IMAGE ENCODING / DECODING METHOD, BITSTREAM TRANSMISSION METHOD, AND RECORDING MEDIUM THAT STORES BITSTREAM

Abstract

An image encoding / decoding method, a bitstream transmission method, and a computer-readable recording medium on which a bitstream is stored are provided.An image decoding method according to the present invention may be an image decoding method carried out by an image decoding device, and the image decoding method comprises the steps of: obtaining an intra-prediction block from a current block and an inter-prediction block from the current block; determining an intra weight for the intra-prediction block and an inter weight for the inter-prediction block; and generating prediction samples from the current block by applying the intra weight to the intra-prediction block and applying the inter weight to the inter-prediction block, wherein the intra weight is determined and applied on a sample-by-sample basis within the intra-prediction block, and the inter weight is determined and applied on a sample-by-sample basis within the inter-prediction block.

Description

Video encoding / decoding method, method for transmitting bitstream, and recording medium storing bitstream

[0001] The present disclosure relates to a video encoding / decoding method, a method for transmitting a bitstream, and a recording medium storing the bitstream, and relates to sample-based combined inter and intra prediction (CIIP).

[0002] Recently, demand for high-resolution, high-quality images, such as HD (High Definition) and UHD (Ultra High Definition) images, has been increasing across various fields. As image data becomes higher resolution and higher quality, the amount of information transmitted, or bits, increases relative to conventional image data. This increase in information or bits transmitted leads to increased transmission and storage costs.

[0003] Accordingly, a highly efficient image compression technology is required to effectively transmit, store, and play high-resolution, high-quality image information.

[0004] The present disclosure aims to provide a video encoding / decoding method and device with improved encoding / decoding efficiency.

[0005] Additionally, the present disclosure aims to propose a sample-based CIIP.

[0006] Additionally, the present disclosure aims to propose an extended intra prediction mode-based CIIP.

[0007] In addition, the present disclosure aims to provide a non-transitory computer-readable recording medium that stores a bitstream generated by an image encoding method according to the present disclosure.

[0008] In addition, the present disclosure aims to provide a non-transitory computer-readable recording medium that stores a bitstream received and decoded by an image decoding device according to the present disclosure and used for restoring an image.

[0009] In addition, the present disclosure aims to provide a method for transmitting a bitstream generated by an image encoding method according to the present disclosure.

[0010] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0011] An image decoding method according to one aspect of the present disclosure is an image decoding method performed by an image decoding device, comprising: obtaining an intra prediction block of a current block and an inter prediction block of the current block; determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and applying the intra weight to the intra prediction block and the inter weight to the inter prediction block to generate prediction samples of the current block, wherein the intra weight is determined and applied on a sample-by-sample basis within the intra prediction block, and the inter weight is determined and applied on a sample-by-sample basis within the inter prediction block.

[0012] According to another aspect of the present disclosure, a video encoding method is performed by a video encoding device, the video encoding method comprising: obtaining an intra prediction block of a current block and an inter prediction block of the current block; determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and applying the intra weight to the intra prediction block and the inter weight to the inter prediction block to generate prediction samples of the current block, wherein the intra weight is determined and applied on a sample-by-sample basis within the intra prediction block, and the inter weight is determined and applied on a sample-by-sample basis within the inter prediction block.

[0013] A computer-readable recording medium according to another aspect of the present disclosure can store a bitstream generated by an image encoding method or device of the present disclosure.

[0014] A transmission method according to another aspect of the present disclosure can transmit a bitstream generated by an image encoding method or device of the present disclosure.

[0015] The features briefly summarized above regarding the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that follows and do not limit the scope of the present disclosure.

[0016] According to the present disclosure, a video encoding / decoding method and device with improved encoding / decoding efficiency can be provided.

[0017] Additionally, according to the present disclosure, since CIIP is performed on a sample-by-sample basis, prediction performance can be improved.

[0018] Additionally, according to the present disclosure, the number of categories used to determine the weights of CIIP increases, so that prediction performance can be improved.

[0019] Additionally, according to the present disclosure, the intra prediction mode used in CIIP is signaled more efficiently, so that coding efficiency can be improved.

[0020] In addition, according to the present disclosure, a non-transitory computer-readable recording medium for storing a bitstream generated by an image encoding method according to the present disclosure can be provided.

[0021] In addition, according to the present disclosure, a non-transitory computer-readable recording medium can be provided that stores a bitstream received and decoded by an image decoding device according to the present disclosure and used for restoring an image.

[0022] Additionally, according to the present disclosure, a method for transmitting a bitstream generated by an image encoding method can be provided.

[0023] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0024] FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.

[0025] FIG. 2 is a schematic diagram of an image encoding device to which an embodiment according to the present disclosure can be applied.

[0026] FIG. 3 is a schematic diagram illustrating an image decoding device to which an embodiment according to the present disclosure can be applied.

[0027] Figure 4 is a flowchart illustrating an image encoding method based on intra prediction.

[0028] Figure 5 is a schematic diagram showing an intra prediction unit in a video encoding device.

[0029] Figure 6 is a flowchart illustrating an image encoding method based on intra prediction.

[0030] Figure 7 is a schematic diagram showing an intra prediction unit in an image decoding device.

[0031] Figure 8 is a diagram illustrating an example of surrounding blocks used to derive weights of CIIP.

[0032] Figure 9 is a diagram for explaining methods of dividing the current block in CIIP.

[0033] FIG. 10 is a flowchart illustrating an image encoding method and an image decoding method according to one embodiment of the present disclosure.

[0034] Figure 11 is a drawing to explain the positions of blocks and samples.

[0035] Figure 12 is a diagram illustrating the categories used in CIIP.

[0036] FIG. 13 is a flowchart illustrating an image encoding method and an image decoding method according to another embodiment of the present disclosure.

[0037] FIG. 14 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure.

[0038] FIG. 15 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure.

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

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

[0041] FIG. 18 is a drawing exemplifying a content streaming system to which an embodiment according to the present disclosure can be applied.

[0042] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0043] In describing embodiments of the present disclosure, detailed descriptions of known configurations or functions will be omitted if they are deemed to obscure the gist of the present disclosure. Furthermore, portions unrelated to the description of the present disclosure in the drawings have been omitted, and similar portions have been designated with similar reference numerals.

[0044] In the present disclosure, when a component is said to be "connected," "coupled," or "connected" to another component, this may include not only a direct connection, but also an indirect connection in which another component exists in between. Furthermore, when a component is said to "include" or "have" another component, unless otherwise specifically stated, this does not exclude the other component, but rather implies that the other component may be included.

[0045] In this disclosure, terms such as first, second, etc. are used solely to distinguish one component from another, and do not limit the order or importance of components unless specifically stated otherwise. Accordingly, within the scope of this 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 this disclosure, distinct components are used to clearly illustrate their respective characteristics, and do not necessarily imply that the components are separated. That is, multiple components may be integrated into a single hardware or software unit, or a single component may be distributed into multiple hardware or software units. Therefore, even if not specifically mentioned, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0047] In the present disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, embodiments comprising a subset of the components described in one embodiment are also within the scope of the present disclosure. Furthermore, embodiments including other components in addition to the components described in various embodiments are also within the scope of the present disclosure.

[0048] The present disclosure relates to encoding and decoding of images, and terms used in the present disclosure may have their usual meanings commonly used in the technical field to which the present disclosure belongs, unless newly defined in the present disclosure.

