, the luma TB is partitioned into four M×32 TBs (horizontally partitioned only), each TB being smaller than a 64×64 block. However, in the current ISP design, the chroma blocks are not partitioned. Therefore, the two chroma components will have a size larger than a 32×32 block. Similar situations may also occur with a 128×N CU using ISP. These two situations cause problems with the 64×64 decoder pipeline. Therefore, the CU size that can use ISP may be limited to a maximum of 64×64.

[0174] Next, Figure 5a and Figure 5b An example of intra-sub-partition segmentation (intra-sub-partition coding mode (ISP)) is shown. Specifically, Figure 5a Examples of partitioning of 4×8 and 8×4 blocks are shown, and Figure 5b Examples of partitioning of all blocks except 4x8, 8x4, and 4x4 blocks are shown.

[0175] In the intra sub-partitioning method, an MPM list is generated according to each partitioning method (horizontal partitioning and vertical partitioning) to reduce the encoding complexity, and the appropriate prediction mode among the prediction modes in the generated MPM list is compared in terms of rate-distortion optimization (RDO) to generate the best mode. In addition, when multiple reference line (MRL) intra prediction is used, the above-mentioned intra sub-partitioning method cannot be used. That is, the intra sub-partitioning method is applied only when the 0th reference line is used (ie, the intra_luma_ref_idx value is 0). In addition, when the above-mentioned intra sub-partitioning method is used, the above-mentioned PDPC cannot be used.

[0176] In the intra subpartitioning method, whether intra subpartitioning is applied is first transmitted block by block, and if the current block uses intra subpartitioning (intra_subpartitions_mode_flag), information about whether it is horizontal partitioning or vertical partitioning (intra_subpartitions_split_flag) is encoded / decoded.

[0177] When the intra sub-partitioning method is applied, the intra prediction mode for the current block is equally applied to the sub-partition, and the intra prediction performance can be improved by deriving and using neighboring reference samples in units of sub-partitions. That is, when the intra sub-partitioning method is applied, the residual sample processing process is performed in units of sub-partitions. In other words, the intra prediction sample is derived for each sub-partition, and it is added to the residual signal (residual sample) for the corresponding sub-partition to obtain the reconstructed sample. The residual signal (residual sample) can be derived through a dequantization / inverse transform process, etc. based on the residual information (quantized transform coefficient information or residual coding syntax) in the bitstream described above. That is, the prediction sample and the residual sample for the first sub-partition are derived, and the reconstructed sample for the first sub-partition can be derived based on the prediction sample and the residual sample. In this case, when deriving the prediction sample for the second sub-partition, some of the reconstructed samples in the first sub-partition (for example, the left neighboring reference sample or the upper neighboring reference sample of the second sub-partition) can be used as the neighboring reference sample for the second sub-partition. Similarly, the prediction samples and residual samples for the second sub-partition may be derived, and the reconstructed samples for the second sub-partition may be derived based on the prediction samples and the residual samples. In this case, when deriving the prediction samples for the third sub-partition, some of the reconstructed samples in the second sub-partition (e.g., the left neighboring reference samples or the upper neighboring reference samples of the third sub-partition) may be used as neighboring reference samples for the third sub-partition.

[0178] Overview of Decoder-side Intra Mode Derivation (DIMD)

[0179] The DIMD mode can be derived and used in the encoder and decoder without directly sending the intra prediction mode information.First, the horizontal gradient and the vertical gradient are obtained from the second neighboring sample columns and rows, and the HoG (Histogram of Gradients) can be constructed therefrom.

[0180] You can Figure 6 The HoG is constructed as shown. The HoG can be obtained by applying a Sobel filter using L-shaped rows and columns of 3 pixels around the current block. If the boundaries of blocks exist in different CTUs, they are not used for texture analysis.

[0181] Afterwards, if Figure 7 As shown, two intra modes with the largest histogram size are selected, and the prediction blocks predicted using these modes and the planar mode are mixed to construct the final prediction block. At this time, the weight for mixing can be derived from the size of the histogram. In addition, the DIMD flag is sent in the block unit to check whether DIMD is used.

