KR20210003005A - Video encoding and decoding method and apparatus using signal change correlation between cross components - Google Patents

Abstract

The present invention provides a method and device for encoding and decoding a video using a signal change correlation between cross-components to improve a coding efficiency of a video signal. The present invention suggests a motion information derivation method used for generating a MERGE/AMVP candidate list.

Description

A video encoding and decoding method and apparatus using the correlation of signal change between cross components{.}

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

Recently, the demand for multimedia data such as video is increasing rapidly on the Internet. However, it is difficult to keep up with the rapidly increasing amount of multimedia data at the rate of development of the bandwidth of the channel. Accordingly, ITU-T's VCEG (Video Coding Expert Group) and ISO/IEC's Moving Picture Expert Group (MPEG), an international standardization organization, revised version 1 of HEVC (High Efficiency Video Coding), a video compression standard, in February 2014. Established.

In HEVC, technologies such as intra prediction (or intra prediction), inter prediction (or inter prediction), transformation, quantization, entropy coding, and in-loop filter are defined.

The present invention is to improve the coding efficiency of a video signal.

The present invention proposes a motion information derivation method used when generating a MERGE/AMVP candidate list.

The video signal processing method and apparatus according to the present invention can improve video signal coding efficiency.

1 is a block diagram showing an image encoding apparatus.
2 is a block diagram illustrating an intra prediction unit of an image encoding apparatus.
3 is a block diagram illustrating an inter prediction unit of an image encoding apparatus.
4 is an example of a reference pixel line that can be used around a current block to describe intra prediction.
5 is an example for explaining an ISP mode in intra-screen prediction of a luminance component.
6 is an example in which block divisions of a luminance component and a color difference component are different from each other at the same position.
7 is an example for explaining an LM mode.
8 is a method of encoding prediction mode information.
9 is a block diagram showing an image decoding apparatus 900 according to the present invention.
10 illustrates an intra-screen prediction unit of an image decoding apparatus.
11 shows an inter prediction unit of an image decoding apparatus.
12 is a method of decoding prediction mode information.
13 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
14 is a flowchart illustrating an intra prediction process of a component 1 predictor and a component 2 predictor of an image encoding apparatus according to an embodiment of the present invention.
15 is an illustration showing component 1 and component 2 blocks according to an embodiment of the present invention.
16 is a block diagram showing an image decoding apparatus according to an embodiment of the present invention.
17 is a flowchart illustrating an intra prediction process of a component 1 predictor and a component 2 predictor of an image decoding apparatus according to an embodiment of the present invention.
18 is a method of encoding prediction mode information according to the present embodiment.
19 is a method of decoding prediction mode information according to the present embodiment.

1 is a block diagram showing an image encoding apparatus. Referring to FIG. 1, the image encoding apparatus 100 includes a block division unit S101, an intra prediction unit S102, an inter prediction unit S103, a subtraction unit S104, a transform unit S105, and a quantization unit. (S106), an entropy encoding unit (S107), an inverse quantization unit (S108), an inverse transform unit (S109), a multiplication unit (S110), a filter unit (S111), and a memory (S112).

RD-Cost (RateDistortion-Cost) is compared to select the optimal information in each device. RD-Cost refers to a cost value calculated using distortion information between the original block and the reconstructed block and the amount of bits generated during transmission of the prediction mode. In this case, sum of absolute difference (SAD), sum of absolute transformed difference (SATD), sum of square for error (SSE), and the like may be used to calculate the cost value.

Each of the components shown in FIG. 1 is independently shown to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is formed of separate hardware or a single software component. That is, each constituent part is listed and included as a constituent part for convenience of explanation, and at least two of the constituent parts are combined to form a single constituent part, or one constituent part is divided into a plurality of constituent parts to perform a function. Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention unless departing from the essence of the present invention.

In addition, some of the components are not essential components that perform essential functions in the present invention, but may be optional components only for improving performance. The present invention can be implemented by including only the components essential to implement the essence of the present invention excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance improvement Also included in the scope of the present invention.

The block dividing unit 100 may divide the input image into at least one block. In this case, the input image may have various shapes and sizes, such as a picture, a slice, a tile, a segment, and a CTU. A block may mean a coding unit (CU), a prediction unit (PU), or a transformation unit (TU). The division may be performed based on at least one of a quad tree, a binary tree, and a ternary tree. Quad tree is a method of dividing 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 whose width or height is half of the upper block. The ternary tree is a method in which an upper block is divided into three parts with either the width or the height of the upper block. Through the aforementioned division based on the binary tree and the ternary tree, the block may have a shape of not only a square but also an irregular shape.

