Source: http://patents.com/us-8964840.html
Timestamp: 2018-12-14 00:33:29
Document Index: 198366876

Matched Legal Cases: ['Application No. 2011239130', 'Application No. 2012146757', 'Application No. 11766126', 'Application No. 2012146757', 'Application No. 2011239130', 'Application No. 10', 'art, 9']

US Patent # 8,964,840. Determining intra prediction mode of image coding unit and image decoding unit - Patents.com
United States Patent 8,964,840
Min , et al. February 24, 2015
Determining intra prediction mode of image coding unit and image decoding unit
Min; Jung-hye (Suwon-si, KR), Alshina; Elena (Suwon-si, KR), Han; Woo-jin (Suwon-si, KR)
Family ID: 1000000940264
13/969,871
US 20130329793 A1 Dec 12, 2013
13080021 Apr 5, 2011 8619858
Apr 5, 2010 [KR] 10-2010-0031145
Current U.S. Class: 375/240.12; 375/240.01; 375/240.03; 375/240.22; 375/240.24
Current CPC Class: H04N 19/00575 (20130101); H04N 19/00315 (20130101); H04N 19/00084 (20130101); H04N 19/0003 (20130101); H04N 19/00278 (20130101); H04N 19/00969 (20130101); H04N 19/00042 (20130101); H04N 19/00763 (20130101)
Current International Class: H04N 7/12 (20060101); H04N 11/04 (20060101); H04N 11/02 (20060101)
2005/0141618 June 2005 Park et al.
2006/0146191 July 2006 Kim et al.
2006/0188023 August 2006 Ju
2006/0215763 September 2006 Morimoto et al.
2008/0253448 October 2008 Lin et al.
2008/0285652 November 2008 Oxman et al.
2009/0190659 July 2009 Lee et al.
2011/0211757 September 2011 Kim et al.
2011/0222723 September 2011 He et al.
2012/0057801 March 2012 Aldrich et al.
2013/0010866 January 2013 Ju
1705920 Sep 2006 EP
1753242 Feb 2007 EP
1950971 Jul 2008 EP
2316909 Feb 2008 RU
Communication from the Australian Patent Office issued Oct. 11, 2013 in counterpart Canadian Application No. 2011239130. cited by applicant .
Communication dated Jan. 20, 2014, issued by the Russian Federal Service for Intellectual Property in counterpart Russian Application No. 2012146757. cited by applicant .
International Search Report (PCT/ISA/210) issued on Dec. 7, 2011 in the International Patent Application No. PCT/KR2011/002375. cited by applicant .
http://web.archive.org/web/20100305134542/http://en.wikipedia.org/wiki/Can- ny.sub.--edge.sub.--detector, Mar. 5, 2010. cited by applicant .
Wiegand T et al: "BoG report: residual quadtree structure", 94. MPEG Meeting; Oct. 11-15, 2010; Guangzhou; (Motion Picture Expert Group or ISO/IEC JTC1/SC29/WG11) No. M18590, Oct. 28, 2010, XP030047180, pp. 1-17. cited by applicant .
Peng X et al: "Improve intra frame coding by PU/TU reordering", 94. MPEG Meeting; Oct. 11-15, 2010; Guangzhou; (Motion Picture Expert Group or ISO/IEC JTC1/SC29/WG11) No. M18318, Oct. 28, 2010, XP030046908, pp. 1-4. cited by applicant .
Communication from the European Patent Office issued Jul. 5, 2013 in counterpart European Application No. 11766126.4. cited by applicant .
Communication dated Sep. 19, 2014, issued by the Russian Federal Service for Intellectual Property in counterpart Russian Application No. 2012146757. cited by applicant .
Communication dated Oct. 27, 2014, issued by the Australian Patent Office in counterpart Australian Application No. 2011239130. cited by applicant.
