Image encoding / decoding method and apparatus, and recording medium having bitstream stored therein

Abstract

Provided are an image encoding / decoding method and apparatus, a recording medium having a bitstream stored therein, and a transmission method. The image decoding method may comprise the steps of: determining a reference candidate block of the current block; determining a first distortion cost for a first region of the reference candidate block and determining a second distortion cost for a second region of the reference candidate block; determining the final distortion cost of the reference candidate block according to the weighted sum of the first distortion cost and the second distortion cost; and on the basis of the final distortion cost, determining the reference candidate block as a reference block of the current block.

Description

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

[0001] The present disclosure relates to a video encoding / decoding method, a device, and a recording medium storing a bitstream. Specifically, the present disclosure relates to a video encoding / decoding method, a device, and a recording medium storing a bitstream that reduce block boundary discontinuity.

[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] Inter-prediction using motion vectors (MVs) is a technique that searches for the reference block most similar to the current block in previously encoded / decoded reference pictures and uses it as the prediction block for the current block. Intra-block copy prediction using block vectors (BVs) is a technique that searches for the reference block most similar to the current block in previously encoded / decoded areas within the current picture and uses it as the prediction block for the current block. When searching and determining the prediction block for the current block, if the surrounding information of the current block (surrounding samples adjacent to the boundary of the current block) is not considered, the correlation between the current block and the surrounding adjacent samples of the current block is not reflected in the prediction block generation, which may result in discontinuities at the boundary of the current block. In particular, since the background around an object often changes as the object moves, the boundary of the block is not considered when searching for motion information, resulting in a large amount of residual signals mainly at the boundary of the block (the edge of the block). This can cause discontinuities in the boundary areas of the current block, resulting in reduced encoding efficiency and deteriorated image quality. Therefore, a discussion of motion vector and block vector search and determination methods is needed to remove or mitigate discontinuities in the boundary areas of the current block.

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

[0005] In addition, the present disclosure aims to provide a recording medium storing a bitstream generated by an image decoding method or device according to the present disclosure.

[0006] A video decoding method according to one embodiment of the present disclosure may be characterized by including the steps of: determining a reference candidate block of a current block; determining a first distortion cost for a first region of the reference candidate block and determining a second distortion cost for a second region of the reference candidate block; and determining a final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; and determining the reference candidate block as a reference block of the current block based on the final distortion cost.

[0007] In the above image decoding method, the first area may represent a sample area of ​​the reference candidate block, and the second area may represent a sample area of ​​a reference template of the reference candidate block.

[0008] In the above image decoding method, the method may include a step of determining a third distortion cost for a third area of ​​the reference candidate block, wherein the final distortion cost is determined according to a weighted sum of the first distortion cost, the second distortion cost, and the third distortion cost.

[0009] In the above image decoding method, the first region may represent a sample region of the reference candidate block, the second region may represent a sample region of an upper reference template of the reference candidate block, and the third region may represent a sample region of a left reference template of the reference candidate block.

[0010] In the above image decoding method, the first region may represent a sample region of an upper reference template of the reference candidate block, the second region may represent a sample region of a left reference template of the reference candidate block, and the third region may represent a sample region of an upper left reference template of the reference candidate block.

[0011] In the above image decoding method, the method may include a step of determining a third distortion cost for a third area of ​​the reference candidate block and a step of determining a fourth distortion cost for a fourth area of ​​the reference candidate block, wherein the final distortion cost is determined according to a weighted sum of the first distortion cost, the second distortion cost, the third distortion cost, and the fourth distortion cost.

[0012] In the above image decoding method, the first region represents a sample region of the reference candidate block, the second region represents a sample region of an upper reference template of the reference candidate block, the third region represents a sample region of a left reference template of the reference candidate block, and the fourth region represents a sample region of an upper left reference template of the reference candidate block.

[0013] In the above image decoding method, in determining the first distortion cost and the second distortion cost, it may be characterized in that the first distortion cost and the second distortion cost are determined based on the sum of absolute differences, the sum of square errors, or the sum of absolute transformation differences for the differences between samples corresponding to the first area and the second area.

[0014] In the above image decoding method, when determining the first distortion cost and the second distortion cost, it may be characterized in that the first distortion cost and the second distortion cost are determined by further considering the bit rate of the first region and the bit rate of the second region.

[0015] In the above image decoding method, the first distortion cost and the second distortion cost may be determined by the difference between samples related to the L0 reference block and samples related to the L1 reference block, respectively, when the current block is predicted by bidirectional inter-screen prediction.