The prediction units 102 and 103 may include an inter prediction unit 103 that performs inter prediction and an intra prediction unit 102 that performs intra prediction. It is possible to determine whether to use inter prediction or to perform intra prediction for the prediction unit, and determine specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. In this case, a processing unit in which prediction is performed may be different from a processing unit in which a prediction method and specific content are determined. For example, a prediction method and a prediction mode are determined in a prediction unit, and prediction may be performed in a transformation unit.

A residual value (residual block) between the generated prediction block and the original block may be input to the transform unit 105. Further, prediction mode information, motion vector information, etc. used for prediction may be encoded by the entropy encoder 107 together with a residual value and transmitted to a decoder. In the case of using a specific encoding mode, it is possible to encode an original block as it is and transmit it to a decoder without generating a prediction block through the prediction units 102 and 103.

The intra prediction unit 102 may generate a prediction block based on reference pixel information around the current block, which is pixel information in the current picture. When the prediction mode of the neighboring block of the current block on which intra prediction is to be performed is inter prediction, the reference pixel included in the adjacent block to which the inter prediction is applied will be replaced with a reference pixel in another block surrounding the intra prediction. I can. That is, when the reference pixel is not available, information on the reference pixel that is not available can 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 prediction is performed. A mode for predicting luminance information and a mode for predicting color difference information may be different, and in-screen prediction mode information or predicted luminance signal information used to predict luminance information may be used to predict chrominance information. .

The intra prediction unit 102 may include an AIS (Adaptive Intra Smoothing) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a filter that performs filtering on a reference pixel of the current block, and may adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter may not be applied.

When the intra prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value interpolated by a reference pixel, the reference pixel interpolation unit of the intra prediction unit 102 interpolates the reference pixel Reference pixels can be created. When 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 inter prediction unit 103 generates a prediction block by using the reconstructed reference image and motion information stored in the memory 112. The motion information may include, for example, a motion vector, a reference picture index, a list 1 prediction flag, and a list 0 prediction flag.

The inter prediction unit 103 may derive the prediction block based on information on at least one picture of a picture before or after a current picture. In addition, a prediction block of the current block may be derived based on information on a partial region of the current picture in which encoding is completed. The inter prediction unit 103 according to an embodiment of the present invention may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

The reference picture interpolation unit may receive reference picture information from the memory 112 and may generate pixel information of an integer number of pixels or less from the reference picture. In the case of a luminance pixel, a DCT-based interpolation filter with different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/4 pixels. In the case of a color difference signal, a DCT-based interpolation filter with 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. Various methods, such as a full search-based block matching algorithm (FBMA), three step search (TSS), and a new three-step search algorithm (NTS), can be used as a method for calculating a motion vector. 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 prediction block of the current block by differently predicting the motion. 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 subtraction unit S104 generates a residual block of the current block by subtracting the block to be currently encoded from the prediction block generated by the intra prediction unit S102 or the inter prediction unit S103. The generated residual block may be input to the transform unit S103 to be transformed.

The transform unit S105 may transform the residual block including the residual data using a transform method such as DCT, DST, or Karhunen Loeve Transform (KLT). In this case, the transformation method may be determined based on the intra prediction mode of the prediction unit used to generate the residual block. For example, depending on the intra prediction mode, DCT may be used in the horizontal direction and DST may be used in the vertical direction.

The quantization unit S106 may quantize values converted into the frequency domain by the transform unit S105. Quantization coefficients may vary depending on the block or the importance of the image. The value calculated by the quantization unit S106 may be provided to the inverse quantization unit S108 and the entropy encoding unit S107.

The transform unit S105 and/or the quantization unit S106 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 transformation nor quantization is performed in the image encoding apparatus S100, or both transformation and quantization are not performed, a block entering the input of the entropy encoder S107 is generally referred to as a transform block. The entropy encoding unit S107 entropy encodes the input data. Entropy coding may use various coding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The entropy encoder S107 includes various types of coefficient information, block type information, prediction mode information, division unit information, prediction unit information, transmission unit information, motion vector information, reference frame information, block interpolation information, filtering information, etc. Information can be encoded. The coefficients of the transform block may be encoded in units of sub-blocks within the transform block.

