Image encoding / decoding method and device

Abstract

The present invention relates to an image encoding / decoding method and device. The image decoding method according to one embodiment of the present invention comprises the steps of: deriving block division permission information about the current block; deriving context information of a multi-type tree division flag on the basis of the block division permission information; deriving a value of the multi-type tree division flag of the current block on the basis of the derived context information; and dividing the current block on the basis of the multi-type tree division flag, wherein, if the tree type of the current block is a dual tree, the block division permission information is derived according to a color component of the current block, and, here, the context information of the multi-type tree division flag can be derived on the basis of block division permission information derived according to the color component.

Description

Video encoding / decoding method and device

[0001] The present invention relates to a video encoding / decoding method and device, and more particularly, to a video encoding / decoding method and device with improved syntax coding and algorithm.

[0002] Recently, the demand for multimedia data, such as video, has been rapidly increasing. In particular, the demand for high-resolution, high-quality video, such as HD (High Definition) and UHD (Ultra High Definition) video, is growing across a wide range of applications. High-resolution, high-quality video data typically requires significantly more data volume than conventional video data. Consequently, the transmission and storage costs for storing and / or transmitting high-resolution, high-quality video data increase compared to conventional video data.

[0003] To solve these problems, high-efficiency image encoding / decoding technology for images with higher resolution and quality is required.

[0004] In order to encode an image, various techniques are used, such as an intra prediction technique that predicts the pixel values ​​included in the current picture using pixel information in the current picture, an intra prediction technique that predicts the pixel values ​​included in the current picture from the pictures before or after the current picture, a transform and quantization technique for compressing the energy of the residual signal, which is the difference between the predicted signal and the original signal, and an entropy coding technique that assigns short codes to values ​​with high appearance frequencies and long codes to values ​​with low appearance frequencies. In addition, various tools are being developed to implement each technique in order to improve the efficiency of image coding. In addition, in order to decode an encoded image, the image can be restored and reproduced through an image decoding technique that uses a technique and tools corresponding to the image coding technique.

[0005] Using these video encoding and decoding technologies, video data can be effectively compressed, transmitted, stored, and played back.

[0006] The present disclosure aims to provide a video encoding / decoding method and device that improves the inefficiency of syntax coding and enhances the compression efficiency of video data.

[0007] In addition, the present disclosure aims to provide a video encoding / decoding method and device that improves the compression efficiency of video data by improving the information reference process in the encoding / decoding process.

[0008] In addition, the present disclosure aims to provide a video encoding / decoding method and device that improves the compression efficiency of video data by improving the algorithm of the encoding / decoding process.

[0009] The technical challenges to be achieved through this disclosure are not limited to the technical challenges mentioned above. Furthermore, other technical challenges not mentioned in this disclosure will be readily apparent to those skilled in the art from this disclosure.

[0010] A video decoding method according to one embodiment of the present invention includes the steps of: deriving block splitting permission information for a current block; deriving context information of a multi-type tree splitting flag based on the block splitting permission information; deriving a value of a multi-type tree splitting flag of the current block based on the derived context information; and splitting the current block based on the multi-type tree splitting flag, wherein when a tree type of the current block is a dual tree, the block splitting permission information is derived according to a color component of the current block, and wherein the context information of the multi-type tree splitting flag can be derived based on the block splitting permission information derived according to the color component.

[0011] An image decoding method, characterized in that in the above image decoding method, the multi-type tree splitting flag is a flag indicating the direction of multi-type tree splitting.

[0012] An image decoding method, characterized in that in the above image decoding method, the block division permission information includes vertical division permission information and horizontal division permission information.

[0013] An image decoding method, characterized in that in the above image decoding method, the vertical direction division permission information includes information on whether vertical direction bi-division is allowed and information on whether vertical direction tri-division is allowed.

[0014] An image decoding method, characterized in that in the above image decoding method, the horizontal direction division permission information includes information on whether horizontal direction bi-division is allowed and information on whether horizontal direction tri-division is allowed.

[0015] An image decoding method, characterized in that, in the above image decoding method, context information of a multi-type tree split flag is derived based on a comparison result between a value of vertical direction splitting permission information and a value of horizontal direction splitting permission information.

[0016] An image decoding method, characterized in that in the above image decoding method, the multi-type tree splitting flag is a flag indicating the type of multi-type tree splitting.

[0017] A video encoding method according to one embodiment of the present invention includes a step of determining block splitting permission information for a current block, a step of determining a multi-type tree splitting flag of the current block, a step of determining context information of the multi-type tree splitting flag based on the block splitting permission information, and a step of encoding the multi-type tree splitting flag based on the context information, wherein when a tree type of the current block is a dual tree, the block splitting permission information may be derived based on a color component of the current block, and the context information of the multi-type tree splitting flag may be derived based on the block splitting permission information derived based on the color component.

[0018] A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method according to one embodiment of the present invention includes a step of determining block splitting permission information for a current block, a step of determining a multi-type tree splitting flag of the current block, a step of determining context information of the multi-type tree splitting flag based on the block splitting permission information, and a step of encoding the multi-type tree splitting flag based on the context information, wherein when the tree type of the current block is a dual tree, the block splitting permission information is derived based on a color component of the current block, and the context information of the multi-type tree splitting flag is derived based on the block splitting permission information derived based on the color component. The bitstream generated by the video encoding method can be stored.

[0019] A method for transmitting a bitstream generated by a video encoding method according to one embodiment of the present invention includes the steps of transmitting the bitstream, determining block splitting permission information for a current block, determining a multi-type tree splitting flag of the current block, determining context information of the multi-type tree splitting flag based on the block splitting permission information, and encoding the multi-type tree splitting flag based on the context information, wherein when the tree type of the current block is a dual tree, the block splitting permission information is derived based on a color component of the current block, and the context information of the multi-type tree splitting flag is derived based on the block splitting permission information derived based on the color component. A bitstream generated by the video encoding method can be transmitted.

[0020] According to the present disclosure, a video encoding / decoding method and device can be provided that improves the inefficiency of syntax coding and enhances the compression efficiency of video data.

[0021] In addition, according to the present disclosure, a method and device for encoding / decoding an image can be provided that improves the compression efficiency of image data by improving an information reference process in an encoding / decoding process.

[0022] In addition, according to the present disclosure, a method and device for encoding / decoding an image can be provided that improves the compression efficiency of image data by improving an algorithm of an encoding / decoding process.

[0023] In addition, according to the present disclosure, a recording medium storing a bitstream generated by the image encoding method or device of the present invention can be provided.

[0024] The effects that can be obtained from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description below.

[0025] FIG. 1 is a block diagram illustrating an image encoding device according to one embodiment of the present disclosure.

[0026] FIG. 2 is a block diagram illustrating an image decoding device according to one embodiment of the present disclosure.

[0027] FIG. 3 is a diagram schematically illustrating a video coding system to which the present disclosure can be applied.

[0028] FIG. 4 is a diagram exemplifying a content streaming system to which an embodiment according to the present disclosure can be applied.

[0029] FIG. 5 is a flowchart illustrating an image decoding method for determining context information of syntax elements for an adaptive loop filter according to an embodiment of the present disclosure.

[0030] FIG. 6 is a flowchart illustrating an image decoding method for determining prediction mode condition information of a current block according to an embodiment of the present disclosure.

[0031] FIG. 7 is a diagram illustrating a signaling mechanism of block division related syntax elements according to one embodiment of the present disclosure.

[0032] FIG. 8 is a flowchart illustrating an image decoding method for determining context information of syntax elements regarding multi-type tree division of a current block according to an embodiment of the present disclosure.

[0033] FIG. 9 is a parameter model for determining a motion vector in an affine model-based inter prediction according to an embodiment of the present disclosure.

[0034] FIG. 10 is a flowchart illustrating an image decoding method for changing the resolution of an affine motion vector difference of a current block according to an embodiment of the present disclosure.

[0035] FIG. 11 is a diagram illustrating a segmentation structure of a current block based on an index indicating a geometric segmentation mode according to one embodiment of the present disclosure.

[0036] FIG. 12 is a diagram illustrating a current block predicted by a geometric segmentation mode according to one embodiment of the present disclosure.

[0037] FIG. 13 is a flowchart illustrating an image decoding method for storing motion information of a current block in a geometric segmentation mode according to an embodiment of the present disclosure.

[0038] The present invention is susceptible to various modifications and embodiments. 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 alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0039] While terms such as "first" and "second" may be used 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 invention, 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.

[0040] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0041] The terminology used in this application is only 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 this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0042] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings. Hereinafter, identical components in the drawings will be designated by the same reference numerals, and redundant descriptions of identical components will be omitted.

[0043] In the description below, "image" may refer to a video or a picture that constitutes a video. The terms "image," "picture," and "frame" may be used interchangeably and have the same meaning.

[0044] An image can be encoded by an image encoding device, and an image encoded by the image encoding device can be decoded by an image decoding device.

[0045] An image encoding device may also be referred to as an encoder or encoder. And, an image decoding device may also be referred to as a decoder or decoder.

[0046] In the description below, the target block may refer to a block being encoded and / or a block being decoded. For example, the target block may be the current block, which is the block currently being encoded or decoded. The terms "target block expression" and "current block" may be used interchangeably and have the same meaning.

[0047] In the description below, the terms "block" and "unit" may be used interchangeably and interchangeably. Alternatively, the term "unit" may refer to a unit comprising a luminance component block and a corresponding chrominance component block. For example, a coding tree unit may comprise a luminance component coding tree block and two corresponding chrominance component coding tree blocks.

[0048] In the description below, a sample may be a unit that constitutes a block. The terms "sample," "pixel," and "pixel" may be used interchangeably and have the same meaning.

[0049] FIG. 1 is a block diagram illustrating an image encoding device according to one embodiment of the present disclosure.

