KR20130041039A - Method and apparatus for encoding and decoding image using large transform unit - Google Patents

Abstract

PURPOSE: A method for encoding and decoding an image using a large-sized conversion unit and a device thereof are provided to efficiently decode an image by setting a conversion unit with a larger size than a prediction unit. CONSTITUTION: A processor(200) determines one or more encoding units, one or more prediction units, and one or more conversion units using information parsed from a received bit stream. A decoding unit(230) restores data on the prediction units from the bit stream, and restores an image using the restored data. The encoding units are hierarchically divided from an encoding unit having the maximum size depending on the depth. The conversion units are determined in a shape having a larger size than the prediction units. [Reference numerals] (230) Image data decoding unit; (AA) Image data obtaining unit; (BB) Encoding information extracting unit;

Description

Method and apparatus for encoding and decoding image using large transform unit {Method and apparatus for encoding and decoding image using large transform unit}

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

Most image encoding and decoding methods and apparatus convert an image of a pixel domain into a frequency domain and encode the image for image compression. Discrete cosine transform, a technique of frequency conversion, is a well-known technique used for video or audio compression. In an image encoding method using a discrete cosine transform, discrete cosine transforms are generated by performing a discrete cosine transform on an image of a pixel domain, and the generated coefficients are quantized and entropy encoded.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method and apparatus for encoding and decoding an image using more efficient discrete cosine transform, and to provide 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: setting one transform unit by selecting a plurality of adjacent prediction units; Generating frequency component coefficients by converting the plurality of prediction units into a frequency domain according to the transformation unit; Quantizing the generated frequency component coefficients; And entropy encoding the quantized frequency component coefficients.

According to another embodiment of the present invention, the setting may be performed based on a depth indicating a degree reduced in steps from a maximum coding unit of the current slice or a current picture to a sub coding unit including the plurality of adjacent prediction units. Setting a conversion unit of.

According to another embodiment of the present invention, the setting may include setting one transform unit by selecting a plurality of adjacent prediction units on which prediction is performed according to the same kind of prediction mode.

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

According to another embodiment of the present invention, the method of encoding the image, selecting a plurality of adjacent prediction units to set one transform unit for a different transform unit, the selected plurality of prediction unit to one transform unit Generating frequency component coefficients by transforming the frequency domain to a frequency domain, repeating the quantizing of the generated frequency component coefficients and entropy encoding the quantized frequency component coefficients to set an optimal transform unit. do.

According to an embodiment of the present invention, an image encoding apparatus selects a plurality of adjacent prediction units to set one transform unit, and converts the plurality of prediction units to a frequency domain according to the transform unit. 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 a method of decoding an image, comprising: entropy decoding frequency component coefficients generated by transforming the frequency domain according to a predetermined conversion unit; Dequantizing the entropy decoded frequency component coefficients; And inversely transforming the frequency component coefficients into the pixel domain to reconstruct a plurality of adjacent prediction units included in the transform unit.

According to an aspect of the present invention, there is provided an apparatus for decoding an image comprising: an entropy decoding unit configured to entropy decode frequency component coefficients generated by transforming a frequency domain according to a predetermined transformation unit; An inverse quantizer for inversely quantizing the entropy decoded frequency component coefficients; And an inverse frequency transformer configured to inversely transform the frequency component coefficients into the pixel domain to restore a plurality of adjacent prediction units included in the transform unit.

In order to solve the above technical problem, an embodiment of the present invention provides a computer-readable recording medium having recorded thereon a program for executing the above-described video 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.
3 illustrates a hierarchical coding 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.
8A and 8B illustrate division forms of a coding unit, a prediction unit, and a transformation unit, according to an embodiment of the present invention.
9 illustrates an image encoding apparatus according to another embodiment of the present invention.
10 illustrates a frequency converter according to an embodiment of the present invention.
11A-11C illustrate types of transformation units in accordance with one embodiment of the present invention.
12 illustrates different transformation units in accordance with an embodiment of the present invention.
13 shows an image decoding apparatus according to another embodiment of the present invention.
14 is a flowchart illustrating a video 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.

Referring to FIG. 1, an image encoding apparatus 100 according to an embodiment of the present invention may include a maximum coding unit splitter 110, a coded depth determiner 120, an image data encoder 130, and an encoding information encoder. 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, a coding unit may be expressed using a maximum coding 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 coding unit may be reduced from the maximum coding unit to the minimum coding unit, the depth of the maximum coding unit may be defined as the minimum depth, and the depth of the minimum coding unit may 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 differently for a picture or a slice, or differently for each maximum coding unit. The determined maximum depth is output to the encoding information encoder 140, and the image data for each maximum coding unit is output to the image data encoder 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 coding unit may be divided into sub-coding units having 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 may perform a plurality of processing steps for image encoding based on various sizes and various types of processing units. In order to encode the image data, processing steps such as prediction, frequency conversion, and entropy encoding are performed, and processing units having the same size may be used in all steps, or processing units having different sizes may be used in stages.

