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

Abstract

Provided are an image encoding / decoding method and device, a recording medium storing a bitstream, and a transmission method. The image decoding method may comprise the steps of: generating a chroma mode list of a current chroma block; deriving a chroma intra prediction mode of the current chroma block on the basis of the chroma mode list; and generating a prediction block of the current chroma block on the basis of the chroma intra prediction mode, wherein the chroma mode list includes at least one candidate intra prediction mode among a default mode, a derivation-based chroma mode, a direct mode, and a direct block vector mode.

Description

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

[0001] The present invention relates to a video encoding / decoding method, a device, and a recording medium storing a bitstream. Specifically, the present invention relates to a video encoding / decoding method, a device, and a recording medium storing a bitstream using a chrominance intra prediction mode list including one or more chrominance intra prediction candidate modes.

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

[0003] Specifically, in a video encoding / decoding method and device, intra prediction is a technology for predicting a current coding unit (CU) block (e.g., a current block) using previously restored reference pixels. At this time, chroma intra prediction, unlike luma intra prediction, performs chroma intra prediction using not only the default intra prediction mode, but also the direct mode (DM), the decoder-side intra mode derivation chroma mode (DIMD chroma mode), and the direct block vector (DBV) mode as chroma intra prediction candidate modes. Specifically, a chroma intra prediction mode list is constructed using the chroma intra prediction candidate modes, and chroma intra prediction can be performed on a current coding unit block, etc., using the constructed chroma intra prediction mode list.

[0004] At this time, the chrominance intra prediction candidate modes can be sorted in a chrominance intra prediction mode list in a fixed order. Therefore, when performing chrominance intra prediction using a chrominance intra prediction mode list in which the chrominance intra prediction candidate modes are sorted in a fixed order, the coding efficiency of chrominance intra prediction may be limited. Therefore, a method for efficiently reordering the candidate modes in the chrominance intra prediction mode list is required.

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

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

[0007] An image decoding method according to one embodiment of the present invention includes the steps of generating a chrominance mode list of a current chrominance block, deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list, and generating a prediction block of the current chrominance block based on the chrominance intra prediction mode, wherein the chrominance mode list may include at least one candidate intra prediction mode among a default mode, a derivation-based chrominance mode, a direct mode, and a direct block vector mode.

[0008] In the above image decoding method, the default mode may be derived using available neighboring blocks among at least one neighboring block adjacent to the current chrominance block.

[0009] In the above image decoding method, when at least one neighboring block is not available, the default mode may be derived using a preset intra prediction mode.

[0010] In the above image decoding method, when the default mode is identical to an intra prediction mode derived by at least one of the induction-based chrominance mode, the direct mode, and the direct block vector mode, the default mode is replaced with a predetermined intra prediction mode and derived, and the predetermined intra prediction mode may be characterized in that it includes at least one of a DC mode, a planar mode, a vertical mode, and a horizontal mode.

[0011] In the above image decoding method, the step of generating the chrominance mode list may be characterized by sorting the at least one candidate intra prediction mode in the chrominance mode list based on an error of each of the at least one candidate intra prediction mode.

[0012] In the above image decoding method, the step of generating the chrominance mode list may be characterized by arranging the derived-based chrominance mode, the direct mode, and the direct block vector mode within the chrominance mode list.

[0013] In the above image decoding method, the error of the inductive-based chrominance mode may be calculated as a difference value between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode derived according to the inductive-based chrominance mode and at least one sample adjacent to the current template.

[0014] In the above image decoding method, the error of the direct mode may be calculated as a difference value between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode derived according to the direct mode and at least one sample adjacent to the current template.

[0015] In the above image decoding method, the error of the direct block vector mode may be calculated as a difference value between a restoration value of a current template including samples adjacent to the current chrominance block and a restoration value of a corresponding template including samples adjacent to a corresponding block indicated by a block vector of the current chrominance block.

[0016] In the above image decoding method, the step of generating the color difference mode list may be characterized by sorting the default modes within the color difference mode list.

[0017] In the above image decoding method, the error of the default mode may be calculated as a difference value between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode, which is the default mode, and at least one sample adjacent to the current template.

[0018] In the above image decoding method, it may be characterized by sorting the default mode, the derived-based chrominance mode, the direct mode, and the direct block vector mode in the chrominance mode list.

[0019] A video encoding method according to one embodiment of the present invention includes the steps of generating a chrominance mode list of a current chrominance block, deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list, and generating a prediction block of the current chrominance block based on the chrominance intra prediction mode, wherein the chrominance mode list may include at least one candidate intra prediction mode among a default mode, a derivation-based chrominance mode, a direct mode, and a direct block vector mode.

[0020] A non-transitory computer-readable recording medium according to one embodiment of the present invention can store a bitstream generated by a video encoding method, the method comprising the steps of: generating a chrominance mode list of a current chrominance block; deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list; and generating a prediction block of the current chrominance block based on the chrominance intra prediction mode, wherein the chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derivation-based chrominance mode, a direct mode, and a direct block vector mode.

[0021] A bitstream transmission method according to one embodiment of the present invention comprises a step of transmitting the bitstream, a step of generating a chrominance mode list of a current chrominance block, a step of deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list, and a step of generating a prediction block of the current chrominance block based on the chrominance intra prediction mode, wherein the chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derivation-based chrominance mode, a direct mode, and a direct block vector mode. A bitstream generated by a video encoding method can be transmitted.

[0022] The features briefly summarized above of the present invention are merely exemplary aspects of the detailed description of the present invention described below and do not limit the scope of the present invention.

[0023] According to the present invention, a video encoding / decoding method and device with improved encoding / decoding efficiency can be provided.

[0024] In addition, according to the present invention, a method for generating a chrominance prediction block using information of previously restored chrominance pixels and / or corresponding luminance blocks surrounding a current coding unit (CU) chrominance block (e.g., a current chrominance block) can be provided.

[0025] In addition, according to the present invention, a method for generating a chrominance prediction block can be provided by rearranging candidate chrominance modes in a chrominance intra prediction mode list using a template-based intra prediction mode derivation method and using the rearranged chrominance intra prediction mode list.

[0026] In addition, according to the present invention, encoding efficiency can be improved in chrominance intra prediction.

[0027] In addition, according to the present invention, the encoding efficiency of chrominance intra prediction can be increased by efficiently reconstructing the chrominance intra prediction mode list and efficiently reducing the bits required to code chrominance intra prediction mode information.

[0028] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0029] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0030] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0031] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0032] FIG. 4 is a diagram illustrating neighboring chrominance blocks used to construct candidate modes of a chrominance intra prediction mode list of a current chrominance block according to one embodiment of the present invention.

[0033] FIG. 5 is a diagram illustrating a method for calculating an error of a chrominance intra prediction mode using a template-based intra prediction mode derivation method according to one embodiment of the present invention.

[0034] FIG. 6 is a diagram illustrating a method for calculating an error of a chrominance intra prediction mode based on a block vector according to one embodiment of the present invention.