[0016] In the above image decoding method, the first distortion cost and the second distortion cost may be determined by the difference between samples related to a reference block and samples related to the current block, respectively, when the current block is predicted by unidirectional inter-screen prediction or inter-screen block copy prediction.

[0017] A video encoding method according to one embodiment of the present disclosure may be characterized by including the steps of: determining a reference candidate block of a current block; determining a first distortion cost for a first region of the reference candidate block and determining a second distortion cost for a second region of the reference candidate block; and determining a final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; and determining the reference candidate block as a reference block of the current block based on the final distortion cost.

[0018] A non-transitory computer-readable recording medium according to one embodiment of the present disclosure can store a bitstream generated by an image encoding method according to various embodiments of the present disclosure.

[0019] A bitstream transmission method according to one embodiment of the present disclosure includes a step of transmitting the bitstream, and can transmit a bitstream generated by an image encoding method according to various embodiments of the present disclosure.

[0020] 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.

[0021] According to the present disclosure, a video encoding / decoding method and device with improved encoding / decoding efficiency can be provided.

[0022] Additionally, according to the present disclosure, a method for searching motion vectors and block vectors to remove or alleviate discontinuities in boundary areas of a current block can be provided.

[0023] Additionally, according to the present disclosure, the efficiency of inter-screen prediction can be improved by improving the accuracy of motion vectors.

[0024] In addition, according to the present disclosure, the efficiency of block copy prediction within a screen can be improved by improving the accuracy of a block vector.

[0025] 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.

[0026] FIG. 1 is a block diagram showing a configuration according to one embodiment of an encoding device to which the present disclosure is applied.

[0027] FIG. 2 is a block diagram showing a configuration according to one embodiment of a decryption device to which the present disclosure is applied.

[0028] FIG. 3 is a diagram schematically illustrating a video coding system to which the present disclosure can be applied.

[0029] Figure 4 illustrates a method for reducing discontinuity of the current block boundary in the process of searching and deriving a prediction block of the current block using motion vector information.

[0030] Figure 5 illustrates a method for reducing discontinuity of the current block boundary in the process of searching and deriving a prediction block of the current block using block vector information.

[0031] FIG. 6 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0032] FIG. 7 is a diagram exemplifying a content streaming system to which an embodiment according to the present disclosure can be applied.

[0033] A video decoding method according to one embodiment of the present disclosure may be characterized by including the steps of: determining a reference candidate block of a current block; determining a first distortion cost for a first region of the reference candidate block and determining a second distortion cost for a second region of the reference candidate block; and determining a final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; and determining the reference candidate block as a reference block of the current block based on the final distortion cost.

[0034] The present disclosure 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 disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. In the drawings, similar reference numerals designate the same or similar functions throughout. The shapes and sizes of elements in the drawings may be provided by way of example only for clarity. The detailed description of the exemplary embodiments described below refers to the accompanying drawings, which illustrate specific embodiments by way of example. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments. It should be understood that the various embodiments, while different from each other, are not necessarily mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present disclosure. Furthermore, it should be understood that the positions or arrangements 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.

[0035] While terms such as "first" and "second" may be used herein to describe various components, these 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 disclosure, a first component may be referred to as a "second component," and similarly, a second component may also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0036] The components shown in the embodiments of the present disclosure are independently depicted to represent different characteristic functions, and do not imply 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 disclosure as long as they do not deviate from the essence of the present disclosure.

[0037] The terminology used in this disclosure is merely used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly dictates otherwise. In addition, some components of the present disclosure may not be essential components that perform essential functions in the present disclosure and may be optional components merely for performance enhancement. The present disclosure may be implemented by including only components essential to implementing the essence of the present disclosure, excluding components used solely for performance enhancement, and a structure including only essential components, excluding optional components used solely for performance enhancement, is also within the scope of the present disclosure.

[0038] 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.

[0039] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In describing the embodiments of this specification, if a detailed description of a related known configuration or function is judged to 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 the same components will be omitted.

[0040] Glossary of Terms

[0041] 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.”

[0042] 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.

[0043] Hereinafter, the terms encoder and image encoding device may be used interchangeably and have the same meaning.

[0044] Hereinafter, the terms decoder and image decoding device may be used interchangeably and have the same meaning.