[0049] In the present disclosure, a "picture" generally refers to a unit representing one image of a specific time period, and a slice / tile is a coding unit that constitutes a part of a picture, and a single picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0050] In the present disclosure, "pixel" or "pel" may refer to the smallest unit that constitutes a picture (or image). Additionally, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel / pixel value of a luma component or only a pixel / pixel value of a chroma component.

[0051] In the present disclosure, a "unit" may represent a basic unit of image processing. A unit may include at least one of a specific region of a picture and information related to the region. In some cases, the term "unit" may be used interchangeably with terms such as "sample array," "block," or "area." In general, an MxN block may include a set (or array) of samples (or sample array) or transform coefficients consisting of M columns and N rows.

[0052] In the present disclosure, the "current block" may mean one of the following: a "current coding block," a "current coding unit," a "block to be encoded," a "block to be decoded," or a "block to be processed." When prediction is performed, the "current block" may mean a "current prediction block" or a "block to be predicted." When transformation (inverse transformation) / quantization (inverse quantization) is performed, the "current block" may mean a "current transformation block" or a "block to be transformed." When filtering is performed, the "current block" may mean a "block to be filtered."

[0053] In the present disclosure, a "current block" may mean a block that includes both a luma component block and a chroma component block, or a "luma block of the current block," unless explicitly described as a chroma block. The luma component block of the current block may be explicitly expressed by including an explicit description of the luma component block, such as "luma block" or "current luma block." Additionally, the chroma component block of the current block may be explicitly expressed by including an explicit description of the chroma component block, such as "chroma block" or "current chroma block."

[0054] In this disclosure, " / " and "," can be interpreted as "and / or". For example, "A / B" and "A, B" can be interpreted as "A and / or B". Additionally, "A / B / C" and "A, B, C" can mean "at least one of A, B, and / or C."

[0055] In this disclosure, "or" may be interpreted as "and / or." For example, "A or B" may mean 1) "A" only, 2) "B" only, or 3) "A and B." Alternatively, "or" in this disclosure may mean "additionally or alternatively."

[0056] Overview of Video Coding Systems

[0057] FIG. 1 is a diagram schematically illustrating a video coding system to which an embodiment according to the present disclosure can be applied.

[0058] A video coding system according to one embodiment may include an encoding device (10) and a decoding device (20). The encoding device (10) may transmit encoded video and / or image information or data to the decoding device (20) in the form of a file or streaming through a digital storage medium or a network.

[0059] An encoding device (10) according to one embodiment may include a video source generation unit (11), an encoding unit (12), and a transmission unit (13). A decoding device (20) according to one embodiment may include a reception unit (21), a decoding unit (22), and a rendering unit (23). The encoding unit (12) may be referred to as a video / image encoding unit, and the decoding unit (22) may be referred to as a video / image decoding unit. The transmission unit (13) may be included in the encoding unit (12). The reception unit (21) may be included in the decoding unit (22). The rendering unit (23) may include a display unit, and the display unit may be configured as a separate device or an external component.

[0060] The video source generation unit (11) can obtain video / images through a process of capturing, synthesizing, or generating video / images. The video source generation unit (11) can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, a virtual video / image can be generated through a computer, etc., in which case the video / image capture process can be replaced with a process of generating related data.

[0061] The encoding unit (12) can encode input video / images. The encoding unit (12) can perform a series of procedures, such as prediction, transformation, and quantization, to improve compression and encoding efficiency. The encoding unit (12) can output encoded data (encoded video / image information) in the form of a bitstream.

[0062] The transmission unit (13) can obtain encoded video / image information or data output in the form of a bitstream, and transmit it to the reception unit (21) of the decoding device (20) or another external object through a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit (13) may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcasting / communication network. The transmission unit (13) may be provided as a separate transmission device from the encoding device (12), and in this case, the transmission device may include at least one processor for obtaining encoded video / image information or data output in the form of a bitstream, and a transmission unit for transmitting it in the form of a file or streaming. The reception unit (21) can extract / receive the bitstream from the storage medium or network and transmit it to the decoding unit (22).

[0063] The decoding unit (22) can decode video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding unit (12).

[0064] The rendering unit (23) can render the decrypted video / image. The rendered video / image can be displayed through the display unit.

[0065] Overview of the video encoding device

[0066] FIG. 2 is a schematic diagram illustrating an image encoding device to which an embodiment according to the present disclosure can be applied.

[0067] As illustrated in FIG. 2, the image encoding device (100) may include an image segmentation unit (110), a subtraction unit (115), a transformation unit (120), a quantization unit (130), an inverse quantization unit (140), an inverse transformation unit (150), an addition unit (155), a filtering unit (160), a memory (170), an inter prediction unit (180), an intra prediction unit (185), and an entropy encoding unit (190). The inter prediction unit (180) and the intra prediction unit (185) may be collectively referred to as a “prediction unit.” The transformation unit (120), the quantization unit (130), the inverse quantization unit (140), and the inverse transformation unit (150) may be included in a residual processing unit. The residual processing unit may further include a subtraction unit (115).

[0068] All or at least some of the plurality of components constituting the video encoding device (100) may be implemented as a single hardware component (e.g., an encoder or a processor) according to an embodiment. In addition, the memory (170) may include a decoded picture buffer (DPB) and may be implemented by a digital storage medium.

[0069] The image segmentation unit (110) can segment an input image (or picture, frame) input to the image encoding device (100) into one or more processing units. For example, the processing unit may be called a coding unit (CU). The coding unit may be obtained by recursively segmenting a coding tree unit (CTU) or a largest coding unit (LCU) according to a QT / BT / TT (Quad-tree / binary-tree / ternary-tree) structure. For example, one coding unit may be segmented into a plurality of coding units of deeper depth based on a quad-tree structure, a binary-tree structure, and / or a ternary-tree structure. For segmenting the coding unit, the quad-tree structure may be applied first, and the binary-tree structure and / or the ternary-tree structure may be applied later. The coding procedure according to the present disclosure may be performed based on the final coding unit that is no longer segmented. The maximum coding unit can be used directly as the final coding unit, and the coding unit of the lower depth obtained by dividing the maximum coding unit can be used as the final concatenated unit. Here, the coding procedure may include procedures such as prediction, transformation, and / or restoration described below. As another example, the processing unit of the coding procedure may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transformation unit may each be divided or partitioned from the final coding unit. The prediction unit may be a unit of sample prediction, and the transformation unit may be a unit that derives a transform coefficient and / or a unit that derives a residual signal from a transform coefficient.

[0070] The prediction unit (inter-prediction unit (180) or intra-prediction unit (185)) can perform prediction on a block to be processed (current block) and generate a predicted block including prediction samples for the current block. The prediction unit can determine whether intra-prediction or inter-prediction is applied to the current block or CU unit. The prediction unit can generate various information regarding the prediction of the current block and transmit the information to the entropy encoding unit (190). The information regarding the prediction can be encoded by the entropy encoding unit (190) and output in the form of a bitstream.

