Image encoding / decoding method and device, and recording medium storing bit stream

Abstract

Provided are an image encoding / decoding method and apparatus, a recording medium storing a bit stream, and a transmission method. The image decoding method comprises the steps of: deriving different cross-component nonlinear model coefficients using reference samples; deriving different cross-component nonlinear models based on different cross-component nonlinear model coefficients; and generating prediction blocks of different chroma component blocks of the current block using different cross-component nonlinear models, the prediction blocks of the different chroma component blocks include a prediction block of a first chroma component block generated based on a first cross-component nonlinear model and a prediction block of a second chroma component block generated based on a second cross-component nonlinear model.

Description

Technical Field

[0001] This invention relates to methods and apparatus for encoding / decoding images, and recording media for storing bitstreams. Specifically, this invention relates to methods and apparatus for encoding / decoding images by utilizing a cross-component nonlinear model, and recording media for storing bitstreams. Background Technology

[0002] Recently, there has been an increasing demand for high-resolution and high-quality images, such as Ultra High Definition (UHD) images, across various application areas. As the resolution and quality of image data increase, the data volume also increases relative to existing image data. Therefore, transmission and storage costs increase when transmitting such image data using existing media such as wired or wireless broadband channels, or when storing such image data using existing storage media. To address these issues arising from the increasing resolution and quality of image data, efficient image encoding / decoding technologies are needed for images with higher resolution and image quality.

[0003] Cross-component linear model (CCLM) can be used to remove redundancy between luminance and chrominance component signals, thereby predicting the chrominance signal.

[0004] However, when there is not only a linear relationship but also a nonlinear relationship between the reconstructed luminance component and chrominance component, the accuracy of chrominance signal prediction based on CCLM may decrease. Summary of the Invention

[0005] Technical issues The purpose of this invention is to provide a method and apparatus for encoding / decoding images, which has improved encoding / decoding efficiency.

[0006] Another object of the present invention is to provide a recording medium for storing a bitstream generated by a method or apparatus for decoding images according to the present invention.

[0007] Another objective of this invention is to provide a method for deriving a cross-component nonlinear model and a method for generating chromaticity prediction blocks based on the cross-component nonlinear model, thereby solving the aforementioned problems.

[0008] Technical solution A method for decoding an image according to an embodiment of the present invention includes: deriving a cross-component model for predicting chroma component blocks of a current block by using reference samples, the cross-component model including a Cb cross-component model and a Cr cross-component model; generating a predicted block of Cb chroma component blocks of the current block by using the Cb cross-component model; and generating a predicted block of Cr chroma component blocks of the current block by 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 methods for decoding images, Cb and Cr cross-component models can be derived based on the parameters, bit depth, and intermediate values ​​of the cross-component models.

[0010] In methods for decoding images, the parameters of the cross-component model can be derived based on any of the decomposition methods, such as LU decomposition, LDL decomposition, and Cholesky decomposition.

[0011] In a method for decoding an image, the reference sample may include: a Cb chromaticity reference sample adjacent to the Cb chromaticity component block of the current block, a luminance reference sample corresponding to the Cb chromaticity reference sample, a Cr chromaticity reference sample adjacent to the Cr chromaticity component block of the current block, and a luminance reference sample corresponding to the Cr chromaticity reference sample.

[0012] In the method used to decode images, the cross-component model can be any one of the top-left cross-component model, the top-left cross-component model, and the left-left cross-component model.

[0013] In a method for decoding an image, when the cross-component model is a top-left cross-component model, the reference sample may include a reference sample located on the top-left side of the chroma component block of the current block and a reference sample located on the top-left side of the luminance component block of the current block.

[0014] In a method for decoding an image, when the cross-component model is an upper cross-component model, the reference sample may include a reference sample located above the chroma component block of the current block and a reference sample located above the luma component block of the current block.

[0015] In a method for decoding an image, when the cross-component model is a left-side cross-component model, the reference sample may include a reference sample located to the left of the chroma component block of the current block and a reference sample located to the left of the luma component block of the current block.

[0016] In the method for decoding images, the luminance reference sample corresponding to the Cb chromaticity reference sample and the luminance reference sample corresponding to the Cr chromaticity reference sample can be reference samples downsampled according to the downsampling rate.

[0017] In the method for decoding images, the downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample can be determined independently of each other.

[0018] In methods for decoding images, deriving the Cb transcomponent model and the Cr transcomponent model may include determining the Cb transcomponent model and the Cr transcomponent model as transcomponent linear models or transcomponent nonlinear models.

[0019] In methods for decoding images, determining whether the Cb cross-component model and the Cr cross-component model are cross-component linear models or cross-component nonlinear models can be based on model information indicating either the cross-component linear model or the cross-component nonlinear model.

[0020] In methods for decoding images, determining whether the Cb cross-component model and the Cr cross-component model are cross-component linear models or cross-component nonlinear models can be based on a comparison between the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component linear model and the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component nonlinear model.

[0021] In a method for decoding an image, 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 chromaticity reference sample and the luminance reference sample corresponding to the Cr chromaticity reference sample can be luminance reference samples adjacent to the matching block indicated by the block vector of the luminance component block of the current block.

[0022] In a method for decoding an image, the predetermined prediction mode can be one of an intra-frame template matching mode and an intra-frame block copying mode.

[0023] A method for encoding an image according to an embodiment of the present invention includes: deriving a Cb cross-component model and a Cr cross-component model for predicting the chroma component blocks of the current block by using reference samples; generating a predicted block of the Cb chroma component blocks of the current block by using the Cb cross-component model; and generating a predicted block of the Cr chroma component blocks of the current block by 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-volatile computer-readable recording medium according to an embodiment of the present invention can store a bitstream generated by a method for encoding an image, wherein the method for encoding the image includes: deriving a Cb cross-component model and a Cr cross-component model for predicting the chroma component blocks of the current block by using reference samples; generating a predicted block of the Cb chroma component blocks of the current block by using the Cb cross-component model; and generating a predicted block of the Cr chroma component blocks of the current block by 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.

[0025] The transmission method according to an embodiment of the present invention includes storing a bitstream generated by a method for encoding an image, wherein the method for encoding the image includes: deriving a Cb cross-component model and a Cr cross-component model for predicting the chroma component blocks of the current block by using reference samples; generating a predicted block of the Cb chroma component blocks of the current block by using the Cb cross-component model; and generating a predicted block of the Cr chroma component blocks of the current block by 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.

[0026] The features briefly outlined above are provided as examples to illustrate the detailed description and should not be construed as limiting the scope of the invention.

[0027] Beneficial effects According to the present invention, a method and apparatus for encoding / decoding images can be provided, which have improved encoding / decoding efficiency.

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

[0029] Furthermore, according to the present invention, chromaticity blocks can be predicted more accurately.

[0030] The effects that can be obtained according to the present invention are not limited to those described above, and those skilled in the art will clearly understand other effects not mentioned from the following description. Attached Figure Description

[0031] Figure 1 This is a block diagram illustrating the configuration of an encoding device according to an embodiment of the present invention.

[0032] Figure 2 This is a block diagram illustrating the configuration of a decoding device according to an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram illustrating a video encoding / decoding system to which the present invention can be applied.

[0034] Figure 4This is a schematic diagram illustrating a reference sample for deriving a nonlinear model across the upper left component according to an embodiment of the present invention.

[0035] Figure 5 This is a schematic diagram illustrating a reference sample for deriving an upper trans-component nonlinear model according to an embodiment of the present invention.

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

[0037] Figure 7 This is a schematic diagram illustrating a reference sample for deriving the upper left cross component model LT_CCM according to an embodiment of the present invention.

[0038] Figure 8 This is a schematic diagram illustrating a reference sample for deriving the upper cross component model T_CCM according to an embodiment of the present invention.

[0039] Figure 9 This is a schematic diagram illustrating a reference sample for deriving the left-side transcomponent nonlinear model L_CCM according to an embodiment of the present invention.

[0040] Figure 10 This is a schematic diagram illustrating a method for calculating cross-component linear model parameters or cross-component nonlinear model parameters using block vector information predicted within a frame, according to an embodiment of the present invention.

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

[0042] Figure 12 This is a schematic diagram illustrating a content streaming system applicable to embodiments of the present invention. Detailed Implementation

[0043] This invention can have various modifications and embodiments, and specific embodiments are shown in the accompanying drawings and described in detail in the specification. However, this is not intended to limit the invention to the specific embodiments, but rather to include all modifications, equivalents, or alternatives contained within the spirit and scope of the invention. The same reference numerals in the drawings indicate the same or similar functions in various aspects. For clarity, the shapes and dimensions of the elements in the drawings are provided by way of example. 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 them. It should be understood that the various embodiments differ from one another but are not necessarily mutually exclusive. For example, the specific shapes, structures, and features described herein may be implemented in other embodiments without departing from the spirit and scope of the invention with reference to one embodiment. It should also be understood that the position or arrangement of the various components within each disclosed embodiment may be changed without departing from the spirit and scope of the embodiments. Accordingly, the detailed description set forth below is not intended to be restrictive, and the scope of the exemplary embodiments is defined only by the appended claims and the full scope of their equivalents (if appropriately described).

