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

Abstract

An image encoding / decoding method and device, a recording medium on which a bitstream is stored, and a transmission method are provided. The image decoding method comprises the steps of: acquiring chrominance intra prediction mode information; determining a chrominance intra prediction mode of the current chrominance block on the basis of the chrominance intra prediction mode information; and generating a prediction block of the current chrominance block on the basis of the determined chrominance intra prediction mode, wherein, if the chrominance intra prediction mode information indicates a direct mode (DM) and the intra prediction mode of a corresponding luminance block corresponding to the current chrominance block is either an intra template matching mode or an intra block copy mode, the chrominance intra prediction mode can be determined on the basis of an intra prediction mode of a matching luminance block indicated by a block vector of the corresponding luminance block.

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 based on chrominance intra prediction mode determination.

[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] Limitations in prediction efficiency may occur when information available in direct mode and direct block vector mode is not available.

[0004] The purpose of the present invention is to provide a video encoding / decoding method and device with improved encoding / decoding efficiency.

[0005] 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.

[0006] In addition, the present invention aims to provide a method for determining a color difference intra prediction mode to solve the problems of the existing direct mode and direct block vector mode as described above.

[0007] An image decoding method according to one embodiment of the present invention includes the steps of obtaining chrominance intra prediction mode information, determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information, and generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode, wherein when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of a corresponding luminance block corresponding to the current chrominance block is any one of an intra template matching mode and an intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of a matching luminance block indicated by a block vector of the corresponding luminance block.

[0008] In the above image decoding method, when the intra prediction mode of the matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode can be determined as a predefined intra prediction mode.

[0009] In the above image decoding method, the predefined intra prediction mode may be any one of a planar mode, a DC mode, a vertical mode, and a horizontal mode.

[0010] In the above image decoding method, when the intra prediction mode of the matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode can be determined based on DIMD (Decoder side intra mode derivation).

[0011] In the above image decoding method, the DIMD method can be performed based on a gradient histogram of pixels within the corresponding luminance block.

[0012] In the above image decoding method, the DIMD method can be performed based on a gradient histogram of surrounding pixels of the corresponding luminance block.

[0013] In the above image decoding method, the DIMD method can be performed based on the difference between the restored pixel in the corresponding luminance block and the predicted pixel of the corresponding luminance block.

[0014] In the above image decoding method, the DIMD method can be performed based on a gradient histogram of pixels within the matching luminance block.

[0015] In the above image decoding method, the DIMD method can be performed based on a gradient histogram of surrounding pixels of the matching luminance block.

[0016] In the above image decoding method, the DIMD method can be performed based on the difference between the restored pixel in the matching luminance block and the predicted pixel of the matching luminance block.

[0017] In the above image decoding method, when the tree structure of the current chrominance block is a dual tree structure, the matching luminance block can be derived based on the intra prediction mode and block vector of any one of the upper left, lower left, center, upper right, and lower right pixels in the corresponding luminance block.

[0018] In the above image decoding method, when the tree structure of the current chrominance block is a single tree structure, the matching luminance block can be derived based on the intra prediction mode and block vector of the central pixel in the corresponding luminance block.

[0019] In the above image decoding method, when a block vector exists in the corresponding luminance block, the chrominance intra prediction mode information may additionally indicate whether it is a DBV (Direct block vector) mode.

[0020] A video encoding method according to one embodiment of the present invention includes the steps of determining chrominance intra prediction mode information, determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information, and generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode, wherein when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of a corresponding luminance block corresponding to the current chrominance block is any one of an intra template matching mode and an intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of a matching luminance block indicated by a block vector of the corresponding luminance block.

[0021] A non-transitory computer-readable recording medium according to one embodiment of the present invention can store a bitstream generated by the image encoding method.

[0022] A bitstream transmission method according to one embodiment of the present invention can transmit a bitstream generated by the image encoding method.

[0023] The features briefly summarized above regarding the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that follows and do not limit the scope of the present disclosure.

[0024] According to the present invention, a video encoding / decoding method and device with improved encoding / decoding efficiency can be provided.

[0025] In addition, according to the present invention, a method for determining a chrominance intra prediction mode in a direct mode and a direct block vector mode can be provided.

[0026] In addition, according to the present invention, the color difference intra prediction efficiency can be improved.

[0027] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects that are not mentioned will be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0028] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0029] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0030] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0031] FIG. 4 is a diagram for explaining an intra template matching mode prediction method according to an embodiment of the present invention.

[0032] FIG. 5 is a diagram for explaining an intra block copy mode prediction method according to an embodiment of the present invention.

[0033] FIG. 6 is a drawing for explaining a direct mode according to one embodiment of the present invention.

[0034] FIG. 7 is a flowchart illustrating a method for determining a color difference intra prediction mode according to one embodiment of the present invention.

[0035] FIG. 8 is a diagram for explaining a method for determining a chrominance intra prediction mode when the intra prediction mode of a corresponding luminance block and a matching luminance block in a direct mode according to one embodiment of the present invention is either an intra template matching mode or an intra block copy mode.

[0036] FIG. 9 is a diagram for explaining a direct block vector mode according to one embodiment of the present invention.