[0050] Referring to FIG. 1, an image encoding device (100) may include an image segmentation unit (101), an intra prediction unit (102), an inter prediction unit (103), a subtraction unit (104), a transformation unit (105), a quantization unit (106), an entropy encoding unit (107), an inverse quantization unit (108), an inverse transformation unit (109), an addition unit (110), a filter unit (111), and a memory (112).

[0051] Each component shown in Fig. 1 is independently depicted to represent different characteristic functions in the video encoding device, and does 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 one 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.

[0052] Additionally, some components may not be essential components that perform the essential functions of the present disclosure, but may be optional components merely used to enhance performance. 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. A structure that includes only essential components, excluding optional components used solely for performance enhancement, is also within the scope of the present disclosure.

[0053] The image segmentation unit (101) can segment an input image into at least one block. At this time, the input image can have various shapes and sizes such as a sequence, a picture, a slice, a tile, a segment, a tile group, a coding tree block, etc. According to another embodiment, the image segmentation unit (101) can segment one input picture into a plurality of sub-pictures defined as a group of rectangular slices, segment each sub-picture into the tiles / slices, and segment the tiles / slices into coding tree blocks.

[0054] In addition, the image segmentation unit (101) can recursively segment the segmented coding tree block. The terminal node segmented from the coding tree block may be referred to as a coding unit (CU). The block may mean a coding unit (CU), or a prediction unit (PU) or a transformation unit (TU) segmented from the coding unit (CU). The segmentation may be performed based on at least one of a quadtree, a binary tree, and a ternary tree. A quadtree is a method of segmenting an upper block into lower blocks whose width and height are half of those of the upper block. A binary tree is a method of segmenting an upper block into lower blocks whose width or height is half of that of the upper block. A ternary tree is a method of segmenting an upper block into three lower blocks. For example, the three lower blocks may be obtained by segmenting the width or height of the upper block at a ratio of 1:2:1. Through the binary tree-based partitioning described above, blocks can have not only square but also non-square shapes. Blocks can first be partitioned into a quad tree. Blocks corresponding to leaf nodes of the quad tree can be left unpartitioned, or can be partitioned into a binary tree or a ternary tree. Leaf nodes of the binary tree or ternary tree can be units of encoding, prediction, and / or transformation.

[0055] The image segmentation unit (101) can recursively segment the CTU into not only a quad tree (QT) but also a multi-type tree (MTT). Here, the MTT can be composed of a binary tree (BT) and a triple tree (TT). For example, the MTT structure can be divided into a vertical binary tree splitting mode (SPLIT_BT_VER), a horizontal binary tree splitting mode (SPLIT_BT_HOR), a vertical ternary tree splitting mode (SPLIT_TT_VER), and a horizontal triple splitting mode (SPLIT_TT_HOR).

[0056] In addition, the image segmentation unit (101) can segment a CTU by applying a dual tree that uses different CTU segmentation structures for luminance and chrominance components, or by applying a single tree in which luminance and chrominance CTBs (Coding Tree Blocks) within a CTU share a coding tree structure.

[0057] The prediction unit (102, 103) may include an intra-prediction unit (102) that performs intra-prediction and an inter-prediction unit (103) that performs inter-prediction. The prediction unit (102, 103) may determine whether to use intra-prediction or inter-prediction for a prediction unit. In addition, the prediction unit (102, 103) may determine specific information (e.g., intra-prediction mode, inter-prediction mode, motion vector, reference picture, etc.) according to the determined prediction method. At this time, the processing unit where the prediction is performed and the processing unit where the prediction method and specific contents are determined may be different. For example, the prediction unit (102, 103) may determine the prediction method and prediction mode for each prediction unit, and perform prediction according to the transformation unit.

[0058] In another embodiment, the prediction unit may encode the input image using a third mode (e.g., IBC mode, Palette mode, etc.) other than the intra mode and the inter mode. However, if the third mode has functional characteristics similar to the intra mode or the inter mode, the third mode may be classified as the intra mode or the inter mode. In this disclosure, the third mode will be described only when a specific description thereof is required.

[0059] The intra prediction unit (102) can generate a prediction block of the current block based on the intra prediction mode of the current block and reference pixel information around the current block, which is pixel information within the current picture. If a neighboring block of the current block is predicted by inter prediction, the reference pixels included in the inter-predicted neighboring block can be replaced with reference pixels within another neighboring block that has been intra-predicted. That is, if a reference pixel is not available, the intra prediction unit (102) can perform intra prediction of the current block by replacing the unavailable reference pixel with at least one reference pixel among the available reference pixels.

[0060] The intra prediction unit (102) can use multiple reference pixel lines for intra prediction of the current block. When multiple reference pixel lines are available, information indicating a reference pixel line used for intra prediction among the multiple reference pixel lines can be signaled.

[0061] Intra prediction modes used for intra prediction may include a directional prediction mode that uses reference pixel information according to the prediction direction, and a non-directional mode that does not use directional information. Additionally, the mode for predicting luminance information and the mode for predicting chrominance information may be different, and the intra prediction mode information of the luminance component block or the predicted luminance signal information may be utilized to predict chrominance information.

[0062] The intra prediction unit (102) may include a reference sample filter, an interpolation filter, and a DC filter. The reference sample filter is a filter that performs filtering on the reference pixels of the current block and may be adaptively applied depending on the prediction mode, size, shape, and / or whether the reference pixel of the current prediction unit is included in a reference pixel line immediately adjacent to the current block. If the prediction mode of the current block is a mode that does not perform reference pixel filtering, the reference pixel filter may not be applied.

[0063] An interpolation filter is a filter that interpolates and filters prediction samples of the current block, and can be adaptively applied depending on the prediction mode, size, shape, and / or whether the reference pixel of the current prediction unit is included in the reference pixel line immediately adjacent to the current block.

[0064] If the prediction mode of the current block is DC mode, a prediction block can be generated by applying a DC filter.

[0065] The inter prediction unit (103) generates a prediction block using the previously restored reference image stored in the memory (112), the inter prediction mode, and the motion information. Here, inter prediction may mean motion prediction or motion compensation.

[0066] The inter prediction unit (103) can set the inter mode of a coding block to one of the Skip Mode, Merge Mode, and Advanced Motion Vector Prediction (AMVP) mode in order to perform motion prediction and / or motion compensation. In addition, the inter prediction unit (103) can perform motion prediction and / or motion compensation for the current block according to the set mode.

[0067] In addition, the inter prediction unit (103) may perform motion prediction and / or motion compensation for a prediction block by applying an affine mode of sub-PU-based prediction, a Subblock-based Temporal Motion Vector Prediction (SbTMVP) mode, and a MMVD (Merge with MVD) mode and a GPM (Geometric Partitioning Mode) mode of PU-based prediction based on the inter prediction mode. In addition, the inter prediction unit (103) may perform motion prediction and / or motion compensation for a prediction block by applying a History-based MVP (HMVP), a Pairwise Average MVP (PAMVP), a Combined Intra / Inter Prediction (CIIP), an Adaptive Motion Vector Resolution (AMVR), a Decoder-side Motion Vector Refinement (DMVR), a Bi-Directional Optical-Flow (BDOF), a Prediction Refinement With Optical Flow (PROF), a Bi-predictive with CU Weights (BCW), etc. to improve the performance of each mode.

[0068] Here, AFFINE mode can be used in both AMVP and MERGE modes. It is a technique with high encoding efficiency. AFFINE mode can be a prediction mode that uses a 4-parameter affine motion model using two control point motion vectors (CPMV) or a 6-parameter affine motion model using three control point motion vectors. Here, CPMV can be a vector representing an affine motion model of any one of the top left, top right, and bottom left of the current block.

[0069] The motion information may include, for example, a motion vector, a reference picture index, a list 1 prediction flag, a list 0 prediction flag, a half-sample interpolation filter index, a bidirectional prediction weight index, etc.

[0070] A residual block containing residual value information, which is the difference value between the prediction unit generated in the prediction unit (102, 103) and the original block of the prediction unit, can be generated. The generated residual block can be input to the transformation unit (130) and transformed.

[0071] The subtraction unit (104) subtracts the block to be encoded from the prediction block generated by the intra prediction unit (102) or inter prediction unit (103) to generate a residual block of the current block. The residual value (residual block) between the generated prediction block and the original block can be input to the transformation unit (105).

[0072] Additionally, the prediction mode information, motion vector information, etc. used for prediction can be encoded together with the residual value in the entropy encoding unit (107) and transmitted to the decoder. When using a specific encoding mode, it is also possible to encode the original block as is and transmit it to the decoding unit without generating a prediction block through the prediction unit (102, 103).

[0073] The transformation unit (105) can perform a transformation on a residual block including residual data to generate and output a transform coefficient. Here, the transform coefficient may be a coefficient value generated by performing a transformation on the residual block. When the transform skip mode is applied, the transformation unit (105) may also skip the transformation on the residual block.

[0074] The conversion unit (105) can determine a conversion type and a conversion kernel based on at least one of encoding parameters such as the size, color component, and prediction mode of the conversion block, and perform conversion on the conversion block using the determined conversion type and conversion kernel.

[0075] According to one embodiment, the transformation unit (105) may perform transformation on a 4x4 luminance residual block generated as an intra prediction result using a transformation type and transformation kernel according to DST (Discrete Sine Transform), and may perform transformation on the remaining residual blocks using a transformation type and transformation kernel according to DCT (Discrete Cosine Transform).

[0076] According to another embodiment, the transform unit (105) may apply the Multiple Transform Selection (MTS) technology that performs the transform by selectively using several transform types and transform kernels. That is, the transform unit (105) may perform the transform in units of sub-blocks using the Sub-block Transform (SBT) technology. Specifically, the SBT may be applied only to inter-prediction blocks, and the current block may be divided into ½ or ¼ sizes in the vertical or horizontal direction, and the transform may be performed on only one of the blocks. For example, the transform unit (105) may perform the transform on the leftmost or rightmost block among the vertically divided current blocks, and may perform the transform on the topmost or bottommost block among the horizontally divided current blocks.

