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: determining a tree type of the current unit included in the current slice; dividing a luminance block of the current unit into sub-luminance blocks on the basis of the tree type; and dividing a chrominance block of the current unit into sub-chrominance blocks on the basis of the tree type, wherein the tree type of the current unit is determined as either a single tree or a dual tree, and the current slice is one from among an I slice, a B slice and a P slice.

Description

Video encoding / decoding method and device

[0001] The present invention relates to a method and device for encoding / decoding an image, and more particularly, to a method and device for encoding / decoding an image for improving prediction performance by independently dividing a luminance component and a chrominance component of a current unit.

[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 method and device for encoding / decoding an image, which improves the inefficiency of block division and enhances the compression efficiency of image data by independently performing block division for a luminance component and a chrominance component.

[0007] In addition, the present disclosure aims to provide an image encoding / decoding method and device that improves the prediction performance of a block by independently performing block division for a luminance component and a chrominance component.

[0008] 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.

[0009] An image decoding method according to one embodiment of the present invention includes the steps of: determining a tree type of a current unit included in a current slice; determining a partitioning mode of a luminance component of the current unit and a partitioning mode of a chrominance component of the current unit based on the tree type; dividing a luminance block of the current unit into lower luminance blocks based on the partitioning mode of the luminance component of the current unit; and dividing a chrominance block of the current unit into lower chrominance blocks based on the partitioning mode of the chrominance component of the current unit, wherein the tree type of the current unit is determined to be one of a single tree and a dual tree, and the current slice may be one of an I slice, a B slice, and a P slice.

[0010] In the above image decoding method, the tree type of the current unit can be determined based on information indicating the tree type of a predefined unit.

[0011] In the above image decoding method, the predefined unit may be at least one of a slice, a coding tree unit, and a coding unit.

[0012] In the above image decoding method, the information indicating the tree type of the predefined unit includes information indicating the tree type of the slice unit and information indicating the tree type of the CTU unit, and the information indicating the tree type of the CTU unit can be obtained based on the information indicating the tree type of the slice unit.

[0013] In the above image decoding method, the tree type of the current unit can be determined based on the coding parameters of the current unit.

[0014] In the above image decoding method, the coding parameter of the current unit may be at least one of the tree depth of the current unit, the segmentation mode of the current block, the size of the current block, and the prediction mode of the current block.

[0015] In the above image decoding method, the current unit may be a unit divided from the upper unit based on information indicating a tree type for the upper unit.

[0016] In the above image decoding method, the information indicating the tree type for the upper unit may be information indicating the tree type of the current slice.

[0017] In the above image decoding method, the tree type of the current unit can be determined based on whether the size of the current unit is within a preset range.

[0018] In the above image decoding method, when the tree type of the current unit is a single tree and the size of the current unit is less than a preset value, the luminance block of the current unit may be divided into lower luminance blocks, and the chrominance block of the current unit may be not divided into lower chrominance blocks.

[0019] In the above image decoding method, when the current unit is intra-predicted, the tree type of the current unit can be determined as one of a single tree or a dual tree.

[0020] In the above image decoding method, if the intra prediction mode of the current unit is a predetermined intra prediction mode, the tree type of the current unit can be determined as a single tree.

[0021] A video encoding method according to one embodiment of the present invention includes the steps of: determining a tree type of a current unit included in a current slice; determining a partitioning mode of a luminance component of the current unit and a partitioning mode of a chrominance component of the current unit based on the tree type; dividing a luminance block of the current unit into lower luminance blocks based on the partitioning mode of the luminance component of the current unit; and dividing a chrominance block of the current unit into lower chrominance blocks based on the partitioning mode of the chrominance component of the current unit, wherein the tree type of the current unit is determined to be one of a single tree and a dual tree, and the current slice may be one of an I slice, a B slice, and a P slice.

[0022] A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method according to one embodiment of the present invention can store a bitstream generated by a video encoding method, comprising: a step of determining a tree type of a current unit included in a current slice; a step of determining a partitioning mode of a luminance component of the current unit and a partitioning mode of a chrominance component of the current unit based on the tree type; a step of partitioning a luminance block of the current unit into lower luminance blocks based on the partitioning mode of the luminance component of the current unit; and a step of partitioning a chrominance block of the current unit into lower chrominance blocks based on the partitioning mode of the chrominance component of the current unit, characterized in that the tree type of the current unit is determined to be one of a single tree and a dual tree, and the current slice is one of an I slice, a B slice, and a P slice.

[0023] A method for transmitting a bitstream generated by a video encoding method according to one embodiment of the present invention comprises the steps of transmitting the bitstream, determining a tree type of a current unit included in a current slice, determining a partitioning mode of a luminance component of the current unit and a partitioning mode of a chrominance component of the current unit based on the tree type, dividing a luminance block of the current unit into lower luminance blocks based on the partitioning mode of the luminance component of the current unit, and dividing a chrominance block of the current unit into lower chrominance blocks based on the partitioning mode of the chrominance component of the current unit, wherein the tree type of the current unit is determined to be one of a single tree and a dual tree, and the current slice is one of an I slice, a B slice, and a P slice.

[0024] According to the present disclosure, a method and device for encoding / decoding an image can be provided that improves the inefficiency of block division and enhances the compression efficiency of image data by independently performing block division for a luminance component and a chrominance component.

