KR20200043352A - Method and apparatus for encoding/decoding a video signal - Google Patents

Abstract

The present invention relates to a method and a device for efficiently encoding/decoding an image signal to improve compression efficiency of an image. According to the present invention, the method for decoding an image signal can comprise the steps of: decoding division information indicating whether or not a current decoding block is divided into two partial blocks; decoding information on a division pattern of the current decoding block, when the division information indicates that the current decoding block is divided into two partial blocks; and dividing the current decoding block into two partial blocks based on the information on the division pattern.

Description

METHOD AND APPARATUS FOR ENCODING / DECODING A VIDEO SIGNAL}

The present invention relates to a method and apparatus for encoding / decoding video signals.

Recently, the demand for multimedia data such as video has been rapidly increasing on the Internet. However, the speed at which the bandwidth of the channel is developing is difficult to keep up with the rapidly increasing amount of multimedia data.

The present invention mainly aims to improve the compression efficiency of an image by efficiently encoding / decoding a method of dividing an encoding / decoding target block in encoding / decoding an image.

The present invention mainly aims to improve the compression efficiency of an image by efficiently encoding / decoding intra prediction mode information of an encoding / decoding target block in encoding / decoding an image.

The video signal decoding method and apparatus according to the present invention decodes split information indicating whether a current decoding block is divided into two sub-blocks, and the split information indicates that the current decoding block is divided into two sub-blocks , The information on the split pattern of the current decoding block may be decoded, and the current decoding block may be divided into two partial blocks based on the information on the split pattern.

In the video signal decoding method and apparatus according to the present invention, the information on the division pattern is precision specifying a direction information indicating a division direction of the current decoding block or a size of a partial block generated by division of the current decoding block It may include at least one of the information.

In the video signal decoding method and apparatus according to the present invention, the horizontal or vertical length of the partial block is a power of 2 (N) of a value (N) of the precision information specifying the horizontal or vertical length of the decoding block (2 ^N ).

In the method and apparatus for decoding a video signal according to the present invention, the information on the divided pattern may include index information specifying a divided form of the current decoding block.

The video signal decoding method and apparatus according to the present invention determines an MPM (Most Probable Mode) candidate for the current decoding block based on the intra prediction mode of a neighboring block adjacent to the current decoding block, and the current decoding block Information indicating whether or not the same MPM candidate as the intra prediction mode of A may be decoded, and according to the information, an intra prediction mode of the current decoding block may be derived.

In the video signal decoding method and apparatus according to the present invention, the number of intra prediction modes that can be used by the current decoding block may be variably determined according to the size, shape, or intra prediction mode of the neighboring block. have.

In the video signal decoding method and apparatus according to the present invention, when the number of intra prediction modes available for the current decoding block is different from the number of intra prediction modes available for the neighboring block, it corresponds to a directional prediction mode The MPM candidate may be set as a prediction angle of the directional prediction mode.

The video signal encoding method and apparatus according to the present invention determines whether the current coding block is divided into two sub-blocks, and according to the determination result, splits indicating whether the current coding block is divided into two sub-blocks When it is determined that the current coding block is divided into two sub-blocks, information about the split pattern of the current coding block is determined based on the determination of the split pattern of the current coding block. Can be coded.

In the video signal encoding method and apparatus according to the present invention, the information on the split pattern is precision specifying a direction information indicating a split direction of the current coding block or a size of a partial block generated by the current coding block splitting It may include at least one of the information.

In the video signal encoding method and apparatus according to the present invention, the horizontal or vertical length of the partial block is a power of 2 (N) of the value (N) of the precision information specifying the horizontal or vertical length of the coding block (2 ^N ).

In the video signal encoding method and apparatus according to the present invention, the information on the split pattern may include index information specifying a split form of the current coding block.

The video signal encoding method and apparatus according to the present invention determines a MPM (Most Probable Mode) candidate for the current coding block based on the intra prediction mode of a neighboring block adjacent to the current coding block, and the current coding block The intra prediction mode of may be determined, and information indicating whether the same MPM candidate as the intra prediction mode of the current coding block exists may be encoded.

In the video signal encoding method and apparatus according to the present invention, the number of intra prediction modes that can be used by the current coding block may be variably determined according to the size, shape, or intra prediction mode of the neighboring block. have.

In the video signal encoding method and apparatus according to the present invention, when the number of intra prediction modes available for the current coding block is different from the number of intra prediction modes available for the neighboring block, it corresponds to a directional prediction mode The MPM candidate may be set as a prediction angle of the directional prediction mode.

According to the present invention, the compression efficiency of an image can be improved by efficiently encoding / decoding a method of dividing a block to be encoded / decoded.

According to the present invention, the compression efficiency of an image can be improved by efficiently encoding / decoding the intra prediction mode information of a block to be encoded / decoded.

1 is a block diagram showing an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram showing an image decoding apparatus according to an embodiment of the present invention.
3 is a diagram for explaining an intra prediction method using a DC mode.
4 is a diagram for explaining an intra prediction method using a planner mode.
5 is a diagram for explaining an intra prediction method using a directional prediction mode.
6 is a diagram illustrating a method of encoding QT split information for an encoding block.
7 is a diagram illustrating a method of encoding BT segmentation information for an encoding block.
8 is a diagram illustrating a method of decoding QT segmentation information for a decoding block.
9 is a diagram illustrating a method of decoding BT segmentation information for a decoding block.
10 is a diagram illustrating a split state in a coding block.
FIG. 11 shows an optimal splitting state of the input coding block shown in FIG. 10 using a tree structure.
12 is a flowchart illustrating a process of controlling the number or type of prediction modes in the encoding device.
13 and 14 show examples of 13 directional prediction modes that can be used in the current coding block.
15 and 16 show examples of 21 directional prediction modes available in the current block.
17 is a flowchart illustrating a process of encoding an optimal intra prediction mode for a current coding block.
18 is a diagram showing an example of setting an MPM candidate.
19 and 20 show an example of quantizing a prediction angle.
21 is a diagram showing another example of setting an MPM candidate.
22 shows an example of a neighboring block used to derive an MPM candidate of a current coding block.
23 is a diagram showing an example of deriving an MPM candidate from neighboring blocks that are not adjacent to the current coding block.
24 is a flowchart illustrating a process of decoding an intra prediction mode for a current decoding block.

The present invention can be applied to various changes and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals are used for similar components.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component. The term and / or includes a combination of a plurality of related described items or any one of a plurality of related described items.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but other components may exist in the middle. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

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

Referring to FIG. 1, the image encoding apparatus 100 includes a picture splitter 110, a prediction unit 120, 125, a transform unit 130, a quantization unit 135, a reordering unit 160, and an entropy coding unit ( 165), an inverse quantization unit 140, an inverse conversion unit 145, a filter unit 150 and a memory 155.

Each component shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is composed of separate hardware or a single software component. That is, for convenience of description, each component is listed and included as each component, and at least two components of each component are combined to form one component, or one component is divided into a plurality of components to perform functions. The integrated and separated embodiments of the components are also included in the scope of the present invention without departing from the essence of the present invention.

Also, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for improving performance. The present invention can be implemented by including only components essential for realizing the essence of the present invention, except components used for performance improvement, and structures including only essential components excluding optional components used for performance improvement. Also included in the scope of the present invention.

The picture division unit 110 may divide the input picture into at least one block. In this case, the block may mean a coding unit (CU), a prediction unit (PU), or a transformation unit (TU). The splitting may be performed based on at least one of a quadtree or a binary tree. Quad tree divides the upper block into lower blocks whose width and height are half of the upper block. The binary tree is a method of dividing the upper block into lower blocks, which are either half or higher of the upper block. Through the above-described binary tree-based partitioning, blocks may have a square shape as well as a square shape.

Hereinafter, in an embodiment of the present invention, a coding unit may be used as a meaning of a unit that performs coding or may be used as a meaning of a unit that performs decoding.

The prediction units 120 and 125 may include an inter prediction unit 120 performing inter prediction and an intra prediction unit 125 performing intra prediction. It is determined whether to use inter prediction or intra prediction for a prediction unit, and specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method can be determined. At this time, the processing unit for which prediction is performed and the processing unit for which the prediction method and specific content are determined may be different. For example, a method of prediction, a prediction mode, and the like are determined in a prediction unit, and prediction performance may be performed in a transformation unit.

The encoding apparatus may determine an optimal prediction mode for the encoding block by using various techniques such as performing rate-distortion optimization (RDO) on the residual block minus the original block and the prediction block. As an example, RDO may be determined by Equation 1 below.

In Equation 1, D represents deterioration due to quantization, R represents a rate of a compressed stream, and J represents an RD cost. In addition, Φ represents an encoding mode, and λ represents a Lagrangian multiplier. [lambda] can be used as a scale correction coefficient to match the unit between the amount of error and the amount of bit. In the encoding process, the encoding apparatus may determine a mode having the smallest RD cost value as an optimal mode for the encoding block. At this time, the RD-cost value is calculated considering both the bit rate and the error at the same time.

Among the intra modes, the DC mode, which is a non-directional prediction mode (or a non-angle prediction mode), uses an average value of surrounding pixels of a current block. 3 is a diagram for explaining an intra prediction method using a DC mode.

After filling the prediction block with the average value of the surrounding pixels, filtering may be performed on pixels located at the boundary of the prediction block. For example, weighted filtering with neighboring reference pixels may be applied to pixels located at the left or upper boundary of the prediction block. As an example, Equation 2 is a view showing an example of generating a prediction pixel through a DC mode for each zone. In Equation 1 below, regions R1, R2, and R3 are regions located at the outermost (ie, boundary) of the prediction block, and weighted filtering may be applied to pixels included in the region.