[0044] In this invention, the terms first, second, etc., may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component. Terms are and / or include combinations of multiple related descriptive terms or any item from multiple related descriptive terms.

[0045] The components shown in the embodiments of the invention are depicted independently to indicate different functional characteristics, and do not represent each component as a separate hardware or software configuration unit. That is, for ease of interpretation, each component is listed and included as a separate component, and at least two components may be combined to form a single component, or a component may be divided into multiple components to perform functions, as long as it does not depart from the spirit of the invention. Embodiments in which components are integrated and embodiments in which each component is divided are also included within the scope of the invention.

[0046] The terminology used in this invention is for describing specific embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, some components of this invention are not essential for performing the necessary functions and may be optional components used only to improve performance. This invention can be implemented by including only the essential components necessary for achieving the spirit of the invention, excluding components used only to improve performance, and structures that include only the essential components and excluding optional components used only to improve performance are also included within the scope of this invention.

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

[0048] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. When describing embodiments of this specification, detailed descriptions will be omitted if determining that a detailed description of a related known configuration or function would obscure the subject matter of this specification; the same reference numerals will be used for the same components in the drawings, and repeated descriptions of the same components will be omitted.

[0049] Description of terms In the following text, "image" can refer to a picture that constitutes a video, or it can refer to the video itself. For example, "encoding and / or decoding of an image" can mean "encoding and / or decoding of a video," or it can mean "encoding and / or decoding of one of the images that constitute a video."

[0050] In the following text, "moving image" and "video" can be used with the same meaning and can be used interchangeably. Additionally, the target image can be an encoded target image that is the target of encoding and / or a decoded target image that is the target of decoding. Furthermore, the target image can be an input image to an encoding device and can also be an input image to a decoding device. Here, the target image can have the same meaning as the current image.

[0051] In the following text, encoder and image encoding device can be used with the same meaning and can be used interchangeably.

[0052] In the following text, "decoder" and "image decoding device" can be used with the same meaning and can be used interchangeably.

[0053] In the following text, “image,” “picture,” “frame,” and “screen” can be used with the same meaning and can be used interchangeably.

[0054] In the following text, "target block" can refer to an encoding target block that is the target of encoding and / or a decoding target block that is the target of decoding. Additionally, a target block can refer to the current block that is the target of the current encoding and / or decoding. For example, "target block" and "current block" can be used with the same meaning and can be used interchangeably.

[0055] In the following text, "block" and "unit" can be used with the same meaning and can be used interchangeably. Additionally, "unit" can refer to a block comprising a luma component block and its corresponding chroma component block, in order to distinguish it from a block. For example, a coding tree unit (CTU) can consist of a luma component (Y) coding tree block (CTB) and two associated chroma component (Cb, Cr) coding tree blocks.

[0056] In the following text, "sample," "image element," and "pixel" can be used with the same meaning and interchangeably. In this article, a sample can represent the basic unit that makes up a block.

[0057] In the following text, "between frames" and "between images" can be used with the same meaning and can be used interchangeably.

[0058] In the following text, "within the frame" and "within the screen" can be used with the same meaning and can be used interchangeably.

[0059] Figure 1 This is a block diagram illustrating the configuration of an encoding device according to an embodiment of the present invention.

[0060] The encoding device 100 may be an encoder, a video encoding device, or an image encoding device. The video may include one or more images. The encoding device 100 may encode one or more images sequentially.

[0061] refer to Figure 1 The encoding device 100 may include: an image partitioning unit 110, an intra-frame prediction unit 120, a motion prediction unit 121, a motion compensation unit 122, a switcher 115, a subtractor 113, a transform unit 130, a quantization unit 140, an entropy coding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 117, a filtering unit 180, and a reference image buffer 190.

[0062] Additionally, the encoding device 100 can generate a bitstream including information encoded by encoding the input image, and output the generated bitstream. The generated bitstream can be stored in a computer-readable recording medium or streamed via a wired / wireless transmission medium.

[0063] Image partitioning unit 110 can partition the input image into various forms to improve the efficiency of video encoding / decoding. That is, the input video consists of multiple images, and for compression efficiency, parallel processing, etc., an image can be partitioned and processed hierarchically. For example, an image can be partitioned into one or more tiles or slices, and then further partitioned into multiple codec tree units (CTUs). Alternatively, an image can first be partitioned into multiple sub-images defined as groups of rectangular slices, and each sub-image can be partitioned into tiles / slices. Here, sub-images can be used to support the function of partially independent encoding / decoding and transmission of images. Since multiple sub-images can be reconstructed individually, this has the advantage of ease of editing in applications where multi-channel input is configured as a single image. Additionally, tiles can be horizontally partitioned to generate bricks. Here, bricks can be used as the basic unit for parallel processing within an image. Furthermore, a CTU can be recursively partitioned into a quad tree (QT), and the terminal node of the partition can be defined as a codec unit (CU). A CTU can be partitioned into a Prediction Unit (PU) as a prediction unit and a Transform Unit (TU) as a transformation unit to perform prediction and partitioning. Alternatively, a CTU can be used as both a prediction unit and / or a transformation unit itself. For flexible partitioning, each CTU can be recursively partitioned into multi-type trees (MTTs) and quadtrees (QTs). Partitioning a CTU into a multi-type tree can begin from the terminal node of a QT, and an MTT can consist of binary trees (BTs) and triple trees (TTs). For example, an MTT structure can be categorized into vertical binary partitioning patterns (SPLIT_BT_VER), horizontal binary partitioning patterns (SPLIT_BT_HOR), vertical ternary partitioning patterns (SPLIT_TT_VER), and horizontal ternary partitioning patterns (SPLIT_TT_HOR). Additionally, during partitioning, the minimum block size (MinQTSize) of the quadtree for the luma block can be set to 16×16, the maximum block size (MaxBtSize) of the binary tree can be set to 128×128, and the maximum block size (MaxTtSize) of the ternary tree can be set to 64×64. Furthermore, the minimum block size (MinBtSize) of the binary tree and the minimum block size (MinTtSize) of the ternary tree can be specified as 4×4, and the maximum depth (MaxMttDepth) of the multi-type tree can be specified as 4. Moreover, to improve the coding efficiency of I-slices, dual-tree CTU partitioning structures utilizing luma and chroma components can be applied.On the other hand, in P and B slices, the luminance and chrominance codec tree blocks (CTBs) within the CTU can be partitioned into single trees sharing a codec tree structure.

[0064] The encoding device 100 can perform encoding on the input image in intra-frame mode and / or inter-frame mode. Alternatively, the encoding device 100 can perform encoding on the input image in a third mode other than intra-frame mode and inter-frame mode (e.g., IBC mode, palette mode, etc.). However, if the third mode has similar functional characteristics to the intra-frame mode or inter-frame mode, it can be classified as an intra-frame mode or inter-frame mode for ease of explanation. In this invention, the third mode is classified and described separately only when a specific explanation of the third mode is required.

[0065] When using intra-frame mode as the prediction mode, switcher 115 can switch to intra-frame mode, and when using inter-frame mode as the prediction mode, switcher 115 can switch to inter-frame mode. Here, intra-frame mode can refer to intra-frame prediction mode, and inter-frame mode can refer to inter-frame prediction mode. Encoding device 100 can generate prediction blocks for input blocks of the input image. In addition, encoding device 100 can encode residual blocks using the residuals of the input block and the prediction block after generating the prediction blocks. The input image can be referred to as the current image as the current coding target. The input block can be referred to as the current block as the current coding target or the coding target block.

[0066] When the prediction mode is intra-frame mode, the intra-frame prediction unit 120 can use samples of already encoded / decoded blocks surrounding the current block as reference samples. The intra-frame prediction unit 120 can perform spatial prediction of the current block using the reference samples, or generate prediction samples for the input block through spatial prediction. In this paper, intra-frame prediction can refer to intra-frame prediction.

[0067] As an intra-frame 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-frame prediction method can be expressed as an intra-frame prediction mode or an intra-frame prediction mode.

[0068] When the prediction mode is inter-frame mode, the motion prediction unit 121 can retrieve the region that best matches the input block from the reference image during motion prediction processing, and derive the motion vector by utilizing the retrieved region. In this case, the search region can be used as the region. The reference image can be stored in the reference image buffer 190. Here, it can be stored in the reference image buffer 190 when encoding / decoding the reference image is performed.

[0069] The motion compensation unit 122 can generate a predicted block for the current block by performing motion compensation using motion vectors. In this paper, inter-frame prediction can refer to inter-picture prediction or motion compensation.