[0025] In addition, according to the present disclosure, an image encoding / decoding method and device can be provided that improves the prediction performance of a block by independently performing block division for a luminance component and a chrominance component.

[0026] 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.

[0027] 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.

[0028] FIG. 1 is a block diagram showing an image encoding device according to one embodiment of the present invention.

[0029] FIG. 2 is a block diagram showing an image decoding device according to one embodiment of the present invention.

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

[0031] FIG. 4 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0032] FIG. 5 is a diagram illustrating an embodiment of block segmentation based on a tree type according to one embodiment of the present disclosure.

[0033] FIG. 6 is a diagram illustrating an embodiment of block partitioning based on a tree type according to one embodiment of the present disclosure.

[0034] FIG. 7 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0035] FIG. 8 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0036] FIG. 9 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0037] FIG. 10 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0038] FIG. 11 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0039] FIG. 12 is a flowchart illustrating an image decoding method for dividing a luminance block and a chrominance block of a current unit based on a tree type according to an embodiment of the present disclosure.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Hereinafter, embodiments of the present invention 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.

[0045] FIG. 1 is a block diagram showing an image encoding device according to one embodiment of the present invention.

[0046] 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).

[0047] Each component shown in Fig. 1 is independently depicted to indicate 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 invention as long as they do not deviate from the essence of the present invention.

[0048] Additionally, some components may not be essential components that perform essential functions of the present invention, but may be optional components merely used to enhance performance. The present invention may be implemented by including only components essential to implementing the essence of the present invention, 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 invention.

[0049] 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 unit, 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 units.

[0050] In addition, the image segmentation unit (101) can recursively segment the segmented coding tree unit. The terminal node segmented from the coding tree unit 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. The quadtree is a method of segmenting an upper block into lower blocks whose width and height are half of those of the upper block. The 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. The 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.

[0051] 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 segmentation mode (SPLIT_BT_VER), a horizontal binary tree segmentation mode (SPLIT_BT_HOR), a vertical ternary tree segmentation mode (SPLIT_TT_VER), and a horizontal ternary tree segmentation mode (SPLIT_TT_HOR).

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Alternatively, the intra prediction unit (102) may perform intra prediction on the current block by applying at least one mode among decoder-side intra mode derivation (DIMD), Occurrence-based intra coding (OBIC), extrapolation filter based intra prediction mode (EIP), template based intra mode derivation (TIMD), spatial geometric partitioning mode (SGPM) mode, intra template matching prediction (IntraTMP), and intra block copy. When the intra prediction mode of the block is a predetermined mode, the intra prediction unit (102) may perform intra prediction on the current block by using a block vector indicating a block other than the current block.

[0059] 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.

[0060] 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.

[0061] If the prediction mode of the current block is DC mode, a prediction block can be generated by applying a DC filter.

[0062] In one embodiment, the intra prediction unit (102) may perform intra prediction using a pre-trained neural network (NN) model. For example, the intra prediction unit (102) may derive an intra prediction mode of a block to which the DIMD mode is applied and use a pre-trained neural network model to perform intra prediction.

[0063] The inter prediction unit (103) generates a prediction block using the previously restored reference image stored in the memory (112) and the inter prediction mode and motion information. Here, inter prediction may mean motion prediction or motion compensation.

[0064] The inter prediction unit (103) can set the inter mode of a prediction unit included in an encoding unit 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. Then, the inter prediction unit (103) can perform motion prediction and / or motion compensation for the prediction unit according to the set mode.

[0065] In addition, the inter prediction unit (103) can perform motion prediction and / or motion compensation for a prediction unit 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 (103) can perform motion prediction and / or motion compensation for the prediction unit by applying HMVP (History based MVP), PAMVP (Pairwise Average MVP), CIIP (Combined Intra / Inter Prediction), AMVR (Adaptive Motion Vector Resolution), DMVR (Decoder side Motion Vector Refinement), BDOF (Bi-Directional Optical-Flow), PROF (Prediction Refinement With Optical Flow), BCW (Bi-predictive with CU Weights), LIC (Local Illumination Compensation), TM (Template Matching), OBMC (Overlapped Block Motion Compensation), etc. to improve the performance of each mode.

[0066] 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.

[0067] 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.

[0068] According to one embodiment, the inter prediction unit (103) may perform inter prediction using a pre-trained neural network model. For example, the inter prediction unit (103) may synthesize a reference frame using a pre-trained neural network model and perform inter prediction based on the synthesized reference frame.

[0069] 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.

[0070] 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).

[0071] 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).

[0072] 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.

[0073] 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.

[0074] 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).

[0075] 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.

[0076] According to another embodiment, the transform unit (105) may apply a non-separable primary transform (NSPT) technique that performs the transform by selectively using multiple transform kernels based on the intra prediction mode or the size and / or shape of the block.

[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), a bilateral filter (BIF), and a LMCS (Luma Mapping with Chroma Scaling) as a filtering technique, in whole or in part, to a restored sample, restored block, or restored image.

[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 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 on which the offset is to be performed, and applying the offset to the regions, or a method of applying the offset by considering edge information of each sample. Here, the sample adaptive offset may be at least one of a general sample adaptive offset, a bilateral filter, and a cross-component sample adaptive offset (CCSAO).

[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 included 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, an ALF filter of the same form (fixed form) can be applied regardless of the characteristics of the target block.