Wid in Equation 2 means the horizontal length of the prediction block, and Hei means the vertical length of the prediction block. x and y denote the coordinate position of each prediction pixel when the upper leftmost point of the prediction block is set to (0,0). R means surrounding pixels. For example, when the s pixel shown in FIG. 3 is defined as R [-1] [-1], the pixels a through i are represented by R [0] [-1] to R [8] [-1]. From j pixels to r pixels, it can be represented by R [-1] [0] to R [-1] [8]. In the example illustrated in FIG. 3, the predicted pixel value Pred is obtained according to a weighted filtering method as shown in Equation 2 for each R1 to R4 region.

Among non-directional modes, a planar mode is a method of linearly interpolating pixels around a current block according to a distance to generate a prediction pixel of the current block. As an example, FIG. 4 is a diagram illustrating an intra prediction method using a planner mode.

For example, it is assumed that Pred shown in FIG. 4 is predicted in an 8x8 coding block. In this case, the vertical prediction value can be obtained by linearly interpolating the distance in the vertical direction by copying the pixel e pixel at the top of the Pred and the r pixel at the bottom of the left at the bottom of the Pred. Also, by copying the n pixels on the left of Pred and the i-pixel on the upper right to the far right of Pred, the horizontal prediction value can be obtained by linear interpolation according to the distance in the horizontal direction. Thereafter, the average value of the horizontal and vertical prediction values may be determined as the value of Pred. Equation 3 expresses the process of obtaining the predicted value Pred under the planner mode as an equation.

Wid in Equation 3 means the horizontal length of the prediction block, and Hei means the vertical length of the prediction block. x and y denote the coordinate position of each prediction pixel when the upper leftmost point of the prediction block is set to (0, 0). R means surrounding pixels. For example, when the s pixel shown in FIG. 4 is defined as R [-1] [-1], the pixels a through i are represented by R [0] [-1] to R [8] [-1]. From j pixels to r pixels, it can be represented by R [-1] [0] to R [-1] [8].

5 is a diagram for explaining an intra prediction method using a directional prediction mode.

The directional prediction mode (or the angular prediction mode) is a method of generating at least one pixel located in any one of N predetermined directions among neighboring pixels of the current block as a prediction sample.

The directional prediction mode may include a horizontal direction mode and a vertical direction mode. Here, the horizontal direction mode means modes in which the horizontal direction is larger than the angle prediction mode in the upper left direction toward the 45 degree direction, and the vertical direction mode means modes in which the vertical direction is larger than the angle prediction mode in the upper left direction toward the 45 degree direction. The directional prediction mode having a prediction direction directed toward the top left in a 45 degree direction may be treated as a horizontal direction mode or a vertical direction mode. In FIG. 5, a horizontal mode and a vertical mode are shown.

Referring to FIG. 5, there is a direction that does not correspond to an integer pixel portion for each direction. In this case, various interpolation methods such as a linear interpolation method, a DCT-IF method, and a cubic convolution interpolation method according to a distance between a peripheral pixel and a pixel, After interpolation using, the pixel value can be put in a pixel position that matches the prediction block direction.

The residual value (residual block or transform block) between the generated prediction block and the original block may be input to the transform unit 130. The residual block is the minimum unit for the transformation and quantization process. A coding block division method may be applied to a transform block. For example, the transform block may be divided into 4 or 2 sub-blocks.

Prediction mode information, motion vector information, and the like used for prediction may be encoded by the entropy encoding unit 165 together with the residual value and transmitted to the decoder. When a specific coding mode is used, it is also possible to encode the original block as it is and transmit it to the decoder without generating a prediction block through the prediction units 120 and 125.

The inter-prediction unit 120 may predict a prediction unit based on information of at least one of a previous picture or a subsequent picture of the current picture, and in some cases, prediction based on information of some regions where encoding in the current picture is completed. Units can also be predicted. The inter prediction unit 120 may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of integer pixels or less in the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter (DCT-based interpolation filter) having different filter coefficients may be used to generate pixel information of integer pixels or less in units of 1/4 pixels. In the case of a color difference signal, a DCT-based interpolation filter (DCT-based interpolation filter) having different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The motion prediction unit may perform motion prediction based on the reference picture interpolated by the reference picture interpolation unit. As a method for calculating the motion vector, various methods such as Full Search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) can be used. The motion vector may have a motion vector value in units of 1/2 or 1/4 pixels based on the interpolated pixels. The motion prediction unit may predict the current prediction unit by differently using a motion prediction method. Various methods such as a skip method, a merge method, and an advanced motion vector prediction (AMVP) method may be used as a motion prediction method.

The encoding device may generate motion information of a current block based on motion estimation or motion information of a neighboring block. Here, the motion information may include at least one of a motion vector, a reference image index, and a prediction direction.

The intra prediction unit 125 may generate a prediction unit based on reference pixel information around a current block, which is pixel information in a current picture. If the neighboring block of the current prediction unit is a block that has undergone inter prediction, and the reference pixel is a pixel that has undergone inter prediction, the reference pixel included in the block that has undergone inter prediction is a reference pixel of the block that has performed intra prediction around it. It can be used as a substitute for information. That is, when the reference pixel is not available, the available reference pixel information may be replaced with at least one reference pixel among the available reference pixels.

In intra prediction, the prediction mode may have a directional prediction mode that uses reference pixel information according to a prediction direction and a non-directional mode that does not use directional information when performing prediction. A mode for predicting luminance information and a mode for predicting color difference information may be different, and intra prediction mode information or predicted luminance signal information used for predicting luminance information may be used to predict color difference information.

The intra prediction method may generate a prediction block after applying an adaptive intra smoothing (AIS) filter to the reference pixel according to the prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When the prediction mode of the current prediction unit is predicted using the mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit are the same, the current prediction unit and the neighboring prediction unit using predetermined flag information It is possible to transmit the information that the prediction mode of is the same, and if the prediction mode of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

In addition, a residual block including prediction unit performing prediction based on the prediction unit generated by the prediction units 120 and 125 and residual information that is a difference value from the original block of the prediction unit may be generated. The generated residual block may be input to the conversion unit 130.

The transform unit 130 converts the residual signal into the frequency domain to generate a residual block (or transform block) having a transform coefficient. Here, in order to transform the residual signal into the frequency domain, various transform techniques such as Discrete Cosine Transform (DCT) based transform, Discreate Sine Transform (DST), and Karhunen Loeve Transform (KLT) can be used. . In order to conveniently use the transformation technique, matrix operations are performed using a basis vector. In this case, depending on which prediction mode the prediction block is coded, various transformation techniques may be mixed and used in matrix calculation. For example, in intra prediction, a discrete cosine transform may be used in the horizontal direction and a discrete sine transform may be used in the vertical direction according to the prediction mode.

The quantization unit 135 may quantize the values converted from the conversion unit 130 to the frequency domain. That is, the quantization unit 135 quantizes transform coefficients of the transform block generated by the transform unit 130 to generate a quantized transform block having quantized transform coefficients. Here, the quantization technique may include Dead Zone Uniform Threshold Quantization (DZUTQ) or Quantization Weighted Matrix. It is also possible to use an improved quantization technique in which these quantization techniques are improved. The quantization coefficient may vary depending on the block or the importance of the image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the rearrangement unit 160.

The transformation unit 130 and / or the quantization unit 135 may be selectively included in the image encoding apparatus 100. That is, the image encoding apparatus 100 may encode the residual block by performing at least one of transformation or quantization on the residual data of the residual block, or skipping both transformation and quantization. Even if neither of the transformation or quantization is performed by the image encoding apparatus 100, or both transformation and quantization are not performed, a block that enters the input of the entropy encoding unit 165 is generally called a transform block (or a quantized transform block). Refers to.

The rearrangement unit 160 may rearrange the coefficient values with respect to the quantized residual value.

The reordering unit 160 may change the block shape coefficient of the 2D into a vector form of the 1D through a coefficient scanning method. For example, the reordering unit 160 may scan a DC coefficient to a coefficient in a high frequency region using a predetermined scan type and change it to a one-dimensional vector form.

The entropy encoding unit 165 may perform entropy encoding based on values calculated by the reordering unit 160. For the entropy encoding, various encoding methods such as exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), and CABAC (Context-Adaptive Binary Arithmetic Coding) can be used.

The entropy encoding unit 165 includes residual value coefficient information of the coding unit and block type information, prediction mode information, split unit information, prediction unit information and transmission unit information, motion from the reordering unit 160 and the prediction units 120 and 125 Various information such as vector information, reference frame information, block interpolation information, and filtering information can be encoded. In the entropy encoding unit 165, coefficients of a transform block are encoded in various block units in a transform block, and non-zero coefficients, coefficients whose absolute value is greater than 1 or 2, and various types of flags indicating codes of the coefficients and the like. Can be. Coefficients not encoded by the flag alone may be encoded through absolute values of differences between coefficients encoded through flags and coefficients of an actual transform block.

The entropy encoding unit 165 may entropy encode the coefficient value of the coding unit input from the reordering unit 160.

The inverse quantization unit 140 and the inverse transformation unit 145 inverse quantize the values quantized by the quantization unit 135 and inversely transform the values converted by the conversion unit 130.

Meanwhile, the inverse quantization unit 140 and the inverse transform unit 145 may perform inverse quantization and inverse transform using the quantization method and the transformation method used by the quantization unit 135 and the transformation unit 130 inversely. Also, if only the quantization unit 130 and the quantization unit 135 do not perform the quantization, only the inverse quantization may be performed and the inverse transformation may not be performed. If both the transform and the quantization are not performed, the inverse quantization unit 140 and the inverse transform unit 145 also do not perform both inverse transform and inverse quantization or may be omitted without being included in the image encoding apparatus 100.