[0077] According to another embodiment, the transform unit (105) may apply LFNST (Low Frequency Non-Separable Transform), which is a technology that applies a secondary transform to a residual signal that has been transformed into a frequency domain through DCT or DST. LFNST additionally performs a transform on a 4x4 or 8x8 low-frequency region in the upper left, thereby concentrating the residual coefficients in the upper left.

[0078] The quantization unit (106) can quantize the transform coefficients or residual signals converted to the frequency domain by the transform unit (105) according to a quantization parameter (QP). The quantization parameter can vary depending on the block or the importance of the image. The value produced by the quantization unit (106) can be provided to the dequantization unit (108) and the entropy encoding unit (107).

[0079] The above transformation unit (105) and / or quantization unit (106) may be optionally included in the image encoding device (100). That is, the image encoding device (100) may encode the residual block by performing at least one of transformation or quantization on the residual data of the residual block, or by skipping both transformation and quantization. Even if neither transformation nor quantization is performed in the image encoding device (100), or neither transformation nor quantization is performed, a block that is input to the entropy encoding unit (107) is typically referred to as a transformation block.

[0080] The entropy encoding unit (107) can generate and output a bitstream by performing entropy encoding according to a probability distribution on values ​​output by the quantization unit (106), coding parameter values ​​output during the encoding process, information for decoding an image, etc. Here, the information for decoding an image may include syntax elements, etc.

[0081] 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.

[0082] The entropy encoding unit (107) can encode various information such as coefficient information of a transform block, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information. The coefficients of a transform block can be encoded in units of sub-blocks within the transform block.

[0083] For encoding the coefficients of a transform block, various syntax elements can be encoded, such as Last_sig, a syntax element indicating the position of the first non-zero coefficient in reverse scan order, Coded_sub_blk_flag, a flag indicating whether there is at least one non-zero coefficient in the subblock, Sig_coeff_flag, a flag indicating whether the coefficient is non-zero, Abs_greater1_flag, a flag indicating whether the absolute value of the coefficient is greater than 1, Abs_greater2_flag, a flag indicating whether the absolute value of the coefficient is greater than 2, and Sign_flag, a flag indicating the sign of the coefficient. The residual value of the coefficient that is not encoded by the above syntax elements alone can be encoded through the syntax element remaining_coeff.

[0084] When entropy coding 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, thereby reducing the size of the bit string for the symbols to be encoded. The input data is entropy encoded. For example, entropy coding can use various coding methods such as Exponential Golomb and CABAC (Context-Adaptive Binary Arithmetic Coding).

[0085] The inverse quantization unit (108) and the inverse transformation unit (109) can inverse quantize the values ​​quantized in the quantization unit (106) and inversely transform the values ​​transformed in the transformation unit (105). The residual values ​​generated in the inverse quantization unit (108) and the inverse transformation unit (109) can be combined with the prediction units predicted through the motion estimation unit, motion compensation unit, and intra prediction unit (102) included in the prediction unit (102, 103) to generate a reconstructed block. The addition unit (110) adds the prediction blocks generated in the prediction units (102, 103) and the residual blocks generated through the inverse transformation unit (109) to generate a reconstructed block.

[0086] The filter unit (111) can apply a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), LMCS (Luma Mapping with Chroma Scaling), etc. as a filtering technique to a restored sample, restored block, or restored image, in whole or in part.

[0087] A deblocking filter can remove block distortion caused by boundaries between blocks in a reconstructed picture. To determine whether to perform deblocking, a deblocking filter can be applied to the current block based on the pixels contained in several columns or rows within the block. When applying a deblocking filter to a block, a strong filter or a weak filter can be applied depending on the required deblocking filtering strength. Furthermore, when applying a deblocking filter, horizontal and vertical filtering can be processed in parallel when performing vertical and horizontal filtering.

[0088] Sample adaptive offset may be a method of correcting the offset from the original image on a sample-by-sample basis for an image on which deblocking has been performed. The filter unit (111) may use a method of dividing the samples included in the image into a certain number of regions, determining the regions to perform the offset, and applying the offset to the regions, or a method of applying the offset by considering the edge information of each sample.

[0089] Adaptive Loop Filtering (ALF) can be performed based on the comparison of the filtered restored image with the original image. After dividing the pixels contained in the image into predetermined groups, a filter to be applied to each group can be determined, and filtering can be performed differentially for each group. Information regarding whether to apply ALF can be transmitted by luminance signal for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied can vary depending on each block. Furthermore, the same type (fixed type) of ALF filter can be applied regardless of the characteristics of the target block.

[0090] An adaptive loop filter can perform filtering based on a comparison of the 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 block, and the shape and filter coefficients of the adaptive loop filter applied to each block can vary.

[0091] The memory (112) can store a restored block or picture produced through the filter unit (111). The memory (112) can include a reference picture buffer. In addition, the restored block or picture stored in the memory (112) can be provided to the prediction unit (102, 103) when performing inter prediction.

[0092] Next, an image decoding device according to one embodiment of the present disclosure will be described with reference to the drawings.

[0093] FIG. 2 is a block diagram illustrating an image decoding device (200) according to one embodiment of the present disclosure.

[0094] Referring to FIG. 2, the image decoding device (200) may include an entropy decoding unit (201), an inverse quantization unit (202), an inverse transformation unit (203), a prediction unit (204, 205), an addition unit (206), a filter unit (207), and a memory (208).

[0095] The image decoding device (200) can receive a bitstream output by the image encoding device (100). The image decoding device (200) can receive a bitstream stored in a computer-readable recording medium, or can receive a bitstream streamed through a wired / wireless transmission medium. The image decoding device (200) can decode the bitstream to generate a restored image or a decoded image, and can output the restored image or the decoded image.

[0096] The entropy decoding unit (201) 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.

[0097] The entropy decoding unit (201) 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).

[0098] The entropy decoding unit (201) can perform entropy decoding in a procedure opposite to that of the entropy encoding unit (107) of the video encoding device (100). For example, various methods such as Exponential Golomb and CABAC (Context-Adaptive Binary Arithmetic Coding) can be applied in response to the method performed in the video encoder.

[0099] When a syntax element is decoded based on a context model, the entropy decoding unit (201) can obtain a bin corresponding to the syntax element from the bitstream and determine a context model using the syntax element and the decoding information of the block to be decoded or the surrounding blocks or the information of the symbol / bin decoded in the previous step. Then, the entropy decoding unit (201) can predict the occurrence probability of the received bin according to the determined context model and perform arithmetic decoding of the bin to derive the value of the syntax element. Thereafter, the context model of the bin to be decoded thereafter can be updated based on the determined context model.

[0100] Additionally, for example, when a syntax element is bypass decoded, the entropy decoding unit (201) can obtain a bin corresponding to the syntax element through a bitstream and decode the input bin by applying a uniform probability distribution.

[0101] A context model can be assigned and updated for each context-coded (regularly coded) bean. The context model can be specified based on a context index (ctxIdx: context index) or a context index increment (ctxInc: context index increment). The context index can be derived based on the context index increment. For example, information indicating a context model for each of the regularly coded bins can be derived based on the sum of context index offsets (ctxIdxOffset: context index offset). For example, the context index increment information can be derived differently for each bin. And, the context index offset can be derived as the lowest value of the context index. The context index offset can be a value generally used to distinguish from context models for other syntax elements, and the context model for a syntax element can be distinguished or derived based on the context index increment information.

[0102] The entropy decoding unit (201) can decode and obtain various information such as coefficient information of the transform block as described above, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference frame information, block interpolation information, and filtering information.

[0103] The entropy decoding unit (201) can decode information related to a coding tree block. The entropy decoding unit (201) can derive information indicating whether splitting is allowed. Here, the information indicating whether splitting is allowed may include allowSplitQt, which is information indicating whether quadtree splitting is allowed, allowSplitBtVer, which is information indicating whether vertical bisector splitting is allowed, allowSplitBtHor, which is information indicating whether horizontal bisector splitting is allowed, allowSplitTtVer, which is information indicating whether vertical trisector splitting is allowed, and allowSplitTtHor, which is information indicating whether horizontal trisector splitting is allowed. The information indicating whether splitting is allowed may be determined based on the width, height, position, tree type information (treeType), split mode information, and mode type information (modeType) of the current coding tree block.

[0104] The entropy decoding unit (201) can decode syntax elements related to division of a coding block based on information indicating whether division is allowed.

[0105] For example, syntax elements related to splitting a coding block may include split_cu_flag indicating whether to split a coding block, split_qt_flag indicating whether to split a coding block into a quadtree, mtt_split_cu_vertical_flag indicating whether to split a coding block into a multi-type tree in the vertical direction, and mtt_split_cu_binary_flag indicating whether to split a coding block into two into a multi-type tree.

[0106] Here, the coding tree block can be partitioned according to a multi-type tree structure, which is a partitioning structure using one of a quadripartite structure and / or a bipartite structure and a ternary partitioning structure.

[0107] First, a coding tree block can be split into four blocks based on the value of split_cu_flag. The quad-split coding block can then be further split into four blocks based on the value of split_qt_flag. A coding block that is not split into a quad-tree can be referred to as a quad-tree leaf node.

[0108] A coding block, which is a quadtree leaf node, can be split according to a multi-type tree structure. That is, the split type of a coding block, which is a quadtree leaf node, can be determined as a bipartition structure or a tripartition structure depending on the values ​​of mtt_split_cu_vertical_flag, which indicates whether a multi-type tree is vertically split, and mtt_split_cu_binary_flag, which indicates whether a multi-type tree is bipartite.