[0182] In addition, in the case of the above-mentioned ISP mode, intra-frame prediction is performed separately for each sub-block of the current block, but the intra-frame prediction mode is equally applied to all sub-blocks of the current block. However, since image characteristics or pixel value changes may be different between sub-blocks, applying the same intra-frame prediction mode to all sub-blocks acts as a factor that reduces prediction accuracy. Therefore, an embodiment of the present disclosure proposes a method for deriving an intra-frame prediction mode for each sub-block in an ISP mode, and a method for generating a prediction signal based on the derived intra-frame prediction mode. Hereinafter, an embodiment of the present disclosure is described in detail with reference to the accompanying drawings.

[0183] Implementation Method 1

[0184] According to embodiment 1, when the current CU is partitioned into sub-blocks due to the ISP mode, each sub-block can use various prediction modes by deriving an intra prediction mode for each sub-block based on reconstructed neighboring pixel values ​​of the current block.

[0185] Specifically, when the prediction block M×N is in the ISP mode of the present application, the prediction block can be divided into N A (=integer greater than or equal to 2) sub-blocks. At this time, more accurate prediction can be performed by using the reconstructed neighboring pixel values ​​for each sub-block.

[0186] Figure 8 An example of the case of the vertical 2-split mode in the ISP mode of the present disclosure is shown. Figure 8 For the first sub-block SB1, the intra prediction mode parsed from the bitstream can be used. In contrast, for the second sub-block SB2, the reconstructed neighboring pixels R ecSB(2) To derive the intra prediction mode, and a prediction mode different from that of the first sub-block SB1 can be used without additional signaling. An example of the case of the horizontal 2 split mode in the ISP mode of the present disclosure is as follows Fig. 9 As shown, and an example of the case of horizontal or vertical 4-split mode is as follows Fig.10 shown.

[0187] In one embodiment, when the ISP 4 split mode is applied to the M×N prediction block, instead of Fig.11 As in the example of , the intra prediction mode is derived from all sub-blocks, the first intra prediction mode ipm1 can be used for (SB1, SB2), and the neighboring pixel region R is reconstructed. ecSB(3，4) The derived second intra prediction mode ipm2 can be used for (SB3, SB4). Here, the first intra prediction mode ipm1 means the intra prediction mode parsed from the bitstream, and the second intra prediction mode ipm2 represents the prediction mode derived from the reconstructed neighboring reference samples of the third subblock SB3 and the fourth subblock SB4.

[0188] In one embodiment, instead of Fig.12 As in the example of , the intra prediction mode is derived from all sub-blocks of the ISP, the first intra prediction mode ipm1 can be used for the first sub-block SB1, and the neighboring pixel region R is reconstructed from the common ecSB(2，3，3，4) The derived second intra prediction mode ipm2 can be used for (SB2, SB3, SB4).

[0189] As described above, in the above-mentioned embodiment 1, the gradient histogram (HoG) can be used as a method for deriving the intra-frame prediction mode of each sub-block, and the DIMD (decoder-side intra-frame mode derivation) technology using this method or the TIMD (template-based intra-frame mode derivation) technology for deriving the template-based intra-frame prediction mode can be used.

[0190] Implementation Method 2

[0191] According to Embodiment 2, in the ISP mode of the present disclosure, different intra prediction modes of subblocks can be mixed. For example, the intra prediction mode parsed from the bitstream and the intra prediction mode derived from the reconstructed neighboring reference samples for each subblock can be mixed.

[0192] Fig.13 An example is shown in which the first intra prediction mode ipm1 and the second intra prediction mode ipm2 can be used together for the second sub-block SB2, assuming that the first intra prediction mode ipm1 parsed from the bitstream is used for the first sub-block SB1, and the second intra prediction mode ipm2 derived from the reconstructed neighboring reference samples of the corresponding block is used for the second sub-block SB2.

[0193] In addition, the kth (=1, 2, ..., N) A ) sub-block to generate a prediction signal, as in the following case.

[0194] -(Case 1): Mixing two signals

[0195] The mixture of the prediction signal PredA and the prediction signal PredB can be derived as in Equation 3 below.

[0196] [Formula 3]

[0197] Pred SB(k) =w×PredA+(1-w)×PredB(k=1, 2,...,N A )

[0198] In the above formula 3, w is the weight value required to mix PredA and PredB, Pred SB(k)is a final prediction signal of the sub-block generated by mixing, and k is a natural number greater than or equal to 2, and can represent the kth sub-block in the current block.