The residual values generated by the inverse quantization unit 140 and the inverse transformation unit 145 are restored by being combined with the prediction units predicted through the motion estimation unit, the motion compensation unit, and the intra prediction unit included in the prediction units 120 and 125 You can create a Reconstructed Block.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove block distortion caused by boundary between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply a deblocking filter to the current block based on pixels included in a few columns or rows included in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, when performing vertical filtering and horizontal filtering, horizontal filtering and vertical filtering may be processed in parallel.

The offset correction unit may correct an offset from the original image in units of pixels for the deblocking image. In order to perform offset correction for a specific picture, after dividing the pixels included in the image into a certain number of regions, determining the region to perform the offset and applying the offset to the region, or offset by considering the edge information of each pixel You can use the method of applying.

ALF (Adaptive Loop Filtering) may be performed based on a value obtained by comparing a filtered reconstructed image with an original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the corresponding group may be determined to perform filtering differently for each group. For information related to whether to apply ALF, the luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficient of the ALF filter to be applied may be changed according to each block. Also, the ALF filter of the same form (fixed form) may be applied regardless of the characteristics of the block to be applied.

The memory 155 may store reconstructed blocks or pictures calculated through the filter unit 150, and the stored reconstructed blocks or pictures may be provided to the predictors 120 and 125 when performing inter prediction.

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

Referring to FIG. 2, the image decoder 200 includes an entropy decoding unit 210, a reordering unit 215, an inverse quantization unit 220, an inverse transform unit 225, a prediction unit 230, 235, and a filter unit ( 240), a memory 245 may be included.

When an image bitstream is input from the image encoder, the input bitstream may be decoded in a procedure opposite to that of the image encoder.

The entropy decoding unit 210 may perform entropy decoding in a procedure opposite to that performed by entropy encoding in the entropy encoding unit of the image encoder. For example, various methods such as Exponential Golomb (CAVLC), Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied to the method performed in the image encoder. In the entropy decoding unit 210, coefficients of a transform block are based on various types of flags indicating a non-zero coefficient, a coefficient whose absolute value is greater than 1 or 2, and a sign of the coefficient, etc., in units of partial blocks in the transform block. Can be decrypted. Coefficients not represented by the flag alone may be decoded through the sum of coefficients expressed through flags and signaled coefficients.

The entropy decoding unit 210 may decode information related to intra prediction and inter prediction performed by the encoder.

The rearrangement unit 215 may rearrange the bitstream entropy-decoded by the entropy decoding unit 210 based on a method of rearranging the bitstream. The coefficients expressed in the form of a one-dimensional vector can be reconstructed into coefficients in a two-dimensional block form and rearranged. The reordering unit 215 may receive information related to coefficient scanning performed by the encoding unit and perform reordering through a reverse scanning method based on a scanning order performed by the encoding unit.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values of the rearranged blocks.

The inverse transform unit 225 may inverse transform the inverse-quantized transform coefficient by a predetermined transform method. In this case, the transform method may be determined based on information on a prediction method (inter / intra prediction), block size / shape, intra prediction mode, and the like.

The prediction units 230 and 235 may generate a prediction block based on prediction block generation related information provided by the entropy decoding unit 210 and previously decoded block or picture information provided by the memory 245.

The prediction units 230 and 235 may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit discrimination unit receives various information such as prediction unit information input from the entropy decoding unit 210, prediction mode information of an intra prediction method, and motion prediction related information of an inter prediction method, classifies the prediction unit in the current coding unit, and predicts It is possible to determine whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 uses the information necessary for inter prediction of the current prediction unit provided by the image encoder to predict the current based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit. Inter prediction for a unit may be performed. Alternatively, inter-prediction may be performed based on information of some regions pre-restored in the current picture including the current prediction unit.

In order to perform inter prediction, whether a motion prediction method of a prediction unit included in a corresponding coding unit based on a coding unit is one of Skip Mode, Merge Mode, and AMVP Mode I can judge.

The intra prediction unit 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit performing intra prediction, intra prediction may be performed based on intra prediction mode information of a prediction unit provided by an image encoder. The intra prediction unit 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a part that performs filtering on the reference pixel of the current block and can be applied by determining whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on a reference pixel of a current block by using prediction mode and AIS filter information of a prediction unit provided by an image encoder. When the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value obtained by interpolating a reference pixel, the reference pixel interpolation unit may interpolate the reference pixel to generate a pixel reference pixel in an integer value or less. If the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating a reference pixel, the reference pixel may not be interpolated. The DC filter may generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

Information about whether a deblocking filter is applied to a corresponding block or picture and information about whether a strong filter is applied or a weak filter is applied may be provided from a video encoder. In the deblocking filter of the video decoder, information related to the deblocking filter provided by the video encoder may be provided, and the video decoder may perform deblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction and offset value information applied to the image during encoding.

ALF may be applied to a coding unit based on ALF application information provided by an encoder, ALF coefficient information, and the like. Such ALF information may be provided by being included in a specific parameter set.

The memory 245 may store the restored picture or block so that it can be used as a reference picture or a reference block, and may also provide the restored picture to an output unit.

The coding block may be divided into at least one block. Specifically, at this time, the coding block may be divided from a maximum size coding block to a minimum size coding block based on quad tree splitting or binary tree splitting (or dual tree splitting). Information on a maximum sized coding block and a minimum sized coding block, or information on a difference value between a maximum sized coding block and a minimum sized coding block, may be signaled to a decoding apparatus through a bitstream.

Quad tree (QT) splitting is a method of dividing a coded block into four blocks. By QT splitting, the coding block can be divided into four blocks whose horizontal and vertical lengths are reduced by 1/2. Maximum or minimum size of QT splittable coding block, number of times of QT splitting (or maximum splitting depth), splitting depth of minimum sized block, depth splittable from maximum sized codingable block capable of QT splitting, or depth splittable in current coding block The back may be signaled through the upper header. Here, the upper header may include a slice layer, a picture layer, a sequence layer, or a video layer.

Binary tree (BT) splitting is a method of dividing a coded block into two blocks. By BT division, the coding block can be divided into two blocks in the horizontal or vertical direction. For example, the coding block may be divided into two blocks in which the horizontal or vertical length is reduced to 1/2 or two blocks in which the horizontal or vertical length is reduced to 3/4 and 1/4, respectively, by BT division. have. As described above, BT division may mean a method of dividing an encoding block with a precision of 1 / N (N≥2). The maximum or minimum size of the BT-encoded coding block, the number of BT divisions (or the maximum division depth), the division depth of the minimum-sized block, the depth that can be divided from the maximum-sized encoding block capable of BT division, and the depth that can be split in the current encoding block Or, the division precision and the like may be signaled through the upper header.

Hereinafter, the QT segmentation and the BT segmentation will be described in detail with reference to the drawings.

6 is a diagram illustrating a method of encoding QT split information for an encoding block. In this embodiment, the 'current' coding block indicates a block to be coded at a specific time point. For example, the current coding block may mean a block having a split depth in which current coding is performed. For example, when an encoding block is input for encoding, the first, input encoding block may be treated as a 'current encoding block'. Subsequently, as the coding block is split, if coding for the split block is performed, the split block may be treated as a 'current coding block'.

When an encoding block is input, the input encoding block may be treated as a 'current encoding block' (S601). The first input encoding block may mean an encoding block having a highest split depth to be encoded (ie, an encoding block having a depth of 0).

The encoding device may encode QT split information for the current coding block (S602). Here, the QT segmentation information indicates whether QT segmentation has been performed for the current coding block. If the current coding block is QT split, the QT split information may be set to 'True', and if the current coding block is not QT split, the QT split information may be set to 'False'.

If it is determined that the current coding block is not QT-divided (S603), the QT splitting process for the current coding block is ended. On the other hand, if it is determined that the current coding block is QT split (S603), four partial blocks (or subblocks) included in the current coding block may be generated through QT splitting (S604).

When the current coding block is divided into four sub-blocks, according to an encoding order, one of the sub-blocks included in the current coding block may be set as the current sub-block, and QT split information of the current sub-block may be encoded ( S605). Here, the encoding order between the partial blocks may follow a raster scan or a Z scan, or may follow a predefined order. That is, according to the coding order of the partial blocks, QT split information of the partial blocks may be sequentially encoded.

If it is determined that the current partial block is not QT-divided (S606), the QT splitting process may be terminated according to whether the current partial block is the last block in the current coding block and the input coding block (S607, S608). For example, if the current partial block is not QT split and the current partial block is the last block in the current coding block and the input coding block, the QT splitting process may end. On the other hand, if the current partial block is not the last partial block of the current coding block, or if the current coding block is the last partial block of the current coding block, but is not the last partial block in the input coding block, the next partial block in the scan order is the current part. As a block, a QT split information encoding process may be performed (S609).

On the other hand, if it is determined that the current partial block is QT divided (S606), the current partial block may be set as the current coding block (S610), and the newly set current coding block may be divided into four partial blocks (S604). When the newly set current coding block is divided into four partial blocks, a QT split information encoding process for the four newly generated partial blocks may be repeatedly performed (S605 to S610).

Based on the split result of the current coding block, the encoding apparatus may encode, through an upper header, a maximum size of a coding block capable of QT splitting and a depth of a coding block capable of QT splitting.

The split result of the current coding block may be used to determine a maximum size of a coding block capable of QT splitting and a depth of a coding block capable of QT splitting, for the next coding block.

7 is a diagram illustrating a method of encoding BT segmentation information for an encoding block.

When an encoding block is input, the input encoding block may be treated as a current encoding block (S701). The first input encoding block may mean an encoding block having a highest split depth to be encoded (ie, an encoding block having a depth of 0).

The encoding apparatus may encode BT splitting information for the current coding block (S702). Here, the BT splitting information indicates whether BT splitting has been performed on the current coding block. If the current coding block is BT split, the BT split information may be set to 'true', and if the current coding block is not BT split, the BT split information may be set to 'false'.