[0109] The binary splitting structure can include vertical binary splitting (SPLIT_BT_VER) and horizontal binary splitting (SPLIT_BT_HOR). Vertical binary splitting (SPLIT_BT_VER) can be a structure that divides the current coding block into two equal parts vertically. On the other hand, horizontal binary splitting (SPLIT_BT_HOR) can be a structure that divides the current coding block into two equal parts horizontally.

[0110] The ternary splitting structure can include vertical ternary splitting (SPLIT_TT_VER) and horizontal ternary splitting (SPLIT_TT_HOR). Vertical ternary splitting (SPLIT_TT_VER) can be a structure that vertically splits the current coding block in a ratio of 1:2:1. On the other hand, horizontal ternary splitting (SPLIT_TT_HOR) can be a structure that horizontally splits the current coding block in a ratio of 1:2:1.

[0111] The multi-type tree split structure can be determined as shown in Table 1 below based on a combination of the values ​​of mtt_split_cu_vertical_flag, which indicates whether to split the coding block vertically, and mtt_split_cu_binary_flag, which indicates whether to split the coding block into which the multi-type tree is split into two.

[0112]

[0113] The inverse quantization unit (202) performs inverse quantization on a quantized transform block to generate a transform block. It operates substantially the same as the inverse quantization unit (108) of Fig. 1.

[0114] The inverse transform unit (203) performs an inverse transform on the transform block to generate a residual block. At this time, the transform method can be determined based on information regarding the prediction method (inter or intra prediction), the size and / or shape of the block, the intra prediction mode, etc. It operates substantially the same as the inverse transform unit (109) of FIG. 1.

[0115] According to one embodiment, the inverse transform unit (203) may perform inverse transform using a transform type and transform kernel according to DST (Discrete Sine Transform) on the transform coefficient levels of the 4x4 luminance component generated as an intra prediction result, and may perform inverse transform using a transform type and transform kernel according to DCT (Discrete Cosine Transform) on the remaining transform coefficient levels.

[0116] According to another embodiment, the inverse transform unit (203) may apply MTS (Multiple Transform Selection) technology to perform transformation by selectively using multiple transformation kernels.

[0117] According to another embodiment, the inverse transform unit (203) may apply LFNST (Low Frequency Non-Separable Transform), which is a technology that applies a secondary inverse transform to a transform coefficient level inversely transformed through a DCT or DST-based transform type and transform kernel.

[0118] The prediction unit (204, 205) can generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit (201) and the previously decoded block or picture information provided by the memory (208).

[0119] The prediction unit (204, 205) may include an intra prediction unit (204) and an inter prediction unit (205). The prediction unit (204, 205) may receive various information such as prediction unit information input from the entropy decoding unit (201), prediction mode information of the intra prediction method, and motion prediction-related information of the inter prediction method, and may distinguish a prediction unit from a current encoding unit and determine a prediction mode of the prediction unit.

[0120] The intra prediction unit (204) can generate a prediction block of the current block based on the intra prediction mode of the current block and reference pixel information around the current block, which is pixel information within the current picture.

[0121] The intra prediction unit (204) can generate a prediction block based on reference pixel information surrounding the current block, which is pixel information within the current picture. The intra prediction unit (204) can use multiple reference pixel lines for intra prediction. When multiple reference pixel lines are available, the intra prediction unit (204) can obtain information indicating a reference pixel line used for intra prediction from among the multiple reference pixel lines.

[0122] The intra prediction mode used for intra prediction may be a directional prediction mode or a non-directional mode. Furthermore, the mode for predicting luminance information may be different from the mode for predicting chrominance information, and the intra prediction mode information of the luminance component block or the predicted luminance signal information may be utilized to predict chrominance information.

[0123] The intra prediction unit (204) operates substantially the same as the intra prediction unit (102) of FIG. 1.

[0124] The inter prediction unit (205) may perform inter prediction on the current prediction unit based on information included in at least one picture among the previous picture or the subsequent picture of the current picture including the current prediction unit, using information necessary for inter prediction of the current prediction unit provided by the image encoding device (100). Alternatively, inter prediction may be performed based on information of some pre-restored area within the current picture including the current prediction unit.

[0125] The inter prediction unit (205) can set the inter mode of a coding block to one of the Skip Mode, Merge Mode, and Advanced Motion Vector Prediction (AMVP) mode in order to perform motion prediction and / or motion compensation. In addition, the inter prediction unit (205) can perform motion compensation on a prediction block according to the set mode.

[0126] In addition, the inter prediction unit (205) can perform motion compensation for a prediction block by applying 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 based on the inter prediction mode. In addition, the inter prediction unit (205) can perform motion compensation for a prediction block by applying 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), etc. to improve the performance of each mode.

[0127] The motion information may include, for example, a motion vector, a reference picture index, a list 1 prediction flag, a list 0 prediction flag, a half-sample interpolation filter index, a bidirectional prediction weight index, etc.

[0128] The inter prediction unit (205) can operate substantially the same as the inter prediction unit (103) of FIG. 1.

[0129] The addition unit (206) adds the prediction block generated by the intra prediction unit (204) or inter prediction unit (205) and the residual block generated by the inverse transformation unit (203) to generate a restored block. It operates substantially the same as the addition unit (110) of Fig. 1.

[0130] The filter unit (207) can reduce various types of noise occurring in restored blocks. The filter unit (207) can include a deblocking filter, a sample adaptive offset, an adaptive loop filter (ALF), and an LMCS.

[0131] The filter unit (207) can receive information on whether each filter is applied, information on the strength of the filter, etc. from the image encoding device (100). The filter unit (207) of the image decoding device (200) can receive filter-related information provided from the image encoding device (100) and perform filtering on the corresponding block in the image decoding device (200).

[0132] The filter unit (207) can operate substantially the same as the filter unit (111) of FIG. 1.

[0133] The memory (208) can store the restoration block generated by the addition unit (206). For example, the memory (208) can include a reference picture buffer. The memory (208) can operate substantially the same as the memory (112) of FIG. 1.

[0134]

[0135] FIG. 3 is a diagram schematically illustrating a video coding system to which the present disclosure can be applied.

[0136] 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.

[0137] An encoding device (10) according to one embodiment may include an image generating unit (11), an encoding unit (12), and a transmission unit (13). A decoding device (20) according to one embodiment may include a receiving unit (21), a decoding unit (22), and an image reproducing unit (23). The encoding unit (12) may be referred to as a video / image encoding unit, and the decoding unit (22) may be referred to as a video / image decoding unit. The transmission unit (13) may be included in the encoding unit (12). The receiving unit (21) may be included in the decoding unit (22). The image reproducing unit (23) may include a display unit, and the display unit may be configured as a separate device or an external component.

[0138] The image generation unit (11) can obtain a video / image through a process of capturing, synthesizing, or generating a video / image. The image 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 a video / image. 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.

[0139] 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 be configured in the same manner as the encoding device (100) of FIG. 1 described above.

[0140] 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).

[0141] 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 be configured identically to the decoding device (200) of FIG. 2 described above.

[0142] The image playback unit (23) can render decrypted video / images. The rendered video / images can be displayed through the display unit.

[0143]

[0144] FIG. 4 is a diagram exemplifying a content streaming system to which an embodiment according to the present disclosure can be applied.

[0145] As illustrated in FIG. 4, a content streaming system to which an embodiment of the present disclosure is applied may largely include a multimedia input device, a media storage, an encoding server, a streaming server, a web server, and a user device.

[0146] The encoding server compresses content input from multimedia input devices such as smartphones, cameras, CCTVs, etc. into digital data, creates a bitstream, and transmits it to the streaming server. Alternatively, the encoding server compresses content already stored in a media storage into digital data, creates a bitstream, and transmits it to the streaming server.

[0147] As another example, if multimedia input devices such as smartphones, cameras, CCTVs, etc. directly generate bitstreams, the encoding server may be omitted.

[0148] 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 or non-temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0149] 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 the user device 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 device. At this time, the content streaming system may include a separate control server, and in this case, the control server may play a role in controlling commands / responses between each device within the content streaming system.

[0150] 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.

[0151] 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.

[0152] 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.

[0153]

[0154] During video decoding, contextual information about the syntax of the current block can be derived using information from adjacent blocks. Based on this derived contextual information, a context model is determined, enabling decoding of the syntax for the block.

[0155] For example, the syntax for the current block may be syntax for an adaptive loop filter. Specifically, the syntax for the adaptive loop filter may include alf_ctb_flag indicating whether to apply the adaptive loop filter, alf_ctb_cc_cb_idc[ctbX][ctbY] indicating whether to apply a cross-component filter to the cb component, and alf_ctb_cc_cr_idc[ctbX][ctbY] indicating whether to apply a cross-component filter to the cr component.

[0156] Here, cIdx can indicate the color component of the current block. In addition, ctbX can indicate the x-axis position of the coding tree block containing the current block within the frame, and ctbY can indicate the y-axis position of the coding tree block containing the current block within the frame. ctbX and ctbY can be derived as follows.

[0157]

[0158] And, the positions of the blocks neighboring the current block, (ctbAx, ctbAy) and (ctbLx, ctbLy), can be derived as follows.

[0159]

[0160]

[0161] The context information of syntax elements for the adaptive loop filter can be derived as follows.

[0162]

[0163] To derive context information, context information (ctxInc) can be derived by utilizing condL, a condition regarding the left neighboring block, which is a block adjacent to the left of the current block, availableL, which indicates the availability of the left neighboring block, condA, a condition regarding the upper neighboring block, which is a block adjacent to the upper of the current block, and availableA, which indicates the availability of the upper neighboring block. Here, condL, availableL, condA, and availableA can be derived as shown in Table 2 below.

