Image encoding / decoding method and device, and recording medium on which bitstream is stored

Abstract

An image encoding / decoding method and device, a recording medium on which a bitstream is stored, and a transmission method are provided. The image decoding method comprises the steps of: using a reference sample to derive different cross-component non-linear model coefficients; deriving different cross-component non-linear models on the basis of the different cross-component non-linear model coefficients; and using the different cross-component non-linear models so as to generate a prediction block for different chrominance component blocks of the current block, wherein the prediction block for the different chrominance component blocks includes: a prediction block for a first chrominance component block generated on the basis of a first cross-component non-linear model; and a prediction block for a second chrominance component block generated on the basis of a second cross-component non-linear model.

Description

Video encoding / decoding method, device, and recording medium storing bitstream

[0001] The present invention relates to a video encoding / decoding method, device, and recording medium storing a bitstream. Specifically, the present invention relates to a video encoding / decoding method, device, and recording medium storing a bitstream using a cross-component nonlinear model.

[0002] Recently, the demand for high-resolution, high-quality images, such as UHD (Ultra High Definition) images, is increasing across various application fields. As image data becomes higher in resolution and quality, the relative amount of data increases compared to conventional image data. Therefore, transmitting image data using existing media such as wired or wireless broadband lines or storing it using existing storage media leads to increased transmission and storage costs. To address these issues arising from the increasing resolution and quality of image data, high-efficiency image encoding / decoding technologies for higher-resolution and higher-quality images are required.

[0003] The chrominance signal can be predicted by removing the redundancy between the luminance component signal and the chrominance component signal using the cross-component linear model (CCLM).

[0004] However, if a nonlinear relationship as well as a linear relationship exists between the restored luminance component and the chrominance component, there is a problem that the chrominance signal prediction based on the cross-component linear model may have low accuracy.

[0005] The purpose of the present invention is to provide a video encoding / decoding method and device with improved encoding / decoding efficiency.

[0006] In addition, it is an object of the present invention to provide a recording medium storing a bitstream generated by an image decoding method or device according to the present invention.

[0007] In addition, the present invention aims to provide a method for deriving a cross-component nonlinear model and a method for generating a color difference prediction block based on a cross-component nonlinear model to solve the above problems.

[0008] An image decoding method according to one embodiment of the present invention comprises the steps of: deriving a cross-component model including a Cb cross-component model and a Cr cross-component model for predicting a chrominance component block of a current block using a reference sample; generating a prediction block for the Cb chrominance component block of the current block using the Cb cross-component model; and generating a prediction block for the Cr chrominance component block of the current block using the Cr cross-component model, wherein the Cb cross-component model and the Cr cross-component model can be determined independently of each other.

[0009] In the above image decoding method, the Cb cross component model and the Cr cross component model may be characterized in that they are derived based on coefficients, bit depth, and intermediate values ​​of the cross component model.

[0010] In the above image decoding method, the coefficients of the cross component model may be derived based on any one of LU decomposition, LDL decomposition, and Cholesky decomposition.

[0011] In the above image decoding method, the reference sample may include a Cb chrominance reference sample neighboring a Cb chrominance component block of the current block, a luminance reference sample corresponding to the Cb chrominance reference sample, a Cr chrominance reference sample neighboring a Cr chrominance component block of the current block, and a luminance reference sample corresponding to the Cr chrominance reference sample.

[0012] In the above image decoding method, the cross component model may be characterized as being any one of an upper left cross component model, an upper cross component model, and a left cross component model.

[0013] In the above image decoding method, when the cross component model is an upper left cross component model, the reference sample may be characterized by including a reference sample located at the upper left of a chrominance component block of the current block and a reference sample located at the upper left of a luminance component block of the current block.

[0014] In the above image decoding method, when the cross component model is an upper cross component model, the reference sample may be characterized by including a reference sample located at the upper end of a chrominance component block of the current block and a reference sample located at the upper end of a luminance component block of the current block.

[0015] In the above image decoding method, when the cross component model is a left cross component model, the reference sample may be characterized by including a reference sample located to the left of a chrominance component block of the current block and a reference sample located to the left of a luminance component block of the current block.

[0016] In the above image decoding method, the luminance reference sample corresponding to the Cb chrominance reference sample and the luminance reference sample corresponding to the Cr chrominance reference sample may be characterized in that they are reference samples downsampled according to a downsampling ratio.

[0017] In the above image decoding method, it may be characterized in that a downsampling ratio applied to a luminance reference sample corresponding to the Cb chrominance reference sample and a downsampling ratio applied to a luminance reference sample corresponding to the Cr chrominance reference sample are determined independently of each other.

[0018] In the above image decoding method, the step of deriving the Cb cross-component model and the Cr cross-component model may be characterized by including a step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model.

[0019] In the above image decoding method, the step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model may be characterized in that the step is determined based on model information indicating either the cross-component linear model or the cross-component nonlinear model.

[0020] In the above image decoding method, the step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model may be characterized in that the step is determined based on a comparison result between an error value of a Cb chrominance reference sample and a Cr chrominance reference sample predicted based on a cross-component linear model and an error value of a Cb chrominance reference sample and a Cr chrominance reference sample predicted based on a cross-component nonlinear model.

[0021] In the above image decoding method, when the intra prediction mode of the luminance component block of the current block is a predetermined prediction mode, the luminance reference sample corresponding to the Cb chrominance reference sample and the luminance reference sample corresponding to the Cr chrominance reference sample may be characterized in that they are luminance reference samples adjacent to a matching block indicated by a block vector of the luminance component block of the current block.

[0022] In the above image decoding method, the predetermined prediction mode may be one of an intra template matching mode and an intra block copy mode.

[0023] A video encoding method according to one embodiment of the present invention comprises the steps of: deriving a Cb cross component model and a Cr cross component model for predicting a chrominance component block of a current block using a reference sample; generating a prediction block for the Cb chrominance component block of the current block using the Cb cross component model; and generating a prediction block for the Cr chrominance component block of the current block using the Cr cross component model, wherein the Cb cross component model and the Cr cross component model can be determined independently of each other.

[0024] A non-transitory computer-readable recording medium according to one embodiment of the present invention can store a bitstream generated by a video encoding method, including the steps of: deriving a Cb cross-component model and a Cr cross-component model for predicting a chrominance component block of a current block using a reference sample; generating a prediction block for the Cb chrominance component block of the current block using the Cb cross-component model; and generating a prediction block for the Cr chrominance component block of the current block using the Cr cross-component model, wherein the Cb cross-component model and the Cr cross-component model are determined independently of each other.

[0025] A transmission method according to one embodiment of the present invention includes a step of transmitting a bitstream, and the encoding method includes a step of deriving a Cb cross-component model and a Cr cross-component model for predicting a chrominance component block of a current block using a reference sample; a step of generating a prediction block for a Cb chrominance component block of the current block using the Cb cross-component model; and a step of generating a prediction block for a Cr chrominance component block of the current block using the Cr cross-component model, wherein the Cb cross-component model and the Cr cross-component model may be determined independently of each other.

[0026] 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.

[0027] According to the present invention, a video encoding / decoding method and device with improved encoding / decoding efficiency can be provided.

[0028] In addition, according to the present invention, a method for deriving a cross-component nonlinear model and a method for generating a color difference prediction block based on a cross-component nonlinear model can be provided.

[0029] Additionally, according to the present invention, color difference blocks can be predicted more accurately.

[0030] 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.

[0031] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0032] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0033] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0034] FIG. 4 is a diagram illustrating a reference sample for deriving a top left cross component nonlinear model according to an embodiment of the present invention.

[0035] FIG. 5 is a diagram illustrating a reference sample for deriving an upper cross component nonlinear model according to one embodiment of the present invention.

[0036] FIG. 6 is a diagram illustrating a reference sample for deriving a left cross component nonlinear model according to an embodiment of the present invention.

[0037] FIG. 7 is a diagram illustrating a reference sample for deriving a left upper cross component model (LT_CCM) according to one embodiment of the present invention.

[0038] FIG. 8 is a diagram illustrating a reference sample for deriving a top cross component model (T_CCM) according to one embodiment of the present invention.

[0039] FIG. 9 is a diagram illustrating a reference sample for deriving a left cross component nonlinear model (L_CCM) according to one embodiment of the present invention.

[0040] FIG. 10 is a diagram illustrating a method for calculating cross-component linear model coefficients or cross-component nonlinear model coefficients using block vector information of intra prediction according to an embodiment of the present invention.

[0041] Figure 11 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

[0042] FIG. 12 is a drawing exemplifying a content streaming system to which an embodiment according to the present invention can be applied.