For encoding the coefficients of the transform block, Last_sig, a syntax element indicating the position of the first non-zero coefficient in the inverse scan order, Coded_sub_blk_flag, a flag indicating whether there is at least one non-zero coefficient in the subblock, Sig_coeff_flag, a flag indicating whether the coefficient is a non-zero coefficient, Abs_greater1_flag, a flag indicating whether the absolute value of the coefficient is greater than 1, Abs_greater2_flag, a flag indicating whether the absolute value of the coefficient is greater than 2, and Sign_flag, a flag indicating the sign of the coefficient. Syntax elements can be encoded. A residual value of a coefficient that is not coded with only the syntax elements may be coded through the syntax element remaining_coeff.

The inverse quantization unit S108 and the inverse transform unit S109 inverse quantize values quantized in the quantization unit S106 and inverse transform the values transformed in the transform unit S105. The residual values generated by the inverse quantization unit S108 and the inverse transform unit S109 are predicted through the motion estimation unit, the motion compensation unit, and the in-screen prediction unit S102 included in the prediction units S102 and 103. It can be combined with the prediction unit to generate a reconstructed block. The multiplier S110 generates a reconstructed block by multiplying the prediction block generated by the prediction units S102 and S103 and the residual block generated through the inverse transform unit S109.

The filter unit S111 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 the boundary between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply the deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When applying a deblocking filter 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, horizontal filtering and vertical filtering may be processed in parallel when performing vertical filtering and horizontal filtering.

The offset correction unit may correct an offset from the original image for the deblocking image in pixel units. In order to perform offset correction for a specific picture, the pixels included in the image are divided into a certain number of areas, and then the area to be offset is determined and the offset is applied to the area, or offset by considering the edge information of each pixel. You can use the method of applying.

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

The memory S112 may store the reconstructed block or picture calculated through the filter unit S111, and the stored reconstructed block or picture may be provided to the prediction units S102 and S103 when inter prediction is performed.

FIG. 2 is a block diagram illustrating an intra prediction unit of an image encoding apparatus, and FIG. 4 is an example of a current block and a reference pixel line that can be used around the screen to describe intra prediction.

After intra prediction (S201) is selected as the prediction mode of the current block, if the current block is a luminance component block, a luminance component reference pixel derivation and filtering process (S202) is performed, and if a color difference component block, a chrominance component reference pixel derivation and filtering ( S207) process is performed. The reference pixel is determined using reconstructed pixels around the current block. When some reconstructed pixels are not available or there are no reconstructed pixels around the current block, the available reference pixels may be padded in an unusable area, or padding may be performed with an intermediate value among a range of possible values of the pixels. After deriving all the reference pixels, filtering is performed using an AIS (Adaptive Intra Smoothing) filter.

Intra prediction of the luminance component is performed by comparing the prediction blocks generated according to the directional prediction modes (S205, S206) and the non-directional prediction modes (S203, S204) using the filtered reference pixels, and then the prediction block most similar to the original block. Find the optimal intra prediction mode that generated In S206, M represents the total number of prediction modes in the screen.

In FIG. 4, a 1st line is a reference pixel line adjacent to a current block, and a 2nd line, a 3rd line, and a 4th line are reference pixel lines separated by 2, 3, and 4 pixels from the current block, respectively. The reference pixel line determiner S208 generates prediction blocks for the optimal intra prediction mode by using reference pixel lines (2nd line, 3rd line, 4th line) that are not adjacent to the current block, and Find an optimal reference pixel line that produces a similar prediction block.

5 is an example for explaining an ISP mode in intra-screen prediction of a luminance component.

In the ISP mode, the current block is divided into N sub-blocks, and coding is performed for each sub-block. In this case, each sub-block uses the same intra prediction mode. The sub-block a generates a prediction block using the optimal intra prediction mode and the 1st reference pixel line of FIG. 4 and reconstructs the corresponding region through a reconstruction process. Thereafter, the transform block b uses the reconstructed pixel of the sub-block a as a reference pixel through a process of deriving and filtering a luminance component reference pixel (S202). A prediction block is generated by applying the same prediction mode as the subblock a to the generated reference pixel line.

In-screen prediction modes of the color difference components include DM(S214), LM(S211), LM-A(S212), and LM-L modes as well as directional prediction modes (S209 and S210) and non-directional prediction modes (S203 and S204). S213) exists.

6 is an example in which block divisions of a luminance component and a color difference component are different from each other at the same location.

In the DM mode (S214), the intra prediction mode of the luminance block existing at the same position as the current color difference block is used as the intra prediction mode of the current DM mode. In this case, when the block division of the chrominance component and the luminance component are different, the intra prediction mode of the luminance block having the same position as the center pixel of the current color difference block is used. For example, if the luminance component block at the same position as the color difference component block in Fig. 6 is divided into Blk1, Blk2, and Blk3, the intra prediction mode of the Blk3 block having the same position as the center pixel of the color difference component block is set to the color difference component. It is used as an intra prediction mode of a block.