When the current coding block is divided into two sub-blocks, the encoding device may further encode information about the split pattern. For example, the information about the division pattern may further include at least one of information about the division direction or precision. Here, the split direction indicates whether the current coding block is split in the horizontal direction or the vertical direction. In addition, the precision of the current block can be used as an element for determining the size of the partial block. As an example, depending on the precision of the current block, two or more partial blocks having a horizontal or vertical length of 1/4 or 3/4 respectively compared to the upper block or two partial blocks having a horizontal or vertical length of 1/2 compared to the upper block. Can be divided.

As another example, the information on the partition pattern may include a partition index. Here, the split index indicates a split form of the current coding block. As an example, if the current coding block is divided into a partial block having a horizontal length of 1/4 compared to an upper block according to precision, when the horizontal block is divided into a partial block having 1/2 of the horizontal length compared to the upper block, the horizontal compared to the upper block When the length is divided into 3/4 partial blocks, when compared to the upper block, when the length is divided into 1/4 partial blocks, when compared to the upper block, when the length is divided into 1/2 partial block and compared to the upper block It may include a case where the length is divided into 3/4 partial blocks. Accordingly, the encoding apparatus may determine which of the seven cases the split pattern of the current decoding block corresponds to, and then encode an index corresponding to the split pattern of the current decoding block according to the determination result.

If it is determined that the current coding block is not BT-divided (S703), the BT splitting process for the current coding block is ended. On the other hand, if it is determined that the current coding block is BT split (S703), two partial blocks (or subblocks) included in the current coding block may be generated through BT splitting (S704).

When the current coding block is divided into two sub-blocks, according to an encoding order, one of the sub-blocks included in the current coding block may be set as the current sub-block, and BT split information of the current sub-block may be encoded ( S705). Here, the encoding order between the partial blocks may follow a raster scan or a Z scan, or may follow a predefined order. That is, according to the coding order of the partial blocks, the BT splitting information of the partial blocks may be sequentially encoded.

If it is determined that the current partial block is not BT-divided (S706), the BT splitting process may be terminated according to whether the current partial block is the last block in the current coding block and the input coding block (S707, S708). For example, if the current partial block is not BT-divided and the current partial block is the last block in the current coding block and the input coding block, the BT splitting process may be terminated. On the other hand, if the current partial block is not the last partial block of the current coding block, or if the current coding block is the last partial block of the current coding block, but is not the last partial block in the input coding block, the next partial block in the scan order is the current part. As a block, a BT split information encoding process may be performed (S709).

On the other hand, if it is determined that the current partial block is BT divided (S706), the current partial block may be set as the current coding block (S710), and the newly set current coding block may be divided into two partial blocks (S704). When the newly set current coding block is divided into two sub-blocks, the BT split information encoding process for the two newly generated sub-blocks may be repeatedly performed (S705 to S710).

Based on the split result of the current coding block, the encoding apparatus may encode a maximum size of a coding block capable of BT splitting, a depth and a splitting accuracy of a coding block capable of BT splitting, through an upper header.

The split result of the current coding block may be used to determine a maximum size of a coding block capable of BT splitting, a depth and a splitting precision of a coding block capable of BT splitting, for the next coding block.

8 is a diagram illustrating a method of decoding QT segmentation information for a decoding block. In the present embodiment, the 'current' decoding block indicates a decoding target block at a specific time. For example, the current decoding block may refer to a block having a split depth in which current decoding is performed. For example, when a decoding block is input for decoding, the first, inputted decoding block may be treated as a 'current decoding block'. Thereafter, as the decoding block is divided, if decoding of the divided block is performed, the divided block may be treated as a 'current decoding block'.

When the decryption block is input, the input decryption block may be treated as a 'current decryption block' (S801). The first input decoding block may mean a decoding block having a highest split depth to be decoded (ie, a decoding block having a depth of 0).

The decoding apparatus may decode the QT segmentation information for the current decoding block (S802). Here, the QT segmentation information indicates whether QT segmentation has been performed for the current decoding block. When the QT split information is 'true', the current decoding block is QT split, and when the QT split information is 'false', the current decoding block may not be QT split.

When the QT split information is false, that is, when it is determined that the current decoding block is not QT split (S803), the QT splitting process for the current decoding block ends. On the other hand, when the QT split information is true, that is, when it is determined that the current decoding block is QT split (S803), four partial blocks (or sub blocks) included in the current decoding block may be generated through the QT split. (S804).

When the current decoding block is divided into four partial blocks, according to a decoding order, any one of the partial blocks included in the current decoding block may be set as the current partial block, and QT split information of the current partial block may be decoded ( S805). Here, the decoding order between partial blocks may follow a raster scan or a Z scan, or may follow a predefined order. That is, according to the decoding order of the partial blocks, QT split information of the partial blocks may be sequentially decoded.

When the QT split information of the current partial block is false, that is, when it is determined that the current partial block is not QT split (S806), depending on whether the current partial block is the last block in the current decoding block and the input decoding block ( S807, S808), the QT splitting process may be ended. For example, if the current partial block is not QT split and the current partial block is the last block in the current decoding block and the input decoding block, the QT splitting process may end. On the other hand, if the current partial block is not the last partial block of the current decoding block, or if the current decoding block is the last partial block of the current decoding block, but not the last partial block in the input decoding block, the next partial block in the scan order is the current portion. As a block, a QT split information decoding process may be performed (S809).

On the other hand, when the QT split information of the current partial block is true, that is, when it is determined that the current partial block is QT split (S806), the current partial block is set as the current decoding block (S810), and the newly set current decoding block is set. It can be divided into four partial blocks (S804). When the newly set current decoding block is divided into four partial blocks, the QT split information decoding process for the four newly generated partial blocks may be repeatedly performed (S805 to S810).

In the above-described embodiment, when the size of the current decoding block is equal to or smaller than the maximum block size capable of QT segmentation signaled from the upper header, or the depth of the current decoding block, the maximum block capable of QT segmentation signaled from the upper header If it is equal to or greater than the depth, decoding of split information for the current decoding block may be omitted, and QT splitting may not be performed for the current decoding block any more.

9 is a diagram illustrating a method of decoding BT segmentation information for a decoding block.

When a decoding block is input, the input decoding block may be treated as a current decoding block (S901). The first input decoding block may mean a decoding block having a highest split depth to be decoded (ie, a decoding block having a depth of 0).

The decoding apparatus may decode BT segmentation information for the current decoding block (S902). Here, the BT splitting information indicates whether BT splitting has been performed on the current decoding block. When the BT split information is 'true', the current decoding block is BT split, and when the BT split information is 'false', the current decoding block may not be BT split.

When the BT split information is true, that is, when the current decoding block is BT split, the decoding apparatus may further decode information related to the split pattern. For example, the information about the division pattern may further include at least one of information about the division direction or precision. The current decoding block may be divided into two sub-blocks based on a horizontal boundary line or two sub-blocks based on a vertical boundary line, according to a division direction. In addition, according to the precision of the current block, the current decoding block has two partial blocks each having a horizontal or vertical length of 1/4 or 3/4 compared to the upper block, or 2 each having a horizontal or vertical length of 1/2 compared to the upper block. It can be divided into four sub-blocks.

As another example, the information on the partition pattern may include a partition index. Here, the split index indicates a split form of the current decoding block. For example, when the current decoding block is divided into a partial block having a horizontal length of 1/4 compared to an upper block according to precision, when the horizontal decoding block is divided into a partial block having 1/2 of the horizontal length compared to the upper block, the horizontal compared to the upper block. When the length is divided into 3/4 partial blocks, when compared to the upper block, when the length is divided into 1/4 partial blocks, when compared to the upper block, when the length is divided into 1/2 partial block and compared to the upper block It may include a case where the length is divided into 3/4 partial blocks. Accordingly, the decoding apparatus may decode index information indicating any one of the seven cases and determine a split pattern (form) for the current decoding block.

When the BT splitting information is false, that is, when it is determined that the current decoding block is not BT-segmented (S903), the BT splitting process for the current decoding block is ended. On the other hand, when the BT partitioning information is true, that is, when it is determined that the current decoding block is BT-segmented (S903), two partial blocks (or sub-blocks) included in the current decoding block may be generated through BT partitioning. (S904).

When the current decoding block is divided into two sub-blocks, according to decoding order, one of the sub-blocks included in the current decoding block may be set as the current sub-block, and BT segmentation information of the current sub-block may be decoded ( S905). Here, the decoding order between partial blocks may follow a raster scan or a Z scan, or may follow a predefined order. That is, according to the decoding order of the partial blocks, BT split information of the partial blocks may be sequentially decoded.

If it is determined that the current partial block is not BT divided (S906), the BT partitioning process may be terminated according to whether the current partial block is the last block in the current decoding block and the input decoding block (S907, S708). For example, if the current partial block is not BT-divided and the current partial block is the last block in the current decoding block and the input sub-block, the BT dividing process may be terminated. On the other hand, if the current partial block is not the last partial block of the current decoding block, or if the current decoding block is the last partial block of the current decoding block, but not the last partial block in the input decoding block, the next partial block in the scan order is the current portion. As a block, a BT segmentation information decoding process may be performed (S909).

On the other hand, if it is determined that the current partial block is BT divided (S906), the current partial block may be set as the current decoding block (S910), and the newly set current decoding block may be divided into two partial blocks (S904). When the newly set current decoding block is divided into two sub-blocks, the BT partition information decoding process for the two newly generated sub-blocks may be repeatedly performed (S905 to S910).