[0070] When the value of the motion vector is not an integer, the motion prediction unit 121 and the motion compensation unit 122 can generate prediction blocks by applying an interpolation filter to a portion of the reference image. To perform inter-frame prediction or motion compensation, the motion prediction and motion compensation modes of the prediction units included in the encoding / decoding unit can be determined based on the encoding / decoding unit. These modes include skip mode, merge mode, advanced motion vector prediction (AMVP) mode, and intra-block copy (IBC) mode, and inter-frame prediction or motion compensation can be performed according to each mode.

[0071] In addition, based on the above inter-frame prediction methods, the following modes can be applied: Affine mode based on sub-PU prediction, Subblock-based Temporal Motion Vector Prediction (SbTMVP) mode, Merge with MVD (MMVD) mode based on PU prediction, and Geometric Partitioning Mode (GPM) mode. In addition, to improve the performance of each mode, the following can be applied: History-based MVP (HMVP), Pairwise Average MVP (PAMVP), Combined Intra / Inter Prediction (CIIP), Adaptive Motion Vector Resolution (AMVR), Bi-Directional Optical-Flow (BDOF), Bi-predictive with CU Weights (BCW), Local Illumination Compensation (LIC), Template Matching (TM), and Overlapped Block Motion Compensation (OBMC).

[0072] Affine mode is a technique used in both AMVP and MERGE modes, and it also boasts high coding efficiency. In existing video codec standards, motion compensation (MC) is performed by considering only the parallel movement of blocks, thus it has the drawback of not being able to adequately compensate for real-world motion (e.g., zooming in / out and rotation). To compensate for this, a four-parameter affine motion model utilizing two control point motion vectors (CPMV) and a six-parameter affine motion model utilizing three control point motion vectors can be used and applied to inter-frame prediction. Here, CPMV is a vector representing one of the affine motion models of the upper left, upper right, and lower left sides of the current block.

[0073] Subtractor 113 can generate a residual block by utilizing the difference between the input block and the prediction block. The residual block can be referred to as a residual signal. The residual signal can represent the difference between the original signal and the prediction signal. Alternatively, the residual signal can be a signal generated by transforming or quantizing, or transforming and quantizing the difference between the original signal and the prediction signal. The residual block can be the residual signal of a block cell.

[0074] Transform unit 130 can generate transform coefficients by performing a transform on the residual block and output the generated transform coefficients. In this document, the transform coefficients can be coefficient values ​​generated by performing a transform on the residual block. When a transform skip mode is applied, transform unit 130 can skip the transform of the residual block.

[0075] Quantization levels can be generated by applying quantization to the transform coefficients or residual signal. In the following text, quantization levels may also be referred to as transform coefficients in the implementation scheme.

[0076] For example, the 4×4 lumen residual block generated by intra-frame prediction can be transformed using basis vectors based on Discrete Sine Transform (DST), and the remaining residual block can be transformed using basis vectors based on Discrete Cosine Transform (DCT). Furthermore, the transformed block can be partitioned into a quadtree shape using Residual Quad Tree (RQT) technology, and after performing transformation and quantization on each transformed block partitioned by RQT, the coded block flag (CBF) can be transmitted when all coefficients become 0 to improve coding efficiency.

[0077] As an alternative, Multiple Transform Selection (MTS) can be applied, selectively utilizing multiple transform bases to perform the transform. That is, instead of partitioning the CU into TUs via RQT, a sub-block transform (SBT) technique can perform a function similar to TU partitioning. Specifically, SBT is applied only to inter-frame prediction blocks, and unlike RQT, it can partition the current block into 1 / 2 or 1 / 4 sizes vertically or horizontally, and then perform the transform on only one block. For example, if the current block is vertically partitioned, the transform can be performed on the leftmost or rightmost block, and if the current block is horizontally partitioned, the transform can be performed on the topmost or bottommost block.

[0078] In addition, the Low Frequency Non-Separable Transform (LFNST) can be applied. This is a secondary transform technique that additionally transforms the residual signal into the frequency domain using DCT or DST. LFNST performs an additional transform on the upper left 4×4 or 8×8 low-frequency region, allowing the residual coefficients to be concentrated on the upper left.

[0079] The quantization unit 140 can generate quantization levels by quantizing the transform coefficients or residual signals according to the quantization parameters (QP), and output the generated quantization levels. In this paper, the quantization unit 140 can quantize the transform coefficients using a quantization matrix.

[0080] For example, quantizers with QP values ​​from 0 to 51 can be used. Alternatively, if the image size is large and high coding efficiency is required, QP values ​​from 0 to 63 can be used. Furthermore, dependent quantization (DQ) methods that utilize two quantizers instead of one can be applied. DQ performs quantization using two quantizers (e.g., Q0 and Q1), but even without signaling information about the use of a particular quantizer, a state transition model can be used to select the quantizer for the next transform coefficient based on the current state.

[0081] Entropy coding unit 150 can generate and output a bitstream by performing entropy coding on values ​​calculated by quantization unit 140 or on encoding / decoding parameter values ​​calculated during encoding, according to a probability distribution. Entropy coding unit 150 can perform entropy coding on information about samples of the image and information used for decoding the image. For example, information used for decoding the image may include syntax elements.

[0082] When entropy coding is applied, symbols are represented such that fewer bits are allocated to symbols with high occurrence probabilities and more bits are allocated to symbols with low occurrence probabilities, thus reducing the size of the bitstream used for encoding the symbols. The entropy coding unit 150 can perform entropy coding using coding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). For example, the entropy coding unit 150 can perform entropy coding by utilizing a variable-length coding / code (VLC) table. Furthermore, the entropy coding unit 150 can derive a binarization method for the target symbol and a probability model for the target symbol / binary representation, and perform arithmetic coding by utilizing the derived binarization method and context model.

[0083] Relatedly, when applying CABAC, to reduce the size of the probability table stored in the decoding device, the table probability update method can be modified into a table update method using a simple equation and then applied. Additionally, two different probability models can be used to obtain more accurate symbol probability values.

[0084] In order to encode the transform coefficient level (quantization level), the entropy coding unit 150 can change the coefficients in two-dimensional block form into one-dimensional vector form by the transform coefficient scanning method.

[0085] The encoding and decoding parameters may include information (flags, indexes, etc.) encoded in the encoding device 100 and signaled to the decoding device 200, such as syntax elements, as well as information derived during the encoding or decoding process, and may represent the information required when encoding or decoding an image.

[0086] In this paper, emitting a flag or index with a signal can indicate that the corresponding flag or index is entropy encoded in the encoder and included in the bitstream, and can also indicate that the corresponding flag or index is entropy decoded from the bitstream in the decoder.

[0087] The encoded current image can be used as a reference image for another image to be processed later. Therefore, 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 image buffer 190.

[0088] The quantization level can be dequantized in dequantization unit 160, or inverse transformed in inverse transform unit 170. The coefficients of dequantization and / or inverse transform can be added to the prediction block via adder 117. In this document, the coefficients of dequantization and / or inverse transform can represent coefficients from which at least one dequantization and inverse transform have been performed, and can represent the reconstructed residual block. Dequantization unit 160 and inverse transform unit 170 can be performed as the inverse of quantization unit 140 and transform unit 130.

[0089] The reconstructed block can be processed by filtering unit 180. Filtering unit 180 can apply all or some of the following filtering techniques to the reconstructed sample, reconstructed block, or reconstructed image: deblocking filter, sample adaptive offset (SAO) filter, adaptive loop filter (ALF), bilateral filter (BIF), luma mapping with chroma scaling (LMCS) filter, etc. Filtering unit 180 can be referred to as an in-loop filter. In this case, it can also be used as a name excluding LMCS.

[0090] Deblocking filters remove block distortion generated at the boundaries between blocks. To determine whether to apply a deblocking filter, the application of the filter to the current block can be determined based on samples included in several rows or columns contained within the block. When applying a deblocking filter to a block, different filters can be applied depending on the desired deblocking filtering intensity.

[0091] To compensate for coding errors using sample-adaptive offsets, appropriate offset values ​​can be added to the sample values. Sample-adaptive offsets can correct the offset between the deblocked image and the original image on a sample-by-sample basis. Methods include dividing the image into a predetermined number of regions, determining the regions to which the offset will be applied, and then applying the offset to those regions; or considering edge information about each sample when applying the offset.

[0092] Bilateral filters (BIF) can also correct the offset from the original image on a sample-by-sample basis for images that have already undergone deblocking.

[0093] Adaptive loop filters can perform filtering based on a comparison between the reconstructed image and the original image. Samples included in the image can be partitioned into predetermined groups, the filter to be applied to each group can be determined, and differential filtering can be performed on each group. Information regarding whether to apply the ALF can be emitted by the codec unit (CU) using a signal, and the form and coefficients of the adaptive loop filter to be applied to each block can vary.

