KR101634253B1 - Method and apparatus for encoding and decoding image using large transform unit - Google Patents

Abstract

Disclosed is a method and apparatus for encoding an image by converting a plurality of prediction units into a frequency domain as one conversion unit, and a method and apparatus for decoding image data encoded by such a coding method.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for encoding and decoding an image using a large-

The present invention relates to a method and apparatus for image encoding and decoding, and more particularly, to a method and apparatus for encoding and decoding an image by converting an image in a pixel domain into coefficients in a frequency domain.

Most video encoding and decoding methods and devices convert an image of a pixel domain into a frequency domain for image compression. Discrete cosine transform, which is one of the frequency transforms, is a well known technique used for image or speech compression. In the image coding method using the discrete cosine transform, the discrete cosine coefficients are generated by discrete cosine transform of the image in the pixel domain, and the generated coefficients are quantized and entropy encoded.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for encoding and decoding an image using a more efficient discrete cosine transform, and a computer-readable recording medium having recorded thereon a program for executing the method .

According to an aspect of the present invention, there is provided an image encoding method comprising: selecting a plurality of prediction units adjacent to each other and setting one conversion unit; Converting the plurality of prediction units into a frequency domain according to the conversion unit to generate frequency component coefficients; Quantizing the generated frequency component coefficients; And entropy encoding the quantized frequency component coefficients.

According to still another embodiment of the present invention, the setting step may include a step of setting, based on a depth indicating a degree of stepwise reduction in a current slice or a sub-coding unit including the adjacent plurality of prediction units in a maximum coding unit of the current picture And setting a conversion unit of the conversion unit.

According to another embodiment of the present invention, the setting step includes a step of selecting a plurality of prediction units adjacent to each other and performing a prediction according to a prediction mode of the same type, and setting one conversion unit.

According to another embodiment of the present invention, the prediction mode of the same kind is an inter prediction mode or an intra prediction mode.

According to another embodiment of the present invention, the image encoding method may further include the steps of: selecting one of the adjacent prediction units for different conversion units to set one conversion unit; converting the selected plurality of prediction units into one conversion unit Converting the frequency component coefficients into frequency domain to generate frequency component coefficients, quantizing the generated frequency component coefficients, and entropy-coding the quantized frequency component coefficients to set an optimal conversion unit do.

According to an aspect of the present invention, there is provided an apparatus and method for encoding an image, the apparatus comprising: a plurality of prediction units adjacent to each other to select one of the prediction units and to convert the plurality of prediction units into a frequency domain A frequency converter for generating frequency component coefficients; A quantizer for quantizing the generated frequency component coefficients; And an entropy encoding unit for entropy encoding the quantized frequency component coefficients.

According to an aspect of the present invention, there is provided an image decoding method comprising: entropy decoding a frequency component coefficient generated by transforming a frequency domain according to a predetermined transform unit; Dequantizing the entropy-decoded frequency component coefficients; And inversely transforming the frequency component coefficients into a pixel domain to reconstruct adjacent prediction units included in the conversion unit.

According to an aspect of the present invention, there is provided an apparatus for decoding an image, comprising: an entropy decoding unit for entropy decoding frequency component coefficients generated by transforming into a frequency domain according to a predetermined conversion unit; A dequantizer for dequantizing the entropy-decoded frequency component coefficients; And an inverse frequency transform unit for inversely transforming the frequency component coefficients into a pixel domain to recover an adjacent plurality of prediction units included in the transform unit.

According to an aspect of the present invention, there is provided a computer-readable recording medium having recorded thereon a program for executing the image encoding and decoding method.

1 illustrates an image encoding apparatus according to an embodiment of the present invention.
FIG. 2 illustrates 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.
FIG. 4 illustrates an image encoding unit based on an encoding unit according to an embodiment of the present invention.
FIG. 5 illustrates an image decoding unit based on an encoding unit according to an embodiment of the present invention.
FIG. 6 illustrates a maximum encoding unit, a sub-encoding unit, and a prediction unit according to an embodiment of the present invention.
7 shows an encoding unit and a conversion unit according to an embodiment of the present invention.
FIGS. 8A and 8B show a division form of an encoding unit, a prediction unit, and a conversion unit according to an embodiment of the present invention.
9 illustrates an image encoding apparatus according to another embodiment of the present invention.
FIG. 10 illustrates a frequency conversion unit according to an embodiment of the present invention.
Figures 11A-11C illustrate types of conversion units in accordance with one embodiment of the present invention.
Figure 12 shows different conversion units according to an embodiment of the present invention.
FIG. 13 illustrates an image decoding apparatus according to another embodiment of the present invention.
14 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.
15 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

1 illustrates 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 may divide 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 can be divided into at least one maximum encoding unit.