This application is a continuation application of U.S. patent application Ser. No. 13/080,021, filed Apr. 5, 2011, which claims priority from Korean Patent Application No. 10-2010-0031145, filed on Apr. 5, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
1. An apparatus for decoding an image, the apparatus comprising: an entropy decoder which obtains first information that indicates an intra prediction mode of a luminance block and second information that indicates an intra prediction mode of a chrominance block corresponding to the luminance block, from a bitstream; and an intra prediction performer that performs intra prediction on the luminance block according to the intra prediction mode of the luminance block and performs intra prediction on the chrominance block according to the intra prediction mode of the chrominance block, wherein the intra prediction mode of the luminance block includes a particular direction among a plurality of directions and the particular direction is indicated by one of dx number in a horizontal direction and a fixed number in a vertical direction, and dy number in the vertical direction and a fixed number in the horizontal direction, and wherein the intra prediction performer determines a number of neighboring pixels to be obtained according to a position of a current pixel and the particular direction indicated by the intra prediction mode of the luminance block, the neighboring pixels being located on a left side of the luminance block or an upper side of the luminance block, and when the second information indicates that the intra prediction mode of the chrominance block is equal to the intra prediction mode of the luminance block, the intra prediction mode of the chrominance block is determined to be equal to the intra prediction mode of the luminance block.
2. The apparatus of claim 1, wherein (dx,dy) has an at least one value selected from among the group consisting of (-32, 32), (-26, 32), (-21, 32), (-17, 32), (-13, 32), (-9, 32), (-5, 32), (-2, 32), (0.32), (2, 32), (5, 32), (9, 32), (13, 32), (17,32), (21, 32), (26, 32), (32, 32), (32, -26), (32, -21), (32, -17), (32, -13), (32, -9), (32, -5), (32, -2), (32, 0), (32, 2), (32, 5), (32, 9), (32, 13), (32, 17), (32, 21), (32, 26) and (32, 32).
3. The apparatus of claim 1, wherein candidate intra prediction modes of the chrominance block comprise a direct current (DC) mode, a horizontal mode, a vertical mode, and a plane mode.
4. The apparatus of claim 1, wherein a usable intra prediction mode applied to the luminance block is determined according to a size of the luminance block.
FIG. 16A through 16C are a reference diagram for explaining intra prediction modes of a luminance component coding unit having various directionalities, according to an exemplary embodiment;
FIG. 19A through 19B are a reference diagram for explaining a mapping process of intra prediction modes between luminance component coding units having different sizes, according to an exemplary embodiment;
Hereinafter, a `coding unit` refers to an encoding data unit in which the image data is encoded at an encoder side, and an encoded data unit in which the encoded image data is decoded at a decoder side. Also, a `coded depth` refers to a depth at which a coding unit is encoded.
For example, the video encoding apparatus 100 may select a data unit that is different from the coding unit, to predict the coding unit. For example, when a coding unit has a size of 2N.times.2N (where N is a positive integer), a data unit for prediction may have a size of 2N.times.2N, 2N.times.N, N.times.2N, or N.times.N. In other words, motion prediction may be performed based on a data unit obtained by splitting at least one of a height and a width of the coding unit. Hereinafter, the data unit that is a basis unit of prediction will be referred to as a "prediction unit".
A prediction mode may be at least one of an intra mode, an inter mode, and a skip mode, wherein a certain prediction mode is only performed on a prediction unit having a certain size or shape. For example, an intra mode may be performed only on a square prediction unit having a size of 2N.times.2N or N.times.N. Also, a skip mode may be performed only on a prediction unit having a size of 2N.times.2N. If a plurality of prediction units are included in the coding unit, prediction may be performed on each prediction unit to select a prediction mode having a minimum error.
Alternatively, the video encoding apparatus 100 may transform the image data based on a data unit that is different from the coding unit. In order to transform the coding unit, transformation may be performed based on a data unit having a size smaller than or equal to the coding unit. A data unit used as a base of the transformation will be referred to as a "transform unit".
In the video encoding apparatus 100, the deeper coding unit may be a coding unit obtained by dividing a height or width of a coding unit of an upper depth, which is one layer above, by two. In other words, when the size of the coding unit of the current depth is 2N.times.2N, the size of the coding unit of the lower depth is N.times.N. Also, the coding unit of the current depth having the size of 2N.times.2N may include a maximum of 4 of the coding units of the lower depth.
Referring to FIG. 3, a size of a coding unit may be expressed in width.times.height, and may be 64.times.64, 32.times.32, 16.times.16, 8.times.8 and 4.times.4. Aside from the coding unit having a square shape, the coding unit may have a size of 64.times.32, 32.times.64, 32.times.16, 16.times.32, 16.times.8, 8.times.16, 8.times.4, or 4.times.8.