[0035] Figure 7 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

[0036] FIG. 8 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0037] The present invention is susceptible to various modifications and embodiments. Therefore, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and substitutes falling within the spirit and scope of the present invention. In the drawings, similar reference numerals designate the same or similar functions throughout. The shape and size of elements in the drawings may be provided by way of example only for clarity. The detailed description of the exemplary embodiments described below refers to the accompanying drawings, which illustrate specific embodiments. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments. It should be understood that the various embodiments, while different, are not necessarily mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention. Furthermore, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be modified without departing from the spirit and scope of the embodiment. Accordingly, the detailed description set forth below is not intended to be taken in a limiting sense, and the scope of the exemplary embodiments, if properly described, is defined only by the appended claims, along with the full scope equivalents to which such claims are entitled.

[0038] In the present invention, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term "and / or" includes a combination of multiple related described items or any of multiple related described items.

[0039] The components shown in the embodiments of the present invention are independently depicted to represent different characteristic functions, and do not mean that each component is composed of separate hardware or a single software component. That is, each component is listed and included as a separate component for convenience of explanation, and at least two components among each component may be combined to form a single component, or a single component may be divided into multiple components to perform a function, and such integrated and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

[0040] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In addition, some components of the present invention are not essential components that perform essential functions in the present invention and may be optional components merely for performance enhancement. The present invention may be implemented by including only components essential to realizing the essence of the present invention, excluding components used only for performance enhancement, and a structure including only essential components, excluding optional components used only for performance enhancement, is also within the scope of the present invention.

[0041] In embodiments, the term "at least one" may mean one of a number greater than or equal to 1, such as 1, 2, 3, and 4. In embodiments, the term "a plurality of" may mean one of a number greater than or equal to 2, such as 2, 3, and 4.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In describing the embodiments of this specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of this specification, the detailed description will be omitted. The same reference numerals will be used for identical components in the drawings, and duplicate descriptions of identical components will be omitted.

[0043] Glossary of Terms

[0044] Hereinafter, “video” may mean a single picture constituting a video, or may refer to the video itself. For example, “encoding and / or decoding of a video” may mean “encoding and / or decoding of a video,” or may mean “encoding and / or decoding of one of the videos constituting the video.”

[0045] Hereinafter, the terms "video" and "movie" may be used interchangeably and have the same meaning. Furthermore, the target image may be an encoding target image, which is the target of encoding, and / or a decoding target image, which is the target of decoding. Furthermore, the target image may be an input image input to an encoding device, or an input image input to a decoding device. Here, the target image may have the same meaning as the current image.

[0046] Hereinafter, the terms encoder and image encoding device may be used interchangeably and have the same meaning.

[0047] Hereinafter, the terms decoder and image decoding device may be used interchangeably and have the same meaning.

[0048] Hereinafter, “image”, “picture”, “frame” and “screen” may be used with the same meaning and may be used interchangeably.

[0049] Hereinafter, the term "target block" may refer to an encoding target block, which is the target of encoding, and / or a decoding target block, which is the target of decoding. Furthermore, the target block may refer to a current block, which is the target of current encoding and / or decoding. For example, the terms "target block" and "current block" may be used interchangeably and have the same meaning.

[0050] Hereinafter, "block" and "unit" may be used with the same meaning and may be used interchangeably. In addition, "unit" may mean including a luminance component block and a corresponding chroma component block to distinguish it from a block. For example, a coding tree unit (CTU) may be composed of one luma component (Y) coding tree block (CTB) and two chroma component (Cb, Cr) coding tree blocks associated with it.

[0051] Hereinafter, the terms “sample,” “pixel,” and “pixel” may be used interchangeably and have the same meaning. Here, a sample may represent a basic unit that constitutes a block.

[0052] Hereinafter, “inter” and “between screens” may be used interchangeably and have the same meaning.

[0053] Hereinafter, “intra” and “within screen” may be used interchangeably and have the same meaning.

[0054]

[0055]

[0056] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0057] The encoding device (100) may be an encoder, a video encoding device, or an image encoding device. A video may include one or more images. The encoding device (100) may sequentially encode one or more images.

[0058] Referring to FIG. 1, the encoding device (100) may include an image segmentation unit (110), an intra prediction unit (120), a motion prediction unit (121), a motion compensation unit (122), a switch (115), a subtractor (113), a transformation unit (130), a quantization unit (140), an entropy encoding unit (150), an inverse quantization unit (160), an inverse transformation unit (170), an adder (117), a filter unit (180), and a reference picture buffer (190).

[0059] Additionally, the encoding device (100) can generate a bitstream including encoded information through encoding an input image and output the generated bitstream. The generated bitstream can be stored in a computer-readable recording medium or can be streamed via a wired / wireless transmission medium.

[0060] The video segmentation unit (110) can segment the input video into various forms to increase the efficiency of video encoding / decoding. That is, the input video is composed of multiple pictures, and one picture can be hierarchically segmented and processed for compression efficiency, parallel processing, etc. For example, one picture can be segmented into one or more tiles or slices, which can then be segmented into multiple Coding Tree Units (CTUs). Alternatively, one picture can first be segmented into multiple sub-pictures defined as groups of rectangular slices, and each sub-picture can then be segmented into the tiles / slices. Here, the sub-pictures can be utilized to support the function of partially independently encoding / decoding and transmitting the picture. Since multiple sub-pictures can each be individually restored, there is an advantage of easy editing in applications that configure multi-channel input into a single picture. In addition, tiles can be segmented horizontally to generate bricks. Here, a brick can be utilized as the basic unit of intra-picture parallel processing. In addition, one CTU can be recursively split into a quadtree (QT), and the terminal node of the split can be defined as a coding unit (CU). The CU can be split into a prediction unit (PU) and a transformation unit (TU), and prediction and splitting can be performed. Meanwhile, the CU can be utilized as a prediction unit and / or a transformation unit itself. Here, for flexible splitting, each CTU can be recursively split into a multi-type tree (MTT) as well as a quadtree (QT). Splitting of a CTU into a multi-type tree can start from the terminal node of a QT, and the MTT can be composed of a binary tree (BT) and a triple tree (TT).For example, the MTT structure can be divided into vertical binary split mode (SPLIT_BT_VER), horizontal binary split mode (SPLIT_BT_HOR), vertical ternary split mode (SPLIT_TT_VER), and horizontal ternary split mode (SPLIT_TT_HOR). In addition, the minimum block size (MinQTSize) of the quad tree of the luminance block during splitting can be set to 16x16, the maximum block size (MaxBtSize) of the binary tree can be set to 128x128, and the maximum block size (MaxTtSize) of the triple tree can be set to 64x64. In addition, the minimum block size (MinBtSize) of the binary tree and the minimum block size (MinTtSize) of the triple tree can be set to 4x4, and the maximum depth (MaxMttDepth) of the multi-type tree can be set to 4. Additionally, to improve the encoding efficiency of the I slice, a dual tree can be applied that uses different CTU partition structures for luminance and chrominance components. On the other hand, in the P and B slices, the luminance and chrominance CTBs (Coding Tree Blocks) within the CTU can be partitioned into a single tree that shares the coding tree structure.

[0061] The encoding device (100) may perform encoding on the input image in intra mode and / or inter mode. Alternatively, the encoding device (100) may perform encoding on the input image in a third mode (e.g., IBC mode, Palette mode, etc.) other than the intra mode and inter mode. However, if the third mode has functional characteristics similar to the intra mode or inter mode, it may be classified as intra mode or inter mode for convenience of explanation. In the present invention, the third mode will be classified and described separately only when a specific description is required.