[0045] Hereinafter, “image”, “picture”, “frame” and “screen” may be used with the same meaning and may be used interchangeably.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Hereinafter, “inter” and “between screens” may be used interchangeably and have the same meaning.

[0050] Hereinafter, “intra” and “within screen” may be used interchangeably and have the same meaning.

[0051]

[0052] FIG. 1 is a block diagram showing a configuration according to one embodiment of an encoding device to which the present disclosure is applied.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] 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 disclosure, the third mode will be classified and described separately only when a specific description is required.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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).

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] For example, a 4x4 luminance residual block generated through intra 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] 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.

[0079] 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.

[0080] 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).

[0081] 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).

[0082] 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.

[0083] 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.

[0084] 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.

[0085] Bilateral filter (BIF) can also compensate for the offset from the original image on a sample-by-sample basis for the deblocked image.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] FIG. 2 is a block diagram showing a configuration according to one embodiment of a decryption device to which the present disclosure is applied.

[0090] The decoding device (200) may be a decoder, a video decoding device, or an image decoding device.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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).

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] FIG. 3 is a diagram schematically illustrating a video coding system to which the present disclosure can be applied.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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).

[0108] 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.

[0109] The rendering unit (23) can render the decrypted video / image. The rendered video / image can be displayed through the display unit.

[0110]

[0111] Hereinafter, with reference to FIGS. 4 to 6, a method for reducing block boundary discontinuity according to an embodiment of the present disclosure will be specifically described.

[0112] In the present disclosure, a method is proposed to reduce discontinuities in block boundaries by searching for and deriving a prediction block of a current block by considering adjacent samples of the current block in the process of searching for and deriving a prediction block of the current block using motion information. The method of the present disclosure can be applied to various prediction modes using motion vectors (MVs) or block vectors (BVs). Specifically, the prediction modes to which the method of the present disclosure is applied may include regular merge mode, merge with motion vector difference (MMVD) mode, advanced motion vector prediction (AMVP) mode, symmetric motion vector prediction (SMVD) mode, decoder side motion vector refinement (DMVR) mode, geometric partitioning mode (GPM) mode, combined inter and intra prediction (CIIP) mode, intra block copy merge (IBC merge) mode, intra block copy enhanced motion vector prediction (IBC AMVP) mode, advanced motion vector prediction-merge (AMVP-MERGE) mode, etc. In addition, the method of the present disclosure may also be applied to prediction modes not listed above.

[0113] According to one embodiment, in a normal merge mode, a merge mode using motion vector difference, or an in-screen block copy merge mode, a merge candidate can be selected from a merge candidate list using the proposed method.

[0114]

[0115] Figure 4 illustrates a method for reducing discontinuity of the current block boundary in the process of searching and deriving a prediction block of the current block using motion vector information.

[0116] In Fig. 4, the current picture (400), the List0 reference picture (420), and the List1 reference picture (440) represent a picture at time t, a reference picture at time t-t0 that is before the current picture in the playback order, and a reference picture at time t-t1 that is after the current picture in the playback order, respectively. In Fig. 4, t0 and t1 are each arbitrary positive integers.

[0117] Additionally, the current template (404), the List0 reference template (424), and the List1 reference template (444) represent an L-shaped current template adjacent to the current block (402), an L-shaped reference template adjacent to the corresponding block in List0 (422) in the List0 direction, and an L-shaped reference template adjacent to the corresponding block in List1 (442) in the List1 direction, respectively.

[0118] Also, MV0(426) and MV1(446) represent the motion vector in the direction of List0 and the motion vector in the direction of List1, respectively. In Fig. 4, the size of the template is L1 x H + W x L2 + L1 x L2. Here, W and H represent the horizontal and vertical lengths of the current block (402). And L1 and L2 represent the width of the template, respectively. And W, H, L1, and L2 are arbitrary positive integers.

[0119] The size and shape of each region (404, 424, 444) of the template adjacent to the current block, the List0 reference block, and the List1 reference block can be arbitrarily determined. For example, the template may include only the left template region, or only the top template region. Furthermore, as shown in Fig. 4, the template may include both the left template region and the top template region, forming an L-shape.

[0120] According to one embodiment, to generate a prediction block for a current block (402), a prediction block having the highest similarity to the current block (402) is searched and derived within List0 reference pictures (420) and List1 reference pictures (440). In this process, instead of performing the search based on the current block (402), List0 reference templates (424) and List1 reference templates (444) may be searched and derived based on a current template (404) adjacent to the current block (402). Alternatively, the search may be performed based on a block (a block of size (L1 + W) x (L2 + H)) containing the current block (402) and the current template (404).