[0164]

[0165] That is, referring to mathematical expression 3 and Table 2, in order to derive condition information condL regarding the left neighboring block, availability information availableL of the left neighboring block, condition information condA regarding the upper neighboring block, and availability information availableA of the upper neighboring block, a block neighboring to the current block must be determined. Then, neighboring blocks are specified based on the color component information (cIdx) and position information (ctbX, ctbY) of the current block, and condition and availability information of each neighboring block can be derived based on the specified neighboring blocks.

[0166] Alternatively, context information for syntax elements can be derived independently of the color components of the current block. Therefore, by using fewer context models during decoding, memory usage can be reduced. Furthermore, by reducing the number of accesses during decoding, encoding and decoding speeds can be improved.

[0167] Specifically, the neighboring blocks of the current block used to derive context information can be determined using values ​​that are not dependent on the color component (e.g., cIdx) value of the current block. For example, the color component value can be a representative value of 0, 1, or 2. Then, the neighboring blocks can be determined based on the representative value of the color component.

[0168] In addition, condition information (e.g., condL, condA) and availability information (e.g., availableL, availableA) about neighboring blocks can be derived using information about neighboring blocks determined based on color component values ​​that are not dependent on the color component cIdx value of the current block. For this purpose, a representative value of cIdx determined by the encoder can be implicitly or explicitly transmitted to the decoder.

[0169] Embodiments of the present disclosure can also be applied to cases where the coding tree structure is independent of color components. Embodiments of the present disclosure can also be applied to cases where the coding tree structure is not independent of color components.

[0170] A method for image decoding that determines context information of syntax elements for an adaptive loop filter may be as described below.

[0171]

[0172] FIG. 5 is a flowchart illustrating an image decoding method for determining context information of syntax elements related to an adaptive loop filter according to an embodiment of the present disclosure. The image decoding method of FIG. 5 may be performed by an image decoding device.

[0173] Referring to FIG. 5, the image decoding device can derive availability information of blocks adjacent to the current block and encoding information related to an adaptive loop filter (S510).

[0174] The image decoding device can derive context information of encoding information related to the adaptive loop filter of the current block based on availability information of blocks adjacent to the current block and encoding information related to the adaptive loop filter (S520).

[0175] The image decoding device can decode encoding information related to the adaptive loop filter of the current block based on the derived context information (S530).

[0176] Here, the encoding information of blocks adjacent to the current block can be determined regardless of the color component of the current block.

[0177] Meanwhile, the steps described in FIG. 5 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. 5. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0178]

[0179] During a video decoding process, prediction mode condition information for each sub-block of a coding tree block can be derived based on coding parameters including information on the partition structure of the coding tree block. Then, prediction mode type information for each sub-block can be determined based on the value of the prediction mode condition information.

[0180] If the value of the prediction mode condition information is a first value (e.g., 1), the prediction mode type information may be determined as a first mode type using one of intra prediction, IBC, and palette modes.

[0181] On the other hand, if the value of the prediction mode condition information is a second value (e.g., 2), information on the availability of the inter prediction mode may be additionally signaled. If the information on the availability of the inter prediction mode indicates that inter prediction cannot be used, the mode type information may be determined as the first mode type. Conversely, if the information on the availability of the inter prediction mode indicates that inter prediction can be used, the mode type information may be determined as the second mode type that uses the inter prediction mode.

[0182] When the value of the prediction mode condition information is a third value (e.g., 0), the mode type information may be set to be the same as the mode type information of the current coding tree. Here, the mode type information may have a value of any one of the first mode type, the second mode type, and the third mode type indicating to use one of all prediction modes including intra prediction, IBC (intra block copy), palette mode, and inter prediction, according to the mode type information of the current coding tree.

[0183] Here, the prediction mode condition information can be derived as shown in Tables 3 to 5 below.

[0184]

[0185] According to Table 3, if one or more of the sub-conditions are satisfied, the value of the prediction mode condition information (e.g., ModeTypeCondition) may be determined as 0. Here, the first condition among the sub-conditions may mean that the type of the current slice is I, and each coding tree block included in the slice is implicitly quadtree split into 64x64 luma sample coding blocks. The second condition may mean that the mode type of the current coding tree block is other than MODE_TYPE_ALL. The third condition may mean that the chrominance component format of the current coding block is monochrome (sps_chroma_format_idc=0). And, the fourth condition may mean that the chrominance component format of the current coding block is a 4:4:4 format (sps_chroma_format_idc=3).

[0186]

[0187] According to Table 4, if the condition defined in Table 3 is not satisfied and at least one of the sub-conditions is satisfied, the value of the prediction mode condition information may be determined as 1. Here, the first condition among the sub-conditions may mean that the area of ​​the current block is 64 and the current block is divided into four. The second condition may mean that the area of ​​the current block is 64 and the current block is divided into three horizontally or vertically. The third condition may mean that the area of ​​the current block is 32 and the current block is divided into two horizontally or vertically.

[0188]

[0189] According to Table 5, when the conditions defined in Tables 3 and 4 are not satisfied and one of the sub-conditions is satisfied, the prediction mode condition information may be determined according to the type of the current slice. Here, the first condition among the sub-conditions may mean that the area of ​​the current block is 64, the current block is horizontally divided into two or vertically divided into two, and the chrominance component format of the current block is a 4:2:0 format (sps_chroma_format_idc=1). The second condition may mean that the area of ​​the current block is 128, the current block is horizontally divided into three or vertically divided into three, and the chrominance component format of the current block is a 4:2:0 format (sps_chroma_format_idc=1). The third condition may mean that the width of the current block is 8, and the current block is horizontally divided into two. And, the fourth condition may mean that the height of the current block is 16 and the current block is divided into three vertical parts.

[0190] And, if one of the sub-conditions is satisfied and the type of the current slice is an I slice, the value of the prediction mode condition information can be determined as 1. On the other hand, if one of the sub-conditions is satisfied and the type of the current slice is not an I slice, the value of the prediction mode condition information can be determined as 2.

[0191] On the other hand, if the sub-conditions are not met or two or more of the sub-conditions are met, the value of the prediction mode condition information may be determined as 0 regardless of the type of the current slice.

[0192] As defined in Table 5, the process of determining the value of the prediction mode condition information based on the current slice type may be used infrequently. This is because situations where only one of the sub-conditions is satisfied occur infrequently. Therefore, the utility of the process of determining the value of the prediction mode condition information based on the current slice type may be low. Consequently, encoding efficiency may be reduced.

[0193] To improve encoding efficiency, conditions for determining the value of prediction mode condition information based on the type of the current slice can be defined as shown in Table 6 below.

[0194]

[0195] Specifically, if the conditions defined in Tables 3 to 4 are not met and one or more of the sub-conditions defined in Table 6 are met, the prediction mode condition information can be determined according to the type of the current slice.

[0196] Here, the first condition among the sub-conditions may mean that the area of ​​the current block is 64, the current block is divided into two horizontally or vertically, and the chrominance component format of the current block is a 4:2:0 format (sps_chroma_format_idc=1). The second condition may mean that the area of ​​the current block is 128, the current block is divided into three horizontally or vertically, and the chrominance component format of the current block is a 4:2:0 format (sps_chroma_format_idc=1). The third condition may mean that the width of the current block is 8, and the current block is divided into two horizontally. And, the fourth condition may mean that the height of the current block is 16, and the current block is divided into three vertically.

[0197] Here, if one or more of the sub-conditions defined in Table 6 are satisfied and the type of the current slice is an I slice, the value of the prediction mode condition information may be determined as 1. On the other hand, if one or more of the sub-conditions defined in Table 6 are satisfied and the type of the current slice is not an I slice, the value of the prediction mode condition information may be determined as 2.

[0198] Alternatively, if the conditions defined in Tables 3 to 4 are not satisfied and a predefined number or more of the sub-conditions defined in Table 6 are satisfied, the prediction mode condition information may be determined according to the type of the current slice. Here, the predefined number may be an integer greater than or equal to 2.

[0199] Alternatively, according to another embodiment of the present disclosure, if the conditions defined in Tables 3 to 4 are not satisfied, and a number of conditions determined by signaling information or more among the sub-conditions defined in Table 6 are satisfied, the prediction mode condition information may be determined according to the type of the current slice. Here, the signaling information may be signaled in units such as sequences, GOP picture slices, and CTUs.

[0200] The method for determining the prediction mode condition information defined in Table 5 and the method for determining the prediction mode condition information defined in Table 6 may differ in the following situations.

[0201] If the current block is a block of 8x8 size, the multi-type division mode of the current block is a vertical bi-division mode, and the chrominance component format of the current block is a 4:2:0 format, the current block can simultaneously satisfy the first and third conditions defined in Tables 5 and 6.

[0202] In the above case, according to Table 5, since the value of the prediction mode condition information can be determined based on the type of the slice when only one of the multiple conditions is satisfied, the prediction mode condition information of the current block can be determined as 0.

[0203] On the other hand, in the case above, according to Table 6, since the value of the prediction mode condition information can be determined based on the type of the slice when one or more of the multiple conditions are satisfied, the value of the prediction mode condition information of the current block can be determined based on the slice type.

[0204] Meanwhile, if the current block is a block of 16x8 size, the multi-type division mode of the current block is a vertical three-division mode, and the chrominance component format of the current block is a 4:2:0 format, the current block can simultaneously satisfy the second and fourth conditions defined in Tables 5 and 6.

[0205] In the above case, according to Table 5, since the value of the prediction mode condition information can be determined based on the type of the slice when only one of the multiple conditions is satisfied, the value of the prediction mode condition information of the current block can be determined as 0.

[0206] On the other hand, in the case above, according to Table 6, since the value of the prediction mode condition information can be determined based on the type of the slice when one or more of the multiple conditions are satisfied, the value of the prediction mode condition information of the current block can be determined based on the slice type.

[0207] That is, according to Table 6, the usability of the process of determining the value of the prediction mode condition information based on the type of the current slice can be increased.

[0208] A video decoding method for determining prediction mode condition information of the current block may be as described below.