[0062] When the intra mode is used as the prediction mode, the switch (115) can be switched to intra, and when the inter mode is used as the prediction mode, the switch (115) can be switched to inter. Here, the intra mode can mean an intra-screen prediction mode, and the inter mode can mean an inter-screen prediction mode. The encoding device (100) can generate a prediction block for an input block of an input image. In addition, after the prediction block is generated, the encoding device (100) can encode a residual block using a residual of the input block and the prediction block. The input image can be referred to as a current image that is currently a target of encoding. The input block can be referred to as a current block that is currently a target of encoding or an encoding target block.

[0063] When the prediction mode is intra mode, the intra prediction unit (120) can use samples of blocks already encoded / decoded around the current block as reference samples. The intra prediction unit (120) can perform spatial prediction on the current block using the reference samples, and can generate prediction samples for the input block through spatial prediction. Here, intra prediction can mean prediction within the screen.

[0064] As an intra prediction method, non-directional prediction modes such as DC mode and Planar mode, as well as directional prediction modes (e.g., 65 directions) can be applied. Here, the intra prediction method can be expressed as an intra prediction mode or an intra-screen prediction mode.

[0065] When the prediction mode is inter mode, the motion prediction unit (121) can search for an area that best matches the input block from the reference image during the motion prediction process and derive a motion vector using the searched area. At this time, the area can be used as a search area. The reference image can be stored in the reference picture buffer (190). Here, when encoding / decoding for the reference image is processed, it can be stored in the reference picture buffer (190).

[0066] The motion compensation unit (122) can generate a prediction block for the current block by performing motion compensation using a motion vector. Here, inter prediction may mean inter-screen prediction or motion compensation.

[0067] The above motion prediction unit (121) and motion compensation unit (122) can generate a prediction block by applying an interpolation filter to a portion of the reference image when the value of the motion vector does not have an integer value. In order to perform inter-screen prediction or motion compensation, it is possible to determine whether the motion prediction and motion compensation method of the prediction unit included in the corresponding encoding unit is one of Skip Mode, Merge Mode, Advanced Motion Vector Prediction (AMVP) mode, and Intra Block Copy (IBC) mode based on the encoding unit, and perform inter-screen prediction or motion compensation according to each mode.

[0068] In addition, based on the above inter-screen prediction method, the AFFINE mode of sub-PU based prediction, the SbTMVP (Subblock-based Temporal Motion Vector Prediction) mode, and the MMVD (Merge with MVD) mode and the GPM (Geometric Partitioning Mode) mode of PU based prediction can be applied. In addition, in order to improve the performance of each mode, the HMVP (History based MVP), the PAMVP (Pairwise Average MVP), the CIIP (Combined Intra / Inter Prediction), the AMVR (Adaptive Motion Vector Resolution), the BDOF (Bi-Directional Optical-Flow), the BCW (Bi-predictive with CU Weights), the LIC (Local Illumination Compensation), the TM (Template Matching), and the OBMC (Overlapped Block Motion Compensation) can be applied.

[0069] Among these, AFFINE mode is a technology that is used in both AMVP and MERGE modes and also has high encoding efficiency. In the existing video coding standard, since MC (Motion Compensation) is performed by considering only the parallel translation of the block, there was a disadvantage in that it could not properly compensate for motions that occur in reality, such as zoom in / out and rotation. To supplement this, a 4-parameter affine motion model using two control point motion vectors (CPMV) and a 6-parameter affine motion model using three control point motion vectors can be applied to inter prediction. Here, CPMV is a vector representing the affine motion model of one of the upper left, upper right, and lower left of the current block.

[0070] The subtractor (113) can generate a residual block using the difference between the input block and the predicted block. The residual block may also be referred to as a residual signal. The residual signal may refer to the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming, quantizing, or transforming and quantizing the difference between the original signal and the predicted signal. The residual block may be a residual signal in block units.

[0071] The transform unit (130) can perform a transform on the residual block to generate a transform coefficient and output the generated transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit (130) may also skip the transform on the residual block.

[0072] Quantized levels can be generated by applying quantization to transform coefficients or residual signals. In the following embodiments, quantized levels may also be referred to as transform coefficients.

[0073] For example, a 4x4 luminance residual block generated through within-screen prediction can be transformed using a basis vector based on DST (Discrete Sine Transform), and the remaining residual blocks can be transformed using a basis vector based on DCT (Discrete Cosine Transform). In addition, through RQT (Residual Quad Tree) technology, the transform block is divided into a quad tree shape for one block, and after performing transformation and quantization on each transform block divided through RQT, a coded block flag (cbf) can be transmitted to increase encoding efficiency when all coefficients become 0.

[0074] Another alternative is to apply Multiple Transform Selection (MTS) technology, which selectively performs transformation using multiple transformation bases. That is, instead of dividing CUs into TUs via RQT, a Sub-block Transform (SBT) technology can perform a function similar to TU division. Specifically, SBT is applied only to inter-screen prediction blocks, and unlike RQT, it can divide the current block into ½ or ¼ blocks vertically or horizontally, and then perform transformation on only one of the blocks. For example, in a vertically divided block, the transformation can be performed on the leftmost or rightmost block, and in a horizontally divided block, the transformation can be performed on the topmost or bottommost block.

[0075] Additionally, LFNST (Low Frequency Non-Separable Transform), a secondary transform technique that further transforms the residual signal converted to the frequency domain through DCT or DST, can be applied. LFNST additionally performs a transform on the low-frequency region of 4x4 or 8x8 in the upper left, which allows the residual coefficients to be concentrated in the upper left.

[0076] The quantization unit (140) can generate a quantized level by quantizing a transform coefficient or residual signal according to a quantization parameter (QP), and can output the generated quantized level. At this time, the quantization unit (140) can quantize the transform coefficient using a quantization matrix.

[0077] For example, a quantizer with QP values ​​of 0 to 51 can be used. Alternatively, if the image size is larger and high encoding efficiency is required, a QP of 0 to 63 can be used. In addition, a Dependent Quantization (DQ) method that uses two quantizers instead of a single quantizer can be applied. DQ performs quantization using two quantizers (e.g., Q0 and Q1), but even without signaling information about the use of a specific quantizer, the quantizer to be used for the next transform coefficient can be selected based on the current state through a state transition model.

[0078] The entropy encoding unit (150) can generate a bitstream by performing entropy encoding according to a probability distribution on values ​​produced by the quantization unit (140) or coding parameter values ​​produced during the encoding process, and can output the bitstream. The entropy encoding unit (150) can perform entropy encoding on information about image samples and information for decoding the image. For example, the information for decoding the image can include syntax elements, etc.

[0079] When entropy encoding is applied, a small number of bits are allocated to symbols with a high occurrence probability, and a large number of bits are allocated to symbols with a low occurrence probability, thereby representing the symbols, whereby the size of the bit string for the symbols to be encoded can be reduced. The entropy encoding unit (150) can use an encoding method such as exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding. For example, the entropy encoding unit (150) can perform entropy encoding using a Variable Length Coding / Code (VLC) table. In addition, the entropy encoding unit (150) may perform arithmetic encoding using the binarization method, probability model, and context model derived from the binarization method of the target symbol and the probability model of the target symbol / bin.