[0071] The intra prediction unit (185) can predict the current block by referring to samples within the current picture. The referenced samples may be located in the neighborhood of the current block or may be located away from it, depending on the intra prediction mode and / or intra prediction technique. The intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, a DC mode and a planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes, depending on the degree of detail in the prediction direction. However, this is merely an example, and a greater or lesser number of directional prediction modes may be used depending on the settings. The intra prediction unit (185) may also determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0072] The inter prediction unit (180) can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter 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 can include a motion vector and a reference picture index. The motion information can further include information on the inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring block can include a spatial neighboring block existing in the current picture and a temporal neighboring block existing 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 from each other. The temporal neighboring block may be called a collocated reference block, a collocated CU (colCU), etc. A reference picture including the above temporal neighboring blocks may be called a collocated picture (colPic). For example, the inter prediction unit (180) may construct a motion information candidate list based on 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, and for example, in the case of skip mode and merge mode, the inter prediction unit (180) may use the motion information of neighboring blocks as the motion information of the current block. In the case of skip mode, unlike the merge mode, a residual signal may not be transmitted.In the motion vector prediction (MVP) mode, the motion vector of the current block can be signaled by using the motion vector of the surrounding blocks as the motion vector predictor and encoding the motion vector difference and an indicator for the motion vector predictor. The motion vector difference can mean the difference between the motion vector of the current block and the motion vector predictor.

[0073] The prediction unit can generate a prediction signal based on various prediction methods and / or prediction techniques described below. For example, the prediction unit can apply intra prediction or inter prediction to predict the current block, and can also apply intra prediction and inter prediction simultaneously. A prediction method that simultaneously applies intra prediction and inter prediction to predict the current block may be called combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra block copy (IBC) to predict the current block. Intra block copy can be used for video / image coding of content such as games, such as screen content coding (SCC). IBC is a method of predicting the current block using a previously restored reference block within the current picture located at a predetermined distance from the current block. When IBC is applied, the location of the reference block within the current picture can be encoded as a vector (block vector) corresponding to the predetermined distance. IBC basically performs prediction within the current picture, but can be performed similarly to inter prediction in that it derives reference blocks within the current picture. That is, IBC can utilize at least one of the inter prediction techniques described in the present disclosure.

[0074] The prediction signal generated through the prediction unit can be used to generate a restoration signal or a residual signal. The subtraction unit (115) can generate a residual signal (residual block, residual sample array) by subtracting the prediction signal (predicted block, predicted sample array) output from the prediction unit from the input image signal (original block, original sample array). The generated residual signal can be transmitted to the conversion unit (120).

[0075] The transform unit (120) can apply a transform technique to the residual signal to generate transform coefficients. For example, the transform technique can include at least one of a Discrete Cosine Transform (DCT), a Discrete Sine Transform (DST), a Karhunen-Loeve Transform (KLT), a Graph-Based Transform (GBT), or a Conditionally Non-linear Transform (CNT). Here, GBT refers to a transform obtained from a graph when the relationship information between pixels is expressed as a graph. CNT refers to a transform obtained based on generating a prediction signal using all previously reconstructed pixels. The transform process can be applied to a pixel block having a square equal size, or can be applied to a block of a non-square variable size.

[0076] The quantization unit (130) can quantize the transform coefficients and transmit them to the entropy encoding unit (190). The entropy encoding unit (190) can encode the quantized signal (information about the quantized transform coefficients) and output it as a bitstream. The information about the quantized transform coefficients can be called residual information. The quantization unit (130) can rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and can also generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0077] The entropy encoding unit (190) can perform various encoding methods, such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoding unit (190) can also encode, together or separately, information necessary for video / image restoration (e.g., values ​​of syntax elements) in addition to quantized transform coefficients. The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream in the form of a network abstraction layer (NAL) unit. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may further include general constraint information. The signaling information, transmitted information and / or syntax elements mentioned in the present disclosure may be encoded through the encoding procedure described above and included in the bitstream.

[0078] The above bitstream may be transmitted via a network or stored in a digital storage medium. Here, the network may include a broadcasting 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 transmission unit (not shown) for transmitting the signal output from the entropy encoding unit (190) and / or a storage unit (not shown) for storing the signal may be provided as an internal / external element of the video encoding device (100), or the transmission unit may be provided as a component of the entropy encoding unit (190).

[0079] The quantized transform coefficients output from the quantization unit (130) can be used to generate a residual signal. For example, by applying inverse quantization and inverse transformation to the quantized transform coefficients through the inverse quantization unit (140) and inverse transformation unit (150), a residual signal (residual block or residual samples) can be restored.

[0080] The addition unit (155) can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the inter prediction unit (180) or the intra prediction unit (185). When there is no residual for the block to be processed, such as when skip mode is applied, the predicted block can be used as the reconstructed block. The addition unit (155) can be called a reconstructor or a reconstructed block generation unit. The generated reconstructed signal can be used for intra prediction of the next block to be processed within the current picture, and can also be used for inter prediction of the next picture after filtering as described below.

[0081] The filtering unit (160) can improve subjective / objective picture quality by applying filtering to the restoration signal. For example, the filtering unit (160) can apply various filtering methods to the restoration picture to generate a modified restoration picture, and store the modified restoration picture in the memory (170), specifically, in the DPB of the memory (170). The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filtering unit (160) can generate various information regarding filtering and transmit the information to the entropy encoding unit (190), as described later in the description of each filtering method. The information regarding filtering may be encoded by the entropy encoding unit (190) and output in the form of a bitstream.

[0082] The modified restored picture transmitted to the memory (170) can be used as a reference picture in the inter prediction unit (180). Through this, when inter prediction is applied, the image encoding device (100) can avoid prediction mismatch between the image encoding device (100) and the image decoding device, and can also improve encoding efficiency.

[0083] The DPB in the memory (170) can store a modified reconstructed picture to be used as a reference picture in the inter prediction unit (180). The memory (170) can store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of blocks in a picture that has already been reconstructed. The stored motion information can be transferred to the inter prediction unit (180) to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory (170) can store reconstructed samples of reconstructed blocks in the current picture and transfer them to the intra prediction unit (185).

[0084] Video Decryption Device Overview

[0085] FIG. 3 is a schematic diagram illustrating an image decoding device to which an embodiment according to the present disclosure can be applied.

[0086] As illustrated in FIG. 3, the image decoding device (200) may be configured to include an entropy decoding unit (210), an inverse quantization unit (220), an inverse transformation unit (230), an addition unit (235), a filtering unit (240), a memory (250), an inter prediction unit (260), and an intra prediction unit (265). The inter prediction unit (260) and the intra prediction unit (265) may be collectively referred to as a “prediction unit.” The inverse quantization unit (220) and the inverse transformation unit (230) may be included in a residual processing unit.

[0087] All or at least some of the plurality of components constituting the video decoding device (200) may be implemented as a single hardware component (e.g., a decoder or processor) depending on the embodiment. In addition, the memory (170) may include a DPB and may be implemented by a digital storage medium.

[0088] The video decoding device (200) that receives a bitstream including video / image information can restore the image by performing a process corresponding to the process performed in the video encoding device (100) of FIG. 2. For example, the video decoding device (200) can perform decoding using a processing unit applied in the video encoding device. Therefore, the processing unit for decoding may be, for example, a coding unit. The coding unit may be a coding tree unit or may be obtained by dividing a maximum coding unit. In addition, the restored image signal decoded and output by the video decoding device (200) can be reproduced through a reproduction device (not shown).

