RU2809684C2 - Method and device for video encoding/decoding based on intra-prediction - Google Patents

Abstract

FIELD: method and device for video encoding/decoding.

SUBSTANCE: defining a reference zone for intra-prediction of the current block; extracting the intra-prediction mode of the current block; and decoding the current block based on the reference zone and the intra-prediction mode.

EFFECT: increase of efficiency of image compression.

8 cl, 15 dwg, 6 tbl

Description

Field of technology to which the invention relates

[0001] The present invention relates to a video encoding/decoding method and apparatus.

State of the art

[0002] Recently, there has been an increasing demand for high-quality, high-resolution images, such as high-definition (HD) and ultra-high-definition (UHD) images, in various applications, and accordingly, high-performance image compression technologies are being discussed.

[0003] There are various technologies, such as inter-prediction technology, which predicts pixel values included in the current frame from a frame before or after the current frame using video compression technology, intra-prediction technology, which predicts pixel values included in the current frame, by using the pixel information in the current frame, an entropy encoding technology that allocates a short code to a value with a high frequency of occurrence and a long code to a value with a low frequency of occurrence. Image data can be efficiently compressed by using such image compression technology and transmitted or stored.

The essence of the invention

Technical problem

[0004] An object of the present invention is to provide an efficient block dividing method and apparatus.

[0005] An object of the present invention is to provide a method and apparatus for extracting an intra-prediction mode.

[0006] An object of the present invention is to provide a method and apparatus for determining a reference region for intra-prediction.

[0007] An object of the present invention is to provide an intra-prediction method and apparatus according to a component type.

Technical solution

[0008] The image encoding/decoding method and apparatus of the present invention can determine a reference region for intra-prediction of a current block, extract the intra-prediction mode of the current block, and decode the current block based on the reference region and the intra-prediction mode.

[0009] In the image encoding/decoding method and apparatus of the present invention, intra-prediction modes preset in the encoding/decoding apparatus may be divided into a group of potentially suitable MPM options and a group of potentially suitable non-MPM options, and a group of potentially suitable The MPM options may include at least one of a first group of potentially suitable options or a second group of potentially suitable options.

[0010] In the image encoding/decoding method and apparatus of the present invention, the intra-prediction mode of the current block may be extracted from the first group of candidate candidates or from the second group of candidate candidates.

[0011] In the image encoding/decoding method and apparatus of the present invention, the first group of potential candidates may be composed of a default mode preset in the decoding apparatus, and the second group of potential candidates may be composed of a plurality of potential MPM candidates.

[0012] In the image encoding/decoding method and apparatus of the present invention, the default mode may be at least one of planar mode, DC mode, vertical mode, horizontal mode, vertical mode or diagonal mode.

[0013] In the image encoding/decoding method and apparatus of the present invention, a plurality of potentially suitable MPM options may include at least one of a neighboring block intra-prediction mode, a mode obtained by subtracting the value n from the neighboring block intra-prediction mode , or the mode obtained by summing the value of n with the intra-prediction mode of the neighboring block. As used herein, n may refer to a natural number representing 1, 2, or greater.

[0014] In the image encoding/decoding method and apparatus of the present invention, a plurality of potentially suitable MPM options may include at least one of DC mode, vertical mode, horizontal mode, mode obtained by subtracting or adding the value m from/ s, vertical mode, or the mode obtained by subtracting or summing the value of m from/s horizontal mode. As used herein, m may be a natural number representing 1, 2, 3, 4 or greater.

[0015] In the image encoding/decoding method and apparatus of the present invention, the encoding device may determine a group of candidate candidates to which the intra-prediction mode of the current block belongs, encode a flag to identify the group of candidate candidates, and the decoding apparatus may select one from the first group potential candidates or a second group of potential candidates based on a flag signaled from the encoder.

[0016] In the image encoding/decoding method and apparatus of the present invention, the extracted intra-prediction mode can be changed by applying a predetermined offset to the extracted intra-prediction mode.

[0017] In the image encoding/decoding method and apparatus of the present invention, applying the offset may be selectively performed based on at least one of size, shape, partition information, intra-prediction mode value, or component type of the current block.

[0018] In the image encoding/decoding method and apparatus of the present invention, determining a reference region may include searching for an unavailable pixel belonging to the reference region and replacing the unavailable pixel with an available pixel.

[0019] In the image encoding/decoding method and apparatus of the present invention, an accessible pixel may be determined based on a bit depth value, or may be a pixel adjacent to at least one of the left, right, top, or bottom of the non-accessible pixel.

Advantages of the invention

[0020] The present invention can improve intra-prediction encoding/decoding efficiency through adaptive block division.

[0021] According to the present invention, prediction can be more accurately and efficiently performed by extracting an intra-prediction mode based on a group of potentially suitable MPM cases.

[0022] According to the present invention, in the case of a chrominance block, by specifying the inter-link prediction mode as a separate group, extraction of the intra-prediction mode of the chroma block can be more efficiently performed.

[0023] According to the present invention, the accuracy and efficiency of intra-prediction can be improved by replacing unavailable pixels in the reference region for intra-prediction with predetermined available pixels.

[0024] According to the present invention, the efficiency of inter-prediction can be improved based on the inter-component link.

Description of drawings

[0025] FIG. 1 is a block diagram showing an image encoding apparatus according to an embodiment of the present invention.

[0026] FIG. 2 is a block diagram showing an image decoding apparatus according to an embodiment of the present invention.

[0027] FIG. 3 illustrates a method of dividing a frame into multiple fragment regions as an embodiment to which the present invention is applied.

[0028] FIG. 4 is an exemplary diagram illustrating an intra-prediction mode preset in an image encoding/decoding apparatus as an embodiment to which the present invention is applied.

[0029] FIG. 5 illustrates a method for decoding a current block based on intra-prediction as an embodiment to which the present invention is applied.

[0030] FIG. 6 illustrates a method for replacing an unavailable pixel in a reference region as an embodiment to which the present invention is applied.

[0031] FIG. 7 illustrates a method for changing/correcting an intra-prediction mode as an embodiment to which the present invention is applied.

[0032] FIG. 8 illustrates an inter-link prediction method as an embodiment to which the present invention is applied.

[0033] FIG. 9 illustrates a method for configuring a support region as an embodiment to which the present invention is applied.

[0034] FIG. 10 is an exemplary diagram for configuring an intra-prediction mode set in stages as an embodiment to which the present invention is applied.

[0035] FIG. 11 illustrates a method for classifying intra-prediction modes into multiple groups of potentially suitable options as an embodiment to which the present invention applies.

[0036] FIG. 12 is an exemplary diagram illustrating a current block and a pixel adjacent thereto as an embodiment to which the present invention is applied.

[0037] FIG. 13 illustrates a method of performing intra-prediction step by step as an embodiment to which the present invention is applied.

[0038] FIG. 14 is an exemplary diagram for an arbitrary pixel for intra-prediction as an embodiment to which the present invention is applied.

[0039] FIG. 15 is an exemplary multi-sub-region division diagram based on a random pixel as an embodiment to which the present invention is applied.

Optimal mode for the invention

[0040] The image encoding/decoding method and apparatus of the present invention can determine a reference region for intra-prediction of a current block, extract the intra-prediction mode of the current block, and decode the current block based on the reference region and the intra-prediction mode.

[0041] In the image encoding/decoding method and apparatus of the present invention, intra-prediction modes preset in the encoding/decoding apparatus may be divided into a group of potentially suitable MPM options and a group of potentially suitable non-MPM options, and a group of potentially suitable The MPM options may include at least one of a first group of potentially suitable options or a second group of potentially suitable options.

[0042] In the image encoding/decoding method and apparatus of the present invention, the intra-prediction mode of the current block may be extracted from the first group of candidate candidates or from the second group of candidate candidates.

[0043] In the image encoding/decoding method and apparatus of the present invention, the first group of potential candidates may be composed of a default mode preset in the decoding apparatus, and the second group of potential candidates may be composed of a plurality of potential MPM candidates.

[0044] In the image encoding/decoding method and apparatus of the present invention, the default mode may be at least one of planar mode, DC mode, vertical mode, horizontal mode, vertical mode or diagonal mode.

[0045] In the image encoding/decoding method and apparatus of the present invention, a plurality of potentially suitable MPM options may include at least one of a neighboring block intra-prediction mode, a mode obtained by subtracting the value n from the neighboring block intra-prediction mode , or the mode obtained by summing the value of n with the intra-prediction mode of the neighboring block. As used herein, n may refer to a natural number representing 1, 2, or greater.

[0046] In the image encoding/decoding method and apparatus of the present invention, a plurality of potentially suitable MPM options may include at least one of DC mode, vertical mode, horizontal mode, mode obtained by subtracting or adding the value m from/ s, vertical mode, or the mode obtained by subtracting or summing the value of m from/s horizontal mode. As used herein, m may be a natural number representing 1, 2, 3, 4 or greater.

[0047] In the image encoding/decoding method and apparatus of the present invention, the encoding apparatus may determine a group of candidate candidates to which the intra-prediction mode of the current block belongs, encode a flag to identify the group of candidate candidates, and the decoding apparatus may select one from the first group potential candidates or a second group of potential candidates based on a flag signaled from the encoder.

[0048] In the image encoding/decoding method and apparatus of the present invention, the extracted intra-prediction mode can be changed by applying a predetermined offset to the extracted intra-prediction mode.

[0049] In the image encoding/decoding method and apparatus of the present invention, applying the offset may be selectively performed based on at least one of size, shape, partition information, intra-prediction mode value, or component type of the current block.

[0050] In the image encoding/decoding method and apparatus of the present invention, determining a reference region may include searching for an unavailable pixel belonging to the reference region and replacing the unavailable pixel with an available pixel.

[0051] In the image encoding/decoding method and apparatus of the present invention, an accessible pixel may be determined based on a bit depth value, or may be a pixel adjacent to at least one of the left, right, top, or bottom of the non-accessible pixel.

Mode for implementing the invention

[0052] The present invention may be changed and modified in various ways and illustrated with respect to various exemplary embodiments, some of which are described and shown in the drawings. However, these embodiments are not intended to limit the invention, but are construed to include all modifications, equivalents and substitutions that fall within the spirit and scope of the invention. Like reference numbers throughout the drawings indicate like elements.

[0053] Although the terms "first", "second", etc. may be used to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another element. For example, the first element may be referred to as the "second element" and the second element similarly may be referred to as the "first element" without departing from the teachings of the present invention. The term "and/or" includes any and all combinations of a plurality of associated listed elements.

[0054] It should be understood that when an element is referred to as being "connected to" or "connected to" another element, the element may be directly connected to or connected to the other element or intermediate elements. In contrast, when an element is referred to as "directly connected to" or "directly connected to" another element, there are no intermediate elements.

[0055] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the invention. When used herein, singular forms are intended to include plural forms unless the context clearly indicates otherwise. It should be further emphasized that the terms "includes" and "has" when used in this detailed description indicate the presence of the set forth features, entire parts, steps, operations, elements or components, but do not preclude the presence or addition of one or more other features, entire parts, stages, operations, elements, components or groups thereof.

[0056] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. Like numeral references throughout the drawings refer to like elements, and redundant descriptions of like elements are omitted herein.

[0057] [0058] FIG. 1 is a block diagram illustrating an encoding apparatus according to one embodiment of the present invention.

[0059] Referring to FIG. 1, the image encoding device 100 includes a frame division unit 110, prediction units 120 and 125, transform unit 130, quantization unit 135, reordering unit 160, entropy encoding unit 165, inverse quantization unit 140, inverse transform unit 145, filtering unit 150 and a storage device 155.

[0060] Each of the elements shown in FIG. 1 is shown independently to represent various characteristic functions in the encoding device, and does not mean that each element consists of separate hardware or a single software element. In other words, the elements are arranged independently for ease of description, and at least two elements may be combined into one element, or one element may be divided into multiple elements to perform functions. It should be noted that embodiments in which certain elements are integrated into one combined element and/or an element is divided into several separate elements are included within the scope of the present invention without departing from the spirit of the present invention.

[0061] Some elements are not essential to the essential functions of the invention and may be optional components simply to improve performance. The invention may be practiced by including only components essential to the embodiment of the invention, excluding components used merely to enhance performance. A structure including only essential components, excluding optical components used to simply improve performance, is within the scope of the invention.

[0062] The frame separator 110 may divide the input frame into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transformation unit (TU), or a coding unit (CU). The frame separating unit 110 can divide one frame into a plurality of combinations of a coding unit, a prediction unit, and a transformation unit, and select one combination of a coding unit, a prediction unit, and a transformation unit based on a predetermined criterion (eg, a cost function) so as to encode the frame. .

[0063] For example, one image may be divided into multiple encoding units. To divide a frame into coding units, a recursive tree structure, such as a quadtree structure, can be used. One picture, maximum coding unit (largest coding unit), or coding tree unit (CTU) as a root can be divided into other coding units and can be divided with a number of child nodes up to the number of coding units divided. An encoding unit that is no longer divided according to certain constraints becomes a leaf node. Thus, when it is assumed that only square division is possible for one coding unit, one coding unit can be divided into a maximum of four different coding units.

[0064] In embodiments of the invention, a coding unit may be used to mean not only an encoding unit, but also a decoding unit.

[0065] A prediction unit may be a block divided in a shape such as at least one square or rectangle of identical size in one coding unit, or one prediction unit of prediction units divided in one coding unit may be shaped and /or size different from the shape and/or size of another prediction unit.

[0066] When a prediction unit that performs intra-prediction based on a coding unit is not a minimum coding unit, intra-prediction can be performed without being divided into a plurality of NxN prediction units.

[0067] The prediction modules 120 and 125 may include an inter-prediction module 120 for performing inter-prediction and an intra-prediction module 125 for performing intra-prediction. The prediction modules 120 and 125 can determine which of inter-prediction and intra-prediction is performed for the PU, and can determine specific information (eg, intra-prediction mode, motion vector, and reference frame) of a certain prediction method. Here, the processing unit for which the prediction is performed may be different from the processing unit for which the prediction method and specific information are determined. For example, a prediction method and a prediction mode may be determined for each PU, while prediction may be performed for each TU. A residual value (residual block) between the generated predicted block and the original block may be input to the transform unit 130. Further, prediction mode information, motion vector information and the like used for prediction can be encoded together with a residual value by the entropy encoding unit 165 and transmitted to the decoding device. When a particular encoding mode is used, the original block can be encoded and transmitted to the decoding apparatus without generating a prediction block by the prediction units 120 and 125.

[0068] The inter-prediction unit 120 may predict a PU based on information about at least one frame of a previous frame relative to the current frame and a subsequent frame relative to the current frame. In some cases, inter-prediction module 120 may predict PUs based on partially encoded region information in the current frame. The inter-prediction module 120 may include a reference frame interpolation module, a motion prediction module, and a motion compensation module.

[0069] The reference frame interpolation module may be provided with reference frame information from the memory 155 and generate pixel information less than or equal to an integer pixel for the reference frame. In the case of luminance pixels, an 8-tap DCT-based interpolation filter with a variable filter coefficient can be used to generate pixel information less than or equal to an integer pixel into a 1/4 pixel unit. In the case of chroma pixels, a 4-tap DCT-based interpolation filter with a variable filter coefficient can be used to generate pixel information less than or equal to an integer pixel into a 1/8 pixel unit.

[0070] The motion prediction module may perform motion prediction based on a reference frame interpolated by the reference frame interpolation module. Various methods, such as full search block-based matching algorithm (FBMA), three-stage search (TSS) algorithm, and updated three-stage search (NTS) algorithm, can be used to calculate the motion vector. The motion vector has a motion vector value unit of 1/2 or 1/4 pixel based on the interpolated pixel. The motion prediction module can predict the current PU using various motion prediction methods. Various methods such as skip mode, merging mode, advanced motion vector prediction (AMVP) mode and intra-block copy mode, etc. can be used as the motion prediction method.

[0071] The intra-prediction module 125 may generate a PU based on information regarding a reference pixel adjacent to the current block. When the reference pixel is a pixel for which inter-prediction is performed, since a block adjacent to the current PU is a block for which inter-prediction is performed, information regarding the reference pixel in the block for which inter-prediction is performed may be replaced with information relative to the reference pixel in the block for which intra-prediction was performed. In other words, when a reference pixel is not available, information regarding the unavailable reference pixel may be replaced with information regarding at least one reference pixel of the available reference pixels.

[0072] The intra-prediction prediction mode includes a directional prediction mode in which the reference pixel information is used according to the prediction direction, and a non-directional prediction mode in which the direction information is not used when making the prediction. The mode for predicting luminance information and the mode for predicting chrominance information may be different from each other. Additionally, intra-prediction mode information used to predict luminance information, or predicted luminance signal information can be used to predict chrominance information.

[0073] When the size of the prediction unit and the size of the transformation unit are identical when performing intra-prediction, intra-prediction for the prediction unit may be performed based on the pixel on the left, the pixel on the top left, and the pixel on top relative to the prediction unit. However, when the size of the prediction unit and the size of the transformation unit are different when performing intra-prediction, intra-prediction may be performed using a reference pixel determined based on the transformation unit. Moreover, intra-prediction using NxN partitioning can only be used for the minimum coding unit.

[0074] In the intra-prediction method, a predicted block may be generated by applying an adaptive intra-smoothing (AIS) filter to reference pixels according to the prediction mode. Various types of AIS filters can be applied to reference pixels. In the intra-prediction method, the intra-prediction mode of the current PU can be predicted from the intra-prediction mode of a PU adjacent to the current PU. When predicting the prediction mode of the current PU using mode information predicted from a neighboring PU, when the current PU and the neighboring PU have identical intra-prediction mode, information indicating that the current PU and the neighboring PU have identical prediction mode can be transmitted using pre-prediction mode. certain flag information. When the current PU and the neighboring PU have different prediction modes, information regarding the prediction mode of the current block can be encoded by entropy encoding.

[0075] A residual block including residual information may be generated. The residual information is the difference between the predicted unit generated by the prediction units 120 and 125 and the original prediction unit block. The generated residual block may be input to the conversion unit 130.