According to an embodiment of the present invention, an encoding unit can be expressed using a maximum encoding unit and a depth. As described above, 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 units are 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. Thus, the sub-encoding unit of k depth may include a sub-encoding unit of depth greater than a plurality of k.

As the size of a picture to be encoded increases, if an image is coded in a larger unit, the image can be encoded with a higher image compression rate. However, if the coding unit is enlarged and its size is fixed, the image can not be efficiently encoded reflecting the characteristics of the continuously changing image.

For example, when coding a flat area with respect to the sea or sky, the compression rate can be improved by increasing the coding unit. However, when coding a complex area for people or buildings, the compression ratio is improved as the coding unit is decreased.

To this end, one embodiment of the present invention sets a maximum image encoding unit of a different size for each picture or slice, and sets a maximum depth. Since the maximum depth means the maximum number of times the encoding unit can be reduced, the minimum encoding unit size included in the maximum image encoding unit can be variably set according to the maximum depth.

The encoding depth determination unit 120 determines the maximum depth. The maximum depth may be determined based on the Rate-Distortion Cost calculation. The maximum depth may be determined as a picture or a slice, or may be determined differently for each maximum encoding unit. 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 maximum depth means the smallest encoding unit, that is, the minimum encoding unit, which can be included in the maximum encoding unit. In other words, the maximum encoding unit may be divided into sub-encoding units of different sizes according to different depths. Will be described later in detail with reference to Figs. 8A and 8B. 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.

If 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 may determine sub-coding units included in the maximum coding unit using Rate-Distortion Optimization based on a Lagrangian Multiplier. In other words, it is possible to determine what type of sub-encoding unit the maximum encoding unit is divided into, wherein the plurality of sub-encoding units have different sizes depending on the depth. Then, the image data encoding unit 130 encodes the maximum encoding unit based on the division type determined by the encoding depth determination unit 120, and outputs the bit stream.

The encoding information encoding unit 140 encodes information on the encoding mode of the maximum encoding unit in the encoding depth determining unit 120. [ Information on the division type of the maximum encoding unit, information on the maximum depth, and information on the encoding mode of the sub-encoding unit by depth, and outputs the bit stream. The information on the encoding mode of the sub-encoding unit may include information on the prediction unit of the sub-encoding unit, prediction mode information per prediction unit, information on the conversion unit of the sub-encoding unit, and the like.

There is a sub-encoding unit of a different size for each maximum encoding unit, and information on the encoding mode is determined for each sub-encoding unit, so that information on at least one encoding mode can be determined for one maximum encoding unit.

As the depth increases, the image encoding apparatus 100 may generate a sub-encoding unit by dividing the maximum encoding unit by half the height and the width. That is, if the size of the encoding unit of the kth depth is 2Nx2N, the size of the encoding unit of the k + 1th depth is NxN.

Accordingly, the image decoding apparatus 100 according to an exemplary embodiment can determine an optimum division type for each maximum encoding unit based on the size and the maximum depth of a maximum encoding unit considering characteristics of an image. It is possible to more efficiently encode images of various resolutions by adjusting the size of the maximum encoding unit in consideration of the image characteristics and encoding the image by dividing the maximum encoding unit into sub-encoding units of different depths.

FIG. 2 illustrates 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 stream 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 data obtaining unit 210 may extract information on the maximum coding unit of the current picture or slice from the header of the current picture or slice. In other words, the bitstream is divided into a maximum encoding unit, and the video data decoding unit 230 decodes the video data per maximum encoding unit.

The encoding information extracting unit 220 parses the bit stream received by the video decoding apparatus 200 and extracts a maximum encoding unit, a maximum depth, a division type of the maximum encoding unit, and a coding mode of the sub-encoding unit from the header for the current picture . The information on the division type and the encoding mode is output to the video data decoding unit 230. [

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 may perform intra prediction or inter prediction based on information on a prediction unit for each sub-coding unit and prediction mode information for prediction of a sub-coding unit. In addition, the image data decoding unit 230 can perform frequency inverse transform for each sub-encoding unit on the basis of the information on the conversion unit of the sub-encoding unit.