[0089] The video decoding device (200) can receive a signal output from the video encoding device of FIG. 2 in the form of a bitstream. The received signal can be decoded through the entropy decoding unit (210). For example, the entropy decoding unit (210) can parse the bitstream to derive information (e.g., video / image information) necessary for image restoration (or picture restoration). The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may further include general constraint information. The video decoding device may additionally use information on the parameter set and / or the general constraint information to decode the image. The signaling information, received information, and / or syntax elements mentioned in the present disclosure can be obtained from the bitstream by being decoded through the decoding procedure. For example, the entropy decoding unit (210) can decode information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the values ​​of syntax elements required for image restoration and the quantized values ​​of transform coefficients for residuals. More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntax element in the bitstream, determines a context model using information of the syntax element to be decoded and the decoding information of the surrounding block and the decoding target block or the information of the symbol / bin decoded in the previous step, and predicts the occurrence probability of the bin according to the determined context model to perform arithmetic decoding of the bin to generate a symbol corresponding to the value of each syntax element.At this time, the CABAC entropy decoding method can update the context model using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Information regarding prediction among the information decoded by the entropy decoding unit (210) is provided to the prediction unit (inter prediction unit (260) and intra prediction unit (265)), and the residual value on which entropy decoding is performed by the entropy decoding unit (210), i.e., quantized transform coefficients and related parameter information, can be input to the inverse quantization unit (220). In addition, information regarding filtering among the information decoded by the entropy decoding unit (210) can be provided to the filtering unit (240). Meanwhile, a receiving unit (not shown) that receives a signal output from an image encoding device may be additionally provided as an internal / external element of the image decoding device (200), or the receiving unit may be provided as a component of an entropy decoding unit (210).

[0090] Meanwhile, the video decoding device according to the present disclosure may be referred to as a video / video / picture decoding device. The video decoding device may include an information decoder (video / video / picture information decoder) and / or a sample decoder (video / video / picture sample decoder). The information decoder may include an entropy decoding unit (210), and the sample decoder may include at least one of an inverse quantization unit (220), an inverse transformation unit (230), an addition unit (235), a filtering unit (240), a memory (250), an inter prediction unit (260), and an intra prediction unit (265).

[0091] The inverse quantization unit (220) can inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit (220) can rearrange the quantized transform coefficients into a two-dimensional block form. In this case, the rearrangement can be performed based on the coefficient scanning order performed in the image encoding device. The inverse quantization unit (220) can perform inverse quantization on the quantized transform coefficients using quantization parameters (e.g., quantization step size information) and obtain transform coefficients.

[0092] In the inverse transform unit (230), the transform coefficients can be inversely transformed to obtain a residual signal (residual block, residual sample array).

[0093] The prediction unit can perform a prediction on the current block and generate a predicted block containing prediction samples for the current block. The prediction unit can determine whether intra-prediction or inter-prediction is applied to the current block based on the prediction information output from the entropy decoding unit (210), and can determine a specific intra / inter-prediction mode (prediction technique).

[0094] The fact that the prediction unit can generate a prediction signal based on various prediction methods (techniques) described below is the same as that mentioned in the description of the prediction unit of the image encoding device (100).

[0095] The intra prediction unit (265) can predict the current block by referring to samples within the current picture. The description of the intra prediction unit (185) can be equally applied to the intra prediction unit (265).

[0096] The inter prediction unit (260) can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter 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 can include a motion vector and a reference picture index. The motion information can further include information on the inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks can include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter prediction unit (260) can construct 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 prediction can be performed based on various prediction modes (techniques), and the information about the prediction can include information indicating the mode (technique) of inter prediction for the current block.

[0097] The addition unit (235) can generate a restoration signal (restored picture, restoration block, restoration sample array) by adding the acquired residual signal to the prediction signal (predicted block, prediction sample array) output from the prediction unit (including the inter prediction unit (260) and / or the intra prediction unit (265)). When there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block can be used as the restoration block. The description of the addition unit (155) can be equally applied to the addition unit (235). The addition unit (235) can be called a restoration unit or a restoration block generation unit. The generated restoration signal can be used for intra prediction of the next block to be processed within the current picture, and can also be used for inter prediction of the next picture after going through filtering as described below.

[0098] The filtering unit (240) can improve subjective / objective image quality by applying filtering to the restored signal. For example, the filtering unit (240) can apply various filtering methods to the restored picture to generate a modified restored picture, and store the modified restored picture in the memory (250), specifically, in the DPB of the memory (250). The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0099] The (modified) reconstructed picture stored in the DPB of the memory (250) can be used as a reference picture in the inter prediction unit (260). The memory (250) can store motion information of a block from which motion information is derived (or decoded) within the current picture and / or motion information of blocks within a picture that has already been reconstructed. The stored motion information can be transferred to the inter prediction unit (260) to be used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory (250) can store reconstructed samples of reconstructed blocks within the current picture and transfer them to the intra prediction unit (265).

[0100] In this specification, the embodiments described in the filtering unit (160), the inter prediction unit (180), and the intra prediction unit (185) of the image encoding device (100) can be applied to the filtering unit (240), the inter prediction unit (260), and the intra prediction unit (265) of the image decoding device (200) in the same or corresponding manner, respectively.

[0101] Intra prediction general

[0102] Intra prediction may refer to a prediction that generates prediction samples for a current block based on reference samples within a picture to which the current block belongs (hereinafter, referred to as the current picture). When intra prediction is applied to a current block, peripheral reference samples to be used for intra prediction of the current block may be derived. The peripheral reference samples of the current block may include a total of 2 x nH samples adjacent to a left boundary and a bottom-left neighboring sample of a current block of a size nW x nH, a total of 2 x nW samples adjacent to a top boundary and a top-right neighboring sample of the current block, and one sample adjacent to the top-left neighboring sample of the current block. Alternatively, the peripheral reference samples of the current block may include upper peripheral samples of multiple columns and left peripheral samples of multiple rows. Additionally, the surrounding reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block of size nWxnH, a total of nW samples adjacent to the bottom boundary of the current block, and one sample adjacent to the bottom-right of the current block.

[0103] However, some of the surrounding reference samples of the current block may not yet have been decoded or may not be available. In this case, the image decoding device (200) may construct surrounding reference samples to be used for prediction by substituting the unavailable samples with available samples. Alternatively, the surrounding reference samples to be used for prediction may be constructed through interpolation of the available samples.

[0104] When neighboring reference samples are derived, (i) a prediction sample can be derived based on the average or interpolation of neighboring reference samples of the current block, and (ii) the prediction sample can be derived based on a reference sample that exists in a specific (prediction) direction with respect to the prediction sample among the neighboring reference samples of the current block. Case (i) may be called a non-directional mode or a non-angular mode, and case (ii) may be called a directional mode or an angular mode. In addition, the prediction sample may be generated through interpolation between the second neighboring sample and the first neighboring sample, which are located in the opposite direction of the prediction direction of the intra prediction mode of the current block with respect to the prediction sample of the current block among the neighboring reference samples. The above-described case may be called linear interpolation intra prediction (LIP). In addition, chroma prediction samples may be generated based on luma samples using a linear model. This case may be called LM mode. In addition, a temporary prediction sample of the current block may be derived based on filtered peripheral reference samples, and a prediction sample of the current block may be derived by weighting at least one reference sample derived according to the intra prediction mode among the existing peripheral reference samples, i.e., unfiltered peripheral reference samples, with the temporary prediction sample. The above-described case may be referred to as PDPC (Position dependent intra prediction).In addition, intra prediction encoding can be performed by selecting a reference sample line with the highest prediction accuracy among the surrounding multiple reference sample lines of the current block, deriving a prediction sample using the reference sample located in the prediction direction from the corresponding line, and instructing (signaling) the image decoding device (200) to use the used reference sample line. The above-described case may be referred to as multi-reference line (MRL) intra prediction or MRL-based intra prediction. In addition, the current block may be divided into vertical or horizontal sub-partitions, and intra prediction may be performed based on the same intra prediction mode, while deriving and using surrounding reference samples for each sub-partition. That is, in this case, the intra prediction mode for the current block is applied equally to the sub-partitions, and by deriving and using surrounding reference samples for each sub-partition, the intra prediction performance may be improved in some cases. This prediction method may be referred to as intra sub-partitions (ISP) or ISP-based intra prediction. The above-described intra prediction methods may be referred to as intra prediction types to distinguish them from the intra prediction modes in Table of Contents 1.2. The above intra prediction type may be called by various terms such as intra prediction technique or additional intra prediction mode. For example, the above intra prediction type (or additional intra prediction mode, etc.) may include at least one of the above-described LIP, PDPC, MRL, and ISP. A general intra prediction method excluding specific intra prediction types such as the above-described LIP, PDPC, MRL, and ISP may be called a normal intra prediction type. The normal intra prediction type may be generally applied when the above-described specific intra prediction types are not applied, and prediction may be performed based on the above-described intra prediction mode. Meanwhile, post-processing filtering may be performed on the derived prediction samples as needed.