[0043] The present invention is susceptible to various modifications and embodiments. Therefore, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and substitutes falling within the spirit and scope of the present invention. In the drawings, similar reference numerals designate the same or similar functions throughout. The shape and size of elements in the drawings may be provided by way of example only for clarity. The detailed description of the exemplary embodiments described below refers to the accompanying drawings, which illustrate specific embodiments by way of example. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments. It should be understood that the various embodiments, while different from each other, are not necessarily mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention. Furthermore, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be modified without departing from the spirit and scope of the embodiment. Accordingly, the detailed description set forth below is not intended to be taken in a limiting sense, and the scope of the illustrative embodiments, if properly described, is defined only by the appended claims, along with the full scope equivalents to which such claims are entitled.

[0044] In the present invention, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term "and / or" includes a combination of multiple related described items or any of multiple related described items.

[0045] The components shown in the embodiments of the present invention are independently depicted to represent different characteristic functions, and do not mean that each component is composed of separate hardware or a single software component. That is, each component is listed and included as a separate component for convenience of explanation, and at least two components among each component may be combined to form a single component, or a single component may be divided into multiple components to perform a function, and such integrated and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

[0046] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In addition, some components of the present invention are not essential components that perform essential functions in the present invention and may be optional components merely for performance enhancement. The present invention may be implemented by including only components essential to realizing the essence of the present invention, excluding components used only for performance enhancement, and a structure including only essential components, excluding optional components used only for performance enhancement, is also within the scope of the present invention.

[0047] In embodiments, the term "at least one" may mean one of a number greater than or equal to 1, such as 1, 2, 3, and 4. In embodiments, the term "a plurality of" may mean one of a number greater than or equal to 2, such as 2, 3, and 4.

[0048] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In describing the embodiments of this specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of this specification, the detailed description will be omitted. The same reference numerals will be used for identical components in the drawings, and duplicate descriptions of identical components will be omitted.

[0049] Glossary of Terms

[0050] Hereinafter, “video” may mean a single picture constituting a video, or may refer to the video itself. For example, “encoding and / or decoding of a video” may mean “encoding and / or decoding of a video,” or may mean “encoding and / or decoding of one of the videos constituting the video.”

[0051] Hereinafter, the terms "video" and "movie" may be used interchangeably and have the same meaning. Furthermore, the target image may be an encoding target image, which is the target of encoding, and / or a decoding target image, which is the target of decoding. Furthermore, the target image may be an input image input to an encoding device, or an input image input to a decoding device. Here, the target image may have the same meaning as the current image.

[0052] Hereinafter, the terms encoder and image encoding device may be used interchangeably and have the same meaning.

[0053] Hereinafter, the terms decoder and image decoding device may be used interchangeably and have the same meaning.

[0054] Hereinafter, “image”, “picture”, “frame” and “screen” may be used with the same meaning and may be used interchangeably.

[0055] Hereinafter, the term "target block" may refer to an encoding target block, which is the target of encoding, and / or a decoding target block, which is the target of decoding. Furthermore, the target block may refer to a current block, which is the target of current encoding and / or decoding. For example, the terms "target block" and "current block" may be used interchangeably and have the same meaning.

[0056] Hereinafter, "block" and "unit" may be used with the same meaning and may be used interchangeably. In addition, "unit" may mean including a luminance component block and a corresponding chroma component block to distinguish it from a block. For example, a coding tree unit (CTU) may be composed of one luma component (Y) coding tree block (CTB) and two chroma component (Cb, Cr) coding tree blocks associated with it.

[0057] Hereinafter, the terms “sample,” “pixel,” and “pixel” may be used interchangeably and have the same meaning. Here, a sample may represent a basic unit that constitutes a block.

[0058] Hereinafter, “inter” and “between screens” may be used interchangeably and have the same meaning.

[0059] Hereinafter, “intra” and “within screen” may be used interchangeably and have the same meaning.

[0060]

[0061] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0062] The encoding device (100) may be an encoder, a video encoding device, or an image encoding device. A video may include one or more images. The encoding device (100) may sequentially encode one or more images.

[0063] Referring to FIG. 1, the encoding device (100) may include an image segmentation unit (110), an intra prediction unit (120), a motion prediction unit (121), a motion compensation unit (122), a switch (115), a subtractor (113), a transformation unit (130), a quantization unit (140), an entropy encoding unit (150), an inverse quantization unit (160), an inverse transformation unit (170), an adder (117), a filter unit (180), and a reference picture buffer (190).

[0064] Additionally, the encoding device (100) can generate a bitstream including encoded information through encoding an input image and output the generated bitstream. The generated bitstream can be stored in a computer-readable recording medium or can be streamed via a wired / wireless transmission medium.

[0065] The video segmentation unit (110) can segment the input video into various forms to increase the efficiency of video encoding / decoding. That is, the input video is composed of multiple pictures, and one picture can be hierarchically segmented and processed for compression efficiency, parallel processing, etc. For example, one picture can be segmented into one or more tiles or slices, which can then be segmented into multiple Coding Tree Units (CTUs). Alternatively, one picture can first be segmented into multiple sub-pictures defined as groups of rectangular slices, and each sub-picture can then be segmented into the tiles / slices. Here, the sub-pictures can be utilized to support the function of partially independently encoding / decoding and transmitting the picture. Since multiple sub-pictures can each be individually restored, there is an advantage of easy editing in applications that configure multi-channel input into a single picture. In addition, tiles can be segmented horizontally to generate bricks. Here, a brick can be utilized as the basic unit of intra-picture parallel processing. In addition, one CTU can be recursively split into a quadtree (QT), and the terminal node of the split can be defined as a coding unit (CU). The CU can be split into a prediction unit (PU) and a transformation unit (TU), and prediction and splitting can be performed. Meanwhile, the CU can be utilized as a prediction unit and / or a transformation unit itself. Here, for flexible splitting, each CTU can be recursively split into a multi-type tree (MTT) as well as a quadtree (QT). Splitting of a CTU into a multi-type tree can start from the terminal node of a QT, and the MTT can be composed of a binary tree (BT) and a triple tree (TT).For example, the MTT structure can be divided into vertical binary split mode (SPLIT_BT_VER), horizontal binary split mode (SPLIT_BT_HOR), vertical ternary split mode (SPLIT_TT_VER), and horizontal ternary split mode (SPLIT_TT_HOR). In addition, the minimum block size (MinQTSize) of the quad tree of the luminance block during splitting can be set to 16x16, the maximum block size (MaxBtSize) of the binary tree can be set to 128x128, and the maximum block size (MaxTtSize) of the triple tree can be set to 64x64. In addition, the minimum block size (MinBtSize) of the binary tree and the minimum block size (MinTtSize) of the triple tree can be set to 4x4, and the maximum depth (MaxMttDepth) of the multi-type tree can be set to 4. Additionally, to improve the encoding efficiency of the I slice, a dual tree can be applied that uses different CTU partition structures for luminance and chrominance components. On the other hand, in the P and B slices, the luminance and chrominance CTBs (Coding Tree Blocks) within the CTU can be partitioned into a single tree that shares the coding tree structure.

[0066] The encoding device (100) may perform encoding on the input image in intra mode and / or inter mode. Alternatively, the encoding device (100) may perform encoding on the input image in a third mode (e.g., IBC mode, Palette mode, etc.) other than the intra mode and inter mode. However, if the third mode has functional characteristics similar to the intra mode or inter mode, it may be classified as intra mode or inter mode for convenience of explanation. In the present invention, the third mode will be classified and described separately only when a specific description is required.

[0067] When the intra mode is used as the prediction mode, the switch (115) can be switched to intra, and when the inter mode is used as the prediction mode, the switch (115) can be switched to inter. Here, the intra mode can mean an intra-screen prediction mode, and the inter mode can mean an inter-screen prediction mode. The encoding device (100) can generate a prediction block for an input block of an input image. In addition, after the prediction block is generated, the encoding device (100) can encode a residual block using a residual of the input block and the prediction block. The input image can be referred to as a current image that is currently a target of encoding. The input block can be referred to as a current block that is currently a target of encoding or an encoding target block.

[0068] When the prediction mode is intra mode, the intra prediction unit (120) can use samples of blocks already encoded / decoded around the current block as reference samples. The intra prediction unit (120) can perform spatial prediction on the current block using the reference samples, and can generate prediction samples for the input block through spatial prediction. Here, intra prediction can mean prediction within the screen.

[0069] As an intra prediction method, non-directional prediction modes such as DC mode and Planar mode, as well as directional prediction modes (e.g., 65 directions) can be applied. Here, the intra prediction method can be expressed as an intra prediction mode or an intra-screen prediction mode.