[0076] The conversion unit 130 can transform a residual block including residual information between a predicted unit generated by prediction units 120 and 125 and an original block by using a transform type such as DCT (Discrete Cosine Transform), DST (Discrete Sine Transform). conversion) or KLT. Whether or not DCT, DST or KLT should be applied to transform the residual block can be determined based on the intra-prediction mode information of the prediction unit used to generate the residual block.

[0077] The quantization unit 135 may quantize the values converted to the frequency domain by the conversion unit 130. The quantization factor may vary depending on the block or importance of the image. The values output from the quantization unit 135 may be provided to the inverse quantization unit 140 and the re-arrangement unit 160.

[0078] Rearrangement module 160 may perform rearrangement of coefficient values for the quantized remainder.

[0079] Rearrangement unit 160 can change coefficients from a two-dimensional coefficient block to coefficients from a one-dimensional coefficient vector through a coefficient scanning method. For example, the re-arrangement unit 160 may scan the DC coefficient into a high-frequency domain coefficient using a pre-zigzag scanning method and change it to a one-dimensional vector form. Depending on the size of the transformation unit and the intra-prediction mode, instead of zigzag scanning, vertical scanning, which scans the 2D block shape factor in the column direction, and horizontal scanning, which scans the 2D block shape factor in the row direction, can be used. Thus, according to the size of the conversion unit and the intra-prediction mode, it is possible to determine which of the zigzag scanning, vertical direction scanning and horizontal direction scanning should be used.

[0080] The entropy encoding unit 165 may perform entropy encoding based on the values obtained by the rearrangement unit 160. Various encoding techniques such as exponential Golomb coding, context-adaptive variable-length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) can be used for entropy encoding.

[0081] The entropy encoding unit 165 can encode various information, for example, residual coefficient information and block type information for a coding unit, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference movie frame information, block interpolation information and filtering information from the re-arrangement module 160 and the prediction modules 120 and 125.

[0082] The entropy encoding unit 165 may entropy encode the CU coefficients input from the rearrangement unit 160.

[0083] The inverse quantization unit 140 and the inverse transform unit 145 dequantize the values that are quantized by the quantization unit 135 and inversely transform the values that are transformed by the transform unit 130. A reconstructed block can be formed by adding the residuals from the predicted PU. Residual values may be generated by an inverse quantization module 140 and an inverse transform module 145 . The predicted PU may be predicted by the motion vector prediction module, the motion compensation module, and the intra-prediction module of the prediction modules 120 and 125.

[0084] Filtering module 150 may include at least one of a deblocking filter, an offset calculation module, and an adaptive loop filter (ALF).

[0085] A deblocking filter may remove blocking artifacts generated by boundaries between blocks in a reconstructed frame. Whether or not a deblocking filter should be applied to the current block may be determined based on the pixels included in multiple rows or columns of the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied depending on the required filtering strength for deblocking. When horizontal filtering and vertical filtering are performed when applying a deblocking filter, horizontal filtering and vertical filtering can be performed in parallel.

[0086] The offset calculation module may apply an offset from the original image to the deblocking filtered image in units of pixels. The area to which the offset can be applied can be determined after segmenting the pixels of the frame into a predetermined number of areas. The offset may be applied to a specific area based on edge information relative to each pixel or the manner in which the offset is applied to a specific area.

[0087] The ALF can perform filtering based on a comparison result between the filtered reconstructed image and the original image. The pixels included in the image can be segmented into predefined groups, the filter to be applied to each group can be determined, and differential filtering can be performed on each group. Information regarding whether or not ALF should be applied may be conveyed by each coding unit, and the shape and filtering coefficients of the ALF that should be applied to each block may vary. Additionally, an ALF with an identical shape (fixed shape) can be applied to a block regardless of the characteristics of the block.

[0088] The storage device 155 may store the reconstructed block or frame output from the filtering unit 150, and the stored reconstructed block or frame may be provided to the prediction units 120 and 125 when performing inter-prediction.

[0089] [0090] FIG. 2 is a block diagram illustrating an image decoding apparatus according to an exemplary embodiment of the present invention.

[0091] Referring to FIG. 2, the image decoding apparatus 200 may include an entropy decoding unit 210, a rearrangement unit 215, a dequantization unit 220, an inverse transform unit 225, prediction units 230 and 235, a filtering unit 240, and a memory unit 245.

[0092] When an image bit stream is input from an image encoding device, the input bit stream may be decoded in a procedure opposite to that of the image encoding device.

[0093] The entropy decoding unit 210 may perform entropy decoding in a procedure opposite to the procedure for performing entropy encoding in the entropy encoding unit of the image encoding device. For example, various methods such as exponential Golomb coding, CAVLC or CABAC coding can be applied according to the method carried out by the image encoding apparatus.

[0094] The entropy decoding unit 210 can decode information associated with intra-prediction and inter-prediction performed by the encoding device.

[0095] The re-arrangement unit 215 can perform re-arrangement for the bit stream entropy decoded by the entropy decoding unit 210 based on the re-arrangement method of the encoding device. The re-arrangement module 215 can recover and re-arrange the one-dimensional vector coefficients into two-dimensional block coefficients. The re-arrangement unit 215 may be provided with information regarding coefficient scanning performed by the encoder, and may perform re-arrangement using a reverse coefficient scanning method based on the scanning order performed by the encoder.

[0096] The dequantization unit 220 may perform dequantization based on the quantization parameter provided by the encoder and the re-arranged block coefficients.

[0097] The inverse conversion unit 225 may perform the inverse conversion, i.e. inverse DCT, inverse DST and inverse KLT, with respect to the conversion performed by the conversion unit, i.e. DCT, DST and KLT, for the quantization result performed by the image encoder. The inverse conversion may be performed based on the transmission unit determined by the image encoding apparatus. The inverse transform unit 225 of the image decoding apparatus may selectively perform a transform technology (eg, DCT, DST, KLT) according to a plurality of pieces of information such as a prediction method, a current block size, and a prediction direction.

[0098] Prediction modules 230 and 235 may generate a prediction block based on the provided information for generating the prediction block and information regarding a previously decoded block or frame. Information for generating a prediction block may be provided from the entropy decoding module 210. Information regarding a previously decoded block or frame may be provided from memory 245.

[0099] As described above, when the size of the prediction unit and the size of the transformation unit are identical, when intra-prediction is performed identically to the operation of the image encoding device, intra-prediction for the prediction unit can be performed based on the pixel on the left, the pixel on the top left, and the pixel on top relative to the unit predictions. However, when the size of the prediction unit and the size of the transformation unit are different from each other when performing intra-prediction, intra-prediction for the prediction unit can be performed using a reference pixel determined based on the transformation unit. In addition, intra-prediction using NxN partitioning can only be used for the minimum coding unit.

[00100] The prediction modules 230 and 235 may include a prediction unit determination module, an inter-prediction module, and an intra-prediction module. The prediction unit determining unit may receive various information such as prediction unit information, intra-prediction method prediction mode information, and motion prediction-related inter-prediction method information, etc., from the entropy decoding unit 210, may determine the prediction unit for the current coding units. The prediction unit determination module may determine which of inter-prediction and intra-prediction is performed for the prediction unit. The inter-prediction unit 230 may perform inter-prediction for the current prediction unit based on information regarding at least one frame of a previous frame and a subsequent frame relative to the current frame including the current prediction unit. Herein, the inter-prediction unit 230 may use the information required for inter-prediction for the current prediction unit provided from the image encoding device. Inter-prediction may be performed based on information of the previously reconstructed partial region in the current frame including the current prediction unit.

[00101] To perform inter-prediction, it may be determined, in a coding unit unit, whether a motion prediction method for a prediction unit included in a coding unit is a skip mode, an aggregation mode, an AMVP mode, or an intra-block copy mode.

[00102] The intra-prediction module 235 may generate a prediction block based on pixel information in the current frame. When the prediction unit is a prediction unit for which intra-prediction is performed, intra-prediction may be performed based on the intra-prediction mode information regarding the prediction unit provided from the image encoding apparatus. The intra-prediction module 235 may include an AIS (adaptive intra-smoothing) filter, a reference pixel interpolation module, and a DC filter. The AIS filter performs filtering on the reference pixels of the current block. The AIS filter can determine whether the filter should be applied or not depending on the prediction mode for the current prediction unit. AIS filtering may be performed on the reference pixels of the current block using a prediction mode for the prediction unit and information regarding the AIS filter provided from the image encoder. When the prediction mode for the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

[00103] When the prediction mode for a prediction unit specifies a prediction mode for performing intra-prediction based on pixel values obtained by interpolating reference pixels, the reference pixel interpolation unit may generate reference pixels in a fractional pixel unit smaller than an integer pixel (i.e., whole pixel), by interpolating reference pixels. When the prediction mode for the current prediction unit specifies the prediction mode for generating a predicted block without interpolating reference pixels, the reference pixels cannot be interpolated. The DC filter may generate a prediction block by filtering when the prediction mode for the current block is a DC mode.

[00104] The reconstructed block or frame may be provided to filtering module 240. The filtering module 240 includes a deblocking filter, an offset calculation module, and an ALF.

[00105] An image encoding apparatus may provide information regarding whether a deblocking filter is applied to a corresponding block or frame, and information regarding which of a strong filter and a weak filter is applied when the deblocking filter is used. The deblocking filter of the image decoding device may contain information regarding the deblocking filter of the image encoding device and may perform deblocking filtering for a corresponding block.

[00106] The offset calculation module may apply an offset to the reconstructed frame based on information regarding the offset type and offset value applied to the frame during the encoding process.

[00107] ALF may be applied to an encoding unit based on information regarding whether or not ALF is applied and ALF coefficient information, etc., provided from the encoding device. ALF information may be included and provided in a specific set of parameters.

[00108] Storage device 245 may store the reconstructed frame or block for use as a reference frame or reference block and may provide the reconstructed frame to an output module.

[00109] In this detailed description, a coding unit, a coding block, a current block, and the like. can be interpreted as having identical semantic meaning. The embodiment that is described below may be implemented by a corresponding image encoding apparatus module and/or an image decoding apparatus.

[00110] [00111] FIG. 3 illustrates a method of dividing a frame into multiple fragment regions as an embodiment to which the present invention is applied.

[00112] One frame may be divided into a predetermined fragment area. A fragment region according to the present invention may include at least one of a subframe, a slice, a tile, a coding tree unit (CTU), or a coding unit (CU).

[00113] Referring to FIG. 3, frame 300 may include one or more subframes. Thus, a frame may consist of a single subframe or may be divided into multiple subframes, as shown in FIG. 3.

[00114] In the case of a subframe, the division information may be configured differently according to the encoding setting. (1) For example, a subframe may be obtained in a burst division method based on a vertical or horizontal line intersecting the frame. (2) Alternatively, a subframe may be obtained by a partial division method based on feature information (position, size, shape, etc., as for the shape described later, assuming a right angle) of each subframe.

[00115] (1) In the first case, the subframe division information may be configured based on a vertical or horizontal line that divides the subframe.

[00116] Line-based division may use uniform or non-uniform division. When the uniform mode is used, information regarding the number of divisions of each line can be generated, and when the non-uniform mode is used, information of the distance (width or height) between the lines can be generated. The uniform or non-uniform division method may be used depending on the encoding setting, or the method selection information may be explicitly generated. The uniform or uneven division method can be applied jointly to the vertical and horizontal lines. Alternatively, the methods applied to the vertical and horizontal lines are different from each other. Information regarding the number of subframes may be extracted based on the division information.

[00117] The line spacing information may be encoded in units such as n-sample units, CTU size, (2 * CTU size), (4 * CTU size), and the like. Here, n may be a natural number representing 4, 8, 16, 32, 64, 128, 256 or greater. The generated information may be signaled to at least one layer of a video parameter set (VPS), a sequence parameter set (SPS), a frame parameter set (PPS), and a frame header (PH).

[00118] (2) In the second case, subframe position information (for example, information indicating the position of the top left, top right, bottom left, and bottom right with respect to each subframe), size information (for example, information indicating the width or height), information regarding the number of subframes, etc. can be used to configure subframe division information.

[00119] Information indicating the number of subframes (hereinafter referred to as number information) may be encoded by the encoding apparatus, and the decoding apparatus may determine the number of subframes configuring one frame based on the encoded number information. The number information may be signaled to at least one layer of the VPS, SPS, PPS and PH. Alternatively, information on the number of subframes may be implicitly derived based on partitioning information (position information, size, etc.) of the subframe.

[00120] Information indicating the position of each subframe (hereinafter in this document, position information) may include an X coordinate or a Y coordinate of a pre-fixed position of the corresponding subframe. The pre-fixed position may be determined from the number left above, right above, left below and right below with respect to the subframe. The position information may be encoded by the encoding device, and the decoding device may determine the position of each subframe based on the encoded position information. Here, the X coordinate/Y coordinate may be expressed in units such as n sample units, CTU size, (2 * CTU size), (4 * CTU size), and the like. Here, n may be a natural number representing 1, 2, 4, 8, 16, 32, 64, 128, 256 or greater. For example, in case the position information is encoded using the X coordinate and Y coordinate of the top left CTU of a subframe, if the width and height are 2 and 3, respectively, in CTU units (CtbSize), the position (top left) of the subframe may be determined as (2 * CtbSize, 3 * CtbSize).

[00121] Information indicating the size of each subframe (hereinafter referred to as size information) may include at least one of width information and height information of the corresponding subframe. Here, the width/height information may be encoded in units such as n-sample units, CTU size, (2 * CTU size), (4 * CTU size), and the like. Here, n may be a natural number representing 4, 8, 16, 32, 64, 128, 256 or greater. For example, in case the width information is encoded in CTU size units (CtbSize), if the width information is 6, the width of the subframe may be determined as (6 * CtbSize).

[00122] The above-described position information and size information may be limited to being encoded/decoded only when the number of subframes belonging to a frame is two or more. That is, if the number of subframes according to the number information is greater than or equal to two, the position information and the size information are signaled. Otherwise, the subframe may be configured to have a position/size identical to the position/size of the frame. However, even when the number of subframes is two or more, the position information for the first subframe located at the top left of the frame may not be signaled and may be signaled from the position information relative to the second subframe. In addition, at least one of the position information or the size information relative to the last subframe of the frame may not be signaled.

[00123] Referring to FIG. 3, one subframe may include one or more slices. Thus, one subframe may consist of one slice or may be divided into multiple slices. A subframe may consist of a plurality of slices divided in a horizontal direction, or may consist of a plurality of slices divided in a vertical direction.

[00124] Information indicating the number of slices belonging to one frame or subframe (hereinafter referred to as number information) is encoded by the encoding device, and the decoding device can determine the number of subframes in one frame or subframe based on the encoded number information. The number information may be signaled to at least one layer of the VPS, SPS, PPS and PH. However, the number information may be signaled only in at least one of the case in which a rectangular slice is enabled or the case in which one subframe does not consist of one slice.

[00125] Information indicating the size of each slice (hereinafter in this document, size information) may include at least one of width information and height information of the corresponding slice. Here, the width/height information may be encoded in tile units or CTU.

[00126] However, it may not be permitted that one slice is divided such that it overlaps multiple subframes. In other words, one subframe may be divided such that it completely includes one or more slices. Alternatively, a slice constituting one subframe may be limited to being divided only in either the horizontal direction or the vertical direction.

[00127] Referring to FIG. 3, one subframe or slice 310 may include one or more tiles. Thus, one slice may consist of one tile or may consist of many tiles. However, the present invention is not limited to this, and multiple slices may be included in one tile. As an example, one slice may consist of a subset of multiple CTU rows belonging to a single tile. In this case, information indicating the number of slices belonging to one tile (hereinafter referred to as number information) is encoded by the encoding device, and the decoding device can determine the number of slices constituting one tile based on the encoded number information. Information indicating the size of each slice (hereinafter herein, size information) may include at least one of width information and height information of the corresponding slice. Here, the width/height information may be encoded in a CTU size unit. However, when one slice consists of a subset of multiple CTU lines, only the height information of the corresponding slice may be signaled, and the width information may not be signaled. The number/size information may be signaled to at least one layer of the VPS, SPS, PPS or PH.

[00128] At least one of the above information regarding number, position and size is requested only when the frame is divided into predetermined fragment areas. For example, information may be signaled only when a frame is divided into multiple slices or tiles. For this purpose, a separate flag may be used to indicate whether or not the current frame is divided into multiple slices or tiles. The flag may be signaled for at least one layer of VPS, SPS, PPS and PH.

[00129] Referring to FIG. 3, one tile may be composed of a plurality of CTUs, and one CTU 320 (hereinafter, the first block) may be divided into a plurality of sub-units (hereinafter, the second block), at least through one of a vertical line or a horizontal line. The number of vertical lines and horizontal lines can be one, two or more. Hereinafter in this document, the first block is not limited to a CTU and may be an encoding unit (CU) divided from a CTU, a prediction unit (PU) which represents a basic predictive encoding/decoding unit, or a transform unit (TU) which represents is the basic unit of encoding/decoding with conversion. The first block may be a square block or a non-square block.

[00130] The division of the first block can be performed based not only on a quadtree, but also on a multi-tree, for example, a binary tree or a ternary tree.

[00131] In particular, quadtree (QT) partitioning is a type of partitioning in which the first block is divided into four second blocks. For example, when the first 2Nx2N block is divided by QT, the first block may be divided into four second blocks having a size of NxN. QT may be limited to applying only to a square block, but it is also applicable to a non-square block.

[00132] Binary tree partitioning (BT) is a type of partitioning in which a first block is divided into two second blocks. The BT may include a horizontal binary tree (hereinafter, horizontal BT) and a vertical binary tree (hereinafter, vertical BT). Horizontal BT is a type of division in which the first block is divided into two second blocks by a single horizontal line. This division can be performed symmetrically or asymmetrically. For example, when the first 2Nx2N block is divided based on the horizontal BT, the first block may be divided into two second blocks with a height ratio of (a:b). Here, a and b may be the same value, and a may be greater or less than b. Vertical BT is a type of division in which the first block is divided into two second blocks by a single vertical line. This division can be performed symmetrically or asymmetrically. For example, when the first 2Nx2N block is divided based on the vertical BT, the first block may be divided into two second blocks with a width ratio of (a:b). Here, a and b may be the same value, and a may be greater or less than b.