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.

Referring to FIG. 3, the maximum encoding unit size is set to 64x64 and the maximum depth is set to 2 for the image data 310 having a resolution of 1920x1080.

The size of the maximum encoding unit is set to 64x64 and the maximum depth is set to 4 for the image data 320 having another resolution of 1920x1080. For the video data 330 having a resolution of 352x288, the size of the maximum encoding unit is set to 16x16 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 size of the maximum encoding unit of the image data 310 and 320 having a higher resolution than the image data 330 can be selected to be 64x64.

The maximum depth indicates the total number of layers in the hierarchical encoding unit. Since the maximum depth of the image data 310 is 2, the coding unit 315 of the image data 310 is divided into sub-coding units 315 having a major axis size of 32 and 16 as the depth increases, .

On the other hand, since the maximum depth of the image data 330 is 2, the encoding unit 335 of the image data 330 is encoded from the maximum encoding units having the major axis size of 16 to the encoding units having the major axis size of 8 and 4 Units.

Since the maximum depth of the video data 320 is 4, the encoding unit 325 of the video data 320 has a length of 32, 16, 8, and 4 as the depth increases, Sub-encoding units. 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 finer scene.

FIG. 4 illustrates an image encoding unit based on an encoding unit according to an embodiment of the present invention.

The intra prediction unit 410 performs intra prediction on a prediction unit of the intra mode of the current frame 405 and the motion estimation unit 420 and the motion compensation unit 425 perform intra prediction on the prediction unit of the intra mode, 405 and a reference frame 495. The inter-prediction and the motion compensation are performed using the reference frame 495 and inter-prediction.

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.

FIG. 5 illustrates an image decoding unit based on an encoding unit according to an embodiment of the present invention.

The bitstream 505 passes through 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, an inverse frequency transforming unit (hereinafter referred to as an inverse quantization unit) 530, 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 the sub-coding unit in consideration of the maximum coding unit and the depth, and the frequency inverse transform unit 540 considers the size of the conversion unit Thereby performing frequency inverse transform.

FIG. 6 illustrates a maximum encoding unit, a sub-encoding 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 of the present invention use a hierarchical encoding unit to perform encoding and decoding in consideration of image characteristics. The maximum encoding unit and the maximum depth may be adaptively set according to the characteristics of the image, or may be variously set according to the demand of the user.

The hierarchical structure 600 of the encoding unit according to an embodiment of the present invention shows a case where the height and the width of the maximum encoding unit 610 are 64 and the maximum depth is 4. The depth increases along the vertical axis of the hierarchical structure 600 of the encoding unit, and the height and width of the sub-encoding units 620 to 650 decrease as the depth increases. Prediction units of the maximum encoding unit 610 and the sub-encoding units 620 to 650 are shown along the horizontal axis of the hierarchical structure 600 of the encoding units.

The maximum encoding unit 610 has a depth of 0, and the size of the encoding unit, i.e., the height and the width, is 64x64. A sub-encoding unit 620 having a depth 1 of 32x32 and a sub-encoding unit 630 having a depth 16x16 having a depth of 16x16, a sub-encoding unit 640 having a depth of 3x8 having a size 8x8, There is a sub-encoding unit 650 of depth 4. A sub-encoding unit 650 of depth 4 with a size of 4x4 is the minimum encoding unit.

Referring to FIG. 6, examples of prediction units along the horizontal axis are shown for each depth. That is, the prediction unit of the maximum coding unit 610 of depth 0 is a prediction unit 610 of size 64x64, a prediction unit 612 of size 64x32, and size 32x64, which are the same or smaller than the coding unit 610 of size 64x64, A prediction unit 614 of size 32x32, and a prediction unit 616 of size 32x32.

The prediction unit of the 32x32 coding unit 620 having the depth 1 has the prediction unit 620 of the size 32x32 which is equal to or smaller than the coding unit 620 of the size 32x32, the prediction unit 622 of the size 32x16, A prediction unit 624 of size 16x16, and a prediction unit 626 of size 16x16.

The prediction unit of the 16x16 encoding unit 630 of depth 2 has a prediction unit 630 of 16x16 size, a prediction unit 632 of size 16x8, and a size of 8x16, which are the same or smaller than the encoding unit 630 of size 16x16. A prediction unit 634 of size 8x8, and a prediction unit 636 of size 8x8.