[0094] In luma mapping with chroma scaling (LMCS), luma mapping (LM) represents remapping luma values ​​using a piecewise linear model, and chroma scaling (CS) represents scaling the residual values ​​of the chroma components based on the average luma values ​​of the predicted signal. Specifically, LMCS can be used as an HDR correction technique that reflects the characteristics of High Dynamic Range (HDR) images.

[0095] The reconstructed block or reconstructed image that has passed through filtering unit 180 can be stored in reference image buffer 190. The reconstructed block that has passed through filtering unit 180 can be a portion of the reference image. That is, the reference image is a reconstructed image composed of the reconstructed blocks that have passed through filtering unit 180. The stored reference image can be used later for inter-frame prediction or motion compensation.

[0096] Figure 2 This is a block diagram illustrating the configuration of a decoding device according to an embodiment of the present invention.

[0097] The decoding device 200 can be a decoder, a video decoding device, or an image decoding device.

[0098] refer to Figure 2 The decoding device 200 may include: an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra-frame prediction unit 240, a motion compensation unit 250, an adder 201, a switcher 203, a filtering unit 260, and a reference image buffer 270.

[0099] 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 it can receive a bitstream streamed via a wired / wireless transmission medium. The decoding device 200 can decode the bitstream in intra-frame mode or inter-frame mode. Furthermore, the decoding device 200 can generate a reconstructed image or a decoded image through decoding, and output the reconstructed image or the decoded image.

[0100] When the prediction mode used for decoding is intra-frame mode, switcher 203 can switch to intra-frame mode. Alternatively, when the prediction mode used for decoding is inter-frame mode, switcher 203 can switch to inter-frame mode.

[0101] The decoding device 200 can obtain a reconstructed residual block and generate a prediction block by decoding the input bitstream. When the reconstructed residual block and prediction block are obtained, the decoding device 200 can add them together to generate a reconstructed block that becomes the decoding target. The decoding target block can be referred to as the current block.

[0102] The entropy decoding unit 210 can generate symbols by entropy decoding the bitstream according to the probability distribution. The generated symbols can include symbols in quantization level form. In this paper, the entropy decoding method can be the inverse process of the entropy encoding method described above.

[0103] The entropy decoding unit 210 can change the coefficients of a one-dimensional vector shape into coefficients of a two-dimensional block shape through the transformation coefficient scanning method to decode the transformation coefficient level (quantization level).

[0104] The quantization level can be dequantized in the dequantization unit 220 or inverse transformed in the inverse transform unit 230. The quantization level can be the result of dequantization and / or inverse transform, and can be generated as a reconstructed residual block. In this document, the dequantization unit 220 can apply a quantization matrix to the quantization level. The dequantization unit 220 and inverse transform unit 230 applied to the decoding device can employ the same techniques as those applied to the dequantization unit 160 and inverse transform unit 170 of the aforementioned encoding device.

[0105] When using intra-frame mode, intra-frame prediction unit 240 can generate a prediction block by performing spatial prediction on the current block, which utilizes sample values ​​from blocks already decoded around the target block. Intra-frame prediction unit 240 applied to the decoding apparatus can employ the same techniques as intra-frame prediction unit 120 applied to the aforementioned encoding apparatus.

[0106] When using inter-frame mode, motion compensation unit 250 can generate a prediction block by performing motion compensation on the current block using motion vectors and a reference image stored in reference image buffer 270. When the value of the motion vector is not an integer value, motion compensation unit 250 can generate a prediction block by applying an interpolation filter to a portion of the reference image. To perform motion compensation, the motion compensation mode of the prediction unit included in the corresponding encoding / decoding unit can be determined based on the encoding / decoding unit, whether it is a skip mode, merge mode, AMVP mode, or current image reference mode, and motion compensation can be performed according to each mode. The motion compensation unit 250 applied to the decoding device can apply the same techniques as the motion compensation unit 122 applied to the encoding device described above.

[0107] Adder 201 generates a reconstructed block by adding the reconstructed residual block and the prediction block. Filtering unit 260 can apply at least one of inverse LMCS, deblocking filter, sample adaptive offset, and adaptive loop filter to the reconstructed block or reconstructed image. Filtering unit 260 applied to the decoding apparatus can apply the same filtering techniques as filtering unit 180 applied to the aforementioned encoding apparatus.

[0108] Filtering unit 260 can output a reconstructed image. The reconstructed block or reconstructed image can be stored in reference image buffer 270 and used for inter-frame prediction. The reconstructed block that has passed through filtering unit 260 can be a portion of the reference image. That is, the reference image can be a reconstructed image composed of reconstructed blocks that have passed through filtering unit 260. The stored reference image can be used later for inter-frame prediction or motion compensation.

[0109] Figure 3 This is a schematic diagram illustrating a video encoding / decoding system to which the present invention can be applied.

[0110] The video encoding / decoding system according to the implementation scheme may include an encoding device 10 and a decoding device 20. The encoding device 10 may send encoded video and / or image information or data to the decoding device 20 in the form of files or streaming via a digital storage medium or network.

[0111] The encoding apparatus 10 according to the embodiment may include a video source generation unit 11, an encoding unit 12, and a transmission unit 13. The decoding apparatus 20 according to the embodiment may include a receiving 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 receiving 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.

[0112] The video source generation unit 11 can obtain video / images through processes of capturing, compositing, or generating video / images. The video source generation unit 11 may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device may include, for example, a computer, tablet computer, and smartphone, and can generate video / images (electronically). For example, virtual video / images can be generated by a computer, etc., in which case the process of generating related data can replace the video / image capture process.

[0113] Encoding unit 12 can encode the input video / image. For compression and encoding efficiency, encoding unit 12 can perform a series of processes such as prediction, transformation, and quantization. Encoding unit 12 can output the encoded data (encoded video / image information) as a bitstream. Detailed configuration of encoding unit 12 can also be found in the above description. Figure 1 The encoding device 100 is configured in the same way.

[0114] The transmitting unit 13 can send encoded video / image information or data, output in bitstream form, to the receiving unit 21 of the decoding device 20 via a digital storage medium or network in the form of a file or stream. The digital storage medium can include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitting unit 13 can include elements for generating media files according to a predetermined file format, and may include elements for transmission via a broadcast / communication network. The receiving unit 21 can extract / receive the bitstream from the storage medium or network and send it to the decoding unit 22.

[0115] Decoding unit 22 can decode video / images by performing a series of processes such as inverse quantization, inverse transform, and prediction, corresponding to the operations of encoding unit 12. Detailed configuration of decoding unit 22 can also be found in... Figure 2 The decoding device 200 described above is configured in the same manner.

[0116] Rendering unit 23 can render decoded video / images. The rendered video / images can be displayed through the display unit.

[0117] In the following text, reference will be made to Figures 4 to 11 The present invention describes a method for deriving a cross-component nonlinear model according to an embodiment of the invention, and a method for generating chromaticity prediction blocks using the cross-component nonlinear model.

[0118] In this invention, the term "cross-component nonlinear model" refers to a nonlinear model that represents the correlation between a sample of a chrominance signal and a reconstructed luminance component sample located at the same position, and may be referred to as a cross-component model utilizing a nonlinear model, a nonlinear cross-component model, or a cross-component model utilizing nonlinear model parameters.

[0119] On the other hand, the cross-component linear model (CCLM) uses a linear model that calculates the correlation between samples of the chrominance signal and reconstructed luminance component samples located at the same position to remove redundancy between the luminance and chrominance signals.

[0120] Equation 1 represents the method of generating chromaticity prediction blocks using CCLM.

[0121] [Equation 1] In Equation 1, pred c (i, j) can represent the chroma component samples predicted in the current coding unit (CU) block, rec' L (i, j) can represent the downsampled sample of the reconstructed luma component in the current CU block. Here, the chroma component sample predicted in the CU block can be called the chroma prediction block, and the reconstructed luma component sample in the CU block can be called the reconstructed luma block.

[0122] Furthermore, the linear model parameters α and β in Equation 1 can each be calculated using the linear minimum mean square error (LMMSE) method. Specifically, the values ​​of the linear model parameters α and β can each be derived from neighboring samples.

[0123] When there is both a linear and a nonlinear relationship between the reconstructed luminance and chrominance components, generating accurate chrominance prediction blocks using CCLM may encounter problems. Accordingly, it may be necessary to use methods that utilize not only linear models but also nonlinear models to generate chrominance prediction blocks.

[0124] Equation 2 represents the method of generating chromaticity prediction blocks using a cross-component nonlinear model.

[0125] [Equation 2] In Equation 2, α0, α1, and α2 are model parameters and can be derived using decomposition methods.

[0126] The decomposition method is a reusable matrix decomposition method, and can be any of the LU decomposition, LDL decomposition, and Cholesky decomposition methods. By using the above decomposition methods, linear or nonlinear systems can be solved more efficiently.

[0127] Specifically, the decomposition method is a matrix decomposition method that decomposes any matrix into a product of matrices, and can be used to efficiently calculate matrices or various model parameters when solving linear equation systems.