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

[0091] According to one embodiment, the filter unit (111) may filter all or part of a restored sample, restored block, or restored image using a pre-trained neural network model. Specifically, the filter unit (111) may apply an adaptive loop filter to all or part of a restored sample, restored block, or restored image using a pre-trained neural network model.

[0092] 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.

[0093] Next, an image decoding device according to one embodiment of the present invention will be described with reference to the drawings.

[0094] FIG. 2 is a block diagram showing an image decoding device (200) according to one embodiment of the present invention.

[0095] 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).

[0096] 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.

[0097] 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.

[0098] 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).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] According to another embodiment, the inverse transform unit (203) may apply a non separable primary transform (NSPT) technique that performs inverse transform by selectively using a transform kernel based on the intra prediction mode or the size and / or shape of the block.

[0107] 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).

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] According to one embodiment, the intra prediction unit (204) can perform intra prediction using a pre-trained neural network model. The intra prediction unit (204) can perform intra prediction using the same neural network model as the intra prediction unit (102) of FIG. 1.

[0113] The intra prediction unit (204) operates substantially the same as the intra prediction unit (102) of FIG. 1.

[0114] 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.

[0115] The inter prediction unit (205) can set the inter mode of a prediction unit included in an encoding unit 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 the prediction unit according to the set mode.

[0116] In addition, the inter prediction unit (205) can perform motion compensation for the prediction unit 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 the prediction unit 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), the LIC (Local Illumination Compensation), the TM (Template Matching), the OBMC (Overlapped Block Motion Compensation), etc. to improve the performance of each mode.

[0117] 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.

[0118] According to one embodiment, the inter prediction unit (205) can perform inter prediction using a pre-trained neural network model. The inter prediction unit (205) can perform inter prediction using the same neural network model as the inter prediction unit (103) of FIG. 1.

[0119] The inter prediction unit (205) can operate substantially the same as the inter prediction unit (103) of FIG. 1.

[0120] 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.

[0121] 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, a bilateral filter, and an LMCS.

[0122] 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).

[0123] According to one embodiment, the filter unit (207) may filter all or part of a restored sample, restored block, or restored image using a pre-trained neural network model. Specifically, the filter unit (207) may apply an adaptive loop filter to all or part of a restored sample, restored block, or restored image using a pre-trained neural network model.

[0124] The filter unit (207) can operate substantially the same as the filter unit (111) of FIG. 1.

[0125] 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.

[0126]

[0127] FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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).

[0133] 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.

[0134] The image playback unit (23) can render decrypted video / images. The rendered video / images can be displayed through the display unit.

[0135]

[0136] FIG. 4 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

[0137] As illustrated in FIG. 4, a content streaming system to which an embodiment of the present invention 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.

[0138] 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.

[0139] As another example, if multimedia input devices such as smartphones, cameras, CCTVs, etc. directly generate bitstreams, the encoding server may be omitted.

[0140] The above bitstream can be generated by a video encoding method and / or a video encoding device to which an embodiment of the present invention is applied, and the streaming server can temporarily or non-temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145]

[0146] According to the existing VVC / H.266 standard, block partitioning can be performed based on quad-tree, binary-tree, and ternary-tree methods. Blocks can be partitioned using quad-tree, binary-tree, and ternary-tree methods until the maximum depth (MaxDepth) is reached, based on the configured CTU size. The encoder can transmit block partitioning information to the decoder for block partitioning. The block partitioning information can include information on whether to partition, partitioning mode information, and partitioning direction information.

[0147] By performing block partitioning based on this information, it is possible to partition into rectangular blocks and optimize the size of coding units compared to the block partitioning technique of the previous generation standard, HEVC / H.265. However, quadtree-based partitioning can only be applied up to a certain depth after the start. On the other hand, binary tree and ternary tree partitioning may not be applied to nodes other than the leaf nodes of the quadtree with mttDepth=0. Therefore, it may be difficult to flexibly combine quadtree partitioning, binary tree partitioning, and ternary tree partitioning, and block partitioning information may be signaled inefficiently.

[0148] Block partitioning can be applied differently depending on the slice type. For example, in the case of an inter-slice including a P slice and a B slice, the tree type of the slice can be applied as a single tree, and the same partitioning structure can be applied to the luminance and chrominance blocks within the slice. On the other hand, in the case of an intra-slice including an I slice, the tree type of the slice can be applied as a dual tree, and independent partitioning structures can be applied to the luminance and chrominance blocks within the slice. Accordingly, the decision on whether to partition the luminance component and the chrominance component, and the related syntax, can exist separately.

[0149] When performing intra prediction, if the characteristics of blocks containing luminance and chrominance components differ, prediction performance can be improved by setting the tree type to a dual tree, independently dividing the blocks containing luminance and chrominance components. However, the dual tree is only applicable to intra slices and may not be applicable to blocks intrapredicted within inter slices. Therefore, a method for setting the tree type to a dual tree may be necessary even for inter slices.

[0150]

[0151] FIG. 5 is a diagram illustrating an embodiment of block segmentation based on a tree type according to one embodiment of the present disclosure.

[0152] Referring to FIG. 5, a slice can be divided into CTUs, and a CTU can be composed of one luminance component coding tree block and two chrominance component coding tree blocks. Here, the CTU can be a CTU included in one of an I slice, a P slice, and a B slice.