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 half of at least one of a height or a width of a coding 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 shape. For example, the intra mode may be performed only for a prediction unit having a square size of 2N × 2N or N × N. 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 the coding unit, a prediction mode having the smallest encoding error may 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. Frequency conversion may be performed based on a data unit having a size smaller than or equal to the coding unit for frequency conversion of the coding unit. Hereinafter, the processing unit which becomes the basis of frequency conversion is called 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.

Referring to FIG. 2, the image decoding apparatus 200 according to an embodiment of the present invention includes an image data acquisition unit 210, an encoding information extractor 220, and an image data decoder 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 starting from a coding unit having a width x height of 64x64. In addition to the square coding units, there may be coding units having a width x height of 64x32, 32x64, 32x16, 16x32, 16x8, 8x16, 8x4, and 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. [

When the resolution is high or the amount of data is large, it is desirable that the maximum size of the coding size be relatively large in order to not only improve the compression ratio but also accurately reflect the image characteristics. 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 represents the total number of layers in the hierarchical coding 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.

Residual values are generated based on the prediction unit output from the intra predictor 410, the motion estimator 420, and the motion compensator 425, and the generated residual values are the frequency converter 430 and the quantizer. 440 is output as a quantized transform coefficient.

The quantized transform coefficients are restored to the residual values through the inverse quantizer 460 and the frequency inverse transformer 470, and the restored residual values are passed through the deblocking unit 480 and the loop filtering unit 490. Processed and output to the reference frame 495. The quantized transform coefficients may be output to the bitstream 455 via the entropy encoder 450.

In order to encode according to an image encoding method according to an embodiment of the present invention, the components of the image encoder 400, an intra predictor 410, a motion estimator 420, a motion compensator 425, and a frequency transform The unit 430, the quantizer 440, the entropy encoder 450, the inverse quantizer 460, the frequency inverse transformer 470, the deblocking unit 480, and the loop filtering unit 490 are all the maximum coding units. The image encoding processes are processed based on a sub coding unit, a prediction unit, and a transformation unit according to the depth.

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 result of the intra prediction of the intra predictor 550 or the result of the motion compensation of the motion compensator 560 and reconstructed for each coding unit. The reconstructed coding unit is used for prediction of the next coding unit or the next picture through the deblocking unit 570 and the loop filtering unit 580.

Parsing unit 510, entropy decoding unit 520, inverse quantization unit 530, frequency inverse transform unit (components) of the image decoding unit 400 to decode according to the image decoding method according to an embodiment of the present invention 540, the intra predictor 550, the motion compensator 560, the deblocking unit 570, and the loop filtering unit 580 are all based on a maximum coding unit, a sub coding unit according to depth, a prediction unit, and a transformation unit. The video decoding processes are performed.

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 coding unit 710 is 64x64 size, frequency conversion may be performed using the 32x32 size transform 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 coding units may be smaller than the sub coding 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 a video encoding apparatus according to another embodiment of the present invention.

Referring to FIG. 9, an image encoding apparatus 900 according to an embodiment of the present invention includes a frequency converter 910, a quantizer 920, and an entropy encoder 930.

The frequency converter 910 receives an image processing unit of a pixel domain and converts the image processing unit into a frequency domain. A plurality of prediction units including residual values generated through intra prediction or inter prediction are received and converted into a frequency domain. The conversion to the frequency domain produces a coefficient of frequency components. According to one embodiment of the invention, the transform to frequency domain may be a discrete cosine transform, where discrete cosine coefficients are generated as a result of the discrete cosine transform. Hereinafter, the discrete cosine transform will be described as an example. However, it will be apparent to those skilled in the art that the present invention may be applied to all transforms for transforming an image of all pixel domains into a frequency domain.

In addition, according to an embodiment of the present invention, the frequency converter 910 sets one transform unit by grouping a plurality of prediction units, and performs discrete cosine transform according to the set transform unit. It will be described in detail with reference to Figures 10, 11a, 11b and 12.

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

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

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

However, due to the header information added to each transformation unit, the smaller the transformation unit, the larger the added overhead, thereby lowering the compression ratio of the video encoding. To solve this problem, the image encoding apparatus 900 according to an embodiment of the present invention groups a plurality of adjacent prediction units into one transform unit and performs discrete cosine transform according to the transform unit generated as a result of the grouping. Since a plurality of neighboring prediction units have a high probability of including similar residual values, if a plurality of adjacent prediction units are bundled and discrete cosine transformed into one transform unit, the compression ratio of encoding may be greatly improved.