[0128] LU decomposition is a method of factoring a matrix into the product of lower triangular and upper triangular matrices. Generally, LU decomposition has the advantage of being computationally fast.

[0129] LDL decomposition is a method for decomposing a symmetric positive definite matrix into a product of a diagonal matrix and a lower triangular matrix. Generally, compared to LU decomposition, LDL decomposition is a numerically stable computational method.

[0130] Cholesky decomposition is a method of decomposing a matrix into the product of a lower triangular matrix and its conjugate transpose. Typically, when computing linear or nonlinear system equations, Cholesky decomposition is about twice as efficient as LU decomposition.

[0131] In Equation 2, bitDepth and midValue are the bit depth and midpoint value, respectively. As an example, in the case of a video sequence utilizing an N-bit image, bitDepth can be set to N, and midValue can be set to 2. N >>1 or 2 N-1 .

[0132] Equation 2 can reconstruct both the linear and nonlinear relationships between the luminance and chrominance components, and thus can generate accurate chrominance prediction blocks.

[0133] Equation 1 represents the formula for calculating the chromaticity prediction block using a linear model. Equation 2 represents the formula for calculating the chromaticity prediction block using a nonlinear model.

[0134] When the chromaticity subsample is YCbCr422 or YCbCr444, the importance of the chromaticity components may be high. In particular, when the chromaticity subsample is YCbCr444, each chromaticity component can have the same importance as the luminance component. In this case, as shown in Equations 1 and 2, applying the same linear model or the same nonlinear model to each chromaticity component may be inefficient.

[0135] Accordingly, different linear or nonlinear models can be applied to each chromaticity component, as shown in the following implementation scheme.

[0136] Equation 3 represents the method of generating chromaticity prediction blocks for each of the different chromaticity components using different linear models.

[0137] [Equation 3] In equation 3, pred cb (i, j) can represent the Cb chromaticity component sample predicted in the current codec unit block, rec' L (i, j) can represent the downsampled sample of the luma component reconstructed in the current codec unit block. Additionally, the linear model parameter α... cb and β cb The linear minimum mean square error (LMMSE) method can be used to calculate the linear model parameter α using neighboring reference samples of the Cb chromaticity block and neighboring reference samples of the corresponding luminance block. cband β cb The value can be derived from neighboring samples instead of being transmitted / parsed.

[0138] In equation 3, pred cr (i, j) can represent the predicted Cr chromaticity component sample in the current codec unit block, rec' L (i, j) can represent the downsampled sample of the luma component reconstructed in the current codec unit block. Additionally, the linear model parameter α... cr and β cr The LMMSE method can be used to calculate the linear model parameter α using adjacent reference samples of the Cr chromaticity block and adjacent reference samples of the corresponding luminance block. cr and β cr The value can be derived from neighboring samples instead of being transmitted / parsed.

[0139] Equation 4 represents a method for generating prediction blocks for the Cb chromaticity component and the Cr chromaticity component using different cross-component nonlinear models.

[0140] [Equation 4] In equation 4, pred cb (i, j) can represent the Cb chromaticity component sample predicted in the current codec unit block, rec' L (i, j) can represent the luminance component samples that are reconstructed and downsampled in the same codec unit block.

[0141] In equation 4, pred cr (i, j) can represent the predicted Cr chromaticity component sample in the current codec unit block, rec' L (i, j) can represent samples of the luminance component that are reconstructed and downsampled within the same encoding / decoding unit block. Model parameter α 0_cb α 1_cb and α 2_cb Or α 0_cr α 1_cr and α 2_cr The decomposition method can be used to derive the results for adjacent reference samples of the Cb chromaticity block and adjacent reference samples of the corresponding luminance block, or adjacent reference samples of the Cr chromaticity block and adjacent reference samples of the corresponding luminance block.

[0142] In Equation 4, bitDepth and midValue are the bit depth and midpoint, respectively. Furthermore, in the case of a video sequence using N-bit images, bitDepth can be set to N, and midValue can be set to 2. N>>1 or 2 N-1 .

[0143] Equation 4 can reconstruct both the linear and nonlinear relationships between the luminance component and each chrominance component, and thus can generate accurate chrominance prediction blocks.

[0144] According to embodiments of the present invention, the cross-component model (CCM) can be classified as upper-left CCM, upper-side CCM, or left-side CCM based on the position of the reference sample used for model derivation.

[0145] Figure 4 This is a schematic diagram illustrating a reference sample for deriving the upper left cross component model LT_CCM according to an embodiment of the present invention.

[0146] refer to Figure 4 When the size of chroma block 410 is W×H, the adjacent reference samples used to derive the cross-component model parameters are the upper reference sample W' and the left reference sample H'. The upper reference sample can be set to W'=W, and the left reference sample can be set to H'=H.

[0147] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of chromaticity block 410 can be used. c 411 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 400 and corresponding to the chrominance reference sample 411. L 401. Deriving the cross-component model parameters. That is, the parameters of the upper left cross-component model can be derived based on the chromaticity reference sample 411 and the downsampled luminance reference sample 401 at the juxtaposed position of the chromaticity reference sample 411. Here, the sampling rate can be arbitrarily determined.

[0148] Figure 5 This is a schematic diagram illustrating a reference sample for deriving the upper cross component model T_CCM according to an embodiment of the present invention.

[0149] refer to Figure 5 When the size of chroma block 510 is W×H, the adjacent reference sample used to derive the cross-component model parameters is the upper reference sample W', and the upper reference sample can be set to W'=W+H.

[0150] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of chromaticity block 510 can be used. c 511 is sampled and selected, and can be downsampled from the luminance reference sample Rec' which is adjacent to the luminance block 500 and corresponds to the juxtaposition position of the chrominance reference sample 511.L 501. Deriving the cross-component model parameters. That is, the upper cross-component model parameters can be derived based on the chromaticity reference sample 511 and the downsampled luminance reference sample 501 at the juxtaposed position of the chromaticity reference sample 511. Here, the sampling rate can be arbitrarily determined.

[0151] On the other hand, the upper reference sample W', which serves as the adjacent reference sample used to derive the upper cross-component model parameters, can be set to W'=W. That is, any adjacent reference sample can be selected as the adjacent reference sample used to derive the nonlinear model parameters.

[0152] Figure 6 This is a schematic diagram illustrating a reference sample for deriving the left-side transcomponent nonlinear model L_CCM according to an embodiment of the present invention.

[0153] refer to Figure 6 When the size of chroma block 610 is W×H, the adjacent reference sample used to derive the cross-component model parameters is the left reference sample H', and the left reference sample H' can be set to H'=W+H.

[0154] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of chromaticity block 610 can be used. c 611 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 600 and corresponding to the chrominance reference sample 611. L 601. Deriving the cross-component model parameters. That is, the left-side cross-component model parameters can be derived based on the chromaticity reference sample 611 and the downsampled luminance reference sample 601 at the juxtaposed position of the chromaticity reference sample 611. Here, the sampling rate can be arbitrarily determined.

[0155] On the other hand, the left reference sample H', which serves as the adjacent reference sample used to derive the parameters of the left-side cross-component model, can be set to H'=H. That is, any adjacent reference sample can be selected as the adjacent reference sample used to derive the parameters of the nonlinear model.

[0156] Figures 4 to 6 The reference samples used in the derivation of the cross-component model when the chromaticity subsampling is YCbCr420 are shown. On the other hand, when the chromaticity subsampling is YCbCr422 or YCbCr444, adjacent reference samples of the luminance block can be determined by using downsampling rates independently determined for the Cb and Cr chromaticity components, and the cross-component model for the Cb and Cr chromaticity components can be derived independently.

[0157] For example, when the chroma subsampling is YCbCr422, the reference sample adjacent to the luma block used in deriving the cross-component model can be a sample with a downsampling factor of 2. On the other hand, when the chroma subsampling is YCbCr444, the adjacent reference sample of the luma block corresponding to the adjacent reference sample of the chroma block can be used as the reference sample adjacent to the luma block used in deriving the cross-component model. In other words, the reference sample used in the cross-component model can be determined without performing downsampling on the reference sample adjacent to the luma block.

[0158] According to an embodiment of the present invention, the cross-component models of the Cb chromaticity component and the Cr chromaticity component can be classified into the upper left cross-component model LT_CCM, the left cross-component model L_CCM, and the upper cross-component model T_CCM based on the position of the reference sample used for model derivation.

[0159] Figure 7 This is a schematic diagram illustrating a reference sample for deriving the upper left cross component model LT_CCM according to an embodiment of the present invention.

[0160] refer to Figure 7 When the Cb chromaticity block 710 and the Cr chromaticity block 720 have a size of W×H, the adjacent reference samples used to derive the cross-component model parameters are the upper reference sample W' and the left reference sample H'. The upper reference sample can be set to W'=W, and the left reference sample can be set to H'=H.