[0080] In this regard, when applying CABAC, the table probability update method can be changed to a simple formula-based table update method to reduce the size of the probability table stored in the decryption device. Furthermore, two different probability models can be used to obtain more accurate symbol probability values.

[0081] The entropy encoding unit (150) can change a two-dimensional block form coefficient into a one-dimensional vector form through a transform coefficient scanning method to encode a transform coefficient level (quantized level).

[0082] Coding parameters may include not only information (flags, indexes, etc.) encoded in an encoding device (100) and signaled to a decoding device (200), such as syntax elements, but also information derived during an encoding process or a decoding process, and may mean information necessary when encoding or decoding an image.

[0083] Here, signaling a flag or index may mean that the encoder entropy encodes the flag or index and includes it in the bitstream, and that the decoder entropy decodes the flag or index from the bitstream.

[0084] The encoded current image can be used as a reference image for other images to be processed later. Accordingly, the encoding device (100) can reconstruct or decode the encoded current image again and store the reconstructed or decoded image as a reference image in the reference picture buffer (190).

[0085] The quantized level can be dequantized in the dequantization unit (160) and inversely transformed in the inverse transformation unit (170). The dequantized and / or inversely transformed coefficients can be combined with a prediction block through an adder (117), and a reconstructed block can be generated by combining the dequantized and / or inversely transformed coefficients and the prediction block. Here, the dequantized and / or inversely transformed coefficients refer to coefficients on which at least one of dequantization and inverse transformation has been performed, and may refer to a reconstructed residual block. The dequantization unit (160) and the inverse transformation unit (170) can be performed in the reverse process of the quantization unit (140) and the transformation unit (130).

[0086] The restoration block may pass through a filter unit (180). The filter unit (180) may apply a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), a bilateral filter (BIF), a Luma Mapping with Chroma Scaling (LMCS), etc. as a filtering technique, in whole or in part, to the restoration sample, restoration block, or restoration image. The filter unit (180) may also be referred to as an in-loop filter. In this case, the in-loop filter is also used as a name excluding LMCS.

[0087] A deblocking filter can remove block distortion that occurs at the boundaries between blocks. Whether to apply a deblocking filter to the current block can be determined based on the samples contained in several columns or rows within the block. When applying a deblocking filter to a block, different filters can be applied depending on the required deblocking filtering strength.

[0088] Sample adaptive offset can be used to compensate for encoding errors by adding an appropriate offset value to sample values. Sample adaptive offset can compensate for the offset from the original image on a sample-by-sample basis for deblocked images. This can be done by dividing the samples contained in the image into a fixed number of regions, determining the regions to be offset, and applying the offset to those regions. Alternatively, the offset can be applied by considering the edge information of each sample.

[0089] Bilateral filter (BIF) can also compensate for the offset from the original image on a sample-by-sample basis for the deblocked image.

[0090] An adaptive loop filter can perform filtering based on a comparison between a reconstructed image and the original image. By dividing the samples contained in the image into predetermined groups and determining the filter to be applied to each group, filtering can be performed differentially for each group. Information regarding whether to apply an adaptive loop filter can be signaled for each coding unit (CU), and the shape and filter coefficients of the adaptive loop filter applied to each block can vary.

[0091] In LMCS (Luma Mapping with Chroma Scaling), luma mapping (LM) refers to remapping luminance values ​​through a piece-wise linear model, and chroma scaling (CS) refers to a technique that scales the residual values ​​of chrominance components according to the average luminance value of the prediction signal. In particular, LMCS can be utilized as an HDR correction technique that reflects the characteristics of HDR (High Dynamic Range) images.

[0092] The restored block or restored image that has passed through the filter unit (180) may be stored in the reference picture buffer (190). The restored block that has passed through the filter unit (180) may be a part of the reference image. In other words, the reference image may be a restored image composed of restored blocks that have passed through the filter unit (180). The stored reference image may be used for inter-screen prediction or motion compensation thereafter.

[0093] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0094] The decoding device (200) may be a decoder, a video decoding device, or an image decoding device.

[0095] Referring to FIG. 2, the decoding device (200) may include an entropy decoding unit (210), an inverse quantization unit (220), an inverse transformation unit (230), an intra prediction unit (240), a motion compensation unit (250), an adder (201), a switch (203), a filter unit (260), and a reference picture buffer (270).

[0096] The decoding device (200) can receive a bitstream output from the encoding device (100). The decoding device (200) can receive a bitstream stored in a computer-readable recording medium, or a bitstream streamed through a wired / wireless transmission medium. The decoding device (200) can perform decoding on the bitstream in intra mode or inter mode. In addition, the decoding device (200) can generate a restored image or a decoded image through decoding, and can output the restored image or the decoded image.

[0097] If the prediction mode used for decryption is intra mode, the switch (203) can be switched to intra. If the prediction mode used for decryption is inter mode, the switch (203) can be switched to inter.

[0098] The decoding device (200) can decode the input bitstream to obtain a reconstructed residual block and generate a prediction block. Once the reconstructed residual block and the prediction block are obtained, the decoding device (200) can generate a reconstructed block to be decoded by adding the reconstructed residual block and the prediction block. The block to be decoded may be referred to as a current block.

[0099] The entropy decoding unit (210) can generate symbols by performing entropy decoding according to a probability distribution for the bitstream. The generated symbols may include symbols in the form of quantized levels. Here, the entropy decoding method may be the reverse process of the entropy encoding method described above.

[0100] The entropy decoding unit (210) can change a one-dimensional vector-shaped coefficient into a two-dimensional block-shaped coefficient through a transform coefficient scanning method to decode a transform coefficient level (quantized level).

[0101] The quantized level can be inversely quantized in the inverse quantization unit (220) and inversely transformed in the inverse transformation unit (230). The quantized level can be generated as a restored residual block as a result of performing inverse quantization and / or inverse transformation. At this time, the inverse quantization unit (220) can apply a quantization matrix to the quantized level. The inverse quantization unit (220) and inverse transformation unit (230) applied to the decoding device can apply the same technology as the inverse quantization unit (160) and inverse transformation unit (170) applied to the encoding device described above.

[0102] When intra mode is used, the intra prediction unit (240) can generate a predicted block by performing spatial prediction on the current block using sample values ​​of already decoded blocks surrounding the block to be decoded. The intra prediction unit (240) applied to the decoding device can apply the same technology as the intra prediction unit (120) applied to the encoding device described above.

[0103] When the inter mode is used, the motion compensation unit (250) can generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer (270) on the current block. The motion compensation unit (250) can generate a prediction block by applying an interpolation filter to a portion of the reference image when the value of the motion vector does not have an integer value. In order to perform motion compensation, it is possible to determine whether the motion compensation method of the prediction unit included in the corresponding encoding unit is skip mode, merge mode, AMVP mode, or current picture reference mode based on the encoding unit, and motion compensation can be performed according to each mode. The motion compensation unit (250) applied to the decoding device can apply the same technology as the motion compensation unit (122) applied to the encoding device described above.