[0037] Figure 10 is a flowchart illustrating an image decoding method according to one embodiment of the present invention.

[0038] FIG. 11 is a drawing exemplifying a content streaming system to which an embodiment according to the present invention can be applied.

[0039] An image decoding method according to one embodiment of the present invention includes the steps of obtaining chrominance intra prediction mode information, determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information, and generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode, wherein when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of a corresponding luminance block corresponding to the current chrominance block is any one of an intra template matching mode and an intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of a matching luminance block indicated by a block vector of the corresponding luminance block.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In an embodiment, 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 an embodiment, the term "a plurality of" may mean one of a number greater than or equal to 2, such as 2, 3, and 4.

[0045] 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.

[0046] Glossary of Terms

[0047] 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.”

[0048] 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.

[0049] Hereinafter, the terms encoder and image encoding device may be used interchangeably and have the same meaning.

[0050] Hereinafter, the terms decoder and image decoding device may be used interchangeably and have the same meaning.

[0051] Hereinafter, “image”, “picture”, “frame” and “screen” may be used with the same meaning and may be used interchangeably.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Hereinafter, “inter” and “between screens” may be used interchangeably and have the same meaning.

[0056] Hereinafter, “intra” and “within screen” may be used interchangeably and have the same meaning.

[0057]

[0058] Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

[0059] 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.

[0060] 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).

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] 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 an area within a 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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).

[0084] 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.

[0085] 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.

[0086] 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).

[0087] 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).

[0088] 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.

[0089] 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.

[0090] 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.

[0091] Bilateral filter (BIF) can also compensate for the offset from the original image on a sample-by-sample basis for the deblocked image.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] Figure 2 is a block diagram showing the configuration according to one embodiment of a decryption device to which the present invention is applied.

[0096] The decoding device (200) may be a decoder, a video decoding device, or an image decoding device.

[0097] 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).

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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).

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0109] A video coding system according to one embodiment may include an encoding device (10) and a decoding device (20). The encoding device (10) may transmit encoded video and / or image information or data to the decoding device (20) in the form of a file or streaming through a digital storage medium or a network.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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).

[0114] 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.

[0115] The rendering unit (23) can render the decrypted video / image. The rendered video / image can be displayed through the display unit.

[0116]

[0117] In this specification, Direct Mode (DM) and Direct Block Vector (DBV) modes for deriving chrominance intra prediction modes are described.

[0118] Direct mode is a mode in which the intra prediction mode of a chrominance block is determined based on the intra prediction mode information of a luminance block corresponding to the chrominance block.

[0119] Direct block vector mode is a mode in which the block vector information of a chrominance block is derived from the block vector information of a luminance block corresponding to the chrominance block.

[0120] To improve the accuracy of the direct mode, the encoder / decoder of the present invention can determine the chrominance intra prediction mode based on the intra prediction mode of the matching block of the corresponding luminance block. Specifically, when the intra prediction mode of the corresponding luminance block in the direct mode is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of the matching block of the corresponding luminance block.

[0121] Here, the chrominance intra prediction mode refers to the intra prediction mode of the chrominance block, and the corresponding luminance block and the matching block may refer to a luminance block corresponding to the current chrominance block and a luminance block indicated by a block vector of the corresponding luminance block, respectively.

[0122] In addition, for the efficiency of deriving the chrominance intra prediction mode, if a block vector exists in the corresponding luminance block, the chrominance intra prediction mode information can additionally indicate whether it is a DBV (Direct block vector) mode.

[0123] Here, the chroma intra prediction mode information is information about the intra prediction mode of the chroma block. And, the chroma intra prediction mode information may be intra_chroma_pred_mode.

[0124] Before explaining the method for deriving the color difference intra prediction mode, an intra template matching prediction (IntraTMP) method and an intra block copy prediction method according to an embodiment of the present invention will be explained with reference to FIGS. 4 and 5.

[0125]

[0126] FIG. 4 is a diagram for explaining an intra template matching mode prediction method according to an embodiment of the present invention.

[0127] The intra template matching mode prediction method means a method of searching for an optimal prediction block in a restored area of ​​the current picture using template matching when the intra prediction mode of the current block is the intra template matching mode, and copying it to generate a prediction block of the current block.

[0128] Referring to FIG. 4, the neighboring ┌ area (i.e., the left, top, and upper left areas) of the current block (Current block, 410) can be defined as the current template (Current template, 420). Then, the reference template (Reference template, 440) most similar to the current template (420) can be searched within the predefined search range (R1, R2, R3, R4) of the reconstructed area (Reconstructed area, 430) of the current picture (Current picture, 400). Then, the prediction block of the current block (410) can be derived based on the corresponding matching block (Matching block, 450) of the determined reference template (440). Then, the block vector (Block vector, 460) is a vector indicating the matching block (450) of the current block in intra template matching prediction.

[0129] The predefined search ranges R1, R2, R3, and R4 in Fig. 4 can be defined as the current CTU (Coding Tree Unit) including the current block, the upper left CTU, the upper CTU, and the left CTU, respectively.

[0130] Additionally, the predefined search range may be searched for reference templates based on a predefined search order. For example, the reference templates may be searched in a zigzag order of R1, R4, R3, R2.