The prediction unit of the 8x8 encoding unit 640 of depth 3 has a prediction unit 640 of size 8x8, a prediction unit 642 of size 8x4, and a size of 4x8, which are the same or smaller than the encoding unit 640 of size 8x8. A prediction unit 644 of size 4x4, and a prediction unit 646 of size 4x4.

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

7 shows 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 encode the maximum encoding unit as a unit or encode the maximum encoding unit in units of sub encoding units smaller than or equal to the maximum encoding unit. The size of a conversion unit for frequency conversion during encoding is selected as a conversion unit that is not larger than each encoding unit. For example, when the current encoding unit 710 is 64x64, the frequency conversion can be performed using the 32x32 conversion unit 720. [

FIGS. 8A and 8B show a division form of an encoding unit, a prediction unit, and a frequency conversion unit according to an embodiment of the present invention.

8A shows an encoding unit and a prediction unit according to an embodiment of the present invention.

The left side of FIG. 8A shows a division type selected by the image encoding apparatus 100 according to an embodiment of the present invention to encode the maximum encoding unit 810. The image encoding apparatus 100 divides the maximum encoding unit 810 into various types, encodes the encoded image, and then selects an optimal division type by comparing the encoding results of various division types based on the R-D cost. When it is optimal to directly encode the maximum encoding unit 810, the maximum encoding unit 800 may be encoded without dividing the maximum encoding unit 810 as shown in FIGS. 8A and 8B.

Referring to the left side of FIG. 8A, a maximum encoding unit 810 having a depth of 0 is divided into sub-encoding units having a depth of 1 or more and encoded. The maximum encoding unit 810 is divided into sub-encoding units of four depths 1, and then all or a part of the sub-encoding units of depth 1 are divided into sub-encoding units of depth 2 again.

Among the sub-coding units of depth 1, sub-coding units coded at the upper right and sub-coding units located at the lower left are divided into sub-coding units of depth 2 or more. Some of the sub-encoding units having depths of 2 or more may be further divided into sub-encoding units having depths of 3 or more.

The right side of FIG. 8B shows the division type of the prediction unit for the maximum coding unit 810.

Referring to the right side of FIG. 8A, the prediction unit 860 for the maximum coding unit can be divided into the maximum coding unit 810 and the prediction unit 860 for the maximum coding unit. In other words, the prediction unit for each of the sub-encoding units may be smaller than the sub-encoding unit.

For example, a prediction unit for a sub-coding unit 854 coded right below the sub-coding unit at depth 1 may be smaller than the sub-coding unit 854. The prediction unit for some of the sub-encoding units 815, 816, 850, and 852 among the sub-encoding units 814, 816, 818, 828, 850, and 852 at the depth 2 may be smaller than the sub- In addition, the prediction unit for the sub-coding units 822, 832, and 848 of depth 3 may be smaller than the sub-coding unit. The prediction unit may be a form in which each sub-coding unit is halved in the height or width direction, or may be divided into four in height and width directions.

FIG. 8B shows a prediction unit and a conversion unit according to an embodiment of the present invention.

The left side of FIG. 8B shows the division form of the prediction unit for the maximum coding unit 810 shown on the right side of FIG. 8A, and the right side of FIG. 8B shows the division form of the conversion unit of the maximum coding unit 810.

Referring to the right side of FIG. 8B, the division type of the conversion unit 870 may be set differently from the prediction unit 860. [

For example, even if the prediction unit for the depth 1 encoding unit 854 is selected to be half the height, the conversion unit may be selected to be the same size as the depth unit 854 encoding unit. Likewise, even if the prediction unit for the depth 2 coding units 814 and 850 is selected in such a manner that the height of the depth level 2 coding units 814 and 850 is halved, the level of the level 2 coding units 814 and 850 It can be selected to be the same size as the original size.

The conversion unit may be selected to be smaller than the prediction unit. For example, if the prediction unit for depth 2 coding unit 852 is chosen to be half the width, the conversion unit may be selected to be half the width and height, which is a smaller size than the prediction unit.

9 illustrates an image encoding apparatus according to another embodiment of the present invention.

9, an image encoding apparatus 900 according to an exemplary embodiment of the present invention includes a frequency transforming unit 910, a quantization unit 920, and an entropy encoding unit 930.