[0070] When the prediction mode is inter mode, the motion prediction unit (121) can search for an area that best matches the input block from the reference image during the motion prediction process and derive a motion vector using the searched area. At this time, the area can be used as a search area. The reference image can be stored in the reference picture buffer (190). Here, when encoding / decoding for the reference image is processed, it can be stored in the reference picture buffer (190).

[0071] The motion compensation unit (122) can generate a prediction block for the current block by performing motion compensation using a motion vector. Here, inter prediction may mean inter-screen prediction or motion compensation.

[0072] The above motion prediction unit (121) and motion compensation unit (122) can generate a prediction block by applying an interpolation filter to a portion of the reference image when the value of the motion vector does not have an integer value. In order to perform inter-screen prediction or motion compensation, it is possible to determine whether the motion prediction and motion compensation method of the prediction unit included in the corresponding encoding unit is one of Skip Mode, Merge Mode, Advanced Motion Vector Prediction (AMVP) mode, and Intra Block Copy (IBC) mode based on the encoding unit, and perform inter-screen prediction or motion compensation according to each mode.

[0073] In addition, based on the above inter-screen prediction method, the AFFINE mode of sub-PU based prediction, the SbTMVP (Subblock-based Temporal Motion Vector Prediction) mode, and the MMVD (Merge with MVD) mode and the GPM (Geometric Partitioning Mode) mode of PU based prediction can be applied. In addition, in order to improve the performance of each mode, the HMVP (History based MVP), the PAMVP (Pairwise Average MVP), the CIIP (Combined Intra / Inter Prediction), the AMVR (Adaptive Motion Vector Resolution), the BDOF (Bi-Directional Optical-Flow), the BCW (Bi-predictive with CU Weights), the LIC (Local Illumination Compensation), the TM (Template Matching), and the OBMC (Overlapped Block Motion Compensation) can be applied.

[0074] Among these, AFFINE mode is a technology that is used in both AMVP and MERGE modes and also has high encoding efficiency. In the existing video coding standard, since MC (Motion Compensation) is performed by considering only the parallel movement of the block, there was a disadvantage in that it could not properly compensate for motions that occur in reality, such as zoom in / out and rotation. To supplement this, a 4-parameter affine motion model using two control point motion vectors (CPMV) and a 6-parameter affine motion model using three control point motion vectors can be applied to inter prediction. Here, CPMV is a vector representing the affine motion model of one of the upper left, upper right, and lower left of the current block.

[0075] The subtractor (113) can generate a residual block using the difference between the input block and the predicted block. The residual block may also be referred to as a residual signal. The residual signal may refer to the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming, quantizing, or transforming and quantizing the difference between the original signal and the predicted signal. The residual block may be a residual signal in block units.

[0076] The transform unit (130) can perform a transform on the residual block to generate a transform coefficient and output the generated transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit (130) may also skip the transform on the residual block.

[0077] Quantized levels can be generated by applying quantization to transform coefficients or residual signals. In the following embodiments, quantized levels may also be referred to as transform coefficients.

[0078] For example, a 4x4 luminance residual block generated through within-screen prediction can be transformed using a basis vector based on DST (Discrete Sine Transform), and the remaining residual blocks can be transformed using a basis vector based on DCT (Discrete Cosine Transform). In addition, through RQT (Residual Quad Tree) technology, the transform block is divided into a quad tree shape for one block, and after performing transformation and quantization on each transform block divided through RQT, a coded block flag (cbf) can be transmitted to increase encoding efficiency when all coefficients become 0.

[0079] Another alternative is to apply Multiple Transform Selection (MTS) technology, which selectively performs transformation using multiple transformation bases. That is, instead of dividing CUs into TUs via RQT, a Sub-block Transform (SBT) technology can perform a function similar to TU division. Specifically, SBT is applied only to inter-screen prediction blocks, and unlike RQT, it can divide the current block into ½ or ¼ blocks vertically or horizontally, and then perform transformation on only one of the blocks. For example, in a vertically divided block, the transformation can be performed on the leftmost or rightmost block, and in a horizontally divided block, the transformation can be performed on the topmost or bottommost block.

[0080] Additionally, LFNST (Low Frequency Non-Separable Transform), a secondary transform technique that further transforms the residual signal converted to the frequency domain through DCT or DST, can be applied. LFNST additionally performs a transform on the low-frequency region of 4x4 or 8x8 in the upper left, which allows the residual coefficients to be concentrated in the upper left.

[0081] The quantization unit (140) can generate a quantized level by quantizing a transform coefficient or residual signal according to a quantization parameter (QP), and can output the generated quantized level. At this time, the quantization unit (140) can quantize the transform coefficient using a quantization matrix.

[0082] For example, a quantizer with QP values ​​of 0 to 51 can be used. Alternatively, if the image size is larger and high encoding efficiency is required, a QP of 0 to 63 can be used. In addition, a Dependent Quantization (DQ) method that uses two quantizers instead of a single quantizer can be applied. DQ performs quantization using two quantizers (e.g., Q0 and Q1), but even without signaling information about the use of a specific quantizer, the quantizer to be used for the next transform coefficient can be selected based on the current state through a state transition model.

[0083] The entropy encoding unit (150) can generate a bitstream by performing entropy encoding according to a probability distribution on values ​​produced by the quantization unit (140) or coding parameter values ​​produced during the encoding process, and can output the bitstream. The entropy encoding unit (150) can perform entropy encoding on information about image samples and information for decoding the image. For example, the information for decoding the image can include syntax elements, etc.

[0084] When entropy encoding is applied, a small number of bits are allocated to symbols with a high occurrence probability, and a large number of bits are allocated to symbols with a low occurrence probability, thereby representing the symbols, whereby the size of the bit string for the symbols to be encoded can be reduced. The entropy encoding unit (150) can use an encoding method such as exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding. For example, the entropy encoding unit (150) can perform entropy encoding using a Variable Length Coding / Code (VLC) table. In addition, the entropy encoding unit (150) may perform arithmetic encoding using the binarization method, probability model, and context model derived from the binarization method of the target symbol and the probability model of the target symbol / bin.

[0085] In this regard, when applying CABAC, the table probability update method can be changed to a simple formula-based table update method to reduce the size of the probability table stored in the decryption device. Furthermore, two different probability models can be used to obtain more accurate symbol probability values.

[0086] The entropy encoding unit (150) can change a two-dimensional block form coefficient into a one-dimensional vector form through a transform coefficient scanning method to encode a transform coefficient level (quantized level).

[0087] Coding parameters may include not only information (flags, indexes, etc.) encoded in an encoding device (100) and signaled to a decoding device (200), such as syntax elements, but also information derived during an encoding process or a decoding process, and may mean information necessary when encoding or decoding an image.

[0088] Here, signaling a flag or index may mean that the encoder entropy encodes the flag or index and includes it in the bitstream, and that the decoder entropy decodes the flag or index from the bitstream.

[0089] The encoded current image can be used as a reference image for other images to be processed later. Accordingly, the encoding device (100) can reconstruct or decode the encoded current image again and store the reconstructed or decoded image as a reference image in the reference picture buffer (190).

[0090] The quantized level can be dequantized in the dequantization unit (160) and inversely transformed in the inverse transformation unit (170). The dequantized and / or inversely transformed coefficients can be combined with a prediction block through an adder (117), and a reconstructed block can be generated by combining the dequantized and / or inversely transformed coefficients and the prediction block. Here, the dequantized and / or inversely transformed coefficients refer to coefficients on which at least one of dequantization and inverse transformation has been performed, and may refer to a reconstructed residual block. The dequantization unit (160) and the inverse transformation unit (170) can be performed in the reverse process of the quantization unit (140) and the transformation unit (130).

[0091] The restoration block may pass through a filter unit (180). The filter unit (180) may apply a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), a bilateral filter (BIF), a Luma Mapping with Chroma Scaling (LMCS), etc. as a filtering technique, in whole or in part, to the restoration sample, restoration block, or restoration image. The filter unit (180) may also be referred to as an in-loop filter. In this case, the in-loop filter is also used as a name excluding LMCS.

[0092] A deblocking filter can remove block distortion that occurs at the boundaries between blocks. Whether to apply a deblocking filter to the current block can be determined based on the samples contained in several columns or rows within the block. When applying a deblocking filter to a block, different filters can be applied depending on the required deblocking filtering strength.

[0093] Sample adaptive offset can be used to compensate for encoding errors by adding an appropriate offset value to sample values. Sample adaptive offset can compensate for the offset from the original image on a sample-by-sample basis for deblocked images. This can be done by dividing the samples contained in the image into a fixed number of regions, determining the regions to be offset, and applying the offset to those regions. Alternatively, the offset can be applied by considering the edge information of each sample.