[0104] The adder (201) can add the restored residual block and the predicted block to generate a restored block. The filter unit (260) can apply at least one of an Inverse-LMCS, a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the restored block or restored image. The filter unit (260) applied to the decoding device can apply the same filtering technology as that applied to the filter unit (180) applied to the encoding device described above.

[0105] The filter unit (260) can output a restored image. The restored block or restored image can be stored in the reference picture buffer (270) and used for inter prediction. The restored block that has passed through the filter unit (260) can be a part of the reference image. In other words, the reference image can be a restored image composed of restored blocks that have passed through the filter unit (260). The stored reference image can be used for inter-screen prediction or motion compensation thereafter.

[0106] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0107] A video coding system according to one embodiment may include an encoding device (10) and a decoding device (20). The encoding device (10) may transmit encoded video and / or image information or data to the decoding device (20) in the form of a file or streaming via a digital storage medium or a network.

[0108] An encoding device (10) according to one embodiment may include a video source generation unit (11), an encoding unit (12), and a transmission unit (13). A decoding device (20) according to one embodiment may include a reception unit (21), a decoding unit (22), and a rendering unit (23). The encoding unit (12) may be referred to as a video / image encoding unit, and the decoding unit (22) may be referred to as a video / image decoding unit. The transmission unit (13) may be included in the encoding unit (12). The reception unit (21) may be included in the decoding unit (22). The rendering unit (23) may include a display unit, and the display unit may be configured as a separate device or an external component.

[0109] The video source generation unit (11) can obtain video / images through a process of capturing, synthesizing, or generating video / images. The video source generation unit (11) can include a video / image capture device and / or a video / image generation device. The video / image capture device can include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, a virtual video / image can be generated through a computer, etc., in which case the video / image capture process can be replaced with a process of generating related data.

[0110] The encoding unit (12) can encode the input video / image. The encoding unit (12) can perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency. The encoding unit (12) can output encoded data (encoded video / image information) in the form of a bitstream. The detailed configuration of the encoding unit (12) can also be configured in the same manner as the encoding device (100) of FIG. 1 described above.

[0111] The transmission unit (13) can transmit encoded video / image information or data output in the form of a bitstream to the reception unit (21) of the decoding device (20) via a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit (13) can include an element for generating a media file through a predetermined file format and can include an element for transmission via a broadcasting / communication network. The reception unit (21) can extract / receive the bitstream from the storage medium or network and transmit it to the decoding unit (22).

[0112] The decoding unit (22) can decode video / image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding unit (12). The detailed configuration of the decoding unit (22) can also be configured in the same manner as the decoding device (200) of FIG. 2 described above.

[0113] The rendering unit (23) can render the decrypted video / image. The rendered video / image can be displayed through the display unit.

[0114]

[0115] Hereinafter, with reference to FIGS. 4 to 7, a method for deriving candidate modes of chrominance intra prediction for chrominance intra prediction according to an embodiment of the present invention and a method for generating a list of chrominance intra prediction modes using chrominance intra prediction candidate modes will be specifically described.

[0116]

[0117] The candidate modes in the chrominance intra prediction mode list may be composed of at least one intra prediction mode among the four default intra prediction modes, the direct mode (DM), the decoder side intra mode derivation chroma mode (DIMD chroma mode), and the direct block vector (DBV) mode.

[0118] Here, the decoder-side intra mode derivation can be abbreviated as ‘induction-based intra prediction mode’.

[0119] Unlike luminance intra prediction, chroma intra prediction requires that candidate modes of a chroma intra prediction mode list be constructed by arranging candidate modes of predetermined intra prediction modes in a predetermined order. Therefore, this may present limitations in efficiently constructing a chroma intra prediction mode list.

[0120] Accordingly, according to the present invention, a candidate mode of a chrominance intra prediction mode list can be configured using intra prediction mode information of a surrounding neighboring block of a current coding unit (CU) chrominance block (current chrominance block).

[0121]

[0122] FIG. 4 is a diagram illustrating neighboring chrominance blocks used to construct candidate modes of a chrominance intra prediction mode list of a current chrominance block according to one embodiment of the present invention.

[0123] Referring to FIG. 4, L0 to L3, A0 to A3, AL, BL, and AR are neighboring chroma blocks adjacent to the current chroma block. Here, the size of the neighboring chroma block may be a minimum unit block for storing intra prediction mode information. According to one embodiment of the present invention, in order to configure a candidate mode of a chroma intra prediction mode list, N intra prediction mode(s) may be derived from neighboring chroma blocks of the current chroma block instead of four predetermined basic intra prediction modes. Here, N may be any positive integer.

[0124] By applying the intra prediction mode of the L3 block and the intra prediction mode of the A3 block to the method of generating the MPM (most probable mode) list for luminance intra prediction, candidate modes for chrominance intra prediction can be derived. Here, using the block at the L3 position and the block at the A3 position to derive candidate modes for chrominance intra prediction may be one embodiment. That is, any block surrounding the current chrominance block can be used to derive candidate modes for chrominance intra prediction.

[0125] Here, in order to derive candidate modes for chrominance intra prediction, only available blocks among the neighboring blocks surrounding the current chrominance block can be used. For example, if an AL ~ AR or AL ~ BL block is located outside the boundary of a picture, slice, tile, etc., is an inter-predicted block, or information about an intra-prediction mode to be referenced from a neighboring block is not derived, the block may be an unavailable block. That is, in order to derive candidate modes for chrominance intra prediction, a neighboring block located within the boundary of a picture, slice, tile, etc. among the neighboring blocks surrounding the current chrominance block and being intra-predicted may be used. Alternatively, the intra-prediction mode of a neighboring block included in an unavailable area may be regarded as a preset non-directional mode (e.g., planar mode or DC mode) to derive a candidate intra-prediction mode.

[0126] According to another embodiment, N intra prediction mode(s) can be derived by searching neighboring chroma blocks(es) of a current chroma block in a predetermined order. The N intra prediction modes can be intra prediction modes of neighboring chroma blocks of the current chroma block. Alternatively, the N intra prediction modes can be intra prediction modes derived based on statistical values ​​of intra prediction modes of neighboring chroma blocks of the current chroma block. Here, the statistical values ​​can be values ​​such as a maximum value, a minimum value, an average value, a mode value, etc. Alternatively, the N intra prediction modes can be intra prediction modes derived by adding or subtracting an offset having a predetermined integer value to the intra prediction mode or statistical values ​​of intra prediction modes of neighboring chroma blocks of the current chroma block. Here, the surrounding neighboring blocks of the current block can be determined arbitrarily. In addition, when determining the N candidate mode(s), only intra prediction modes that do not overlap through a redundancy check can be used as candidate modes. In addition, N here can be any positive integer.

[0127] Here, in order to derive candidate modes for chrominance intra prediction, only available blocks among the surrounding neighboring blocks of the current chrominance block can be used. For example, if an AL ~ AR or AL ~ BL block is located outside the boundary of a picture, slice, tile, etc., is an inter-predicted block, or information about an intra-prediction mode to be referenced from a neighboring block is not derived, the block may be an unavailable block. That is, in order to derive candidate modes for chrominance intra prediction, a neighboring block that is located inside the boundary of a picture, slice, tile, etc., among the surrounding neighboring blocks of the current chrominance block, and has been intra-predicted, can be used. Alternatively, the intra-prediction mode of a neighboring block included in an unavailable area may be regarded as a preset non-directional mode (e.g., a planar mode or a DC mode), and a candidate intra-prediction mode may be derived.