[0199] Various hybrid combinations may be used to generate prediction signals for sub-blocks. According to one embodiment, (PredA, PredB) may include ((Pred SB(k)_ipm1 ,Pred SB(k)_first )、(Pred SB(k)_ipm1 ,Pred SB(k)_second ) and (Pred SB(k)_first ,Pred SB(k)_second ). Here, Pred SB(k) Represents the final prediction signal of the k-th sub-block, Pred SB(k)_first Indicates that from Rec SB(k) The prediction signal predicted in the first intra-frame prediction mode is derived, Rec SB(k) is the neighboring reference sample of the k-th sub-block, Pred SB(k)_second Indicates that from Rec SB(k) The predicted signal Rec SB(k) is the neighboring reference sample of the kth sub-block, and Pred SB(k)_ipm1 may represent a prediction signal predicted in the first intra prediction mode ipm1 parsed from a bitstream for the k-th subblock.

[0200] In one embodiment, by setting w=1 / 2, it is possible to SB(k)_ipm1 With Pred SB(k)_first The final prediction signal of the kth sub-block is generated with equal weights between them, as shown in Equation 4.

[0201] [Formula 4]

[0202]

[0203] In one embodiment, when ipm1 and ipm2_ first In the same mode, by setting w = 1 / 2, you can SB(k)_ipm1 With Pred SB(k)_second The final prediction signal of the kth sub-block is generated with equal weights between them, as shown in Equation 5.

[0204] [Formula 5]

[0205]

[0206] In one embodiment, by mixing Pred SB(k)_first and Pred SB(k)_secondTo generate the final prediction signal, as shown in the following equation 6. In this case, by using the neighboring reference area Rec from the kth sub-block SB(k) The size of the gradient obtained can be used to apply different weights to Pred SB(k)_first and Pred SB(k)_second For example, when the magnitude of the gradient is G SB(k)_first and G SB(k)_second When we set the weight w = G SB(k)_first / (G SB(k)_first +G SB(k)_second ) to generate the final prediction signal.

[0207] [Formula 6]

[0208]

[0209] As an implementation method for obtaining the gradient direction and magnitude, HoG (Histogram of Gradients) may be used, and the gradient magnitudes for the horizontal gradient Gx and the vertical gradient Gy may be used as |G x |+|G y |or Therefore, using the SB(k) The gradient direction and magnitude obtained can be used to obtain the maximum magnitude G in a specific direction (or direction mode). SB(k)_first and G SB(k)_second .

[0210] In one embodiment, when ipm1, ipm2_first, and ipm2_second are all in the same mode, Pred SB(1) The prediction signal can be used as the final prediction signal without mixing as in the following Equation 7 by setting w=1.

[0211] [Formula 7]

[0212] Pred SB(k) =Pred SB(1) (k=1,2,...,N A )

[0213] Furthermore, w can be determined based on the magnitude of the gradient, or can be implicitly predefined between the encoder and decoder. In addition, blending can be applied starting from sub-blocks with k>1, which can be agreed between the encoder and decoder or specified in the bitstream.

[0214] In one embodiment, in the case of 2-split sub-blocks, the use of the above formula 6 may be limited for sub-blocks with k>1. In this case, the above formula 7 may be applied, or the use of the ISP mode according to the present disclosure may be limited.

[0215] -(Case 2): Mixing three signals

[0216] Prediction signal Pred SB(k)_ipm1 、Pred SB(k)_first and Pred SB(k)_second The mixture can be derived using the following formula 8.

[0217] [Formula 8]

[0218]

[0219] Here, w is Pred SB(k)_first With Pred SB(k)_second The weight value required for mixing between SB(k)_ipm1 and the mixed prediction signal Pred SB(k)_first and Pred SB(k)_second The weight value between , and Pred SB(k) It can be expressed as the kth (=1, 2, ..., N) generated by mixing A )The final prediction signal of the sub-block.

[0220] In one embodiment, when k=3, p=1 / 3 and w=2 / 3, the final prediction signal of the third sub-block SB3 can be generated as follows: SB(k)_ipm1 With Pred SB(k)_ipm2_first have equal weights.

[0221] [Formula 9]

[0222]

[0223] Furthermore, w can be determined based on the magnitude of the gradient, or can be implicitly predefined between the encoder and decoder. In addition, blending can be applied starting from sub-blocks with k>1, which can be agreed between the encoder and decoder or specified in the bitstream.