In addition, if the DM mode (S214) overlaps with one of DC (S203), Planar (S204), Angular#50 (S209), and Angular#18 mode (S210), the overlapping mode is replaced with Angular#66 mode. do.

7 is an example for explaining an LM mode.

The LM, LM-A, and LM-L modes are modes for generating predictive blocks of chrominance components using the restored luminance component. After finding the luminance component restoration block having the same position as the current color difference component block, a prediction block is generated using Equation 1.

는 색차 성분 블록 주변 화소와 휘도 성분 블록 주변 화소를 이용하여 구한 파라미터이다. 파라미터를 유도하기 위해 LM 모드에서는 도 7의 그림과 같이 휘도 성분과 색차 성분에서 각각 현재 블록 상단에 가로 길이의 4분의 1, 4분의 3 위치에 존재하는 화소와 현재 블록 좌측에 세로 길이의 4분의 1, 4분의 3 위치에 존재하는 화소를 이용한다. 휘도 성분 화소 4개를 화소값의 크기에 따라 2개의 그룹으로 나누어 각각 평균을 내고, 색차 성분 화소 4개는 동일 위치의 휘도 성분 화소가 속한 그룹으로 나누어 평균을 낸 후, 수학식2, 수학식3을 이용하여 파라미터를 유도한다.The reconstructed block (x,y) refers to a reconstructed luminance component block down-sampled to fit the color difference component block size,

Is a parameter obtained using pixels around the color difference component block and pixels around the luminance component block. To derive the parameters, in the LM mode, as shown in Fig. 7, in the luminance component and the chrominance component, pixels existing at positions of 1/4 and 3/4 of the horizontal length at the top of the current block and the vertical length at the left of the current block, respectively. Pixels present in the quarter and three quarters are used. The four luminance component pixels are divided into two groups according to the size of the pixel value and averaged, and the four chrominance component pixels are divided into groups to which the luminance component pixels at the same location belong to the average, and then, Equation 2, Equation 2 Use 3 to derive the parameter.

In Equations 2 and 3, Xa denotes the average value of two small luminance component pixels, Xb denotes the average value of two large luminance component pixels, and Ya and Yb denote the average values of the luminance component and the chrominance component at the mapped position, respectively. it means.

The LM-A mode and the LM-L mode differ only in the pixel positions for finding α and β parameters, but the method of generating a prediction block is the same as in the LM mode. In the LM-A mode, α and β parameters are derived using only the pixels present at the top of the current block, and the LM-L mode derives the α and β parameters using only the pixels present at the left of the current block.

RD-Cost is compared for each intra prediction mode of the color difference component, and one intra prediction mode with the lowest cost value is selected.

3 is a block diagram showing in detail an inter prediction unit of an image encoding apparatus.

The inter prediction unit may be divided into a merge candidate search unit S302 and an AMVP candidate search unit S304 according to a method of inducing motion information. The merge candidate search unit S302 sets a reference block using inter prediction among blocks reconstructed around the current block as a merge candidate. Merge candidates are derived by the same method in the encoding/decoding apparatus, and the same number is used, and the number of merge candidates is transmitted from the encoding apparatus to the decoding apparatus. In this case, when it is not possible to set as many Megre candidates as the predetermined number of reference blocks restored around the current block, motion information of a block existing at the same position as the current block in a picture other than the current picture is obtained. Alternatively, a merge candidate is set by combining motion information in the past and future directions based on the current picture and filling them with candidates, or by setting a block at the same position of another reference picture as motion information.

The AMVP candidate search unit S304 determines motion information of the current block in the motion estimation unit S305. The motion estimation unit S305 finds a prediction block that is most similar to the current block among reconstructed pictures.

The inter prediction unit determines motion information of the current block using one of the merge candidate search unit and the AMVP candidate search unit, and then generates a prediction block through motion compensation (S306).

8 is a method of encoding prediction mode information.

The skip mode operation information encoding (S801) is information indicating whether the prediction mode information of the current block is used for inter prediction merge information, and whether the decoding apparatus uses the prediction block as a reconstructed block.

If the skip mode operates, the determined merge candidate index coding (S803) is performed, and if not, the prediction mode coding (S804) is performed.

