KR101671934B1 - Method and apparatus for decoding an image - Google Patents

Abstract

A method and an apparatus for determining an intra prediction mode of an image encoding unit are disclosed. Candidate intra prediction modes of a chrominance block including an intra prediction mode of a block of luminance components are determined and the intra prediction mode of the chrominance block having the minimum cost is determined by comparing the cost of the chrominance block according to the candidate intra prediction modes.

Description

[0001] The present invention relates to a video decoding method and apparatus,

More particularly, the present invention relates to a method and apparatus for coding and decoding an image, which performs intraprediction on a video encoding unit of a chrominance component by applying an intra prediction mode determined for a video encoding unit of a luminance component And apparatus.

In an image compression method such as MPEG-1, MPEG-2, MPEG-4, and H.264 / MPEG-4 Advanced Video Coding (AVC), one picture is divided into macroblocks to encode an image. Then, each macroblock is encoded in all coding modes available for inter prediction and intra prediction, and then an encoding mode is selected according to the bit rate required for encoding the macroblock and the degree of distortion between the original macroblock and the decoded macroblock. And the macro block is encoded.

Background of the Invention [0002] As the development and dissemination of hardware capable of playing back and storing high-resolution or high-definition video content increases the need for video codecs to effectively encode or decode high-definition or high-definition video content. According to the existing video codec, video is encoded according to a limited prediction mode based on a macroblock of a predetermined size.

The present invention relates to a method for determining an intra prediction mode of a luminance component image encoding unit having various directions based on hierarchical encoding units of various sizes and a method for determining a color component Image coding that performs intra prediction on a component encoding unit. A decoding method and apparatus are provided.

According to an embodiment of the present invention, there is provided a method of decoding an image, the method comprising: obtaining first information indicating a intra-prediction mode of a luminance block from a bitstream; Obtaining second information from the bitstream indicating an intra prediction mode of a chrominance block corresponding to the luminance block; Performing intra prediction on the luminance block based on an intra prediction mode of the luminance block; And performing intra prediction on the color difference block based on an intra prediction mode of the color difference block, wherein the intra prediction mode of the luminance block includes a specific direction among a plurality of directions, (Dx is an integer) and dy in a vertical direction (dy is an integer), wherein performing the intra prediction on the luminance block comprises: determining a position of the current pixel based on the position of the current pixel, Determining a number of peripheral pixels located on the left side or the upper side of the luminance block according to a specific direction indicated by the intra prediction mode of the luminance block; Obtaining a predicted value of a current pixel based on one surrounding pixel when the number of neighboring pixels is determined to be one; And obtaining a predicted value of the current pixel based on a weighted average value of two neighboring pixels when the number of neighboring pixels is determined to be two, wherein the weighted average value includes at least one of dx and dy, Wherein the step of performing intra prediction on the color difference block uses a weight determined based on the position of the luminance block and the intra prediction mode of the luminance block based on the second information, Prediction mode of the chrominance block, and when the second information indicates that the intra prediction mode of the chrominance block is the same as the intra-prediction mode of the luminance block, It is determined in the same manner as in the prediction mode.

An image decoding apparatus according to an embodiment of the present invention includes an entropy decoding unit for obtaining first information indicating an intra prediction mode of a luminance block and second information indicating an intra prediction mode of a chrominance block corresponding to the luminance block; And an intra prediction unit performing intra prediction on the luminance block based on an intra prediction mode of the luminance block and performing intra prediction on the color difference block based on an intra prediction mode of the color difference block, The intraprediction mode of the luminance block includes a specific direction among a plurality of directions, and the specific direction is indicated by at least one of dx in the horizontal direction (dx is an integer) and dy in the vertical direction (dy is an integer) The intra prediction performing unit determines the number of surrounding pixels located on the left side or the upper side of the luminance block according to the position of the current pixel and the specific direction indicated by the intra prediction mode of the luminance block based on the first information, Acquires a predicted value of a current pixel based on one surrounding pixel when the number is determined to be one, A horizontal mode, a vertical mode, and a luminance block of the luminance block, based on the second information, based on the weighted average value of the two surrounding pixels when the number of surrounding pixels is determined to be two, Prediction mode of the chrominance block among the plurality of intra-prediction modes including the intra-prediction mode, and when the second information indicates that the intra-prediction mode of the luminance block is the same, Prediction mode of the luminance block, and the weighted average value is obtained using a weight determined based on at least one of dx and dy and the position of the current pixel.

According to embodiments of the present invention, by adding an intra prediction mode determined for a luminance component image encoding unit having various directions as an intra prediction mode for a chrominance component image encoding unit, prediction efficiency of a chrominance component image can be improved without increasing a calculation amount And improve the prediction efficiency of the overall image.

1 is a block diagram of an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram of an image decoding apparatus according to an embodiment of the present invention.
FIG. 3 illustrates a hierarchical encoding unit according to an embodiment of the present invention.
4 is a block diagram of an image encoding unit based on an encoding unit according to an embodiment of the present invention.
5 is a block diagram of an image decoding unit based on an encoding unit according to an embodiment of the present invention.
FIG. 6 illustrates a depth-based coding unit and a prediction unit according to an embodiment of the present invention.
FIG. 7 shows a relationship between an encoding unit and a conversion unit according to an embodiment of the present invention.
FIG. 8 illustrates depth-specific encoding information, in accordance with an embodiment of the present invention.
FIG. 9 shows a depth encoding unit according to an embodiment of the present invention.
FIGS. 10A and 10B show a relationship between an encoding unit, a prediction unit, and a frequency conversion unit according to an embodiment of the present invention.
FIG. 11 shows encoding information for each encoding unit according to an embodiment of the present invention.
12A to 12C show a format of a luminance component and a chrominance component image according to an embodiment of the present invention.
13 shows the number of intra prediction modes according to the size of a coding unit of a luminance component image according to an exemplary embodiment of the present invention.
14A to 14C are views for explaining an example of an intra prediction mode applied to a luminance component encoding unit of a predetermined size according to an embodiment of the present invention.
15 is a view for explaining another example of an intra prediction mode applied to a luminance component encoding unit of a predetermined size according to an embodiment of the present invention.
16 is a reference diagram for explaining intra prediction modes of a luminance component encoding unit having various directions according to an embodiment of the present invention.
17 is a reference diagram for explaining a bilinear mode according to an embodiment of the present invention.
18 is a diagram for explaining a process of generating a prediction value of an intra prediction mode of a current luminance component encoding unit according to an embodiment of the present invention.
19 is a reference diagram for explaining a process of mapping an intra prediction mode between luminance component encoding units having different sizes according to an embodiment of the present invention.
20 is a reference diagram for explaining a process of mapping intra-prediction modes of the surrounding luminance component encoding unit to one of the representative intra-prediction modes according to an embodiment of the present invention.
21 is a diagram for explaining an example of a candidate intra prediction mode applied to a chrominance component encoding unit according to an embodiment of the present invention.
22 is a block diagram illustrating an apparatus for intra prediction of an image according to an embodiment of the present invention.
23 is a flowchart illustrating a method of determining an intra prediction mode of an image encoding unit according to an embodiment of the present invention.
23 is a flowchart illustrating a method of determining an intra prediction mode of a video decoding unit according to an embodiment of the present invention.

Hereinafter, an image encoding apparatus, an image decoding apparatus, an image encoding method, and an image decoding method according to preferred embodiments of the present invention will be described with reference to the accompanying drawings.

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

1, an image encoding apparatus 100 according to an exemplary embodiment of the present invention includes a maximum encoding unit division unit 110, an encoding depth determination unit 120, an image data encoding unit 130, (140).

The maximum coding unit division unit 110 divides the current picture or the current slice based on the maximum coding unit which is the coding unit of the maximum size. The current picture or current slice is divided into at least one maximum encoding unit. The divided image data may be output to the coding depth determination unit 120 for each of at least one maximum coding unit.

According to an embodiment of the present invention, an encoding unit can be expressed using a maximum encoding unit and a depth. The maximum coding unit indicates the largest coding unit among the coding units of the current picture, and the depth indicates the size of the sub-coding unit in which the coding unit is hierarchically reduced. As the depth increases, the encoding unit can be reduced from the maximum encoding unit to the minimum encoding unit, the depth of the maximum encoding unit can be defined as the minimum depth, and the depth of the minimum encoding unit can be defined as the maximum depth. As the depth of the maximum encoding unit increases, the size of the depth-dependent encoding unit decreases. Therefore, the sub-encoding unit of k depth may include a plurality of sub-encoding units having a depth of k + 1 or more.

As described above, according to the maximum size of an encoding unit, the image data of the current picture is divided into a maximum encoding unit, and each maximum encoding unit may include encoding units reduced by depth. Since the maximum encoding unit according to an embodiment of the present invention is reduced by depth, image data of a spatial domain included in the maximum encoding unit can be hierarchically classified according to depth.