The frequency converter 910 receives the image processing unit of the pixel domain and converts the image processing unit into the frequency domain. A plurality of prediction units including residual values generated through intraprediction or inter prediction are input and converted into a frequency domain. Converting to the frequency domain results in a coefficient of frequency components. According to an embodiment of the present invention, the transform to the frequency domain may be a discrete cosine transform and a discrete cosine transform produces discrete cosine coefficients. Hereinafter, discrete cosine transform will be described as an example. However, those skilled in the art will readily understand that the present invention can be applied to all transforms for transforming images of all pixel domains into the frequency domain.

Also, according to an embodiment of the present invention, the frequency converter 910 groups a plurality of prediction units, sets one conversion unit, and performs discrete cosine transformation according to the set conversion unit. 10, 11A, 11B, and 12 will be described in detail.

FIG. 10 shows a frequency converter 910 according to an embodiment of the present invention.

10, a frequency converter 910 according to an embodiment of the present invention includes a selector 1010 and a converter 1020.

The selection unit 1010 selects a plurality of adjacent prediction units and sets one conversion unit. According to conventional image encoding apparatuses, intraprediction or inter prediction is performed according to a block of a predetermined size, that is, a prediction unit, and discrete cosine transformation is performed with a size smaller than or equal to the prediction. In other words, conventional image encoding apparatuses perform discrete cosine transform based on a transform unit smaller than or equal to the prediction unit.

However, due to the header information added for each conversion unit, the overhead to be added increases as the conversion unit becomes smaller, thereby lowering the compression rate of the image encoding. In order to solve such a problem, the image encoding apparatus 900 according to an embodiment of the present invention groups adjacent prediction units into one conversion unit and performs discrete cosine transformation according to the conversion unit generated as the grouping result. Since a plurality of adjacent prediction units have a high probability of including similar residual values, if a plurality of adjacent prediction units are combined and subjected to discrete cosine transformation in a single conversion unit, the compression rate of coding can be greatly improved.

For this, the selector 1010 groups adjacent prediction units to select a plurality of adjacent prediction units to perform discrete cosine transform. Will be described in detail with reference to Figs. 11A to 11C and 12. Fig.

Figures 11A-11C illustrate types of conversion units in accordance with one embodiment of the present invention.

11A to 11C, the prediction unit 1120 for a predetermined coding unit 1110 may be a form in which the width of the coding unit 1110 is halved. The encoding unit 1110 may be the above-described maximum encoding unit or a sub-encoding unit having a size smaller than the maximum encoding unit.

The conversion units 1130 to 1150 may be different even when the encoding unit 1110 and the prediction unit 1120 are the same. 11A, the size of the conversion unit 1130 may be smaller than the prediction unit 1120, or the size of the conversion unit 1140 may be the same as that of the prediction unit 1120, as shown in FIG. 11B. In addition, the conversion unit 1150 according to an embodiment of the present invention may be larger than the size of the prediction unit 1120 as shown in FIG. 11C.

Referring again to FIG. 10, there is no limitation on the criterion that the selection unit 1010 selects a plurality of adjacent prediction units. However, according to an embodiment of the present invention, the selection unit 1010 can select a conversion unit based on the depth. The depth indicates the degree of stepwise reduction from the maximum encoding unit of the current slice or the current picture to the size of the sub-encoding unit, as described above. As described above with reference to FIGS. 3 and 6, the larger the depth, the smaller the size of the sub-encoding unit, and accordingly the included prediction unit becomes smaller. In this case, if discrete cosine transform is performed according to a transform unit having a size smaller than or equal to the predicted unit, header information is added for each transform unit as described above, and the compression rate of the image encoding is lowered.

Therefore, it is preferable that the sub-encoding units having a predetermined depth or more are grouped into prediction units included in the sub-encoding unit, set as one conversion unit, and subjected to discrete cosine transformation. For this, the selection unit 1010 sets a conversion unit based on the depth of the sub-encoding unit. For example, when the depth of the coding unit 1110 shown in FIG. 11C is larger than k, the selecting unit 1010 groups the prediction units 1120 into one conversion unit 1150.

In addition, according to another embodiment of the present invention, the selection unit 1010 can set a plurality of adjacent prediction units, which are predicted according to the same type of prediction mode, as one conversion unit. A plurality of adjacent prediction units predicted using intra prediction or inter prediction are set as one conversion unit. Since a plurality of adjacent prediction units predicted according to the same type of prediction mode have a high probability of including similar residual values, they can be grouped into one conversion unit and subjected to discrete cosine transform.