[0094] Bilateral filter (BIF) can also compensate for the offset from the original image on a sample-by-sample basis for the deblocked image.

[0095] An adaptive loop filter can perform filtering based on a comparison between a reconstructed image and the original image. By dividing the samples contained in the image into predetermined groups and determining the filter to be applied to each group, filtering can be performed differentially for each group. Information regarding whether to apply an adaptive loop filter can be signaled for each coding unit (CU), and the shape and filter coefficients of the adaptive loop filter applied to each block can vary.

[0096] In LMCS (Luma Mapping with Chroma Scaling), luma mapping (LM) refers to remapping luminance values ​​through a piece-wise linear model, and chroma scaling (CS) refers to a technique that scales the residual values ​​of chrominance components according to the average luminance value of the prediction signal. In particular, LMCS can be utilized as an HDR correction technique that reflects the characteristics of HDR (High Dynamic Range) images.

[0097] The restored block or restored image that has passed through the filter unit (180) may be stored in the reference picture buffer (190). The restored block that has passed through the filter unit (180) may be a part of the reference image. In other words, the reference image may be a restored image composed of restored blocks that have passed through the filter unit (180). The stored reference image may be used for inter-screen prediction or motion compensation thereafter.

[0098] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0099] The decoding device (200) may be a decoder, a video decoding device, or an image decoding device.

[0100] Referring to FIG. 2, the decoding device (200) may include an entropy decoding unit (210), an inverse quantization unit (220), an inverse transformation unit (230), an intra prediction unit (240), a motion compensation unit (250), an adder (201), a switch (203), a filter unit (260), and a reference picture buffer (270).

[0101] The decoding device (200) can receive a bitstream output from the encoding device (100). The decoding device (200) can receive a bitstream stored in a computer-readable recording medium, or a bitstream streamed through a wired / wireless transmission medium. The decoding device (200) can perform decoding on the bitstream in intra mode or inter mode. In addition, the decoding device (200) can generate a restored image or a decoded image through decoding, and can output the restored image or the decoded image.

[0102] If the prediction mode used for decryption is intra mode, the switch (203) can be switched to intra. If the prediction mode used for decryption is inter mode, the switch (203) can be switched to inter.

[0103] The decoding device (200) can decode the input bitstream to obtain a reconstructed residual block and generate a prediction block. Once the reconstructed residual block and the prediction block are obtained, the decoding device (200) can generate a reconstructed block to be decoded by adding the reconstructed residual block and the prediction block. The block to be decoded may be referred to as a current block.

[0104] The entropy decoding unit (210) can generate symbols by performing entropy decoding according to a probability distribution for the bitstream. The generated symbols may include symbols in the form of quantized levels. Here, the entropy decoding method may be the reverse process of the entropy encoding method described above.

[0105] The entropy decoding unit (210) can change a one-dimensional vector-shaped coefficient into a two-dimensional block-shaped coefficient through a transform coefficient scanning method to decode a transform coefficient level (quantized level).

[0106] The quantized level can be inversely quantized in the inverse quantization unit (220) and inversely transformed in the inverse transformation unit (230). The quantized level can be generated as a restored residual block as a result of performing inverse quantization and / or inverse transformation. At this time, the inverse quantization unit (220) can apply a quantization matrix to the quantized level. The inverse quantization unit (220) and inverse transformation unit (230) applied to the decoding device can apply the same technology as the inverse quantization unit (160) and inverse transformation unit (170) applied to the encoding device described above.

[0107] When intra mode is used, the intra prediction unit (240) can generate a predicted block by performing spatial prediction on the current block using sample values ​​of already decoded blocks surrounding the block to be decoded. The intra prediction unit (240) applied to the decoding device can apply the same technology as the intra prediction unit (120) applied to the encoding device described above.

[0108] When the inter mode is used, the motion compensation unit (250) can generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer (270) on the current block. The motion compensation unit (250) can generate a prediction block by applying an interpolation filter to a portion of the reference image when the value of the motion vector does not have an integer value. In order to perform motion compensation, it is possible to determine whether the motion compensation method of the prediction unit included in the corresponding encoding unit is skip mode, merge mode, AMVP mode, or current picture reference mode based on the encoding unit, and motion compensation can be performed according to each mode. The motion compensation unit (250) applied to the decoding device can apply the same technology as the motion compensation unit (122) applied to the encoding device described above.

[0109] The adder (201) can add the restored residual block and the predicted block to generate a restored block. The filter unit (260) can apply at least one of an Inverse-LMCS, a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the restored block or restored image. The filter unit (260) applied to the decoding device can apply the same filtering technology as that applied to the filter unit (180) applied to the encoding device described above.

[0110] The filter unit (260) can output a restored image. The restored block or restored image can be stored in the reference picture buffer (270) and used for inter prediction. The restored block that has passed through the filter unit (260) can be a part of the reference image. In other words, the reference image can be a restored image composed of restored blocks that have passed through the filter unit (260). The stored reference image can be used for inter-screen prediction or motion compensation thereafter.

[0111] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0112] 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 via a digital storage medium or a network.

[0113] 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.

[0114] 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.

[0115] The encoding unit (12) can encode the input video / image. The encoding unit (12) can perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency. The encoding unit (12) can output encoded data (encoded video / image information) in the form of a bitstream. The detailed configuration of the encoding unit (12) can also be configured in the same manner as the encoding device (100) of FIG. 1 described above.

[0116] The transmission unit (13) can transmit encoded video / image information or data output in the form of a bitstream to the reception unit (21) of the decoding device (20) via a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit (13) can include an element for generating a media file through a predetermined file format and can include an element for transmission via a broadcasting / communication network. The reception unit (21) can extract / receive the bitstream from the storage medium or network and transmit it to the decoding unit (22).

[0117] 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). The detailed configuration of the decoding unit (22) can also be configured in the same manner as the decoding device (200) of FIG. 2 described above.

[0118] The rendering unit (23) can render the decrypted video / image. The rendered video / image can be displayed through the display unit.

[0119]

[0120] Hereinafter, with reference to FIGS. 4 to 11, a method for deriving a cross-component nonlinear model and a method for generating a color difference prediction block using a cross-component nonlinear model according to an embodiment of the present invention will be described.

[0121] In the present invention, a 'cross-component non-linear model' means a non-linear model that represents the correlation between a sample of a chrominance signal and a restored luminance component sample at the same location, and may be named a 'cross-component model using a non-linear model', a 'nonlinear cross-component model', or a 'cross-component model using non-linear model coefficients'.

[0122]

[0123] Meanwhile, the cross-component linear model (CCLM) uses a linear model that calculates the correlation between the chrominance signal sample and the restored luminance component sample at the same location to remove the redundancy between the luminance signal and the chrominance signal.

[0124] Mathematical expression 1 shows a method for generating a color difference prediction block using a cross component linear model.

[0125]

[0126] In mathematical expression 1, pred C (i,j) represents the predicted chrominance component sample in the current coding unit (CU) block, and rec' L (i,j) may represent a down-sampled sample of a luminance component restored from the current encoding unit block. Here, a chrominance component sample predicted from the encoding unit block may be named a 'chrominance prediction block', and a luminance component sample restored from the encoding unit block may be named a 'luminance restoration block'.

[0127] Additionally, the linear model coefficients α and β of Equation 1 can be calculated using the linear minimum mean square error (LMMSE) method, respectively. Specifically, the values ​​of the linear model coefficients α and β can be derived from neighboring samples.

[0128]

[0129] If a nonlinear relationship exists between the restored luminance and chrominance components, as well as a linear one, generating accurate chrominance prediction blocks using a cross-component linear model may be limited. Therefore, a method that can generate chrominance prediction blocks by considering nonlinear models as well as linear models may be needed.

[0130] Mathematical expression 2 shows a method for generating a color difference prediction block using a cross-component nonlinear model.

[0131]

[0132] In mathematical expression 2, α0, α1, and α2 can be derived as model parameters using the decomposition method.

[0133] The above decomposition method is a reusable matrix decomposition method, and may be any one of LU decomposition, LDL decomposition, and Cholesky decomposition. Using the above-described decomposition method, linear or nonlinear systems can be solved more efficiently.

[0134] Specifically, the decomposition method is a matrix decomposition method that decomposes an arbitrary matrix into a product of matrices, and can be used to efficiently calculate matrices or various model coefficients, etc. when solving a system of linear equations.

[0135] LU decomposition is a method for factoring a matrix by multiplying a lower triangular matrix by an upper triangular matrix. Generally, LU decomposition has the advantage of being computationally fast.

[0136] LDL decomposition is a method for decomposing a symmetric positive-definite matrix into the product of a diagonal matrix and a lower triangular matrix. In general, LDL decomposition is a more stable numerical method than LU decomposition.