[0128] A candidate mode of a chrominance intra prediction mode list can be determined using at least two modes from among the N intra prediction mode(s), the direct mode, the derived-based intra prediction mode, and the direct block vector mode determined through the above-described embodiment. Here, if some of the N intra prediction modes determined through the above-described embodiment are identical to the direct mode or the derived-based intra prediction mode, the overlapping mode can be replaced with any mode from among the basic intra prediction modes (e.g., the planar mode, the horizontal mode, the vertical mode, the DC mode). Replacing the overlapping mode with the planar mode, the horizontal mode, the vertical mode, and the DC mode can be one embodiment. That is, the overlapping mode can be replaced with any intra prediction mode.

[0129] In another embodiment, the overlapping modes and the replaced intra prediction modes may be configured differently for each specific coding unit, such as a picture, slice, tile, or coding tree unit (CTU). For example, the replaced intra prediction modes may be configured with the most frequently occurring modes in the corresponding picture, slice, tile, or coding tree unit (CTU).

[0130] According to one embodiment of the present invention, the chrominance intra prediction mode list may include candidate modes constructed using N intra prediction mode(s) derived from surrounding neighboring blocks of the current chrominance block, a direct mode, a derived-based intra prediction mode, and a direct block vector mode instead of the existing four basic intra prediction modes.

[0131] That is, according to one embodiment of the present invention, instead of using preset intra prediction modes, a chrominance intra prediction candidate mode list can be constructed by variably deriving chrominance intra prediction mode information of neighboring blocks surrounding the current block.

[0132] According to one embodiment of the present invention, neighboring chrominance blocks used to construct candidate modes of the chrominance intra prediction mode list of the current chrominance block may be as illustrated in FIG. 4. However, this may be an embodiment for constructing candidate modes of the chrominance intra prediction mode list of the current chrominance block. In order to construct candidate modes of the chrominance intra prediction mode list of the current chrominance block, any number of neighboring chrominance blocks at any position adjacent to the current chrominance block may be used.

[0133]

[0134] According to the present invention, a list of chrominance intra prediction modes can be constructed by rearranging the derived chrominance intra prediction candidate modes.

[0135] According to one embodiment of the present invention, candidate modes of a chrominance intra prediction mode list can be rearranged using a template-based intra prediction mode derivation (TIMD) method. A method for rearranging candidate modes of a chrominance intra prediction mode list according to the template-based intra prediction mode derivation method can be as described below.

[0136]

[0137] The list of existing chrominance intra prediction modes using the four basic intra prediction modes, direct mode, derived-based intra prediction mode, and direct block vector mode can be expressed as shown in Table 1 below.

[0138]

[0139] As shown in Table 1, the candidate intra prediction modes for the grayscale region may include an inductive-based intra prediction mode, a direct mode, and a direct block vector mode. According to one embodiment of a method for deriving a list of chrominance intra prediction modes, the list of chrominance intra prediction modes may be composed of the inductive-based intra prediction mode, the direct mode, and the direct block vector mode in a predetermined order. Therefore, limitations may arise in the efficiency of chrominance intra coding.

[0140] To improve the efficiency of chrominance intra coding, the positions of the direct mode, the derived-based intra prediction mode, and the direct block vector mode within the chrominance intra prediction mode list can be variably changed.

[0141] That is, according to one embodiment of the present invention, among the candidate modes of the chrominance intra prediction mode list, a direct mode (DM), an inductive-based intra prediction mode (e.g., DIMD), and a direct block vector (DBV) mode can be rearranged.

[0142] Here, the candidate intra prediction modes can be reordered based on the error value of each candidate intra prediction mode. The error value of each candidate intra prediction mode can be calculated according to the method described below.

[0143]

[0144] FIG. 5 is a diagram illustrating a method for calculating an error of a chrominance intra prediction mode using a template-based intra prediction mode derivation method according to one embodiment of the present invention.

[0145] Referring to FIG. 5, a template-based intra prediction mode derivation method can calculate an intra prediction mode error based on a prediction template derived using a neighboring template (503) of a current chroma block (501) and a reference pixel of the template (504) located in a reconstructed area (502). Here, the size of the template (503) can be L1×N, M×L2. L1 and L2 are arbitrary positive integers, M is the horizontal length of the current chroma block, and N is the vertical length of the current chroma block.

[0146] A template-based intra prediction mode derivation method applies the directionality of the intra prediction mode to the reference pixel (504) of the template to generate a prediction value of the template (503) and calculates an error between the pixel of the predicted template (503) and the pixel of the already restored template (503).

[0147] Here, the error can be calculated by selecting any of various error measurement methods, such as the sum of absolute differences (SAD), the sum of square errors (SSE), the sum of absolute transformed differences (SATD), and the mean-removed sum of absolute differences (MR-SAD).

[0148] As illustrated in FIG. 5, the template-based intra prediction mode derivation method can calculate an error value using both the left template and the top template. However, this is only one embodiment, and the error value can be calculated using templates of various shapes. For example, in the template-based intra prediction mode derivation method, only the left template or the top template can be used. Alternatively, in the template-based intra prediction mode derivation method, templates of any shape can be used. The template-based intra prediction mode derivation method described in FIG. 5 can be applied to an intra prediction mode derived from a direct mode and an intra prediction mode derived from an induction-based intra prediction mode, and the respective errors can be calculated.

[0149]

[0150] FIG. 6 is a diagram illustrating a method for calculating an error of a chrominance intra prediction mode based on a block vector according to one embodiment of the present invention.

[0151] Referring to FIG. 6, the direct block vector mode of chrominance intra prediction may be a mode that generates a chrominance intra prediction block from block vector (BV) (613) information of a corresponding luma block (611) of a luma picture (610) corresponding to a prediction block of a current chroma block (601) in a chrominance picture (600), unlike the direct mode and the induction-based intra prediction mode that induce the intra prediction mode.

[0152] As illustrated in FIG. 6, if the current chroma block (601) is a direct block vector mode and the intra prediction mode of a specific position (C, TL, TR, BL, BR) (612) within the corresponding luma block (611) is an intra template matching prediction (IntraTMP) mode or an intra block copy (IBC) mode, a matching luma block (614) can be indicated by a block vector (613) of the corresponding position. In addition, information on a block vector (BV) for the current chroma block (603) for chroma intra prediction can be derived by scaling the block vector information of the intra template matching prediction mode or the block vector information of the intra block copy mode of the corresponding position (612). A matching chroma block (604) indicated by a block vector (603) for derived chroma intra prediction can be selected as a prediction block of the current chroma block (601).

[0153] As illustrated in FIG. 6, an error for the direct block vector mode can be calculated using a prediction block generation method of the direct block vector mode. The error of the direct block vector mode can be calculated using pixels of a neighboring template (602) of a current chroma block (601) and pixels of a neighboring template (605) of a matching chroma block (604) derived from a block vector (BV) for current chroma block (603) for chroma intra prediction illustrated in FIG. 6. Here, the error can be calculated by selecting any one of various error measurement methods, such as a sum of absolute differences (SAD), a sum of square errors (SSE), a sum of absolute transformed differences (SATD), or a mean-removed sum of absolute differences (MR-SAD).