In the above-described embodiment, when the size of the current decoding block is equal to or smaller than the maximum block size capable of BT division signaled from the upper header, or the depth of the current decoding block is the maximum block capable of BT division signaled from the upper header. If it is equal to or greater than the depth, omitting decoding of the split information for the current decoding block may be omitted, and BT splitting may not be performed for the current decoding block.

In the example illustrated in FIGS. 6 to 9, a method of recursively dividing a coding / decoding block having the largest size using QT splitting or BT splitting has been described. At this time, in dividing the coding / decoding block into a plurality of sub-blocks, a QT splitting method and a BT splitting method are used interchangeably, and the order of the QT splitting and BT splitting may be variously set. For example, the coding apparatus divides the largest coding block by using QT splitting, and when a partial block for which BT splitting is optimally found, ends the QT splitting and splits the partial block through BT splitting. I can do it. Alternatively, even if a partial block generated by BT partitioning is determined to be optimal for QT partitioning, the partial block may be further divided using QT partitioning. In this way, the encoding device can grasp the optimal division method for each block, and accordingly encode information indicating the optimal division method for each block.

As another example, the decoding apparatus decodes QT segmentation information or BT segmentation information to determine an optimal segmentation state of the decoding block. At this time, either the QT splitting method or the BT splitting method may be applied only when the other one cannot be applied. For example, the BT splitting information for a given block can be decoded only when the QT splitting information for a given block is false or when an upper block including the given block is BT-split.

In encoding the block division information, the encoding device may encode information indicating whether each division method is used through an upper header. For example, the encoding device may encode information indicating whether QT splitting is used or whether BT splitting is used through an upper header. For example, QT splitting is used, but when it is determined that BT splitting is not used, the coding block may be split using only QT splitting. In this case, encoding for BT splitting information indicating whether or not the coding block is BT splitted may be omitted. As another example, when it is determined that both the QT split and the BT split are used, the coding block may be split using the QT and BT split modes.

10 is a diagram illustrating a split state in a coding block.

For convenience of description, when a block is BT-divided, it is assumed that a partial block generated by BT dividing can no longer be divided into a BT block. In the example shown in Fig. 10, a solid line indicates division using the QT division method, and a dotted line indicates division using the BT division method. Referring to FIG. 10, sub-locks in which the horizontal and vertical lengths are reduced by 1/2 from the upper block are generated by QT division, and by BT division, either the horizontal or vertical length is reduced by 1/2 from the upper block. It has been shown that a sub-block in which any one of the vertical lengths of the sub-blocks or higher blocks is reduced to 1/4 is generated. Accordingly, in the illustrated example, the maximum division precision of the coding block may be 1/4. The number indicated on each dividing line indicates the dividing order.

Referring to FIG. 10, a dividing line 1 indicates that the QT split is optimal in the first input coding block. The division line ② indicates that the BT horizontal 1/2 division is the optimal division in the upper left partial block divided through the division line ①. As for the division line ③, the BT vertical 1/2 division is determined as the optimal division in the upper part block divided through the division line ②. The division line ④ indicates that the BT horizontal 1/2 division is the optimal division in the lower part block divided through the division line ②. The division line ⑤ indicates that the BT vertical 1/2 division is the optimal division in the upper right partial block divided through the division line ①. The division line ⑥ indicates that the BT vertical 1/2 division is the optimal division in the left part block divided through the division line ⑤. The division line ⑦ indicates that the BT vertical 1/2 division is the optimal division in the right part block divided through the division line ⑤. The division line ⑧ indicates that the QT division is the optimal division in the lower left partial block divided through the division line ①. The division line ⑨ indicates that the BT horizontal 1/2 division is the optimal division in the upper left partial block divided through the division line ⑧. The dividing line ⑩ indicates that the BT 3/4 horizontal dividing is optimal in the lower partial block divided through the dividing line ⑨. The division line ⑪ indicates that the BT horizontal quarter division is the optimal division in the lower left sub-block divided through the division line ⑧. The dividing line ⑫ indicates that the BT horizontal 1/2 dividing is the optimal dividing in the lower right part block divided through dividing line ①. The division line ⑬ indicates that the BT vertical 3/4 division is the optimal division in the upper part block divided through the division line ⑫. The division line ⑭ indicates that the BT vertical 1/2 division is the optimal division in the lower part block divided through the division line ⑫. The division line ⑮ indicates that the BT vertical 3/4 division is the optimal division in the right part block divided through the division line 선.

FIG. 11 shows an optimal splitting state of the input coding block shown in FIG. 10 using a tree structure.

In the case of QT partitioning, QT partitioning information is 0 because QT partitioning is not performed, and according to QT partitioning, the block is divided into 4 sub-blocks (that is, horizontally and vertically divided into 1/2). Or it can be expressed as 1. In the case of BT partitioning, a case in which BT partitioning is not performed and a block is divided into two partial blocks according to BT partitioning may be included. In this case, when a block is divided into two partial blocks, according to precision, when a block is divided into a partial block having a horizontal length of 1/4 compared to an upper block, the block is divided into a partial block having a horizontal length of 1/2 compared to the upper block. In case, it is divided into sub-blocks whose horizontal length is 3/4 compared to the upper block, and if it is divided into partial blocks whose vertical length is 1/4 compared to the upper block, it is divided into partial blocks whose vertical length is 1/2 compared to the upper block. And a partial block having a vertical length of 3/4 compared to an upper block. Accordingly, the BT segmentation information can be expressed as segmentation information from 0 to 6.

In FIG. 11, QT segmentation information and BT segmentation information are indicated in a tree structure.

Based on the above description, the number or type of intra prediction modes in the encoding / decoding block is controlled, and a method of encoding / decoding it will be described in detail.

12 is a flowchart illustrating a process of controlling the number or type of prediction modes in the encoding device. In FIG. 12, each process is shown as being connected in a series of flows, but each process is not required to be performed in the order shown. As an example, if there is no influence on the determination result of the number or type of intra prediction modes of the prediction block, the order may be changed. For example, even if the order of steps S1201 and S1202 is changed, if there is no change in the number or type of intra prediction modes, their order may be changed. In addition, some of the steps illustrated in FIG. 12 may be omitted. For example, if it is possible to control the number or type of intra prediction modes regardless of the shape of the prediction block, step S1202 may be omitted.

In the present embodiment, the current coding block may represent a prediction block or a coding block including a prediction block. Hereinafter, the present invention will be described in detail with reference to FIG. 12.

In S1201, it has been shown that the number or type of intra prediction modes can be controlled according to the size of the current coding block. In detail, the number of intra prediction modes that can be used by the current coding block may be variably determined according to the size of the current coding block. For example, the number of intra prediction modes that the current coding block can use may increase as the size of the current coding block increases. For example, assuming that the minimum size of the prediction block is 4x4 and the maximum size is 256x256, if the size of the current coding block is 4x4 or more and 32x32 or less, the number of intra prediction modes available for the current coding block is set to 35, If the size of the current coding block is 64x64 or less and 256x256 or less, the number of intra prediction modes available for the current coding block may be set to 67.

Conversely, the number of intra prediction modes that can be used by the current coding block may increase as the size of the current coding block is smaller. For example, assuming that the minimum size of the prediction block is 4x4 and the maximum size is 256x256, if the size of the current coding block is 4x4 or more and 32x32 or less, the number of intra prediction modes available for the current coding block is set to 67, If the size of the current coding block is 64x64 or less and 256x256 or less, the number of intra prediction modes available for the current coding block may be set to 35.

The number of intra prediction modes that can be used by the current coding block may be determined according to a comparison result of a size of the current coding block with a reference size. Here, the reference size may be signaled through an upper header or may be derived under the same conditions in the encoding device and the decoding device. For example, assuming that the reference size is 32x32, information about the reference size may be defined as 'log ₂ 32' taking a log function and transmitted through a bitstream. As the size of the current coding block is smaller or larger than the reference size, the number of intra prediction modes that the current coding block can use may increase. For example, if the size of the current coding block is 32x32, the number of intra prediction modes available for the current coding block is 19, and if the size of the current coding block is 64x64 or more and 128x128 or less, the intra prediction mode available for the current coding block The number of is 35, and if the size of the current coding block is 256x256, the number of intra prediction modes available for the current coding block may be 67. When the size of the current coding block is 16x16 or less and 8x8 or more, the number of intra prediction blocks that can be used by the current coding block is 35, and when the size of the current coding block is 4x4, intra prediction blocks that can be used by the current coding block The number of may be 67.

Conversely, as the size of the current coding block is smaller or larger than the reference size, the number of intra prediction modes that can be used by the current coding block may decrease. For example, when the size of the current coding block is 32x32, the current coding block is If the number of available intra prediction modes is 67, and the size of the current coding block is 64x64 or more and 128x128 or less, the number of intra prediction modes available for the current coding block is 35, and the size of the current coding block is 256x256, The number of intra prediction modes currently available for the coding block may be 19. When the size of the current coding block is 16x16 or less and 8x8 or more, the number of intra prediction blocks that can be used by the current coding block is 35, and when the size of the current coding block is 4x4, intra prediction blocks that can be used by the current coding block The number of may be 19.

Regardless of the size of the current coding block, an intra prediction mode that can be used by the current coding block may include a non-directional intra prediction mode (or a non-angular prediction mode). That is, regardless of the size of the current coding block, the current coding block can be coded using a non-directional intra prediction mode. On the other hand, the number of directional prediction modes (ie, angular prediction modes) that can be used by the current coding block may vary according to the size of the current coding block. As the number of intra prediction modes available for the current coding block decreases or increases, the number of directional prediction modes available for the current coding block may decrease or increase.

When the number of directional prediction modes that can be used by the current coding block decreases, the current coding block may use an integer unit directional prediction mode or a similar mode. Here, the integer unit directional prediction mode refers to a mode that can perform intra prediction using an integer unit reference sample. Here, the integer unit reference sample may mean the reference sample itself, not an additional reference sample generated through interpolation of the reference sample. For example, an intra prediction mode in a horizontal direction, a vertical direction, or a diagonal direction may be an integer unit directional prediction mode.