The maximum depth for limiting the total number of times the height and width of the current encoding unit are hierarchically reduced from the maximum encoding unit to the highest encoding unit and the maximum size of the encoding unit may be preset. The maximum encoding unit and the maximum depth may be set in units of pictures or slices. That is, each picture or slice may have a different maximum coding unit and maximum depth, and the minimum coding unit size included in the maximum image coding unit may be variably set according to the maximum depth. By setting the maximum coding unit and the maximum depth for each picture or slice in this manner, it is possible to improve the compression ratio by coding the image of the flat area using a larger maximum coding unit, and the image with a large complexity can be encoded The compression efficiency of the image can be improved by using the unit.

The encoding depth determination unit 120 determines a maximum depth that is different for each maximum encoding unit. The maximum depth may be determined based on the Rate-Distortion Cost calculation. The determined maximum depth is output to the encoding information encoding unit 140, and the image data for each maximum encoding unit is output to the image data encoding unit 130.

The image data in the maximum encoding unit is encoded based on the depth encoding unit according to at least one depth below the maximum depth, and the encoding results based on the respective depth encoding units are compared. As a result of the comparison of the encoding error of the depth-dependent encoding unit, the depth with the smallest encoding error can be selected. At least one coding depth may be determined for each maximum coding unit.

As the depth of the maximum coding unit increases, the coding unit is hierarchically divided and reduced, and the number of coding units increases. In addition, even if encoding units of the same depth included in one maximum encoding unit, the encoding error of each data is measured and it is determined whether or not the encoding units are reduced to a higher depth. Therefore, even if the data included in one maximum coding unit has a different coding error according to the position, the coding depth can be determined depending on the position. In other words, the maximum encoding unit may be divided into sub-encoding units of different sizes according to different depths. One or more encoding depths may be set for one maximum encoding unit, and data of the maximum encoding unit may be set to one or more encoding depths As shown in FIG.

Further, the sub-encoding units of different sizes included in the maximum encoding unit can be predicted or frequency-converted based on the processing units of different sizes. In other words, the image encoding apparatus 100 can perform a plurality of processing steps for image encoding based on various sizes and processing units of various types. In order to encode video data, processing steps such as prediction, frequency conversion, and entropy encoding are performed. Processing units of the same size may be used in all stages, and processing units of different sizes may be used in each step.

For example, in order to predict a coding unit, the image coding apparatus 100 may select a coding unit and a different processing unit. For example, when the size of the encoding unit is 2Nx2N (where N is a positive integer), the processing unit for prediction may be 2Nx2N, 2NxN, Nx2N, NxN, and the like. In other words, motion prediction may be performed based on a processing unit of a type that halves at least one of a height or a width of an encoding unit. Hereinafter, a data unit serving as a basis of prediction is referred to as a 'prediction unit'.

The prediction mode may be at least one of an intra mode, an inter mode, and a skip mode, and the specific prediction mode may be performed only for a prediction unit of a specific size or type. For example, the intra mode can be performed only for a 2Nx2N, NxN sized prediction unit, which is a square. In addition, the skip mode can be performed only for a prediction unit of 2Nx2N size. If there are a plurality of prediction units in an encoding unit, a prediction mode having the smallest coding error can be selected by performing prediction for each prediction unit.

Also, the image encoding apparatus 100 can frequency-convert image data based on a processing unit having a different size from the encoding unit. The frequency conversion may be performed based on a data unit having a size smaller than or equal to the encoding unit for frequency conversion of the encoding unit. Hereinafter, a processing unit serving as a basis of frequency conversion is referred to as a 'conversion unit'.

The coding depth determiner 120 measures the coding error of each depth coding unit using a Lagrangian Multiplier based Rate-Distortion Optimization technique and calculates the maximum coding unit having the optimal coding error Can be determined. In other words, the coding depth determiner 120 can determine which type of the maximum coding unit is divided into a plurality of sub-coding units, wherein the plurality of sub-coding units have different sizes depending on the depth.

The image data encoding unit 130 encodes the image data of the maximum encoding unit based on at least one encoding depth determined by the encoding depth determination unit 120 and outputs the bit stream. Since the encoding depth determination unit 120 has already performed the encoding process for measuring the minimum encoding error, the encoded data stream may be output using the encoding process.

The encoding information encoding unit 140 encodes information on the depth encoding mode for each maximum encoding unit based on at least one encoding depth determined by the encoding depth determining unit 120 and outputs a bit stream. The information on the depth-dependent coding mode may include coding depth information, division type information of a prediction unit of a coding unit of coding depth, prediction mode information per prediction unit, size information of a conversion unit, and the like.

The encoding depth information may be defined using depth reduction information indicating whether or not encoding is performed in a high-depth encoding unit without encoding at the current depth. If the current depth of the current encoding unit is the encoding depth, the current encoding unit is encoded in the current depth encoding unit, so that the reduction information of the current depth can be defined not to be further reduced to the higher depth. Conversely, if the current depth of the current encoding unit is not the encoding depth, encoding using the higher-depth encoding unit should be attempted, so that the current depth reduction information can be defined to be reduced to higher-depth encoding units.

If the current depth is not the depth of the encoding, encoding is performed for the lower-depth encoding unit. Since at least one coding unit of higher depth is present in the coding unit of the current depth, the coding is repeatedly performed for each coding unit of the higher depth so that recursive coding can be performed for each coding unit of the same depth.

At least one coding depth is determined in one maximum coding unit and at least one coding mode information is determined for each coding depth so that information on at least one coding mode can be determined for one maximum coding unit. In addition, since the data of the maximum encoding unit is hierarchically divided according to the depth and the depth of encoding may be different for each position, information on the encoding depth and the encoding mode can be set for the data.

Therefore, the encoding information encoding unit 140 according to the embodiment can set the encoding information for each minimum encoding unit included in the maximum encoding unit. That is, the coding unit of the coding depth includes at least one minimum coding unit that holds the same coding information. By using this, if the neighboring minimum encoding units have the same depth encoding information, it can be the minimum encoding unit included in the same maximum encoding unit.

According to the simplest embodiment of the image encoding apparatus 100, the depth-of-coded unit is a unit of a size which is halved in height and width of a single-layer low-depth encoding unit. That is, if the size of the encoding unit of the current depth (k) is 2Nx2N, the size of the encoding unit of the higher depth (k + 1) is NxN. Therefore, the current coding unit of 2Nx2N size can include up to 4 upper depth coding units of NxN size.

Therefore, the image decoding apparatus 100 according to an exemplary embodiment can determine an optimum shape division type for each maximum encoding unit based on the size and the maximum depth of the maximum encoding unit determined in consideration of the characteristics of the current picture. In addition, since each encoding unit can be encoded by various prediction modes, frequency conversion methods, and the like, an optimal encoding mode can be determined in consideration of image characteristics of encoding units of various image sizes.

If an image having a very high image resolution or a very large data amount is encoded in units of a conventional 16x16 macroblock, the number of macroblocks per picture becomes excessively large. This increases the amount of compression information generated for each macroblock, so that the burden of transmission of compressed information increases and the data compression efficiency tends to decrease. Therefore, the image encoding apparatus according to the embodiment of the present invention can increase the maximum size of the encoding unit in consideration of the image size, and adjust the encoding unit in consideration of the image characteristic, so that the image compression efficiency can be increased .

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

2, an image decoding apparatus 200 according to an exemplary embodiment of the present invention includes an image data obtaining unit 210, an encoding information extracting unit 220, and an image data decoding unit 230.

The image-related data acquisition unit 210 parses the bit string received by the image decoding apparatus 200, acquires image data for each maximum encoding unit, and outputs the image data to the image data decoding unit 230. The image-related data obtaining unit 210 may extract information on the maximum encoding unit of the current picture or slice from the header of the current picture or slice. The image decoding apparatus 200 according to an embodiment of the present invention decodes image data in units of a maximum encoding unit.

The encoding information extracting unit 220 parses the bit stream received by the video decoding apparatus 200 and extracts information on the encoding depth and the encoding mode for each maximum encoding unit from the header of the current picture. The information on the extracted coding depth and coding mode is output to the image data decoding unit 230.

Information on the coding depth and the coding mode per coding unit may be set for one or more coding depth information, and the information on the coding mode according to the coding depth includes information on division type information, prediction mode information, Size information of the conversion unit, and the like. In addition, reduction information for each depth may be extracted as the encoding depth information.

The information on the division type of the maximum encoding unit may include information on sub-encoding units of different sizes according to the depth included in the maximum encoding unit, the information on the encoding mode may include information on a prediction unit for each sub- Information on the prediction mode, information on the conversion unit, and the like.