[0121] According to one embodiment, the final prediction block of the current block (402) can be determined within a search range of motion vectors. The motion vector MV0 (426) in the List0 direction and the motion vector MV1 (446) in the List1 direction for deriving the final prediction block of the current block (402) are determined within the search range. In addition, the final prediction block of the current block (402) is determined from the reference block (422) in the List0 direction indicated by the motion vector MV0 (426) in the List0 direction and the reference block (442) in the List1 direction indicated by the motion vector MV1 (446) in the List1 direction. At this time, the reference blocks (422, 442) used for deriving the final prediction block are blocks having the smallest distortion cost among the List0 reference picture (420) and the List1 reference picture (440) within a predetermined search range.

[0122] Distortion cost is an indicator used to evaluate the distortion (or loss) of image information that occurs during the video compression process. This distortion cost can be utilized for rate distortion optimization. Therefore, a video codec can balance compression efficiency and image quality by selecting an appropriate encoding method based on the ultimately calculated distortion cost.

[0123] Here, distortion refers to the difference between the original image and the compressed image, and can be generally evaluated using various distortion functions (mean squared error (MSE), sum of absolute differences (SAD), sum of squared error (SSE), sum of absolute transformed differences (SATD), mean-removed sum of absolute differences (mean removed SAD), etc.). In addition, rate refers to the number of bits of the bitstream per unit time.

[0124] In the present disclosure, encoding efficiency can be improved by referring to low candidate blocks based on a distortion cost derived according to a reliable distortion cost calculation method.

[0125] According to one embodiment, a distortion cost may be calculated for a block (a block of size (L1 + W) x (L2 + H)) containing a reference template. The distortion cost may be determined as a weighted sum of the distortion cost of the block and the distortion cost of the reference template. In this case, the distortion cost may be calculated based on mathematical expression 1.

[0126] [Mathematical Formula 1]

[0127] Distortion cost = w 블록 x D_cost 블록 + w 참조템플릿 x D_cost 참조템플릿

[0128]

[0129] D_cost in Equation 1 블록 and D_cost 참조템플릿 represents the distortion cost value calculated from each block and the distortion cost value calculated from the reference template. D_cost 블록D_cost is a distortion cost value derived by weighting the distortion cost value between the current block (402) and the reference block (422) of List0 and the distortion cost value between the current block (402) and the reference block (442) of List1. 참조템플릿 is a distortion cost value derived by weighting the distortion cost value between the current template (404) and the reference template (424) of List0 and the distortion cost value between the current template (404) and the reference template (444) of List1.

[0130] Also, w 블록 and w 참조템플릿 is the weighted value of the distortion cost calculated from each block and the distortion cost calculated from the reference template. w 블록 and w 참조템플릿 0 ≤ w 현재블록 ≤ 1, 0 ≤ w 참조템플릿 ≤ 1, and w 블록 + w 참조템플릿 = Any real number satisfying 1.

[0131] In one embodiment, w 블록 and w 참조템플릿 can be determined by considering the distance between the current picture (400) and the List0 reference picture (420) and the distance between the current picture (400) and the List1 reference picture (440).

[0132] In one embodiment, w 블록 and w 참조템플릿 can be determined by considering the ratio of the area of ​​the block and the reference template. For example, w is proportional to the size of the block (WxH) and the size of the template (L1xH+WxL2+L1xL2). 블록 and w 참조템플릿 can be decided.

[0133] In one embodiment, w 블록 This w 참조템플릿It can be determined to be larger. This is because the motion vector of a block is determined for prediction of the block, not the template, and when more weight is given to the distortion cost of the block, the accuracy of the motion vector can be improved.

[0134] Or according to one embodiment, w 블록 and w 참조템플릿 can be a fixed predefined value or w 블록 and w 참조템플릿 may be a value obtained from a bitstream.

[0135] In mathematical expression 1, the same weight value (w) is applied to the entire region of the reference template. 참조템플릿 ) is assigned. However, according to one embodiment, the area of ​​the reference template may be divided, and different weights may be applied to the divided areas. For example, the reference template may be divided into an upper template area, a left template area, and an upper left template area, and different weight values ​​(w) may be applied to each area. 상단템플릿 , w 좌측템플릿 , w 좌상단템플릿 ) can be applied. In this case, the distortion cost can be calculated as in mathematical expression 2.