To this end, the selector 1010 selects a plurality of adjacent prediction units to perform discrete cosine transform by grouping into one transform unit. This will be described in detail with reference to FIGS. 11A-11C and 12.

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

11A to 11C, the prediction unit 1120 may have a shape in which the width of the coding unit 1110 is half divided with respect to a predetermined coding unit 1110. The coding unit 1110 may be the maximum coding unit described above or may be a sub-coding unit having a smaller size than the maximum coding unit.

Even when the coding unit 1110 and the prediction unit 1120 are the same, the transformation units 1130 to 1150 may be different. As illustrated in FIG. 11A, the size of the transform unit 1130 may be smaller than the prediction unit 1120, or as illustrated in FIG. 11B, the size of the transform unit 1140 may be the same as the prediction unit 1120. In addition, the transform unit 1150 according to an embodiment of the present invention may be larger than the size of the prediction unit 1120 as illustrated in FIG. 11C.

Referring again to FIG. 10, the criterion for the selection unit 1010 to select a plurality of adjacent prediction units is not limited. However, according to an embodiment of the present invention, the selector 1010 may select a conversion unit based on the depth. As described above, the depth represents the degree of reduction in stages from the maximum coding unit of the current slice or the current picture to the size of the sub coding unit. As described above with reference to FIGS. 3 and 6, the larger the depth, the smaller the size of the sub coding unit, and the smaller the prediction unit included. In this case, when the discrete cosine transform is performed according to a transform unit having a size smaller than or equal to the prediction unit, as described above, header information is added to each transform unit to reduce the compression rate of the image encoding.

Therefore, it is preferable that a sub coding unit having a predetermined depth or more is set as one transformation unit by grouping prediction units included in the sub coding unit, and discrete cosine transforming is performed. To this end, the selector 1010 sets a transformation unit based on the depth of the sub coding unit. For example, when the depth of the coding unit 1110 illustrated in FIG. 11C is greater than k, the selector 1010 sets the prediction units 1120 as one transformation unit 1150.

In addition, according to another embodiment of the present invention, the selector 1010 may set a plurality of adjacent prediction units on which prediction is performed according to the same kind of prediction mode as one transformation unit. A plurality of adjacent prediction units predicted using intra prediction or inter prediction are set as one transform unit. Since a plurality of adjacent prediction units subjected to prediction according to the same kind of prediction mode have a high probability of including similar residual values, the discrete cosine transform may be grouped into one transformation unit.

When the selector 1010 sets a transform unit, the transform performer 1020 converts the plurality of prediction units into the frequency domain according to the set transform unit. Discrete cosine transforms the selected plurality of prediction units into one transform unit to generate discrete cosine coefficients.

Referring back to FIG. 9, the quantization unit 920 quantizes frequency component coefficients generated by the frequency converter 910, for example, discrete cosine coefficients. Discrete cosine coefficients input according to a predetermined quantization step may be quantized.

 The entropy encoder 930 entropy encodes the discrete cosine coefficients quantized by the quantizer 920. Discrete cosine coefficients are entropy coded using CABAC (Context-Adaptive Binary Arithmetic Coding) or CAVLC (Context-Adaptive Variable Length Coding).

According to another embodiment of the present invention, the image encoding apparatus 900 may determine the optimal transform unit by repeating the above-described discrete cosine transform, quantization, and entropy encoding for different transform units. The process of selecting a plurality of adjacent prediction units is mechanically repeated to determine an optimal transform unit. The optimal conversion unit may be determined in consideration of the R-D cost, which will be described in detail with reference to FIG. 12.

12 illustrates different transformation units in accordance with an embodiment of the present invention.

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

As illustrated in FIG. 12, a predetermined coding unit 1210 may be predictively encoded based on a prediction unit 1220 having a smaller size than the coding unit. The residual values generated as a result of the prediction are discrete cosine transformed, and may be discrete cosine transformed based on different transformation units as shown in FIG. 12.

The transform unit 1230 shown first is a transform unit having the same size as the coding unit 1210 and is a transform unit having a size in which all prediction units included in the coding unit 1210 are grouped.

The second transform unit 1240 is a transform unit having a size obtained by dividing the width of the coding unit 1210 by half, and a transform unit having a size of grouping two adjacent prediction units in the vertical direction.

The third transform unit 1250 is a transform unit having a size obtained by dividing the height of the coding unit 1210 by half, and a transform unit having a size of grouping two adjacent prediction units in the horizontal direction.