[0137] Cholesky decomposition is a method for factoring a matrix by multiplying a lower triangular matrix by its conjugate transpose. In general, Cholesky decomposition can be about twice as efficient as LU decomposition in solving linear or nonlinear systems of equations.

[0138] In Equation 2, bitDepth and midValue are the bit depth and the mid value. For example, for a video sequence using N-bit images, bitDepth is set to N and midValue is set to 2. N ≫1 or 2 N-1 can be set to .

[0139] Mathematical expression 2 can consider both linear and nonlinear relationships between the restored luminance component and chrominance component, and thus can generate an accurate chrominance prediction block.

[0140]

[0141] Mathematical expression 1 represents a formula for calculating a chrominance prediction block using a linear model. And, mathematical expression 2 represents a formula for calculating a chrominance prediction block using a nonlinear model.

[0142] If the chrominance subsampling is YCbCr422 or YCbCr444, the importance of the chrominance components may be high. In particular, if the chrominance subsampling is YCbCr444, each chrominance component may have the same importance as the luminance component. In such cases, applying the same linear model or the same nonlinear model to all chrominance components, as in Equations 1 and 2, may be inefficient.

[0143] Therefore, different linear models or different nonlinear models can be applied to each color difference component, as in the examples below.

[0144]

[0145] Mathematical expression 3 shows a method for generating a chrominance prediction block for each different chrominance component using different linear models.

[0146]

[0147] In mathematical expression 3, pred Cb (i,j) represents the predicted Cb chrominance component sample in the current encoding unit block, and rec' L (i,j) can represent down-sampled samples of the luminance component restored from the current encoding unit block. In addition, the linear model coefficients α cb and β cb can be calculated using the linear minimum mean square error (LMMSE) method on the surrounding reference samples of the Cb chrominance block and the surrounding reference samples of the luminance block corresponding to the Cb chrominance block. That is, the linear model coefficient α cb and β cb Values ​​can be derived from surrounding samples without being transmitted / parsed.

[0148] In mathematical expression 3, pred Cr (i,j) represents the predicted Cr chrominance component sample in the current encoding unit block, and rec' L (i,j) can represent down-sampled samples of the luminance component restored from the current encoding unit block. In addition, the linear model coefficients α cr and β cr can be calculated using the linear least mean square error method on the surrounding reference samples of the Cr chrominance block and the surrounding reference samples of the luminance block corresponding to the Cr chrominance block. That is, the linear model coefficient α cr and β crValues ​​can be derived from surrounding samples without being transmitted / parsed.

[0149]

[0150] Mathematical expression 4 shows a method for generating prediction blocks for each of the Cb chrominance component and the Cr chrominance component using different cross-component nonlinear models.

[0151]

[0152] In mathematical expression 4, pred Cb (i,j) represents the predicted Cb chrominance component sample in the current encoding unit block and rec' L (i,j) represents the restored and downsampled luminance component samples from the same coding unit block.

[0153] In mathematical expression 4, pred Cr (i,j) represents the predicted Cr chrominance component sample in the current encoding unit block and rec' L (i,j) represents a sample of the luminance component restored and downsampled from the same coding unit block. Model coefficient α 0_cb , α 1_cb , α 2_cb or α 0_cr , α 1_cr , α 2_cr can be derived using a decomposition method for the peripheral reference samples of the luminance block corresponding to the peripheral reference samples of the Cb chrominance block or the peripheral reference samples of the luminance block corresponding to the peripheral reference samples of the Cr chrominance block, respectively.

[0154] In mathematical expression 4, bitDepth and midValue are the bit depth and the mid value, respectively. For a video sequence using N-bit images, bitDepth is N and midValue is 2. N ≫1 or 2 N-1 can be set to .

[0155] Mathematical expression 4 can consider both linear and nonlinear relationships between the restored luminance component and each chrominance component, and thus can generate an accurate chrominance prediction block.

[0156]

[0157] A cross-component model (CCM) according to an embodiment of the present invention can be classified into an upper left cross-component model, an upper cross-component model, and a left cross-component model, depending on the location of a reference sample used for model derivation.

[0158] FIG. 4 is a diagram illustrating a reference sample for deriving a left upper cross component model (LT_CCM) according to one embodiment of the present invention.

[0159] Referring to FIG. 4, when the size of the color difference block (410) is W x H, the surrounding reference samples used for deriving the cross-component model parameter are the upper reference sample W' and the left reference sample H', and the upper reference sample can be set as W' = W and the left reference sample can be set as H' = H.

[0160] In addition, in order to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the chrominance block (410) C , 411) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (400) and corresponding to the same position of the chrominance reference sample (411) is selected. L , 401) can be derived from the cross-component model coefficients. That is, the upper left cross-component model coefficients can be derived based on the chrominance reference sample (411) and the down-sampled luminance reference sample (401) corresponding to the same position. Here, the sampling ratio can be arbitrarily determined.

[0161]

[0162] FIG. 5 is a diagram illustrating a reference sample for deriving a top cross component model (T_CCM) according to one embodiment of the present invention.

[0163] Referring to FIG. 5, when the size of the color difference block (510) is W x H, the surrounding reference sample used for deriving the cross-component model parameter is the upper reference sample W', and the upper reference sample can be set as W' = W + H.

[0164] In addition, in order to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the chrominance block (510) C , 511) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (500) and corresponding to the same position of the chrominance reference sample (511) is selected. L , 501) can be derived from the cross-component model coefficients. That is, the upper cross-component model coefficients can be derived based on the chrominance reference sample (511) and the down-sampled luminance reference sample (501) corresponding to the same position. Here, the sampling ratio can be arbitrarily determined.

[0165] Meanwhile, the upper reference sample W', which is a peripheral reference sample used to derive the upper cross component model coefficients, can be set as W' = W. That is, the peripheral reference sample used to derive the nonlinear model coefficients can be selected as an arbitrary peripheral reference sample.

[0166]

[0167] FIG. 6 is a diagram illustrating a reference sample for deriving a left cross component nonlinear model (L_CCM) according to one embodiment of the present invention.

[0168] Referring to FIG. 6, when the size of the color difference block (610) is W x H, the surrounding reference sample used for deriving the cross-component model parameter is the left reference sample H', and the left reference sample can be set as H' = W + H.

[0169] In addition, in order to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the chrominance block (610) C , 611) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (600) and corresponding to the same position of the chrominance reference sample (611) is selected. L , 601) can be derived from the cross-component model coefficients. That is, the left cross-component model coefficients can be derived based on the chrominance reference sample (611) and the down-sampled luminance reference sample (601) corresponding to the same position. Here, the sampling ratio can be arbitrarily determined.

[0170] Meanwhile, the left reference sample H', which is a peripheral reference sample used to derive the left cross-component model coefficients, can be set as H' = H. That is, the peripheral reference sample used to derive the nonlinear model coefficients can be selected as an arbitrary peripheral reference sample.

[0171]

[0172] Figures 4 to 6 illustrate reference samples used in the process of deriving a cross-component model when the chrominance subsampling is YCbCr420. On the other hand, when the chrominance subsampling is YCbCr422 or YCbCr444, the peripheral reference samples of the luminance block are determined using independently determined downsampling ratios for the Cb chrominance component and the Cr chrominance component, and the cross-component models of the Cb chrominance component and the Cr chrominance component can be independently derived.

[0173] For example, when the chrominance subsampling is YCbCr422, the luminance block peripheral reference sample used in the cross-component model derivation process may be a sample downsampled by 2. On the other hand, when the chrominance subsampling is YCbCr444, the luminance block peripheral reference sample used in the cross-component model derivation process may use the luminance block peripheral reference sample corresponding to the chrominance block peripheral reference sample. In other words, the reference sample used in the cross-component model can be determined without performing downsampling on the luminance block peripheral reference sample.

[0174] According to one embodiment of the present invention, the cross component models for the Cb chrominance component and the Cr chrominance component can be classified into a left upper cross component model (LT_CCM), a left lower cross component model (L_CCM), and a top cross component model (T_CCM) depending on the position of the reference sample used for model derivation.

[0175]

[0176] FIG. 7 is a diagram illustrating a reference sample for deriving a left upper cross component model (LT_CCM) according to one embodiment of the present invention.

[0177] Referring to FIG. 7, when the sizes of the Cb chrominance block (710) and the Cr chrominance block (720) are W x H, the surrounding reference samples used for deriving the cross-component model parameter are the upper reference sample W' and the left reference sample H', and the upper reference sample can be set as W' = W and the left reference sample can be set as H' = H.