[0153] As illustrated in Fig. 5, a CTU of a slice can be quad-tree partitioned into four sub-CTUs. Here, the tree type of the CTU can be a single tree. Accordingly, the luminance component and chrominance component of the CTU can be quad-tree partitioned. In addition, at least some of the quad-tree partitioned CTUs can be CTUs that include an intra-predicted region.

[0154] Here, a tree type is determined for the intra-predicted sub-CTU, and the sub-CTU can be split based on the determined tree type. For example, if the tree type of the sub-CTU is a dual tree, different splitting methods can be applied to the luminance component and chrominance component of the sub-CTU. Conversely, if the tree type of the sub-CTU is a single tree, the same splitting method can be applied to the luminance component and chrominance component of the sub-CTU.

[0155] That is, according to the present disclosure, the tree type can be selectively set to single tree and dual tree for CTUs of not only I slices but also P slices and B slices. The method for setting the tree type of a CTU to single tree and dual tree can be as described below.

[0156]

[0157] According to one embodiment of the present disclosure, the tree type can be explicitly set to single tree or dual tree.

[0158] For example, information for setting the tree type to single tree or dual tree in units of sequence, GOP, intra frame period, picture, slice, tile, CTU, CU, TU, and tree depth can be transmitted from the encoder to the decoder.

[0159] According to one embodiment, the tree type can be set on a slice-by-slice basis, and can be set to use a single tree or a dual tree in intra-slices and inter-slices. In the case of a slice with a single tree tree type, units within the slice can be equally divided for luminance and chrominance components. On the other hand, in the case of a slice with a dual tree tree type, units within the slice can be independently divided for luminance and chrominance components. Accordingly, decisions on whether to divide for luminance components and whether to divide for chrominance components, and related syntax, can exist separately.

[0160] In another embodiment, the tree type can be set on a CTU basis. If the tree type is a single tree, the CTU can be equally partitioned into luminance and chrominance components. On the other hand, if the tree type is a dual tree, the CTU can be independently partitioned into luminance and chrominance components. Accordingly, decisions regarding partitioning for the luminance component and the chrominance component, as well as the related syntax, can exist separately.

[0161] In another embodiment, the tree type can be set on a CU basis. If the tree type is a single tree, the CU can be equally partitioned for luminance and chrominance components. On the other hand, if the tree type is a dual tree, the CU can be independently partitioned for luminance and chrominance components. Accordingly, decisions regarding partitioning for the luminance component and partitioning for the chrominance component, as well as related syntax, can exist separately.

[0162] In addition to the embodiments described above, the tree type can be set as a single tree or a dual tree for each preset unit.

[0163] Alternatively, by combining at least one of the embodiments described above, the tree type may be set to a single tree or a dual tree for each preset unit. In one embodiment, for intra-slices and inter-slices, the tree type may be set to a dual tree for each slice. In addition, the tree type may be set to a single tree or a dual tree for each CTU. When setting the tree type for each slice and CTU, information for applying a single tree or a dual tree for each CTU may be transmitted for all slices.

[0164] In another embodiment, the tree type of an intra-slice may be set to a single tree, and that of an inter-slice may be set to a dual tree. In this case, in the intra-slice, the tree type may be set to a single tree or a dual tree on a CTU basis. Accordingly, information for applying a single tree or a dual tree on a CTU basis may be transmitted in the intra-slice. On the other hand, in the inter-slice, there may be no need to transmit information for applying a single tree or a dual tree on a CTU basis.

[0165] In addition to the embodiments described above, the tree type may be set to a single tree or a dual tree by combining one or more preset units. For example, if the tree type of the upper unit is set to not use a single tree or a dual tree, information indicating the tree type of the lower unit as a single tree or a dual tree may not be additionally transmitted. On the other hand, if the tree type of the upper unit is set to use a single tree or a dual tree, information indicating the tree type of the lower unit as a single tree or a dual tree may be additionally transmitted. Accordingly, the tree type of each lower unit may be set to a single tree or a dual tree.

[0166] If the tree type of the upper unit is set to use a single tree or dual tree, and information indicating the tree type of the lower unit is not transmitted, the tree type of each lower unit can be set to be the same as the tree type of the upper unit.

[0167]

[0168] According to one embodiment of the present disclosure, the tree type can be implicitly set to a single tree or a dual tree.

[0169] For example, in units of sequence, GOP, intra frame period, picture, slice, tile, CTU, CU, TU, and tree depth, the tree type can be implicitly set to single tree or dual tree depending on the condition.

[0170] Specifically, the tree type can be implicitly set to a single tree or a dual tree based on encoding information. Here, the encoding information can include information such as the resolution of the sequence, the color format, the GOP, the QTMTT depth, the QT depth, the MTT depth, the segmentation mode of the current block, the size of the current block, the width of the current block, the height of the current block, the number of pixels in the current block, the shape of the current block, the prediction mode of the current block, the QP value of the current block, the segmentation mode of the upper block, the size of the upper block, the width of the upper block, the height of the upper block, the number of pixels in the upper block, the shape of the upper block, the prediction mode of the upper block, and the QP value of the upper block.

[0171] Conditions regarding encoding information for implicitly setting a tree type may be applied differently for sequences, GOPs, intra-frame periods, pictures, slices, tiles, CTUs, CUs, TUs, and tree depths. Alternatively, more than one condition may be used to implicitly set a tree type.