In video data 310, a resolution is 1920.times.1080, a maximum size of a coding unit is 64, and a maximum depth is 2. In video data 320, a resolution is 1920.times.1080, a maximum size of a coding unit is 64, and a maximum depth is 4. In video data 330, a resolution is 352.times.288, a maximum size of a coding unit is 16, and a maximum depth is 2.
Partial data units are shown in FIG. 6 as the prediction units of a coding unit along the horizontal axis according to each depth. In other words, if the coding unit 610 having the size of 64.times.64 and the depth of 0 is a prediction unit, the prediction unit may be split into partial data units included in the encoding unit 610, i.e. a partial data unit 610 having a size of 64.times.64, partial data units 612 having the size of 64.times.32, partial data units 614 having the size of 32.times.64, or partial data units 616 having the size of 32.times.32.
A prediction unit of the coding unit 620 having the size of 32.times.32 and the depth of 1 may be split into partial data units included in the coding unit 620, i.e. a partial data unit 620 having a size of 32.times.32, partial data units 622 having a size of 32.times.16, partial data units 624 having a size of 16.times.32, and partial data units 626 having a size of 16.times.16.
A prediction unit of the coding unit 630 having the size of 16.times.16 and the depth of 2 may be split into partial data units included in the coding unit 630, i.e. a partial data unit having a size of 16.times.16 included in the coding unit 630, partial data units 632 having a size of 16.times.8, partial data units 634 having a size of 8.times.16, and partial data units 636 having a size of 8.times.8.
A prediction unit of the coding unit 640 having the size of 8.times.8 and the depth of 3 may be split into partial data units included in the coding unit 640, i.e. a partial data unit having a size of 8.times.8 included in the coding unit 640, partial data units 642 having a size of 8.times.4, partial data units 644 having a size of 4.times.8, and partial data units 646 having a size of 4.times.4.
The coding unit 650 having the size of 4.times.4 and the depth of 4 is the minimum coding unit and a coding unit of the lowermost depth. A prediction unit of the coding unit 650 is only assigned to a partial data unit having a size of 4.times.4.
The video encoding apparatus 100 or 200 encodes or decodes an image according to coding units having sizes smaller than or equal to a maximum coding unit for each maximum coding unit. Sizes of transform units for transform during encoding may be selected based on data units that are not larger than a corresponding coding unit. For example, in the video encoding apparatus 100 or 200, if a size of the coding unit 710 is 64.times.64, transform may be performed by using the transform units 720 having a size of 32.times.32. Also, data of the coding unit 710 having the size of 64.times.64 may be encoded by performing the transform on each of the transform units having the size of 32.times.32, 16.times.16, 8.times.8, and 4.times.4, which are smaller than 64.times.64, and then a transform unit having the least coding error may be selected.
The information 800 includes information about a split type of a prediction unit of a current coding unit, wherein a split prediction unit is a data unit for prediction encoding the current coding unit. For example, a current coding unit CU.sub.--0 having a depth 0 and size of 2N.times.2N may be split into any one of a prediction unit 802 having a size of 2N.times.2N, a prediction unit 804 having a size of 2N.times.N, a prediction unit 806 having a size of N.times.2N, and a prediction unit 808 having a size of N.times.N. Here, the information 800 about a split type is set to indicate one of the prediction unit 804 having a size of 2N.times.N, the prediction unit 806 having a size of N.times.2N, and the prediction unit 808 having a size of N.times.N
The encoding information extractor 220 of the video decoding apparatus 200 may extract and use the information 800, 810, and 820 for decoding, according to each deeper coding unit FIG. 9 is a diagram of deeper coding units according to depths, according to an exemplary embodiment.
A prediction unit 910 for prediction encoding a coding unit having a depth of 0 and a size of 2N.sub.--0.times.2N.sub.--0 may include a split type 912 having a size of 2N.sub.--0.times.2N.sub.--0, a split type 914 having a size of 2N.sub.--0.times.N.sub.--0, a split type 916 having a size of N.sub.--0.times.2N.sub.--0, and a split type 918 having a size of N.sub.--0.times.N.sub.--0.