[0178] In addition, in order to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cb chrominance block (710) Cb, 711) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (700) and corresponding to the same position of the chrominance reference sample (711) is selected. L , 701), the cross component model coefficients for the Cb chrominance component can be derived. That is, the upper left cross component model coefficients for the Cb chrominance component can be derived based on the chrominance reference sample (711) and the down-sampled luminance reference sample (701) corresponding to the same position.

[0179] In addition, to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cr chrominance block (720) Cr , 721) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (700) and corresponding to the same position of the chrominance reference sample (721) is selected. L , 701), the cross component model coefficients for the Cr chrominance component can be derived. That is, the upper left cross component model coefficients for the Cr chrominance component can be derived based on the chrominance reference sample (721) and the down-sampled luminance reference sample (701) corresponding to the same position.

[0180] Here, the sampling ratio can be determined arbitrarily. In addition, the sampling ratio can be determined differently depending on the chrominance component. That is, the downsampling ratio applied to the luminance reference sample corresponding to the Cb chrominance reference sample and the downsampling ratio applied to the luminance reference sample corresponding to the Cr chrominance reference sample can be determined independently of each other.

[0181]

[0182] FIG. 8 is a diagram illustrating a reference sample for deriving a top cross component model (T_CCM) according to one embodiment of the present invention.

[0183] Referring to FIG. 8, when the sizes of the Cb chrominance block (810) and the Cr chrominance block (820) are W x H, the surrounding reference sample used for deriving the cross-component model parameter is the upper reference sample W', and the upper reference sample can be set as W' = W + H.

[0184] In addition, in order to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cb chrominance block (810) Cb , 811) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (800) and corresponding to the same position of the chrominance reference sample (811) is selected. L , 801) can be used to derive the cross-component model coefficients for the Cb chrominance component. That is, the upper cross-component model coefficients for the Cb chrominance component can be derived based on the chrominance reference sample (811) and the down-sampled luminance reference sample (801) corresponding to the same position.

[0185] In addition, to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cr chrominance block (820) Cr , 821) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (800) and corresponding to the same position of the chrominance reference sample (821) is selected. L , 801) can be used to derive the cross-component model coefficients for the Cr chrominance component. That is, the upper cross-component model coefficients for the Cr chrominance component can be derived based on the chrominance reference sample (821) and the down-sampled luminance reference sample (801) corresponding to the same position.

[0186] Meanwhile, the upper reference sample W', which is a peripheral reference sample used to derive the upper cross component model coefficients, can be set as W' = W. That is, the peripheral reference sample used to derive the nonlinear model coefficients can be selected as an arbitrary peripheral reference sample.

[0187] And, the sampling ratio can be determined arbitrarily. In addition, the sampling ratio can be determined differently depending on the chrominance component. That is, the downsampling ratio applied to the luminance reference sample corresponding to the Cb chrominance reference sample and the downsampling ratio applied to the luminance reference sample corresponding to the Cr chrominance reference sample can be determined independently of each other.

[0188]

[0189] FIG. 9 is a diagram illustrating a reference sample for deriving a left cross component nonlinear model (L_CCM) according to one embodiment of the present invention.

[0190] Referring to FIG. 9, when the sizes of the Cb chrominance block (910) and the Cr chrominance block (920) are W x H, the surrounding reference sample used for deriving the cross-component model parameter is the left reference sample H', and the left reference sample can be set as H' = W + H.

[0191] In addition, to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cb chrominance block (910) Cb , 911) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (900) and corresponding to the same position of the chrominance reference sample (911) is selected. L, 901) can be derived from the cross component model coefficients for the Cb chrominance component. That is, the left cross component model coefficients for the Cb chrominance component can be derived based on the chrominance reference sample (911) and the down-sampled luminance reference sample (901) corresponding to the same position.

[0192] In addition, to reduce the computational complexity of the cross-component model coefficient derivation process, the surrounding neighboring chrominance reference samples (Rec') of the Cr chrominance block (920) Cr , 921) is sampled and selected, and a down-sampled luminance reference sample (Rec') adjacent to the luminance block (900) and corresponding to the same position of the chrominance reference sample (921) is selected. L , 901) can be derived from the cross component model coefficients for the Cr chrominance component. That is, the left cross component model coefficients for the Cr chrominance component can be derived based on the chrominance reference sample (921) and the down-sampled luminance reference sample (901) corresponding to the same position.

[0193] Meanwhile, the left reference sample H', which is a peripheral reference sample used to derive the left cross-component model coefficients, can be set as H' = H. That is, the peripheral reference sample used to derive the nonlinear model coefficients can be selected as an arbitrary peripheral reference sample.

[0194] And, the sampling ratio can be determined arbitrarily. In addition, the sampling ratio can be determined differently depending on the chrominance component. That is, the downsampling ratio applied to the luminance reference sample corresponding to the Cb chrominance reference sample and the downsampling ratio applied to the luminance reference sample corresponding to the Cr chrominance reference sample can be determined independently of each other.

[0195]

[0196] According to an embodiment of the present invention, a method for generating a prediction block of a chrominance component by applying a cross component model (CCM) with non-linear model parameters may be as described below.

[0197]

[0198] According to one embodiment of the present invention, a chrominance prediction block can be generated using a method using only a cross-component nonlinear model instead of a method using a cross-component linear model. Accordingly, a chrominance prediction block can be generated using an upper-left cross-component nonlinear model, an upper cross-component nonlinear model, and a left cross-component nonlinear model using the nonlinear model coefficients of Equation 2.

[0199] The proposed method can use a cross-component nonlinear model instead of the existing cross-component linear model. Therefore, the method for transmitting / parsing syntax for a cross-component nonlinear model can be used as an alternative to the method used for transmitting / parsing syntax for a conventional cross-component linear model. One embodiment of the method for transmitting / parsing syntax for a cross-component nonlinear model can be as shown in Table 1 below.

[0200]

[0201] In Table 1, ccmEnabled may be information indicating whether a cross-component nonlinear model is available. In one embodiment, a value of ccmEnabled of 1 may indicate that a cross-component nonlinear model is available, and a value of ccmEnabled of 0 may indicate that a cross-component nonlinear model is not available. Meanwhile, if the value of ccmEnabled is 1, ccm_mode_flag may be signaled.

[0202] ccm_mode_flag is flag information indicating a chrominance intra prediction mode based on a cross-component nonlinear model. According to an embodiment, when the value of ccm_mode_flag is 1, it may indicate a chrominance intra prediction mode based on a cross-component nonlinear model, and when the value of ccm_mode_flag is 0, it may indicate a general chrominance intra prediction mode not based on a cross-component nonlinear model. Meanwhile, when the value of ccm_mode_flag is 1, ccm_mode_idx may be signaled, and when the value of ccm_mode_flag is 0, intra_chroma_pred_mode indicating the type of the general chrominance intra prediction mode may be signaled. Here, intra_chroma_pred_mode may indicate any one of direct mode (DM), planar mode, DC mode, vertical mode, and horizontal mode. Meanwhile, when ccm_mode_flag is not signaled, the value of ccm_mode_flag may be regarded as 0.

[0203] ccm_mode_idx is index information indicating the type of cross-component nonlinear model, and can indicate any one of the upper left cross-component nonlinear model, upper cross-component nonlinear model, and left cross-component nonlinear model.

[0204]

[0205] According to another embodiment of the present invention, a color difference prediction block can be generated by selectively using a cross-component linear model and a cross-component nonlinear model.

[0206] According to a method of selectively using a cross-component linear model and a cross-component nonlinear model, a syntax that distinguishes whether a cross-component linear model or a cross-component nonlinear model is used can be used. For example, when a chrominance prediction block for a current block is derived using a cross-component model, flag information distinguishing whether a cross-component linear model or a cross-component nonlinear model is used can be additionally transmitted / parsed. Afterwards, an index indicating a specific one of the three cross-component models can be transmitted / parsed. Accordingly, a cross-component model can be derived based on the transmitted / parsed information, and a chrominance prediction block for the current block can be derived based on the cross-component model. One embodiment of a method for transmitting / parsing syntax related to a cross-component model can be as expressed in Table 2 below.

[0207]

[0208] In Table 2, ccmEnabled is information indicating whether a cross-component model is available. In one embodiment, a value of 1 for ccmEnabled indicates that a cross-component model is available, and a value of 0 for ccmEnabled indicates that a cross-component model is not available. Here, the cross-component model may include a cross-component linear model and a cross-component nonlinear model. Meanwhile, if the value of ccmEnabled is 1, ccm_mode_flag may be signaled.