[0161] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cb chromaticity block 710 can be used. cb 711 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 700 and corresponding to the chrominance reference sample 711. L 701. Derive the cross-component model parameters of the Cb chromaticity component. That is, the upper left cross-component model parameters of the Cb chromaticity component can be derived based on the chromaticity reference sample 711 and the juxtaposed downsampled luminance reference sample 701.

[0162] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cr chromaticity block 720 can be used. cr 721 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 700 and corresponding to the chrominance reference sample 721. L 701. Derive the cross-component model parameters of the Cr chromaticity component. That is, the upper left cross-component model parameters of the Cr chromaticity component can be derived based on the chromaticity reference sample 721 and the juxtaposed downsampled luminance reference sample 701.

[0163] Here, the sampling rate can be arbitrarily determined. Furthermore, the sampling rate can be determined differently depending on the chromaticity component. That is, the downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample can be determined independently of each other.

[0164] Figure 8 This is a schematic diagram illustrating a reference sample for deriving the upper cross component model T_CCM according to an embodiment of the present invention.

[0165] refer to Figure 8 When the size of Cb chromaticity block 810 and Cr chromaticity block 820 is W×H, the adjacent reference sample used to derive the cross-component model parameters is the upper reference sample W', and the upper reference sample can be set to W'=W+H.

[0166] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cb chromaticity block 810 can be used. cb 811 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 800 and corresponding to the chrominance reference sample 811. L 801. Derive the cross-component model parameters of the Cb chromaticity component. That is, the upper cross-component model parameters of the Cb chromaticity component can be derived based on the chromaticity reference sample 811 and the juxtaposed downsampled luminance reference sample 801.

[0167] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cr chromaticity block 820 can be used. cr 821 performs sampling and selection, and can downsample the luminance reference sample Rec' from the juxtaposed position adjacent to the luminance block 800 and corresponding to the chrominance reference sample 821. L 801. Derive the cross-component model parameters of the Cr chromaticity component. That is, the upper cross-component model parameters of the Cr chromaticity component can be derived based on the chromaticity reference sample 821 and the juxtaposed downsampled luminance reference sample 801.

[0168] On the other hand, the upper reference sample W', which serves as the adjacent reference sample used to derive the upper cross-component model parameters, can be set to W'=W. That is, any adjacent reference sample can be selected as the adjacent reference sample used to derive the nonlinear model parameters.

[0169] Furthermore, the sampling rate can be arbitrarily determined. Additionally, the sampling rate can be determined based on the different chromaticity components. That is, the downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample can be determined independently of each other.

[0170] Figure 9 This is a schematic diagram illustrating a reference sample for deriving the left-side transcomponent nonlinear model L_CCM according to an embodiment of the present invention.

[0171] refer to Figure 9 When the size of Cb chromaticity block 910 and Cr chromaticity block 920 is W×H, the adjacent reference sample used to derive the cross-component model parameters is the left reference sample H', and the left reference sample can be set to H'=W+H.

[0172] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cb chromaticity block 910 can be used. cb 911 is sampled and selected, and can be downsampled from the luminance reference sample Rec' located adjacent to luminance block 900 and corresponding to the juxtaposition position of chrominance reference sample 911. L 901. Derive the cross-component model parameters of the Cb chromaticity component. That is, the left-side cross-component model parameters of the Cb chromaticity component can be derived based on the chromaticity reference sample 911 and the juxtaposed downsampled luminance reference sample 901.

[0173] In addition, to reduce the computational complexity of deriving the cross-component model parameters, the adjacent chromaticity reference samples Rec' of the Cr chromaticity block 920 can be used. cr 921 is sampled and selected, and can be downsampled from the luminance reference sample Rec' located adjacent to luminance block 900 and corresponding to the juxtaposition position of chrominance reference sample 921. L 901. Derive the cross-component model parameters of the Cr chromaticity component. That is, the left-side cross-component model coefficients of the Cr chromaticity component can be derived based on the chromaticity reference sample 921 and the juxtaposed downsampled luminance reference sample 901.

[0174] On the other hand, the left reference sample H', which serves as the adjacent reference sample used to derive the parameters of the left-side cross-component model, can be set to H'=H. That is, any adjacent reference sample can be selected as the adjacent reference sample used to derive the parameters of the nonlinear model.

[0175] Furthermore, the sampling rate can be arbitrarily determined. Additionally, the sampling rate can be determined based on the different chromaticity components. That is, the downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample can be determined independently of each other.

[0176] According to an embodiment of the present invention, a method for generating prediction blocks of chromaticity components by applying a CCM with nonlinear model parameters can be described as follows.

[0177] According to an embodiment of the present invention, instead of using a cross-component linear model, a method utilizing only a cross-component nonlinear model can be used to generate chromaticity prediction blocks. Accordingly, chromaticity prediction blocks can be generated using the upper left cross-component nonlinear model, the upper cross-component nonlinear model, and the left cross-component nonlinear model utilizing the nonlinear model parameters of Equation 2.

[0178] The proposed method can utilize cross-component nonlinear models to replace existing cross-component linear models. Correspondingly, the method for transmitting / parsing the syntax for cross-component nonlinear models can replace existing methods for transmitting / parsing the syntax for cross-component linear models. Implementation schemes for the method of transmitting / parsing the syntax for cross-component nonlinear models are shown in Table 1 below.

[0179] [Table 1] In Table 1, ccmEnabled can be information indicating whether the cross-component nonlinear model is available. According to the implementation, when ccmEnabled is 1, it indicates that the cross-component nonlinear model is available; when ccmEnabled is 0, it indicates that the cross-component nonlinear model is unavailable. Alternatively, when ccmEnabled is 1, the ccm_mode_flag can be emitted using a signal.

[0180] `ccm_mode_flag` is a flag indicating the chroma intra-prediction mode based on a cross-component nonlinear model. According to the implementation, when `ccm_mode_flag` is 1, it indicates a chroma intra-prediction mode based on a cross-component nonlinear model; when it is 0, it indicates a normal chroma intra-prediction mode not based on a cross-component nonlinear model. Conversely, when `ccm_mode_flag` is 1, the signal `ccm_mode_idx` can be emitted; when it is 0, the signal `intra_chroma_pred_mode` indicating the type of normal chroma intra-prediction mode can be emitted. Here, `intra_chroma_pred_mode` can indicate any one of Direct Mode (DM), Planar Mode, DC Mode, Vertical Mode, and Horizontal Mode. Conversely, when `ccm_mode_flag` is not emitted, its value is considered to be 0.

[0181] ccm_mode_idx is an index indicating the type of cross-component nonlinear model, and can indicate any one of the top-left cross-component nonlinear model, the top-left cross-component nonlinear model, and the left-left cross-component nonlinear model.

[0182] According to another embodiment of the invention, chromaticity prediction blocks can be generated by selectively utilizing cross-component linear models and cross-component nonlinear models.

[0183] Based on the method of selectively utilizing cross-component linear and cross-component nonlinear models, a syntax for identifying whether a cross-component linear or nonlinear model is used can be employed. For example, when using a cross-component model to derive the chroma prediction block of the current block, additional flag information for identifying whether a cross-component linear or nonlinear model is used can be transmitted / parsed. Then, an index indicating a specific model among the three types of cross-component models can be transmitted / parsed. Accordingly, the cross-component model can be derived based on the transmitted / parsed information, and the chroma prediction block of the current block can be derived based on the cross-component model. An implementation scheme for transmitting / parsed the syntax for the cross-component model can be shown in Table 2 below.

[0184] [Table 2] In Table 2, `ccmEnabled` indicates whether the cross-component model is available. According to the implementation, a value of 1 for `ccmEnabled` indicates that the cross-component model is available, while a value of 0 indicates that the cross-component model is unavailable. Here, the cross-component model can include both linear and nonlinear cross-component models. Alternatively, when the value of `ccmEnabled` is 1, the `ccm_mode_flag` signal can be emitted.

[0185] `ccm_mode_flag` is a flag indicating the chroma intra-prediction mode based on a cross-component model. According to the implementation, when `ccm_mode_flag` is 1, it indicates a chroma intra-prediction mode based on a cross-component model; when it is 0, it indicates a normal chroma intra-prediction mode not based on a cross-component model. Conversely, when `ccm_mode_flag` is 1, `ccm_linear_model_flag` and `ccm_mode_idx` can be emitted using signals. Conversely, when `ccm_mode_flag` is 0, `intra_chroma_pred_mode`, indicating the type of normal chroma intra-prediction mode, can be emitted using signals. Here, `intra_chroma_pred_mode` can indicate any one of direct mode (DM), planar mode, DC mode, vertical mode, and horizontal mode. Conversely, when `ccm_mode_flag` is not emitted using signals, its value can be considered to be 0.