[0131] Meanwhile, information regarding the search range and the size and shape of the current template can be determined by the encoder and transmitted to the decoder. Furthermore, the search range and the size and shape of the current template can be set to preset values ​​in the encoder / decoder.

[0132] For example, instead of a ┌-shaped template that uses both the left restoration area and the top restoration area, you can use only the top restoration area or the left restoration area as a template.

[0133] For example, the size of the current template can be determined as (w x L2) + (L1 xh) + (L1 x L2) as shown in Fig. 4. Here, w and h represent the width and height of the current block, and the values ​​of L1 and L2 can be determined as any positive integer.

[0134] With respect to the template shape, the example of FIG. 4 uses one ┌-shaped template to search for a reference template most similar to the current template, but this can also be done using, for example, a ┌-shaped template, a template using only the top region, a template using only the left region, or a template of any shape to search for a reference template most similar to the current template.

[0135] Meanwhile, the current block (410) in FIG. 4 may be a luma block. At this time, the current picture (400) to which the luma block belongs may be a luma picture. In addition, the matching block (450) indicated by the block vector (460) may be a matching luma block of the luma block.

[0136]

[0137] FIG. 5 is a diagram for explaining an intra block copy mode prediction method according to an embodiment of the present invention.

[0138] The intra block copy prediction method means a method of searching for an optimal prediction block in a restored area of ​​the current picture using a block vector when the intra prediction mode of the current block is the intra block copy mode, and copying it to generate a prediction block of the current block.

[0139] Referring to FIG. 5, a matching block (Matching Block, 540) can be derived within a predefined search range (R1, R2, R3, R4) of a reconstructed area (530) of a current picture (500) based on a block vector (Block vector, 520) of a current block (510). In addition, a prediction block of the current block (510) can be derived based on the matching block (540). Meanwhile, the block vector (520) is a vector indicating a matching block (540) of the current block (510) in intra block copy prediction.

[0140] The predefined search ranges R1, R2, R3, and R4 in Fig. 5 can be defined as the current CTU (Coding Tree Unit) including the current block, the upper left CTU, the upper CTU, and the left CTU, respectively.

[0141] Additionally, matching blocks may be searched based on a predefined search order within a predefined search range. For example, matching blocks may be searched in a zigzag order of R1, R4, R3, R2.

[0142] Meanwhile, information about the search range can be determined by the encoder and transmitted to the decoder. Furthermore, the search range can be set to a preset value in the encoder / decoder.

[0143] Meanwhile, the current block (510) in FIG. 5 may be a luma block. At this time, the current picture (500) to which the luma block belongs may be a luma picture. In addition, the matching block (540) indicated by the block vector (520) may be a matching luma block of the luma block.

[0144]

[0145] Hereinafter, with reference to FIGS. 6 and 8, a direct mode for deriving a color difference intra prediction mode according to one embodiment of the present invention will be described.

[0146] Direct mode is a mode in which the intra prediction mode of the current chrominance block is determined based on the intra prediction mode information of the corresponding luminance block. Therefore, if the chrominance intra prediction mode information indicates direct mode, the chrominance intra prediction mode is determined based on the intra prediction mode information of the corresponding luminance block.

[0147] FIG. 6 is a drawing for explaining a direct mode according to one embodiment of the present invention.

[0148] In Fig. 6, the corresponding luma block (610) represents a luma block corresponding to the current chroma block (600). And the luma picture (611) represents a picture including the corresponding luma block (610).

[0149] Referring to FIG. 6, if the chrominance intra prediction mode information indicates DM (Direct Mode), the chrominance intra prediction mode can be determined based on the intra prediction mode of the corresponding luminance block (610).

[0150] For example, the intra prediction mode of the current chrominance block (600) can be determined based on the intra prediction mode of the center position pixel (C) in the corresponding luminance block (610). As another example, the intra prediction mode of the current chrominance block (600) can be determined based on the intra prediction mode of the lower right pixel (B) in the corresponding luminance block (610). R ) can be determined based on the intra prediction mode.

[0151] Meanwhile, if the intra prediction mode of the corresponding luminance block (610) is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode may be determined based on the matching block of the corresponding luminance block (610). Here, the matching block may mean a matching luma block (612) indicated by the block vector (613) of the corresponding luminance block (610).

[0152] Specifically, the restored pixel (C, T) at a predetermined position of the corresponding luminance block (610) L , T R, B L, B R ) is derived based on one of the intra prediction modes and block vectors, and a chrominance intra prediction mode can be determined based on the intra prediction mode of the matching luminance block (612).

[0153] For example, if the intra prediction mode of the corresponding luminance block (610) is either an intra template matching mode or an intra block copy mode, the intra prediction mode of the current chrominance block (600) may be determined based on the intra prediction mode of the centrally located pixel (C') in the matching luminance block (612). Accordingly, if the intra prediction mode of the centrally located pixel (C') of the matching luminance block (612) is a DC mode, the intra prediction mode of the current chrominance block (600) may be determined as the DC mode. As another example, if the intra prediction mode of the corresponding luminance block (610) is either an intra template matching mode or an intra block copy mode, the intra prediction mode of the current chrominance block (600) may be determined based on the intra prediction mode of the lower right pixel (B) in the matching luminance block (612). R ') can be determined based on the intra prediction mode. Accordingly, the lower right pixel (B) in the matching luminance block (612) R ') is the Planar mode, the intra prediction mode of the current chrominance block (600) can be determined as the Planar mode.