[0136] [Equation 2]

[0137] Distortion cost = w 블록 x D_cost 블록 + w 상단템플릿 x D_cost 상단템플릿 + w 좌측템플릿 x D_cost 좌측템플릿 + w 좌상단템플릿 x D_cost 좌상단템플릿

[0138]

[0139] D_cost in Equation 2 상단템플릿 , D_cost 좌측템플릿 , and D_cost 좌상단템플릿represents the distortion cost calculated from the upper template area, the distortion cost calculated from the left template area, and the distortion cost calculated from the upper left area, respectively. Also, w 상단템플릿 , w 좌측템플릿 , and w 좌상단템플릿 are the weighted values ​​of the distortion costs calculated from each area. w 상단템플릿 , w 좌측템플릿 , and w 좌상단템플릿 0 ≤ w 상단템플릿 ≤ 1, 0 ≤ w 좌측템플릿 ≤ 1, 0 ≤ w 좌상단템플릿 ≤ 1 and w 현재블록 + w 상단템플릿 + w 좌측템플릿 + w 좌상단템플릿 = Any real number satisfying 1.

[0140] The distortion cost of the above block can be derived from the difference value between the samples of the current block and the reference block in the List0 direction referred to in the bidirectional prediction. In addition, the distortion cost of the block can be derived from the difference value between the samples of the current block and the reference block in the List1 direction referred to in the bidirectional prediction. The distortion cost of the above block can be derived from the difference value between the samples of the reference block in the List0 direction and the reference block in the List1 direction referred to in the bidirectional prediction. The distortion cost of the above block can be determined by weighting the difference values ​​between the various types of samples listed above.

[0141] The distortion cost of the above template can be derived from the difference value between the sample of the current template and the reference template in the List0 direction referenced in the bidirectional prediction. In addition, the distortion cost of the block can be derived from the difference value between the sample of the current template and the reference template in the List1 direction referenced in the bidirectional prediction. The distortion cost of the above template can be derived from the difference value between the sample of the reference template in the List0 direction and the reference template in the List1 direction referenced in the bidirectional prediction. The distortion cost of the above template can be determined by weighting the difference values ​​between the various types of samples listed above.

[0142] At this time, the distortion cost can be calculated using various correlation measures such as the sum of absolute differences (SAD) of the difference values ​​between samples in the referenced area, the sum of square errors (SSE), or the sum of absolute transformed differences (SATD).

[0143] In one embodiment, in calculating the distortion cost, the block area may not be considered, and only the template area may be considered. In this case, different weights may be applied to the areas of each divided template. As in mathematical expression 2, the reference template is divided into the upper template area, the left template area, and the upper left template area, and a different weight value (w) is applied to each area. 상단템플릿 , w 좌측템플릿 , w 좌상단템플릿 ) can be applied. In this case, the distortion cost can be calculated as in mathematical expression 3.

[0144] [Equation 3]

[0145] Distortion cost = w 상단템플릿 x D_cost 상단템플릿 + w 좌측템플릿 x D_cost 좌측템플릿 + w 좌상단템플릿x D_cost 좌상단템플릿

[0146]

[0147] In Equations 2 and 3, the distortion cost and weight values ​​for the upper left template were determined independently from the upper and left templates. However, depending on the embodiment, the upper left template may be included in either the upper template or the left template. In this case, only the distortion costs and weight values ​​of the upper and left templates may be used in calculating the overall distortion cost.

[0148] Additionally, only the distortion cost was considered in Equations 1 to 3 to determine the reference block corresponding to the current block. However, a rate-distortion cost considering the bit rate is calculated, and the final prediction block of the current block (402) can be determined based on the rate-distortion cost.

[0149] Additionally, Fig. 4 illustrates a method for reducing discontinuities at block boundaries using Bi-predictive Advanced Motion Vector Prediction as an example. This can be applied to any method that uses motion vector (MV) information to search for and determine a prediction block, as an example.

[0150] For example, decoder-based motion vector compensation (DMVR) is an encoding tool that reduces prediction error and saves bitrate by having the decoder finely compensate for motion vectors in two-way inter-picture prediction using merge mode. To compensate for motion vectors, L0, 쪧L1 block pairs are searched for within a predetermined sample range based on the motion vector determined by the merge candidate. Then, the distortion cost for the searched L0, 쪧L1 block pairs is calculated. In calculating such distortion costs, the distortion cost calculation method proposed above can be applied.