[0209]

[0210] FIG. 6 is a flowchart illustrating an image decoding method for determining prediction mode condition information of a current block according to an embodiment of the present disclosure. The image decoding method of FIG. 6 can be performed by an image decoding device.

[0211] Referring to FIG. 6, the image decoding device can determine condition information of the prediction mode of the current coding tree block (S610).

[0212] The video decoding device can determine the prediction mode of blocks divided from the current coding tree block based on condition information of the prediction mode (S620).

[0213] Here, if at least one condition among the conditions of the first condition set is true, the condition information of the prediction mode can be set to the first value.

[0214] Here, the first set of conditions may include a first condition that is satisfied when the type of the current slice is I and each coding tree block included in the slice is implicitly divided into 64x64 luma sample coding blocks, a second condition that is satisfied when the current coding tree block can use all prediction modes, a third condition that is satisfied when the chrominance component format of the current coding tree block is monochrome, and a fourth condition that is satisfied when the chrominance component format of the current coding tree block is a 4:4:4 format.

[0215] Here, if at least one condition among the conditions of the first condition set is not true and at least one condition among the conditions of the second condition set is true, the condition information of the prediction mode can be set to a second value.

[0216] Here, the second set of conditions may include a first condition that is satisfied when the area of ​​the current coding tree block is 64 and the current coding tree block is divided into four, a second condition that is satisfied when the area of ​​the current coding tree block is 64 and the current coding tree block is divided into three, and a third condition that is satisfied when the area of ​​the current coding tree block is 32 and the current coding tree block is divided into two.

[0217] Here, if at least one condition of the first condition set is not true, at least one condition of the second condition set is not true, and at least one condition of the third condition set is true, the condition information of the prediction mode may be determined based on the slice type. Here, the condition information of the prediction mode may be determined based on whether the slice type is an I slice.

[0218] Here, the third set of conditions may include a first condition that is satisfied when the area of ​​the current coding tree block is 64, the current coding tree block is horizontally divided into two or vertically divided into two, and the chrominance component format of the current coding tree block is a 4:2:0 format, a second condition that is satisfied when the area of ​​the current coding tree block is 128, the current coding tree block is horizontally divided into three or vertically divided into three, and the chrominance component format of the current coding tree block is a 4:2:0 format, a third condition that is satisfied when the width of the current coding tree block is 8, and the current coding tree block is horizontally divided into two, and a fourth condition that is satisfied when the height of the current coding tree block is 16, and the current coding tree block is vertically divided into three.

[0219] Here, if at least one condition among the conditions of the first condition set is not true, at least one condition among the conditions of the second condition set is not true, and at least one condition among the conditions of the third condition set is not true, the condition information of the prediction mode can be set to the first value.

[0220] Here, if the condition information of the prediction mode is the first value, the prediction mode of the block to be split may be set to be the same as the prediction mode of the current coding tree block. If the condition information of the prediction mode is the second value, the prediction mode of the block to be split may be determined as one of the intra prediction, IBC, and palette modes. If the condition information of the prediction mode is the third value, the prediction mode of the block to be split may be determined as the inter prediction mode based on additional information.

[0221] The video decoding device can generate prediction blocks of blocks divided from the current coding tree block based on the prediction mode (S630).

[0222] 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).

[0223]

[0224] During a video decoding process, the tree type of a sub-block can be determined based on the prediction mode type information of the sub-blocks divided from the current coding tree block. Specifically, the tree type can be determined as a single tree or a dual tree depending on the value of the prediction mode condition information of the sub-block.

[0225] If the prediction mode type information of the sub-block indicates a first mode type indicating that intra prediction, IBC, and palette modes are available, the tree type may be determined as a dual tree. In this case, the tree type of the sub-block of the luminance component may be dual tree luma (DUAL_TREE_LUMA), and the tree type of the sub-block of the chrominance component may be dual tree chroma (DUAL_TREE_CHROMA).

[0226] If the tree type is determined to be a dual tree, block partition information of a sub-block of a luminance component can be derived. Then, a block partition structure of a sub-block of a luminance component can be determined based on the derived block partition information. Separately, block partition information of a sub-block of a color component can be derived. Then, a block partition structure of a sub-block of a color component can be determined based on the derived block partition information.

[0227] That is, if the tree type is a dual tree, block partition information can be derived based on the color component. Accordingly, the partition structure of the luminance component sub-block may be different from the partition structure of the chrominance component sub-block.

[0228] Here, the block partition information may include syntax elements related to partitioning of a coding tree block. The syntax elements related to partitioning of a coding tree block may be signaled as follows.

[0229]

[0230] FIG. 7 is a diagram illustrating a signaling mechanism of block division related syntax elements according to one embodiment of the present disclosure.

[0231] Referring to FIG. 7, an initial coding tree block may be a root node of a quadtree. The coding tree block, which is the root node, may be split into four. Information (e.g., qt_split_flag) indicating whether to perform quadrupling for the current coding block (e.g., coding tree unit / quadtree node (CTU / QT_node) or coding unit node (CU_node)) may be signaled. For example, if qt_split_flag is a first value (e.g., "1"), the current coding block may be split into four. On the other hand, if qt_split_flag is a second value (e.g., "0"), the current coding block may not be split into four. A coding block that is not split into four may be referred to as a leaf node (QT_leaf_node) of the quadtree.

[0232] The coding block, which is a leaf node of each quadtree, can be further divided into a multi-type tree structure. That is, the coding block, which is a leaf node of the quadtree, can be a coding unit node (MTT_CU_node) of the multi-type tree.

[0233] In a multi-type tree structure, a multi-type tree split direction flag (e.g., mtt_split_cu_vertical_flag) of the current coding unit may be signaled. For example, if the value of the multi-type tree split direction flag is 1, the current coding unit may be split in the vertical direction. On the other hand, if the value of the multi-type tree split direction flag is 0, the current coding unit may be split in the horizontal direction.

[0234] Afterwards, the multi-type tree split type flag (e.g., mtt_split_cu_binary_flag) of the current coding unit may be signaled. For example, if the value of the multi-type tree split type flag is 1, the current coding unit may be split into two. On the other hand, if the value of the multi-type tree split type flag is 0, the current coding unit may be split into three.

[0235] Here, in order to decode the multi-type tree splitting direction flag, context information can be derived as defined in Table 7 below. Then, the multi-type tree splitting direction flag can be entropy decoded based on the derived context information.

[0236]

[0237] As defined in Table 7, if the sum of the values ​​of vertical direction split permission information (e.g., allowSplitBtVer, allowSplitTtVer) is greater than the sum of horizontal direction split permission information (e.g., allowSplitBtHor, allowSplitTtHor, etc.), the context information ctxInc of the multi-type tree split direction flag (e.g., mtt_split_cu_vertical_flag) may be set to 4.

[0238] On the other hand, if the sum of the values ​​of vertical direction split permission information (e.g., allowSplitBtVer, allowSplitTtVer) is less than the sum of horizontal direction split permission information (e.g., allowSplitBtHor, allowSplitTtHor, etc.), the context information ctxInc of the multi-type tree split direction flag (e.g., mtt_split_cu_vertical_flag) can be set to 3.

[0239] Additionally, to derive context information of a multi-type tree split type flag, context information of a multi-type tree split direction flag can be used.

[0240] However, as defined in Table 7, the context information of the multi-type tree splitting direction flag can be derived regardless of the color components of the current block.

[0241] According to the dual-tree partitioning structure, block partitioning-related syntax elements can be obtained for each of the luminance and chrominance components. However, the multi-type tree partitioning direction flags for each of the luminance and chrominance components can be decoded using the same context information, regardless of the color information. Therefore, encoding efficiency may be reduced.

[0242] To improve encoding efficiency, when the tree type is a dual tree, context information of the multi-type tree splitting direction flag can be derived for each of the luminance component and the chrominance component.

[0243] Specifically, when the tree type is a dual tree, block splitting permission information can be derived based on the color component. Then, context information of a multi-type tree splitting direction flag can be derived based on the block splitting permission information. For example, context information of a multi-type tree splitting direction flag of a luminance component can be derived based on block splitting permission information of a luminance component. Then, context information of a multi-type tree splitting direction flag of a chrominance component can be derived based on block splitting permission information of a chrominance component. Therefore, context information of a multi-type tree splitting direction flag suitable for a color component of a coding block can be derived.

[0244] In addition, when context information of the multi-type tree split direction flag is derived for each of the luminance component and the chrominance component, context information of the multi-type tree split type flag can be derived for each of the luminance component and the chrominance component.

[0245] That is, when the tree type is a dual tree, context information of the multi-type tree split type flag of the luminance component can be derived using the value and context information of the multi-type tree split direction flag of the luminance component. And, context information of the multi-type tree split type flag of the chrominance component can be derived using the value and context information of the multi-type tree split direction flag of the chrominance component.

[0246] Alternatively, if information indicating that context information of a multi-type tree splitting direction flag is to be derived regardless of the color component of the current block is signaled, the context information of the multi-type tree splitting direction flag can be derived based on block splitting permission information derived according to a predetermined color component. Here, the signaling information can include information indicating a predetermined color component. In addition, the signaling information can be signaled in units such as a sequence, a GOP picture slice, and a CTU.

[0247] A method for image decoding that determines context information of syntax elements regarding multi-type tree partitioning of the current block may be as described below.

[0248]

[0249] FIG. 8 is a flowchart illustrating an image decoding method for determining context information of syntax elements related to multi-type tree partitioning of a current block according to an embodiment of the present disclosure. The image decoding method of FIG. 8 may be performed by an image decoding device.

[0250] Referring to FIG. 8, the image decoding device can derive block splitting permission information for the current block (S810). Here, if the tree type of the current block is a dual tree, the block splitting permission information can be derived based on the color components of the current block.