The image data decoding unit 230 decodes the image data of each maximum encoding unit based on the information extracted by the encoding information extracting unit to restore the current picture. The image data decoding unit 230 can decode the sub-encoding unit included in the maximum encoding unit based on the information on the division type of the maximum encoding unit. The decoding process may include a motion prediction process including intra prediction and motion compensation, and an inverse frequency conversion process.

The image data decoding unit 230 decodes the image data of each maximum encoding unit based on the information on the encoding depth and the encoding mode for each maximum encoding unit to reconstruct the current picture. The image data decoding unit 230 can decode the image data for each coding unit of at least one coding depth based on the coding depth information for each coding unit. The decoding process may include a prediction process including intra prediction and motion compensation and an inverse process.

The image data decoding unit 230 performs intra prediction or motion prediction in each prediction unit and prediction mode for each coding unit on the basis of the division type information and the prediction mode information of the prediction unit of the coding unit for each coding depth, Compensation can be performed. In addition, the image data decoding unit 230 may perform inverse conversion on each conversion unit for each encoding unit, based on the size information of the conversion unit of the encoding unit by encoding depth, for inverse conversion for each maximum encoding unit.

The image data decoding unit 230 can determine the coding depth of the current maximum encoding unit using the depth-dependent reduction information. If the reduced information indicates that the current depth is to be decoded, the current depth is the depth of the encoding. Accordingly, the image data decoding unit 230 can decode the current depth encoding unit for the current image data of the maximum encoding unit using the division type, the prediction mode, and the conversion unit size information of the prediction unit. That is, it is possible to observe the coding information set for the minimum coding unit, and collect the minimum coding units holding the coding information including the same reduction information, and decode them into one data unit.

The image decoding apparatus 200 according to an exemplary embodiment recursively performs encoding for each maximum encoding unit in the encoding process to obtain information on the encoding unit that has generated the minimum encoding error and can use it for decoding the current picture have. That is, it is possible to decode video data in the optimal encoding unit for each maximum encoding unit. Accordingly, even if an image with a high resolution or an excessively large amount of data is used, the information on the optimal encoding mode transmitted from the encoding end is used, and the image data is efficiently encoded according to the encoding unit size and encoding mode, Can be decoded and restored.

FIG. 3 illustrates a hierarchical encoding unit according to an embodiment of the present invention.

Referring to FIG. 3, the hierarchical coding unit according to the present invention may include 32x32, 16x16, 8x8, and 4x4 from a coding unit having a width x height of 64x64. In addition to the square-shaped encoding units, there may be encoding units whose width x height is 64x32, 32x64, 32x16, 16x32, 16x8, 8x16, 8x4, 4x8.

3, the resolution is set to 1920 x 1080, the size of the maximum encoding unit is set to 64, and the maximum depth is set to 2 for the video data 310. For the video data 320, the resolution is set to 1920 x 1080, the maximum size of the encoding unit is set to 64, and the maximum depth is set to 4. [ For the video data 330, the resolution is set to 352 x 288, the maximum size of the encoding unit is set to 16, and the maximum depth is set to 2.

It is desirable that the maximum size of the encoding size is relatively large in order to accurately reflect not only the compression ratio but also the image characteristic when the resolution is high or the data amount is large. Therefore, the maximum size of the video data 310 and 320 having the higher resolution than the video data 330 can be selected to be 64. FIG.

The maximum depth indicates the total number of layers in the hierarchical encoding unit. Accordingly, since the maximum depth of the video data 310 is 2, the encoding unit 315 of the video data 310 is encoded in units of 32, 16, Units. On the other hand, since the maximum depth of the video data 330 is 2, the encoding unit 335 of the video data 330 has the depth of two layers increased from the encoding units having the major axis size of 16, Units.

Since the maximum depth of the video data 320 is 4, the encoding unit 325 of the video data 320 has a depth of four layers with a major axis size of 32, 16, 8, 4 Encoding unit. As the depth increases, the image is encoded based on a smaller sub-encoding unit, which makes it suitable for encoding an image including a more detailed scene.

4 is a block diagram of an image encoding unit based on an encoding unit according to an embodiment of the present invention.

4, the intra-prediction unit 410 performs intra-prediction on a prediction unit of an intra mode in the current frame 405, and the motion estimation unit 420 and the motion compensation unit 425 perform intra- Inter prediction and motion compensation are performed using the current frame 405 and the reference frame 495 with respect to the unit.

The residual values are generated based on the prediction unit output from the intra prediction unit 410, the motion estimation unit 420 and the motion compensation unit 425, and the generated residual values are input to the frequency conversion unit 430 and the quantization unit 420. [ (440) and output as quantized transform coefficients.

The quantized transform coefficients are restored to a residual value through the inverse quantization unit 460 and the frequency inverse transform unit 470. The restored residual values are passed through the deblocking unit 480 and the loop filtering unit 490, And output to the reference frame 495. [ The quantized transform coefficient may be output to the bitstream 455 via the entropy encoding unit 450.

In order to perform encoding according to the image encoding method according to an embodiment of the present invention, an intra prediction unit 410, a motion estimation unit 420, a motion compensation unit 425, The inverse quantization unit 460, the inverse quantization unit 470, the deblocking unit 480 and the loop filtering unit 490 of the quantization unit 430, the quantization unit 440, the entropy coding unit 450, the inverse quantization unit 460, , Sub-encoding units according to depth, prediction units, and conversion units. In particular, the intra prediction unit 410, the motion estimation unit 420, and the motion compensation unit 425 determine the prediction unit and the prediction mode in the coding unit in consideration of the maximum size and depth of the coding unit, and the frequency conversion unit 430 ) Should consider the size of the conversion unit considering the maximum size and depth of the encoding unit. As described later, the intraprediction unit 410 applies the intra prediction mode determined for the image encoding unit of the luminance component to the image encoding unit of the chrominance component to perform intraprediction, thereby determining the prediction efficiency for the chrominance component image encoding unit .

5 is a block diagram of an image decoding unit based on an encoding unit according to an embodiment of the present invention.

Referring to FIG. 5, the bitstream 505 is parsed by the parser 510, and the encoded image data to be decoded and the encoding information necessary for decoding are parsed. The encoded image data is output as inverse-quantized data through the entropy decoding unit 520 and the inverse quantization unit 530, and is restored to the residual values through the frequency inverse transform unit 540. [ The residual values are added to the intraprediction result of the intraprediction unit 550 or the motion compensation result of the motion compensation unit 560, and restored for each encoding unit. The reconstructed coding unit is used for predicting the next coding unit or the next picture through the deblocking unit 570 and the loop filtering unit 580.

A parsing unit 510, an entropy decoding unit 520, an inverse quantization unit 530, and an inverse frequency transforming unit 530, which are components of the image decoding unit 500 for decoding according to an image decoding method according to an embodiment of the present invention, The intra prediction unit 550, the motion compensation unit 560, the deblocking unit 570 and the loop filtering unit 580 are all based on the maximum encoding unit, the depth-dependent sub-encoding unit, the prediction unit, And processes the image decoding processes. In particular, the intra prediction unit 550 and the motion compensation unit 560 determine a prediction unit and a prediction mode in an encoding unit in consideration of the maximum size and depth of an encoding unit, and the frequency inverse transform unit 540 transforms the maximum size And the depth of the conversion unit.

FIG. 6 illustrates a depth-based coding unit and a prediction unit according to an embodiment of the present invention.

The image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment use a hierarchical encoding unit to consider image characteristics. The maximum height, width, and maximum depth of the encoding unit may be adaptively determined according to the characteristics of the image, or may be variously set according to the demand of the user. The size of each coding unit may be determined according to a maximum size of a predetermined coding unit.

The hierarchical structure 600 of the encoding unit according to an embodiment of the present invention shows a case where the maximum height and width of the encoding unit is 64 and the maximum depth is 4. Since the depth increases along the vertical axis of the hierarchical structure 600 of the coding unit according to the embodiment, the height and width of the coding unit for each depth are reduced. In addition, along the horizontal axis of the hierarchical structure 600 of the coding unit, a prediction unit which is a partial data unit which is a prediction base of each coding unit of depth is shown.

The maximum coding unit 610 is the largest coding unit among the hierarchical structures 600 of the coding units and has a depth of 0, and the size of the coding units, i.e., the height and the width, is 64x64. The depth of the image is increased along the vertical axis, and a depth 1 encoding unit 620 having a size of 32x32, a depth 2 encoding unit 630 having a size 16x16, a depth encoding unit 640 having a depth 8x8, a depth 4x4 having a size 4x4 There is an encoding unit 650. An encoding unit 650 of depth 4 of size 4x4 is the minimum encoding unit.