[0224] Implementation 3

[0225] According to Embodiment 3, in the case of intra prediction mode of inter-frame slices, various blending can be performed using intra prediction mode information of the current block and the neighboring blocks. In one embodiment, for vertically partitioned sub-blocks, the intra prediction mode stored near the reconstructed PU of each sub-block can be as follows: Fig.14 Each sub-block can select and use one of the available intra prediction modes (ie, if the intra prediction mode is stored in the buffer of the reconstructed PU).

[0226] exist Fig.14 In Pred SB(k)_ipmRefIt can refer to the signal predicted for the k-th sub-block in the intra-frame prediction mode ipmRef. Ref It can mean posAL stored in the kth sub-block SB(k) ,posA B(k) ,posAR SB(k) ,posL SB(k) and posLB SB(k) One of the available intra prediction modes among the intra prediction modes in position. Here, posAL SB(k) It can refer to the upper left PU position of the kth sub-block, posAS B(k) It can refer to the upper PU position of the k-th sub-block, posAR SB(k) It can refer to the upper right PU position of the k-th sub-block, posL SB(k) It can mean the left PU position of the k-th sub-block, and posLB SB(k) It can mean the lower left PU position of the k-th sub-block. In addition, if posAL SB(k) ,posA SB(k) ,posAR SB(k) ,posL SB(k) and posLB SB(k) Positions are outside of picture boundaries, virtual boundaries, CTU / slice / tile regions, these positions may not be used. In addition, if the intra prediction mode is not stored in posAL SB(k) ,posA SB(k) ,posAR SB(k) ,posL SB(k) and posLB SB(k) locations, you do not need to use these locations.

[0227] In one embodiment, the position posAL may be SB(k) ,posA SB(k) ,posAR SB(k) ,posL SB(k) and posLB SB(k) A candidate list L is constructed to check whether an intra prediction mode is stored at a corresponding position. For example, L1 = {posAL SB(1) ,posA SB(1) ,posAR SB(1) ,posL SB(1) and posLB SB(1)}, and L2 = {posA SB(1) ,posAR SB(1) ,posA SB(2) ,posAR SB(2)}. In addition, the list L can be predefined according to the commitment between the encoder and the decoder.

[0228] Each subblock can select and use one of the intra prediction modes stored in the candidate position of the candidate list L. For example, if L2={posA SB(1) ,posAR SB(1) ,posA SB(2) ,posAR SB(2)}, you can check whether the intra prediction mode is posA SB(1) →posAR SB(1) →posA SB(2) →posAR SB(2) The order of storage, and according to the present disclosure, the first confirmed available intra prediction mode can be used for mixing. At this point, it should be understood that the order can be predefined according to the commitment between the encoder and the decoder.

[0229] In one embodiment, the candidate list can be constructed as a method of constructing an MPM for each CU or each sub-block. At this time, if the list is not filled with all candidates, the predefined intra prediction mode can be filled in the list according to the commitment between the encoder and the decoder. Then, it can be encoded as one of the MPM modes for each CU or each sub-block.

[0230] The mixing according to Embodiment 3 can be applied as follows.

[0231] If the ipm mode of the reconstructed PU position stored in each sub-block is available, then i) the prediction signal combination (Pred SB(k)_ipmRef ,Pred SB(k)_first )、(Pred SB(k)_ipmRef ,Pred SB(k)_first ) and (Pred SB(k)_ipm1 ,Pred SB(k)_second ) can be applied to the formula for dual signal mixing described above with reference to Embodiment 2. Alternatively, ii) prediction signal combination (Pred SB(k)_ipmRef 、Pred SB(k)_first 、Pred SB(k)_second ) can be applied to the formula for three-signal mixing described above with reference to Implementation 2.

[0232] In contrast, if the ipm mode of the reconstructed PU position stored in each sub-block is not available, the hybrid method described above with reference to Embodiment 2 may be equally applied.

[0233] Implementation 4

[0234] According to Embodiment 4, syntax for supporting the above-mentioned embodiments can be provided.

[0235] Examples of Coding_unit syntax according to one embodiment are shown in Table 5 and Table 6.