[0105] Specifically, the intra prediction procedure may include an intra prediction mode / type determination step, a surrounding reference sample derivation step, and an intra prediction mode / type-based prediction sample derivation step. Additionally, a post-processing filtering step may be performed on the derived prediction samples, if necessary.

[0106] Meanwhile, in addition to the intra prediction types described above, affine linear weighted intra prediction (ALWIP) may be used. The ALWIP may also be called linear weighted intra prediction (LWIP) or matrix weighted intra prediction (MIP or matrix based intra prediction). When the MIP is applied to the current block, prediction samples for the current block may be derived by i) performing a matrix-vector-multiplication procedure using surrounding reference samples on which an averaging procedure has been performed, ii) further performing a horizontal / vertical interpolation procedure as necessary. The intra prediction modes used for the MIP may be configured differently from the intra prediction modes used in the LIP, PDPC, MRL, ISP intra prediction, or normal intra prediction described above. The intra prediction mode for the MIP may be called a MIP intra prediction mode, a MIP prediction mode, or a MIP mode. For example, the metrics and offsets used in the matrix vector multiplication may be set differently depending on the intra prediction mode for the MIP. Here, the metrics may be referred to as (MIP) weight metrics, and the offset may be referred to as (MIP) offset vectors or (MIP) bias vectors. A specific MIP method will be described later.

[0107] A block restoration procedure based on intra prediction and an intra prediction unit (185) within an image encoding device (100) may schematically include, for example, FIGS. 4 and 5.

[0108] S400 may be performed by the intra prediction unit (185) of the video encoding device (100), and S410 may be performed by the residual processing unit of the video encoding device (100). Specifically, S410 may be performed by the subtraction unit (115) of the video encoding device (100). In S420, the prediction information may be derived by the intra prediction unit (185) and encoded by the entropy encoding unit (190). In S420, the residual information may be derived by the residual processing unit and encoded by the entropy encoding unit (190). The residual information is information about the residual samples. The residual information may include information about quantized transform coefficients for the residual samples. As described above, the residual samples are derived as transform coefficients through the transform unit (120) of the image encoding device (100), and the transform coefficients can be derived as quantized transform coefficients through the quantization unit (130). Information about the quantized transform coefficients can be encoded in the entropy encoding unit (190) through a residual coding procedure.

[0109] The video encoding device (100) performs intra prediction on the current block (S400). The video encoding device (100) can derive an intra prediction mode / type for the current block, derive surrounding reference samples of the current block, and generate prediction samples within the current block based on the intra prediction mode / type and the surrounding reference samples. Here, the intra prediction mode / type determination, the surrounding reference sample derivation, and the prediction sample generation procedures may be performed simultaneously, or one procedure may be performed before the other. For example, the intra prediction unit (185) of the video encoding device (100) may include an intra prediction mode / type determination unit (186), a reference sample derivation unit (187), and a prediction sample derivation unit (188). The intra prediction mode / type determination unit (186) may determine an intra prediction mode / type for the current block, the reference sample derivation unit (187) may derive surrounding reference samples of the current block, and the prediction sample derivation unit (188) may derive prediction samples of the current block. Meanwhile, although not illustrated, when a prediction sample filtering procedure described below is performed, the intra prediction unit (185) may further include a prediction sample filtering unit (not illustrated). The video encoding device (100) may determine a mode / type to be applied to the current block among a plurality of intra prediction modes / types. The video encoding device (100) can compare the RD costs for the intra prediction modes / types and determine the optimal intra prediction mode / type for the current block.

[0110] Meanwhile, the video encoding device (100) may also perform a prediction sample filtering procedure. Prediction sample filtering may be referred to as post-filtering. Some or all of the prediction samples may be filtered through the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.

[0111] The video encoding device (100) generates residual samples for the current block based on (filtered) prediction samples (S410). The video encoding device (100) can compare the prediction samples with the original samples of the current block based on phase and derive the residual samples.

[0112] The video encoding device (100) can encode video information including information about the intra prediction (prediction information) and residual information about the residual samples (S420). The prediction information can include the intra prediction mode information and the intra prediction type information. The video encoding device (100) can output the encoded video information in the form of a bitstream. The output bitstream can be transmitted to the video decoding device (200) via a storage medium or a network.

[0113] The residual information may include the residual coding syntax described below. The video encoding device (100) may transform / quantize the residual samples to derive quantized transform coefficients. The residual information may include information about the quantized transform coefficients.

[0114] Meanwhile, as described above, the video encoding device (100) can generate a restored picture (including restored samples and restored blocks). To this end, the video encoding device (100) can inversely quantize / inversely transform the quantized transform coefficients to derive (corrected) residual samples. The reason for performing inverse quantization / inverse transformation on the residual samples after transforming / quantizing them in this way is to derive residual samples that are identical to the residual samples derived from the video decoding device (200) as described above. The video encoding device (100) can generate a restored block including restored samples for the current block based on the predicted samples and the (corrected) residual samples. A restored picture for the current picture can be generated based on the restored block. As described above, an in-loop filtering procedure, etc. can be further applied to the restored picture.

[0115] A video / image decoding procedure based on intra prediction and an intra prediction unit within an image decoding device (200) may schematically include, for example, the following.

[0116] The image decoding device (200) can perform an operation corresponding to the operation performed in the image encoding device (100).

[0117] S600 to S620 may be performed by the intra prediction unit (265) of the image decoding device (200), and the prediction information of S600 and the residual information of S630 may be obtained from the bitstream by the entropy decoding unit (210) of the image decoding device (200). The residual processing unit of the image decoding device (200) may derive residual samples for the current block based on the residual information. Specifically, the inverse quantization unit (220) of the residual processing unit may perform inverse quantization based on the quantized transform coefficients derived based on the residual information to derive transform coefficients, and the inverse transform unit (230) of the residual processing unit may perform inverse transformation on the transform coefficients to derive residual samples for the current block. S640 can be performed by the addition unit (235) or restoration unit of the image decoding device (200).