[0154] Meanwhile, Fig. 6 shows a dual-tree structure in which the current chrominance block and the corresponding luminance block have different segmentation information, but this is only one example, and the current chrominance block and the corresponding luminance block may have a single-tree structure in which the segmentation information is the same. In this case, the matching luminance block may be derived based on the intra-prediction mode and block vector of the central pixel in the corresponding luminance block.

[0155]

[0156] Meanwhile, if the intra prediction mode of the matching luminance block (612) is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode may be determined based on the intra prediction mode of the matching block searched based on the block vector of the matching luminance block. In this case, if the block indicated by the block vector of the matching luminance block is searched and the intra prediction mode of the searched block is neither the intra template matching mode nor the intra block copy mode, the chrominance intra prediction mode may be determined based on the intra prediction mode of the searched block.

[0157] Meanwhile, if the intra prediction mode of the searched block is either the intra template matching mode or the intra block copy mode, the block indicated by the block vector of the searched block is searched. This process is repeated N times until the intra prediction mode of the searched block is neither the intra template matching mode nor the intra block copy mode, and the chrominance intra prediction mode can be finally determined based on the intra prediction mode of the searched block. At this time, N is a positive integer, and can be preset in the encoder and decoder, or can be determined by the encoder and signaled to the decoder.

[0158]

[0159] In the direct mode described in FIG. 6, when the intra prediction mode of the corresponding luminance block is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode is determined based on the intra prediction mode of the matching luminance block (612). At this time, when the intra prediction mode of the matching luminance block (612) is either the intra template matching mode or the intra block copy mode, the intra prediction mode information of the matching luminance block cannot be directly used, which may lower the coding efficiency. Therefore, in the present invention, the chrominance intra prediction mode may be determined based on DIMD (Decoder side intra mode derivation).

[0160]

[0161] Fig. 7 is a flowchart illustrating a method for determining a chrominance intra prediction mode according to one embodiment of the present invention. The method for determining a chrominance intra prediction mode of Fig. 7 can be performed by an image decoding device and an image encoding device.

[0162] If the chrominance intra prediction mode information does not directly indicate the mode (S700-No), the image decoding device and the image encoding device can determine the chrominance intra prediction mode of the current chrominance block as the mode indicated by the chrominance intra prediction mode information (S701).

[0163] Additionally, if the chrominance intra prediction mode information indicates a direct mode (S700-Yes) and the intra prediction mode of the corresponding luminance block is not an intra template matching mode and an intra block copy mode (S702-No), the image decoding device and the image encoding device can determine the chrominance intra prediction mode of the current chrominance block as the intra prediction mode of the corresponding luminance block (S703).

[0164] In addition, if the chrominance intra prediction mode information indicates a direct mode (S700-yes), the intra prediction mode of the corresponding luminance block is one of the intra template matching mode and the intra block copy mode (S702-yes), and the intra prediction mode of the matching luminance block is neither the intra template matching mode nor the intra block copy mode (S704-no), the image decoding device and the image encoding device can determine the chrominance intra prediction mode of the current chrominance block as the intra prediction mode of the matching luminance block (S705).

[0165] In addition, if the chrominance intra prediction mode information indicates a direct mode (S700-yes), the intra prediction mode of the corresponding luminance block is one of the intra template matching mode and the intra block copy mode (S702-yes), and the intra prediction mode of the matching luminance block is one of the intra template matching mode and the intra block copy mode (S704-yes), the image decoding device and the image encoding device can determine the chrominance intra prediction mode of the current chrominance block as a predefined intra prediction mode or based on DIMD (S706).

[0166]

[0167] FIG. 8 is a diagram for explaining a method for determining a chrominance intra prediction mode when the intra prediction mode of a corresponding luminance block and a matching luminance block in a direct mode according to one embodiment of the present invention is either an intra template matching mode or an intra block copy mode.

[0168] In Fig. 8, the corresponding luma block (810) represents a luma block corresponding to the current chroma block (800). And the luma picture (811) represents a picture including the corresponding luma block (810).

[0169] And, the matching luma block (812) is a block indicated by the block vector (813) of the corresponding luma block when the intra prediction mode of the corresponding luma block (810) is either the intra template matching mode or the intra block copy mode.

[0170] And, the pixels in the ┌ area neighboring the left, top, and upper left of the corresponding luminance block (810) represent the surrounding reference pixels (Reference sample for corresponding luma block, 814) of the corresponding luminance block (810), and the pixels in the ┌ area neighboring the left, top, and upper left of the matching luminance block (812) represent the surrounding reference pixels (Reference sample for matching luma block, 815) of the matching luminance block (812).

[0171] In FIG. 8, if the chrominance intra prediction mode information indicates a direct mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of the corresponding luminance block (810).

[0172] At this time, if the intra prediction mode of the corresponding luminance block (810) is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of the matching luminance block (812) indicated by the block vector (813) of the corresponding luminance block.