[0236] [Table 5]

[0237]

[0238] [Table 6]

[0239]

[0240] Whether to mix can be determined by a separate flag. For example, as shown in Table 5, after determining whether to split horizontally / vertically (intra_subpartitions_split_flag), intra_subpartitions_blending_flag can be parsed to determine whether to mix. Alternatively, as shown in Table 6, if it is determined that the ISP mode of the present disclosure is applied, intra_subpartitions_blending_flag can be parsed before determining whether to split horizontally / vertically (intra_subpartitions_split_flag) to determine whether to mix.

[0241] Unlike the examples in Table 5 and Table 6, a flag for determining whether to mix may not be sent. In this case, whether to mix may be determined in advance according to a commitment between the encoder and the decoder.

[0242] In one embodiment, if whether to mix can be resolved by a flag or known implicitly, the mixed combination (eg, (Pred SB(k)_ipm1 ,Pred SB(k)_first )、(Pred SB(k)_ipm1 ,Pred SB(k)_second )、(Pred SB(k)_first ,Pred SB(k)_second )、(Pred SB(k)_ipm1 ,Pred SB(k)_first ,Pred SB(k)_second )) can be predetermined by a commitment between the encoder and the decoder.

[0243] In one embodiment, the REC SB(k) The number of available reference samples determines whether to parse the blending flag (i.e., intra_subpartitions_blending_flag). For example, if REC SB(k) If the number of available pixels is not sufficient to obtain the gradient, the parsing of the blend flag can be omitted.

[0244] Implementation method 5

[0245] According to Embodiment 5, various reconstructed reference sample regions for deriving the intra prediction mode of the kth subblock may be defined. Here, k may be less than or equal to N A (an integer greater than or equal to 2).

[0246] Fig.15 FIG. 4 shows an available reconstruction reference sample area of ​​the second sub-block SB2 according to one embodiment. Fig.15 , when the size of the second sub-block SB2 is M SB(2) ×N SB(2) When the available reconstruction area of ​​the second sub-block SB2 can be A (2) , L (2) and AL (2) Here, A (2) The size of the region can be, for example, H AL(2) ×W A(2) , L (2) The size of the region can be, for example, H L(2) ×W AL(2) , and AL (2) The size of the region can be, for example, H AL(2) ×W AL(2) .

[0247] In one embodiment, H AL(k) and W AL(k) Can be equal or different. In addition, W A(k) Can be smaller or larger than M SB(k) , or they can be equal. In addition, H L(k) Can be less than or greater than N SB(k) , or they may be equal.

[0248] Area A of the kth sub-block (k) , L (k) and AL (k) Can be used in the following combinations.

[0249] -(A (k) ,L (k) ,AL (k) )、(A (k) ,L (k) )、(A (k) ,AL (k) )、(L (k) ,AL (k) )、(A (k) )、(L (k) )、(AL (k) )

[0250] - If the number of available reconstructed pixels in each region is less than a predetermined threshold, the region may not be used, and the threshold may be predefined as a commitment between the encoder and the decoder.

[0251] - If each region is located outside the picture boundary, virtual boundary or CTU / slice / tile area, the region may not be used. In addition, if each region is located outside a specific area predefined by the commitment between the encoder and the decoder, the region may not be used.

[0252] According to the ISP mode according to the embodiment of the present disclosure described above, the intra-frame prediction mode can be determined separately for each sub-block. In addition, the intra-frame prediction mode of the sub-block can be derived from the reconstructed neighboring reference pixel values ​​adjacent to the corresponding sub-block, or can be determined based on the available intra-frame prediction mode at a predetermined position. Therefore, each sub-block can be predicted more accurately in the ISP mode.

[0253] In the following, reference will be made to Fig.16 and Fig.17 An image encoding / decoding method according to one embodiment of the present disclosure is described in detail.

[0254] Fig.16 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure. Fig.16 The image encoding method can be Figure 2 The image encoding device is executed.

[0255] Reference Fig.16 , the image encoding device may divide the current block into a plurality of sub-blocks based on applying ISP (Intra Sub Partitioning) prediction to the current block (S1610). The image encoding device may determine an intra prediction mode for each of the plurality of sub-blocks (S1620). Then, the image encoding device may generate a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode (S1630).

[0256] In one embodiment, the plurality of subblocks may include at least one first subblock and at least one second subblock. In this case, only information about the intra prediction mode of the first subblock among the first subblock and the second subblock may be encoded in the bitstream.

[0257] In one embodiment, the intra prediction mode of the second subblock may be derived from neighboring reference samples of the second subblock based on decoder-side intra mode derivation (DIMD) or template-based intra mode derivation (TIMD).