Referring also to FIG. 6, partial data units are shown along the horizontal axis for each depth, as a prediction unit of an encoding unit. That is, the prediction unit of the maximum encoding unit 610 having a depth 0 size of 64x64 is a partial data unit 610 of size 64x64, partial data units 612 of size 64x32 included in the encoding unit 610 of size 64x64, Partial data units 614 of size 32x64, and partial data units 616 of size 32x32.

The prediction unit of the 32x32 coding unit 620 having the depth 1 is the partial data unit 620 of the size 32x32 included in the coding unit 620 of the size 32x32, the partial data units 622 of the size 32x16, Partial data units 624 of size 16x16, and partial data units 626 of size 16x16.

The prediction unit of the 16x16 coding unit 630 of depth 2 is a partial data unit 630 of size 16x16, partial data units 632 of size 16x8, a size of 8x16 16x16 included in the coding unit 630 of size 16x16, Partial data units 634 of size 8x8, and partial data units 636 of size 8x8.

The prediction unit of the encoding unit 640 having the depth 3 of 8x8 is a partial data unit 640 of the size 8x8, partial data units 642 of the size 8x4, a size 4x8 of the size 8x8 included in the encoding unit 640 of the size 8x8, Partial data units 644 of size 4x4, and partial data units 646 of size 4x4.

Finally, a coding unit 650 of size 4x4 is a minimum coding unit and a coding unit of the highest depth, and the prediction unit is a data unit 650 of size 4x4.

In order to determine the depth of encoding of the maximum encoding unit 610, the encoding depth determining unit 120 of the image encoding apparatus according to an exemplary embodiment may perform encoding for each depth unit included in the maximum encoding unit 610 Should be performed.

The number of coding units per depth to include data of the same range and size increases as the depth of field increases. For example, for data containing one coding unit at depth 1, four coding units at depth 2 are required. Therefore, in order to compare the encoding results of the same data by depth, they should be encoded using a single depth 1 encoding unit and four depth 2 encoding units, respectively.

For each depth-of-field coding, encoding is performed for each prediction unit of the depth-dependent coding unit along the horizontal axis of the hierarchical structure 600 of the coding unit, and a representative coding error, which is the smallest coding error at the corresponding depth, is selected . In addition, the minimum coding error can be searched by increasing the depth along the vertical axis of the hierarchical structure 600 of the coding unit, performing coding for each depth, and comparing representative coding errors per depth. The depth at which the minimum coding error occurs among the maximum coding units 610 can be selected as the coding depth and the division type of the maximum coding unit 610. [

FIG. 7 shows a relationship between an encoding unit and a conversion unit according to an embodiment of the present invention.

The image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment of the present invention divide and encode or decode an image with a coding unit smaller than or equal to the maximum encoding unit for each maximum encoding unit. The size of the conversion unit for frequency conversion during encoding can be selected based on data units that are not larger than the respective encoding units. For example, when the current encoding unit 710 is 64x64, the frequency conversion can be performed using the 32x32 conversion unit 720. [ In addition, the data of the encoding unit 710 of 64x64 size is encoded by performing the frequency conversion with the conversion units of 32x32, 16x16, 8x8, and 4x4 size of 64x64 or smaller, respectively, and then the conversion unit having the smallest error with the original Can be selected.

FIG. 8 illustrates depth-specific encoding information, in accordance with an embodiment of the present invention.

The encoding information encoding unit of the image encoding apparatus 100 according to an exemplary embodiment of the present invention includes information on the encoding mode and information on the division type 800 and information on the prediction mode 810 ), And information 820 on the conversion unit size may be encoded and transmitted.

The division type information 800 indicates information on a type in which the current coding unit is divided as a prediction unit for motion prediction of the current coding unit. For example, the current encoding unit CU_0 of depth 0 and size 2Nx2N includes a prediction unit 802 of size 2Nx2N, a prediction unit 804 of size 2NxN, a prediction unit 806 of size Nx2N, a prediction unit 808 of size NxN ) And can be used as a prediction unit. In this case, information 800 regarding the division type of the current encoding unit includes a prediction unit 802 of size 2Nx2N, a prediction unit 804 of size 2NxN, a prediction unit 806 of size Nx2N, and a prediction unit 808 of size NxN. Lt; / RTI >

The prediction mode information 810 indicates a motion prediction mode of each prediction unit. The prediction unit indicated by the information 800 regarding the division type is predicted to be one of the intra mode 812, the inter mode 814 and the skip mode 816 through the prediction mode information 810 Can be set.

In addition, the information 820 on the conversion unit size indicates whether to perform frequency conversion on the basis of which conversion unit the current encoding unit is performed. For example, the conversion unit may be one of a first intra-conversion unit size 822, a second intra-conversion unit size 824, a first inter-conversion unit size 826, have.

The encoding information extracting unit of the image decoding apparatus 200 according to an embodiment of the present invention extracts information on the division type 800, information on the prediction mode 810, Information 820 can be extracted and used for decoding.

FIG. 9 shows a depth encoding unit according to an embodiment of the present invention.

Reduced information may be used to indicate whether the depth is increased. The reduction information indicates whether or not the current-depth encoding unit is reduced to a higher-depth encoding unit.

A prediction unit 910 for motion prediction of a coding unit of depth 0 and 2N_0x2N_0 size includes a division type 912 of 2N_0x2N_0 size, a division type 914 of 2N_0xN_0 size, a division type 916 of N_0x2N_0 size, a division of N_0xN_0 size Type < / RTI >

For each segmentation type, it is necessary to repeatedly perform motion prediction through a prediction unit of 2N_0xN_0 size, two prediction units of 2N_0xN_0 size, two prediction units of N_0x2N_0 size, and prediction units of four N_0xN_0 sizes. For the prediction unit of size 2N_0xN_0 and size N_0xN_0, motion prediction can be performed in intra mode and inter mode, and motion prediction can be performed only in inter mode as a prediction unit of size N_0x2N_0 and size N_0xN_0. The skip mode can be performed only for the prediction unit of size 2N_0xN_0.

If the coding error by the division type 918 of the size N_0xN_0 is the smallest, the depth 0 is increased to 1 (920), and the coding units 922, 924, 926 and 928 of the division type of the depth 2 and the size N_0xN_0 The minimum coding error can be repeatedly searched for.

Since encoding is repeatedly performed on the encoding units 922, 924, 926, and 928 of the same depth, encoding of only one of the encoding units of depth 1, for example, will be described. A prediction unit 930 for motion prediction of a coding unit of depth 1 and a size 2N_1x2N_1 (= N_0xN_0) includes a division type 932 of size 2N_1x2N_1, a division type 934 of size 2N_1xN_1, a division type 936 of size N_1x2N_1, , And a division type 938 of size N_1xN_1. For each segmentation type, it is necessary to repeatedly perform motion prediction through a prediction unit of a size 2N_1x2N_1, a prediction unit of two sizes 2N_1xN_1, a prediction unit of two sizes N_1x2N_1, and a prediction unit of four sizes N_1xN_1.

If the coding error by the division type 938 of the size N_1xN_1 is the smallest, the coding units 942, 944, 946 and 948 of the depth 2 and the size N_2xN_2 are increased while the depth 1 is increased to the depth 2 (940) The minimum coding error can be repeatedly searched for.

If the maximum depth is d, the depth reduction information can be set until the depth d-1. That is, the prediction unit 950 for motion prediction of the coding unit of the depth d-1 and the size 2N_ (d-1) x2N_ (d-1) A division type 954 of size N_ (d-1) xN_ (d-1), a division type 956 of size N_ 1) xN_ (d-1).

(D-1) x2N_ (d-1), a prediction unit of two sizes 2N_ (d-1) ) x2N_ (d-1), and four sizes N_ (d-1) xN_ (d-1). Since the maximum depth is d, the encoding unit 952 of depth d-1 no longer undergoes the reduction process.

The image encoding apparatus 100 according to an exemplary embodiment of the present invention compares depth-based encoding errors to determine depths for encoding units 912 and selects the depths at which the smallest encoding error occurs. For example, a coding error for a coding unit of depth 0 is determined by performing motion prediction for each of the division types 912, 914, 916, and 918, and a prediction unit in which the smallest coding error occurs is determined. Similarly, a prediction unit having the smallest coding error can be searched for every depth 0, 1, ..., d-1. At the depth d, the coding error can be determined through motion prediction based on the prediction unit 960, which is a coding unit of size 2N_dx2N_d. In this way, the minimum coding errors of the depths 0, 1, ..., d-1, and d are compared with each other, and the depth with the smallest error is selected to be determined as the coding depth. The coding depth and the prediction unit of the corresponding depth can be encoded and transmitted as information on the coding mode. In addition, since the coding unit must be reduced from the depth 0 to the coding depth, only the coding depth reduction information is set to '0', and the reduction information by depth is set to '1' except for the coding depth.