When the selecting unit 1010 sets a conversion unit, the conversion performing unit 1020 converts a plurality of prediction units into the frequency domain according to the set conversion unit. And generates discrete cosine coefficients by performing discrete cosine transformation of the selected plurality of prediction units in one conversion unit.

Referring again to FIG. 9, the quantizer 920 quantizes the frequency component coefficients, for example, discrete cosine coefficients, generated by the frequency converter 910. The input discrete cosine coefficients can be quantized according to a predetermined quantization step.

 The entropy encoding unit 930 entropy-codes the quantized discrete cosine coefficients in the quantization unit 920. Entropy-encodes discrete cosine coefficients using CABAC (Context-Adaptive Binary Arithmetic Coding) or CAVLC (Context-Adaptive Variable Length Coding).

The image encoding apparatus 900 according to another embodiment of the present invention can determine the optimal conversion unit by repeating the above-described discrete cosine transform, quantization, and entropy encoding on different conversion units. The process of selecting a plurality of adjacent prediction units is repeated mechanically to determine an optimum conversion unit. The optimal conversion unit can be determined in consideration of the R-D cost (Rate-Distortion Cost), which will be described in detail with reference to FIG.

Figure 12 shows different conversion units according to an embodiment of the present invention.

Referring to FIG. 12, the image encoding apparatus 900 according to the present invention repeats encoding for different conversion units.

As shown in FIG. 12, a predetermined encoding unit 1210 can be predictively encoded based on a prediction unit 1220 having a size smaller than an encoding unit. The residual values generated as a result of the prediction are subjected to the discrete cosine transform, which can be discrete cosine transformed based on different transform units as shown in FIG.

The first conversion unit 1230 is a conversion unit of the same size as the encoding unit 1210 and is a conversion unit of a size obtained by grouping all the prediction units included in the encoding unit 1210. [

The second conversion unit 1240 is a conversion unit having a half size of the width of the encoding unit 1210. The conversion unit 1240 is a conversion unit having a size obtained by grouping two prediction units adjacent in the vertical direction.

The third conversion unit 1250 is a conversion unit having a half size of the height of the encoding unit 1210. The conversion unit 1250 is a conversion unit having a size obtained by grouping two prediction units adjacent in the horizontal direction.

The fourth conversion unit 1250 is a conversion unit used when performing conversion to the same size as the prediction unit 1220. [

FIG. 13 illustrates an image decoding apparatus according to another embodiment of the present invention.

13, an image decoding apparatus 1300 according to an embodiment of the present invention includes an entropy decoding unit 1310, an inverse quantization unit 1320, and an inverse frequency transform unit 1330.

The entropy decoding unit 1310 entropy-decodes frequency component coefficients for a predetermined conversion unit. As described above with reference to Figs. 11A to 11C and 12, the conversion unit may be a conversion unit generated by grouping a plurality of adjacent prediction units.

As described above in connection with the image encoding apparatus 900, the conversion unit may be a conversion unit obtained by grouping a plurality of adjacent prediction units on the basis of depth, or a conversion unit obtained by grouping prediction units of the same type, And may be a changed unit obtained by grouping a plurality of adjacent prediction units performed. Also, as described above with reference to FIG. 12, the process of grouping a plurality of adjacent prediction units may be mechanically repeated to perform an ideal cosine transformation, a quantization, and an entropy decoding on different transformation units, .

The inverse quantization unit 1320 dequantizes the entropy-decoded frequency component coefficients in the entropy decoding unit 1310. And dequantizes the entropy-decoded frequency component coefficients according to the quantization step used in encoding the transform unit.

The inverse frequency transform unit 1330 inversely transforms the inversely quantized frequency component coefficients into a pixel domain. The transform unit of the pixel domain is restored by inverse discrete cosine transform of the inversely quantized discrete cosine coefficients. The restored transform unit may include a plurality of adjacent prediction units.

14 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

Referring to FIG. 14, in step 1410, an image encoding apparatus according to an exemplary embodiment of the present invention selects a plurality of adjacent prediction units and sets one conversion unit. It is possible to select a plurality of adjacent prediction units based on the depth or to select a plurality of adjacent prediction units on which prediction has been performed in the same type of prediction mode.

In step 1420, the image encoding apparatus converts a plurality of prediction units into the frequency domain according to the conversion unit set in step 1420. A plurality of prediction units are grouped and subjected to discrete cosine transform to generate a discrete cosine coefficient.