Prediction mode encoding (S804) encodes whether the prediction mode of the current block is inter prediction and intra prediction. When the inter prediction mode is selected, the merge mode operation information is encoded (S806). If the merge mode operates (S807), merge candidate index encoding (S803) is performed. If the merge mode does not operate, prediction direction encoding is performed (S808). The prediction direction encoding (S808) indicates whether the direction of the reference picture to be used is in the past direction, the future direction, or both directions with respect to the current picture. When the prediction direction is past or bidirectional (S809), past direction reference picture index information is encoded (S810), past direction MVD information is encoded (S811), past direction MVP information is encoded (S812), and the prediction direction is future or bidirectional. In the case (S813), future direction reference picture index information encoding (S814), future direction MVD information encoding (S815), and future direction MVP information may be encoded (S816) to inform the inter prediction motion information of the current block. Information encoded in the inter prediction process is referred to as inter prediction unit mode information encoding (80).

When the prediction mode is an intra prediction mode, prediction information of luminance and color difference components is respectively encoded. The prediction information of the luminance component is subjected to Ref_idx encoding (S817). Ref_idx is information indicating the reference pixel line of the current block. When Ref_idx is greater than 0 (S818), MPM index encoding (S819) is performed, and when 0 (S818), ISP mode encoding (S820) is performed. When the ISP mode is true (S821), the ISP segmentation information is encoded to inform the direction of the current block, and then MPM index encoding (S819) is performed. If the ISP mode is false, the MPM operation information is encoded (S823). MPM motion information encoding is information indicating that the prediction mode information of the current block is not encoded and the same prediction mode information as the reconstructed block is used when the reconstructed blocks around the current block have the same prediction mode information as the current block. . When the MPM operation is performed (S824), the prediction mode of which reconstructed block is used as the prediction mode of the current block by performing MPM index encoding (S819), and when the MPM operation is not performed (S824), the residual prediction mode encoding is performed. Do (S825). In the residual prediction mode encoding, a prediction mode index used as a prediction mode of a current block is encoded among the remaining prediction modes by subtracting a prediction mode selected as an MPM candidate. Thereafter, color value prediction mode encoding is performed in order to encode the prediction information of the color difference component (S826). Information encoded in the intra prediction process is referred to as intra prediction mode information encoding (81).

Next, a video decoding apparatus according to the present invention will be described with reference to the drawings. 9 is a block diagram showing an image decoding apparatus 900 according to the present invention.

Referring to FIG. 9, the image decoding apparatus 900 includes an entropy decoding unit 901, an inverse quantization unit 902, an inverse transform unit 903, a multiplication unit 904, a filter unit 905, a memory 906, and It may include prediction units 907 and 908.

When the image bitstream generated by the image encoding apparatus 100 is input to the image decoding apparatus 500, the input bitstream may be decoded according to a process opposite to that performed by the image encoding apparatus 100. .

The entropy decoding unit 901 may perform entropy decoding in a procedure opposite to that performed by the entropy encoding unit 907 of the image encoding apparatus 100. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied in response to the method performed by the image encoder. The entropy decoding unit 201 may decode the syntax elements as described above, that is, Last_sig, Coded_sub_blk_flag, Sig_coeff_flag, Abs_greater1_flag, Abs_greater2_flag, Sign_flag and remaining_coeff. In addition, the entropy decoder 901 may decode information related to intra prediction and inter prediction performed by the image encoding apparatus 100.

The inverse quantization unit 902 generates a transform block by performing inverse quantization on the quantized transform block. It operates substantially the same as the inverse quantization unit 108 of FIG. 1.

The inverse transform unit 903 generates a residual block by performing inverse transform on the transform block. In this case, the transformation method may be determined based on information about a prediction method (inter prediction or intra prediction), a size and/or shape of a block, and an intra prediction mode. It operates substantially the same as the inverse transform unit 909 of FIG. 1.

The multiplication unit 904 generates a reconstructed block by multiplying the prediction block generated by the intra prediction unit 907 or the inter prediction unit 908 and the residual block generated through the inverse transform unit 903. It operates substantially the same as the multiplication unit 110 of FIG. 1.

The filter unit 905 reduces various types of noise generated in reconstructed blocks. In addition, it may include a deblocking filter, an offset correction unit, and an ALF.

Information on whether a deblocking filter is applied to a corresponding block or picture, and when a deblocking filter is applied, information on whether a strong filter or a weak filter is applied may be provided from the image encoding apparatus 100. The deblocking filter of the image decoding apparatus 900 may receive information related to the deblocking filter provided from the image encoding apparatus 100, and the image decoding apparatus 900 may perform deblocking filtering on a corresponding block.

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

The ALF may be applied to a coding unit based on information on whether to apply ALF and information on ALF coefficients provided from the image encoding apparatus 100. Such ALF information may be provided by being included in a specific parameter set. The filter unit 505 operates substantially the same as the filter unit 111 of FIG. 1.