[0151] Additionally, when correcting and improving motion information on the decoder side, such as through improved motion vector prediction-merge (AMVP-MERGE), the distortion cost calculation method proposed above can be applied. Alternatively, when determining motion information on the decoder side by performing the same process as on the encoder side, the distortion cost calculation method proposed above can be applied.

[0152]

[0153] Figure 5 illustrates a method for reducing discontinuity of the current block boundary in the process of searching and deriving a prediction block of the current block using block vector (BV) information.

[0154] In Fig. 5, a current picture (500) includes a current block (510) and a reference block (520) referenced by the current block (510). The reference block (520) is a block pointed to by a block vector (BV) (530) of the current block (510) within a reconstructed area. The current template (512) and the reference template (522) are templates of the current block (510) and the reference block (520), respectively.

[0155] In Fig. 5, the size of the template is L1 x H + W x L2 + L1 x L2. Here, W and H represent the horizontal and vertical lengths of the current block. And L1 and L2 represent the width of the template, respectively. And W, H, L1, and L2 are arbitrary positive integers.

[0156] The size and shape of each region (512, 522) of the template adjacent to the current block and the reference block can be arbitrarily determined. For example, the template may include only the left template region, or only the top template region. Furthermore, as shown in Fig. 5, the template may include both the left template region and the top template region, forming an L-shape.

[0157] In one embodiment, in intra block copy (IBC) prediction, to generate a prediction block for a current block, a prediction block with the highest similarity to the current block may be searched and derived within a reconstructed region. In this process, instead of performing the search based on the current block (510), a reference template (522) may be searched and derived based on the current template (512). Alternatively, the search may be performed based on a block (a block of size (L1 + W) x (L2 + H)) containing the current block (510) and the current template (512).

[0158] According to one embodiment, the final prediction block of the current block (510) can be determined within a search range of block vectors. A block vector BV (530) for deriving the final prediction block of the current block (510) is determined within the search range. And the final prediction block of the current block (510) is determined from a reference block (520) indicated by the block vector BV (530). At this time, the reference block (520) used for deriving the final prediction block is a block with the smallest distortion cost within a predetermined search range.

[0159] According to one embodiment, a distortion cost may be calculated for a block (a block of size (L1 + W) x (L2 + H)) containing a reference template. The distortion cost may be determined as a weighted sum of the distortion cost of the block and the distortion cost of the template. In this case, the distortion cost may be calculated based on the mathematical expression 1 introduced above.

[0160] According to one embodiment, the region of the reference template may be divided, and different weights may be applied to the divided regions. For example, the reference template may be divided into an upper template region, a left template region, and an upper left template region, and a different weight value (w) may be applied to each region. 상단템플릿, w 좌측템플릿 , w 좌상단템플릿 ) can be applied. In this case, the distortion cost can be calculated as in the mathematical expression 2 introduced above.

[0161] In one embodiment, in calculating the distortion cost, the block area may not be considered, and only the template area may be considered. In this case, different weights may be applied to the areas of each divided template. For example, the reference template may be divided into the upper template area, the left template area, and the upper left template area, and a different weight value (w) may be applied to each area. 상단템플릿 , w 좌측템플릿 , w 좌상단템플릿 ) can be applied. In this case, the distortion cost can be calculated as in the mathematical expression 3 introduced above.

[0162] In the embodiment according to FIG. 5, the upper left template is included in the upper template or the left template, and in calculating the overall distortion cost, only the distortion cost and weight values ​​of the upper template and the left template can be used.

[0163] Distortion costs can be calculated using various correlation measures, such as sum of absolute differences (SAD), sum of square error (SSE), or sum of absolute transformed differences (SATD).

[0164] Additionally, only the distortion cost was considered in Equations 1 to 3 to determine the reference block corresponding to the current block. However, a bit-rate-distortion cost considering the bit rate is calculated, and the final prediction block of the current block (510) can be determined based on the bit-rate-distortion cost.

[0165] The method described based on FIG. 5 can be used in all intra-screen block copy prediction modes that use block vector (BV) information to search for and determine a prediction block.

[0166] By the method proposed in the present disclosure, a prediction block of the current block is generated, so that discontinuities that may occur at the boundary of the block can be removed.

[0167]

[0168] FIG. 6 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure. The image decoding method of FIG. 6 can be performed by an image decoding device.

[0169] At step 610, a reference candidate block of the current block can be determined.

[0170] In step 620, a first distortion cost is determined for a first region of the reference candidate block, and a second distortion cost is determined for a second region of the reference candidate block.