Alternatively, the directional prediction mode that can be used by the current coding block may be determined by dividing (equal to N-1) by the number (N) of directional prediction modes to use the entire section of the directional prediction mode.

13 and 14 show examples of 13 directional prediction modes that can be used in the current coding block.

Referring to FIG. 13, an intra prediction mode in which the current coding block is available may be an integer directional prediction mode and an directional prediction mode adjacent to the integer directional prediction mode. As an example, in FIG. 13, vertical prediction mode, horizontal prediction direction, and three diagonal prediction modes and adjacent prediction modes (intra prediction modes with an offset of ± 1) are directional prediction modes that can be used by the current coding block. As shown.

Referring to FIG. 14, the directional prediction modes in which the current coding block is available may be 13 directional prediction modes allocated at equal intervals by dividing the entire section of the directional prediction mode into 12 equal parts.

When the number of intra prediction modes that can be used by the current prediction block increases, the intra prediction mode adjacent to the integer unit directional prediction mode may be used more or the total section of the directional prediction mode may be divided into more sections.

As an example, FIGS. 15 and 16 show an example of a case in which there are 21 directional prediction modes available in the current block.

In FIG. 15, the intra prediction modes in which the current coding block is available include the vertical, horizontal and three diagonal intra prediction modes and the intra prediction modes adjacent thereto (intra prediction modes with offset ± 2). It has been shown that this is the directional prediction mode available.

In FIG. 16, the intra prediction mode that can be used for the current coding block is shown as 21 directional prediction modes allocated at equal intervals by dividing the entire section of the directional prediction mode into 20 equal parts.

The encoding apparatus may encode the number of available intra prediction modes for each size of the prediction block and transmit it to the decoder. At this time, information indicating the number of intra prediction modes available for each size of the prediction block may be encoded in an upper header. For example, assuming that the minimum size of the prediction block is 4x4 and the maximum size is 256x256, when the number of intra prediction modes that can be used by prediction blocks smaller than or equal to 32x32 blocks is determined to be 64, log the available number of logs. The taken value (log ₂ 64) can be encoded and transmitted to a decoding device. If the number of intra prediction modes that can be used by the 64x64 prediction block is determined to be 32, the value (log ₂ 32) that has been logged to the available number is encoded, and the number of intra prediction modes that can be used by the 128x128 prediction block is 16. If the number of available logs is logged (log ₂ 16), and the number of intra prediction modes available for the 256x256 prediction block is 8, the number of logged values (log ₂ 8) is used. Can be coded.

As another example, in the upper header, the number of intra prediction modes available for each size of the prediction block is preset, and an optimal number of intra prediction modes is determined for each prediction block, and an index indicating the number of intra prediction modes available for each prediction block unit Information can be encoded. For example, if the number of intra prediction modes for which a 32x32 prediction block is available is 19, 35, or 67, an index indicating which of 19, 35, or 67 is optimal for a prediction block of 32x32 size Information can be encoded.

The encoding apparatus may encode information indicating whether to adjust the number or type of intra prediction modes according to the size of the prediction block. The coded information may transmit a decoder through an upper header. At this time, the information may be a flag of 1 bit, but is not limited thereto. The decoding apparatus may determine in advance whether the number or type of intra prediction modes is adjusted for each prediction block size based on the flag information.

Even if the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the size of the prediction block, the current coding block may perform intra prediction in a conventional method, or the above-described prediction block Intra prediction may be performed by adjusting the number of available intra prediction modes according to the size of. Accordingly, when the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the size of the prediction block, the encoding device, in units of prediction blocks, uses the corresponding prediction block in a conventional method (ie , Using a fixed number of intra prediction modes) or information indicating whether the number of available intra prediction modes is adjusted according to a prediction block size may be additionally encoded. In this case, the encoded information may be a flag of 1 bit, but is not limited thereto.

In S1202, it is illustrated that the number or type of intra prediction modes can be controlled according to the type of the current coding block. In detail, the number of intra prediction modes that can be used by the current coding block may be variably determined according to the type of the current coding block. For example, when the current coding block is non-square (eg, rectangular), the current coding block may use the intra prediction mode in the horizontal direction more than the intra prediction mode in the vertical direction, or the vertical direction than the intra prediction mode in the horizontal direction. It can be set to use more of the intra prediction mode.

Specifically, when the shape of the current coding block is non-square, the number of horizontal prediction modes and vertical prediction modes that are available for the current block may be determined according to the width and height ratios of the current coding block. For example, when the size of the current coding block is 8x16, since the height of the current coding block is twice the width, the number of horizontal intra prediction modes that the current coding block can use is twice that of the vertical intra prediction modes. It can be about. For example, if the number of directional intra prediction modes available for the current coding block is 25, the current coding block may be set to use 16 transverse intra prediction modes and 9 vertical intra prediction modes.

The number of intra prediction modes available for the current coding block may be determined by comparing the width or height of the current coding block with a preset threshold. Here, the threshold may be signaled through the upper header. As an example, a value obtained by taking a log (Log ₂ ) as a threshold value may be signaled through an upper header. Or, the encoding device and the decoding device may derive the threshold under the same condition. In this case, the threshold may be set for each of the width and height, or the same value may be used for the width and height. For example, when the threshold for width is 32, if the width of the current coding block is smaller than the threshold, only 1 / 2N of the N horizontal intra prediction modes may be used for the current coding block. For example, if there are 33 transverse directional prediction modes, the current coding block may use 17 transverse directional prediction modes.

Regardless of the form of the current coding block, the intra prediction mode that can be used by the current coding block may include a non-directional intra prediction mode (or a non-angular prediction mode). On the other hand, the number of directional prediction modes (ie, angle prediction modes) that can be used by the current coding block may vary according to the type of the current coding block. As the number of intra prediction modes available for the current coding block decreases or increases, the number of directional prediction modes available for the current coding block may decrease or increase.

The directional prediction mode that the current coding block can use may be determined as an integer unit directional prediction mode or a similar mode. Alternatively, the directional prediction mode that can be used by the current coding block may be determined by dividing (equal to N-1) by the number (N) of directional prediction modes to use the entire section of the directional prediction mode. This has been described with reference to FIGS. 13 to 16 above, and thus detailed description thereof will be omitted.

The encoding apparatus may encode information indicating whether to adjust the number or type of intra prediction modes according to the shape of the prediction block. The coded information may transmit a decoder through an upper header. At this time, the information may be a flag of 1 bit, but is not limited thereto. The decoding apparatus may determine in advance whether the number or type of intra prediction modes is adjusted for each type of prediction block based on the flag information.

Even if the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the type of the prediction block, the current coding block may perform intra prediction in a conventional method or the above-described prediction block Intra prediction may be performed by adjusting the number of available intra prediction modes according to the form of. Accordingly, when the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the type of the prediction block, the encoding device, in units of prediction blocks, uses the corresponding prediction block in a conventional method (ie , Using a fixed number of intra prediction modes) or information indicating whether the number of available intra prediction modes is adjusted according to a prediction block type may be additionally encoded. In this case, the encoded information may be a flag of 1 bit, but is not limited thereto.

In S1203, it has been shown that the number or type of intra prediction modes can be controlled according to the neighboring blocks of the current sub-block. In detail, the number of intra prediction modes that can be used by the current coding block may be determined according to intra prediction modes of neighboring blocks neighboring the current coding block.

For example, when referring to statistics of intra prediction modes of blocks around a current coded block, a non-directional prediction mode and a directional prediction mode are mixed, so that the ratio of the non-directional prediction mode and the directional prediction mode is not greater than or equal to a threshold ratio. If not, the intra prediction characteristic of the current coding block may be determined to be ambiguous. When it is determined that the intra prediction characteristics of the current coding block are ambiguous, a change may not be applied to the number or type of intra prediction modes that the current coding block can use. Accordingly, all intra prediction modes can be used for the current coding block.

For example, when referring to intra prediction modes of a block around a current coding block, if there are 9 non-directional modes, 8 directional modes, and 4 directional modes and 4 vertical modes among directional modes, , It is difficult to determine whether the current coding block should be used in a non-directional, vertical or horizontal direction. As such, when the ratio of the non-directional prediction mode and the directional prediction mode of the neighboring blocks around the current prediction block is close to 1: 1, it is difficult to determine the intra prediction mode mainly used by the neighboring prediction blocks, or the neighboring prediction blocks are the directional prediction mode It is coded using, but if the horizontal direction mode and the vertical direction mode are mixed and it is difficult to determine the main directionality of neighboring prediction blocks, the number or type of intra prediction modes that the current coding block can use may not be changed. .

On the other hand, when the statistics of the intra prediction mode around the current coding block are referred to, when it is determined that the non-directional prediction mode is used more than a threshold ratio than the directional prediction mode, the prediction characteristic of the current coding block is that the non-directional mode I can judge. In this case, the intra prediction mode in which the current coding block is available necessarily includes a non-directional mode and, incidentally, a predetermined number of directional modes. When the neighboring blocks of the current coding block are mostly coded through the non-directional prediction mode, the probability that a contour having a specific directionality appears in the current coding block is very low. Accordingly, even if only the non-directional prediction mode is used or only the non-directional prediction mode and a predetermined number of directional prediction modes (for example, two vertical prediction modes and two horizontal prediction modes) are used, optimal intra prediction for the current coding block I can figure out the mode.