[0118] Specifically, the video decoding device (200) can derive an intra prediction mode / type for the current block based on the received prediction information (intra prediction mode / type information) (S600). The video decoding device (200) can derive surrounding reference samples of the current block (S610). The video decoding device (200) generates prediction samples within the current block based on the intra prediction mode / type and the surrounding reference samples (S620). In this case, the video decoding device (200) can perform a prediction sample filtering procedure. The prediction sample filtering procedure may be referred to as post-filtering. Some or all of the prediction samples may be filtered by the prediction sample filtering procedure. In some cases, the prediction sample filtering procedure may be omitted.

[0119] The video decoding device (200) generates residual samples for the current block based on the received residual information. The video decoding device (200) generates reconstructed samples for the current block based on the prediction samples and the residual samples, and can derive a reconstructed block including the reconstructed samples (S630). A reconstructed picture for the current picture can be generated based on the reconstructed block. As described above, an in-loop filtering procedure, etc. can be further applied to the reconstructed picture.

[0120] Here, the intra prediction unit (265) of the video decoding device (200) may include an intra prediction mode / type determination unit (266), a reference sample derivation unit (267), and a prediction sample derivation unit (268). The intra prediction mode / type determination unit (266) determines the intra prediction mode / type for the current block based on intra prediction mode / type information generated and signaled by the intra prediction mode / type determination unit (186) of the video encoding device (100), the reference sample derivation unit (266) may derive surrounding reference samples of the current block, and the prediction sample derivation unit (267) may derive prediction samples of the current block. Meanwhile, although not illustrated, when the above-described prediction sample filtering procedure is performed, the intra prediction unit (265) may further include a prediction sample filtering unit (not illustrated).

[0121] The intra prediction mode information may include, for example, flag information (e.g., intra_luma_mpm_flag) indicating whether the most probable mode (MPM) or the remaining mode is applied to the current block, and when the MPM is applied to the current block, the prediction mode information may further include index information (e.g., intra_luma_mpm_idx) indicating one of the intra prediction mode candidates (MPM candidates). The intra prediction mode candidates (MPM candidates) may be configured as an MPM candidate list or an MPM list. In addition, when the MPM is not applied to the current block, the intra prediction mode information may further include remaining mode information (e.g., intra_luma_mpm_remainder) indicating one of the remaining intra prediction modes excluding the intra prediction mode candidates (MPM candidates). The image decoding device (200) may determine the intra prediction mode of the current block based on the intra prediction mode information. A separate MPM list can be configured for the above-described MIP.

[0122] In addition, the intra prediction type information can be implemented in various forms. For example, the intra prediction type information can include intra prediction type index information indicating one of the intra prediction types. As another example, the intra prediction type information can include at least one of reference sample line information (e.g., intra_luma_ref_idx) indicating whether the MRL is applied to the current block and, if so, which reference sample line is used, ISP flag information (e.g., intra_subpartitions_mode_flag) indicating whether the ISP is applied to the current block, ISP type information (e.g., intra_subpartitions_split_flag) indicating a split type of subpartitions if the ISP is applied, flag information indicating whether PDCP is applied, or flag information indicating whether LIP is applied. In addition, the intra prediction type information can include a MIP flag indicating whether MIP is applied to the current block.

[0123] The intra prediction mode information and / or the intra prediction type information may be encoded / decoded using the coding method described in this document. For example, the intra prediction mode information and / or the intra prediction type information may be encoded / decoded using entropy coding (e.g., CABAC, CAVLC) based on a truncated (rice) binary code.

[0124] CIIP (combined inter and intra prediction)

[0125] CIIP can be applied to the current block. An additional flag (e.g., ciip_flag) can be signaled to indicate whether CIIP mode is applied to the current CU. For example, if the CU is coded in merge mode, and the CU contains at least 64 luma samples (i.e., the product of the CU width and the CU height is 64 or more), and both the CU width and the CU height are less than 128 luma samples, the additional flag can be signaled to indicate whether CIIP is applied to the current CU. As the name suggests, CIIP prediction can combine inter prediction signals and intra prediction signals. The inter prediction signal P_inter of the CIIP mode can be derived using the same process as the inter prediction process applied to the regular merge mode. The intra prediction signal P_intra can be derived according to the regular intra prediction process using the planar mode. Then, the intra-prediction signal and the inter-prediction signal can be combined using a weighted average. Here, the weight value can be calculated as follows depending on the coding modes of the upper and left neighboring blocks.

[0126] - If the upper surrounding block is available and intra-coded, set isIntraTop to 1; otherwise, set isIntraTop to 0.

[0127] - If the left surrounding block is available and intra-coded, set isIntraLeft to 1; otherwise, set isIntraLeft to 0.

[0128] - If (isIntraTop + isIntraLeft) is equal to 2, set wt to 3

[0129] - Otherwise, if (isIntraTop + isIntraLeft) is equal to 1, set wt to 2.

[0130] - Otherwise, set wt to 1

[0131] The CIIP prediction can be constructed as shown in the mathematical formula 1 below.

[0132]

[0133] A combination of CIIP and TIMD (template-based intra mode derivation) and TM (template matching) merge

[0134] In CIIP mode, prediction samples can be generated by weighting the inter-prediction signal predicted using the CIIP-TM merge candidate and the intra-prediction signal predicted using the TIMD-induced intra-prediction mode. This method can only be applied to coding blocks with an area of ​​1024 or less.

[0135] The TIMD derivation method can be used to derive intra prediction modes for CIIP. Specifically, the intra prediction mode with the smallest SATD within the TIMD mode list is selected and mapped to one of the 67 regular intra prediction modes.

[0136] Additionally, if the derived intra prediction mode is an angular mode, it may be proposed to modify the weights (wIntra, wInter) for the two tests. For near-horizontal modes (2 <= angular mode index < 34), the current block can be split in the vertical direction, as illustrated in (a) of Fig. 8. For near-vertical modes (34 <= angular mode index <= 66), the current block can be split in the horizontal direction, as illustrated in (b) of Fig. 8.

[0137] The weights (wIntra, wInter) for different sub-blocks can be as shown in Table 1.

[0138]

[0139] Using CIIP-TM, a list of CIIP-TM merge candidates can be constructed for CIIP-TM mode. Merge candidates can be refined through template matching. CIIP-TM merge candidates can be reordered into regular merge candidates using the ARMC method. The maximum number of CIIP-TM merge candidates can be 2.

[0140] Example

[0141] The present disclosure proposes a method for setting weights for a CIIP prediction method and a method for expanding the available intra prediction modes for the CIIP prediction method. According to the embodiments proposed in the present disclosure, the encoding performance of intra prediction can be improved.

[0142] The embodiments described below can be performed by an image encoding device (100) or an image decoding device (200). For example, the image encoding method described below can be performed by an image encoding device (100), and the image decoding method described below can be performed by an image decoding device (200).

[0143] An image encoding method and an image decoding method according to one embodiment of the present disclosure are shown in FIG. 10.

[0144] Referring to FIG. 10, an intra-prediction block of a current block and an inter-prediction block of the current block can be obtained (S1010). The intra-prediction block of the current block can be obtained through intra-prediction for the current block, and the inter-prediction block of the current block can be obtained through inter-prediction for the current block.

[0145] Weights for the intra-prediction block of the current block and weights for the inter-prediction block of the current block may be determined (S1020). The weights for the intra-prediction block of the current block may be referred to as "intra weights," and the weights for the inter-prediction block of the current block may be referred to as "inter weights."