[0258] In one embodiment, based on the hybrid mode being applied to the current block, a prediction block for each of the plurality of sub-blocks may be generated by a weighted sum of the plurality of prediction blocks. In addition, predetermined hybrid flag information indicating whether the hybrid mode is applied may be encoded in a bitstream.

[0259] Fig.17 is a flowchart illustrating an image decoding method according to one embodiment of the present disclosure. Fig.17 The image decoding method can be Figure 3 The image decoding device is executed.

[0260] Reference Fig.17 , the image decoding device may divide the current block into a plurality of sub-blocks based on applying ISP (Intra Sub-Partitioning) prediction to the current block (S1710). The image decoding device may determine an intra prediction mode for each of the plurality of sub-blocks (S1720). Then, the image decoding device may generate a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode (S1730).

[0261] In one embodiment, the plurality of subblocks may include a first subblock and a second subblock. In this case, the intra prediction mode of the first subblock may be determined based on the prediction mode information of the first subblock or the first neighboring reference sample of the first subblock. In addition, the intra prediction mode of the second subblock may be determined based on the second neighboring reference sample of the second subblock.

[0262] In one embodiment, the intra prediction mode of the second subblock may be derived from the second neighboring reference samples based on decoder-side intra mode derivation (DIMD) or template-based intra mode derivation (TIMD).

[0263] In one embodiment, the final prediction block of the second sub-block may be generated by a weighted sum of the first prediction block and the second prediction block of the second sub-block. In this case, the first prediction block may be generated based on an intra prediction mode of the first sub-block, and the second prediction block may be generated based on an intra prediction mode of the second sub-block. In addition, the weight applied to the weighted sum may be determined based on a gradient obtained from a second neighboring reference sample according to a gradient histogram (HoG).

[0264] In one embodiment, the final prediction block of the second sub-block may be generated by a weighted sum of the first prediction block, the second prediction block, and the third prediction block of the second sub-block. In this case, the first prediction block may be generated based on the intra-frame prediction mode of the first sub-block, the second prediction block may be generated based on the first intra-frame prediction mode of the second sub-block, and the third prediction block may be generated based on the second intra-frame prediction mode of the second sub-block.

[0265] In this way, based on the hybrid mode being applied to the current block, a prediction block for each of the plurality of sub-blocks may be generated by a weighted sum of the plurality of prediction blocks. In this case, whether to apply the hybrid mode may be determined based on predetermined hybrid flag information.

[0266] In one embodiment, the intra prediction mode of the second subblock may be selected from among available intra prediction modes mapped to a predetermined position adjacent to the second subblock.

[0267] In one embodiment, the neighboring reference samples of the second sub-block may be obtained from at least one of an upper reference sample region, a left reference sample region, or an upper-left reference sample region of the second sub-block.

[0268] 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 disclosure, 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] In addition, the image decoding device and the image encoding device to which the embodiments of the present disclosure are applied may be included in a multimedia broadcast sending and receiving device, a mobile communication terminal, a home theater video device, a digital theater video device, a surveillance camera, a video chat device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camera, a video on demand (VoD) service provider, an OTT video (over the top video) device, an Internet streaming service provider, a three-dimensional (3D) video device, a video phone video device, a medical video device, etc., and may be used to process a video signal or a data signal. For example, an OTT video device may include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smart phone, a tablet PC, a digital video recorder (DVR), etc.

[0273] Fig.18 is a diagram showing a content streaming system to which an embodiment of the present disclosure can be applied.

[0274] like Fig.18 As shown, the content streaming system to which the embodiments of the present disclosure are applied may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0275] The encoding server compresses the content input from the multimedia input device such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bit stream and sends the bit stream to the streaming server. As another example, when the multimedia input device such as a smart phone, a camera, a camcorder, etc. directly generates a bit stream, the encoding server can be omitted.

[0276] A bitstream may be generated by an image encoding method or an image encoding device to which an embodiment of the present disclosure is applied, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0277] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server is used as a medium to inform 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 is used to control the command / response between the devices in the content streaming system.

[0278] The streaming server may receive content from a media storage device and / or an encoding server. For example, when receiving content 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 within a predetermined time.