[0171] According to one embodiment, the first region may represent a sample region of the reference candidate block, and the second region may represent a sample region of a reference template of the reference candidate block.

[0172] According to one embodiment, a third region and / or a fourth region of the reference candidate block may be further defined. If the third region is defined, a third distortion cost may be determined for the third region of the reference candidate block. If the fourth region is defined, a fourth distortion cost may be determined for the fourth region of the reference candidate block.

[0173] According to one embodiment, the first region may represent a sample region of the reference candidate block, the second region may represent a sample region of an upper reference template of the reference candidate block, and the third region may represent a sample region of a left reference template of the reference candidate block.

[0174] According to one embodiment, the first region may represent a sample region of an upper reference template of the reference candidate block, the second region may represent a sample region of a left reference template of the reference candidate block, and the third region may represent a sample region of an upper left reference template of the reference candidate block.

[0175] According to one embodiment, the first region may represent a sample region of the reference candidate block, the second region may represent a sample region of an upper reference template of the reference candidate block, the third region may represent a sample region of a left reference template of the reference candidate block, and the fourth region may represent a sample region of an upper left reference template of the reference candidate block.

[0176] According to one embodiment, the distortion cost corresponding to each region may be determined based on the sum of absolute differences, sum of squared errors, or sum of absolute transformed differences of the differences between samples corresponding to each region.

[0177] In one embodiment, the distortion cost corresponding to each region can be determined by further considering the bit rate of each region.

[0178] According to one embodiment, when the current block is predicted by bidirectional inter-screen prediction, the distortion cost corresponding to each region can be determined by the difference between samples related to the L0 reference block and samples related to the L1 reference block.

[0179] In one embodiment, when the current block is predicted by unidirectional inter-screen prediction or intra-screen block copy prediction, the distortion cost corresponding to each region can be determined by the difference between samples related to the reference block and samples related to the current block.

[0180] In step 630, the final distortion cost of the reference candidate block is determined based on the weighted sum of the first distortion cost and the second distortion cost.

[0181] In one embodiment, when a third region is defined, the final distortion cost may be determined based on a weighted sum of the first distortion cost, the second distortion cost, and the third distortion cost. Furthermore, when a third region and a fourth region are defined, the final distortion cost may be determined based on a weighted sum of the first distortion cost, the second distortion cost, the third distortion cost, and the fourth distortion cost.

[0182] In one embodiment, when the first region represents a sample region of the reference candidate block and the second region represents a sample region of a reference template of the reference candidate block, the first distortion cost and the second distortion cost are the distortion cost of the block and the distortion cost of the reference template, respectively. That is, the weights applied to the first distortion cost and the second distortion cost represent the weights of the distortion cost of the block and the distortion cost of the reference template.

[0183] According to one embodiment, the weight of the block and the weight of the reference template may be determined by considering the distance between the current picture and the List0 reference picture and the distance between the current picture and the List1 reference picture.

[0184] In one embodiment, the weight of a block and the weight of a reference template may be determined by considering the ratio of the areas of the block and the reference template. For example, the weight of a block and the weight of a reference template may be determined in proportion to the size of the block (WxH) and the size of the template (L1xH+WxL2+L1xL2).

[0185] In one embodiment, the weight of a block may be determined to be greater than the weight of a reference template. This is because the motion vector of a block is determined for prediction of the block, not the template, and when more weight is given to the distortion cost of the block, the accuracy of the motion vector may be improved.

[0186] Alternatively, according to one embodiment, the weight of the block and the weight of the reference template may be fixed, predefined values. Alternatively, the weight of the block and the weight of the reference template may be values ​​obtained from the bitstream.

[0187]

[0188] At step 640, based on the final distortion cost, a reference candidate block is determined as the reference block of the current block.

[0189] Meanwhile, the steps described in FIG. 6 can be performed in the same manner in an image encoding method. Furthermore, a bitstream can be generated by an image encoding method including the steps described in FIG. 6. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0190]

[0191] FIG. 7 is a diagram exemplifying a content streaming system to which an embodiment according to the present disclosure can be applied.

[0192] As illustrated in FIG. 7, a content streaming system to which an embodiment of the present disclosure is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

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

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

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

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

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

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

[0199]

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

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

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

[0203] In the above embodiments, the methods are described based on a flowchart as a series of steps or units. However, the present disclosure 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 disclosure.