[0146] Prediction samples of the current block can be generated by applying the determined weights to the intra-prediction block of the current block and the inter-prediction block of the current block (S1030). For example, prediction samples of the current block can be generated by applying the intra weights to the intra-prediction block of the current block and applying the inter weights to the inter-prediction block of the current block.

[0147] Below, embodiments proposed through the present disclosure will be specifically described. The embodiments described below may be performed alone, or two or more embodiments may be combined.

[0148] Example 1

[0149] Example 1 describes a method for deriving intra and inter weights of CIIP.

[0150] As illustrated in FIG. 9, in the conventional CIIP, an intra prediction signal (intra prediction block) can be predicted using a TIMD-derived intra prediction mode. If the derived intra prediction mode is an angular mode, the current block can be divided into four sub-blocks in the vertical or horizontal direction depending on whether the intra prediction mode is a horizontal intra prediction mode (2 <= angular mode index < 34) or a vertical intra prediction mode (34 <= angular mode index <= 66). For each sub-block from 0 to 3, the intra weight (wIntra) and the inter weight (wInter) can be assigned fixed weights of (6, 2), (5, 3), (3, 5), and (2, 6), respectively, as described in Table 1.

[0151] However, because the weight changes are not gradual at the boundaries of sub-blocks, blocking artifacts and loss of compression efficiency can occur. Furthermore, classifying angular modes into only horizontal and vertical modes may be too coarse to capture detailed pixel value changes. Therefore, a more accurate and detailed angular representation can lead to better coding efficiency.

[0152] In the present disclosure, intra- and inter-weights can be derived based on sample distances from reference pixels, angular modes, block sizes, and weights of neighboring blocks in CIIP. This embodiment can provide better prediction performance than the conventional sub-block-based weight determination method described above. In general, the closer a sample is to a block boundary, the more weight can be obtained for intra-prediction, and vice versa.

[0153] The process below shows how to determine weight factors depending on intra prediction mode, block size, pixel location, etc.

[0154] (1) If the intra prediction mode is a horizontal mode (2 <= angular mode index < DIAG_MODE_IDX - N), the intra weight and inter weight can be derived as in Equation 2.

[0155]

[0156] (2) If the intra prediction mode is a vertical mode (angular mode index > DIAG_MODE_IDX + N), the intra weight and inter weight can be derived as in mathematical expression 3.

[0157]

[0158] (3) If the intra prediction mode is a diagonal mode (i.e., if the angular mode index is within the range of DIAG_MODE_IDX - N to DIAG_MODE_IDX + N), the intra weight and inter weight can be derived as in Equation 4.

[0159]

[0160] In Equations 2 to 4, x and y may represent the location of a sample within a current block, as illustrated in FIG. 11. In addition, as illustrated in FIG. 11, width-x and height-y may represent a sample distance. Specifically, width-x may represent the distance between the left boundary of a block and a sample, and height-y may represent the distance between the upper boundary of the block and a sample. N represents a number between 0 and DIAG_MODE_IDX - HOR_MODE_IDX, and offset1 and offset2 may be constants or vary depending on the block size. Their effect is to adaptively determine the weights depending on the block size. The weights may be clipped to a minimum and / or maximum range. The division operation may be replaced with a fixed-point operation.

[0161] In Equations 2 to 4, the angular modes can be classified into horizontal modes, vertical modes, and diagonal modes, as shown in Fig. 12. However, the sample distance-based weighting is not limited to this angular mode classification, and can be more accurately calculated based on the angle of each angular mode.

[0162] As shown in Equations 2 to 4, the intra weight can be determined and applied on a sample-by-sample basis within the current block (intra prediction block). In addition, since the inter weight is determined by the difference between a predetermined value (scale) and the intra weight, the inter weight can also be determined and applied on a sample-by-sample basis within the current block (inter prediction block). Furthermore, the intra weight can be determined based on the distance between the boundary of the current block and a sample within the current block (width-x, height-y), the intra prediction mode of the current block (angular mode), and the size of the current block (width, height).

[0163] FIG. 13 is a diagram showing an example of an image encoding method and an image decoding method that determine weights based on the category to which the weights belong.

[0164] Referring to FIG. 13, a category to which an intra prediction mode belongs among predetermined categories can be determined (S1310). The predetermined categories may include a horizontal direction category (horizontal direction mode), a vertical direction category (vertical direction mode), and a diagonal direction category (diagonal direction mode).

[0165] If the intra prediction mode belongs to the horizontal direction category, the intra weight may be determined based on the distance (width - x) between the left boundary of the current block and a sample within the current block, and the width (width) of the current block (S1320). If the intra prediction mode belongs to the vertical direction category, the intra weight may be determined based on the distance (height-y) between the upper boundary of the current block and a sample within the current block, and the height (height) of the current block (S1340). If the intra prediction mode belongs to the diagonal direction category, the intra weight may be determined based on the distance (width-x) between the left boundary of the current block and a sample within the current block, the distance (height-y) between the upper boundary of the current block and a sample within the current block, the width (width) of the current block, and the height (height) of the current block. In S1320 to S1340, the current block may be a sub-block divided from the current block.

[0166] Example 2

[0167] Example 2 describes a method for performing CIIP using an extended intra prediction mode.

[0168] In the case of conventional CIIP, a flag (ciip_flag) indicating CIIP mode is signaled for each CU, and if ciip_flag is true (ciip_flag == 1), ciip_pdpc_flag can be additionally signaled. If ciip_pdpc_flag is true (ciip_pdpc_flag == 1), the intra (prediction) mode is selected as the planar mode, otherwise (ciip_pdpc_flag == 0), the intra (prediction) mode can be determined using the intra mode derived from TIMD.

[0169] In this disclosure, we propose an improved CIIP encoding structure as follows, extending from the conventional CIIP that derives the intra (prediction) mode using only the planar mode and TIMD.

[0170] First, ciip_flag is signaled per CU, and when ciip_flag is true, index information can be signaled instead of ciip_pdpc_flag. The index information can indicate an intra prediction mode selected from among predefined intra prediction modes (predetermined intra prediction mode candidates). For example, when the predetermined intra prediction mode candidates are {PLANAR, HOR_MODE, VER_MODE, DIAG_MODE, DIMD, TIMD}, index information for selecting one from these six intra prediction mode candidates is signaled, and the intra prediction mode to be used in the CIIP mode can be specified using the index information. As another example, if the predetermined intra prediction mode candidates are {PLANAR, HOR_MODE, VER_MODE, DIAG_MODE, DIMD, TIMD, 66, 2}, index information for selecting one of these eight intra prediction mode candidates is signaled, and the intra prediction mode candidate to be used in the CIIP mode can be specified using the index information. In the above examples, the six or eight predetermined intra prediction mode candidates represent examples, and according to embodiments, the predetermined intra prediction mode candidates can be configured with values ​​representing a specific intra prediction mode. Considering that the CIIP mode is used in inter prediction, in order to reduce signaling overhead, the predetermined intra prediction mode candidates can be configured with 16 or fewer. The index information can be encoded using Truncated Unary encoding or Fixed Length encoding.