[0154] As illustrated in Figure 6, the error in the direct block vector mode can be calculated using both the left template and the top template. However, this is only one embodiment, and the error in the direct block vector mode can be calculated using templates of various shapes. For example, the error in the direct block vector mode can be derived using only the left template or only the top template. Alternatively, the error in the direct block vector mode can be derived using templates of any shape.

[0155] According to the present invention, errors in the direct mode, the guided-based intra prediction mode, and the direct block vector mode can be calculated to reorder candidate modes. Furthermore, according to a method for reordering candidate modes, a shorter bit string can be assigned to a mode with a smaller error based on the calculated error.

[0156]

[0157] According to another embodiment of the present invention, among the candidate modes of the chrominance intra prediction mode list, default modes may be rearranged. Here, the default mode may be a preset basic intra prediction mode or an intra prediction mode derived based on the intra prediction modes of neighboring blocks adjacent to the current chrominance block.

[0158] As previously described, the area other than the gray shaded area of ​​the chrominance intra prediction mode list shown in Table 1 represents four basic intra prediction modes (List[0], List[1], List[2], List[3]) among the candidate modes of the chrominance intra prediction mode list. As shown in Table 1, if bit strings of the same length are assigned to the four basic intra prediction modes, there is no need to rearrange the four basic intra prediction modes. On the other hand, if bit strings of different lengths are assigned to the four basic intra prediction modes, there is a need to rearrange the four basic intra prediction modes in order to improve encoding efficiency by assigning a bit string of a shorter length to an intra prediction mode that is used frequently.

[0159] Here, the four basic intra prediction modes can be rearranged using the template-based intra prediction mode derivation method described above. That is, according to one embodiment of the present invention, the template-based intra prediction mode derivation method described above is applied to the four basic intra prediction modes to calculate the error of each mode, and a shorter bit string is assigned to the mode with the smaller calculated error, thereby rearranging the four basic intra prediction modes.

[0160]

[0161] According to another embodiment of the present invention, N intra prediction modes derived from neighboring blocks surrounding a current chrominance block can also be reordered. Here, N can be any positive integer. If all N intra prediction mode(s) are assigned bit strings of the same length, there is no need to reorder the N intra prediction mode(s). On the other hand, if the N intra prediction mode(s) are assigned bit strings of different lengths, there is a need to reorder the N intra prediction mode(s).

[0162] Here, the N intra prediction mode(s) can be rearranged using the template-based intra prediction mode derivation method described above. That is, according to one embodiment of the present invention, the template-based intra prediction mode derivation method is applied to the N intra prediction mode(s) to calculate the error of each mode, and a short bit string is assigned to modes with small calculated errors, thereby rearranging the N intra prediction mode(s).

[0163]

[0164] According to another embodiment of the present invention, in deriving a chrominance intra prediction mode list, four basic intra prediction modes or N intra prediction mode(s) derived from neighboring chrominance blocks surrounding a current chrominance block, a direct mode, a derived-based intra prediction mode, and a direct block vector mode can be rearranged. That is, the method for deriving a chrominance intra prediction mode list of the present invention can rearrange all chrominance candidate modes in the chrominance intra prediction mode list. Here, the chrominance candidate modes in the chrominance intra prediction mode list can be configured using at least two or more modes among the modes described above.

[0165] According to one embodiment of the present invention, in order to rearrange candidate modes in a chrominance intra prediction mode list, a template-based intra prediction mode derivation method may be applied to each intra prediction mode for four basic intra prediction modes or N intra prediction mode(s) derived from surrounding neighboring blocks of a current chrominance block, a direct mode, and an inductive-based intra prediction mode, to calculate an error for each intra prediction mode. Alternatively, according to one embodiment of the present invention, in order to rearrange candidate modes in a chrominance intra prediction mode list, an error calculation method of a direct block vector mode may be applied to a direct block vector mode, to calculate an error.

[0166] Then, by calculating the error for all candidate modes in the chrominance intra prediction mode list, the candidate modes in the chrominance intra prediction mode list can be rearranged to allocate a bit string of a shorter length to a mode with a smaller error. Here, the four basic intra prediction modes or the N intra prediction mode(s) can be rearranged only when the bit strings of the same length are not allocated to each intra prediction mode.

[0167]

[0168] Figure 7 is a flowchart illustrating an image decoding method according to an embodiment of the present invention. The image decoding method of Figure 7 can be performed by an image decoding device.

[0169] Referring to FIG. 7, at step S710, the image decoding device can generate a list of chrominance modes of the current chrominance block.

[0170] At step S720, the image decoding device can derive a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list.

[0171] At step S730, the video decoding device can generate a prediction block of the current chrominance block based on the chrominance intra prediction mode.

[0172] Here, the chrominance mode list may include at least one candidate intra prediction mode among the default mode, the derived-based chrominance mode, the direct mode, and the direct block vector mode.

[0173] Here, the default mode can be derived using available neighboring blocks among at least one neighboring block adjacent to the current chrominance block.

[0174] Here, if at least one neighboring block is not available, the default mode can be derived using a preset intra prediction mode.

[0175] Here, if the default mode is identical to an intra prediction mode derived by at least one of the derived-based chrominance mode, the direct mode, and the direct block vector mode, the default mode can be derived by replacing it with a given intra prediction mode.

[0176] Here, the given intra prediction mode may include at least one of a DC mode, a planar mode, a vertical mode, and a horizontal mode.

[0177] The process of deriving a default mode using at least one neighboring block adjacent to the current chroma block has been specifically described in Fig. 4 and related content.

[0178] Here, the step of generating a chroma mode list may be characterized by sorting at least one candidate intra prediction mode within the chroma mode list based on an error of each of the at least one candidate intra prediction mode.

[0179] Specifically, the step of generating a chrominance mode list may be characterized by sorting the derived-based chrominance mode, the direct mode, and the direct block vector mode within the chrominance mode list.

[0180] Here, the error of the derived-based chrominance mode can be calculated as a difference value between a restoration value of the current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode derived according to the derived-based chrominance mode and at least one sample adjacent to the current template.

[0181] Here, the error of the direct mode can be calculated as a difference value between a restoration value of the current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode induced according to the direct mode and at least one sample adjacent to the current template.

[0182] The process of calculating the error of the inductive-based chromatic mode and the direct mode is described in detail in Fig. 5 and related contents.

[0183] Here, the error of the direct block vector mode can be calculated as the difference between the restoration value of the current template including samples adjacent to the current chrominance block and the restoration value of the corresponding template including samples adjacent to the corresponding block indicated by the block vector of the current chrominance block.

[0184] The process of calculating the error in direct block vector mode is described in detail in Fig. 6 and related contents.

[0185] Here, the step of generating a color difference mode list may be characterized by sorting default modes within the color difference mode list.

[0186] Specifically, the error of the default mode can be calculated as a difference value between a restoration value of the current template including samples adjacent to the current chrominance block and a prediction value of the current template using the intra prediction mode, which is the default mode, and at least one sample adjacent to the current template.