When it is determined that the directional prediction mode is used more than a threshold ratio more than the non-directional prediction mode when referring to the statistics of the intra prediction mode around the current coding block, it may be determined that the prediction characteristic of the current coding block is the directional mode. have. The ratio of the horizontal prediction modes to the intra prediction modes of neighboring blocks and the vertical prediction modes is skewed to one side (for example, when the horizontal prediction mode is used more than a threshold ratio than the vertical prediction mode) Or, when the vertical prediction mode is used more than a threshold ratio than the horizontal prediction mode, etc.), the current coding block using the directional prediction mode, which is the more used of the horizontal prediction mode and the vertical prediction mode The intra prediction mode that can be used can be configured. In this case, the intra prediction mode that can be used by the current coding block may further include a non-directional prediction mode along with a horizontal or vertical prediction mode.

For example, if all of the intra prediction modes around the current coding block are directional prediction modes, and 11 horizontal modes and 2 vertical modes are among the intra prediction modes of the neighboring blocks, the current block will also have lateral characteristics. Predictable. Accordingly, the optimal intra prediction mode for the current coding block may be determined using the non-directional prediction mode and the horizontal prediction mode.

In the above-described example, a threshold ratio (such as a threshold ratio that is a reference between a directional mode and a non-directional mode and a threshold ratio that is a reference between a horizontal mode and a vertical mode) may be signaled through an upper header. For example, a value obtained by taking a log (log ₂ ) for a threshold ratio may be transmitted through an upper header.

Regardless of the intra prediction mode around the current coding block, the intra prediction mode that can be used by the current coding block may include a non-directional intra prediction mode (or a non-angular prediction mode). On the other hand, the number of directional prediction modes (ie, angle prediction modes) that can be used by the current coding block may vary according to the usage pattern of the intra prediction mode around the current coding block. As the number of intra prediction modes available for the current coding block decreases or increases, the number of directional prediction modes available for the current coding block may decrease or increase.

The directional prediction mode that the current coding block can use may be determined as an integer unit directional prediction mode or a similar mode. Alternatively, the directional prediction mode that can be used by the current coding block may be determined by dividing (equal to N-1) by the number (N) of directional prediction modes to use the entire section of the directional prediction mode. This has been described with reference to FIGS. 13 to 16 above, and thus detailed description thereof will be omitted.

The encoding apparatus may encode information indicating whether to adjust the number or type of intra prediction modes according to the intra prediction mode usage pattern of neighboring blocks around the prediction block. The coded information may transmit a decoder through an upper header. At this time, the information may be a flag of 1 bit, but is not limited thereto. The decoding apparatus may determine in advance whether the number or type of intra prediction modes is adjusted for each type of prediction block based on the flag information.

Although the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the intra prediction mode usage pattern of neighboring blocks around the prediction block, the current coding block performs intra prediction in a conventional method Alternatively, intra prediction may be performed by adjusting the number of available intra prediction modes according to the above-described intra prediction mode usage pattern of neighboring blocks. Accordingly, when the information encoded in the upper header indicates that the number of available intra prediction modes can be adjusted according to the intra prediction mode usage pattern of the neighboring block, the encoding apparatus, in prediction block units, the prediction block is conventional Information indicating whether it is encoded using the method of (i.e., using a fixed number of intra prediction modes) or by using a method in which the number of available intra prediction modes is adjusted according to the intra prediction mode usage pattern of neighboring blocks. May be additionally encoded. In this case, the encoded information may be a flag of 1 bit, but is not limited thereto.

12 illustrates the encoding process, it is also possible to adjust the number of intra prediction modes that can be used by the current decoding target block in the decoding process. Based on the information signaled through the bitstream, the decoding apparatus may adjust the number of intra prediction modes that can be used by the current decoding block in consideration of the size, shape of the current decoding block, or a pattern of using the intra prediction mode of neighboring blocks. have.

If the number of intra prediction modes available for the current coding block is determined, the encoding apparatus may determine an intra prediction mode of the current coding block among intra prediction modes that can be used by the current coding block, and encode information about the intra prediction mode. Hereinafter, a method of encoding / decoding an intra prediction mode for a current block will be described in detail.

17 is a flowchart illustrating a process of encoding an optimal intra prediction mode for a current coding block.

Referring to FIG. 17, first, the encoding apparatus may determine an MPM candidate for the current coding block (S1701). In this case, the encoding apparatus considers the number of directional prediction modes that can be used by the current coding block and blocks around the current coding block, and for the directional prediction mode, the quantized directional prediction mode (or the angle of the quantized directional prediction mode) ) As an MPM candidate.

As an example, FIG. 18 is a diagram illustrating an example of setting an MPM candidate. In FIG. 18, three MPM candidates are illustrated as being used. In the example shown in FIG. 18, L is an intra prediction mode having the highest frequency among neighboring blocks adjacent to the left side of the current coding block, or a neighboring block (or an arbitrary neighboring block) at a predetermined location adjacent to the left side of the current coding block. It may be an intra prediction mode. A may be an intra prediction mode having the highest frequency among neighboring blocks adjacent to the top of the current coding block, or an intra prediction mode of a neighboring block (or an arbitrary neighboring block) at a predetermined position adjacent to the top of the current coding block.

The L, L-1, L + 1 and A may represent the index of the intra prediction mode. However, when the number of directional prediction modes that can be used by the current coding block and the neighboring blocks is different, a case in which the directional prediction mode used by the neighboring blocks cannot be used in the current coding block may appear. For example, 18 of the intra prediction modes that can be used by the current coding block means a horizontal prediction mode, whereas 18 of the directional prediction modes that can be used by neighboring blocks indicate a prediction mode in the upper left direction rather than the horizontal direction. It can also mean.

To solve this mismatch, when the non-directional prediction mode is allocated to the MPM candidate, index information is used as it is, and when the directional prediction mode is allocated to the MPM candidate, a prediction angle corresponding to the directional prediction mode can be allocated. have. As the quantized angle is set as the MPM candidate, the encoding apparatus determines the intra prediction mode of the current coding block based on whether the prediction angle of the optimal directional prediction mode for the current coding block is the same as the quantization angle included in the MPM candidate. Can decide. Accordingly, when the MPM candidate is a non-directional prediction mode, indexes of intra prediction modes such as L, L-1, L + 1, and A are used as MPM candidates, whereas when the MPM candidate is a directional prediction mode, L ', The angles of the intra prediction modes such as (L-1) ', (L + 1)' and A 'can be used as MPM candidates.

If the current coding block cannot use the directional prediction mode matching the prediction angle of the neighboring block, quantization is performed to reduce the prediction angle of the neighboring block to the most similar prediction angle of the directional mode available to the current prediction block. can do. Accordingly, when the MPM candidate is a directional prediction mode, an MPM candidate indicating a quantized angle of a directional prediction mode such as L ', (L-1)', (L + 1) ', A' can be used.

As an example, FIGS. 19 and 20 show an example of quantizing a prediction angle. FIG. 20 shows a directional prediction mode that can be used in neighboring blocks adjacent to the current coding block, and FIG. 19 shows a directional prediction mode that can be used in the current coding block. 19 and 20, it can be confirmed that the directional prediction mode indicated by the dotted line in FIG. 20 is not available in the current coding block. Accordingly, when the neighboring block is encoded using the directional prediction mode indicated by a dotted line, the prediction angle of the directional prediction mode indicated by a dotted line is the prediction angle of the most similar prediction mode among the directional prediction modes that can be used by the current block. By converting, the converted angle can be set as an MPM candidate.

In the above-described embodiment, it has been described that the MPM candidate is set as the prediction angle for the directional prediction mode in consideration of the case where the number of intra prediction modes that can be used by the current coding block and neighboring blocks is different.

As another example, if the number of intra prediction modes that can be used by the current coding block and neighboring blocks is the same, the MPM candidate may indicate an index of the intra mode also for the directional prediction mode. Alternatively, even if the number of intra prediction modes available for the current coding block and neighboring blocks is different, the MPM candidate may be set to indicate an intra prediction mode index even for the directional prediction mode. In this case, the directional prediction mode of the neighboring block may be quantized (or transformed) into an index of a mode having the most similar direction among the directional prediction modes that the current block can use.

21 is a diagram showing another example of setting an MPM candidate.

The encoding apparatus may derive an MPM candidate for the current coding block based on neighboring blocks adjacent to the current coding block. In this case, the neighboring block adjacent to the current coding block may include at least one of a block adjacent to the top of the current coding block, a block adjacent to the left of the current coding block, and a block adjacent to a corner of the current coding block.

As an example, FIG. 22 shows an example of a neighboring block used to derive an MPM candidate of a current coding block. Referring to FIG. 22, in order to derive an MPM candidate of a current coding block, a left neighboring block (A), a top neighboring block (B), a bottom left neighboring block (C), and a top right neighboring block (D) of the current coding block And the upper left neighboring block E may be used.

The encoding apparatus may generate an MPM candidate according to the priority shown in FIG. 21. Assuming that the number of MPM candidates of the current coding block is 5, first, the intra prediction mode of the neighboring blocks may be added as MPM candidates in the order of neighboring blocks A and B. Next, non-directional modes such as a Planar mode and a DC mode can be added as MPM candidates. Next, the intra prediction mode of the neighboring blocks may be added as an MPM candidate in the order of the neighboring blocks C, D, and E.

If the number of MPM candidates has not reached the maximum number, the encoding apparatus MPMs a mode having a direction similar to the directional mode (eg, a directional mode with an offset of ± 1) if a directional mode is among the determined MPM candidates so far. Can be added as a candidate.

Nevertheless, if the number of MPM candidates has not reached the maximum number, the vertical mode, the horizontal mode, the prediction mode in the diagonal direction (eg, the prediction mode in the lower left direction (the prediction mode with index 2), the prediction in the upper left direction Mode or a prediction mode in the upper right).