[0171] Second, ciip_flag is signaled per CU, and when ciip_flag is true, index information may be signaled instead of ciip_pdpc_flag. The index information may indicate an intra prediction mode selected from predefined intra prediction modes (predetermined intra prediction mode candidates). A set of predetermined intra prediction mode candidates may be referred to as a CIIP intra mode set. For example, eight CIIP intra mode sets, such as {PLANAR, HOR_MODE, VER_MODE, DIAG_MODE, DIMD, TIMD, 66, 2}, may be used as the set of predetermined intra prediction mode candidates. A CIIP intra mode set may be updated per CTU. As another example, a CIIP intra mode set may also be updated per parameter set, such as a high level syntax (HLS) such as a PPS or SPS. To signal a CIIP intra mode set, information on the number of intra prediction mode candidates within the CIIP intra mode set and an index value of each intra prediction mode candidate can be signaled.

[0172] FIG. 14 is a drawing showing an example of an image encoding method for the first CIIP encoding structure, and FIG. 15 is a drawing showing an example of an image decoding method for the first CIIP encoding structure.

[0173] Referring to FIG. 14, it may be determined whether CIIP is applied to the current block (S1410). If it is determined that CIIP is applied to the current block, an intra prediction mode to be used for CIIP may be selected from among predetermined intra prediction mode candidates (S1420). Additionally, index information indicating the selected intra prediction mode and ciip_flag == 1 may be encoded in the bitstream (S1430). Alternatively, if it is determined that CIIP is not applied to the current block, ciip_flag == 0 may be encoded in the bitstream (S1440).

[0174] Referring to FIG. 15, ciip_flag is acquired from a bitstream (S1510), and based on ciip_flag, it can be determined whether CIIP is applied to a current block (S1520). If it is determined that CIIP is applied to the current block (ciip_flag == 1), index information can be acquired from the bitstream (S1530). The index information can indicate any one of predetermined intra prediction mode candidates. Among the predetermined intra prediction mode candidates, an intra prediction mode candidate indicated by the index information can be determined as an intra prediction mode to be used for CIIP (S1540).

[0175] FIG. 16 is a drawing showing an example of an image encoding method for a second CIIP encoding structure, and FIG. 17 is a drawing showing an example of an image decoding method for a second CIIP encoding structure.

[0176] Referring to FIG. 16, it may be determined whether CIIP is applied to the current block (S1610). If it is determined that CIIP is applied to the current block, count information indicating the number of intra prediction mode candidates, the index value of each intra prediction mode candidate, and ciip_flag == 1 may be encoded in the bitstream (S1620). Alternatively, if it is determined that CIIP is not applied to the current block, ciip_flag == 0 may be encoded in the bitstream (S1630).

[0177] Referring to FIG. 17, ciip_flag is acquired from a bitstream (S1710), and based on ciip_flag, it can be determined whether CIIP is applied to the current block (S1720). If it is determined that CIIP is applied to the current block (ciip_flag == 1), count information and index values ​​can be acquired from the bitstream (S1730). In addition, based on the count information and index values, intra prediction mode candidates (CIIP intra mode set) can be configured (S1740).

[0178] FIG. 18 is a diagram illustrating an example of a content streaming system to which an embodiment according to the present disclosure can be applied.

[0179] As illustrated in FIG. 18, a content streaming system to which an embodiment of the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0180] The encoding server compresses content input from multimedia input devices such as smartphones, cameras, and camcorders into digital data, generates a bitstream, and transmits it to the streaming server. Alternatively, if multimedia input devices such as smartphones, cameras, and camcorders directly generate bitstreams, the encoding server may be omitted.

[0181] The above bitstream can be generated by an image encoding method and / or an image encoding device to which an embodiment of the present disclosure is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0182] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server can act as an intermediary to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, and the streaming server can transmit multimedia data to the user. At this time, the content streaming system may include a separate control server, and in this case, the control server may control commands / responses between each device within the content streaming system.

[0183] The streaming server can receive content from a media repository and / or an encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0184] Examples of the user devices may include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, HMDs), digital TVs, desktop computers, digital signage, etc.

[0185] Each server within the above content streaming system can be operated as a distributed server, in which case data received from each server can be processed in a distributed manner.

[0186] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer.

[0187] Embodiments according to the present disclosure can be used to encode / decode images.

Claims

1. An image decoding method performed by an image decoding device, A step of obtaining an intra prediction block of a current block and an inter prediction block of the current block; A step of determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and A step of applying the intra weight to the intra prediction block and applying the inter weight to the inter prediction block to generate prediction samples of the current block, A video decoding method, wherein the intra weight is determined and applied in units of samples within the intra prediction block, and the inter weight is determined and applied in units of samples within the inter prediction block.

2. In paragraph 1, A method for decoding an image, wherein the intra weight is determined based on the distance between the boundary of the current block and the sample within the current block, the intra prediction mode of the current block, and the size of the current block.

3. In paragraph 2, The above intra weight is determined based on the category to which the intra prediction mode belongs among predetermined categories, A method for decoding an image, wherein the above-described categories include a horizontal direction category, a vertical direction category, and a diagonal direction category.

4. In paragraph 3, A method for decoding an image, wherein the intra weight is determined based on the distance between the left boundary of the current block and a sample within the current block, and the width of the current block, based on the intra prediction mode belonging to the horizontal direction category.

5. In paragraph 3, A method for decoding an image, wherein the intra weight is determined based on the distance between the upper boundary of the current block and a sample within the current block, and the height of the current block, based on the intra prediction mode belonging to the vertical direction category.

6. In paragraph 3, A method for decoding an image, wherein the intra weight is determined based on a distance between a left boundary of the current block and a sample within the current block, a distance between an upper boundary of the current block and a sample within the current block, a width of the current block, and a height of the current block, based on whether the intra prediction mode belongs to the diagonal category.

7. In paragraph 2, A step of obtaining index information from a bitstream; and A video decoding method further comprising a step of determining an intra prediction mode candidate indicated by the index information among predetermined intra prediction mode candidates as the intra prediction mode.

8. In paragraph 7, A video decoding method, wherein the number of intra prediction mode candidates is 16 or less.

9. In paragraph 7, A method for decoding an image, wherein the intra prediction mode candidates are updated in units of CTU (coding tree unit) or parameter set.

10. In paragraph 7, A video decoding method, wherein the number information of the intra prediction mode candidates and the index value of each intra prediction mode candidate are obtained from the bitstream.

11. An image encoding method performed by an image encoding device, A step of obtaining an intra prediction block of a current block and an inter prediction block of the current block; A step of determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and A step of applying the intra weight to the intra prediction block and applying the inter weight to the inter prediction block to generate prediction samples of the current block, A video encoding method, wherein the intra weight is determined and applied in units of samples within the intra prediction block, and the inter weight is determined and applied in units of samples within the inter prediction block.

12. A computer-readable recording medium storing a bitstream generated by an image encoding method, wherein the image encoding method comprises: A step of obtaining an intra prediction block of a current block and an inter prediction block of the current block; A step of determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and A step of applying the intra weight to the intra prediction block and applying the inter weight to the inter prediction block to generate prediction samples of the current block, A recording medium wherein the intra weight is determined and applied on a sample basis within the intra prediction block, and the inter weight is determined and applied on a sample basis within the inter prediction block.

13. A method for transmitting a bitstream generated by a video encoding device, wherein the video encoding method comprises: A step of obtaining an intra prediction block of a current block and an inter prediction block of the current block; A step of determining an intra weight for the intra prediction block and an inter weight for the inter prediction block; and A step of applying the intra weight to the intra prediction block and applying the inter weight to the inter prediction block to generate prediction samples of the current block, A method wherein the intra weight is determined and applied on a sample basis within the intra prediction block, and the inter weight is determined and applied on a sample basis within the inter prediction block.