Encoding via motion prediction is repeatedly performed on one prediction unit having a size of 2N.sub.--0.times.2N.sub.--0, two prediction units having a size of 2N.sub.--0.times.N.sub.--0, two prediction units having a size of N.sub.--0.times.2N.sub.--0, and four prediction units having a size of N.sub.--0.times.N.sub.--0, according to each split type. The prediction in an intra mode and an inter mode may be performed on the prediction units having the sizes of 2N.sub.--0.times.N.sub.--0, N.sub.--0.times.2N.sub.--0 and N.sub.--0.times.N.sub.--0 and N.sub.--0.times.N.sub.--0. The motion prediction in a skip mode is performed only on the prediction unit having the size of 2N.sub.--0.times.2N.sub.--0.
If the encoding error is the smallest in the split type 918 having the size N.sub.--0.times.N.sub.--0, a depth is changed from 0 to 1 to split the partition type 918 in operation 920, and encoding is repeatedly performed on coding units 922, 924, 926, and 928 having a depth of 2 and a size of N.sub.--0.times.N.sub.--0 to search for a minimum encoding error.
Since the encoding is repeatedly performed on the coding units 922, 924, 926, and 928 having the same depth, only encoding of a coding unit having a depth of 1 will be described as an example. A prediction unit 930 for motion predicting a coding unit having a depth of 1 and a size of 2N.sub.--1.times.2N.sub.--1 (=N.sub.--0.times.N.sub.--0) may include a split type 932 having a size of 2N.sub.--1.times.2N.sub.--1, a split type 934 having a size of 2N.sub.--1.times.N.sub.--1, a split type 936 having a size of N.sub.--1.times.2N.sub.--1, and a split type 938 having a size of N.sub.--1.times.N.sub.--1. Encoding via motion prediction is repeatedly performed on one prediction unit having a size of 2N.sub.--1.times.2N.sub.--1, two prediction units having a size of 2N.sub.--1.times.N.sub.--1, two prediction units having a size of N.sub.--1.times.2N.sub.--1, and four prediction units having a size of N.sub.--1.times.N.sub.--1, according to each split type.
If an encoding error is the smallest in the split type 938 having the size of N.sub.--1.times.N.sub.--1, a depth is changed from 1 to 2 to split the split type 938 in operation 940, and encoding is repeatedly performed on coding units 942, 944, 946, and 948, which have a depth of 2 and a size of N.sub.--2.times.N.sub.--2 to search for a minimum encoding error.
When a maximum depth is d, split information according to each depth may be set up to when a depth becomes d-1. In other words, a prediction unit 950 for motion predicting a coding unit having a depth of d-1 and a size of 2N_(d-1).times.2N_(d-1) may include a split type 952 having a size of 2N_(d-1).times.2N_(d-1), a split type 954 having a size of 2N_(d-1).times.N_(d-1), a split type 956 having a size of N_(d-1).times.2N_(d-1), and a split type 958 having a size of N_(d-1).times.N_(d-1).
Encoding via motion prediction may be repeatedly performed on one prediction unit having a size of 2N_(d-1).times.2N_(d-1), two prediction units having a size of 2N_(d-1).times.N_(d-1), two prediction units having a size of N_(d-1).times.2N_(d-1), and four prediction units having a size of N_(d-1).times.N_(d-1), according to each split type. Since the maximum depth is d, a coding unit 952 having a depth of d-1 is not split.
In order to determine a coded depth for the coding unit 912, the video encoding apparatus 100 selects a depth having the least encoding error by comparing encoding errors according to depths. For example, an encoding error of a coding unit having a depth of 0 may be encoded by performing motion prediction on each of the split types 912, 914, 916, and 918, and than a prediction unit having the least encoding error may be determined. Similarly, a prediction unit having the least encoding error may be searched for, according to depths 0 through d-1. In a depth of d, an encoding error may be determined by performing motion prediction on the prediction unit 960 having the size of 2N_d.times.2N_d. As such, the minimum encoding errors according to depths are compared in all of the depths of 1 through d, and a depth having the least encoding error may be determined as a coded depth. The coded depth and the prediction unit of the corresponding coded depth mode may be encoded and transmitted as information about an encoding mode. Also, since a coding unit is split from a depth of 0 to a coded depth, only split information of the coded depth is set to 0, and split information of depths excluding the coded depth is set to 1.