The fourth transform unit 1250 is a transform unit used when the transform is performed in the same size as the prediction unit 1220.

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

Referring to FIG. 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 converter 1330.

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

As described above with respect to the image encoding apparatus 900, a transform unit may be a transform unit that groups a plurality of adjacent prediction units based on a depth, or may be predicted according to the same type of prediction mode, that is, an intra prediction mode or an inter prediction mode. It may be a changed unit grouping a plurality of adjacent prediction units performed. In addition, as described above with reference to FIG. 12, the method may be an optimal transform unit selected by mechanically repeating a process of grouping a plurality of adjacent prediction units to perform abnormal cosine transform, quantization, and entropy decoding on different transform units. .

The inverse quantization unit 1320 dequantizes the frequency component coefficients entropy decoded by the entropy decoding unit 1310. Inverse quantization of the entropy decoded frequency component coefficients is performed according to a quantization step used in encoding a transform unit.

The inverse frequency converter 1330 inversely transforms the inversely quantized frequency component coefficients into the pixel domain. Inverse discrete cosine transforms the inverse quantized discrete cosine coefficients to reconstruct the transform unit of the pixel domain. The reconstructed transform unit may include a plurality of adjacent prediction units.

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

Referring to FIG. 14, in operation 1410, the apparatus for encoding an image sets one transform unit by selecting a plurality of adjacent prediction units. A plurality of adjacent prediction units may be selected based on the depth, or a plurality of adjacent prediction units in which prediction is performed in the same kind of prediction mode may be selected.

In operation 1420, the image encoding apparatus converts the plurality of prediction units into the frequency domain according to the transformation unit set in operation 1420. Discrete cosine coefficients are generated by grouping a plurality of prediction units and performing discrete cosine transform.

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

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

The image encoding method according to another embodiment of the present invention may further include setting the optimal conversion unit by repeating steps 1410 to 1440 described above for different conversion units. Discrete cosine transform, quantization and entropy coding may be repeated for different transform units as shown in FIG. 12 to set an optimal transform unit.

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

Referring to FIG. 15, in operation 1510, the image decoding apparatus entropy-decodes frequency component coefficients for a predetermined transform unit. The frequency component coefficients may be discrete cosine coefficients.

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

In operation 1530, the image decoding apparatus inversely transforms inversely quantized frequency component coefficients into the pixel domain to restore a transform unit. The reconstructed transform unit is a transform unit set by grouping a plurality of adjacent prediction units. As described above, the transform unit may be a transform unit set by grouping a plurality of adjacent prediction units based on depth, or a transform unit set by grouping a plurality of adjacent prediction units on which prediction is performed according to the same prediction mode.

According to the present invention, the transform unit may be set to a size larger than the prediction unit, and the discrete cosine transform may be performed, thereby compressing and encoding the image more efficiently.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited to the above-described embodiments, which can be variously modified and modified by those skilled in the art. Modifications are possible. Accordingly, the spirit of the invention should be understood only by the claims set forth below, and all equivalent or equivalent modifications will fall within the scope of the 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 embodiment of the present invention, respectively, as shown in FIGS. 1, 2, 4, 5, 9, 10, and 14, respectively. A bus coupled to units of, may include 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.

The computer-readable recording medium also includes all kinds of recording devices 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 can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Claims (4)

In the image decoding apparatus,
At least one coding unit of a hierarchical structure for decoding an image, using information on a split form of a coding unit parsed from a received bitstream, information on a prediction unit, and information on a transformation unit, and each coding unit A processor that determines at least one prediction unit for prediction for and at least one transform unit for inverse transform for each coding unit; And
Parse the transform coefficients generated by converting each coding unit according to a predetermined transform unit from the bitstream, entropy decode, dequantize, and inverse transform the transform coefficients to restore data of the at least one prediction unit. And a decoder configured to reconstruct the image by performing intra prediction and inter prediction using the reconstructed data.
The coding units of the hierarchical structure are hierarchically divided according to depth from coding units of the largest size in which the image is divided.
And the predetermined transform unit is determined to have a larger size than the prediction unit. The method of claim 1,
The at least one prediction unit includes a plurality of prediction units, and a transform unit that is determined to have a larger size than the prediction unit is generated by combining the plurality of prediction units. The method of claim 1,
The size of the at least one transform unit is different from the size of the at least one prediction unit and the size of the coding unit. The method of claim 1,
The image is hierarchically divided from a maximum coding unit according to the maximum coding unit size information to coding units of the coded depth according to a depth,
The encoding unit of the current depth is one of the square data units divided from the encoding unit of the higher depth,
The coding unit of the current depth is divided into coding units of a lower depth up to a corresponding coding depth independently of neighboring coding units.

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