[0173] Meanwhile, when the intra prediction mode of the matching luminance block (812) is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode can be determined based on the DIMD.

[0174]

[0175] According to one embodiment of the present invention, a DIMD method for deriving a chrominance intra prediction mode can be performed based on pixels within a corresponding luminance block (810).

[0176] Specifically, the DIMD method can be performed based on a gradient histogram of pixels within a corresponding luminance block (810). First, at least one edge detection filter among a Sobel filter, a Roberts cross filter, a Prewitt filter, a Scharr filter, and a Laplacian filter is applied to pixels within the corresponding luminance block (810), and the gradient of the restored pixels is calculated, and a gradient histogram (HoG) can be generated based on this.

[0177] Then, a gradient having the largest value may be selected from the gradient histogram and mapped to an intra prediction mode. And the chrominance intra prediction mode may be determined as the mapped intra prediction mode. Alternatively, N gradients may be selected from the gradient histogram, and the selected gradients may be mapped to intra prediction modes respectively. Then, the chrominance intra prediction mode may be determined as the intra prediction mode having the smallest prediction mode number among the mapped intra prediction modes. At this time, N is any positive integer. Meanwhile, if the strength of the selected gradient is less than or equal to a preset value, the gradient may be mapped to the Planar mode or the DC mode.

[0178] Meanwhile, the DIMD method may also be performed using a gradient histogram of pixels within a down-sampled corresponding luminance block (810). That is, downsampling is performed on the restored pixels within the corresponding luminance block (810), an edge detection filter is applied to the downsampled pixels to calculate the gradient, and a gradient histogram can be generated based on this. At this time, the downsampling ratio can be arbitrarily determined. For example, the restored pixels within the corresponding luminance block can be downsampled at a ratio of 2 to 1.

[0179] Meanwhile, in the DIMD method, the size and shape of the area to which the boundary detection filter is applied can be arbitrarily determined.

[0180]

[0181] According to another embodiment, the DIMD method for deriving a chrominance intra prediction mode can be performed based on the surrounding pixels (814) of the corresponding luminance block (810).

[0182] Specifically, the DIMD method can be performed based on a gradient histogram of surrounding pixels (814) of the corresponding luminance block (810). First, at least one edge detection filter among a Sobel filter, a Roberts cross filter, a Prewitt filter, a Schar filter, and a Laplacian filter is applied to surrounding reference pixels (814) of the corresponding luminance block (810), and the gradient of the restored pixel is calculated, and a gradient histogram can be generated based on the calculated gradient. Then, a gradient having the largest value is selected from the gradient histogram, and the selected gradient can be mapped to an intra prediction mode. And the chrominance intra prediction mode can be determined as the mapped intra prediction mode. Alternatively, N gradients are selected from the gradient histogram, and the selected gradients are respectively mapped to intra prediction modes, and then the chrominance intra prediction mode can be determined as an intra prediction mode having a smallest prediction mode number among the mapped intra prediction modes. At this time, N is any positive integer.

[0183] In addition, the DIMD method can be performed based on the difference between the restored pixel in the corresponding luminance block (810) and the predicted pixel of the corresponding luminance block. Specifically, the predicted pixel to which the non-directional intra prediction mode and the directional intra prediction mode (e.g., 65 directions) are applied to the pixel in the corresponding luminance block (810) are respectively obtained, and the difference between each predicted pixel and the restored pixel in the corresponding luminance block (810) is calculated. Then, the chrominance intra prediction mode can be determined as the intra prediction mode applied to the predicted pixel having the smallest difference from the restored pixel in the corresponding luminance block (810). At this time, the difference can be calculated by any one of the Sum of Absolute Difference (SAD) method, the Sum of Squared Difference (SSD) method, and the Sum of Absolute Transformed Difference (SATD) method.

[0184] Meanwhile, in Fig. 8, the peripheral reference pixels of the corresponding luminance block are pixels in the ┌ region adjacent to the left, top, and upper left, but this is just one example, and the peripheral reference pixels of the corresponding luminance block can be determined as any pixel around the corresponding luminance block. For example, the peripheral reference pixels of the corresponding luminance block can be peripheral pixels of the corresponding luminance block sampled at any rate.

[0185] Meanwhile, in the DIMD method, the size and shape of the area to which the boundary detection filter is applied can be arbitrarily determined.

[0186]

[0187] According to another embodiment, the DIMD method for deriving a chrominance intra prediction mode can be performed based on pixels within a matching luminance block (812).

[0188] Specifically, the DIMD method can be performed based on a gradient histogram of pixels within a matching luminance block (812). First, at least one edge detection filter among a Sobel filter, a Roberts cross filter, a Prewitt filter, a Schar filter, and a Laplacian filter is applied to pixels within the matching luminance block (812), and the gradient of the restored pixels is calculated, and a gradient histogram can be generated based on this.

[0189] Then, a gradient having the largest value is selected from the gradient histogram, and the selected gradient can be mapped to an intra prediction mode. And the chrominance intra prediction mode can be determined as the mapped intra prediction mode. Alternatively, N gradients are selected from the gradient histogram, and after the selected gradients are each mapped to an intra prediction mode, the chrominance intra prediction mode can be determined as the intra prediction mode having the smallest prediction mode number among the mapped intra prediction modes. At this time, N is any positive integer. Meanwhile, if the intensity of the selected gradient is less than or equal to a preset value, the gradient can be mapped to the Planar mode or the DC mode.