The memory 906 stores the reconstructed block generated by the multiplication unit 904. It operates substantially the same as the memory 112 of FIG. 1.

10 and 11 illustrate an intra prediction unit and an inter prediction unit of an image decoding apparatus.

In the intra prediction unit 1000, only the process of determining the optimal prediction mode of FIG. 2 is omitted, and the process of generating the prediction block by receiving the prediction mode determined to be optimal is substantially the same as that of the intra prediction unit of the video encoding apparatus. Works well.

The inter prediction unit 1100 only skips the process of determining the optimal prediction mode in FIG. 3, and the process of generating a prediction block by receiving the prediction mode determined to be optimal is substantially the same as that of the inter prediction unit of the video encoding apparatus. Works well.

12 is a method of decoding prediction mode information. It operates substantially the same as the method of encoding prediction mode information of FIG. 8.

(Example 1)

In the present embodiment, a method of generating a second component prediction block using component 1 reconstruction information and component 1 prediction information will be described. Here, component 1 may be a luminance component and component 2 may be a color difference component. Alternatively, component 1 may be a color difference component and component 2 may be a luminance component. Alternatively, other components of the image may be included as components 1 and 2. In this case, the components 1 and 2 may be different or the same component.

13 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention. Referring to FIG. 13, an image encoding apparatus 1300 includes a block division unit S301, a subtraction unit S1304, a transform unit S1305, a quantization unit S1306, an entropy encoding unit S1307, and an inverse quantization unit S1308. ), an inverse transform unit S1309, a multiplication unit S1310, a filter unit S1311, and a memory S1312. Each component performs the same role as the component of FIG. 1. The component 1 and component 2 are stored in the component 1 memory and component 2 memory, respectively, and the component 1 and component 2 predictors each store the 1st component prediction and 2nd component screen. Do my predictions

14 is a flowchart illustrating an intra prediction process of a component 1 predictor and a component 2 predictor of an image encoding apparatus according to an embodiment of the present invention.

After intra prediction (S1401) is selected as the prediction mode of the current block, if the current block is a component block 1, the process of deriving and filtering component 1 reference pixels (S1402) is performed, and if the current block is component 2, the component reference pixel 2 Derivation and filtering (S1407) is performed. The reference pixel is determined using reconstructed pixels around the current block. When some reconstructed pixels are not available or there are no reconstructed pixels around the current block, the available reference pixels may be padded in an unusable area, or padding may be performed with an intermediate value among a range of possible values of the pixels. After deriving all the reference pixels, filtering is performed using an AIS (Adaptive Intra Smoothing) filter.

Intra prediction of component 1 is performed by comparing prediction blocks generated according to directional prediction modes (S1405, S1406) and non-directional prediction modes (S1403, S1404) using filtered reference pixels, and then predicts the most similar to the original block. The optimal intra prediction mode that generated the block is found.

The reference pixel line determiner S1408 generates prediction blocks for the prediction mode using reference pixel lines that are not adjacent to the current block (2nd line, 3rd line, and 4th line in FIG. 4), and then generates the prediction blocks that are most similar to the original block. An optimal reference pixel line that generates a prediction block is found.

In the ISP mode, the current block is divided into N sub-blocks, and coding is performed for each sub-block. In this case, each sub-block uses the same intra prediction mode. The sub-block a generates a prediction block using the optimal intra prediction mode and the 1st reference pixel line of FIG. 4 and reconstructs the corresponding region through a reconstruction process. Thereafter, the transform block b uses the reconstructed pixel of the sub-block a as a reference pixel through a process of deriving and filtering a color difference component reference pixel (S1402). A prediction block is generated by applying the same prediction mode as the subblock a to the generated reference pixel line.

In-screen prediction modes of component 2 are directional prediction modes (S1409, S1410), non-directional prediction modes (S1403, S1404), as well as DM (S1414), LM (S1411), LM-A (S1412), and LM-L modes. (S1413) exists.

In the DM mode (S1414), the intra prediction mode of block 1 existing at the same position as the current secondary block is used as the intra prediction mode of the current DM mode. In this case, if the block divisions of the first component and the second component are different, the intra prediction mode of the first block having the same position as the center pixel of the current block 2 is used. For example, if the luminance (No. 1) component block at the same position as the color difference (No. 2) component block in Fig. 6 is divided into Blk1, Blk2, and Blk3, the same position as the center pixel of the color difference (No. 2) component block The intra prediction mode of the Blk3 block having the luminance (No. 1) component is used as the intra prediction mode of the color difference (No. 2) component block.