In the prediction units 1060, some encoding units 1014, 1016, 1022, 1032, 1048, 1050, 1052, and 1054 are obtained by splitting the coding units in the encoding units 1010. In other words, split types in the coding units 1014, 1022, 1050, and 1054 have a size of 2N.times.N, split types in the coding units 1016, 1048, and 1052 have a size of N.times.2N, and a split type of the coding unit 1032 has a size of N.times.N. Prediction units of the coding units 1010 are smaller than or equal to each coding unit.
The information about a split type may indicate a split type of a transform unit of a coding unit in a coded depth as one of 2N.times.2N, 2N.times.N, N.times.2N, and N.times.N. The prediction mode may indicate a motion prediction mode as one of an intra mode, an inter mode, and a skip mode. The intra mode may be defined only in the split types of 2N.times.2N and N.times.N, and the skip mode may be only defined in the split type of 2N.times.2N. The transform unit may have two sizes in the intra mode, and two sizes in the inter mode.
The chrominance data may be expressed using a lower amount of data than the luminance data, based on the premise that a person is generally more sensitive to the luminance information than the chrominance information. Referring to FIG. 12A, one coding unit having a 4:2:0 format includes luminance data 1210 having a size of H.times.W (H and W are positive integers), and two pieces of chrominance data 1220 and 1230 having a size of (H/2).times.(W/2) obtained by sampling the chrominance components Cb and Cr by 1/4. Referring to FIG. 12B, one coding unit having a 4:2:2 format includes luminance data 1240 having a size of H.times.W (H and W are positive integers), and two pieces of chrominance data 1250 and 1260 having a size of H.times.(W/2) obtained by sampling the chrominance components Cb and Cr by 1/2 in a horizontal direction. Also, referring to FIG. 12C, when one coding unit has a 4:4:4 format, the coding unit includes luminance data 1270, and chrominance data 1280 and 1290, each having a size of H.times.W without sampling the chrominance components Cb and Cr, to precisely express a chrominance component image.
According to an exemplary embodiment, the number of intra prediction modes to be applied to a luminance component coding unit (a decoding unit in a decoding process) may be variously set. For example, referring to FIG. 13, if the size of a luminance component coding unit is N.times.N, on which intra prediction is performed, the numbers of intra prediction modes actually performed on 2.times.2, 4.times.4, 8.times.8, 16.times.16, 32.times.32, 64.times.64, and 128.times.128-sized luminance component coding units may be respectively set as 5, 9, 9, 17, 33, 5, and 5 (in Example 2). For another example, when a size of a luminance component coding unit to be intra-predicted is N.times.N, numbers of intra prediction modes to be actually performed on coding units having sizes of 2.times.2, 4.times.4, 8.times.8, 16.times.16, 32.times.32, 64.times.64, and 128.times.128 may be set to be 3, 17, 34, 34, 34, 5, and 5. The numbers of intra prediction modes to be actually performed are differently set according to the sizes of luminance component coding units because overheads for encoding prediction mode information differ according to the sizes of the luminance component coding units. In other words, a small luminance component coding unit occupies a small portion of entire image data but may have a large overhead in order to transmit additional information, such as prediction mode information of the luminance component coding unit. Accordingly, if a luminance component small coding unit is encoded by using an excessively large number of prediction modes, the number of bits may be increased and thus compression efficiency may be reduced. Also, a luminance component large coding unit, e.g., a luminance component coding unit equal to or greater than 64.times.64, generally corresponds to a plain region of image data, and thus encoding of the large luminance component coding unit by using an excessively large number of prediction modes may also reduce compression efficiency.
Thus, according to an exemplary embodiment, luminance component coding units are roughly classified into at least three sizes such as N1.times.N1 (where 2.ltoreq.N1.ltoreq.4, and N1 is an integer), N2.times.N2 (where 8.ltoreq.N2.ltoreq.32, and N2 is an integer), and N3.times.N3 (where 64.ltoreq.N3, and N3 is an integer). If the number of intra prediction modes performed on the luminance component coding units of N1.times.N1 is A1 (where A1 is a positive integer), the number of intra prediction modes performed on the luminance component coding units of N2.times.N2 is A2 (where A2 is a positive integer), and the number of intra prediction modes performed on the luminance component coding units of N3.times.N3 is A3 (where A3 is a positive integer). The numbers of intra prediction modes performed according to the sizes of the luminance component coding units may be set to satisfy A3.ltoreq.A1.ltoreq.A2. That is, if a current picture is split into small luminance component coding units, medium luminance component coding units, and large luminance component coding units, the medium luminance component coding units may be set to have the largest number of prediction modes and the small luminance component coding units and the large luminance component coding units may be set to have a relatively small number of prediction modes. However, the exemplary embodiment is not limited thereto, and the small and large luminance component coding units may also be set to have a large number of prediction modes. The numbers of prediction modes according to the sizes of luminance component coding units in FIG. 13 are merely exemplarily and may be changed.