[0190] Meanwhile, the DIMD method may also be performed based on a gradient histogram of pixels within a downsampled matching luminance block (812). That is, downsampling is performed on the restored pixels within the matching luminance block (812), an edge detection filter is applied to the downsampled pixels to calculate the gradient, and a gradient histogram can be generated based on this. At this time, the downsampling ratio can be arbitrarily determined. For example, the restored pixels of the matching luminance block can be downsampled at a ratio of 2 to 1.

[0191] Meanwhile, in the DIMD method, the size and shape of the area to which the boundary detection filter is applied can be arbitrarily determined.

[0192]

[0193] According to another embodiment, the DIMD method for deriving a chrominance intra prediction mode can be performed based on the surrounding pixels (815) of the matching luminance block (812).

[0194] Specifically, the DIMD method can be performed based on a gradient histogram of surrounding pixels (815) of the matching luminance block (812). First, at least one edge detection filter among a Sobel filter, a Roberts cross filter, a Prewitt filter, a Schar filter, and a Laplacian filter is applied to surrounding reference pixels (815) of the matching luminance block (812), and the gradient of the restored pixel is calculated, and a gradient histogram can be generated based on the calculated gradient. Then, a gradient having the largest value is selected from the gradient histogram, and the selected gradient can be mapped to an intra prediction mode. And the chrominance intra prediction mode can be determined as the mapped intra prediction mode. Alternatively, after N gradients are selected from the gradient histogram and the selected gradients are respectively mapped to intra prediction modes, the chrominance intra prediction mode can be determined as an intra prediction mode having a smallest prediction mode number among the mapped intra prediction modes. At this time, N is any positive integer.

[0195] In addition, the DIMD method can be performed based on the difference between the restored pixel in the matching luminance block (812) and the predicted pixel of the matching luminance block. Specifically, the predicted pixel to which the non-directional intra prediction mode and the directional intra prediction mode (e.g., 65 directions) are applied to the pixel in the matching luminance block (812) are respectively obtained, and the difference between each predicted pixel and the restored pixel in the matching luminance block (812) is calculated. Then, the chrominance intra prediction mode can be determined as the intra prediction mode applied to the predicted pixel having the smallest difference from the restored pixel in the matching luminance block. At this time, the difference can be calculated by any one of the Sum of Absolute Difference (SAD) method, the Sum of Squared Difference (SSD) method, and the Sum of Absolute Transformed Difference (SATD) method.

[0196] Meanwhile, in FIG. 8, the peripheral reference pixels (815) of the matching luminance block (812) are pixels in the ┌ region neighboring the left, top, and upper left, but this is just one example, and the peripheral reference pixels of the matching luminance block can be determined as any pixel around the matching luminance block. For example, the peripheral reference pixels of the matching luminance block can be peripheral pixels of the matching luminance block sampled at any rate.

[0197] Meanwhile, in the DIMD method, the size and shape of the area to which the boundary detection filter is applied can be arbitrarily determined.

[0198]

[0199] Meanwhile, if the intra prediction mode of the matching luminance block (812) is either the intra template matching mode or the intra block copy mode, the chrominance intra prediction mode can be determined as the intra prediction mode predefined in the encoder / decoder.

[0200] Meanwhile, the predefined intra prediction mode can be any one of Planar mode, DC mode, vertical mode, and horizontal mode.

[0201]

[0202] FIG. 9 is a diagram for explaining a direct block vector mode according to one embodiment of the present invention.

[0203] Direct block vector mode is a prediction mode in which the block vector information of a chrominance block is derived from the block vector information of a luminance block corresponding to the chrominance block.

[0204] In Fig. 9, the corresponding luminance block (910) represents a luminance block corresponding to the current chrominance block (900). And the luminance picture (911) represents a picture including the corresponding luminance block.

[0205] And, the matching luminance block (913) is a block indicated by the block vector (912) of the restored pixel of the corresponding luminance block (910) when the intra prediction mode of the corresponding luminance block is either the intra template matching mode or the intra block copy mode.

[0206] In Fig. 9, if the chrominance intra prediction mode information indicates a direct block vector (DBV) mode, a block vector for the current chroma block (902) can be derived using the block vector (912) information of the corresponding luminance block (910). Specifically, a restored pixel (C, T) at a predetermined position of the corresponding luminance block L , T R, B L, B R) is scaled to derive a block vector (902) of the current chroma block, and the derived block vector can point to a matching chroma block (Matching luma block, 903) of the current chroma block (900) included in the chroma picture (901). In addition, a prediction block of the current chroma block can be derived based on the matching chroma block (903).

[0207] Meanwhile, the chroma intra prediction mode information can be intra_chroma_pred_mode.

[0208] Here, scaling may mean adjusting the size of the block vector (912) of the corresponding luminance block to match the size of the current chrominance block. For example, if the ratio of the size of the corresponding luminance block (910) to the size of the current chrominance block (900) is 2:1, scaling may be performed so that the ratio of the size of the block vector (912) of the corresponding luminance block pixel to the size of the block vector (902) of the current chrominance block also becomes 2:1.