[00133] Ternary tree (TT) partitioning is a type of partitioning in which a first block is partitioned into three second blocks. Likewise, the TT may include a horizontal ternary tree (hereinafter, horizontal TT) and a vertical ternary tree (hereinafter, vertical TT). Horizontal TT is a type of division in which the first block is divided into three second blocks by two horizontal lines. For example, when the first 2Nx2N block is divided based on the horizontal TT, the first block may be divided into three second blocks with a height ratio of (a:b:c). Here, a, b and c can be identical value. Alternatively, a and c may be identical, and b may be greater or less than a. For example, a and c may be equal to 2, and b may be equal to 1. Vertical TT is a type of division in which the first block is divided into three second blocks by two vertical lines. For example, when the first 2Nx2N block is divided based on the vertical TT, the first block may be divided into three second blocks with a width ratio of (a:b:c). Here, a, b and c may be the same value or different values. Alternatively, a and c may be identical, while b may be greater or less than a. Alternatively, a and b may be identical, while c may be greater or less than a. Alternatively, b and c are identical, while a may be greater or less than b. For example, a and c could be 2, and b could be 1.

[00134] The division described above may be performed based on the division information signaled from the encoding device. The partition information may include at least one of partition type information, partition direction information, or partition relationship information.

[00135] The division type information may indicate any of the division types that are preset in the encoding/decoding apparatus. The predetermined partition type may include at least one of QT, horizontal BT, vertical BT, horizontal TT, vertical TT, or non-partition mode (no splitting). Alternatively, the partition type information may mean information regarding whether QT, BT or TT is applied, and may be encoded in the form of a flag or an index. As an example, the partition type information may include at least one of a first flag indicating whether QT is applied or not, or a second flag indicating whether BT or TT is applied. BT or TT may be selectively used according to the second flag. However, the first flag may only be signaled when the size of the first block is less than or equal to a predefined threshold size. The threshold size may be a natural number representing 64, 128, or greater. When the size of the first block exceeds the threshold size, the first block can only be forced to be split using QT. In addition, the second flag may be signaled only when QT is not applied according to the first flag.

[00136] In the case of BT or TT, the dividing direction information may indicate whether it is divided horizontally or vertically. In the case of BT or TT, the division ratio information may indicate the width and/or height ratio of the second block.

[00137] Block 320 illustrated in FIG. 3 is supposed to be a square block (hereinafter referred to as the first block) having a size of 8Nx8N and a division depth of k. When the division information of the first block indicates a QT division, the first block may be divided into four sub-blocks (hereinafter in this document, the second block). The second block may be 4Nx4N in size and may have a partition depth of (k+1).

[00138] The four second blocks may be divided again on a QT, BT, TT basis or on a non-divided basis. For example, when the division information of the second block indicates horizontal BT, the second block is divided into two sub-blocks (hereinafter in this document, the third block). In this case, the third block may have a size of 4Nx2N and may have a partition depth of (k+2).

[00139] The third block may also be divided again either on a QT, BT, TT basis or on a non-divided basis. For example, when the third block division information indicates vertical BT, the third block is divided into two subblocks 321 and 322. In this case, the subblocks 321 and 322 may have a size of 2Nx2N and a division depth of (k+3). Alternatively, when the third block partitioning information indicates horizontal BT, the third block may be divided into two sub-blocks 323 and 324. In this case, sub-blocks 323 and 324 may have a size of 4NxN and a partition depth of (k+3).

[00140] The division may be performed independently or in parallel with an adjacent block, or may be performed sequentially according to a predetermined priority order.

[00141] The division information of the current block may be determined depending on at least one of the division information of an upper block relative to the current block or the division information of an adjacent block. For example, when the second block is divided based on the horizontal BT, and the upper third block is divided based on the vertical BT, the lower third block should not be divided based on the vertical BT. If the lower third block is divided by a vertical BT, this presents an identical result as when the second block is divided by a QT. Therefore, encoding to obtain division information (in particular, division direction information) of the lower third block can be skipped, and the decoding device can be set such that the lower third block is divided in the horizontal direction.

[00142] An upper block may mean a block having a smaller division depth than the division depth of the current block. For example, when the division depth of the current block is (k+2), the division depth of the upper block may be (k+1). An adjacent block can be a block adjacent to the top or left side of the current block. The adjacent block may be a block having a division depth identical to the division depth of the current block.

[00143] The above division may be repeatedly performed down to a minimum encoding/decoding unit. When divided by a minimum unit, the division information for the block is no longer signaled from the encoder. Information regarding the minimum unit may include at least one of the size or shape of the minimum unit. The size of the minimum unit can be expressed in terms of width, height, minimum or maximum value of width and height, sum of width and height, number of pixels, or division depth. Information regarding the minimum unit may be signaled in at least one of a video sequence unit, frame, slice, or block. Alternatively, the information regarding the minimum unit may be a value preset in the encoding/decoding apparatus. Information regarding the minimum unit may be signaled for each of the CU, PU and TU. Information regarding one minimum unit can be applied to CU, PU and TU equally. The blocks in the embodiments described below can be obtained through the block division described above.

[00144] The block division according to an embodiment of the present invention can be obtained in a supported range, and the block division setting information for this can be maintained. For example, the blocking settings information may include a size mxn associated with a maximum coding unit (CTU), a minimum coding unit, a maximum transform unit, and a minimum transform unit (e.g., m and n are natural numbers, e.g., 2, 4 , 8, 16, 32, 64, 128, etc.) and a maximum division depth of k for each block (e.g. encoding/transformation x Intra/Inter x QT/BT/TT, etc.; k is 0 , 1, 2 or more). It may also be signaled for at least one layer of the VPS, SPS, PPS, PH or slice header.

[00145] In the case of some of the above-described fragment regions (subframe, slice, tile, etc.), in order to segment/divide each fragment region (for example, to extract position and size information of the fragment region), predefined basic information (for example , information regarding the bottom or base unit of the corresponding fragment area, such as a CTU or tile). In this case, VPS-SPS-PPS may be sequentially traversed, but for simultaneous encoding/decoding, it may be necessary to provide basic information at a level that supports segmentation/division of each fragment region.

[00146] For example, CTU information may be generated (fixed) in the SPS, and the CTU information may be used (when divided) according to whether or not to be divided into subframes (subject to processing in the SPS). Alternatively, the CTU information may be generated (when divided, further generated) according to whether or not to be divided into slices or tiles (subject to processing in the PPS), and it may be divided into slices and tiles based on this.

[00147] In general, the basic information used to segment/divide a fragmented image may be generated at a single level. Alternatively, the base information used for segmentation/division may be formed into two or more levels according to the type of fragmented image.

[00148] Regardless of the type of the fragment image, the basic information (syntax or flag) referenced in the fragment image segment may be generated at the same level. Alternatively, the basic information referenced in a segment of each sub-image may be generated at multiple levels according to the sub-image. In this case, even though the basic information may arise and exist at two or more levels, an identical effect with the appearance and existence at the same level can be maintained through such an adjustment that they have identical meaning or information with each other. However, in the case of basic information, the default setting may be that they have identical meaning or information, but there is no restriction on this, and it may be possible to change them so that they have different meanings or information.

[00149] [00150] FIG. 4 is an exemplary diagram illustrating an intra-prediction mode preset in an image encoding/decoding apparatus as an embodiment to which the present invention is applied.

[00151] Referring to FIG. 4, the intra-prediction preset modes may be defined as a group of potentially suitable prediction mode options consisting of 67 modes, and may specifically include 65 directional modes (No. 2-66) and two (DC-, planar) non-directional mode. In this case, the directional mode can be identified based on tilt (eg, dy/dx) or angle (degrees) information. All or some of the intra-prediction modes described in the above example may be included in the group of potentially suitable luminance component or chrominance component prediction mode options, and other additional modes may be included in the group of potentially suitable prediction mode options.

[00152] In addition, a reconstructed block of another color space that is encoded/decoded using correlation between color spaces can be used to predict the current block, and a prediction mode supporting this can be turned on. For example, in the case of a chrominance component, a prediction block of the current block may be generated by using a reconstructed luma component block corresponding to the current block. Thus, a prediction block can be generated based on the reconstructed block, taking into account the correlation between color spaces.

[00153] A group of potentially suitable prediction mode options may be adaptively determined according to the encoding/decoding setting. The number of candidate groups may be increased for the purpose of improving prediction accuracy, and the number of candidate groups may be decreased for the purpose of reducing the number of bits according to the prediction mode.

[00154] For example, one of group A of potential candidates (67, 65 directional modes and 2 non-directional modes), group B of potential candidates (35, 33 directional modes and 2 non-directional modes), or group C of potential candidates (18, 17 directional modes and one non-directional mode) can be selected, and a group of potential candidates can be adaptively selected or determined based on the size and shape of the block.

[00155] In addition, it is possible to have various configurations of a group of potentially suitable prediction mode options according to the encoding/decoding setting. For example, as shown in FIG. 4, a group of potentially suitable prediction mode options may be configured such that the interval between modes is even, or a group of potentially suitable prediction mode options may be configured such that the number of modes between modes 18 and 34 in FIG. 4 exceeds the number of modes between modes 2 and 18. The opposite case may be possible. The group of potential candidates may be adaptively configured according to the shape of the block (ie, square, non-square with width, taller than square, non-square with height, larger than width, etc.).

[00156] For example, when the width of the current block exceeds the height, all or some of the intra-prediction modes belonging to modes 2-18 may not be used and may be replaced by all or some of the intra-prediction modes belonging to modes 67-80. On the other hand, when the width of the current block is less than the height, all or some of the intra-prediction modes belonging to modes 50 to 66 may not be used and may be replaced by all or some of the intra-prediction modes belonging to modes -14 to -1.

[00157] In the present invention, unless otherwise stated, it is assumed that intra-prediction is performed with one group of candidate candidates of a preset prediction mode (with group A of candidate candidates) having a uniform interval between modes, but the basic elements of the present invention also can be applied to adaptive intra-prediction settings.

[00158] [00159] FIG. 5 illustrates a method for decoding a current block based on intra-prediction as an embodiment to which the present invention is applied.

[00160] Referring to FIG. 5, a reference area for intra-prediction of the current block may be determined (S500).

[00161] The reference region according to the present invention may be a region adjacent to at least one of the left, top, top left, bottom left, or top right of the current block. In addition, although not shown in FIG. 5, the reference region may further include a region adjacent to at least one of the right, bottom right, or bottom of the current block, and may be selectively used based on the intra-prediction mode of the current block, encoding/decoding order, scanning order etc.

[00162] The encoding/decoding apparatus may define a plurality of pixel lines available for intra-prediction. The plurality of pixel lines may include at least one of a first pixel line adjacent to the current block, a second pixel line adjacent to the first pixel line, a third pixel line adjacent to the second pixel line, or a fourth pixel line adjacent to the third pixel line. line.

[00163] For example, depending on the encoding/decoding setting, the plurality of pixel lines may include all of the first to fourth pixel lines, or may include only the remaining pixel lines excluding the third pixel line. Alternatively, the plurality of pixel lines may include only the first pixel line and the fourth pixel line, or may include only the first to third pixel lines.

[00164] The current block may select one or more of a plurality of pixel lines and use it as a reference region. In this case, the selection may be made based on the index (refIdx) signaled from the encoding device. Alternatively, the selection may be made based on predetermined encoding information. Here, the encoding information may include at least one of a size, a shape and a division type of the current block, whether or not an intra-prediction mode is an omnidirectional mode, whether or not an intra-prediction mode is a horizontal directionality, a mode angle intra-prediction or component type.

[00165] For example, when the intra-prediction mode is a planar mode or a DC mode, use may be limited to only the first pixel line. Alternatively, when the current block size is less than or equal to a predetermined threshold, usage may be limited to only the first pixel line. Here, the size may be expressed as any of the width or height of the current block (eg, maximum value, minimum value, etc.), the sum of the width and height, or the number of samples belonging to the current block. Alternatively, when the intra-prediction mode has an angle greater than a predetermined threshold angle (or less than a predetermined threshold angle), only the first pixel line may be used. The threshold angle may be an intra-prediction mode angle corresponding to mode 2 or mode 66 in the above group of potentially suitable prediction mode options.

[00166] Meanwhile, a case may arise where at least one of the pixels of the reference area is not available, in which case, the unavailable pixel may be replaced by a predetermined default value or an available pixel. This will be described in detail below with reference to FIG. 6.

[00167] Referring to FIG. 5, the intra-prediction mode of the current block may be retrieved (S510).

[00168] The current block is a concept including a luma block and a chrominance block, and an intra-prediction mode may be determined for each of the luma block and the chroma block. Hereinafter in this document, it is assumed that the intra-prediction mode preset in the decoding apparatus consists of non-directional modes (planar mode, DC mode) and 65 directed modes.

[00169] 1. In case of brightness block

[00170] The above-described predefined intra-prediction modes can be divided into a group of potentially suitable MPM options and a group of potentially suitable non-MPM options. The intra-prediction mode of the current block may be retrieved selectively using either a group of potentially eligible MPM candidates or a group of potentially eligible non-MPM candidates. For this purpose, a flag (hereinafter in this document, the first flag) may be used indicating whether or not the intra-prediction mode of the current block is retrieved from the group of potentially eligible MPM candidates. For example, when the first flag has a first value, a group of potentially eligible MPM options can be used, and when the first flag has a second value, a group of potentially eligible non-MPM options can be used.

[00171] In particular, when the first flag has a first value, the intra-prediction mode of the current block may be determined based on a group (candModeList) of potentially suitable MPM options, including at least one potentially suitable MPM option and an MPM index. The MPM index may be information indicating any of the potential MPM candidates belonging to a group of potential MPM candidates. The MPM index can only be signaled when the set of potential MPM candidates belongs to the group of potential MPM candidates.

[00172] On the other hand, when the first flag has a second value (i.e., when a candidate MPM candidate identical to the intra-prediction mode candidate MPM candidate of the current block does not exist in the group of candidate MPM candidates), the mode intra-predictions of the current block can be determined based on the signaled information of the remaining modes. The remaining mode information may indicate any of the remaining modes except the potentially eligible MPM option.

[00173] Later in this document, a method for identifying a group of potentially suitable MPM options is described.

[00174] (Embodiment 1) The group of potentially suitable MPM options may include at least one of intra-adjacent block prediction mode (Mode A), A-n mode, A+n mode, or default mode. The value of n can be an integer representing 1, 2, 3, 4 or greater. Adjacent block can mean a block adjacent to the left and/or top of the current block. However, the present invention is not limited to this, and a neighboring block may include at least one of a left upper neighboring block, a left lower neighboring block, or a right upper neighboring block. The default mode may be at least one of a planar mode, a DC mode, or a predetermined directional mode. The predetermined directional mode may include at least one of horizontal mode (V mode), vertical mode (H mode), V-k mode, V+k mode, H-k mode, or H+k mode. Here, k may be an integer representing 1, 2, 3, 4, 5 or more.

[00175] The MPM index may indicate an MPM identical to the intra-prediction mode MPM of the current block from among the MPMs of a group of potentially eligible MPM candidates. Thus, the MPM indicated by the MPM index can be set as the intra-prediction mode of the current block.

[00176] (Embodiment 2) The group of potentially suitable MPM options may be divided into groups of potentially suitable options m; m can be an integer representing 2, 3, 4 or more. Hereinafter in this document, for convenience of description, it is assumed that the group of potential MPM candidates is divided into a first group of potential candidates and a second group of potential candidates.

[00177] The encoding/decoding apparatus may select a first group of potential candidates or a second group of potential candidates. The selection may be made based on a flag (hereinafter hereinafter, a second flag) that indicates whether the intra-prediction mode of the current block belongs to the first group of candidates or the second group of candidates. For example, if the second flag has the first value, the intra-prediction mode of the current block may be retrieved from the first group of candidates, otherwise, the intra-prediction mode of the current block may be retrieved from the second group of candidates.

[00178] Specifically, when the first group of candidates is used according to the second flag, a first MPM index indicating any of a plurality of default modes belonging to the first group of candidates may be signaled. The default mode corresponding to the signaled first MPM index may be set as the intra-prediction mode of the current block. On the other hand, when the first candidate group consists of one default mode, the first MPM index is not signaled and the intra-prediction mode of the current block may be set as the default mode of the first candidate group.

[00179] When the second group of candidates is used according to the second flag, a second MPM index indicating any of a plurality of candidate MPM candidates belonging to the second group of candidates may be signaled. A potentially suitable MPM option corresponding to the signaled second MPM index may be set as the intra-prediction mode of the current block. On the other hand, when the second candidate candidate group consists of one MPM candidate candidate, the second MPM index is not signaled and the intra-prediction mode of the current block may be set as the MPM candidate candidate of the second candidate candidate group.

[00180] Meanwhile, the second flag can be signaled only when the above-described first flag has the first value (condition 1). In addition, the second flag may be signaled only when the reference area of the current block is determined to be the first pixel line. When the current block references non-contiguous pixel lines, the potential MPM candidates of the first group of potential candidates may be limited such that they are not used. Alternatively, on the other hand, when the intra-prediction mode of the current block is retrieved from the first group of candidates according to the second flag, the current block may be constrained such that it refers only to the first pixel line.

[00181] In addition, the second flag may be signaled only when the current block does not perform intra-prediction in subblock units (condition 2). On the other hand, when the current block performs intra-prediction in units of subblocks, the flag may not be signaled and may be set to a second value in the decoder.

[00182] When either of the above conditions 1 or 2 is satisfied, the second flag may be signaled, or when both conditions 1 and 2 are satisfied, the second flag may be signaled.

[00183] The first group of potentially suitable options may consist of a predefined default mode. The default mode may be at least one of a directional mode or an omnidirectional mode. For example, the directional mode may include at least one of a vertical mode, a horizontal mode, or a diagonal mode. The omnidirectional mode may include at least one of a planar mode and a DC mode.