[0187] The process of calculating the error in the default mode is described in detail in Fig. 5 and related content.

[0188] Here, the step of generating a chrominance mode list may be characterized by sorting a default mode, a derived-based chrominance mode, a direct mode, and a direct block vector mode within the chrominance mode list.

[0189] Meanwhile, the steps described in FIG. 7 can be performed in the same manner in an image encoding method. Furthermore, a bitstream can be generated by an image encoding method including the steps described in FIG. 7. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0190]

[0191] FIG. 8 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0192] As illustrated in FIG. 8, a content streaming system to which an embodiment of the present invention is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0193] The encoding server compresses content input from multimedia input devices such as smartphones, cameras, and CCTVs into digital data, generates a bitstream, and transmits it to the streaming server. Alternatively, if multimedia input devices such as smartphones, cameras, and CCTVs directly generate bitstreams, the encoding server may be omitted.

[0194] The above bitstream can be generated by an image encoding method and / or an image encoding device to which an embodiment of the present invention is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0195] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server can act as an intermediary to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, and the streaming server can transmit multimedia data to the user. At this time, the content streaming system may include a separate control server, and in this case, the control server may control commands / responses between each device within the content streaming system.

[0196] The streaming server can receive content from a media repository and / or encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0197] Examples of the user devices may include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, HMDs), digital TVs, desktop computers, digital signage, etc.

[0198] Each server within the above content streaming system can be operated as a distributed server, in which case data received from each server can be processed in a distributed manner.

[0199]

[0200] The above embodiments can be performed in the same or corresponding manner in an encoding device and a decoding device. In addition, an image can be encoded / decoded using at least one or a combination of at least one of the above embodiments.

[0201] The order in which the above embodiments are applied may be different in the encoding device and the decoding device. Alternatively, the order in which the above embodiments are applied may be the same in the encoding device and the decoding device.

[0202] The above embodiments can be performed for each of the luminance and chrominance signals. Alternatively, the above embodiments can be performed identically for the luminance and chrominance signals.

[0203] In the above embodiments, the methods are described based on a flowchart as a series of steps or units. However, the present invention is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps described above. Furthermore, those skilled in the art will understand that the steps depicted in the flowchart are not exclusive, and that other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

[0204] The above embodiments may be implemented in the form of program commands that can be executed by various computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program commands, data files, data structures, etc., either singly or in combination. The program commands recorded on the computer-readable recording medium may be those specifically designed and constructed for the present invention, or may be known and usable by those skilled in the art of computer software.

[0205] The bitstream generated by the encoding method according to the above embodiment can be stored in a non-transitory computer-readable recording medium. In addition, the bitstream stored in the non-transitory computer-readable recording medium can be decoded by the decoding method according to the above embodiment.

[0206] Here, examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, and hardware devices specifically configured to store and execute program instructions such as ROMs, RAMs, and flash memories. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices may be configured to operate as one or more software modules to perform processing according to the present invention, and vice versa.

[0207] Although the present invention has been described above with specific details such as specific components and limited examples and drawings, these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations from this description.

[0208] Therefore, the idea of ​​the present invention should not be limited to the embodiments described above, and all things that are modified equally or equivalently to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

[0209] The present invention can be used in a device for encoding / decoding an image and a recording medium storing a bitstream.

Claims

1. In the video decryption method, A step for generating a list of chroma modes for the current chroma block; A step of deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list; and A step of generating a prediction block of the current chrominance block based on the chrominance intra prediction mode is included. A method for decoding an image, characterized in that the chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derived-based chrominance mode, a direct mode, and a direct block vector mode.

2. In paragraph 1, An image decoding method, characterized in that the default mode is derived using available neighboring blocks among at least one neighboring block adjacent to the current chrominance block.

3. In paragraph 2, A method for decoding an image, characterized in that when at least one of the neighboring blocks is not available, the default mode is derived using a preset intra prediction mode.

4. In paragraph 1, If the above default mode is identical to an intra prediction mode derived by at least one of the derived-based chrominance mode, the direct mode, and the direct block vector mode, The above default mode is characterized in that it is derived by being replaced with a predetermined intra prediction mode, The above-mentioned intra prediction mode is, An image decoding method characterized by comprising at least one of a DC mode, a planar mode, a vertical mode and a horizontal mode.

5. In paragraph 1, The steps for generating the above color difference mode list are: A video decoding method characterized by sorting the at least one candidate intra prediction mode in the chrominance mode list based on an error of each of the at least one candidate intra prediction mode.

6. In paragraph 5, The steps for generating the above color difference mode list are: An image decoding method characterized by sorting the derived-based chrominance mode, the direct mode, and the direct block vector mode within the chrominance mode list.

7. In paragraph 6, The error of the above inductive-based chromatic mode is An image decoding method characterized in that the difference value is calculated between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode derived according to the induction-based chrominance mode and at least one sample adjacent to the current template.

8. In paragraph 6, The error of the above direct mode is, An image decoding method characterized in that the difference value is calculated between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using an intra prediction mode induced according to the direct mode and at least one sample adjacent to the current template.

9. In paragraph 6, The error of the above direct block vector mode is, An image decoding method characterized in that the difference value is calculated between a restoration value of a current template including samples adjacent to the current chrominance block and a restoration value of a corresponding template including samples adjacent to a corresponding block indicated by a block vector of the current chrominance block.

10. In paragraph 5, The steps for generating the above color difference mode list are: An image decoding method characterized by sorting default modes within the above color difference mode list.

11. In paragraph 10, The error in the above default mode is, An image decoding method characterized in that the difference value is calculated between a restoration value of a current template including samples adjacent to the current chrominance block and a prediction value of the current template using the intra prediction mode, which is the default mode, and at least one sample adjacent to the current template.

12. In paragraph 5, The steps for generating the above color difference mode list are: An image decoding method characterized by sorting the default mode, the derived-based chrominance mode, the direct mode, and the direct block vector mode within the chrominance mode list.

13. In the video encoding method, A step for generating a list of chroma modes for the current chroma block; A step of deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list; and A step of generating a prediction block of the current chrominance block based on the chrominance intra prediction mode is included. A method for encoding an image, characterized in that the chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derived-based chrominance mode, a direct mode, and a direct block vector mode.

14. A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method, The above image encoding method is, A step for generating a list of chroma modes for the current chroma block; A step of deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list; and A step of generating a prediction block of the current chrominance block based on the chrominance intra prediction mode is included. A non-transitory computer-readable recording medium, characterized in that the chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derived-based chrominance mode, a direct mode, and a direct block vector mode.

15. A method for transmitting a bitstream generated by a video encoding method, The above transmission method comprises a step of transmitting the bitstream, The above image encoding method is, A step for generating a list of chroma modes for the current chroma block; A step of deriving a chrominance intra prediction mode of the current chrominance block based on the chrominance mode list; and A step of generating a prediction block of the current chrominance block based on the chrominance intra prediction mode is included. A transmission method, characterized in that the above chrominance mode list includes at least one candidate intra prediction mode among a default mode, a derived-based chrominance mode, a direct mode, and a direct block vector mode.

Images