[0209] Meanwhile, if a block vector (912) exists in the corresponding luminance block (910), the chrominance intra prediction mode information can additionally indicate whether it is DBV mode.

[0210]

[0211]

[0212] Referring to Table 1, when a block vector (912) exists in a corresponding luminance block (910), the chrominance intra prediction mode can be determined as one of List[0], List[1], List[2], List[3], DIMD chroma mode, DM (direct mode), and DBV (direct block vector) mode, and intra_chroma_pred_mode can indicate each in the order of the indexes 0, 1, 2, 3, 4, 5, and 6. That is, the chrominance intra prediction mode information can indicate whether it is DBV mode.

[0213] Additionally, the bin string of intra_chroma_pred_mode for the chrominance intra prediction mode can be implemented with up to 5 bits as shown in Table 1. Here, List[0]-[3] can be the default mode, List[0] can be the Planar mode, List[1] can be 50 (i.e., vertical mode), List[2] can be 18 (i.e., horizontal mode), and List[3] can be the DC mode.

[0214] For example, if a chrominance block is predicted in DBV mode, the encoder determines intra_chroma_pred_mode as 6 and signals it with an empty string of '0', and the decoder can obtain intra_chroma_pred_mode through this. Then, the decoder restores the restored pixel (C, T) of the predetermined position of the corresponding luminance block (910). L , T R, B L, B R ) can be used to derive the block vector for the current chroma block (902).

[0215]

[0216] Meanwhile, if the intra prediction mode of the corresponding luminance block (910) is neither the intra template matching mode nor the intra block copy mode, the block vector of the corresponding luminance block (910) does not exist. Therefore, the block vector information of the corresponding luminance block cannot be used in the prediction of the current chrominance block. In this case, for the efficiency of prediction, the chrominance intra prediction mode information may not indicate whether the DBV mode is used. In addition, the current chrominance block (900) can perform prediction using an intra prediction mode other than the DBV mode.

[0217]

[0218]

[0219] Referring to Table 2, when the block vector of the corresponding luminance block does not exist, the chrominance intra prediction mode of the current chrominance block (900) can be determined as one of List[0], List[1], List[2], List[3], DIMD chroma mode, and DM (direct mode) excluding the DBV mode, and intra_chroma_pred_mode can indicate each in the order of the indexes 0, 1, 2, 3, 4, and 5. That is, the chrominance intra prediction mode information may not indicate whether it is the DBV mode.

[0220] Additionally, the bin string of intra_chroma_pred_mode for the chroma intra prediction mode can be implemented with up to 4 bits. Here, List[0]-[3] can be the default mode, List[0] can be Planar mode, List[1] can be 50 (i.e. vertical mode), List[2] can be 18 (i.e. horizontal mode), and List[3] can be DC mode.

[0221] For example, if a block vector of a corresponding luminance block does not exist, the chrominance intra prediction mode information may not indicate whether it is a DBV mode.

[0222]

[0223] Fig. 10 is a flowchart illustrating an image decoding method according to one embodiment of the present invention. Specifically, Fig. 10 is a flowchart illustrating a method for determining a chrominance intra prediction mode in an image decoding method. The chrominance intra prediction mode determination method of Fig. 10 can be performed by a decoding device.

[0224] The video decoding device can obtain color difference intra prediction mode information (S1000).

[0225] And, the image decoding device can determine the chrominance intra prediction mode of the current chrominance block based on the chrominance intra prediction mode information (S1001).

[0226] Meanwhile, if the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of the corresponding luminance block corresponding to the current chrominance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode can be determined based on the intra prediction mode of the matching luminance block indicated by the block vector of the corresponding luminance block.

[0227] Meanwhile, when the intra prediction mode of the above-mentioned matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode can be determined as a predefined intra prediction mode.

[0228] Meanwhile, the above-described intra prediction mode may be any one of Planar mode, DC mode, vertical mode, and horizontal mode.

[0229] Meanwhile, when the intra prediction mode of the above-mentioned matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode can be determined based on DIMD (Decoder side intra mode derivation).

[0230] Meanwhile, the DIMD method can be performed based on a gradient histogram of pixels within the corresponding luminance block.

[0231] Meanwhile, the DIMD method can be performed based on a gradient histogram of surrounding pixels of the corresponding luminance block.

[0232] Meanwhile, the DIMD method can be performed based on the difference between the restored pixel in the corresponding luminance block and the predicted pixel of the corresponding luminance block.

[0233] Meanwhile, the DIMD method can be performed based on a gradient histogram of pixels within the matching luminance block.

[0234] Meanwhile, the DIMD method can be performed based on a gradient histogram of surrounding pixels of the matching luminance block.

[0235] Meanwhile, the DIMD method can be performed based on the difference between the restored pixel in the matching luminance block and the predicted pixel of the matching luminance block.

[0236] Meanwhile, if the tree structure of the current chrominance block is a dual tree structure, the matching luminance block can be derived based on the intra prediction mode and block vector of any one of the upper left, lower left, center, upper right, and lower right pixels in the corresponding luminance block.