The encoding information extracting unit 220 of the image decoding apparatus 200 according to an embodiment of the present invention extracts information on the encoding depth and the prediction unit for the encoding unit 912 and uses the information on the encoding depth 912 to decode the encoding unit 912 . The video decoding apparatus 200 according to an exemplary embodiment of the present invention uses the reduced information according to the depth to determine the depth with the reduced information of '0' as a coding depth and use the information on the coding mode for the corresponding depth to decode have.

FIGS. 10A and 10B show a relationship between an encoding unit, a prediction unit, and a frequency conversion unit according to an embodiment of the present invention.

The coding unit 1010 is coding units for coding depth determined by the image coding apparatus 100 according to the embodiment with respect to the maximum coding unit 1000. [ The prediction unit 1060 is a prediction unit of each coding depth unit among the coding units 1010 and the conversion unit 1070 is a conversion unit of each coding depth unit.

When the depth of the maximum coding unit 1000 is 0, the coding units 1012 and 1054 have depths 1 and coding units 1014, 1016, 1018, 1028, 1050 and 1052 The depths of the encoding units 1020, 1022, 1024, 1026, 1030, 1032 and 1038 are 3 and the depths of the encoding units 1040, 1042, 1044 and 1046 are 4, respectively.

A portion (1014, 1016, 1022, 1032, 1048, 1050, 1052, 1054) of the prediction units 1060 is a type in which the coding unit is divided. That is, the prediction units 1014, 1022, 1050 and 1054 are divided into 2NxN, the prediction units 1016, 1048 and 1052 are divided into Nx2N, and the prediction unit 1032 is divided into NxN. That is, the prediction unit of the depth-dependent coding units 1010 is smaller than or equal to each coding unit.

Frequency conversion or inverse frequency conversion is performed on the image data of a part (1052, 1054) of the conversion units (1070) in units of data smaller in size than the encoding unit. The conversion units 1014, 1016, 1022, 1032, 1048, 1050, 1052, and 1054 are data units of different sizes or types when compared with the prediction units of the prediction units 1060. That is, the image encoding apparatus 100 and the image decoding apparatus 200 according to an exemplary embodiment of the present invention perform prediction and frequency conversion / inverse transform operations on the same encoding unit, respectively, based on separate data units .

FIG. 11 shows encoding information for each encoding unit according to an embodiment of the present invention.

The encoding information encoding unit 140 of the image encoding apparatus 100 according to an exemplary embodiment of the present invention encodes encoding information of each encoding unit and extracts encoding information of the image encoding apparatus 200 according to an embodiment of the present invention Unit 220 can extract the encoding information for each encoding unit.

The encoding information may include reduction information for a coding unit, division type information, prediction mode information, and conversion unit size information. The encoding information shown in FIG. 11 is only an example that can be set in the image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment of the present invention, and is not limited to the illustrated ones.

The reduction information may indicate the coding depth of the encoding unit. That is, since the depth that is not further reduced according to the reduction information is the encoding depth, the division type information, the prediction mode, and the conversion unit size information can be defined with respect to the encoding depth. In the case where it is required to be further reduced according to the reduction information, the encoding should be performed independently for each of the reduced four higher-depth encoding units.

As the division type information, the division type of the conversion unit of the coding unit of the coding depth can be represented by 2Nx2N, 2NxN, Nx2N and NxN. The prediction mode may indicate the motion prediction mode as one of an intra mode, an inter mode, and a skip mode. The intra mode can be defined only in the split type 2Nx2N and NxN, and the skip mode can be defined only in the split type 2Nx2N. The conversion unit size can be set to two kinds of sizes in the intra mode and two kinds of sizes in the inter mode.

The encoding unit-specific encoding information of the belonging encoding depth may be stored for each minimum encoding unit in the encoding unit. Therefore, if encoding information held in each of the adjacent minimum encoding units is checked, it can be confirmed whether or not the encoding information is included in the encoding unit of the same encoding depth. In addition, since the encoding unit of the encoding depth can be identified by using the encoding information held in the minimum encoding unit, the distribution of encoding depths in the maximum encoding unit can be inferred.

The intraprediction performed by the intraprediction unit 410 of the video encoding apparatus 100 and the intraprediction unit 550 of the video decoding apparatus 200 according to an embodiment of the present invention shown in FIG. This will be described in detail. In the following description, a coding unit is a term referred to in an image coding step, and a coding unit may be defined as a decoding unit in terms of a decoding step of an image. That is, the terms coding unit and decoding unit are different only in terms of the coding and decoding stages of the image, and the coding unit in the coding step may be referred to as a decoding unit in the decoding step. For the sake of uniformity of terms, except for special cases, they shall be uniformly coded in the coding step and the decoding step in the same coding unit.

12A to 12C show formats of a luminance component and a chrominance component image encoding unit according to an embodiment of the present invention.

Each coding unit constituting one frame can be expressed using three components of Y, Cb and Cr. Y is luminance data having brightness information, and Cb and Cr are chrominance data having color information.

In general, based on the fact that human eyes are more sensitive to brightness information than color information, color difference data may be represented by a smaller amount of data than brightness data. Referring to FIG. 12A, one encoding unit converts HxW (H and W are positive integers) luminance data (Y) 1210 and chrominance components (Cb, Cr) into 1/4 (Cb, Cr) 1220 and 1230 of two (H / 2) x (W / 2) Referring to FIG. 12B, one coding unit converts HxW (H and W are positive integers) luminance data (Y) 1240 and chrominance components (Cb and Cr) in the horizontal direction (Cb, Cr) 1250 and 1260 of two Hx (W / 2) size, which are half-sampled with each other. 12C, in order to represent the chrominance component image more precisely, one encoding unit may output the luminance data (Y) 1270 and the chrominance data 1270 without sampling process for the chrominance component in the 4: 4: 4 format. (Cb, Cr) 1280 and 1290 are all composed of image data of HxW size.

In the following description, a luminance component encoding unit and a chrominance component encoding unit to be intrapredicted are images in a color format of 4: 2: 0, 4: 2: 2 and 4: 4: 4 defined in a YCbCr (or YUV) Signal.

According to the present invention, in consideration of the correlation between the luminance component and the chrominance component, the intra prediction mode determined for the luminance component coding unit is included in the candidate intra prediction mode applied to the chrominance component coding unit, .

13 shows the number of intra prediction modes according to the size of a luminance component image encoding unit according to an embodiment of the present invention.

According to an embodiment of the present invention, the number of intraprediction modes to be applied to the encoding unit of the luminance component may be variously set according to the size of the luminance component encoding unit (decoding unit in the decoding step). For example, referring to FIG. 13, when the size of an encoding unit of an intrapredicted luminance component is NxN, intraprediction is performed for each of 2x2, 4x4, 8x8, 16x16, 32x32, 64x64, and 128x128- The number of modes can be set to 5, 9, 9, 17, 33, 5, and 5 (for Example 2) respectively. The reason for differentiating the number of actually performed intraprediction modes according to the size of the luminance component encoding unit is that the overhead for encoding the prediction mode information differs depending on the size of the luminance component encoding unit. In other words, in the case of a small-sized luminance component coding unit, the overhead for transmitting the additional information such as the prediction mode of the small luminance component coding unit may increase although the portion occupying the entire image is small. Therefore, when a small luminance component encoding unit is encoded in too many prediction modes, the bit amount may increase and the compression efficiency may be lowered. In addition, since a luminance component coding unit having a large size, for example, a luminance component coding unit having a size of 64x64 or more is generally selected as a coding unit for a flat region of an image, Encoding a large-sized encoding unit into too many prediction modes may also be inefficient in terms of compression efficiency.

Therefore, according to an embodiment of the present invention, the luminance component encoding unit is composed of N1xN1 (2? N1? 8, N1 is an integer), N2xN2 (16? N2? 32, N2 is an integer), N3xN3 (A1 is a positive integer) and the number of intraprediction modes to be performed for each luminance component encoding unit having a size of N1xN1 is divided into at least three kinds of sizes When the number of intra prediction modes is A2 (A2 is a positive integer) and the number of intra prediction modes to be performed for each luminance component encoding unit having a size of N3xN3 is A3 (A3 is a positive integer), A3? A1? A2 It is preferable to set the number of intra prediction modes to be performed according to the size of each luminance component encoding unit so as to satisfy the following expression. That is, when it is assumed that the current picture is largely divided into a luminance component coding unit of a small size, a luminance component coding unit of a middle size, and a luminance component coding unit of a large size, It is preferable that the luminance component coding unit of a small size and the luminance component coding unit of a large size are set to have a relatively smaller number of prediction modes. However, the present invention is not limited to this, and it may be possible to set a larger number of prediction modes for small and large size coding units. The number of prediction modes according to the size of each coding unit shown in FIG. 13 is only one embodiment, and the number of prediction modes according to the size of each coding unit can be changed.