[0209] ccm_mode_flag is flag information indicating a chroma intra prediction mode based on a cross-component model. According to an embodiment, when the value of ccm_mode_flag is 1, it may indicate a chroma intra prediction mode based on a cross-component model, and when the value of ccm_mode_flag is 0, it may indicate a general chroma intra prediction mode not based on a cross-component model. Meanwhile, when the value of ccm_mode_flag is 1, ccm_linear_model_flag and ccm_mode_idx may be signaled. On the other hand, when the value of ccm_mode_flag is 0, intra_chroma_pred_mode indicating the type of the general chroma intra prediction mode may be signaled. Here, intra_chroma_pred_mode may indicate any one of direct mode (DM), planar mode, DC mode, vertical mode, and horizontal mode. Meanwhile, if ccm_mode_flag is not signaled, the value of ccm_mode_flag can be considered as 0.

[0210] ccm_linear_model_flag is flag information that distinguishes between a cross-component linear model and a cross-component nonlinear model. If the ccm_linear_model_flag value is 1, it indicates a cross-component linear model, and if the ccm_linear_model_flag value is 0, it indicates a cross-component nonlinear model.

[0211] ccm_mode_idx is index information indicating the type of cross component model, and can indicate any one of the cross component models among the upper left cross component model, the upper cross component model, and the left cross component model.

[0212] For example, when the ccm_linear_model_flag value is 1, one of the cross-component linear models among the upper-left cross-component linear model, the upper cross-component linear model, and the left cross-component linear model can be used depending on the ccm_mode_idx value. In addition, when the ccm_linear_model_flag value is 0, one of the cross-component nonlinear models among the upper-left cross-component nonlinear model, the upper cross-component nonlinear model, and the left cross-component nonlinear model can be used depending on the ccm_mode_idx value.

[0213] Meanwhile, in Table 2, ccm_mode_idx is signaled after ccm_linear_model_flag is signaled, but the signaling order of the two syntax elements can be determined arbitrarily.

[0214] The syntax structure proposed in Table 2 can be used to generate a chrominance prediction block by selecting linear model coefficients and nonlinear model coefficients at the encoding unit level according to the signaled syntax elements.

[0215]

[0216] According to another embodiment of the present invention, a color difference prediction block can be generated using a method of implicitly determining a cross-component model among a cross-component linear model and a cross-component nonlinear model.

[0217] That is, instead of using information such as cclm_linear_model_flag, an appropriate model can be selected between a cross-component linear model and a cross-component nonlinear model through an implicit method.

[0218] For example, the decoder may have a linear model coefficient α cb, β cb, α cr, β cr, Based on this, a cross-component linear model is derived, and the nonlinear model coefficient α 0_cb , α 1_cb , α 2_cb, α 0_cr , α 1_cr , α 2_cr Based on this, a cross-component nonlinear model can be derived. The decoder can apply each derived cross-component model to the surrounding reference samples of the luminance block corresponding to the current chrominance block to calculate a predicted reference sample for the surrounding reference samples of the current chrominance block.

[0219] And, the decoder uses the cross-component linear model to produce a predicted reference sample (PredC_ref _linear ) and the restored reference sample (RecC_ref) value and the difference between the predicted reference sample (PredC_ref_non-linear) and the restored reference sample (RecC_ref) value calculated using the cross-component nonlinear model, and the optimal cross-component model can be selected. That is, the decoder can select the optimal cross-component model among the cross-component linear model and the cross-component nonlinear model based on the error value of the predicted reference sample calculated using the cross-component linear model and the error value of the predicted reference sample calculated using the cross-component nonlinear model.

[0220] At this time, the comparison between the cross-component linear model and the cross-component nonlinear model can be made using various methods, such as the sum of absolute differences (SAD), the sum of square error (SSE), and the sum of absolute transformed differences (SATD).

[0221]

[0222] According to one embodiment of the present invention, when a luminance block corresponding to a current chrominance block is coded in an intra template matching prediction (IntraTMP) mode or an intra block copy (IBC) mode, cross-component linear model coefficients or cross-component nonlinear model coefficients can be derived using block vector (BV) information used for intra prediction. A method for calculating cross-component linear model coefficients or cross-component nonlinear model coefficients using block vector information can be as described below.

[0223]

[0224] FIG. 10 is a diagram illustrating a method for calculating cross-component linear model coefficients or cross-component nonlinear model coefficients using block vector information of intra prediction according to an embodiment of the present invention.

[0225] Referring to FIG. 10, when a reconstructed luma block (Corresponding luma block, 1021) corresponding to a current chroma block (Current chroma block, 1011) of a chroma picture (Chroma picture, 1010) is encoded based on intra template matching or intra block copying, a matching luma block (Matching luma block, 1024) indicated by a block vector (Block vector, BV, 1023) of the corresponding intra mode in the reconstructed luma picture (Luma picture, 1020) can be determined.

[0226] According to one embodiment of the present invention, instead of calculating the cross-component model coefficients through the correlation between the chroma reference sample (1012) of the current chroma component block (1011) and the luminance reference sample (1022) of the corresponding restored luminance block (1021), the cross-component model coefficients can be calculated through the correlation between the reference sample (1012) of the current chroma component block and the reference sample (1025) of the matching luminance signal (1024).

[0227] At this time, the cross-component linear model coefficients or the cross-component nonlinear model coefficients can be calculated for the Cb chrominance component and the Cr chrominance component using mathematical expression 3 or mathematical expression 4. Alternatively, the cross-component linear model coefficients or the cross-component nonlinear model coefficients can be calculated using mathematical expression 1 or mathematical expression 2.

[0228] Also, as illustrated in FIG. 10, the cross-component linear model coefficients or the cross-component nonlinear model coefficients can be derived using the reference sample for inducing the upper left cross-component model (LT_CCM) as illustrated in FIG. 4. However, as an example, the cross-component linear model coefficients or the cross-component nonlinear model coefficients can be derived using the reference sample for inducing the upper cross-component model (T_CCM) as illustrated in FIG. 5 or the reference sample for inducing the left cross-component model (L_CCM) as illustrated in FIG. 6.

[0229] When calculating the cross-component linear model coefficients or cross-component nonlinear model coefficients for each color difference component, the cross-component linear model coefficients or cross-component nonlinear model coefficients for each color difference component can be derived using a reference sample for deriving the upper left cross-component model (LT_CCM) as illustrated in FIG. 7, a reference sample for deriving the upper cross-component model (T_CCM) as illustrated in FIG. 8, or a reference sample for deriving the left cross-component nonlinear model (L_CCM) as illustrated in FIG. 9.

[0230]

[0231] Figure 11 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

[0232] The image decoding device can derive a cross-component model including a Cb cross-component model and a Cr cross-component model for predicting a chrominance component block of a current block using a reference sample (S1110).

[0233] The image decoding device can generate a prediction block for the Cb chrominance component block of the current block using the Cb cross component model (S1120).

[0234] The image decoding device can generate a prediction block for the Cr chrominance component block of the current block using the Cr cross component model (S1130).

[0235] Here, the Cb cross-component model and the Cr cross-component model can be determined independently of each other.

[0236] Here, the Cb cross-component model and the Cr cross-component model can be derived based on the coefficients, bit depth, and intermediate values ​​of the cross-component model.

[0237] Here, the coefficients of the cross-component model can be derived based on any one of the decomposition methods of LU decomposition, LDL decomposition, and Cholesky decomposition.

[0238] Here, the reference sample may include a Cb chrominance reference sample neighboring the Cb chrominance component block of the current block, a luminance reference sample corresponding to the Cb chrominance reference sample, a Cr chrominance reference sample neighboring the Cr chrominance component block of the current block, and a luminance reference sample corresponding to the Cr chrominance reference sample.

[0239] Here, the cross-component model can be any one of the upper left cross-component model, the upper cross-component model, and the left cross-component model.

[0240] Here, if the cross component model is an upper left cross component model, the reference sample may include a reference sample located at the upper left of the chrominance component block of the current block and a reference sample located at the upper left of the luminance component block of the current block.

[0241] Here, if the cross component model is an upper cross component model, the reference sample may include a reference sample located at the upper end of the chrominance component block of the current block and a reference sample located at the upper end of the luminance component block of the current block.

[0242] Here, if the cross component model is a left cross component model, the reference sample may include a reference sample located on the left side of the chrominance component block of the current block and a reference sample located on the left side of the luminance component block of the current block.

[0243] Here, the luminance reference sample corresponding to the Cb chrominance reference sample and the luminance reference sample corresponding to the Cr chrominance reference sample may be reference samples downsampled according to the downsampling ratio.

[0244] Here, the downsampling ratio applied to the luminance reference sample corresponding to the Cb chrominance reference sample and the downsampling ratio applied to the luminance reference sample corresponding to the Cr chrominance reference sample can be determined independently of each other.

[0245] Here, the step of deriving the Cb cross-component model and the Cr cross-component model may include a step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model.