[0172] For example, the tree type may be set to a single tree or a dual tree based on the size information of the current block. Here, from the CTU, the tree type of a unit with a size of 64x64 may be set to a single tree, and the tree type of the smallest unit from the unit smaller than 64x64 may be set to a dual tree. For another example, from the CTU, the tree type of a unit with cqtDepth=3 may be set to a single tree, and the tree type of the smallest unit from the unit with cqtDepth=4 may be set to a dual tree. For another example, from the CTU, the tree type of a unit with cqtDepth=0 may be set to a single tree, and the tree type of the smallest unit from the unit with cqtDepth=1 may be set to a dual tree. For another example, from the CTU, the tree type of a unit that is split into a quad tree may be set to a single tree, and the tree type of a unit that is split into a multi-tree type may be set to a dual tree.

[0173] The embodiment described above is an embodiment that sets the tree type to a single tree or a dual tree based on conditions related to the depth and / or size of the block being split when splitting a block, but the tree type can be set to a single tree or a dual tree by utilizing conditions other than the depth and / or size of the block.

[0174] Alternatively, in the process of implicitly setting the tree type based on conditions regarding the encoded information, the threshold value regarding the encoded information can be determined experimentally. Here, the threshold value can be stored in the encoder and decoder through a table. Alternatively, the threshold value can be determined through a preset formula.

[0175] For example, starting from CTU, the tree type of the unit with cqtDepth=3, which is a threshold value for depth, may be set to a single tree, and the tree type of the unit with cqtDepth=4 and the minimum size may be set to a dual tree. Here, the threshold value cqtDepth=3 may be stored in the encoder and decoder through a table. According to another example, when the size of CTU is 256×256, the tree type up to the unit with a size of 16×16 corresponding to cqtDepth=3 may be set to a single tree, and the tree type of the unit with a size smaller than 16×16 may be set to a dual tree. Here, the threshold value for the size may be set as CTU >> cqtDepth.

[0176]

[0177] According to one embodiment of the present disclosure, the tree type can be set to a single tree or a dual tree by combining explicit and implicit methods.

[0178] For example, the tree types of intra-slice and inter-slice can be explicitly set to dual trees, and the tree type of a CU can be set to single trees or dual trees. In this case, tree type information per CU can be transmitted for each slice.

[0179] Alternatively, the tree type of a CU can be implicitly set, along with explicit conditions. For example, the tree type from a CTU to a unit of size 32×32 can be implicitly set to a single tree. Furthermore, the encoder can set the tree type from units smaller than 32×32 to the smallest unit.

[0180] As a result, the encoder can transmit to the decoder information about the tree type of the slice unit and information about the tree type from the unit smaller than 32×32 size to the minimum size unit, and can not transmit to the decoder information about the tree type from the CTU to the unit of 32×32 size.

[0181] To set a tree type, the explicit and implicit conditions described above can be combined and multiple conditions can be used. If the tree types set differently based on the explicit and implicit conditions, the tree type based on the implicit conditions may take precedence. In this case, information about the tree type may not be transmitted to the decoder.

[0182]

[0183] According to one embodiment of the present disclosure, the tree type can be independently set for each of the luminance component and the chrominance component. Here, the tree type of each of the luminance component and the chrominance component can be explicitly or implicitly set to a single tree or a dual tree.

[0184] For example, if the tree types of intra-slice and inter-slice are explicitly set to dual trees, the tree type of the luminance component can be explicitly set to single tree or dual tree on a CU basis. Meanwhile, the tree type of the chrominance component is implicitly set to single tree from CTU to units of size 32×32, and the tree type of units of size less than 32×32 can be set to single tree.

[0185] As previously explained, the tree type can be configured as a single tree or a dual tree based on multiple explicit or implicit conditions, depending on the luminance and chrominance components. In this case, information regarding the explicit conditions can be signaled and transmitted to the decoder. Conversely, information regarding the implicit conditions can be shared in advance between the encoder and decoder in the form of threshold values ​​or tables.

[0186] For example, when the tree type is explicitly or implicitly set to a single tree, the tree type can be explicitly or implicitly set for luminance blocks and chrominance blocks of a certain size or larger. When the tree type is explicitly or implicitly set to a single tree, the size of the luminance block and chrominance block for which the tree type is explicitly or implicitly set can be 4x4, or the number of pixels of the luminance block and chrominance block can be 16 or larger.

[0187] For example, if the size of the divided luminance block is 8x8 and the size of the chrominance block is 4x4 as a result of applying a single tree to the current unit, the single tree can be applied to the current unit. On the other hand, if the size of the divided luminance block is 4x4 and the size of the chrominance block is 2x2 by applying a single tree to the current unit, the size of the divided chrominance block is smaller than the minimum block size of 4x4, which may cause inefficiencies in encoding and decoding.

[0188] Therefore, block partitioning according to a single tree can be restricted to not partition into luminance blocks smaller than 8×8 and chrominance blocks smaller than 4×4. Alternatively, when performing block partitioning according to a single tree, when a luminance block of 8×8 size is partitioned using a quadtree, the chrominance block of 4×4 size can be partitioned instead of being partitioned into 2×2 blocks by applying the quadtree partitioning. Therefore, the chrominance block can maintain its 4×4 size.