[0186] ccm_linear_model_flag is a flag used to distinguish between cross-component linear models and cross-component nonlinear models. When the value of ccm_linear_model_flag is 1, it indicates a cross-component linear model, and when the value of ccm_linear_model_flag is 0, it indicates a cross-component nonlinear model.

[0187] ccm_mode_idx is an index indicating the type of cross-component model, and can indicate any one of the top-left cross-component model, the top cross-component model, and the left cross-component model.

[0188] As an example, when the value of ccm_linear_model_flag is 1, any one of the following cross-component linear models can be used, depending on the value of ccm_mode_idx: the upper left cross-component linear model, the upper cross-component linear model, and the left cross-component linear model. Conversely, when the value of ccm_linear_model_flag is 0, any one of the following cross-component nonlinear models can be used, depending on the value of ccm_mode_idx: the upper left cross-component nonlinear model, the upper cross-component nonlinear model, and the left cross-component nonlinear model.

[0189] On the other hand, in Table 2, the ccm_linear_model_flag signal is emitted, and then the ccm_mode_idx signal is emitted, but the order in which the signals are emitted for the two syntaxes can be arbitrarily determined.

[0190] The syntax structure proposed in Table 2 can be used to generate chroma prediction blocks by selecting linear and nonlinear model parameters at the encoder / decoder unit level based on the syntax elements emitted by the signal.

[0191] According to another embodiment of the invention, chromaticity prediction blocks can be generated by utilizing a method that implicitly determines the cross-component model in the cross-component linear model and the cross-component nonlinear model.

[0192] In other words, instead of using information such as cclm_linear_model_flag, an implicit method can be used to select the appropriate model from cross-component linear and cross-component nonlinear models.

[0193] For example, the decoder can be based on α as a parameter of the linear model. cb β cb α cr and β cr A cross-component linear model is derived, based on α as a parameter of the nonlinear model. 0_cb α 1_cb α 2_cb α 0_cr α 1_cr and α 2_cr The cross-component nonlinear model is derived. The decoder can apply each of the derived cross-component models to the neighboring reference samples of the luma block corresponding to the current chroma block, thereby calculating the predicted reference samples of the neighboring reference samples of the current chroma block.

[0194] Additionally, the decoder can be based on the prediction reference sample PredC_ref_ calculated using a cross-component linear model. linear The difference between the value of the reconstructed reference sample RecC_ref and the value of the predicted reference sample PredC_ref calculated using the cross-component nonlinear model.non-linear The optimal cross-component model is selected based on the difference between the value of the predicted reference sample and the value of the reconstructed reference sample RecC_ref. In other words, the decoder can select the optimal cross-component model from both linear and nonlinear models based on the error values ​​of the predicted reference sample calculated using the linear cross-component model and the error values ​​of the predicted reference sample calculated using the nonlinear cross-component model.

[0195] Here, the comparison between cross-component linear models and cross-component nonlinear models can be achieved using various methods, such as the sum of absolute differences (SAD), the sum of square errors (SSE), and the sum of absolute transformed differences (SATD).

[0196] According to an embodiment of the present invention, when encoding and decoding a luma block corresponding to the current chroma block in intra template matching prediction (IntraTMP) mode or intra block copy (IBC) mode, cross-component linear model parameters or cross-component nonlinear model parameters can be derived using block vector (BV) information used for intra-frame prediction. The method for calculating cross-component linear model parameters or cross-component nonlinear model parameters using BV information can be described as follows.

[0197] Figure 10 This is a schematic diagram illustrating a method for calculating cross-component linear model parameters or cross-component nonlinear model parameters using block vector information predicted within a frame, according to an embodiment of the present invention.

[0198] refer to Figure 10 When the reconstructed luminance block 1021 corresponding to the current chroma block 1011 of the chroma picture 1010 is encoded based on intra-frame template matching or intra-frame block copying, the matching luminance block 1024 indicated by the block vector 1023 of the corresponding intra-frame mode can be determined in the reconstructed luminance picture 1020.

[0199] According to an embodiment of the present invention, the cross-component model parameters can be calculated by the correlation between the reference sample 1012 of the current chroma component block and the reference sample 1025 of the matched luminance signal 1024, instead of by the correlation between the chroma reference sample 1012 of the current chroma component block 1011 and the luminance reference sample 1022 of the corresponding reconstructed luminance block 1021.

[0200] Here, Equation 3 or Equation 4 can be used to calculate the cross-component linear model parameters or cross-component nonlinear model parameters for the Cb and Cr chromaticity components. Alternatively, Equation 1 or Equation 2 can be used to calculate the cross-component linear model parameters or cross-component nonlinear model parameters.

[0201] In addition, such as Figure 10 As shown, it can be used as follows Figure 4 The reference sample shown is used to derive the cross-component model LT_CCM on the upper left side to derive the cross-component linear model parameters or the cross-component nonlinear model parameters. However, this is only one implementation scheme, and it can be used with, for example, Figure 5 The reference sample shown is used to derive the upper cross component model T_CCM, or as... Figure 6 The reference sample shown is used to derive the parameters of the cross-component linear model or the cross-component nonlinear model.

[0202] When calculating cross-component linear model parameters or cross-component nonlinear model parameters for each chromaticity component, one can utilize, for example... Figure 7 The reference sample shown is used to derive the upper left cross-component model LT_CCM, such as... Figure 8 The reference sample shown is used to derive the upper cross component model T_CCM, or as... Figure 9 The reference sample shown is used to derive the left-side cross-component nonlinear model L_CCM to derive the cross-component linear model parameters or cross-component nonlinear model parameters for each chromaticity component.

[0203] Figure 11 This is a flowchart illustrating a method for decoding an image according to an embodiment of the present invention.

[0204] The image decoding device can derive a cross-component model, including the Cb cross-component model and the Cr cross-component model, for predicting the chromaticity component block of the current block by using reference samples (S1110).

[0205] The image decoding device can generate a prediction block of the Cb chromaticity component block of the current block by utilizing the Cb cross-component model (S1120).

[0206] The image decoding device can generate a prediction block of the Cr chromaticity component block of the current block by utilizing the Cr cross-component model (S1130).

[0207] Here, the Cb transcomponent model and the Cr transcomponent model can be determined independently of each other.

[0208] Here, the Cb cross-component model and the Cr cross-component model can be derived based on the parameters, bit depth and intermediate values ​​of the cross-component model.

[0209] Here, the parameters of the cross-component model can be derived based on any of the decomposition methods, such as LU decomposition, LDL decomposition, and Cholesky decomposition.

[0210] Here, the reference sample may include a Cb chromaticity reference sample adjacent to the Cb chromaticity component block of the current block, a luminance reference sample corresponding to the Cb chromaticity reference sample, a Cr chromaticity reference sample adjacent to the Cr chromaticity component block of the current block, and a luminance reference sample corresponding to the Cr chromaticity reference sample.

[0211] Here, the cross-component model can be one of the upper left cross-component model, the upper cross-component model, and the left cross-component model.

[0212] Here, when the cross-component model is the top-left cross-component model, the reference sample may include the reference sample located on the top-left side of the chroma component block of the current block and the reference sample located on the top-left side of the luminance component block of the current block.

[0213] Here, when the cross-component model is the upper cross-component model, the reference sample may include the reference sample located above the chromaticity component block of the current block and the reference sample located above the luminance component block of the current block.

[0214] Here, when the cross-component model is a left-side cross-component model, the reference sample may include a reference sample located to the left of the chroma component block of the current block and a reference sample located to the left of the luminance component block of the current block.

[0215] Here, the luminance reference sample corresponding to the Cb chromaticity reference sample and the luminance reference sample corresponding to the Cr chromaticity reference sample can be reference samples downsampled according to the downsampling rate.

[0216] Here, the downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample can be determined independently of each other.

[0217] Here, deriving the Cb transcomponent model and the Cr transcomponent model may include determining the Cb transcomponent model and the Cr transcomponent model as transcomponent linear models or transcomponent nonlinear models.

[0218] Here, determining whether the Cb transcomponent model and the Cr transcomponent model are transcomponent linear models or transcomponent nonlinear models can be based on model information indicating either the transcomponent linear model or the transcomponent nonlinear model.

[0219] Here, the determination of whether the Cb cross-component model and the Cr cross-component model are cross-component linear models or cross-component nonlinear models can be based on the comparison between the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component linear model and the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component nonlinear model.

[0220] Here, when the intra-prediction mode of the current block's luminance component block is a predetermined prediction mode, the luminance reference sample corresponding to the Cb chromaticity reference sample and the luminance reference sample corresponding to the Cr chromaticity reference sample can be luminance reference samples adjacent to the matching block indicated by the block vector of the current block's luminance component block.

[0221] Here, the predetermined prediction mode can be either intra-frame template matching mode or intra-frame block copy mode.

[0222] On the other hand, it can also be performed in the image encoding method. Figure 11 The steps described herein. Additionally, it can be achieved by including... Figure 11 The image encoding method described in the document generates a bitstream. The bitstream can be stored on a non-volatile computer-readable recording medium and can also be transmitted (or streamed).