[00184] The first group of potentially suitable options may consist of only r non-directional modes or directional modes; r may be an integer representing 1, 2, 3, 4, 5 or greater; r may be a fixed value predetermined in the encoding/decoding apparatus, or may be variably determined based on a predetermined encoding parameter.

[00185] The second group of potentially suitable options may include a plurality of potentially suitable MPM options. However, the second group of potential candidates may be limited such that it does not include the default mode belonging to the first group of potential candidates. The number of potentially suitable MPM options can be 2, 3, 4, 5, 6 or more. The number of potentially eligible MPM candidates may be a fixed value predetermined in the encoding/decoding apparatus, or may be variably determined based on the encoding parameter. A potentially suitable MPM candidate can be retrieved based on the intra-prediction mode of a neighboring block adjacent to the current block. An adjacent block may be a block adjacent to at least one of the left, top, top left, bottom left, or top right of the current block.

[00186] In particular, a potentially suitable MPM variant may be determined by considering whether or not the intra-prediction mode (candIntraPredModeA) of the left block and the intra-prediction mode (candIntraPredModeB) of the upper block are identical, and whether candIntraPredModeA and candIntraPredModeB are the same or no omnidirectional modes.

[00187] [Case 1]. For example, when candIntraPredModeA and candIntraPredModeB are identical, and candIntraPredModeA is not an undirected mode, a potentially suitable MPM variant of the current block may include at least one of candIntraPredModeA, (candIntraPredModeA-n), (candIntraPredModeA+n), or an undirected mode. Here, n may be an integer representing 1, 2 or more. The omnidirectional mode may include at least one of a planar mode or a DC mode. As an example, a potential MPM candidate of the current block may be determined as shown in Table 1 below. The index of Table 1 indicates the position or priority of the potential MPM candidate, but is not limited to it.

[00188] Table 1

Index Potentially suitable MPM option 0 candIntraPredModeA 1 2+((candIntraPredModeA+61)%64) 2 2+((candIntraPredModeA-1)%64) 3 2+((candIntraPredModeA+60)%64) 4 2+((candIntraPredModeA%64)

[00189] [Case 2] Alternatively, when candIntraPredModeA and candIntraPredModeB are not identical, and both candIntraPredModeA and candIntraPredModeB are not undirected mode, potentially suitable MPM variants of the current block may include at least one of candIntraPredModeA, candIntraPredModeB, (maxAB-n), (maxAB+n), (minAB-n), (minAB+n) or non-directional mode. Here, maxAB and minAB mean the maximum value and minimum value of candIntraPredModeA and candIntraPredModeB, respectively, and n may be an integer representing 1, 2 or more. The omnidirectional mode may include at least one of a planar mode or a DC mode. As an example, based on the difference value D between candIntraPredModeA and candIntraPredModeB, the mode candidate of the second group of candidate candidates may be determined as shown in Table 2 below. The index of Table 2 indicates the position or priority of the candidate MPM candidate, but is not limited thereto .

[00190] Table 2

Index Potentially suitable mode option
(D=1) Potentially suitable mode option
(D=2) Potentially suitable mode option
(D>=62) Potentially suitable mode option
(Another) 0 candIntraPredModeA candIntraPredModeA candIntraPredModeA candIntraPredModeA 1 candIntraPredModeB candIntraPredModeB candIntraPredModeB candIntraPredModeB 2 2+((minAB+61)%64) 2+((minAB-1)%64) 2+((minAB-1)%64) 2+((minAB+61)%64) 3 2+((maxAB-1)%64) 2+((minAB+61)%64) 2+((maxAB+61)%64) 2+((minAB-1)%64) 4 2+((minAB+60)%64) 2+((maxAB-1)%64) 2+(minAB%64) 2+((maxAB+61)%64)

[00191] In Table 2 above, one of the potential candidate MPM candidates is retrieved based on minAB, and the other is retrieved based on maxAB. However, the present invention is not limited to this, and a potentially suitable MPM variant can be retrieved based on maxAB independently of minAB, and on the other hand, can be retrieved based on minAB independently of maxAB.

[00192] [Case 3]. When candIntraPredModeA and candIntraPredModeB are not identical, and only one of candIntraPredModeA and candIntraPredModeB is an undirected mode, a potentially suitable MPM variant of the current block may include at least one of maxAB, (maxAB-n), (maxAB+n), or non-directional mode. Here, maxAB denotes the maximum value of candIntraPredModeA and candIntraPredModeB, and n may be an integer representing 1, 2 or more. The omnidirectional mode may include at least one of a planar mode or a DC mode. As an example, the candidate MPM candidate of the current block may be determined as shown in Table 3 below. The index of Table 3 indicates the position or priority of the candidate MPM candidate, but is not limited to it.

[00193] Table 3

Index Potentially suitable MPM option 0 maxAB 1 2+((maxAB+61)%64) 2 2+((maxAB-1)%64) 3 2+((maxAB+60)%64) 4 2+(maxAB%64)

[00194] [Case 4] When candIntraPredModeA and candIntraPredModeB are not identical, and both candIntraPredModeA and candIntraPredModeB are omnidirectional modes, potentially suitable MPM variants of the current block may include omnidirectional mode, vertical mode, horizontal mode, (vertical mode - m), (vertical mode+m), (horizontal mode - m) or (horizontal mode+m). Here, m may be an integer representing 1, 2, 3, 4 or more. The omnidirectional mode may include at least one of a planar mode or a DC mode. As an example, the candidate MPM candidate of the current block may be determined as shown in Table 4 below. The index of Table 4 indicates the position or priority of the candidate MPM candidate, but is not limited to it. For example, index 1 may be assigned to the horizontal mode, or the largest index may be assigned to it. Additionally, a potentially suitable MPM option may include at least one of diagonal mode (eg, mode 2, mode 34, mode 66), (diagonal mode - m) or (diagonal mode + m).

[00195] Table 4

Index Potentially suitable MPM option 0 INTRA_DC 1 Vertical mode 2 Horizontal mode 3 (Vertical mode - 4) 4 (Vertical mode+4)

[00196] The intra-prediction mode (IntraPredMode) decoded by the above process can be changed/adjusted based on the predetermined offset, which is described in detail with reference to FIG. 7.

2. In case of chroma blocks

[00197] The preset intra-prediction modes for the chrominance block may be divided into a first group and a second group. Here, the first group may be configured with inter-reference based prediction modes, and the second group may be configured with all or some of the above-described predefined intra-prediction modes.

[00198] The chrominance block intra-prediction mode may be selectively extracted using either the first group or the second group. The selection may be made based on a predefined third flag. The third flag may indicate whether the chrominance block intra-prediction mode is retrieved based on the first group or the second group.

[00199] For example, when the third flag has the first value, the intra-prediction mode of the chroma block may be determined as one of one or more inter-link based prediction modes belonging to the first group. This will be described in detail below with reference to FIG. 8.

[00200] On the other hand, when the third flag has a second value, the chrominance block intra-prediction mode may be determined as one of a plurality of intra-prediction modes belonging to the second group. As an example, the second group may be set as shown in Table 5, and the chroma block intra-prediction mode can be extracted based on the information (intra_chroma_pred_mode) signaled by the encoder and the luminance block intra-prediction mode (IntraPredModeY).

[00201] Table 5

intra_chroma_pred_mode[xB][yB] IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] 0 50 18 1 X (0<=X<34) 0 66 0 0 0 0 1 50 66 50 50 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

[00202] According to Table 5, the chrominance block intra-prediction mode can be determined based on the signaled information and the luminance block intra-prediction mode. The mode numbers listed in Table 5 correspond to the mode numbers in FIG. 4. For example, when the intra_chroma_pred_mode signal information value is 0, the chroma block intra-prediction mode may be determined as a diagonal mode 66 or a planar mode (0) according to the luminance block intra-prediction mode. Alternatively, when the intra_chroma_pred_mode signal information value is 4, the chroma block intra-prediction mode may be set to be identical to the luminance block intra-prediction mode. Meanwhile, the luminance block intra-prediction mode (IntraPredModeY) may be a sub-block intra-prediction mode including a specific position in the luminance block. Here, a specific position in the luma block may correspond to a central position in the chrominance block.

[00203] However, it may be the case that a subblock in the luma block corresponding to the center position in the chrominance block is not available. Here, "not available" may represent a case in which the corresponding sub-block is not encoded in intra-mode. For example, when a sub-block does not have an intra-prediction mode, for example, when a corresponding sub-block is encoded in inter-mode or reference mode based on current frames, it may be determined that the corresponding sub-block is not available. In this case, the intra-prediction mode (IntraPredModeY) of the luminance block may be set to a mode previously fixed in the encoding/decoding apparatus. Here, the pre-fixed mode may be any of a planar mode, a DC mode, a vertical mode or a horizontal mode.

[00204] Referring to FIG. 5, the current block can be decoded based on the reference region for intra-prediction and the intra-prediction mode (S520).

[00205] Decoding of the current block may be performed in units of subblocks of the current block. For this purpose, the current block may be divided into multiple subblocks. Here, the current block can correspond to a leaf node. A leaf node can mean a coding block that is no longer divided into smaller coding blocks. Thus, a leaf node can mean a block that is no longer partitioned through the tree-based block partitioning described above.

[00206] The division may be performed based on the size of the current block (Embodiment 1).

[00207] For example, when the size of the current block is less than a predetermined threshold size, the current block may be divided into two vertically or horizontally. On the other hand, when the size of the current block is greater than or equal to the threshold size, the current block may be split into four vertically or horizontally. The threshold size may be signaled by the encoding device or may be a fixed value preset in the decoding device. For example, the threshold size is expressed as NxM, and N and M can be 4, 8, 16, or greater. N and M may be identical or may be specified differently from each other.

[00208] Alternatively, if the size of the current block is less than a predetermined threshold size, the current block is not split (not split). Otherwise, the current block may be divided into two or four.

[00209] The division may be performed based on the shape of the current block (embodiment 2).

[00210] For example, if the shape of the current block is a square, the current block is divided into four, otherwise, the current block may be divided into two. On the other hand, if the shape of the current block is a square, the current block is divided into two, otherwise, the current block can be divided into four.

[00211] Alternatively, if the shape of the current block is a square, the current block is divided into two or four, otherwise, the current block may not be divided. On the other hand, when the shape of the current block is a square, the current block is not divided, otherwise, the current block may be divided into two or four.

[00212] The separation may be performed by selectively applying any of the above-described embodiment 1 or 2, or the separation may be performed based on a combination of embodiments 1 and 2.

[00213] Dividing by two means dividing by two in the vertical or horizontal direction, and dividing by four may include dividing by four in the vertical or horizontal direction, or dividing by four in the vertical and horizontal directions.

[00214] In the above embodiment, dividing into two or dividing into four is described, but the present invention is not limited to this, and the current block may be divided into three in the vertical or horizontal direction. In this case, the ratio of width or height may be (1:1:2), (1:2:1) or (2:1:1).

[00215] Information regarding whether or not to divide into subblock units, whether or not to divide into four, the direction of division and the number of divisions may be signaled from the encoding device or variably determined by the decoding device based on a predetermined encoding parameter. Here, the encoding parameter may mean block size/shape, partition type (four-partition, two-partition, three-partition), intra-prediction mode, neighboring pixel range/position for intra-prediction, component type (eg luminance signal and chrominance signal), maximum/minimum conversion block size, conversion type (for example, skip conversion, DCT2, DST7, DCT8), etc.

[00216] Sub-blocks relative to the current block can be sequentially predicted/restored according to a predetermined priority. In this case, the first sub-block with respect to the current block can be predicted/reconstructed, and the second sub-block can be predicted/reconstructed with reference to the previously decoded first sub-block. With respect to priority, it is predicted/reconstructed in top->down order, but each sub-block above and below can be predicted/reconstructed in left->right order. Alternatively, it is predicted/reconstructed in top->down order, but each sub-block above and below may be predicted/reconstructed in right->left order. Alternatively, it is predicted/reconstructed in bottom->up order, but each sub-block below and above can be predicted/reconstructed in left->right order. Alternatively, it is predicted/reconstructed in bottom->up order, but each sub-block below and above can be predicted/reconstructed in right->up order. Alternatively, it is predicted/reconstructed in left->right order, but each sub-block on the left and right may be predicted/reconstructed in top->down order. Alternatively, it is predicted/reconstructed in left->right order, but each sub-block on the left and right can be predicted/reconstructed in bottom->up order. Alternatively, it is predicted/reconstructed in right->left order, but each sub-block on the right and left may be predicted/reconstructed in top->down order. Alternatively, it is predicted/reconstructed in right->left order, but each sub-block on the right and left may be predicted/reconstructed in bottom->up order.

[00217] The encoding/decoding apparatus may set any of the above-described orders and use them. Alternatively, the encoding/decoding device may define at least two or more of the above-described orders and selectively use any of them. To this end, an index or flag indicating any of the predefined orders may be encoded and signaled.

[00218] [00219] FIG. 6 illustrates a method for replacing an unavailable pixel in a reference region as an embodiment to which the present invention is applied.

[00220] As described above, the reference area may be defined as one of the first to fourth pixel lines. However, in the present embodiment, for convenience of description, it is assumed that the reference area is the first pixel line. The present embodiment may be applied identically or similarly to the second to fourth pixel lines.

[00221] When all pixels in the reference region are not available, the corresponding pixel may be replaced by one of a range of pixel values expressed in terms of bit depth, or a range of actual pixel values of the image. For example, maximum value, minimum value, median value, mean value, etc. range of pixel values can correspond to the value that is to be replaced. When the bit depth is 8, all pixels in the reference region can be filled with 128 when replaced by the median bit depth value.

[00222] However, if not, i.e. not all pixels of the reference region are not available, but at least one of the pixels of the reference region is not available, the replacement process may be performed for at least one of the top reference region, left reference region, right reference region or bottom reference region of the current block. For ease of explanation, the description focuses on the left, top and right support areas of the current block.

[00223] (Step 1) It is determined whether the upper left TL pixel adjacent to the current block (prediction block) is not available or accessible. If the top left TL pixel is not available, the pixel may be replaced by the middle bit depth value.

[00224] (Step 2) A search can be made sequentially regarding whether or not an inaccessible pixel exists in the upper reference region. Here, the top reference region may include a pixel line adjacent to at least one of the top or top right of the current block. The length of the upper support area can be equal to the width of the current block (nW), (2*nW) or the sum of (nW+nH) width and height.

[00225] Here, the search direction may be performed from left to right. In this case, when it is determined that pixel p[x][-1] is not available, pixel p[x][-1] may be replaced by neighboring pixel p[x-1][-1]. Alternatively, the search direction may be from right to left. In this case, when it is determined that pixel p[x][-1] is not available, pixel p[x][-1] may be replaced by neighboring pixel p[x+1][-1].

[00226] (Step 3) A search can be made sequentially regarding whether or not an inaccessible pixel exists in the left reference region. Here, the left reference region may include a pixel line adjacent to at least one to the left or bottom left of the current block. The length of the left support area can be equal to the height (nH) of the current block, (2*nH) or the sum (nW+nH) of the width and height.

[00227] Here, the search direction may be performed from top to bottom. In this case, when it is determined that pixel p[-1][y] is not available, pixel p[-1][y] may be replaced by neighboring pixel p[-1][y-1]. Alternatively, the search direction may be from bottom to top. In this case, when it is determined that pixel p[-1][y] is not available, pixel p[-1][y] may be replaced by neighboring pixel p[-1][y+1].

[00228] (Step 4) A search can be made sequentially regarding whether or not an inaccessible pixel exists in the right reference area. Here, the right reference region may include a pixel line adjacent to the right of the current block. The length of the right support area can be identical to the height (nH) of the current block.

[00229] Here, the search direction may be performed from top to bottom. In this case, when it is determined that pixel p[nW][y] is not available, pixel p[nW][y] may be replaced by neighboring pixel p[nW][y-1]. Alternatively, the search direction may be from bottom to top. In this case, when it is determined that pixel p[nW][y] is not available, pixel p[nW][y] may be replaced by neighboring pixel p[nW][y+1].

[00230] Alternatively, a separate search process may be omitted for the right reference region. Instead, the unavailable pixel in the right reference region may be filled with the median bit depth value. Alternatively, the unavailable pixel in the right reference region may be replaced by one of the upper right pixel TR or the lower right pixel BR adjacent to the current block, or may be replaced by a representative value thereof. Here, the representative value may be expressed as an average value, a maximum value, a minimum value, a mode value, a median value, and the like. Alternatively, the unavailable pixel in the right reference region may be extracted by applying a predetermined weighting factor to each of the upper right pixel TR and the lower right pixel BR. In this case, the weight coefficient may be determined taking into account a first distance between the unavailable pixel in the right reference region and the upper right pixel TR and a second distance between the unavailable pixel in the right reference region and the lower right pixel BR. The lower right pixel BR may be filled with one of the upper left TL pixel, the upper right pixel TR, or the lower left BL pixel adjacent to the current block, or may be replaced with a representative value of at least two of the upper left TL pixel, the upper right pixel TR, or bottom left pixel BL. Here, the representative value is as described above. Alternatively, the lower right pixel BR may be extracted by applying a predetermined weight coefficient to at least two of the upper left pixel TL, the upper right pixel TR, or the lower left pixel BL, respectively. Here, the weighting factor may be determined taking into account the distance from the lower right pixel BR.

[00231] Meanwhile, the above-described replacement process is not limited to being executed in top->left->right priority. For example, the replacement process can be performed in left->up->right priority. Alternatively, the replacement process may be performed in parallel for the top and left support regions and then may be performed for the right support region. In addition, the stage 1 process can be omitted when the replacement process is executed in left->up->right priority.

[00232] [00233] FIG. 7 illustrates a method for changing/correcting an intra-prediction mode as an embodiment to which the present invention is applied.

[00234] The decoded mode (IntraPredMode) of the intra prediction may be changed based on a predetermined offset. Applying the offset may be selectively performed based on at least one of the block properties, i.e. size, shape, partition information, partition depth, intra-prediction mode value, or component type. Here, a block may mean the current block and/or a neighboring block relative to the current block.