[0189] For example, when the tree type is explicitly or implicitly set to a dual tree, the size of the luminance block and the chrominance block for which the tree type is explicitly or implicitly set may be 4x4, or the number of pixels of the luminance block and the chrominance block may be 16 or more. For example, when the tree type is a dual tree, the luminance component and the chrominance component may be independently split. Therefore, the luminance component and the chrominance component may be split up to blocks of size 4x4. Here, when the tree type is explicitly set to a dual tree for each CU unit, the tree type setting information for a block larger than 8x8 or consisting of 64 or more pixels may be transmitted to the decoder for each CU unit. On the other hand, the tree type setting information for a block smaller than 8x8 or consisting of less than 64 pixels may not be transmitted to the decoder.

[0190]

[0191] FIG. 6 is a diagram illustrating an embodiment of block partitioning based on a tree type according to one embodiment of the present disclosure.

[0192] Referring to FIG. 6, a slice can be divided into CTUs, and a CTU can be composed of one luminance component coding tree block and two chrominance component coding tree blocks. Here, the CTU can be a CTU included in one of an I slice, a P slice, and a B slice.

[0193] As illustrated in FIG. 6, a CTU of a slice can be quad-tree partitioned into four sub-CUs. Here, the tree type of the CTU can be a single tree. Accordingly, the luminance component and chrominance component of the CTU can be quad-tree partitioned. In addition, at least some of the quad-tree partitioned CTUs can be CUs that include an intra-predicted region.

[0194] Here, a tree type is determined for the intra-predicted CU, and the CU can be split according to the determined tree type. For example, if the tree type of the CU is a dual tree, different splitting methods can be applied to the luminance component and the chrominance component of the CU. On the other hand, if the tree type of the CU is a single tree, the same splitting method can be applied to the luminance component and the chrominance component of the CU. However, even if the tree type for the CU is set explicitly or implicitly, the CU can be adaptively split into the luminance component and the chrominance component according to its size.

[0195] For example, if the width and height of the CU are greater than 8, the sizes of the luminance component blocks and chrominance component blocks partitioned from the CU may be 4×4 or larger. Accordingly, the luminance component and chrominance component of the CU may be partitioned based on the tree type. For example, if the tree type of the CU is single tree and the partitioning mode of the CU is quad tree, the luminance component and chrominance component of the CU may be quad tree partitioned.

[0196] On the other hand, if the width and height of the CU are 8 or less, the sizes of the luminance component blocks and chrominance component blocks split from the CU may be less than 4×4. Therefore, the luminance component and chrominance component of the CU may not be split despite the set tree type. For example, if the tree type of the CU is a single tree and the split mode of the CU is a quad tree, the luminance component of the CU may be split, but the chrominance component may not be split.

[0197]

[0198] According to one embodiment of the present disclosure, the tree type can be set to single tree or dual tree, explicitly or implicitly, depending on the prediction mode of the current unit.

[0199] In one embodiment, in an inter-slice where the tree type can be set to a single tree or a dual tree, the dual tree can be set only in the intra block.

[0200] In another embodiment, in an inter-slice where the tree type can be set to a single tree or a dual tree, the dual tree can be set only for intra-predicted blocks. Here, if the tree type is set implicitly, the tree type of the intra-predicted block of the inter-slice can always be set to a dual tree. On the other hand, if the tree type is explicitly set, information about the tree type of the intra-predicted block of the inter-slice can be transmitted to the decoder for each predetermined unit (e.g., CTU, CU, etc.).

[0201] According to another embodiment, the tree type may be explicitly or implicitly set to a single tree or a dual tree depending on the intra prediction mode of the current unit. Specifically, the tree type of a block to be intra-predicted in an inter slice may be set to a dual tree. However, the tree type of a block to be intra-predicted using a predetermined intra prediction mode may be arbitrarily set to a single tree. Here, the predetermined mode may be a mode that predicts the current block through an operation similar to inter prediction, and specifically, may be an intra prediction mode that uses block vectors, such as intra template matching (IntraTMP), intra block copy (IBC), or auto-relocated block vector prediction (AR-BVP). That is, when setting the tree type of a unit that uses a prediction mode that uses block vectors, only a single tree may be set without applying a dual tree. Here, if the block predicted using IBC is not determined to be an intra block, a dual tree may not be applied to the IBC predicted block, and only a single tree may be set.

[0202]

[0203] As previously explained, information for setting a tree type can be signaled in syntax form. The method for transmitting information for setting a tree type in syntax form can be as described below.

[0204]

[0205] To set the tree type to single type or dual type, the encoder can determine the tree type and transmit a bitstream containing syntax elements regarding information about the tree type to the decoder.

[0206] When transmitting information that sets the tree type in units of sequence, GOP, intra frame cycle, picture, slice, and tile, syntax elements regarding the tree type information can be transmitted by being included in the SPS, PPS, APS, and slice header of the bitstream.

[0207] Alternatively, when transmitting information for setting a tree type in units of CTU, CU, TU, and tree depth, syntax elements related to information on the tree type may be included in the syntax of each unit and transmitted. In particular, when syntax elements related to information on the tree type are transmitted in units of CU, the position of the syntax elements related to information on the tree type may be determined in conjunction with a segmentation information syntax element, a prediction mode syntax element, and the like. Here, the prediction mode syntax element may include a skip flag, a coding mode information-related flag, and an IBC mode-related flag.