In addition, if the DM mode (S1414) overlaps with one of DC (S1403), Planar (S1404), Angular#50 (S1409), and Angular#18 mode (S1410), the overlapping mode is replaced with Angular#66 mode. do.

The LM, LM-A, and LM-L modes are modes for generating a prediction block of component 2 by using the reconstructed component 1. After finding the first component reconstructed block having the same position as the current luminance component block, a prediction block is generated using Equation 1.

The reconstructed block (x,y) refers to the reconstructed component block 2 obtained by up/down sampling according to the size of the component block 2, and α and β are the pixels around the component block 1 and the pixels around the component block 2. This is the calculated parameter. To derive the parameters, in the LM mode, as shown in the figure of Fig. 7, in the 1st and 2nd components, the pixels existing at the top of the current block and at the positions of 1/4 and 3/4 of the horizontal length and the vertical on the left of the current block, respectively. Use pixels that exist at positions 1/4 and 3/4 of the length. Divide the 4 pixels of the 1st component into 2 groups according to the size of the pixel value, and average them, and the 4 of the 2nd component pixels are divided by the group to which the 1st component pixel belongs to the same location and average them, and then Equation 2 , The parameter is derived using Equation 3.

In Equations 2 and 3, Xa denotes the average value of two pixels of the first component having a small size, Xb denotes the average value of two pixels of the first component having a large size, and Ya and Yb denotes the second component of the mapped position with the first component. Means the average value of the components.

The LM-A mode and the LM-L mode differ only in the pixel positions for finding α and β parameters, but the method of generating a prediction block is the same as in the LM mode. In the LM-A mode, α and β parameters are derived using only the pixels present at the top of the current block, and the LM-L mode derives the α and β parameters using only the pixels present at the left of the current block.

15 is an illustration showing component 1 and component 2 blocks according to an embodiment of the present invention.

In the process of performing the intra prediction of the second component, after generating the second component prediction block using the intra prediction mode of the second component, the prediction block modifying unit S1415 may correct the prediction block. A region of FIG. 15 denotes a region in which some predicted pixel values are corrected in the second component prediction block and a first component region used for correction. This is called a correction area. The component 1 reconstructed block at the same position as the current component block 2 to be encoded is obtained, and a prediction block using an optimal component 1 prediction mode is generated. Thereafter, M prediction blocks using M prediction modes are generated for only the modified area of the prediction block, and the RD-Cost between the reconstructed block of the luminance component and the M prediction blocks is compared to determine the optimal luminance component modified area. The intra prediction mode is used as the intra prediction mode of the color difference component correction area. In this case, the RD-Cost comparison may be performed by comparing the reconstructed block of the first component and the corrected prediction block of the first component, or the correction region of the reconstructed block and the correction region of the prediction block may be compared. In addition, after comparing the correction region of the reconstructed block with the correction region of the prediction block, the reconstructed block and the modified prediction block may be compared. For example, the correction region of the reconstructed block and the correction region of the prediction block may be compared by SSE, and the reconstructed block and the modified prediction block may be compared by SATD. The RD-cost comparison method between the reconstructed block and the prediction block may be performed in the same manner as a preset method in the encoding/decoding apparatus or may be transmitted in an upper header.

In this case, the size and shape of the correction area may be set to only the lower right area, the lower area, and the right area, as in the example of area A of FIG. 15, or may be set to the entire block area. In addition, it can be set in various ways, such as a quarter area at the bottom right and a 3/4 area. Alternatively, the correction area may be set differently according to the prediction mode in the screen. For example, when the current intra prediction mode is in the vertical direction, the corrected area is set to the lower area, and when the current intra prediction mode is in the horizontal direction, the corrected area is set to the right area, and In this case, the correction area may be set as the lower right area. Alternatively, you can divide the area according to the ISP mode without separately setting the modified area. In the encoding/decoding apparatus, the size and shape of the correction region may be used in the same manner by a preset method or may be transmitted from an upper header.

Also, the modified region may be divided into sub-block units. For each sub-block, M prediction blocks of component 1 and reconstructed blocks may be compared, and the selected optimal prediction mode may be used as a prediction mode of component 2. Also, as in the example of FIG. 4, an optimal modified prediction block may be found using a different reference pixel line for each sub-block. For example, 0 is selected as the intra prediction mode of the current color difference component, and in FIG. 15, sub-block A-1 is 2, sub-block A-2 is 4, sub-block A-3 is 6, and A The -4 subblock can use the 3rd prediction mode. Also, the shape and size of the sub-block can be set differently according to the shape of the correction area. For example, the lower right A region of FIG. 15 may have a sub-block in the form of a quad tree, and in the case of the lower A region and the right A region, the sub-block may have a binary tree form. Alternatively, they may have sub-blocks of the same shape regardless of the shape and size of the correction region, and may be used in the same manner by a preset method in the encoding/decoding apparatus or transmitted from an upper header.