[0251] The video decoding device can derive context information of a multi-type tree split flag based on block split permission information (S820). Here, the context information of the multi-type tree split flag can be derived based on block split permission information derived according to a color component.

[0252] Here, the block splitting permission information may include vertical splitting permission information and horizontal splitting permission information. The vertical splitting permission information may include information on whether vertical bisection is allowed and information on whether vertical trisection is allowed. In addition, the horizontal splitting permission information may include information on whether horizontal bisection is allowed and information on whether horizontal trisection is allowed.

[0253] Here, the context information of the multi-type tree split flag can be derived based on the result of comparing the value of the vertical split permission information and the value of the horizontal split permission information.

[0254] The image decoding device can derive the value of the multi-type tree split flag of the current block based on the derived context information (S830).

[0255] The video decoding device can split the current block based on a multi-type tree split flag (S840). Here, the multi-type tree split flag may be a flag indicating the direction of the multi-type tree split. Alternatively, the multi-type tree split flag may be a flag indicating the type of the multi-type tree split.

[0256]

[0257] Meanwhile, the image encoding device can perform the following image encoding method.

[0258] Specifically, the video encoding device can determine block splitting allowance information for the current block.

[0259] The video encoding device can determine the multi-type tree split flag of the current block.

[0260] The video encoding device can determine context information of a multi-type tree split flag based on block splitting permission information.

[0261] The video encoding device can encode the multi-type tree split flag based on context information.

[0262] Here, if the tree type of the current block is a dual tree, the block splitting permission information can be derived based on the color component of the current block.

[0263] Here, the context information of the multi-type tree split flag can be derived based on the block split permission information derived according to the color component.

[0264] A bitstream can be generated by the image encoding method described above. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0265]

[0266] During video decoding, inter-prediction can be performed based on the inter-prediction mode of the current block. For example, the inter-prediction mode can be affine model-based inter-prediction. In affine model-based inter-prediction, the motion vector of the current block can be determined as follows.

[0267] FIG. 9 is a parameter model for determining a motion vector in an affine model-based inter prediction according to an embodiment of the present disclosure.

[0268] Referring to Fig. 9, the motion vector of the current block to be inter-predicted based on an affine model can be derived by a motion model using two or more control point motion vectors (CPMVs). When the current block is inter-predicted based on an affine model, the motion vector can be derived using either a 4-parameter model or a 6-parameter model.

[0269] Specifically, the parameter model illustrated in Fig. 9(a) may be a four-parameter model using two control point motion vectors mv0 and mv1. In the four-parameter model, the motion vector of a pixel within the current block can be derived according to the mathematical formula below.

[0270]

[0271]

[0272] And, the parameter model illustrated in Fig. 9(b) may be a 6-parameter model using three control point motion vectors mv0, mv1, and mv2. In the 6-parameter model, the motion vector of a pixel within the current block can be derived according to the mathematical formula below.

[0273]

[0274]

[0275] Here, mv0 = {mv 0x , mv 0y} is the control point motion vector adjacent to the upper left corner of the current block, and mv1 = {mv 1x , mv 1y} is the control point motion vector at the upper right position of the current block, and mv2 = {mv 2x , mv 2y} can be the control point motion vector at the lower left position of the current block. And, W and H indicate the width and height of the current block, respectively, and mv = {mv x , mv y} can mean the motion vector of pixel location {x, y}.

[0276]

[0277] Additionally, during the inter-prediction process of the current block, the Adaptive Motion Vector Resolution (AMVR) technique can be applied. AMVR can be a technique for decoding the motion vector difference of the current block at various resolutions. In other words, when AMVR is applied, the resolution of the motion vector difference of the current block can be determined differently depending on the coding parameters of the current block.

[0278] First, based on the value of the affine indicator, it can be determined whether the current block is inter-predicted based on the affine model. Then, the resolution of the motion vector difference can be determined based on at least one of the affine indicator, the prediction mode of the current block, and information regarding the resolution of the motion vector difference. Information regarding the resolution of the motion vector difference can include a flag indicating whether AMVR is applied and information regarding the precision index of the AMVR. For example, the resolution of the motion vector difference of the current block can be determined according to Table 8 below.

[0279]

[0280] According to Table 8, when affine model-based motion compensation is applied (i.e., when the inter_affine_flag value is 1), the resolution of the motion vector difference of the current block can be determined as one of 1 / 4 sample, 1 / 16 sample, and 1 sample unit based on the amvr_flag and amvr_precision_idx values. Or, when the prediction mode of the current block is the IBC mode (i.e., CuPredMode[chType][x0][y0] == MODE_IBC), the resolution of the motion vector difference of the current block can be determined as one of 1 sample unit and 4 sample units based on the amvr_flag and amvr_precision_idx values. Alternatively, if the affine model-based motion compensation is not applied (i.e., the inter_affine_flag value is 0) and the prediction mode of the current block is other than the IBC mode (i.e., CuPredMode[chType][x0][y0] != MODE_IBC), the resolution of the motion vector difference of the current block can be determined as one of 1 / 4 sample unit, 1 / 2 sample unit, 1 sample unit, and 4 sample unit based on the amvr_flag and amvr_precision_idx values. Then, a shift value corresponding to the value of the resolution can be determined.

[0281] And, based on the affine indicator and the determined shift value, the motion vector difference of the current block can be changed as shown in Table 9 below.

[0282]

[0283] If inter prediction based on an affine model is not applied to the current block, the resolution of the motion vector difference in the first prediction direction and the motion vector difference in the second prediction direction may be changed.

[0284] According to mathematical expressions (161) to (164) in Table 9, a shift operation can be applied to MvdL0[x0][y0][compIdx] and MvdL1[x0][y0][compIdx] by the AMVRShift value. Here, compIdx can be a vector component index having a value of 0 to 1.

[0285] On the other hand, when inter prediction based on an affine model is applied to the current block, the resolution of the affine motion vector difference in the first prediction direction and the affine motion vector difference in the second prediction direction may be changed. Here, the affine motion vector difference may be a control point motion vector difference (MvdCp).

[0286] According to mathematical expressions (165) to (170) in Table 9, a shift operation can be applied to MvdCpL0[x0][y0][0][0], MvdCpL1[x0][y0][0][1], MvdCpL0[x0][y0][1][0], MvdCpL1[x0][y0][1][1], MvdCpL0[x0][y0][2][0], and MvdCpL1[x0][y0][2][1] by the AMVRShift value. Here, cpIdx can be an index of a control point having a value of 0 to 2. And, compIdx can be a vector component index having a value of 0 to 1.

[0287] However, as defined in Table 9, when inter prediction based on an affine model is applied to the current block, the resolution of some components of the affine motion vector difference may not be changed. That is, the shift operation may be applied only to some vector components of the affine motion vector difference.

[0288] As defined in Table 9, a shift operation can be applied only to the x-component of the affine motion vector difference in the first direction, and a shift operation can be applied only to the y-component of the affine motion vector difference in the second direction. As a result, different resolutions can be set for each affine motion vector difference vector component.

[0289] To uniformly change the resolution of the affine motion vector difference vector components, a shift operation can be applied to the affine motion vector differences in all prediction directions and to all components of the affine motion vector differences. That is, if the inter prediction of the current block is an inter prediction based on an affine model, the resolution of the motion vector difference of the current block can be changed as shown in Table 10 below.

[0290]

[0291] As defined in Table 10, shift operations can be applied to all vector components of the affine motion vector differences in the first and second directions. Therefore, the resolution of the affine motion vector differences can be uniformly changed for all vector components. This minimizes errors resulting from differences in the resolution of the affine motion vector differences. Consequently, decoding efficiency can be improved.

[0292] An image decoding method for changing the resolution of the affine motion vector difference of the current block may be as described below.

[0293]

[0294] FIG. 10 is a flowchart illustrating an image decoding method for changing the resolution of an affine motion vector difference of a current block according to an embodiment of the present disclosure. The image decoding method of FIG. 10 can be performed by an image decoding device.

[0295] Referring to FIG. 10, the image decoding device can derive an affine motion vector difference of a current block (S1010). Here, the affine motion vector difference can include a first prediction direction affine motion vector difference and a second prediction direction affine motion vector difference. The first prediction direction affine motion vector difference and the second prediction direction affine motion vector difference can be defined by a control point indicator and a motion vector component indicator. Here, the control point indicator can indicate a value of 0, 1, or 2. In addition, the motion vector component indicator can indicate 0 indicating an x ​​component and 1 indicating a y component.

[0296] The video decoding device can derive shift information (S1020). Here, the shift information can be derived based on the resolution of the motion vector. The resolution of the motion vector can be derived based on the affine indicator of the current block and information about the adaptive motion vector resolution (AMVR). In addition, the information about the adaptive motion vector resolution can include a flag indicating whether AMVR is applied and a precision index of the AMVR.

[0297] The image decoding device can change the resolution of the affine motion vector difference based on shift information (S1030).

[0298] Meanwhile, the steps described in FIG. 10 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. 10. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0299]

[0300] During video decoding, the prediction mode of the current block can be determined by geometric partitioning mode (GPM), a submode of inter prediction. In geometric partitioning mode, the current block can be divided into two blocks by a single straight line. The straight line dividing the current block can be derived from the partitioning direction and the partitioning offset. Each block divided from the current block can be inter-predicted using differently derived motion information.

[0301] When the geometric partitioning mode is used, indices indicating the geometric partitioning mode and merge indices may be signaled. Here, the indices indicating the geometric partitioning mode may indicate a combination of the direction and offset of a straight line that divides the current block. The indices indicating the geometric partitioning mode may indicate a combination of the direction and offset of a straight line that divides the current block, as shown in Table 11 below.

[0302]

[0303] The current block can be split according to an index that indicates the geometric splitting mode, as described below.