[0246] Here, the step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model may be characterized in that the determination is made based on model information indicating either the cross-component linear model or the cross-component nonlinear model.

[0247] Here, the step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model may be characterized in that the step is determined based on a comparison result between the error values ​​of the Cb chrominance reference sample and the Cr chrominance reference sample predicted based on the cross-component linear model and the error values ​​of the Cb chrominance reference sample and the Cr chrominance reference sample predicted based on the cross-component nonlinear model.

[0248] Here, if the intra prediction mode of the luminance component block of the current block is a predetermined prediction mode, the luminance reference sample corresponding to the Cb chrominance reference sample and the luminance reference sample corresponding to the Cr chrominance reference sample may be luminance reference samples adjacent to a matching block indicated by the block vector of the luminance component block of the current block.

[0249] Here, the given prediction mode may be one of intra template matching mode and intra block copy mode.

[0250] Meanwhile, the steps described in FIG. 11 can also be performed in an image encoding method. Furthermore, a bitstream can be generated by an image encoding method including the steps described in FIG. 11. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0251]

[0252] FIG. 12 is a drawing exemplifying a content streaming system to which an embodiment according to the present invention can be applied.

[0253] As illustrated in FIG. 12, a content streaming system to which an embodiment of the present invention 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.

[0254] The encoding server compresses content input from multimedia input devices such as smartphones, cameras, and CCTVs into digital data, generates a bitstream, and transmits it to the streaming server. Alternatively, if multimedia input devices such as smartphones, cameras, and CCTVs directly generate bitstreams, the encoding server may be omitted.

[0255] The above bitstream can be generated by an image encoding method and / or an image encoding device to which an embodiment of the present invention is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0256] 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.

[0257] The streaming server can receive content from a media repository and / or 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.

[0258] 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.

[0259] 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.

[0260]

[0261] The above embodiments can be performed in the same or corresponding manner in an encoding device and a decoding device. In addition, an image can be encoded / decoded using at least one or a combination of at least one of the above embodiments.

[0262] The order in which the above embodiments are applied may be different in the encoding device and the decoding device. Alternatively, the order in which the above embodiments are applied may be the same in the encoding device and the decoding device.

[0263] The above embodiments can be performed for each of the luminance and chrominance signals. Alternatively, the above embodiments can be performed identically for the luminance and chrominance signals.

[0264] In the above embodiments, the methods are described based on a flowchart as a series of steps or units. However, the present invention is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps described above. Furthermore, those skilled in the art will understand that the steps depicted in the flowchart are not exclusive, and that other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

[0265] The above embodiments may be implemented in the form of program commands that can be executed by various computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program commands, data files, data structures, etc., either singly or in combination. The program commands recorded on the computer-readable recording medium may be those specifically designed and constructed for the present invention, or may be known and usable by those skilled in the art of computer software.

[0266] The bitstream generated by the encoding method according to the above embodiment can be stored in a non-transitory computer-readable recording medium. In addition, the bitstream stored in the non-transitory computer-readable recording medium can be decoded by the decoding method according to the above embodiment.

[0267] Here, examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices specifically configured to store and execute program instructions such as ROMs, RAMs, and flash memories. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices may be configured to operate as one or more software modules to perform processing according to the present invention, and vice versa.

[0268] Although the present invention has been described above with specific details such as specific components and limited examples and drawings, these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations from this description.

[0269] Therefore, the idea of ​​the present invention should not be limited to the embodiments described above, and all things that are modified equally or equivalently to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

[0270] The present invention can be used in a device for encoding / decoding an image and a recording medium storing a bitstream.

Claims

1. In the video decryption method, A step of deriving a cross-component model including a Cb cross-component model and a Cr cross-component model for predicting a chrominance component block of a current block using a reference sample; A step of generating a prediction block for a Cb chrominance component block of a current block using the above Cb cross component model; and A step of generating a prediction block for a Cr chrominance component block of a current block using the Cr cross component model, An image decoding method in which the Cb cross-component model and the Cr cross-component model are determined independently.

2. In paragraph 1, The above Cb cross component model and the above Cr cross component model, An image decoding method characterized in that it is derived based on coefficients, bit depth and intermediate values ​​of a cross component model.

3. In paragraph 2, The coefficients of the above cross component model are: An image decoding method characterized in that it is derived based on any one of LU decomposition, LDL decomposition and Cholesky decomposition.

4. In paragraph 1, A method for decoding an image, wherein the reference sample includes a Cb chrominance reference sample neighboring a Cb chrominance component block of the current block, a luminance reference sample corresponding to the Cb chrominance reference sample, a Cr chrominance reference sample neighboring a Cr chrominance component block of the current block, and a luminance reference sample corresponding to the Cr chrominance reference sample.

5. In paragraph 4, An image decoding method, characterized in that the above cross component model is any one of an upper left cross component model, an upper cross component model, and a left cross component model.

6. In paragraph 5, If the above cross component model is the upper left cross component model, An image decoding method, characterized in that the reference sample includes a reference sample located at the upper left of a chrominance component block of the current block and a reference sample located at the upper left of a luminance component block of the current block.

7. In paragraph 5, If the above cross component model is the upper cross component model, An image decoding method, characterized in that the reference sample includes a reference sample located at the top of a chrominance component block of the current block and a reference sample located at the top of a luminance component block of the current block.

8. In paragraph 5, If the above cross component model is a left cross component model, An image decoding method, characterized in that the reference sample includes a reference sample located to the left of a chrominance component block of the current block and a reference sample located to the left of a luminance component block of the current block.

9. In paragraph 4, A luminance reference sample corresponding to the above Cb chrominance reference sample and a luminance reference sample corresponding to the above Cr chrominance reference sample are, An image decoding method characterized in that the reference sample is downsampled according to a downsampling ratio.

10. In paragraph 9, An image decoding method, characterized in that a downsampling ratio applied to a luminance reference sample corresponding to the Cb chrominance reference sample and a downsampling ratio applied to a luminance reference sample corresponding to the Cr chrominance reference sample are determined independently of each other.

11. In paragraph 4, The steps of deriving the Cb cross component model and the Cr cross component model are: An image decoding method, characterized by including a step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model.

12. In paragraph 11, The step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model is: An image decoding method, characterized in that the method comprises determining based on model information indicating either a cross-component linear model or a cross-component nonlinear model.

13. In paragraph 11, The step of determining the Cb cross-component model and the Cr cross-component model as a cross-component linear model or a cross-component nonlinear model is: An image decoding method, characterized in that the determination is made based on a comparison result between the error values ​​of the Cb chrominance reference sample and the Cr chrominance reference sample predicted based on a cross-component linear model and the error values ​​of the Cb chrominance reference sample and the Cr chrominance reference sample predicted based on a cross-component nonlinear model.

14. In paragraph 4, If the intra prediction mode of the luminance component block of the current block above is a predetermined prediction mode, A luminance reference sample corresponding to the above Cb chrominance reference sample and a luminance reference sample corresponding to the above Cr chrominance reference sample are, An image decoding method, characterized in that the luminance reference sample is a neighboring luminance reference sample of a matching block indicated by a block vector of a luminance component block of the current block.

15. In paragraph 14, The above-mentioned predetermined prediction mode is, A video decoding method, characterized in that it is one of intra template matching mode and intra block copy mode.

16. In a video encoding method, A step of deriving a Cb cross component model and a Cr cross component model for predicting a chrominance component block of a current block using a reference sample; A step of generating a prediction block for a Cb chrominance component block of a current block using the above Cb cross component model; and A step of generating a prediction block for a Cr chrominance component block of a current block using the Cr cross component model, An image encoding method in which the Cb cross-component model and the Cr cross-component model are determined independently of each other.

17. A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method, The above image encoding method is, A step of deriving a Cb cross component model and a Cr cross component model for predicting a chrominance component block of a current block using a reference sample; A step of generating a prediction block for a Cb chrominance component block of a current block using the above Cb cross component model; and A step of generating a prediction block for a Cr chrominance component block of a current block using the Cr cross component model, A non-transitory computer-readable recording medium, wherein the Cb cross-component model and the Cr cross-component model are determined independently of each other.

18. A method for transmitting a bitstream generated by a video encoding method, The above transmission method comprises a step of transmitting the bitstream, The above encoding method is, A step of deriving a Cb cross component model and a Cr cross component model for predicting a chrominance component block of a current block using a reference sample; A step of generating a prediction block for a Cb chrominance component block of a current block using the above Cb cross component model; and A step of generating a prediction block for a Cr chrominance component block of a current block using the Cr cross component model, The Cb cross-component model and the Cr cross-component model are transmission methods that are determined independently of each other.

Images