[00235] The partition information may include at least one of first information indicating whether or not the current block is divided into a plurality of sub-blocks, second information indicating a direction of division (eg, horizontal or vertical), or third information regarding the number of divided sub-blocks . Information may be encoded and signaled by means of an encoding device. Alternatively, the division information portion may be variably determined in the decoding apparatus based on the above-described block property, or may be set to a fixed value preset in the encoding/decoding apparatus.

[00236] For example, if the first information has a first value, the current block is divided into a plurality of subblocks, otherwise, the current block may not be divided into a plurality of subblocks (NO_SPLIT). When the current block is divided into a plurality of sub-blocks, the current block may be horizontally divided (HOR_SPLIT) or vertically divided (VER_SPLIT) based on the second information. In this case, the current block can be divided into k subblocks. The k value can be an integer representing 2, 3, 4 or more. Alternatively, k may be limited to a power of 2, such as 1, 2, 4, etc. Alternatively, in the case of a block in which at least one of the width or height of the current block is 4 (for example, 4x8, 8x4), k is set to 2, otherwise, k is set to 4, 8, or 16. When the current the block is not split (NO_SPLIT), k can be set to 1.

[00237] The current block may be divided into subblocks having identical width and height, or may be divided into subblocks having different widths and heights. The current block can be divided into NxM block units (for example, 2x2, 2x4, 4x4, 8x4, 8x8, etc.) pre-fixed in the encoding/decoding device, regardless of the property of the above-described block .

[00238] An offset can only be applied when the current block size is less than or equal to a predetermined threshold T1. Here, the threshold value T1 may indicate the maximum block size to which the offset is applied. Alternatively, it may only be applied when the current block size is greater than or equal to a predefined threshold T2. In this case, the threshold T2 may indicate the minimum block size to which the offset is applied. The threshold value may be signaled via a bit stream. Alternatively, it may be variably determined by the decoding apparatus based on at least one of the above-described block properties, or may be a fixed value predetermined in the encoding/decoding apparatus.

[00239] Alternatively, the offset may only be applied when the shape of the current block is non-square. For example, when the following conditions are satisfied, a predetermined offset (eg, 65) may be added to the IntraPredMode of the current block.

[00240] - nW exceeds nH

[00241] - IntraPredMode is greater than or equal to 2

[00242] - IntraPredMode less (whRatio>1)? (8+2*whRatio): 8

[00243] Here, nW and nH denote the width and height of the current block, respectively, and whRatio may be set to Abs (Log2(nW/nH)).

[00244] Alternatively, when the following conditions are satisfied, a predetermined offset (eg, 67) may be subtracted from the IntraPredMode of the current block.

[00245] - nH exceeds nW

[00246] - IntraPredMode is less than or equal to 66

[00247] - IntraPredMode exceeds (whRatio>1)? (60-2*whRatio): 60

[00248] As described above, the final intra-prediction mode may be determined by adding/subtracting the offset to/from the intra-prediction mode (IntraPredMode) of the current block, taking into account a property of the current block. However, the present invention is not limited to this, and applying the offset can be done in an identical/similar manner by taking into account the properties (eg, size, shape) of the sub-block instead of the current block.

[00249] [00250] FIG. 8 illustrates an inter-link prediction method in an embodiment to which the present disclosure applies.

[00251] The current block may be divided into a luma block and a chrominance block according to the component type. The chrominance block can be predicted using a pixel of the reconstructed luminance block. This is referred to as an intercomponent link. In this embodiment, it is assumed that the chrominance block has a size of (nTbW x nTbH), and the luma block corresponding to the chroma block has a size of (2*nTbW x 2*nTbH).

[00252] Referring to FIG. 8, the chrominance block intra-prediction mode may be determined (S800).

[00253] As described in FIG. 5, an intra-prediction mode of a chrominance block may be determined as one of one or more prediction modes based on inter-links belonging to the first group according to the third flag. The first group can only consist of interlink-based prediction modes. The encoding/decoding apparatus may set at least one of INTRA_LT_CCLM, INTRA_L_CCLM, or INTRA_T_CCLM as the intercomponent link prediction mode. INTRA_LT_CCLM is a mode that refers to the left and top regions adjacent to the luma/chroma blocks, INTRA_L_CCLM is a mode that refers to the left region adjacent to the luma/chromina blocks, and INTRA_T_CCLM is a mode that refers to the top area adjacent to the luminance signal/chrominance blocks.

[00254] A predetermined index can be used to select any of the interlink-based prediction modes. The index may be information indicating any of INTRA_LT_CCLM, INTRA_L_CCLM or INTRA_T_CCLM. The index can only be signaled when the third flag has the first value. The interlink prediction modes belonging to the first group and the indexes assigned to each prediction mode are shown in Table 6 below.

[00255] Table 6

Idx Interlink Prediction Mode 0 INTRA_LT_CCLM 1 INTRA_L_CCLM 2 INTRA_T_CCLM

[00256] Table 6 is only an example of the index assigned to each prediction mode, but is not limited to it. Thus, as shown in Table 6, indexes can be assigned in order of priority in INTRA_LT_CCLM, INTRA_L_CCLM, INTRA_T_CCLM, or indexes can be assigned in order of priority in INTRA_LT_CCLM, INTRA_T_CCLM, INTRA_L_CCLM. Alternatively, INTRA_LT_CCLM may have a lower priority order than INTRA_T_CCLM or INTRA_L_CCLM. The third flag may be selectively signaled based on information indicating whether or not the intercomponent link is enabled. For example, if the information value is 1, the third flag may be signaled, otherwise, the third flag may not be signaled. Here, the information may be determined to be 0 or 1 based on a predetermined condition described later.

[00257] (Condition 1) When the fourth flag indicating whether or not inter-link prediction is enabled is 0, the information may be set to 0. The fourth flag may be signaled in at least one of the VPS, SPS, PPS, PH and slice header.

[00258] (Condition 2) When at least one of the following sub-conditions is satisfied, the information may be set to 1.

[00259] - qtbtt_dual_tree_intra_flag is 0

[00260] - slice type is not I-slice

[00261] - coding tree block size is less than 64×64

[00262] In condition 2, qtbtt_dual_tree_intra_flag may indicate whether or not a coding tree block is implicitly split into a 64x64 coding block, and whether or not a 64x64 coding block is split based on a dual tree. A dual tree may mean a method in which a luma component and a chrominance component are separated with an independent partition structure. The coding tree block size (CtbLog2Size) may be a size (eg, 64×64, 128×128, 256×256) preset in the encoding/decoding apparatus, or may be encoded and signaled by the encoding apparatus.

[00263] (Condition 3) When at least one of the following sub-conditions is satisfied, the information may be set to 1.

[00264] - the width and height of the first top block are 64

[00265] - The depth of the first top block is identical (CtbLog2Size-6), the first top block is divided based on horizontal BT, and the second top block is 64x32

[00266] - the depth of the first upper block exceeds (CtbLog2Size-6)

[00267] - The depth of the first top block is identical (CtbLog2Size-6), the first top block is divided based on the horizontal BT, and the second top block is divided based on the vertical BT

[00268] In condition 3, the first upper block may be a block including the current chroma block as a lower block. For example, when the depth of the current chrominance block is k, the depth of the first upper block is (k-n), and n may be 1, 2, 3, 4 or more. The depth of the first top block may mean only a depth according to a quadtree partition, or may mean a depth according to a partition of at least one of a quadtree, a binary tree, or a ternary tree. The second top block is a bottom block belonging to the first top block, and may have a depth less than the current chrominance block and a depth greater than the first top block. For example, when the depth of the current chrominance block is k, the depth of the second upper block is (k-m), and m can be a natural number less than n.

[00269] When none of the above conditions 1-3 are satisfied, the information may be set to 0.

[00270] However, even when at least one of the conditions 1-3 is satisfied, when at least one of the following sub-conditions is satisfied, the information may be reset to 0.

[00271] - the first upper block is 64x64, and the above subblock-based prediction is performed

[00272] - at least one of the width or height of the first top block is less than 64, and the depth of the first top block is (CtbLog2Size-6)

[00273] Referring to FIG. 8, a luminance region for a chroma block inter-reference may be specified (S810).

[00274] The luma region may include at least one of a luma block or a neighboring region adjacent to the luma block. Here, the luminance block may be specified as an area including pixels pY[x][y] (x=0...nTbW*2-1, y=0...nTbH*2-1). Pixels may indicate reconstructed values before the in-loop filter is applied.

[00275] An adjacent region may include at least one of a left adjacent region, an upper adjacent region, or a left upper adjacent region. The left adjacent region can be specified as a region including the pixels pY[x][y] (x=-1...-3, y=0...2*numSampL-1). The setting can only be performed when the value of numSampL is greater than 0. The upper adjacent region can be set as the region including the pixels pY[x][y] (x=0...2*numSampT-1, y=-1. ..-3). The setting can only be performed when the value of numSampT is greater than 0. The upper left adjacent region can be set as the region including the pixels pY[x][y] (x=-1, y=-1,-2). The adjustment can only be made when the upper left area of the brightness block is available.

[00276] The above-described numSampL and numSampT may be determined based on the intra-prediction mode of the current block. Herein, the current block may denote a chrominance block.

[00277] For example, when the intra-prediction mode of the current block is INTRA_LT_CCLM, it may be extracted based on Equation 9. Here, INTRA_LT_CCLM may mean a mode in which inter-component reference is performed based on the left and upper neighboring regions of the current block.

[00278] equation 1

[00279] numSampT=availT? nTbW: 0

[00280] numSampL=availL? nTbH: 0

[00281] According to Equation 1, numSampT is retrieved as nTbW when the upper adjacent region with respect to the current block is available. Otherwise, numSampT may be retrieved as 0. Likewise, numSampL is retrieved as nTbH when the left neighbor of the current block is accessible. Otherwise, numSampL may be retrieved as 0.

[00282] On the contrary, when the intra prediction mode of the current block is not INTRA_LT_CCLM, it can be retrieved based on Equation 2 below.

[00283] equation 2

[00284] numSampT=(availT && predModeIntra==INTRA_T_CCLM)? (nTbW+numTopRight): 0

[00285] numSampL=(availL && predModeIntra==INTRA_L_CCLM)? (nTbH+numLeftBelow): 0

[00286] In Equation 2, INTRA_T_CCLM may mean a mode in which the inter-component link is performed based on the upper neighbor region with respect to the current block. INTRA_L_CCLM may indicate a mode in which inter-component linking is performed based on the left neighbor of the current block. numTopRight can mean the number of all or some pixels belonging to the top right adjacent region with respect to the chroma block. Some pixels may mean available pixels from pixels belonging to the lowest row of pixels of the corresponding region. When determining accessibility, whether pixels are accessible or not can be determined sequentially in a left-to-right direction. This process can continue until the inaccessible pixel is found; numLeftBelow can mean the number of all or some pixels belonging to the lower left adjacent region with respect to the chrominance block. Some pixels may mean available pixels from pixels belonging to the rightmost pixel line (column) of the corresponding region. When determining availability, whether pixels are available or not can be determined sequentially in a top-to-bottom direction. This process can continue until the inaccessible pixel is found.

[00287] Referring to FIG. 8, downsampling may be performed on the luminance region indicated by S810 (S820).

[00288] Downsampling may include at least one of: 1. downsampling a luminance block, 2. downsampling a left adjacent region relative to a luminance block, or 3. downsampling a top adjacent region relative to a luminance block. This is described in more detail below.

[00289] 1. Luminance block downsampling

[00290] First embodiment

[00291] Pixel pDsY[x][y] (x=0...nTbW-1, y=0...nTbH-1) of the downsampled luminance block may be extracted based on the corresponding pixel pY[2*x][2 *y] of the brightness block and the neighboring pixel. An adjacent pixel may mean at least one of a left adjacent pixel, a right adjacent pixel, an upper adjacent pixel, or a lower adjacent pixel with respect to the corresponding pixel. For example, the pixel pDsY[x][y] can be extracted based on Equation 3 below.

[00292] equation 3

[00293] pDsY[x][y]=(pY[2 * x][2 * y-1]+pY[2 * x-1][2 * y]+4 * pY[2 * x][2 * y]+pY[2 * x+1][2 * y]+pY[2 * x][2 * y+1]+4)>>3

[00294] However, it may be the case that the left/upper adjacent region with respect to the current block is not accessible. When the left adjacent region with respect to the current block is not available, the pixel pDsY[0][y] (y=1...nTbH-1) of the downsampled luminance block can be extracted based on the corresponding pixel pY[0[2*y] of the block brightness and the neighboring pixel relative to the corresponding pixel. An adjacent pixel may mean at least one of an upper adjacent pixel or a lower adjacent pixel with respect to the corresponding pixel. For example, the pixel pDsY[0][y] (y=1...nTbH-1) can be extracted based on Equation 4 below.

[00295] equation 4

[00296] pDsY[0][y]=(pY[0][2 * y-1]+2 * pY[0][2 * y]+pY[0][2 * y+1]+2) >>2

[00297] When the upper adjacent region with respect to the current block is not available, the pixel pDsY[x][0] (x=1...nTbW-1) of the downsampled luminance block can be extracted based on the corresponding pixel pY[2*x] [0] of the brightness block and the neighboring pixel relative to the corresponding pixel. An adjacent pixel may mean at least one of a left adjacent pixel or a right adjacent pixel with respect to the corresponding pixel. For example, the pixel pDsY[x][0] (x=1...nTbW-1) can be extracted based on Equation 5 below.

[00298] equation 5

[00299] pDsY[x][0]=(pY[2 * x-1][0+2 * pY[2 * x][0+pY[2 * x+1][0+2)>>2

[00300] The pixel pDsY[0][0] of the downsampled luminance block may be extracted based on the corresponding pixel pY[0[0] of the luminance block and/or a neighboring pixel relative to the corresponding pixel. The position of a neighboring pixel can vary depending on whether the left/top neighboring regions are accessible or not with respect to the current block.

[00301] For example, when the left neighboring region is available but the upper neighboring region is not accessible, pDsY[0][0] can be extracted based on Equation 6 below.

[00302] equation 6

[00303] pDsY[0][0]=(pY[0][-1]+2 * pY[0][0]+pY[0][1]+2)>>2

[00304] On the contrary, when the left neighboring region is not available, but the upper neighboring region is available, pDsY[0][0] can be extracted based on Equation 7 below.

[00305] equation 7

[00306] pDsY[0][0]=(pY[0][-1]+2 * pY[0][0]+pY[0][1]+2)>>2

[00307] In another example, when the left and top adjacent regions are not available, pDsY[0][0] may be set as the corresponding pixel pY[0[0] of the luminance block.

[00308] Second embodiment

[00309] Pixel pDsY[x][y] (x=0...nTbW-1, y=0...nTbH-1) of the downsampled luminance block may be extracted based on the corresponding pixel pY[2*x][2 *y] of the brightness block and the neighboring pixel relative to the corresponding pixel. An adjacent pixel may mean at least one of a lower neighboring pixel, a left neighboring pixel, a right neighboring pixel, a lower left neighboring pixel, or a lower right neighboring pixel with respect to the corresponding pixel. For example, the pixel pDsY[x][y] can be extracted based on Equation 8 below.

[00310] equation 8

[00311] pDsY[x][y]=(pY[2 * x-1][2 * y]+pY[2 * x-1][2 * y+1]+2* pY[2 * x] [2 * y]+2*pY[2 * x][2 * y+1]+pY[2 * x+1][2 * y]+pY[2 * x+1][2 * y+1 ]+4)>>3

[00312] However, when the left adjacent region with respect to the current block is not available, the pixel pDsY[0][y] (y=0...nTbH-1) of the downsampled luminance block can be extracted based on the corresponding pixel pY[ 0[2*y] of the brightness block and the lower adjacent pixel in relation to it. For example, the pixel pDsY[0][y] (y=0...nTbH-1) can be extracted based on Equation 9 below.

[00313] equation 9

[00314] pDsY[0][y]=(pY[0][2 * y]+pY[0][2 * y+1]+1)>>1

[00315] Luminance block downsampling may be performed based on one of embodiments 1 and 2 as described above. Here, one of embodiments 1 and 2 may be selected based on a predetermined flag. The flag may indicate whether or not the downsampled luminance pixel has a position identical to that of the original luminance pixel. For example, when the flag is set to the first value, the downsampled luma pixel has a position identical to the position of the original luma pixel. Conversely, when the flag is set to the second value, the downsampled luminance pixel has a position identical to the position of the original luminance pixel in the horizontal direction, but has a position shifted by half a pel in the vertical direction.

[00316] [00317] 2. Downsampling the left adjacent region with respect to the luminance block

[00318] First embodiment

[00319] The downsampled left neighbor region pixel pLeftDsY[y] (y=0...numSampL-1) may be extracted based on the corresponding left neighbor region pixel pY[-2][2*y] and the neighbor pixel relative to the corresponding pixel. An adjacent pixel may mean at least one of a left adjacent pixel, a right adjacent pixel, an upper adjacent pixel, or a lower adjacent pixel with respect to the corresponding pixel. For example, the pixel pLeftDsY[y] can be extracted based on Equation 10 below.

[00320] equation 10

[00321] pLeftDsY[y]=(pY[-2][2 * y-1]+pY[-3][2 * y]+4 * pY[-2][2 * y]+pY[-1 ][2 * y]+pY[-2][2 * y+1]+4)>>3

[00322] However, when the upper left neighbor region with respect to the current block is not available, the downsampled left neighbor region pixel pLeftDsY[0] can be extracted based on the corresponding left neighbor region pixel pY[-2][0] and the neighbor pixel relative to the corresponding pixel. An adjacent pixel may mean at least one of a left adjacent pixel or a right adjacent pixel with respect to the corresponding pixel. For example, the pixel pLeftDsY[0] may be extracted based on Equation 11 below.

[00323] equation 11

[00324] pLeftDsY[0]=(pY[-3][0]+2 * pY[-2][0]+pY[-1][0]+2)>>2

[00325] Second embodiment

[00326] The downsampled left neighbor region pixel pLeftDsY[y] (y=0...numSampL-1) may be extracted based on the corresponding left neighbor region pixel pY[-2][2*y] and a neighbor pixel near the corresponding pixel. An adjacent pixel may mean at least one of a lower neighboring pixel, a left neighboring pixel, a right neighboring pixel, a lower left neighboring pixel, or a lower right neighboring pixel with respect to the corresponding pixel. For example, the pixel pLeftDsY[y] can be extracted based on the following equation 12.