[0279] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0280] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0281] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations of methods according to various embodiments to be performed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0282] Industrial Applicability

[0283] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Splitting the current block into a plurality of sub-blocks based on the intra sub-partition ISP prediction being applied to the current block; determining an intra prediction mode for each of the plurality of subblocks; as well as generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode, The multiple sub-blocks include a first sub-block and a second sub-block, The intra prediction mode of the first sub-block is determined based on the prediction mode information of the first sub-block or the first neighboring reference sample of the first sub-block, and The intra prediction mode of the second sub-block is determined based on a second adjacent reference sample of the second sub-block.

2. The image decoding method according to claim 1, wherein: The intra prediction mode of the second subblock is derived from the second neighboring reference samples based on a decoder-side intra mode derivation DIMD or a template-based intra mode derivation TIMD.

3. The image decoding method according to claim 1, wherein: The final prediction block of the second sub-block is generated by a weighted sum of the first prediction block and the second prediction block of the second sub-block.

4. The image decoding method according to claim 3, wherein: The first prediction block is generated based on the intra prediction mode of the first subblock, and the second prediction block is generated based on the intra prediction mode of the second subblock.

5. The image decoding method according to claim 3, wherein: The weight applied to the weighted sum is determined based on a gradient obtained from the second neighboring reference sample according to a histogram of gradients HoG.

6. The image decoding method according to claim 1, wherein: The final prediction block of the second sub-block is generated by a weighted sum of the first prediction block, the second prediction block, and the third prediction block of the second sub-block.

7. The image decoding method according to claim 6, wherein: The first prediction block is generated based on an intra prediction mode of the first subblock, the second prediction block is generated based on a first intra prediction mode of the second subblock, and the third prediction block is generated based on a second intra prediction mode of the second subblock.

8. The image decoding method according to claim 1, wherein: The intra prediction mode of the second subblock is selected from among available intra prediction modes mapped to a predetermined position adjacent to the second subblock.

9. The image decoding method according to claim 1, in, Based on the hybrid mode being applied to the current block, generating a prediction block for each of the plurality of sub-blocks by a weighted sum of the plurality of prediction blocks, and Wherein, whether to apply the hybrid mode is determined based on predetermined hybrid flag information.

10. The image decoding method according to claim 1, wherein: The neighboring reference samples of the second sub-block are obtained from at least one of an upper reference sample region, a left reference sample region, or an upper-left reference sample region of the second sub-block.

11. An image decoding device comprising a memory and at least one processor, in, The at least one processor is configured to: Splitting the current block into a plurality of sub-blocks based on the intra sub-partition ISP prediction being applied to the current block; determining an intra prediction mode for each of the plurality of subblocks; as well as generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode, The multiple sub-blocks include a first sub-block and a second sub-block, The intra prediction mode of the first sub-block is determined based on the prediction mode information of the first sub-block or the first neighboring reference sample of the first sub-block, and The intra prediction mode of the second sub-block is determined based on a second adjacent reference sample of the second sub-block.

12. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: Splitting the current block into a plurality of sub-blocks based on the intra sub-partition ISP prediction being applied to the current block; determining an intra prediction mode for each of the plurality of subblocks; as well as generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode, The plurality of sub-blocks include a first sub-block and a second sub-block, and Among them, only information about the intra prediction mode of the first subblock among the first subblock and the second subblock is encoded in the bitstream.

13. The image encoding method according to claim 12, wherein: The intra prediction mode of the second subblock is derived from second neighboring reference samples based on a decoder-side intra mode derivation DIMD or a template-based intra mode derivation TIMD.

14. The image encoding method according to claim 12, in, Based on the hybrid mode being applied to the current block, generating a prediction block for each of the plurality of sub-blocks by a weighted sum of the plurality of prediction blocks, and Wherein, predetermined mix flag information indicating whether to apply the mix mode is encoded in the bit stream.

15. A computer-readable recording medium storing a bit stream generated by an image encoding method, the image encoding method comprising the steps of: Splitting the current block into a plurality of sub-blocks based on the intra sub-partition ISP prediction being applied to the current block; determining an intra prediction mode for each of the plurality of subblocks; as well as generating a prediction block for each of the plurality of sub-blocks based on the determined intra prediction mode, The plurality of sub-blocks include a first sub-block and a second sub-block, and Among them, only information about the intra prediction mode of the first subblock among the first subblock and the second subblock is encoded in the bitstream.

Images