In the present embodiment, for convenience of explanation, the process of finding the optimal prediction mode of the correction region is performed for all the prediction modes in the component 2 screen, but it is also possible to perform the process only in a specific intra prediction mode. For example, only when the intra prediction mode of the current component 2 is the DM mode, the process of finding the prediction mode of the correction region may be performed.

In addition, it is possible to perform a process of finding the optimal prediction mode only for some modes, not M modes, of the optimal prediction mode of the correction region. For example, when the prediction mode in the current screen is the PLANAR mode, the prediction mode of the correction region may be performed only for the DC mode. In addition, when the prediction mode in the current screen is the directional prediction mode, only prediction modes with a current prediction mode index of +, -2 may be performed. In addition, in the LM-related mode, a modified prediction block can be found using the modified region. The number and type of intra prediction modes to be applied to the correction region may be equally applied by using a preset method in the encoding/decoding apparatus or may be transmitted in units of higher headers or blocks.

16 is a block diagram illustrating a video decoding apparatus according to an embodiment of the present invention. Referring to FIG. 16, the image decoding apparatus 1600 is shown. Each component performs the same role as the component of FIG. 9. The component 1 and component 2 are stored in the component 1 memory and component 2 memory, respectively, and the component 1 and component 2 predictors each store the 1st component prediction and 2nd component screen. Do my predictions

17 is a flowchart illustrating an intra prediction process of a component 1 predictor and a component 2 predictor of an image decoding apparatus according to an embodiment of the present invention.

In the intra prediction of the decoding device, after finding the optimal component 1 prediction mode in the same manner as the intra prediction of FIG. 10, the corrected region is the same as the encoding device only for the optimal component 2 prediction mode transmitted from the encoding device. A process of finding the optimal prediction mode of is performed using the reconstruction information of component 1 and M pieces of prediction information.

Using FIGS. 8 and 12, prediction mode information is encoded and decoded.

When the prediction mode is an intra prediction mode, prediction information of components 1 and 2 is encoded/decoded, respectively. The prediction information of the second component is Ref_idx encoded/decoded (S817/S1217). Ref_idx is information indicating the reference pixel line of the current block. When Ref_idx is greater than 0, MPM index encoding/decoding is performed (S819/S1219), and when it is 0, ISP mode encoding/decoding is performed (S820/S1220). If the ISP mode is true (S821/S1221), the ISP segmentation information is encoded/decoded (S822/S1222) to indicate the direction of the current block and then MPM index encoding/decoding is performed (S819/S1219), and the ISP mode is false. In case (S821/S1221), MPM motion information is encoded/decoded (S823/S1223). MPM motion information encoding/decoding is a reminder to use the same prediction mode information as the reconstructed block without encoding the prediction mode information of the current block when the reconstructed blocks around the current block have the same prediction mode information as the current block. Information. When the MPM operation is performed (S824/S1224), the MPM index encoding/decoding (S819/S1219) is performed to inform which prediction mode of the reconstructed block is used as the prediction mode of the current block, and when the MPM operation is not performed (S824/ S1224), encoding/decoding of the residual prediction mode is performed (S825/S1225). The residual prediction mode encoding encodes/decodes a prediction mode index used as a prediction mode of the current block among the remaining prediction modes by subtracting the prediction mode selected as an MPM candidate. After that, in order to encode the prediction information of the second component, the second component prediction mode is encoded/decoded (S826/S1226).

Alternatively, in the present embodiment, the first coding order may be selected from the first component and the second component.

18 and 19 are methods of encoding and decoding prediction mode information according to the present embodiment. First, information indicating a component to be encoded/decoded first among components 1 and 2 is transmitted in the process of selecting a component to be encoded/decoded and the encoding/decoding process (S1827/S1927), and the remaining processes are the processes of FIGS. Perform the same process as

Alternatively, in the present embodiment, the intra prediction mode of the first component and the second component may be simultaneously performed. In the process of searching for an optimal intra prediction mode, intra prediction may be performed by simultaneously considering the component prediction block 1 and the component prediction block 2.

Claims (1)

A video encoding method using signal change correlation between cross components.

Images