In operation 1430, the image encoding apparatus quantizes the frequency component coefficients generated in operation 1420, that is, the discrete cosine coefficients according to a predetermined quantization step.

In operation 1440, the image encoding apparatus entropy-codes the quantized frequency component coefficients in operation 1430. Entropy-encode the discrete cosine coefficients using CABAC or CAVLC.

The image encoding method according to another embodiment of the present invention may further include setting an optimal conversion unit by repeating the above steps 1410 to 1440 for different conversion units. The optimal conversion unit can be set by repeating discrete cosine transform, quantization, and entropy encoding on different conversion units as shown in Fig.

15 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

Referring to FIG. 15, in step 1510, an apparatus for decoding an image according to an embodiment of the present invention entropy decodes frequency component coefficients for a predetermined conversion unit. The frequency component coefficients may be discrete cosine coefficients.

In operation 1520, the image decoding apparatus dequantizes entropy-decoded frequency component coefficients in operation 1510. And dequantizes the discrete cosine coefficients using the quantization step used at the time of encoding.

In step 1530, the image decoding apparatus inverse transforms the dequantized frequency component coefficients into the pixel domain in step 1530, and restores the transform unit. The restored conversion unit is a conversion unit set by grouping adjacent prediction units. As described above, the conversion unit may be a conversion unit set by grouping a plurality of adjacent prediction units based on depth, or a conversion unit set by grouping a plurality of adjacent prediction units that have been predicted according to the same prediction mode.

According to the present invention, a conversion unit can be set to a size larger than a prediction unit, discrete cosine transformation can be performed, and the image can be compression-encoded more efficiently.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the following claims, and all of the equivalent or equivalent variations will fall within the scope of the present invention. In addition, the system according to the present invention can be embodied as computer-readable codes on a computer-readable recording medium.

For example, the image encoding apparatus, the image decoding apparatus, the image encoding unit, and the image decoding unit according to the exemplary embodiments of the present invention may be implemented by the apparatuses shown in FIGS. 1, 2, 4, 5, 9, 10 and 14 A bus coupled to the units of the processor, and at least one processor coupled to the bus. It may also include a memory coupled to the bus for storing instructions, received messages or generated messages and coupled to the at least one processor for performing the instructions as described above.

In addition, the computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the recording medium include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like. The computer-readable recording medium may also be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner.

Claims (3)

In the image decoding method,
Determining a maximum encoding unit from the received bit stream and determining the encoding unit hierarchically divided from the maximum encoding unit using the division information of the encoding unit parsed from the bit stream;
Performing entropy decoding on the bitstream to obtain quantized transform coefficients of a transform unit included in the encoded unit;
Performing inverse quantization and inverse transform on the quantized transform coefficients to obtain residual values of the transform unit; And
Determining a prediction image by performing prediction using at least one prediction unit included in the coding unit and restoring the coding unit using the residual values and the prediction image,
Wherein the size of the conversion unit included in the encoding unit and the size of the prediction unit included in the encoding unit are individually determined,
Wherein when the segmentation information indicates that the segmentation information is not segmented, at least one prediction unit is obtained from the encoding unit, and at least one conversion unit is obtained from the encoding unit.
The method according to claim 1,
Wherein the maximum coding unit is hierarchically divided into a coding unit of depth including at least one of a current depth and a low depth according to the division information,
Wherein when the division information indicates that the division information is divided at the current depth, the coding unit of the current depth is divided into four coding units of the lower depth, which are square independently of neighboring coding units. .
In the image decoding apparatus,
Determining a maximum encoding unit from the received bitstream, determining the encoding unit hierarchically divided from the maximum encoding unit using the division information of the encoding unit parsed from the bitstream, and performing entropy decoding on the bitstream To obtain quantized transform coefficients of a transform unit included in the encoding unit; And
Determining a prediction image by performing prediction using at least one prediction unit included in the coding unit by performing inverse quantization and inverse transformation on the quantized transform coefficients to obtain residual values of the conversion unit, And a decoding unit for decoding the encoding unit using the residual values and the prediction image,
Wherein the size of the conversion unit included in the encoding unit and the size of the prediction unit included in the encoding unit are individually determined,
Wherein at least one prediction unit is obtained from an encoding unit and at least one conversion unit is obtained from an encoding unit when the segmentation information indicates that the segmentation information is not segmented.

Images