14A is a diagram for explaining an example of an intra prediction mode applied to a luminance component encoding unit of a predetermined size according to an embodiment of the present invention.

Referring to FIGS. 13 and 14A, for example, a vertical mode (mode 0), a horizontal mode (mode 1), and a DC (direct current) mode are used for intraprediction of a luminance component encoding unit having a size of 4 × 4, ) Mode (Mode 2), Diagonal Down-Left Mode (Mode 3), Diagonal Down-Right Mode (Mode 4), Vertical-Right Mode (Mode 5) (Mode 6), a vertical left (Vertical-Left) mode (Mode 7), and a Horizontal-Up (Mode 8) mode.

14B is a diagram showing the directions of the intra prediction modes of FIG. 14A. The number at the end of the arrow in FIG. 14B indicates the corresponding mode value when the prediction is performed in that direction. Mode 2 is not shown as a directional DC prediction mode.

FIG. 14C is a diagram illustrating an intra prediction method for the luminance component encoding unit shown in FIG. 14A.

Referring to FIG. 14C, a predictive encoding unit is generated using A - M, which is a peripheral pixel of a current luminance component encoding unit, according to an available intra prediction mode determined by the size of a luminance component encoding unit. For example, an operation of predicting a 4x4 current encoding unit according to mode 0, that is, a vertical mode in Fig. 14A will be described. First, the pixel values of the pixels A to D adjacent to the upper side of the current encoding unit of 4 × 4 size are predicted as pixel values of the 4 × 4 current encoding unit. That is, the value of the pixel A is divided into four pixel values included in the first column of the 4x4 current coding unit, the pixel B is divided into four pixel values included in the second column of the 4x4 current coding unit, Is predicted to the four pixel values included in the third column of the 4x4 current encoding unit and the pixel D value is predicted to the four pixel values included in the fourth column of the 4x4 current encoding unit. Next, an error value is calculated by subtracting the 4x4 current encoding unit predicted using the pixels A to D and the actual value of the pixel included in the original 4x4 current encoding unit, and the error value is encoded.

15 is a view for explaining another example of an intra prediction mode applied to a luminance component encoding unit of a predetermined size according to an embodiment of the present invention.

Referring to FIGS. 13 and 15, for example, in the intra prediction of a 2 × 2 encoding unit, a vertical mode, a horizontal mode, a DC (Direct Current) mode, a plane mode, And a right (Diagonal Down-Right) mode.

On the other hand, as shown in FIG. 13, when a luminance component encoding unit having a size of 32x32 has 33 intra-prediction modes, it is necessary to set the directions of 33 intra-prediction modes. In an embodiment of the present invention, in addition to the intra-prediction mode as shown in FIGS. 14 and 15, in order to set intra-prediction modes in various directions, a peripheral pixel to be used as a reference pixel around a pixel in a luminance- Is set using the dx and dy parameters. For example, when 33 prediction modes are defined as mode N (N is an integer from 0 to 32), mode 0 is a vertical mode, mode 1 is a horizontal mode, mode 2 is a DC mode, and mode 3 is a plane mode (1, 1), (1,1), (1,2), (2,1), (1, -2), (2) (1, -2), (2, -1), (2, -11), (5, -7) , (1,11), (1,1), (12,3), (1,11), (1,7), (3,10), 7, -6), (7, -4), (11,1), (6,1), (8,3), (5,3), (5,7) 5, -7), (4, 3) by using a (dx, dy) is expressed with a value of can be defined as a prediction mode having a directionality of tan ^-1 (dy / dx).

mode # dx dy mode # dx dy mode 4 One -One mode 18 One -11 mode 5 One One mode 19 One -7 mode 6 One 2 mode 20 3 -10 mode 7 2 One mode 21 5 -6 mode 8 One -2 mode 22 7 -6 mode 9 2 -One mode 23 7 -4 mode 10 2 -11 mode 24 11 One mode 11 5 -7 mode 25 6 One mode 12 10 -7 mode 26 8 3 mode 13 11 3 mode 27 5 3 mode 14 4 3 mode 28 5 7 mode 15 One 11 mode 29 2 7 mode 16 One -One mode 30 5 -7 mode 17 12 -3 mode 31 4 -3 mode 0 is a vertical mode, mode 1 is a horizontal mode, mode 2 is a DC mode, mode 3 is a plane mode, and mode 32 is a bi-linear mode.

The last mode 32 may be set to a bilinear mode using bilinear interpolation as described below using FIG.

16 is a reference diagram for explaining intra prediction modes having various directions according to an embodiment of the present invention.

As described above with reference to Table 1, the intra-prediction modes according to an exemplary embodiment of the present invention may have various directions of tan ^-1 (dy / dx) using a plurality of (dx, dy)

Referring to FIG. 16, the value of tan ^-1 (dy / dx) determined according to the value of each mode (dx, dy) shown in Table 1 about the current pixel P to be predicted in the current luminance- The neighboring pixels A and B located on the extension line 150 having an angle can be used as a predictor of the current pixel P. [ In this case, the neighboring pixels used as the predictor are pixels of the previous luminance component encoding unit on the upper side and the left side of the current luminance component encoding unit, which have been previously encoded and restored. Further, a peripheral pixel closer to the extension line 160 can be used as a predictor of the current pixel P when the extension line 160 passes between pixels around an integer position rather than a peripheral pixel at an integer position. As shown in the figure, when two peripheral pixels of the upper side peripheral pixel A and the left side peripheral pixel B that meet the extension line 160 exist, the upper peripheral pixel A and the left peripheral pixel B Is used as the predictor of the current pixel P or when the dx * dy value is positive, the upper neighboring pixel A is used and when the dx * dy value is negative, the neighboring pixel B is used. Can be used.

It is preferable that the intraprediction modes having various directions as shown in Table 1 are set in the encoding and decoding stages in advance so that only the corresponding indexes of the intra prediction modes set for each luminance component encoding unit are transmitted.

17 is a reference diagram for explaining a bilinear mode according to an embodiment of the present invention.

Referring to FIG. 17, a bi-linear mode is a mode in which a current pixel P and its neighboring pixel values around the current pixel P to be predicted in the current luminance component encoding unit, P), and uses the result as a predictor of the current pixel (P). That is, in the bilinear mode, the pixel A 171, the pixel B 172, the pixel D 176, and the pixel E 177 located at the upper, lower, left, and right boundaries of the current pixel P as a predictor of the current pixel P A geometric average value of the distances to the upper, lower, left, and right boundaries of the current pixel P is used. In this case, since the bilinear mode is also one of the intra prediction modes, it is necessary to use the reconstructed upper and left surrounding pixels as reference pixels at the time of prediction. Therefore, instead of using the corresponding pixel values in the current luminance component encoding unit as the pixel A 171 and the pixel B 172, the virtual pixel values generated using the neighboring pixels on the upper and left sides are used.

Specifically, the average value of the leftmost neighboring pixel (RightUpPixel) 164 and the leftmost lowermost neighboring pixel (LeftDownPixel) 175 adjacent to the current luminance component encoding unit is calculated as shown in the following Equation 1, The virtual pixel C (173) at the bottom right position of the unit is calculated.

[Equation 1]

C = 0.5 (LeftDownPixel + RightUpPixel)

The virtual pixel A 161 located at the lowermost boundary when the current pixel P is extended to the lower end in consideration of the distance W 1 to the left border of the current pixel P and the distance W 2 to the right border ) Is calculated as shown in the following equation (2).

&Quot; (2) "

A = (C * W1 + LeftDownPixel * W2) / (W1 + W2)

Similarly, when the current pixel P is extended to the right in consideration of the distance h1 to the upper boundary of the current pixel P and the distance h2 to the lower boundary, the imaginary pixel B ( 162) is calculated according to the following equation (3).

&Quot; (3) "

B = (C * h1 + RightUpPixel * h2) / (h1 + h2)

When the values of the virtual pixel A 171 on the lower boundary line of the current pixel P 170 and the imaginary pixel B 172 on the right boundary line are determined using Equations 1 to 3, the average value of A + B + D + E May be used as the predictor of the current pixel P (170). Such a bilinear prediction process is applied to all the pixels in the current luminance component encoding unit, and a predictive encoding unit of the current luminance component encoding unit according to the bilinear prediction mode is generated.

According to an embodiment of the present invention, predictive encoding is performed according to various intra-prediction modes set according to the size of a luminance component encoding unit, thereby enabling more efficient compression depending on the characteristics of an image.