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

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

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

[0207] Although the present disclosure 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 disclosure, and the present disclosure is not limited to the above examples, and a person having ordinary knowledge in the technical field to which the present disclosure belongs can make various modifications and variations from this description.

[0208] Therefore, the spirit of the present disclosure should not be limited to the embodiments described above, and all modifications that are equivalent or equivalent to the following claims as well as the claims are considered to fall within the scope of the spirit of the present disclosure.

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

Claims

A step of determining a reference candidate block of the current block; A step of determining a first distortion cost for a first region of the reference candidate block and a second distortion cost for a second region of the reference candidate block; and A step of determining the final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; An image decoding method comprising a step of determining the reference candidate block as a reference block of the current block based on the final distortion cost. In the first paragraph, The above first region represents a sample region of the reference candidate block, An image decoding method characterized in that the second region represents a sample region of a reference template of the reference candidate block. In the first paragraph, The above video decryption method is, comprising a step of determining a third distortion cost for a third region of the above reference candidate block; An image decoding method, characterized in that the final distortion cost is determined based on a weighted sum of the first distortion cost, the second distortion cost, and the third distortion cost. In the third paragraph, The above first region represents a sample region of the reference candidate block, The above second area represents a sample area of ​​the upper reference template of the above reference candidate block, An image decoding method, characterized in that the third region represents a sample region of a left reference template of the reference candidate block. In the third paragraph, The above first area represents a sample area of ​​the upper reference template of the above reference candidate block, The above second area represents a sample area of ​​the left reference template of the above reference candidate block, An image decoding method, characterized in that the third region represents a sample region of a reference template on the upper left side of the reference candidate block. In the first paragraph, The above video decryption method is, A step of determining a third distortion cost for a third region of the above reference candidate block and a step of determining a fourth distortion cost for a fourth region of the above reference candidate block, An image decoding method, characterized in that the final distortion cost is determined based on a weighted sum of the first distortion cost, the second distortion cost, the third distortion cost, and the fourth distortion cost. In paragraph 6, The above first region represents a sample region of the reference candidate block, The above second area represents a sample area of ​​the upper reference template of the above reference candidate block, The third region above represents a sample region of the left reference template of the reference candidate block, An image decoding method, characterized in that the fourth region represents a sample region of a reference template on the upper left side of the reference candidate block. In the first paragraph, In determining the first distortion cost and the second distortion cost, An image decoding method, characterized in that the first distortion cost and the second distortion cost are determined based on the sum of absolute differences, the sum of square errors, or the sum of absolute transformation differences of the differences between samples corresponding to the first region and the second region. In paragraph 8, In determining the first distortion cost and the second distortion cost, An image decoding method characterized in that the first distortion cost and the second distortion cost are determined by further considering the bit rate of the first region and the bit rate of the second region. In the first paragraph, The first distortion cost and the second distortion cost are respectively, An image decoding method characterized in that, when the current block is predicted by bidirectional inter-screen prediction, the difference between samples related to an L0 reference block and samples related to an L1 reference block is determined. In the first paragraph, The first distortion cost and the second distortion cost are respectively, A video decoding method characterized in that, when the current block is predicted by unidirectional inter-screen prediction or inter-screen block copy prediction, the difference between samples related to a reference block and samples related to the current block is determined. A step of determining a reference candidate block of the current block; A step of determining a first distortion cost for a first region of the reference candidate block and a second distortion cost for a second region of the reference candidate block; and A step of determining the final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; An image encoding method comprising a step of determining the reference candidate block as a reference block of the current block based on the final distortion cost. In 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 a reference candidate block of the current block; A step of determining a first distortion cost for a first region of the reference candidate block and a second distortion cost for a second region of the reference candidate block; and A step of determining the final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; A non-transitory computer-readable recording medium, characterized in that it comprises a step of determining the reference candidate block as a reference block of the current block based on the final distortion cost. In a bitstream transmission method for transmitting a bitstream generated by a video encoding method, A step of encoding an image based on the above image encoding method; and A step of transmitting a bitstream including the encoded image, The above image encoding method is, A step of determining a reference candidate block of the current block; A step of determining a first distortion cost for a first region of the reference candidate block and a second distortion cost for a second region of the reference candidate block; and A step of determining the final distortion cost of the reference candidate block according to a weighted sum of the first distortion cost and the second distortion cost; A transmission method, characterized in that it comprises a step of determining the reference candidate block as a reference block of the current block based on the final distortion cost.

Images