In FIG. 22, it is shown that MPM candidates can be derived from neighboring blocks adjacent to the current coding block. In the embodiments shown in FIGS. 18 and 21, the MPM candidates are intra predicted of neighboring blocks not adjacent to the current coding block, depending on the size, shape, or decoding state of the current coding block or neighboring blocks adjacent to the current coding block. It may be derived based on the mode.

For example, FIG. 23 is a diagram illustrating an example of deriving an MPM candidate from neighboring blocks that are not adjacent to the current coding block.

If the non-square block (eg, a rectangular block having a width greater than a height) continuously in the upper direction of the current coding block, and the height of the upper peripheral block adjacent to the current coding block is less than the height of the current coding block, the encoding device It may be predicted that the intra prediction mode of the upper neighboring block is not the same as the intra prediction mode of the current coding block. Alternatively, if the intra prediction mode of the neighboring block adjacent to the top of the current coding block is one of the vertical prediction modes, the encoding apparatus may predict that the intra prediction mode of the upper neighboring block is not the same as the intra prediction mode of the current coding block. have.

In this case, the encoding apparatus may consider deriving an additional MPM candidate from at least one of blocks adjacent to the current encoding block, that is, a left, upper left, upper right, and lower left peripheral blocks. Alternatively, the encoding apparatus may derive additional MPM candidates from blocks adjacent to the current block, but not adjacent to the current block. For example, in the example shown in Figure 23, the encoder is a block adjacent to the upper direction of the current coded block (i.e., 1 ^st upper block) instead of the second upper block (i.e., 2 ^nd upper block) or smaller blocks in the further top Based on the MPM candidate can be derived. Alternatively, the encoding apparatus may consider the MPM candidate by using only the intra prediction mode of neighboring blocks in a specific direction, not the top direction.

In addition, when the non-square block (eg, a rectangular block having a height greater than the width) continuously in the left direction of the current coding block, and the width of the left peripheral block adjacent to the current coding block is smaller than the width of the current coding block, The encoding apparatus may predict that the intra prediction mode of the left neighboring block is not the same as the intra prediction mode of the current coding block. Alternatively, if the intra prediction mode of the neighboring block adjacent to the left side of the current coding block is one of the horizontal prediction modes, the encoding apparatus may predict that the intra prediction mode of the left neighboring block is not the same as the intra prediction mode of the current coding block. have.

In this case, the encoding apparatus may consider deriving an additional MPM candidate from at least one of blocks adjacent to the current coding block, that is, upper, upper left, upper right, and lower left peripheral blocks. Alternatively, the encoding apparatus may derive additional MPM candidates from blocks adjacent to the current block, but not adjacent to the current block. For example, in the example shown in Figure 23, the encoder is now a block adjacent to the left direction of the encoded block (i.e., 1 ^st left block) instead of the second left block (i.e., 2 ^nd left blocks), or block than the more left Based on the MPM candidate can be derived. Alternatively, the encoding apparatus may consider the MPM candidate by using only the intra prediction mode of neighboring blocks in a specific direction, not the left direction.

When the MPM candidate of the current coding block is determined, it is possible to compare the intra prediction mode and the MPM candidates of the current coding block to determine whether there is the same MPM candidate as the intra prediction mode of the current coding block. According to the determination result, the encoding apparatus may encode information indicating whether an MPM candidate identical to the intra prediction mode of the current coding block exists (S1702). For example, if the same MPM candidate as the intra prediction mode of the current coding block exists, the information is indeed encoded, and if the same MPM candidate as the intra prediction mode of the current coding block does not exist, the information is falsely encoded Can be.

When it is determined that the same MPM candidate as the intra prediction mode of the current coding block exists (S1703), the encoding apparatus may encode index information specifying the same MPM candidate as the intra prediction mode of the current coding block among the MPM candidates (S1703). S1704).

On the other hand, if it is determined that the current coding block does not have the same MPM candidate as the intra prediction mode (S1703), the encoding device is the intra intra optimal for the current coding block among the intra prediction modes except the intra prediction mode set as the MPM candidate. The prediction mode is encoded (S1705). Specifically, in all intra prediction modes that can be used by the current coding block, after excluding intra prediction modes set as MPM candidates, bits are allocated to express the remaining intra prediction modes, and the current coding block among the remaining prediction modes is Information corresponding to the intra prediction mode can be encoded.

When encoding the residual intra prediction modes, while allocating bits, bits sufficient to express the residual intra prediction modes may be fixedly allocated, but the remaining intra prediction modes are divided into N groups and allocated bits for each group. Can be set differently. For example, when the number of intra prediction modes available in the current coding block is 67 and the number of MPM candidates is 6, the number of remaining intra prediction modes is 61. At this time, when the remaining intra prediction modes are divided into two groups (A, B), 16 intra prediction modes are assigned to the A group, and 45 intra prediction modes are assigned to the B group. Here, flag information indicating to which group the intra prediction mode of the current coding block belongs may be encoded. The group A can allocate 4 bits to encode the intra prediction mode of the current coding block, and the group B is divided into (B-1, B-2) two subgroups, and 19 intra predictions for the group B-1. 26 intra prediction modes are allocated to the mode and the B-2 group, and 5 bits are allocated to the B-1 group and 6 bits are allocated to the B-2 group to encode the intra prediction mode of the current coding block. The encoded information may be encoded and transmitted to a decoding device through a bitstream.

Next, decoding of the intra prediction mode for the current decoding block in the decoding apparatus will be described.

24 is a flowchart illustrating a process of decoding an intra prediction mode for a current decoding block.

Referring to FIG. 24, first, the decoding apparatus may determine an MPM candidate for the current decoding block (S2401). The decoding apparatus may determine the MPM candidate for the current decoding block in consideration of the intra prediction mode of neighboring blocks neighboring the current decoding block, as in the encoding process described above.

Thereafter, the decoding apparatus may decode information indicating whether an MPM candidate identical to the intra prediction mode of the current decoding block is present among the MPM candidates from the bitstream (S2402). The information may be a flag of 1 bit, but is not limited thereto.

Based on the above information, when it is determined that the same MPM candidate as the intra prediction mode of the current decoding block exists (S2403), the decoding apparatus index information specifying the same MPM candidate as the intra prediction mode of the current decoding block among the MPM candidates Can be decoded (S2404).

On the other hand, if it is determined that the same MPM candidate as the intra prediction mode of the current decoding block does not exist (S2403), the decoding apparatus is optimal for the current decoding block among the remaining intra prediction modes except the intra prediction mode set as the MPM candidate. Residual prediction mode information indicating the prediction mode may be decoded (S2405).

In the above-described example, the intra prediction mode of the current encoding / decoding block is determined by using the MPM candidate, but the intra prediction mode of the current encoding / decoding block may be determined without using the MPM candidate. In this case, information specifying the intra prediction mode of the current encoding / decoding block may be transmitted to the decoding apparatus through a bitstream.

Exemplary methods of the present disclosure are expressed as a series of operations for clarity of description, but are not intended to limit the order in which the steps are performed, and each step may be performed simultaneously or in a different order if necessary. In order to implement the method according to the present disclosure, the steps illustrated may include other steps in addition, other steps may be included in addition to the remaining steps, or other additional steps may be included in addition to some steps.

Various embodiments of the present disclosure are not intended to list all possible combinations, but are intended to describe representative aspects of the present disclosure, and the items described in various embodiments may be applied independently or in combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For implementation by hardware, 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 It can be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor.

The scope of the present disclosure includes software or machine-executable instructions (eg, operating systems, applications, firmware, programs, etc.) that cause an operation according to the method of various embodiments to be executed on a device or computer, and such software or Instructions include a non-transitory computer-readable medium that is stored and executable on a device or computer.

Claims (9)

Deriving an intra prediction mode of the current coding block among intra prediction modes in which the current coding block is available; And
And performing intra prediction based on the derived intra prediction mode to generate a prediction block of the current coding block,
The intra prediction mode in which the current coding block is available is divided into K groups,
The intra prediction mode of the current coding block is derived from any one of the K groups,
The K is a natural number of 3 or more, video signal decoding method. According to claim 1,
Obtaining, from a bitstream, a flag specifying a group to which the intra prediction mode of the current coding block belongs among the K groups; And
And determining a group to which the intra prediction mode of the current coding block belongs, based on the obtained flag. According to claim 2,
The maximum number of flags acquired for the current coding block is (K-1) individual, and the video signal decoding method. According to claim 1,
Any one of the K groups is composed of 5 MPM candidates, video signal decoding method. According to claim 4,
The MPM candidate is derived based on an intra prediction mode of neighboring blocks adjacent to the current coding block,
The peripheral block includes at least one of a left peripheral block or an upper peripheral block of the current coding block. The method of claim 5,
When there are a plurality of upper peripheral blocks, a block located at the rightmost of the upper peripheral blocks is used to derive an MPM candidate of the current block. The method of claim 5,
When there are a plurality of left peripheral blocks, a block located at the bottom-most of the left peripheral blocks is used to derive an MPM candidate of the current block. Determining an intra prediction mode of the current coding block among intra prediction modes in which the current coding block is available; And
And performing intra prediction based on the determined intra prediction mode to generate a prediction block of the current coding block,
The intra prediction mode in which the current coding block is available is divided into K groups,
The intra prediction mode of the current coding block is determined from any one of the K groups,
The K is a natural number of 3 or more, video signal encoding method. A computer-readable recording medium storing a bitstream decoded by a video signal decoding method, comprising:
The video signal decoding method,
Deriving an intra prediction mode of the current coding block among intra prediction modes in which the current coding block is available; And
And performing intra prediction based on the derived intra prediction mode to generate a prediction block of the current coding block,
The intra prediction mode in which the current coding block is available is divided into K groups,
The intra prediction mode of the current coding block is derived from any one of the K groups,
Where K is a natural number of 3 or more, computer-readable recording medium.

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