[00327] equation 12

[00328] pLeftDsY[y]=(pY[-1][2 * y]+pY[-1][2 * y+1]+2* pY[-2][2 * y]+2*pY[ -2][2 * y+1]+pY[-3][2 * y]+pY[-3][2 * y+1]+4)>>3

[00329] Likewise, downsampling of the left adjacent region can be performed based on one of embodiments 1 and 2 as described above. Here, one of embodiments 1 and 2 may be selected based on a predetermined flag. The flag indicates whether or not the downsampled luma pixel has a position identical to the position of the original luma pixel. This is identical to what is described above.

[00330] Downsampling of the left neighboring region can only be performed when the value of numSampL is greater than 0. When the value of numSampL is greater than 0, it may indicate that the left neighboring region of the current block is available, and the intra-prediction mode of the current block is INTRA_LT_CCLM or INTRA_L_CCLM.

[00331] [00332] 3. Downsampling the upper adjacent region with respect to the luminance block

[00333] First embodiment

[00334] The pixel pTopDsY[x] (x=0...numSampT-1) of the downsampled upper neighboring region may be extracted based on whether or not the upper neighboring region belongs to a CTU different from the CTU to which the luminance block belongs.

[00335] When the top neighbor region belongs to a CTU identical to the luma block CTU, the pixel pTopDsY[x] of the downsampled top neighbor region may be extracted based on the corresponding pixel pY[2*x][-2] of the top neighbor region and the neighbor pixel relative to the corresponding pixel . An adjacent pixel may mean at least one of a left adjacent pixel, a right adjacent pixel, an upper adjacent pixel, or a lower adjacent pixel with respect to the corresponding pixel. For example, the pixel pTopDsY[x] can be extracted based on Equation 13 below.

[00336] equation 13

[00337] pTopDsY[x]=(pY[2 * x][-3]+pY[2 * x-1][-2]+4 * pY[2 * x][-2]+pY[2 * x+1][-2]+pY[2 * x][-1]+4)>>3

[00338] Conversely, when the top neighbor region belongs to a CTU different from the luminance block, the pixel pTopDsY[x] of the downsampled top neighbor region may be extracted based on the corresponding pixel pY[2*x][-1] of the top neighbor region and the neighbor pixel with respect to the corresponding pixel. An adjacent pixel may mean at least one of a left adjacent pixel or a right adjacent pixel with respect to the corresponding pixel. For example, the pixel pTopDsY[x] can be extracted based on Equation 14 below.

[00339] equation 14

[00340] pTopDsY[x]=(pY[2 * x-1][-1]+2* pY[2 * x][-1]+pY[2 * x+1][-1]+2) >>2

[00341] Alternatively, when the upper left adjacent region with respect to the current block is not available, the adjacent pixel may mean at least one of an upper adjacent pixel or a lower adjacent pixel with respect to the corresponding pixel. For example, pixel pTopDsY[0] can be extracted based on Equation 15 below.

[00342] equation 15

[00343] pTopDsY[0]=(pY[0][-3]+2 * pY[0][-2]+pY[0][-1]+2)>>2

[00344] Alternatively, when the top left neighbor region with respect to the current block is inaccessible and the top neighbor region belongs to a CTU different from the luminance block, pixel pTopDsY[0] may be set as top neighbor pixel pY[0][-1] areas.

[00345] Second embodiment

[00346] The pixel pTopDsY[x] (x=0...numSampT-1) of the downsampled upper neighbor region may be extracted based on whether or not the upper neighbor region belongs to a CTU different from the luminance block.

[00347] When the top neighbor region belongs to a CTU identical to the luma block CTU, the pixel pTopDsY[x] of the downsampled top neighbor region can be extracted based on the corresponding pixel pY[2*x][-2] of the top neighbor region and the neighbor pixel relative to the corresponding pixel . An adjacent pixel may mean at least one of a lower neighboring pixel, a left neighboring pixel, a right neighboring pixel, a lower left neighboring pixel, or a lower right neighboring pixel with respect to the corresponding pixel. For example, the pixel pTopDsY[x] can be extracted based on Equation 16 below.

[00348] equation 16

[00349] pTopDsY[x]=(pY[2 * x-1][-2]+pY[2 * x-1][-1]+2* pY[2 * x][-2]+2* pY[2 * x][-1]+pY[2 * x+1][-2]+pY[2 * x+1][-1]+4)>>3

[00350] Conversely, when the top neighbor region belongs to a CTU different from the luminance block, the pixel pTopDsY[x] of the downsampled top neighbor region may be extracted based on the corresponding pixel pY[2*x][-1] of the top neighbor region and the neighbor pixel with respect to the corresponding pixel. An adjacent pixel may mean at least one of a left adjacent pixel or a right adjacent pixel with respect to the corresponding pixel. For example, the pixel pTopDsY[x] can be extracted based on Equation 17 below.

[00351] equation 17

[00352] pTopDsY[x]=(pY[2 * x-1][-1]+2* pY[2 * x][-1]+pY[2 * x+1][-1]+2) >>2

[00353] Alternatively, when the upper left adjacent region with respect to the current block is not available, the adjacent pixel may mean at least one of an upper adjacent pixel or a lower adjacent pixel with respect to the corresponding pixel. For example, the pixel pTopDsY[0] may be extracted based on Equation 18 below.

[00354] equation 18

[00355] pTopDsY[0]=(pY[0][-2]+pY[0][-1]+1)>>1

[00356] Alternatively, when the upper left neighboring region with respect to the current block is inaccessible and the upper neighboring region belongs to a CTU other than the luminance block, pixel pTopDsY[0] may be set as upper neighboring pixel pY[0][-1] areas.

[00357] Likewise, downsampling of the upper adjacent region can be performed based on one of embodiments 1 and 2 as described above. Here, one of embodiments 1 and 2 may be selected based on a predetermined flag. The flag indicates whether or not the downsampled luma pixel has a position identical to the position of the original luma pixel. This is identical to what is described above.

[00358] Meanwhile, downsampling of the upper neighboring region can be performed only when the value of numSampT exceeds 0. When the value of numSampT exceeds 0, it may indicate that the upper neighboring region with respect to the current block is available, and the intra-prediction mode of the current block is INTRA_LT_CCLM or INTRA_T_CCLM.

[00359] Downsampling of at least one of the left or top adjacent regions for a luminance block (hereinafter in this document, for the luminance reference region) can only be performed using the corresponding pixel pY[-2][2*y] at a specific position and surrounding pixels. Here, a specific position may be determined based on the position of a selected pixel from a plurality of pixels belonging to at least one of the left or upper adjacent regions for a chrominance block (hereinafter referred to as a “chroma reference region”).

[00360] The selected pixel may be an odd-numbered pixel or an even-numbered pixel in the chroma reference region. Alternatively, the selected pixel may be a starting pixel and one or more pixels positioned at predetermined intervals relative to the starting pixel. Here, the starting pixel may be a pixel positioned at a first, second or third position in the chrominance reference region. The interval may be 1, 2, 3, 4 or more sample intervals. For example, when the interval is one sample interval, the selected pixel may include the nth pixel, the (n+2)th pixel, and the like. The number of pixels selected may be 2, 4, 6, 8 or more.

[00361] The number of selected pixels, start pixel, and interval may be variably determined based on at least one of the length of the chroma reference region (ie, numSampL and/or numSampT) or the intra-prediction mode of the chroma block. Alternatively, the number of selected pixels may be a fixed number (eg, 4) fixed in advance in the encoding/decoding apparatus, regardless of the length of the chrominance reference region and the intra-prediction mode of the chrominance block.

[00362] Referring to FIG. 8, a parameter for the chroma block inter-link may be retrieved (S830).

[00363] The parameter may include at least one of a weight or an offset. The parameter can be determined taking into account the intra-prediction mode of the current block. The parameter may be extracted using a selected pixel of the chroma reference region and a pixel obtained by downsampling the luminance reference region.

[00364] Specifically, n pixels may be classified into two groups by performing size comparisons between n pixels obtained by downsampling a luminance reference region. For example, the first group may be a group of pixels having a relatively large value of n pixels, and the second group may be a group of pixels different from the pixels of the first group of n samples. Thus, the second group may be a group of pixels having a relatively small value. Here, n can be 4, 8, 16 or more. The average value of the pixels belonging to the first group may be set as the maximum value MaxL, and the average value of the pixels belonging to the second group may be set as the minimum value MinL.

[00365] According to the grouping of n pixels obtained by downsampling the luminance reference region, selected pixels of the chroma reference region may be grouped. The first group for the chrominance reference region is configured by using pixels of the chroma reference region corresponding to the pixels of the first group of the luminance reference region. The second group for the chroma reference region may be configured by using pixels of the chroma reference region corresponding to the pixels of the second group of the luminance reference region. Likewise, the average value of the pixels in the first group may be set as the maximum value MaxC, and the average value of the pixels in the second group may be set as the minimum value MinC.

[00366] Based on the calculated maximum values (MaxL, MaxC) and minimum values (MinL, MaxC), a weighting factor and/or parameter offset may be extracted.

[00367] The chrominance block may be predicted based on the downsampled luminance block and parameter (S840).

[00368] A chrominance block may be predicted by applying at least one of a pre-extracted weight or a per-pixel offset of the downsampled luminance block.

[00369] [00370] FIG. 9 illustrates a method for configuring a support region as an embodiment to which the present invention is applied.

[00371] The reference region according to the present invention may be a region adjacent to the current block. Next, a method for configuring each reference area as available pixels by classifying the reference area according to categories is described. For ease of explanation, the description focuses on the left, top, right support areas of the current block. Descriptions not mentioned in the embodiments that are described below may be referenced or retrieved through the embodiment described with reference to FIGS. 6.

[00372] Referring to FIG. 9, pixels in the reference region may be classified according to a predetermined category (SA00).

[00373] The reference region may be identified/classified into k categories, and k may be an integer representing 1, 2, 3 or more. Alternatively, k may be limited to an integer that is 2 or less. The reference area can be classified as one of the predefined categories based on image type (I/P/B), component type (Y/Cb/Cr, etc.), block property (size, shape, division information, division depth etc.) and the position of the reference pixel. Here, a block may mean the current block and/or a neighboring block relative to the current block.

[00374] For example, it may be classified according to a predefined category according to the block size. In the case of a block size, the supported range may be determined by a threshold size. Each threshold size can be expressed as W, H, WxH and W*H based on width (W) and height (H). W and H can be natural numbers, for example 4, 8, 16, 32, etc. Two or more threshold sizes are supported and can be used to specify the supported range, for example, the minimum value and maximum value that a block can have.

[00375] Alternatively, it may be classified according to a predefined category according to the position of the reference pixel. In this case, the position of the reference pixel may be specified in units of pixels, or may be specified as the direction of the block to which the reference pixel belongs (left, right, top, bottom, top left, top right, bottom left, bottom right).

[00376] Referring to FIG. 6, it may be specified as whether or not it is included in the positions of the upper left pixel TL, the upper right pixel TR, the lower left pixel BL, and the lower right pixel BR. In addition, it can be specified as whether or not it is included in the number of pixel positions TL0, TL1, TR0, TR1, BL0, BL1, BR0, BR1, located based on the width (2*nW) of the current block, height (2*nH ) or the sum (nW+nH) of width and height. In addition, referring to FIG. 12, it can be specified as whether or not it is included in the number of pixel positions T0, T3, B0, B3, L0, L3, R0 and R3, which are pixels located at both ends of the upper, lower , left and right blocks. Alternatively, it may be specified as whether or not it is included in the number of pixels (T1, L2, B2, R1, etc.) located in the middle of each block.

[00377] The reference area (reference pixel) may be classified according to each category based on various encoding elements.

[00378] Referring to FIG. 9, an unavailable pixel belonging to the reference area (SA10) can be searched.

[00379] It is possible to sequentially search regarding whether or not an inaccessible pixel exists in the reference region. Referring to FIG. 6, the search starting position may be determined from, but is not limited to, TL, TR, BL, and BR. In this case, when searching is carried out sequentially, the search starting position number may be set to one, but for the case of parallel processing, it may be set to two or more.

[00380] The search area of the unreachable pixel may be determined based on the starting position of the search. If one search position is designated (under the TL condition), the upper reference region or the left reference region can be searched before the right reference region, but this may not be the case in the encoding setting (parallel processing).

[00381] Here, the search direction may be defined as one of clockwise or counterclockwise. In this case, one of clockwise or counterclockwise can be selected for the entire reference area. Alternatively, it may be adaptively selected according to the position of the reference region. Thus, one clockwise or counterclockwise search direction can be supported for each of the top/bottom/left/right reference regions. Here, it should be understood that the position of the reference area is not limited only by the width (nW) and height (nH) of the current block (i.e., including the reference area included in 2*nW, 2*nH, nW+nH, etc.). d.).

[00382] Here, in the case of a clockwise direction, it may mean a bottom-up direction in a left reference region, a left-to-right direction in an upper reference region, a top-down direction in a right reference region, and a right-to-left direction in a bottom reference region. Counterclockwise can be extracted from the clockwise opposite.

[00383] For example, when the search starts from the top left TL pixel adjacent to the current block, the top reference region and the right reference region can be searched in a clockwise direction (left->right, top->down). In addition, the left reference area and bottom reference area can be searched in a counterclockwise direction (top->down, left->right). However, the above description is only a partial example, and examples of various modifications may be possible.

[00384] Referring to FIG. 9, it can be replaced with an available pixel by using the method specified for each category (SA20).

[00385] An unavailable pixel may be replaced with a predetermined default value (eg, the midpoint of a range of pixel values). Alternatively, it may be replaced based on a predetermined available pixel, and the unavailable pixel may be replaced with a value obtained by copying, linear extrapolation, interpolation, or the like. one or more adjacent available pixels. Firstly, before this, a category classification process is performed based on the position of each pixel. Below is an example of how each method is applied according to multiple categories, and the unreachable pixel is referred to as the target pixel.

[00386] As an example <1>, when an available pixel exists in the reference region, the target pixel can be replaced by using a pixel value obtained based on the available pixel, and when an available pixel does not exist in the reference region, it can be replaced with a default value.

[00387] As an example <2>, when an available pixel exists before the target pixel and at the search start position, the target pixel may be replaced by using a pixel value derived from the available pixel, and when an available pixel does not exist before the target pixel, it may be replaced with the default value.

[00388] As an example <3>, the target pixel may be replaced with a default value.

[00389] In the case of <1>, a method of replacing with an available pixel according to whether or not an available pixel exists in the reference region is described. In the case of <2>, a method of replacing with an available pixel according to whether or not an available pixel exists during the previous search process is described. In case <3>, a replacement method with one fixed available pixel is described.

[00390] If one category is supported, one method from <1>-<3> may be used. If more than one category is supported, one reference pixel belonging to any category can select and use one of <1>-<3>, and a reference pixel belonging to another category can select and use one of <1>-<3>.

[00391] Referring to FIG. 9, the reference area may be configured as an available pixel (SA30). In addition, intra-prediction can be performed (SA40).

[00392] A method of replacing an available pixel according to categories by classifying unavailable pixels in a reference area into a category is described through the above-described embodiments. In addition, not only the unavailable pixel, but also the available pixel may be replaced by a default value, another available pixel, or a value derived from another available pixel.

[00393] [00394] FIG. 10 is an exemplary diagram for configuring an intra-prediction mode set in stages as an embodiment to which the present invention is applied.

[00395] With regard to (step 1) of FIG. 10, a configuration of different groups of potentially suitable prediction mode options may be maintained, and one of them may be implicitly or explicitly selected. A group of potentially suitable prediction mode candidates may be identified by the number of modes, directional mode slope (dy/dx) information, supported directional mode range, and the like. In this case, even if the number of modes is k (a directional, b non-directional), potentially suitable prediction mode options with different a or b can be provided.

[00396] Group selection information of potentially suitable prediction mode candidates may be explicitly generated and signaled to at least one layer of the VPS, SPS, PPS, PH, and slice header. Alternatively, a group of potentially suitable prediction mode candidates may be implicitly selected according to the encoding setting. In this case, the encoding setting can be set based on the image type (I/P/B), component type, and block property (size, shape, partition information, partition depth, etc.). Here, a block may mean the current block and/or a neighboring block relative to the current block, and in the present embodiment, the same description may apply.

[00397] When one group of potentially suitable prediction mode candidates is selected through (step 1) (B is selected in this example), intra-prediction or prediction mode coding can be performed based on it. Alternatively, a process for efficiently configuring groups of potential candidates can be followed and this is described through (Step 2).

[00398] Regarding (step 2) of FIG. 10, the configuration of some prediction modes may be configured in various ways, and one of them may be implicitly or explicitly selected. (B0)-(B2) may represent potentially suitable configuration options provided that the prediction modes (dashed lines in the drawing) in some directions are not optimally used.

[00399] Group selection information of potentially suitable prediction mode candidates may be explicitly generated and signaled in a CTU, encoding unit, prediction unit, transform unit, or the like. Alternatively, a group of potentially suitable prediction mode candidates may be implicitly selected according to an encoding setting, and the encoding setting may be specified as previous various encoding elements.

[00400] Here, the block shape may be subdivided according to the width/height (W:H) ratio of the block, and a group of potentially suitable prediction mode options may be configured differently according to all possible W:H ratios or only according to a certain W:H ratio.

[00401] When one group of potentially suitable prediction mode candidates is selected through (step 2) (B1 is selected in this example), intra-prediction or prediction mode coding can be performed based on it. Alternatively, a process for efficiently configuring groups of potential candidates can be followed and this is described through (step 3).

[00402] Referring to (step 3) of FIG. 10, potentially suitable configurations may be provided provided that some prediction modes (dashed lines in the figure) are not optimally used, since the number of groups of potentially suitable prediction modes is significant.