[0304] FIG. 11 is a diagram illustrating a segmentation structure of a current block based on an index indicating a geometric segmentation mode according to one embodiment of the present disclosure.

[0305] Referring to Figure 11, the solid line within the square may be a straight line that divides the current block. The blocks of the square may be geometrically divided according to the solid line.

[0306] Referring to Figure 11, the straight lines dividing each of the 20 squares may have different angles (angleIdx). Here, the straight lines may have different offsets (distanceIdx). Furthermore, the straight lines indicated by solid lines are defined by indices indicating geometric segmentation modes and can segment the current block. Conversely, the straight lines indicated by dotted lines may not be defined by indices indicating geometric segmentation modes.

[0307] Furthermore, merge indices can indicate merge candidates for deriving motion information for each block split from the current block. Accordingly, motion information for each block split from the current block can be derived based on the motion information of merge candidates indicated by different merge indices. Furthermore, based on the derived motion information, prediction values ​​for each block split from the current block can be generated.

[0308] Then, based on the straight line dividing the current block, the predicted values ​​for each block can be weighted and combined to generate a predicted block for the current block. Furthermore, motion information for the predicted current block can be stored using a geometric segmentation mode.

[0309] FIG. 12 is a diagram illustrating a current block predicted by a geometric segmentation mode according to one embodiment of the present disclosure.

[0310] Referring to FIG. 12, a first prediction value, which is a prediction value for a first split block (1210), and a second prediction value, which is a prediction value for a second split block (1220), are generated, and the first prediction value and the second prediction value can be weighted.

[0311] Then, based on the division direction (φ) and offset (ρ) of the straight line that divides the current block, the distance (d) between the sample in the current block and the straight line that divides the current block can be derived. Then, based on the derived distance value, the weight value ω0 applied to the sample in the current block can be derived. The predicted value of the sample in the current block can be derived by applying ω0 to the first predicted value and applying 1- ω0 to the second predicted value.

[0312] That is, when inter prediction is applied to the current block by applying the geometric partitioning mode, the motion information of the current block can be stored based on the motion information of the first partition block and the second partition block. In addition, the motion information of the current block can be used in the decoding process of the subsequent block. Here, the motion information of the current block can be stored in units of 4x4 blocks. Here, the motion information of the current block can be stored as shown in Table 12 below.

[0313]

[0314] Referring to Table 12, motion information of the current block in geometric segmentation mode can be stored. Here, the motion information of the current block can include motion vector information, reference picture information, prediction direction utilization information, and bidirectional prediction index.

[0315] However, as defined in Table 12, unlike the motion information of the current block predicted in the general inter mode, the motion information of the current block in the geometric partition mode does not include interpolation filter information. Here, the interpolation filter may be an interpolation filter for inter-predicted luma samples. For example, the interpolation filter may be a half-sample interpolation filter. And, the interpolation filter information may be an index (e.g., hpelIfIdx) indicating the type of the interpolation filter, which is an interpolation filter for fractional sample positions.

[0316] The motion information of the current block in geometric segmentation mode does not include interpolation filter information. Therefore, when utilizing the motion information of the current block during the inter-prediction process of a subsequently predicted block, interpolation filter information may not be obtained.

[0317] In order to utilize the interpolation filter information of the current block in geometric segmentation mode, the motion information of the current block predicted in geometric segmentation mode can be stored as shown in Table 13 below.

[0318]

[0319] Referring to Table 13, motion information of the current block in geometric segmentation mode can be stored. Here, the motion information of the current block may further include motion vector information, reference picture information, prediction direction utilization information, bidirectional prediction index, and interpolation filter information. Therefore, when the motion information of the current block is used in the inter prediction process of a block to be predicted later, motion information including the interpolation filter information of the current block can be obtained.

[0320] Specifically, during the inter prediction process of a block referencing the current block, fractional sample interpolation may be applied to the samples of the current block. Fractional sample interpolation may be performed by applying interpolation filter coefficients to the samples of the current block in the vertical and horizontal directions. Here, the interpolation filter coefficients may be defined as shown in Table 14 below.

[0321]

[0322] As defined in Table 14, the interpolation coefficient can be determined based on the interpolation filter information (e.g., hpelIfIdx) of the current block.

[0323] That is, an interpolation filter coefficient is determined based on the interpolation filter information of the current block, and the interpolation filter coefficient is applied to the prediction sample of the current block, so that a prediction block of a block referencing the current block can be generated.

[0324]

[0325] An image decoding method for storing motion information of the current block in geometric segmentation mode may be as described below.

[0326]

[0327] FIG. 13 is a flowchart illustrating an image decoding method for storing motion information of a current block in a geometric segmentation mode according to an embodiment of the present disclosure. The image decoding method of FIG. 13 may be performed by an image decoding device.

[0328] Referring to FIG. 13, the image decoding device can derive a geometric segmentation index of the current block (S1310). Here, the geometric segmentation index can be used to derive the angle of the segmentation line and the distance between the block center and the segmentation line. Here, the segmentation line can asymmetrically segment the current block.

[0329] The video decoding device can generate a final prediction block by weighting the first prediction block and the second prediction block of the current block based on the geometric segmentation index (S1320). Here, the first prediction block may be generated based on the first motion information, and the second prediction block may be generated based on the second motion information. In addition, the first motion information may be different from the second motion information.

[0330] And, the weight applied to the sample of the first prediction block can be derived based on the distance between the dividing line and the sample.

[0331] The video decoding device can store motion information of the current block based on motion information of the first prediction block and the second prediction block (S1330). Here, the motion information of the current block can be stored in units of 4x4 blocks.

[0332] In the step of storing motion information of the current block, the motion information of the current block to be stored may include a motion vector, reference picture information, prediction direction information, bidirectional prediction index information, and interpolation filter information. Here, the value of the bidirectional prediction index information may be fixed to 0.

[0333] Meanwhile, the steps described in FIG. 13 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. 13. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0334]

[0335] While the exemplary methods of this disclosure are presented as a series of operations for clarity of description, this is not intended to limit the order in which the steps are performed, and individual steps may be performed simultaneously or in different orders, if desired. To implement a method according to this disclosure, additional steps may be included in addition to the steps illustrated, some steps may be excluded and the remaining steps included, or some steps may be excluded and additional steps included.

[0336] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combinations of two or more.

[0337] Various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0338] Alternatively, various embodiments of the present disclosure 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. Furthermore, a bitstream generated by the encoding method according to the above embodiment may be stored on a non-transitory computer-readable recording medium.

[0339] 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 available to those skilled in the art of computer software.

[0340] As described above, the present disclosure has been described based on specific details, such as specific components, and limited embodiments and drawings. However, the embodiments of the present disclosure are provided merely to facilitate a general understanding of the present disclosure and are not intended to limit the present disclosure to these embodiments. Accordingly, those skilled in the art will appreciate that various modifications and variations can be made based on the description.

[0341] 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.

[0342] The present invention can be used in a device for encoding an image, a device for decoding an image, and a recording medium for storing a bitstream.

Claims

1. In the video decryption method, A step of deriving block splitting permission information for the current block; A step of deriving context information of a multi-type tree split flag based on the above block splitting permission information; A step of deriving a value of a multi-type tree split flag of the current block based on the derived context information; and A step of splitting the current block based on the multi-type tree split flag, If the tree type of the current block is a dual tree, the block splitting permission information is derived according to the color component of the current block, An image decoding method, characterized in that the context information of the above multi-type tree split flag is derived based on block splitting permission information derived according to a color component.

2. In paragraph 1, An image decoding method, characterized in that the above multi-type tree splitting flag is a flag indicating the direction of multi-type tree splitting.

3. In paragraph 1, An image decoding method, characterized in that the block division permission information includes vertical division permission information and horizontal division permission information.

4. In paragraph 3, An image decoding method, characterized in that the vertical direction division allowance information includes information on whether vertical direction bisection is allowed and information on whether vertical direction trisection is allowed.

5. In paragraph 3, An image decoding method, characterized in that the horizontal direction division allowance information includes information on whether horizontal direction bisection is allowed and information on whether horizontal direction trisection is allowed.

6. In paragraph 3, A method for decoding an image, characterized in that context information of a multi-type tree split flag is derived based on a comparison result between a value of vertical split permission information and a value of horizontal split permission information.

7. In paragraph 3, An image decoding method, characterized in that the above multi-type tree split flag is a flag indicating the type of multi-type tree split.

8. In the video encoding method, A step for determining block splitting permission information for the current block; A step of determining a multi-type tree split flag of the current block; A step of determining context information of the multi-type tree split flag based on the block splitting permission information; and A step of encoding the multi-type tree split flag based on the context information, If the tree type of the current block is a dual tree, the block splitting permission information is derived according to the color component of the current block, A video encoding method, characterized in that the context information of the above multi-type tree split flag is derived based on block splitting permission information derived according to a color component.

9. In a non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method, The above image encoding method is, A step for determining block splitting permission information for the current block; A step of determining a multi-type tree split flag of the current block; A step of determining context information of the multi-type tree split flag based on the block splitting permission information; and A step of encoding the multi-type tree split flag based on the context information, If the tree type of the current block is a dual tree, the block splitting permission information is derived according to the color component of the current block, A non-transitory computer-readable recording medium, characterized in that the context information of the above multi-type tree split flag is derived based on block split permission information derived according to a color component.

10. In a method for transmitting a bitstream generated by a video encoding method, The above transmission method includes a step of transmitting the bitstream, The above image encoding method is, A step for determining block splitting permission information for the current block; A step of determining a multi-type tree split flag of the current block; A step of determining context information of the multi-type tree split flag based on the block splitting permission information; and A step of encoding the multi-type tree split flag based on the context information, If the tree type of the current block is a dual tree, the block splitting permission information is derived according to the color component of the current block, A transmission method, characterized in that the context information of the above multi-type tree split flag is derived based on block splitting permission information derived according to a color component.

Images