[0223] Figure 12 An exemplary content streaming system applicable to embodiments of the present invention is shown.

[0224] like Figure 12 As shown, the content streaming system implementing the present invention can mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0225] The encoding server compresses content received from multimedia input devices such as smartphones, cameras, and CCTV into digital data to generate a bitstream, which is then sent to the streaming server. As another example, if multimedia input devices such as smartphones, cameras, and CCTV directly generate the bitstream, the encoding server can be omitted.

[0226] The bitstream can be generated by the image encoding method and / or image encoding apparatus of the present invention, and the streaming server can temporarily store the bitstream during the sending or receiving of the bitstream.

[0227] A streaming server sends 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 notify the user of any available services. When a user requests a desired service from the web server, the web server sends it to the streaming server, and the streaming server can send multimedia data to the user. In this case, the content streaming system may include a separate control server, which can control the commands / responses between devices within the content streaming system.

[0228] A streaming server can receive content from media storage devices and / or encoding servers. For example, when receiving content from an 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 period of time.

[0229] Examples of user devices may include mobile phones, smartphones, laptops, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, board PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, HMDs), digital televisions, desktop computers, digital signage, etc.

[0230] In the above-mentioned content streaming system, each server can operate as a distributed server, in which case the data received from each server can be distributed and processed.

[0231] The above embodiments can be performed in the same or corresponding manner as the encoding and decoding devices. Furthermore, at least one or a combination of the above embodiments can be used to encode / decode images.

[0232] The order in which the above-described embodiments are applied can differ in the encoding and decoding devices. Alternatively, the order in which the above-described embodiments are applied can be the same in both the encoding and decoding devices.

[0233] The above-described implementation scheme can be performed on each of the luminance and chrominance signals. Alternatively, the above-described implementation scheme can be performed on both the luminance and chrominance signals in the same way.

[0234] In the above embodiments, the method is described based on a flowchart having a series of steps or units. However, the present invention is not limited to the order of the steps; on the contrary, some steps may be performed simultaneously with other steps or in a different order. Furthermore, those skilled in the art should understand that the steps in the flowchart are not mutually exclusive, and other steps may be added to the flowchart or some steps may be deleted from the flowchart without affecting the scope of the present invention.

[0235] The implementation scheme can be implemented in the form of program instructions, which can be executed by various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include individual program instructions, data files, data structures, or combinations thereof. The program instructions recorded in the computer-readable recording medium may be specifically designed and constructed for this invention or may be well known to those skilled in the art of computer software.

[0236] The bitstream generated by the encoding method according to the above embodiment can be stored in a non-volatile computer-readable recording medium. Furthermore, the bitstream stored in the non-volatile computer-readable recording medium can be decoded by the decoding method according to the above embodiment.

[0237] Examples of computer-readable recording media include: magnetic recording media such as hard disks, floppy disks, and magnetic tapes; optical data storage media such as CD-ROMs or DVD-ROMs; magneto-optical media such as floppy disks; and hardware devices such as read-only memory (ROM), random access memory (RAM), flash memory, etc., specifically configured to store and execute program instructions. Examples of program instructions include not only machine language code formatted by a compiler but also high-level language code that can be implemented by a computer using an interpreter. The hardware device may be configured to operate by one or more software modules or vice versa to perform the processes according to the invention.

[0238] While the invention has been described with respect to specific items such as detailed elements, as well as limited embodiments and drawings, these are provided only to aid in a more complete understanding of the invention, and the invention is not limited to the embodiments described above. Those skilled in the art will understand that various modifications and changes can be made based on the above description.

[0239] Therefore, the spirit of the present invention should not be limited to the above embodiments, and the entire scope of the appended claims and their equivalents shall fall within the scope and spirit of the present invention.

[0240] Industrial applicability This invention can be used in apparatuses for encoding / decoding images and in recording media for storing bit streams.

Claims

1. A method for decoding an image, the method comprising: The cross-component model for predicting the chromaticity component block of the current block is derived by using reference samples. The cross-component model includes the Cb cross-component model and the Cr cross-component model. By utilizing the Cb cross-component model, a predicted block of the Cb chromaticity component block of the current block is generated; as well as The predicted block for the Cr chromaticity component of the current block is generated by utilizing the Cr cross-component model. Among them, the Cb cross-component model and the Cr cross-component model are determined independently of each other.

2. The method according to claim 1, wherein, The Cb and Cr cross-component models are derived based on the parameters, bit depth, and intermediate values ​​of the cross-component model.

3. The method according to claim 2, wherein, The parameters of the cross-component model are derived using one of the following decomposition methods: LU decomposition, LDL decomposition, and Cholesky decomposition.

4. The method according to claim 1, wherein, The reference samples include Cb chromaticity reference samples adjacent to the Cb chromaticity component block of the current block, luminance reference samples corresponding to the Cb chromaticity reference samples, Cr chromaticity reference samples adjacent to the Cr chromaticity component block of the current block, and luminance reference samples corresponding to the Cr chromaticity reference samples.

5. The method according to claim 4, wherein, The cross-component model is one of the upper left cross-component model, the upper cross-component model, and the left cross-component model.

6. The method according to claim 5, wherein, When the cross-component model is the top-left cross-component model, the reference samples include the reference sample located on the top-left side of the chroma component block of the current block and the reference sample located on the top-left side of the luma component block of the current block.

7. The method according to claim 5, wherein, When the cross-component model is the upper cross-component model, the reference samples include the reference samples located above the chrominance component block of the current block and the reference samples located above the luma component block of the current block.

8. The method according to claim 5, wherein, When the cross-component model is a left-side cross-component model, the reference samples include the reference samples to the left of the chroma component block of the current block and the reference samples to the left of the luma component block of the current block.

9. The method according to claim 4, wherein, The luminance reference samples corresponding to the Cb chromaticity reference sample and the luminance reference samples corresponding to the Cr chromaticity reference sample are reference samples downsampled according to the downsampling rate.

10. The method according to claim 9, wherein, The downsampling rate applied to the luminance reference sample corresponding to the Cb chromaticity reference sample and the downsampling rate applied to the luminance reference sample corresponding to the Cr chromaticity reference sample are determined independently of each other.

11. The method according to claim 4, wherein, The derivation of the Cb transcomponent model and the Cr transcomponent model includes determining whether the Cb transcomponent model and the Cr transcomponent model are transcomponent linear models or transcomponent nonlinear models.

12. The method according to claim 11, wherein, The Cb transcomponent model and the Cr transcomponent model are determined to be either transcomponent linear models or transcomponent nonlinear models, based on model information indicating one of the transcomponent linear models and transcomponent nonlinear models.

13. The method according to claim 11, wherein, The Cb cross-component model and the Cr cross-component model are determined as either cross-component linear models or cross-component nonlinear models, based on the comparison between the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component linear model and the error values ​​of the Cb chromaticity reference samples and Cr chromaticity reference samples predicted based on the cross-component nonlinear model.

14. The method according to claim 4, wherein, When the intra-prediction mode of the current block's luminance component block is a predetermined prediction mode, the luminance reference sample corresponding to the Cb chromaticity reference sample and the luminance reference sample corresponding to the Cr chromaticity reference sample are luminance reference samples adjacent to the matching block indicated by the block vector of the current block's luminance component block.

15. The method according to claim 14, wherein, The predetermined prediction mode is one of the intra-frame template matching mode and the intra-frame block copy mode.

16. A method for encoding an image, the method comprising: The Cb cross-component model and Cr cross-component model for predicting the chromaticity component block of the current block are derived by using reference samples. By utilizing the Cb cross-component model, a predicted block of the Cb chromaticity component block of the current block is generated; as well as The predicted block for the Cr chromaticity component of the current block is generated by utilizing the Cr cross-component model. Among them, the Cb cross-component model and the Cr cross-component model are determined independently of each other.

17. A non-volatile computer-readable recording medium for storing a bitstream, said bitstream being generated by a method for encoding images. in, Methods for encoding images include: The Cb cross-component model and Cr cross-component model for predicting the chromaticity component block of the current block are derived by using reference samples. By utilizing the Cb cross-component model, a predicted block of the Cb chromaticity component block of the current block is generated; and The predicted block for the Cr chromaticity component of the current block is generated by utilizing the Cr cross-component model. Among them, 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 method for encoding an image, the method comprising transmitting the bitstream, in, Methods for encoding images include: The Cb cross-component model and Cr cross-component model for predicting the chromaticity component block of the current block are derived by using reference samples. By utilizing the Cb cross-component model, a predicted block of the Cb chromaticity component block of the current block is generated; and The predicted block for the Cr chromaticity component of the current block is generated by utilizing the Cr cross-component model. Among them, the Cb cross-component model and the Cr cross-component model are determined independently of each other.

Images