[00403] Group selection information of potentially suitable prediction mode candidates may be explicitly generated and signaled in a CTU, encoding unit, prediction unit, transform unit, or the like. Alternatively, a group of potentially suitable prediction mode candidates may be implicitly selected according to an encoding setting, and the encoding setting may be specified as previous various encoding elements. In addition, prediction mode, position, etc. blocks may represent elements that are additionally considered in the encoding settings task.

[00404] In this case, the prediction mode and the block position may indicate information regarding a neighboring block adjacent to the current block. Thus, based on the property information of the current block and the neighboring block, a prediction mode that is judged to be not being used optimally can be retrieved, and the corresponding mode can be eliminated from the group of potentially suitable prediction mode options.

[00405] For example, when the adjacent block includes positions TL, T0, TR0, L0 and BL0 in FIG. 12, it is assumed that the prediction mode of the corresponding block has some directionality (from the top left position to the bottom right position). In this case, the prediction mode of the current block is expected to have some directionality with high probability, and the next processing opportunity may exist.

[00406] For example, intra-prediction may be performed for all modes in a group of potentially suitable prediction mode options. In addition, prediction mode coding may be performed based on a group of potentially suitable prediction mode candidates.

[00407] Alternatively, intra-prediction may be performed on a mode in a group of potentially suitable prediction mode candidates from which some modes have been removed. In addition, prediction mode coding may be performed based on a group of potentially suitable prediction mode candidates from which some modes have been removed.

[00408] When comparing the above examples, it can be distinguished whether a prediction mode that is supposed to have a low probability of occurrence is included or removed in the actual prediction and encoding process (which may be included as non-MPM, etc.).

[00409] In case (B21) in which a prediction mode having a different directionality from the prediction mode of an adjacent block may be partially removed, it may be an example in which some sparsely allocated modes are removed for the case in which the corresponding directional mode actually occurs .

[00410] [00411] FIG. 11 illustrates a method for classifying intra-prediction modes into multiple groups of potentially suitable options as an embodiment to which the present invention applies.

[00412] A case of classification into one or more groups of potential candidates for intra-prediction mode decoding is described below, and it may be identical or similar to the above group of potential MPM candidates and the group of potential non-MPM candidates. Therefore, parts not mentioned in the present embodiment can be retrieved identically or similarly through the previous embodiment. In the case of the present embodiment, a method for expanding the number of candidate candidate groups and configuring the candidate candidate group will be described below.

[00413] The intra-prediction mode of the current block may be selectively retrieved using any of a plurality of groups of potential candidates. For this purpose, the selection flag can be used up to (number of groups of 1 potentially suitable options) or less.

[00414] For example, when the prediction mode is classified into three groups (A, B, C) of candidates, a flag (first flag) may be used to indicate whether or not the intra-prediction mode of the current block is extracted from group A of candidates.

[00415] In this case, when the first flag has a first value, the candidate group A is used, and when the first flag has a second value, a flag (second flag) indicating whether or not the intra-prediction mode of the current block is extracted from group B of potentially suitable options.

[00416] In this case, when the second flag has a first value, a group B of potential candidates is used, and when the second flag has a second value, a group C of potential candidates can be used. In the above example, three groups of potential matches are supported, and the first flag and the second flag can be used for this, i.e. the sum of two selection flags.

[00417] When one of the candidate groups is selected, the intra-prediction mode of the current block may be determined based on the candidate group and the candidate group index. The candidate group index may be information indicating any of the candidates belonging to the group of candidates. The candidate candidate group index may be signaled only when the plurality of candidate candidates belong to the candidate candidate group.

[00418] The configuration of the selection flag when three groups of potential candidates are supported is described through the above example. Similar to the above configuration, flags indicating whether or not the prediction mode of the current block is retrieved from a group of candidates having a high priority may be maintained sequentially (eg, in the order first flag->second flag). Thus, when a predetermined candidate group selection flag is generated and a corresponding candidate group is not selected, a candidate group selection flag having the next priority can be generated.

[00419] Alternatively, it may be a configuration having a semantic meaning different from the selection flag (EE). For example, a flag (first flag) may be used indicating whether or not the intra-prediction mode of the current block is retrieved from groups A or B of candidates.

[00420] In this case, when the first flag has a first value, a group C of potential candidates is used, and when the first flag has a second value, a flag (second flag) indicating whether or not the intra-prediction mode of the current block is extracted from group A of potentially suitable options.

[00421] In this case, when the second flag has a first value, group A of potential candidates can be used, and when the second flag has a second value, group B of potential candidates can be used.

[00422] Groups A, B, and C of candidates may each have m, n, and p candidates, and m may be an integer representing 1, 2, 3, 4, 5, 6, or greater; n can be an integer representing 1, 2, 3, 4, 5, 6 or greater. Alternatively, n can be an integer between 10 and 40; p can be (total number of prediction modes - m - n). Here, m may be less than or equal to n, and n may be less than or equal to p.

[00423] As another example, when the prediction mode is classified into four groups of potential candidates (A, B, C, D), flags may be used to indicate whether or not the intra-prediction mode of the current block is extracted from groups A, B, C potentially suitable options (first flag, second flag, third flag).

[00424] In this case, the second flag may be generated when the first flag has a second value, and the third flag may be generated when the second flag has a second value. Thus, when the first flag has the first value, group A of potential candidates can be used, and when the second flag has the first value, group B of potential candidates can be used. In addition, when the third flag has a first value, a group C of potential candidates can be used, and when the third flag has a second value, a group D of potential candidates can be used. In this example, the opposite configuration is also possible, as indicated in some examples (EE) of the configuration of three groups of potentially suitable options.

[00425] Alternatively, the second flag may be generated when the first flag has a first value, and the third flag may be generated when the first flag has a second value. When the second flag has a first value, group A of potential candidates can be used, and when the second flag has a second value, group B of potential candidates can be used. When the third flag has a first value, group C of potential candidates can be used, and when the second flag has a second value, group D of potential candidates can be used.

[00426] Groups A, B, C, and D of candidates may each have m, n, p, and q candidates, and m may be an integer representing 1, 2, 3, 4, 5, 6, or more; n can be an integer representing 1, 2, 3, 4, 5, 6 or greater. Alternatively, n may be an integer between 8 and 24. p may be an integer such as 6, 7, 8, 9, 10, 11, 12, etc. Alternatively, p can be an integer between 10 and 32; q can be (total number of prediction modes - m - n - p). Here, m may be less than or equal to n, n may be less than or equal to p, and p may be less than or equal to q.

[00427] Next, when multiple groups of candidates are supported, a method for configuring each group of candidates is described. The reason for maintaining multiple groups of potential candidates is for purpose; efficient decoding of intra-prediction mode. That is, a prediction mode that is expected to be identical to the intra-prediction mode of the current block is configured as a group of high priority candidates, and a prediction mode that is not expected to be identical to the intra-prediction mode of the current block is configured as a group of potential candidates. low priority options.

[00428] For example, in FIG. 11, when category 2(a), category 3(b and c) and category 4(d) are groups of candidates with the lowest priority, respectively, groups of candidates can be configured using a prediction mode that is not enabled by either to one of the potentially suitable options with the previous priority. In this embodiment, since the candidate group consists of the remaining prediction modes that are not included in the previous candidate group, it is assumed to be a candidate group irrelevant to the priority between the prediction modes configuring each candidate group , which is described below (i.e., the remaining prediction modes that are not included in the previous group of potential candidates without regard to priority). Also, it is assumed that the priority (priority) between groups of potentially suitable options is set in ascending order (category 1->category 2->category 3->category 4), as shown in Fig. 11, and priority in the examples described below is the term used in the mode listing to configure each group of potential candidates.

[00429] Similar to the above group of MPM candidate candidates, the group of candidate candidates may be configured with an adjacent block prediction mode, a default mode, a predefined directional mode, and the like. For the purpose of assigning fewer bits to the prediction mode with the highest probability of occurrence, a group of candidates may be configured by determining a predetermined priority for configuring the group of candidates.

[00430] Referring to FIG. 11A, priority may be maintained for the first group of potential candidates (category 1). When the first group of candidates is configured based on the number of the first group of candidates according to the priority, the remaining prediction modes (b, j, etc.) can be configured as the second group of candidates (category 2).

[00431] Referring to FIG. 11B, a common priority may be maintained for the first group of potential candidates and the second group of potential candidates. According to the priority, the first group of candidates is configured based on the number of the first group of candidates. The second group of candidates is configured based on the number of the second group of candidates according to the priority (after c) after the prediction mode (e) ultimately included in the first group of candidates. In addition, the remaining prediction modes (b, j, etc.) can be configured as a third group of potential candidates (category 3).

[00432] Referring to FIG. 11C, separate priorities (first priority, second priority) for the first group of potential candidates and the second group of potential candidates may be maintained. The first group of candidates is configured based on the number of the first group of candidates according to the first priority. Then, the second group of candidates is configured based on the number of the second group of candidates according to the second priority. In addition, the remaining prediction modes (b, w, x, etc.) can be configured as a third group of potential candidates.

[00433] Here, the second priority may be set based on the neighboring block prediction mode <1>, the default mode <2>, the predetermined directional mode <3>, etc., similar to the existing priority (first priority). However, the priority may be set based on a different importance from the first priority (eg, if the first priority is configured in the order 1-2-3, the second priority is configured in the order 3-2-1, etc.). In addition, the second priority may be variably configured according to a mode included in the previous group of candidates and may be affected by the mode of an adjacent block of the current block. The second priority may be configured differently from the first priority, but it will be appreciated that the configuration of the second priority may be partially affected by the configuration of the first group of potential candidates. In this paragraph, it should be understood that the first priority (previous ranking), first group of potential candidates (previous group of potential candidates) and second priority (current ranking) and second group of potential candidates (current group of potential candidates) are not described in fixed ranking such as number.

[00434] Referring to FIG. 11D, a common priority (first priority) may be maintained for a first group of candidates and a second group of candidates, and a separate priority (second priority) may be maintained for a third group of candidates. The first group of candidates is configured based on the number of the first group of candidates according to the first priority. The second group of candidates is configured based on the number of the second group of candidates according to the priority (after e) after the prediction mode (d) ultimately included in the first group of candidates. Then, according to the second priority, the third group of potential candidates is configured based on the number of the third group of potential candidates. In addition, the remaining prediction modes (u, f, etc.) can be configured as a fourth group of potential candidates.

[00435] According to an embodiment of the present invention, in the case of a current block intra-prediction mode, prediction modes can be configured with one or more groups of potential candidates, and decoding in the prediction mode can be performed based on it. In this case, one or more priorities may be maintained and used to configure a group of potential candidates. The priority may be used in the process of configuring one or more groups of potential candidates.

[00436] In the above example, when two or more priorities are supported, a priority (second priority) separate from the priority (first priority) used in the previous group of candidates (first group of candidates) is used for the other group of candidates (the second group of potentially suitable options). This may correspond to a case in which all candidates in one group of candidates are configured according to the same priority.

[00437] In addition, the first priority used for the first group of candidates may be used to configure some candidates of the second group of candidates. Thus, some potential candidates (cand_A) of the second group of candidates can be determined based on the first priority (starting with the mode not included in the first group of candidates) and some candidates (or remaining candidates, cand_B) a second group of potentially suitable options can be determined based on the second priority. In this case, cand_A may be an integer representing 0, 1, 2, 3, 4, 5 or more. Thus, when configuring the first group of candidates, a prediction mode that is not included in the first group of candidates may be included in the second group of candidates.

[00438] For example, three groups of candidates are supported, and the first group of candidates consists of two candidates, and the first priority may be determined between an adjacent block prediction mode (e.g., left, top), a predetermined directional mode (e.g., Ver, Hor, etc.), a predefined non-directional mode (e.g. DC-, planar, etc.) (e.g. Pmode_L-Pmode_U-DC-Planar-Ver-Hor, etc.). The candidate group is configured based on the number of the first candidate group according to the first priority (eg, Pmode_L, Pmode_U).

[00439] In this case, the second group of candidates is configured with 6 candidates, and the second priority may be determined for the directed mode having a predetermined interval (1, 2, 3, 4 or more integer) from the adjacent block prediction mode, and a directional mode having a predefined slope (dy/dx: 1:1, 1:2, 2:1, 4:1, 1:4, etc.) (for example, down and left diagonally - down and right diagonally - up and to the right diagonally - <Pmode_L+2>, <Pmode_U+2>, etc.).

[00440] The second group of candidates may be configured based on the number of the second group of candidates according to the second priority. Alternatively, the two candidates of the second group of candidates may be configured (DC-, planar) based on the first priority, and the remaining four candidates may be configured (DDL, DDR, DUR) based on the second priority.

[00441] For convenience of explanation, terms identical to those of the foregoing description are used, such as first candidate group, second candidate group, and first priority, but it should be noted that the priority between candidate groups of a plurality of candidate groups is not is fixed as the first and second.

[00442] In general, when classification into a plurality of groups of candidates for predictive decoding is performed and one or more priorities are supported, a predefined group of candidates can be configured based on the one or more priorities.

[00443] [00444] FIG. 12 is an exemplary diagram illustrating a current block and a pixel adjacent thereto as an embodiment to which the present invention is applied.

[00445] Referring to FIG. 12, pixels (a-p) belonging to the current block and pixels adjacent to it are shown. In detail, it represents pixels (Ref_T, Ref_L, Ref_TL, Ref_TR and Ref_BL) that are adjacent to the current block and have linkability, and pixels (B0 in B3, R0 in R3, BR) that are adjacent to the current block but do not have the possibility of reference. This scheme is specified under the condition that a certain encoding order, scanning order, etc. is fixed (can refer to the left, top, left top, right top and left bottom blocks relative to the current block), and can be changed to a different configuration according to the encoding setting change.

[00446] [00447] FIG. 13 illustrates a method of performing intra-prediction step by step as an embodiment to which the present invention is applied.

[00448] The current block may perform intra-prediction using pixels located in the left, right, up, and down directions. In this case, as shown in FIG. 12, not only mono-referenced pixels, but also non-referenced pixels may exist. Encoding efficiency can be improved by estimating pixel values not only for linkable pixels, but also for non-linkable pixels and their use.

[00449] Referring to FIG. 13, an arbitrary pixel value may be obtained (SB00).

[00450] Here, a random pixel may be a pixel that cannot be referenced near the current block or a pixel within the current block. In the following, the position of an arbitrary pixel will be described with reference to the following drawing.

[00451] FIG. 14 is an exemplary diagram for an arbitrary pixel for intra-prediction as an embodiment to which the present invention is applied.

[00452] Referring to FIG. 14, not only the pixel (c) located outside the current block that cannot be referenced, but also the pixel (a, b) located inside the current block may be an arbitrary pixel. The following assumes that the size of the current block is "height x width" and the top left coordinate is (0, 0).

[00453] In FIG. 14, a and b can be positioned from (0, 0) to (width-1, height-1).

[00454] For example, they can be located on the boundary line (left, right, top, bottom) relative to the current block. For example, they can be located in the right column of the current block, from (width-1, 0) to (width-1, height-1) or in the bottom row of the current block, from (0, height-1) to (width -1, height 1).

[00455] For example, they may be located in the odd or even column and row of the current block. For example, they can be located in the even row of the current block, or they can be located in the odd column of the current block. Alternatively, they may be located in the even row and odd column of the current block, or they may be located in the odd row and odd column of the current block. Here, in addition to an odd or even number, they can be arranged in a column or row corresponding to multiple k or exponent (2k), and k can be an integer representing 1, 2, 3, 4, 5 or more.

[00456] In FIG. 14, c can be located outside the pixel with the possibility of reference and the current block.

[00457] As an example, it may be located on the boundary line of the current block (in this example, right, bottom). For example, it can be located at the right border of the current block, from (width, 0) to (width, height), or at the bottom border of the current block, from (0, height) to (width, height).

[00458] For example, it may be located in the odd or even column and row of the current block. For example, it may be located in an even row beyond the right border of the current block, or it may be located in an odd column beyond the bottom border of the current block. Here, in addition to an odd or even number, it can be located in a column or row corresponding to multiple k or exponent (2k), and k can be an integer representing 1, 2, 3, 4, 5 or more.

[00459] The number of arbitrary pixels used/referenced for intra-prediction of the current block may be m, and m may be 1, 2, 3, 4 or more. Alternatively, the number of arbitrary pixels can be set based on the size (width or height) of the current block. For example, the number of random pixels used for intra-prediction may be Width/w_factor, Height/h_factor, or (Width*Height)/wh_factor. Here, w_factor and h_factor can be predefined values used as partition values based on the width and height of each block, and can be integers such as 1, 2, 4 and 8. Here, wh_factor can be predefined value used as a split value based on block size, and can be an integer such as 2, 4, 8, 16, etc.

[00460] In addition, the number of arbitrary pixels may be determined based on all or some encoding elements such as image type, component type, block property, and intra-prediction mode.

[00461] An arbitrary pixel obtained through the above process may be obtained from a region that may reference a corresponding pixel value. For example, a pixel value may be derived from a referenceable pixel located in the horizontal or vertical direction of an arbitrary pixel.

[00462] In this case, the pixel value of an arbitrary pixel may be obtained as a value obtained through copying or weighting averaging using one or more pixels (k; k is an integer representing 1, 2, 3, 4, 5, 6, etc.) located in (<1>horizontal direction/<2>vertical direction). In (<1>horizontal direction/<2>vertical direction), a referenceable pixel having identical or similar (<1>Y-axis component/<2>X-axis component) from among the coordinates of an arbitrary pixel can be used/ used for reference to get the pixel value. However, in a broad sense, a referenceable pixel located in (<1>left direction/<2>up direction) the current block can be used to obtain the pixel value of an arbitrary pixel.

[00463] The pixel value may be obtained based on either the horizontal direction or the vertical direction, or may be obtained based on both directions. In this case, the pixel value acquisition setting may be determined based on various encoding elements (described in the above example, such as image type and block property).