On the other hand, in order to decode a luminance component encoding unit encoded through intraprediction, prediction mode information on which intra-prediction mode the current luminance component encoding unit is encoded is required. Therefore, when encoding the image, information about the intra-prediction mode of the current luminance component encoding unit is added to the bit stream. When the intraprediction mode information is directly added to the bit stream for each luminance component encoding unit, overhead is increased, The efficiency can be lowered.

Therefore, in an embodiment of the present invention, instead of directly transmitting the information on the intra-prediction mode of the current luminance component encoding unit determined as a result of encoding of the current luminance component encoding unit, the predicted value of the intra- And only the difference value between the actual intra prediction mode is transmitted.

18 is a diagram for explaining a process of generating a prediction value of an intra prediction mode of a current luminance component encoding unit according to an embodiment of the present invention.

Referring to FIG. 18, when the current luminance component encoding unit is A (180), the intra prediction mode of the current luminance component encoding unit A 180 can be predicted from the intra prediction mode determined in the surrounding luminance component encoding units . For example, if the determined intra prediction mode of the left luminance component coding unit B 181 of the current luminance component coding unit A 180 is mode 3 and the intra prediction mode of the upper luminance component coding unit C 182 is mode 4 , The intra prediction mode of the current luminance component coding unit A 180 can be predicted as a mode 3 having a smaller one of the prediction modes of the upper luminance component coding unit C 182 and the left luminance component coding unit B 181 . If the intraprediction mode determined as a result of the actual intraprediction encoding for the current luminance component encoding unit A 180 is mode 4, the intraprediction mode information of mode 3, which is the value of the intra prediction mode predicted from the surrounding luminance component encoding units, The predictive value of the intra-prediction mode of the current luminance component decoding unit is generated in the same manner as described above at the time of decoding, and the mode difference value transmitted through the bit stream is added to the predicted value of the intra-prediction mode, The intra prediction mode information actually applied to the decoding unit can be obtained. In the above description, only the surrounding encoding units located at the upper and left sides of the current luminance encoding unit are mainly described. However, the present invention is not limited to the use of other peripheral luminance encoding units such as E and D in FIG. 18, Prediction mode of the intra prediction mode. The intraprediction mode process of the luminance component encoding unit described above can also be applied to predict an intra prediction mode determined for a chrominance component encoding unit described later.

The intraprediction mode predicted from the surrounding luminance component encoding units may not be matched with the intraprediction mode of the current luminance component encoding unit because intraprediction modes actually performed depend on the magnitude of the luminance component encoding units. Therefore, in order to predict the intra-prediction mode of the current luminance component encoding unit from surrounding luminance component encoding units having different sizes, it is necessary to perform a mapping operation for unifying the intra-prediction modes between the luminance component encoding units having different intra- ) Process.

19 is a reference diagram for explaining a process of mapping an intra prediction mode between luminance component encoding units having different sizes according to an embodiment of the present invention.

19, it is assumed that the current luminance component encoding unit A 190 has a size of 16 × 16, the left luminance component encoding unit B 191 has an 8 × 8 size, and the upper luminance component encoding unit 192 has a size of 4 × 4 . It is also assumed that the number of intra prediction modes available in the 4x4, 8x8, and 16x16 luminance component encoding units is 9, 9, and 33, respectively, as in the first example of FIG. In this case, since the intra prediction modes available in the left luminance component coding unit B 191 and the upper luminance component coding unit C 192 are different from the intra prediction modes available in the current luminance component coding unit A 190, The intra prediction mode predicted from the component coding unit B (191) and the upper luminance component coding unit C (192) is not suitable for use as the predicted value of the intra prediction mode of the current luminance component coding unit A (190). Therefore, according to an embodiment of the present invention, the intra-prediction mode of the surrounding luminance component encoding units B and C (191, 192) is divided into the first and second representative intra-prediction modes And selects the final representative intra prediction mode having the smaller one of the first and second representative intra prediction modes. The intraprediction mode having the direction most similar to the selected representative intra prediction mode among the available intra prediction modes according to the size of the current luminance component coding unit A 190 is predicted in the intra prediction mode of the current luminance component encoding unit.

20 is a reference diagram for explaining a process of mapping intra-prediction modes of the surrounding luminance component encoding unit to one of the representative intra-prediction modes according to an embodiment of the present invention. 20 shows a case in which vertical, horizontal, DC, diagonal left, diagonal right, vertical right, vertical left, horizontal upper and horizontal lower modes are set as the representative intra prediction modes have. However, the representative intra-prediction mode is not limited to the illustrated one, and may be set to have various numbers of directions.

Referring to FIG. 20, a predetermined number of representative intraprediction modes are set in advance, and an intra prediction mode of the surrounding luminance component encoding unit is mapped to a representative intra prediction mode in the most similar direction. For example, if the determined intra-prediction mode of the upper luminance-component coding unit A has the directionality shown by the MODE_A 200, the intra-prediction mode MODE_A 200 of the upper luminance- And is mapped to MODE 1 having the most similar direction among the set representative intra prediction modes 1 to 9. Likewise, if the determined intra prediction mode of the left luminance component coding unit B has a directionality indicated by MODE_B 201, then the intra prediction mode MODE_B 191 of the left luminance component coding unit B includes nine preset representatives And is mapped to MODE 5 having the most similar direction among the intra prediction modes 1 to 9.

An intra prediction mode having a smaller mode value from among the first representative intra prediction mode and the second representative intra prediction mode is selected as the representative intra prediction mode of the final peripheral luminance component coding unit. The reason why the representative intra prediction mode having such a smaller mode value is selected is because a smaller mode value is set for the more frequently occurring intra prediction modes. That is, when a different intra-prediction mode is predicted from surrounding luminance component encoding units, the intra-prediction mode having a smaller mode value is a prediction mode having a higher probability of occurrence. Therefore, It is preferable to select a prediction mode having a smaller mode value as a predictor of a prediction mode of a unit.

Even if the representative intra prediction mode is selected from the surrounding luminance component coding unit, the representative intra prediction mode may not be used as the predictor of the intra prediction mode of the current luminance component coding unit. If the current luminance component coding unit A 190 has 33 intra prediction modes and the representative intra prediction mode has only 9 intra prediction modes as shown in FIG. 19, the current luminance component encoding corresponding to the representative intra prediction mode The intra prediction mode of the unit A 190 does not exist. In such a case, similarly to mapping the intra-prediction mode of the surrounding luminance component encoding unit to the representative intra-prediction mode, in the same direction as the selected representative intra-prediction mode among the intra-prediction modes according to the current size of the luminance- Can be finally selected as the intra prediction mode predictor of the current luminance component encoding unit. For example, if the representative intraprediction mode finally selected from the surrounding luminance component encoding unit is mode 1 in FIG. 20, the most similar intra prediction mode among the available intra prediction modes according to the size of the current luminance component encoding unit The intra prediction mode is finally selected as the predictor of the intra prediction mode of the current luminance component encoding unit.

21 is a diagram for explaining an example of a candidate intra prediction mode applied to a chrominance component encoding unit according to an embodiment of the present invention.

Referring to FIG. 21, the candidate intra prediction mode to be applied to the intra prediction of the chrominance component coding unit may be a vertical mode, a horizontal mode, a DC (Direct Current) mode, a plane mode, The intra prediction mode finally determined for the luminance component coding unit corresponding to the current chrominance component coding unit is included. In addition, as described above, the intraprediction-based luminance component encoding unit and the chrominance-component encoding unit are arranged in a color format of 4: 2: 0, 4: 2: 2 and 4: 4: 4 defined in the YCbCr (or YUV) Or a video signal. The intra prediction mode of the luminance component encoding unit is determined to be the final intra prediction mode having the minimum cost among the plurality of intra prediction modes available based on cost calculation such as Rate-Distortion Cost. The intraprediction mode of the chrominance component encoding unit applies the intraprediction mode finally determined for the luminance component encoding unit corresponding to the above-described vertical mode, horizontal mode, DC mode, plane mode, and current chrominance encoding unit, , And the intra prediction mode having the minimum cost is determined as the final intra prediction mode of the chrominance component encoding unit.

22 is a block diagram illustrating an apparatus for intra prediction of an image according to an embodiment of the present invention. The intra prediction apparatus 2200 according to an exemplary embodiment of the present invention includes an intra prediction unit 410 of the image coding apparatus 400 and an intra prediction unit 550 of the image decoding apparatus 500 of FIG. As shown in FIG.

22, the intraprediction apparatus 2200 includes a luminance intraprediction unit 2210 and a color difference intra prediction unit 2220. [ The luminance intraprediction unit 2210 selects the intra prediction mode candidates to be applied according to the size of the current luminance component encoding unit according to the size of each divided luminance component encoding unit based on the maximum encoding unit and the depth as described above, Intra prediction for each luminance component encoding unit is performed by applying intra prediction mode candidates to a luminance component encoding unit. The luminance intraprediction unit 2200 predicts an optimal intra prediction mode having a minimum cost based on the cost based on the error value between the predicted encoding unit generated as the intra prediction result and the original luminance component encoding unit as the final intraprediction Mode.