[0208] For example, in a CU syntax consisting of a split information flag, a skip flag, a coding mode information-related flag, and an IBC flag in that order, the position of a syntax element regarding tree type information can be set as described below.

[0209]

[0210] FIG. 7 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0211] Referring to FIG. 7, the syntax of a CU may be composed of a syntax element related to tree type information (e.g., cu_treetype_flag), a partition information syntax element, a skip flag (e.g., cu_skip_flag), a flag related to coding mode information (e.g., pred_mode_flag), and a flag related to IBC mode information (e.g., pred_mode_ibc_flag), in that order.

[0212] When signaling syntax elements regarding tree type information in this way, it may be appropriate to set the tree type of the upper unit to single tree and the tree type of the lower unit to single tree or dual tree.

[0213]

[0214] FIG. 8 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0215] Referring to FIG. 8, the syntax of a CU may be composed of a partition information syntax element, a syntax element related to tree type information (e.g., cu_treetype_flag), a skip flag (e.g., cu_skip_flag), a coding mode information related flag (e.g., pred_mode_flag), and an IBC mode information related flag (e.g., pred_mode_ibc_flag), in that order.

[0216] When signaling syntax elements regarding tree type information in this way, it may be appropriate to set the tree type of the upper unit to single tree and the tree type of the lower unit to single tree or dual tree.

[0217]

[0218] FIG. 9 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0219] Referring to FIG. 9, the syntax of a CU may be composed of a partition information syntax element, a skip flag (e.g., cu_skip_flag), a syntax element related to tree type information (e.g., cu_treetype_flag), a flag related to coding mode information (e.g., pred_mode_flag), and a flag related to IBC mode information (e.g., pred_mode_ibc_flag), in that order.

[0220] That is, syntax elements regarding tree type information can be signaled after the skip flag. Signaling syntax elements regarding tree type information in this way may be suitable when setting the tree type to a single tree or dual tree in situations where skip mode is highly usable.

[0221]

[0222] FIG. 10 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0223] Referring to FIG. 10, the syntax of a CU may be composed of a partition information syntax element, a skip flag (e.g., cu_skip_flag), a coding mode information related flag (e.g., pred_mode_flag), a syntax element related to tree type information (e.g., cu_treetype_flag), and an IBC mode information related flag (e.g., pred_mode_ibc_flag) in that order.

[0224] That is, syntax elements related to tree type information can be signaled after flags related to coding mode information. When signaling syntax elements related to tree type information in this way, tree type information can be efficiently transmitted by utilizing coding mode information.

[0225] For example, when encoding a unit of an inter slice, the tree type of the intra-predicted unit can be set to a single tree or a dual tree, and the tree type of the inter-predicted unit can be set to a single tree.

[0226]

[0227] FIG. 11 is a diagram illustrating one embodiment of a syntax including a syntax element relating to tree type information according to one embodiment of the present disclosure.

[0228] Referring to FIG. 11, the syntax of a CU may be composed of a partition information syntax element, a skip flag (e.g., cu_skip_flag), a coding mode information related flag (e.g., pred_mode_flag), an IBC mode information related flag (e.g., pred_mode_ibc_flag), and a syntax element related to tree type information (e.g., cu_treetype_flag) in that order.

[0229] That is, syntax elements related to tree type information can be signaled after the IBC mode-related flag. When signaling syntax elements related to tree type information in this way, tree type information can be efficiently transmitted by utilizing coding mode information and IBC mode-related information.

[0230] For example, when encoding a unit of an intra slice, the tree type of the intra-predicted unit can be set to a single tree or a dual tree, and the tree type of the inter-predicted unit or IBC-predicted unit can be set to a single tree.

[0231]

[0232] An image decoding method and an image encoding method for dividing a luminance block and a chrominance block of a current unit based on a tree type according to an embodiment of the present disclosure may be as described below.

[0233]

[0234] FIG. 12 is a flowchart illustrating an image decoding method for dividing a luminance block and a chrominance block of a current unit based on a tree type according to an embodiment of the present disclosure. The image decoding method of FIG. 12 can be performed by an image decoding device.

[0235] Referring to FIG. 12, the image decoding device can determine the tree type of the current unit included in the current slice (S1210).

[0236] Here, the current slice can be one of an I slice, a B slice, and a P slice. And, the tree type of the current unit can be determined as one of a single tree and a dual tree.

[0237] Here, the tree type of the current unit can be determined based on information indicating the tree type of a predefined unit. The predefined unit can be at least one of a slice, a coding tree unit, and a coding unit.

[0238] Here, information indicating a tree type of a predefined unit may include information indicating a tree type of a slice unit and information indicating a tree type of a CTU unit. In addition, information indicating a tree type of a CTU unit may be acquired based on information indicating a tree type of a slice unit.

[0239] Meanwhile, the tree type of the current unit may be determined based on the coding parameters of the current unit. Here, the coding parameters of the current unit may be at least one of the tree depth of the current unit, the segmentation mode of the current block, the size of the current block, and the prediction mode of the current block.

[0240] Here, the current unit may be a unit split from the upper unit based on information indicating the tree type of the upper unit. For example, the information indicating the tree type of the upper unit may be information indicating the tree type of the current slice.

[0241] Here, the tree type of the current unit may be determined based on whether the size of the current unit is within a preset range. For example, if the tree type of the current unit is a single tree and the size of the current unit is less than a preset value, the luminance block of the current unit may be divided into sub-luminance blocks, and the chrominance block of the current unit may not be divided into sub-chrominance blocks.