[00464] For example, when the current block has a rectangular shape having a width greater than the height, the pixel value of an arbitrary pixel can be obtained based on a referenceable pixel located in the vertical direction. Alternatively, when primary pixel values are obtained based on each of the referenceable pixels located in the vertical direction and the horizontal direction, the secondary pixel value (i.e., the pixel value of an arbitrary pixel) may be obtained by further applying a weighting factor to the primary pixel value obtained in the vertical direction rather than the primary pixel value obtained in the horizontal direction

[00465] Alternatively, when the current block has a rectangular shape having a height greater than the width, the pixel value of an arbitrary pixel can be obtained based on a referenceable pixel located in the horizontal direction. Alternatively, when primary pixel values are obtained based on each of the referenceable pixels located in the vertical direction and the horizontal direction, the secondary pixel value (i.e., the pixel value of an arbitrary pixel) may be obtained by further applying a weighting factor to the primary pixel value obtained in the horizontal direction rather than the primary pixel value obtained in the vertical direction. Of course, this is not limited to the above example, and the opposite configuration may also be possible.

[00466] In addition, a predetermined list of potential candidates may be configured, and a pixel value of a random pixel may be obtained by selecting at least one of them. It may be signaled in one of units such as a CTU, a coding unit, a prediction unit, and a transform unit. In this case, the list of potential candidates may be configured with a predetermined value or may be configured based on the above-described linkable pixel adjacent to the current block. In this case, the number of candidate lists may be an integer representing 2, 3, 4, 5 or more. Alternatively, it may be an integer between 10 and 20, an integer between 20 and 40, or an integer between 10 and 40.

[00467] Here, in the list of potential candidates, a pixel value may be configured as a potential candidate, or an equation for outputting a pixel value, a feature value, or the like. can be configured as a potentially suitable option. In the second case, various pixel values can be extracted in a random pixel unit based on an equation to obtain a position (X or Y coordinate) of a random pixel and a pixel value or feature value.

[00468] As described above, one or more random pixels may be obtained, and intra-prediction may be performed based on them. Below, for convenience of explanation, the number of random pixels is assumed to be 1. However, it will be appreciated that the example described below can be extended to an identical or similar case even when two or more random pixels are obtained.

[00469] Referring to FIG. 13, division into multiple sub-regions can be performed based on a random pixel (SB10).

[00470] Here, sub-regions may be segmented based on a horizontal or vertical line including an arbitrary pixel, and the number of sub-regions may be an integer representing 2, 3, 4 or more. In the following, the configuration of the sub-area will be described with reference to the following drawing.

[00471] FIG. 15 is an exemplary multi-sub-region division diagram based on a random pixel as an embodiment to which the present invention is applied.

[00472] Referring to FIG. 15, a predetermined sub-region (b, c) that is a vertical or horizontal line of an arbitrary pixel d can be obtained, and a predetermined sub-region (a) can be obtained based on the vertical and horizontal lines.

[00473] In this case, sub-region (b) may be obtained between an arbitrary pixel and pixel T, which can be referenced in the vertical direction, and sub-region (c) may be obtained between an arbitrary pixel and pixel L, which can be referenced in the horizontal direction. In this case, sub-regions b and c may not always occur fixedly, and only one of the two may occur according to the random pixel-related setting of the current block (eg, b or c is also a random pixel, etc.). If only one of subregions b and c occurs, subregion a may not arise.

[00474] As shown in FIG. 15, T or L refer to means a linkable pixel adjacent to the current block. Alternatively, T or L may refer to any pixel (e, f) other than d located in the vertical or horizontal direction of an arbitrary pixel (d). This means that any pixel d can also represent T or L for any other pixel.

[00475] As indicated in the above example, the size of the sub-region may be determined based on the number and arrangement of random pixels in the current block.

[00476] For example, when two or more random pixels exist and are spaced at one time slice interval, each of the sub-regions a, b and c may have a size of 1×1. Alternatively, when one arbitrary pixel exists and is located at c in FIG. 14, sub-regions a, b and c may have dimensions of (height x width), (1 x height) and (width x 1), respectively.

[00477] Referring to FIG. 13, intra-prediction may be performed according to a predetermined order (SB20).

[00478] Here, according to the position of the arbitrary pixel, some sub-regions can be used as a prediction value for intra-prediction or can be used as a temporary reference value for intra-prediction.

[00479] For example, when an arbitrary pixel (or sub-region d) is located at c in FIG. 14, sub-regions b and c are located outside the current block, and only sub-region a can represent an intra-prediction target. Alternatively, when an arbitrary pixel is located above c in FIG. 14, sub-region b is located outside the current block, and sub-regions a and c may represent intra-prediction targets. Alternatively, when an arbitrary pixel is located relative to c in FIG. 14, sub-region c is located outside the current block, and sub-regions a and b may represent intra-prediction targets. Alternatively, when an arbitrary pixel is located in the current block, subregions a, b, and c may represent intra-prediction targets.

[00480] As indicated in the above example, according to the position of the arbitrary pixel, it may represent an intra-prediction target or may be used as a temporary reference value.

[00481] The following description assumes a case in which an arbitrary pixel is located in the current block, but even if a position change occurs, the following example can be applied and understood in an identical or similar manner.

[00482] Since the position and pixel value of a random pixel are obtained through the previous steps, each sub-region obtaining process can be performed according to a predetermined priority for sub-regions a, b and c. For example, the pixel value of each sub-region can be obtained in the order b->c or c->b, and the pixel value of sub-region a can be obtained.

[00483] In the case of sub-region b, the pixel value may be obtained based on an arbitrary pixel d or T. In the case of a sub-region c, the pixel value may be obtained based on an arbitrary pixel d or L.

[00484] Although not shown in the drawing, let us assume that the upper left pixel represents TL (ie, the intersection of the horizontal line T and the vertical line L). When TL and T are located on top of the current block, you can reference the pixel between TL and T. Additionally, when TL and L are located to the left of the current block, you can reference the pixel between TL and L. This is because the referenceable pixel belongs to block adjacent to the current block.

[00485] On the other hand, when at least one TL or T is located in the current block, a pixel between TL and T can be referenced. In addition, when at least one of the TL or L is located in the current block, it is possible to reference a pixel between TL and L. This is because a referenceable pixel can be a subregion derived from another arbitrary pixel.

[00486] Therefore, in the case of sub-region a, the pixel value can be obtained based on sub-regions b and c, the linkable region between TL and T, and the linkable region between TL and L. Of course, TL, T, L and d can be used in order to obtain the pixel values of subregion a. Here, this means that any pixel can also be referenced.

[00487] Through the above process, intra-prediction of the current block can be performed based on an arbitrary pixel.

[00488] Performing intra-prediction based on a random pixel can be configured as one of the intra-prediction modes or can be included as a replacement for an existing mode.

[00489] Alternatively, it may be classified as one potentially suitable prediction method candidate, and selection information for it may be generated. For example, it can be considered as a complementary prediction method to a method of performing intra-prediction based on a directed mode or an undirected mode. The selection information may be signaled in a CTU, a coding block, a prediction block, a transform block, and the like.

[00490] [00491] The following is described on the assumption that the position of the arbitrary pixel is c in FIG. 14. However, the present invention is not limited to this, and the content described below can be used in the same or similar manner, even when arranged in different positions. Hereinafter, the following will be described with reference to FIGS. 12.

[00492] Although the current block and the right and lower blocks relative to the current block are not encoded, they can be estimated based on the referenceable region data.

[00493] For example, data can be copied or retrieved from Ref_TR, Ref_BL, etc., which are areas adjacent to the right and bottom boundaries of the current block, and then the right or bottom border of the current block can be filled with data. As an example, the right border may be filled by copying one of the pixels, for example, T3, TR0 and TR1 as is, or with a value obtained by applying filtering to T3, TRO and TR1.

[00494] Alternatively, data may be copied or retrieved from Ref_TL, Ref_T, Ref_L, Ref_TR, Ref_BL, etc., which are regions adjacent to the current block, and the lower right boundary of the current block may be filled with data. For example, the bottom right border of the current block may be filled with a value derived from one or more pixels in the adjacent region.

[00495] Here, the right boundary of the current block may be (d~p) or (R0~R3). The lower bound of the current block can be (m~p) or (B0~B3). The lower right border of the current block may be one of p, BR, R3, and B3.

[00496] In the following example, it is assumed that the right boundary is R0~R3, the lower boundary is B0~B3, and the lower right boundary is BR.

[00497] Processing for right border and bottom border

[00498] For example, the right border may be filled by copying one of T3, TR0 and TR1 adjacent to the vertical direction, and the bottom border may be filled by copying one of L3, BL0 and BL1 adjacent to the horizontal direction.

[00499] Alternatively, the right boundary may be filled with the average value of the weighting factor in T3, TR0 and TR1 adjacent to the vertical direction, and the lower boundary may be filled with the average value of the weighting factor in L3, BL0 and BL1 adjacent to the horizontal direction.

[00500] After receiving the values of the right bound and lower bound, intra-prediction of the current block can be performed based on the values.

[00501] Processing for right lower border

[00502] For example, the lower right border may be filled by copying one of T3, TR0, TR1, L3, BL0 and BL1. Alternatively, it may be filled with the average weight of one of T3, TR0 and TR1 and one of L3, BL0 and BL1. Alternatively, it may be filled with one of the average of the weights T3, TR0 and TR1 and the average of the weights L3, BL0 and BL1. Alternatively, it may be filled with a second average weight of the first average weight T3, TR0 and TR1 and the first average weight L3, BL0 and BL1.

[00503] After obtaining the right lower bound value, the right bound or lower bound value can be obtained based on the value, and intra-prediction of the current block can be performed based on the right bound or lower bound.

[00504] Next, a description of the processing of the right lower boundary continues.

[00505] Assume a configuration that considers positions TL, TR0, BL0 and BR. Here, BR may represent a pixel at the lower right boundary, TR0 may represent a linkable pixel located in the vertical direction of BR, BL0 may represent a linkable pixel located in the horizontal direction of BR, and TL may represent a linkable pixel , located at the upper left border of the current block or at the intersection between the horizontal direction TR0 and the vertical direction BL0.

[00506] Based on the pixel position, the directionality of the current block and feature information (eg, edges, etc.) can be estimated.

[00507] As an example <1>, the pixel value may gradually increase or decrease as it moves diagonally from TL to BR. In case TL is greater than or equal to TR0 and BL0, BR may be less than or equal to TR0 and BL0. Alternatively, it may be the opposite configuration.

[00508] As an example <2>, the pixel value may gradually increase or decrease as it moves diagonally from BL0 to TR0. In case BL0 is greater than or equal to TL and BR, TR0 may be less than or equal to TL and BR. Alternatively, it may be the opposite configuration.

[00509] As an example <3>, the pixel value may gradually increase or decrease when moving in the horizontal direction from left (TL, BL0) to right (TR0, BR). In this case, if TL is greater than or equal to TR0, BL0 may be greater than or equal to BR. Alternatively, it may be the opposite configuration.

[00510] As an example <4>, the pixel value may gradually appear or decrease when moving in the vertical direction from top (TL, TR0) to bottom (BL0, BR). In the event that TL is greater than or equal to BL0, TR0 may be greater than or equal to BR. Alternatively, it may be the opposite configuration.

[00511] If an image feature, as indicated in the above example, exists in the current block, the right lower boundary can be predicted using it. In this case, a pixel located in the vertical or horizontal direction of the evaluation target pixel and a pixel that is an intersection point in the vertical or horizontal direction of each pixel may be required, and the evaluation target pixel may be predicted based on a comparison of their pixel values.

[00512] <1> Example: When TL<=TR0 and TL<=BL0, the BR value can be extracted (predicted) based on the difference between pixels by judging that there is an increasing trend from TL to BR.

[00513] For example, the pixel value BR may be retrieved by adding the value (BL0-TL) to TR0 or by adding the value (TR0-TL) to BL0. Alternatively, the pixel BR value may be extracted by averaging or weighting the two values.

[00514] <2> Example: When TL>=BL0 and TL<=TR0, the BR value can be extracted based on the difference between pixels by judging that there is an increasing trend from BL0 to TR0.

[00515] For example, the BR pixel value may be retrieved by subtracting the (TL-BL0) value from TR0 or by adding the (TR0-TL) value to BL0. Alternatively, the pixel BR value may be extracted by averaging or weighting the two values.

[00516] In the above example, a case is described in which an arbitrary pixel BR is predicted by estimating a block-based feature on a predetermined pixel adjacent to the current block. Meanwhile, it may be difficult to accurately capture block characteristics due to the limited pixel. For example, when an impulse component is present in some of the pixels referenced to output BR, it may be difficult to accurately capture features.

[00517] To this end, characteristic information (eg, variance, standard deviation, etc.) of the upper region and left region of the current block can be calculated. As an example, if it is determined that the pixel characteristic information between TL and TR0 or the pixel characteristic information between TL and BL0 optimally reflects the increase or decrease of a block, a method for extracting the value of an arbitrary pixel such as BR based on a predetermined pixel of the current block may be used. such as TL, TR0, BL0, etc.

[00518] [00519] The various embodiments of the disclosure are not intended to be all-inclusive and are intended to illustrate characteristic aspects of the disclosure, and the features described in the various embodiments may be applied independently or in combination of two or more of them.

[00520] In addition, various embodiments of the present disclosure may be implemented through hardware, firmware, software, or a combination of the foregoing. In the case of hardware implementation, the hardware may be implemented through 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), universal processor, controller, microcontroller, microprocessor, etc.

[00521] The scope of the present disclosure includes software or computer-executable instructions (e.g., operating system, applications, firmware, program, etc.) that instruct operations according to methods of various embodiments on a device or computer, and non-transitory computer-readable media , which stores such software or instructions running on a device or computer.

Industrial applicability

[00522] The present invention can be used to encode/decode a video signal.

Claims (32)

1. A method for decoding an image based on intra-prediction by means of a decoding device, comprising the steps of: determining a reference pixel line for intra-prediction of the current block in the image; determining the intra-prediction mode of the current block; And predict the current block based on the reference pixel line and intra-prediction mode, wherein the current block includes a luma block and a chrominance block, and the intra-prediction mode of the current block is determined for the luma block and the chroma block, respectively, and In this case, determining the intra-prediction mode of a chrominance block contains the steps of: selecting one of the first group of modes and the second group of modes based on the first flag signaled from the encoder, the first group of modes including only inter-reference prediction modes, the second group of modes including 67 intra-prediction modes preset in a decoding device, which 67 intra-prediction modes are composed of 2 omnidirectional modes and 65 directed modes, and the first flag indicates whether the chrominance block intra-prediction mode belongs to the first mode group or the second mode group; And extracting the intra-prediction mode of the chrominance block from the selected one group of modes. 2. The method of claim 1, wherein, in response to said selection whereby the chrominance block intra-prediction mode is extracted from the second group of modes, the chrominance block intra-prediction mode is determined based on the luminance block intra-prediction mode. 3. The method according to claim 2, wherein when the luminance block intra-prediction mode is unavailable, the luminance block intra-prediction mode is set equal to the intra-prediction mode preset in the decoding device. 4. The method of claim 1, wherein a reference pixel line for the luminance block is determined based on index information signaled from the encoder and a plurality of potentially suitable reference pixel line candidates, wherein the index information indicates one of the plurality of potentially suitable reference pixel line candidates wherein the plurality of potentially suitable reference pixel line embodiments includes at least one of a first pixel line adjacent the luminance block, a second pixel line adjacent to the first pixel line, and a third pixel line adjacent to the second pixel line. 5. The method according to claim 4, in which determining the intra-prediction mode of the brightness block contains the steps of: selecting one of a first group of potentially eligible MPM options and a second group of potentially eligible MPM options based on a second flag signaled from the encoder, wherein the first group of potentially eligible MPM options includes only at least one omnidirectional mode, the second group the potential candidate candidates includes only the plurality of potential candidate MPM candidate directional modes, and the second flag indicates whether the luminance block intra-prediction mode belongs to the first group of potential candidate MPM candidates or the second group of potential candidate MPM candidates; And extracting the luminance block intra-prediction mode from the selected one group of potentially suitable MPM candidates. 6. The method of claim 5, wherein when the luminance block intra-prediction mode is retrieved from the first group of potential MPM candidates, the luminance block is predicted using only the first pixel line adjacent to the luminance block. 7. A method for encoding an image based on intra-prediction by means of an encoding device, comprising the steps of: determining a reference pixel line for intra-prediction of the current block in the image; determining the intra-prediction mode of the current block; obtaining a residual block of the current block based on an original block of the current block and a prediction block of the current block, wherein the prediction block is obtained based on the reference pixel line and the intra-prediction mode; And encode the residual block to form a bitstream of the encoded image, wherein the current block includes a luma block and a chrominance block, and the intra-prediction mode of the current block is determined for the luma block and the chroma block, respectively, and wherein the chrominance block intra-prediction mode belongs to one of the first group of modes and the second group of modes, wherein the first group of modes includes only prediction modes based on intercomponent links, the second group of modes includes 67 intra-prediction modes preset in the device encoding, which 67 intra-prediction modes consist of 2 undirected modes and 65 directed modes, and wherein a flag for indicating whether the chrominance block intra-prediction mode belongs to the first mode group or the second mode group is encoded and included in the bitstream. 8. A bit stream transmission method for transmitting a bit stream that is generated by encoding an image, the method comprising the steps of: determining a reference pixel line for intra-prediction of the current block in the image; determining the intra-prediction mode of the current block; obtaining a residual block of the current block based on an original block of the current block and a prediction block of the current block, wherein the prediction block is obtained based on the reference pixel line and the intra-prediction mode; generating a bitstream by encoding a residual block of the current block; And transmit the generated bit stream, wherein the current block includes a luma block and a chrominance block, and the intra-prediction mode of the current block is determined for the luma block and the chroma block, respectively, and wherein the chrominance block intra-prediction mode belongs to one of the first group of modes and the second group of modes, wherein the first group of modes includes only prediction modes based on intercomponent links, the second group of modes includes 67 intra-prediction modes preset in the device encoding, which 67 intra-prediction modes consist of 2 undirected modes and 65 directed modes, and wherein a flag for indicating whether the chrominance block intra-prediction mode belongs to the first mode group or the second mode group is encoded and included in the bitstream.

Images