The chrominance intra prediction unit 2220 applies the intra prediction mode finally determined for the luminance component coding unit corresponding to the vertical mode, the horizontal mode, the DC mode, the plane mode, and the current chrominance component coding unit, And determines the intra prediction mode having the minimum cost as the final intra prediction mode of the chrominance component encoding unit.

On the other hand, when the intra prediction apparatus 2200 shown in FIG. 22 is used in the decoding apparatus, the maximum encoding unit extracted from the bit stream encoded by the entropy decoding unit 520 of FIG. 5, the hierarchical division of the maximum encoding unit Determines the size of the decoding unit of the current luminance component and the chrominance component using the in-depth information, and determines an intra prediction mode to be performed using the current intra-prediction mode information applied to the luminance component and the decoding unit of the chrominance component. In addition, the intra prediction apparatus 2200 performs intraprediction on a decoding unit of each luminance component and chrominance component according to the extracted intra prediction mode, thereby generating a predictive decoding unit. The prediction decoding unit is combined with the residual data reconstructed from the bitstream to decode the decoding unit of the luminance component and chrominance component.

23 is a flowchart illustrating a method of determining an intra prediction mode for an image encoding unit according to an embodiment of the present invention.

Referring to FIG. 23, in step 2310, the current picture of the luminance component is divided into at least one coding unit based on the depth, which is hierarchical division information of the maximum coding unit and the maximum coding unit, which are coding units having the maximum size.

In step 2320, the intra prediction mode of the luminance component divided by the luminance component is determined. As described above, the intraprediction mode of the luminance component encoding unit selects the intra prediction mode candidates to be applied according to the size of each divided luminance component encoding unit, applies the intra prediction mode candidates to the luminance component encoding unit, The intra prediction for the coding unit is performed, and the optimal intra prediction mode having the minimum cost is determined as the final intra prediction mode for the luminance component coding unit.

Prediction modes of the chrominance component encoding unit including the intra-prediction mode of the encoding unit of the luminance component determined in step 2330 are determined. As described above, the candidate intra prediction modes applied to the chrominance component coding unit include the vertical mode, the horizontal mode, the DC mode, and the plane mode in addition to the final intra prediction mode determined in the corresponding luminance component encoding unit.

In step 2340, the intra prediction mode of the encoding unit of the chrominance component having the minimum cost is determined by comparing the cost of the encoding unit of the chrominance component according to the determined candidate intra prediction modes.

24 is a flowchart illustrating a method of determining an intra prediction mode of a video decoding unit according to an embodiment of the present invention.

Referring to FIG. 24, in step 2410, a maximum coding unit, which is a coding unit having a maximum size, and depth information, which is hierarchical division information of the maximum coding unit, are extracted from the bit stream encoded.

The luminance component and chrominance component of the current picture to be decoded based on the maximum encoding unit and the depth extracted in step 2420 are divided into decoded units.

In step 2430, intraprediction mode information applied to the decoded unit of the luminance component and chrominance component, which are obtained from the bitstream, is extracted.

In step 2440, the luminance component and chrominance component decoding unit are decoded by performing intra prediction on the decoding unit of the luminance component and chrominance component according to the extracted intra prediction mode.

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium. The computer readable recording medium may be a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: image encoding apparatus 110: maximum encoding unit division unit
120: encoding depth determination unit 130: video data encoding unit
140: Encoded information encoding unit 200: Video decode device
210: image data acquisition unit 220: encoding information extraction unit
230, an image data decoding unit 310, 320, 330,
400: Image coding unit 410: Intra prediction unit
420: motion estimation unit 425: motion compensation unit
430: frequency conversion unit 440: quantization unit
450: Entropy coding unit 460: Inverse quantization unit
470: frequency inverse transform unit 480: deblocking unit
490: Loop filtering unit 500: Image decoding unit
510: parsing unit 520: entropy decoding unit
530: Inverse quantization unit 540: Inverse frequency transform unit
550: Intra prediction unit 560: Motion compensation unit
570: deblocking unit 580: loop filtering unit
600: hierarchical structure of encoding units 610: maximum encoding unit
620: coding unit of depth 1 630: coding unit of depth 2
640: Encoding unit of depth 3 650: Encoding unit of depth 4
2200 Intra prediction unit 2210: Intensity prediction unit 2210
2220: chrominance intra prediction unit

Claims (2)

Obtaining first information from a bitstream indicating an intra prediction mode of a luminance block;
Obtaining second information from the bitstream indicating an intra prediction mode of a chrominance block corresponding to the luminance block;
Performing intra prediction on the luminance block based on an intra prediction mode of the luminance block; And
And performing intra prediction on the color difference block based on an intra prediction mode of the color difference block,
Wherein the intra-prediction mode of the luminance block includes a specific direction among a plurality of directions, and the specific direction is indicated by at least one of dx in the horizontal direction (dx is an integer) and dy in the vertical direction (dy is an integer)
Wherein performing the intra prediction on the luminance block comprises:
Determining the number of neighboring pixels located on the left side or the upper side of the luminance block according to a position of the current pixel and a specific direction indicated by the intra prediction mode of the luminance block based on the first information;
Obtaining a predicted value of a current pixel based on one surrounding pixel when the number of neighboring pixels is determined to be one; And
Obtaining a predicted value of the current pixel based on a weighted average value of two neighboring pixels when the number of neighboring pixels is determined to be two,
Wherein the weighted average value uses a weight determined based on at least one of dx and dy and a position of the current pixel,
Wherein performing the intra prediction on the color difference block comprises:
Determines an intra prediction mode of the color difference block among a plurality of intra prediction modes including a DC mode, a horizontal mode, a vertical mode, and an intra prediction mode of the luminance block based on the second information, Prediction mode of the luminance block is the same as the intra prediction mode of the luminance block,
The image is divided into a plurality of maximum encoding units according to information on the size of the maximum encoding unit,
Wherein one of the plurality of maximum encoding units is hierarchically divided into a plurality of encoding units having a depth based on the reduction information,
The encoding unit of the current depth is one of the four square data units divided from the encoding unit of the lower depth,
Wherein the encoding unit of the current depth is divided into encoding units of higher depth independently of the surrounding encoding units when the reduction information indicates that the reduction information is divided at the current depth,
At least one prediction unit is obtained from an encoding unit of the current depth when the reduction information indicates that the reduction information is not divided at the current depth,
Wherein the luminance block is one of at least one prediction unit obtained from the current depth coding unit. An entropy decoding unit for obtaining first information indicating an intra prediction mode of a luminance block and second information indicating an intra prediction mode of a color difference block corresponding to the luminance block; And
And an intra prediction unit that performs intra prediction on the luminance block based on the intra prediction mode of the luminance block and performs intra prediction on the color difference block based on the intra prediction mode of the color difference block,
Wherein the intra-prediction mode of the luminance block includes a specific direction among a plurality of directions, and the specific direction is indicated by at least one of dx in the horizontal direction (dx is an integer) and dy in the vertical direction (dy is an integer)
The intra prediction unit
Determines the number of neighboring pixels located on the left side or the upper side of the luminance block according to the position of the current pixel and the specific direction indicated by the intra prediction mode of the luminance block based on the first information,
When the number of neighboring pixels is determined to be one, obtaining a predicted value of a current pixel based on one surrounding pixel,
Obtaining a predicted value of the current pixel based on a weighted average value of two neighboring pixels when the number of neighboring pixels is determined to be two,
Determines an intra prediction mode of the color difference block among a plurality of intra prediction modes including a DC mode, a horizontal mode, a vertical mode, and an intra prediction mode of the luminance block based on the second information, Prediction mode of the luminance block is the same as the intra prediction mode of the luminance block,
Wherein the weighted average value is obtained using a weight determined based on at least one of dx and dy and a position of the current pixel,
The image is divided into a plurality of maximum encoding units according to information on the size of the maximum encoding unit,
Wherein one of the plurality of maximum encoding units is hierarchically divided into a plurality of encoding units having a depth based on the reduction information,
The encoding unit of the current depth is one of the four square data units divided from the encoding unit of the lower depth,
Wherein the encoding unit of the current depth is divided into encoding units of higher depth independently of the surrounding encoding units when the reduction information indicates that the reduction information is divided at the current depth,
At least one prediction unit is obtained from an encoding unit of the current depth when the reduction information indicates that the reduction information is not divided at the current depth,
Wherein the luminance block is one of at least one prediction unit obtained from the current depth coding unit.

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