[0242] Here, if the current unit is intra-predicted, the tree type of the current unit may be determined as either a single tree or a dual tree. Meanwhile, if the intra-prediction mode of the current unit is a predetermined intra-prediction mode, the tree type of the current unit may be determined as a single tree.

[0243] The image decoding device can determine the division mode of the luminance component of the current unit and the division mode of the chrominance component of the current unit based on the tree type (S1220).

[0244] The image decoding device can divide the luminance block of the current unit into lower luminance blocks based on the division mode of the luminance component of the current unit (S1230).

[0245] The image decoding device can divide the chrominance block of the current unit into lower luminance blocks based on the division mode of the chrominance component of the current unit (S1240).

[0246]

[0247] Meanwhile, the steps described in FIG. 12 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. 12. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

[0248]

[0249] 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.

[0250] 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.

[0251] 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.

[0252] 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.

[0253] 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.

[0254] 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.

[0255] Therefore, the idea of ​​the present invention should not be limited to the embodiments described above, and all things that are modified equally or equivalently to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

[0256] 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 determining the tree type of the current unit included in the current slice; A step of determining a division mode of a luminance component of a current unit and a division mode of a chrominance component of the current unit based on the above tree type; A step of dividing a luminance block of a current unit into sub-luminance blocks based on a division mode of a luminance component of the current unit; and A step of dividing a chrominance block of a current unit into sub-chrominance blocks based on a division mode of a chrominance component of the current unit, The tree type of the current unit above is determined as either single tree or dual tree, A method for decoding an image, characterized in that the current slice is one of an I slice, a B slice, and a P slice.

2. In paragraph 1, An image decoding method, characterized in that the tree type of the current unit is determined based on information indicating the tree type of a predefined unit.

3. In paragraph 2, The above predefined units are, A video decoding method characterized by at least one of a slice, a coding tree unit, and a coding unit.

4. In paragraph 2, Information indicating the tree type of the above predefined unit, Information indicating the tree type of the slice unit; and Contains information indicating the tree type of the CTU unit, Information indicating the tree type of the above CTU unit is: An image decoding method characterized in that it is obtained based on information indicating a tree type of the above slice unit.

5. In paragraph 1, The tree type of the current unit above is, An image decoding method, characterized in that it is determined based on the coding parameters of the current unit.

6. In paragraph 5, The coding parameters of the current unit above are: An image decoding method characterized by at least one of the tree depth of the current unit, the segmentation mode of the current block, the size of the current block, and the prediction mode of the current block.

7. In paragraph 1, The above current unit is, An image decoding method, characterized in that the unit is divided from the upper unit based on information indicating a tree type for the upper unit.

8. In paragraph 7, A video decoding method, characterized in that the information indicating the tree type for the upper unit is information indicating the tree type of the current slice.

9. In paragraph 7, The tree type of the current unit above is, An image decoding method characterized in that the size of the current unit is determined based on whether the size is within a preset range.

10. In paragraph 7, The tree type of the current unit above is a single tree, If the size of the current unit above is less than the preset value, An image decoding method, characterized in that the luminance block of the current unit is divided into lower luminance blocks, and the chrominance block of the current unit is not divided into lower chrominance blocks.

11. In paragraph 1, An image decoding method, characterized in that when the current unit is intra-predicted, the tree type of the current unit is determined as one of a single tree or a dual tree.

12. In paragraph 11, If the intra prediction mode of the current unit above is a predetermined intra prediction mode, An image decoding method, characterized in that the tree type of the current unit is determined as a single tree.

13. In the video encoding method, A step of determining the tree type of the current unit included in the current slice; A step of determining a division mode of a luminance component of a current unit and a division mode of a chrominance component of the current unit based on the above tree type; A step of dividing a luminance block of a current unit into sub-luminance blocks based on a division mode of a luminance component of the current unit; and A step of dividing a chrominance block of a current unit into sub-chrominance blocks based on a division mode of a chrominance component of the current unit, The tree type of the current unit above is determined as either single tree or dual tree, A video encoding method, characterized in that the current slice is one of an I slice, a B slice, and a P slice.

14. In a non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method, A step of determining the tree type of the current unit included in the current slice; A step of determining a division mode of a luminance component of a current unit and a division mode of a chrominance component of the current unit based on the above tree type; A step of dividing a luminance block of a current unit into sub-luminance blocks based on a division mode of a luminance component of the current unit; and A step of dividing a chrominance block of a current unit into sub-chrominance blocks based on a division mode of a chrominance component of the current unit, The tree type of the current unit above is determined as either single tree or dual tree, A non-transitory computer-readable recording medium, characterized in that the current slice is one of an I slice, a B slice, and a P slice.

15. 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 of determining the tree type of the current unit included in the current slice; A step of determining a division mode of a luminance component of a current unit and a division mode of a chrominance component of the current unit based on the above tree type; A step of dividing a luminance block of a current unit into sub-luminance blocks based on a division mode of a luminance component of the current unit; and A step of dividing a chrominance block of a current unit into sub-chrominance blocks based on a division mode of a chrominance component of the current unit, The tree type of the current unit above is determined as either single tree or dual tree, A transmission method, characterized in that the current slice is one of an I slice, a B slice, and a P slice.

Images