[0237] Meanwhile, if the tree structure of the current chrominance block is a single tree structure, the matching luminance block can be derived based on the intra prediction mode and block vector of the central pixel in the corresponding luminance block.

[0238] Meanwhile, if block vector information exists in the corresponding luminance block, the chrominance intra prediction mode information may additionally indicate whether it is a DBV (Direct block vector) mode.

[0239] And, the image decoding device can generate a prediction block of the current chrominance block based on the determined chrominance intra prediction mode (S1002).

[0240]

[0241] Meanwhile, the steps described in FIG. 10 can be performed in the same manner in an image encoding method, except for step S1000. The encoder can determine chrominance intra prediction mode information rather than acquiring chrominance intra prediction mode information. In addition, a bitstream can be generated by an image encoding method including these steps. The bitstream can be stored in a non-transitory computer-readable recording medium, and can also be transmitted (or streamed).

[0242]

[0243] FIG. 11 is a drawing exemplifying a content streaming system to which an embodiment according to the present invention can be applied.

[0244] As illustrated in FIG. 11, 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.

[0245] 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.

[0246] 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.

[0247] 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.

[0248] 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.

[0249] 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.

[0250] 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.

[0251]

[0252] 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.

[0253] 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.

[0254] 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.

[0255] 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.

[0256] 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.

[0257] 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.

[0258] 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.

[0259] 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.

[0260] 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.

[0261]

[0262] The present invention can be used in a device for encoding / decoding an image and a recording medium storing a bitstream.

Claims

1. In the video decryption method, A step of obtaining color difference intra prediction mode information; A step of determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information; and A step of generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode is included, An image decoding method, characterized in that when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of the corresponding luminance block corresponding to the current chrominance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined based on the intra prediction mode of the matching luminance block indicated by the block vector of the corresponding luminance block.

2. In paragraph 1, An image decoding method, characterized in that when the intra prediction mode of the above matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined as a predefined intra prediction mode.

3. In paragraph 2, An image decoding method, characterized in that the above-described intra prediction mode is any one of a planar mode, a DC mode, a vertical mode, and a horizontal mode.

4. In paragraph 1, An image decoding method, characterized in that when the intra prediction mode of the above matching luminance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined based on DIMD (Decoder side intra mode derivation).

5. In paragraph 4, An image decoding method, characterized in that the DIMD method is performed based on a gradient histogram of pixels within the corresponding luminance block.

6. In paragraph 4, An image decoding method, characterized in that the above DIMD method is performed based on a gradient histogram of surrounding pixels of the corresponding luminance block.

7. In paragraph 4, An image decoding method, characterized in that the DIMD method is performed based on the difference between a restored pixel in the corresponding luminance block and a predicted pixel of the corresponding luminance block.

8. In paragraph 4, An image decoding method, characterized in that the DIMD method is performed based on a gradient histogram of pixels within the matching luminance block.

9. In paragraph 4, An image decoding method, characterized in that the DIMD method is performed based on a gradient histogram of surrounding pixels of the matching luminance block.

10. In paragraph 4, An image decoding method, characterized in that the DIMD method is performed based on the difference between a restored pixel in the matching luminance block and a predicted pixel of the matching luminance block.

11. In paragraph 1, If the tree structure of the current color difference block above is a dual tree structure, An image decoding method, characterized in that the above matching luminance block is derived based on an intra prediction mode and a block vector of any one of the upper left, lower left, center, upper right, and lower right pixels in the corresponding luminance block.

12. In paragraph 1, If the tree structure of the current color difference block above is a single tree structure, An image decoding method, characterized in that the matching luminance block is derived based on the intra prediction mode and block vector of the central pixel in the corresponding luminance block.

13. In paragraph 1, An image decoding method, characterized in that when a block vector exists in the corresponding luminance block, the chrominance intra prediction mode information additionally indicates whether it is a DBV (Direct block vector) mode.

14. In the video encoding method, A step of determining color difference intra prediction mode information; A step of determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information; and A step of generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode is included, An image encoding method, characterized in that when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of the corresponding luminance block corresponding to the current chrominance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined based on the intra prediction mode of the matching luminance block indicated by the block vector of the corresponding luminance block.

15. A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method, The above image encoding method is, A step of determining color difference intra prediction mode information; A step of determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information; and A step of generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode is included, A non-transitory computer-readable recording medium, characterized in that when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of the corresponding luminance block corresponding to the current chrominance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined based on the intra prediction mode of the matching luminance block indicated by the block vector of the corresponding luminance block.

16. In a method of transmitting a bitstream generated by a video encoding method, The above transmission method comprises a step of transmitting the bitstream, The above encoding method is, A step of determining color difference intra prediction mode information; A step of determining a chrominance intra prediction mode of a current chrominance block based on the chrominance intra prediction mode information; and A step of generating a prediction block of the current chrominance block based on the determined chrominance intra prediction mode is included, A transmission method, characterized in that when the chrominance intra prediction mode information indicates DM (Direct Mode) and the intra prediction mode of the corresponding luminance block corresponding to the current chrominance block is one of the intra template matching mode and the intra block copy mode, the chrominance intra prediction mode is determined based on the intra prediction mode of the matching luminance block indicated by the block vector of the corresponding luminance block.

Images