Referring to FIGS. 13 and 14A, for example, when intra prediction is performed on a luminance component coding unit having a 4.times.4 size, the luminance component coding unit may have a vertical mode (mode 0), a horizontal mode (mode 1), a direct current (DC) mode (mode 2), a diagonal down-left mode (mode 3), a diagonal down-right mode (mode 4), a vertical-right mode (mode 5), a horizontal-down mode (mode 6), a vertical-left mode (mode 7), and a horizontal-up mode (mode 8).
Referring to FIG. 14C, a prediction coding unit is generated according to an available intra prediction mode determined according to the size of a current luminance component coding unit by using neighboring pixels A through M of the current luminance component coding unit. For example, an operation of performing prediction encoding on a current coding unit having a 4.times.4 size according to mode 0, i.e., a vertical mode, shown in FIG. 14A will be described. Initially, values of the neighboring pixels A through D at an upper side of the current coding unit are predicted as pixel values of the current coding unit. That is, the value of the neighboring pixel A is predicted as a value of four pixels in a first column of the current coding unit, the value of the neighboring pixel B is predicted as a value of four pixels in a second column of the current coding unit, the value of the neighboring pixel C is predicted as a value of four pixels in a third column of the current coding unit, and the value of the neighboring pixel D is predicted as a value of four pixels in a fourth column of the current coding unit. After that, the pixel values of the current coding unit predicted by using the neighboring pixels A through D are subtracted from the pixel values of the original current coding unit to calculate an error value and then the error value is encoded.
Referring to FIGS. 13 and 15, for example, when intra prediction is performed on a coding unit having a 2.times.2 size, the coding unit may have a total of five modes, such as a vertical mode, a horizontal mode, a DC mode, a plane mode, and a diagonal down-right mode.
Meanwhile, if a luminance component coding unit having a 32.times.32 size has 33 intra prediction modes, as shown in FIG. 13, directions of the 33 intra prediction modes need to be set. According to an exemplary embodiment, in order to set intra prediction modes having various directions in addition to the intra prediction modes illustrated in FIGS. 14 and 15, prediction directions for selecting neighboring pixels used as reference pixels of pixels of the luminance component coding unit are set by using (dx, dy) parameters. For example, if each of the 33 prediction modes is defined as mode N (where N is an integer from 0 to 32), mode 0 may be set as a vertical mode, mode 1 may be set as a horizontal mode, mode 2 may be set as a DC mode, mode 3 may be set as a plane mode, and each of mode 4 through mode 31 may be defined as a prediction mode having a directionality of tan.sup.-1(dy/dx) by using (dx, dy) represented as one of (1,-1), (1,1), (1,2), (2,1), (1,-2), (2,1), (1,-2), (2,-1), (2,-11), (5,-7), (10,-7), (11,3), (4,3), (1,11), (1,-1), (12,-3), (1,-11), (1,-7), (3,-10), (5,-6), (7,-6), (7,-4), (11,1), (6,1), (8,3), (5,3), (5,7), (2,7), (5,-7), and (4,-3) as shown in Table 1.
TABLE-US-00001 TABLE 1 mode # dx dy mode 4 1 -1 mode 5 1 1 mode 6 1 2 mode 7 2 1 mode 8 1 -2 mode 9 2 -1 mode 10 2 -11 mode 11 5 -7 mode 12 10 -7 mode 13 11 3 mode 14 4 3 mode 15 1 11 mode 16 1 -1 mode 17 12 -3 mode 18 1 -11 mode 19 1 -7 mode 20 3 -10 mode 21 5 -6 mode 22 7 -6 mode 23 7 -4 mode 24 11 1 mode 25 6 1 mode 26 8 3 mode 27 5 3 mode 28 5 7 mode 29 2 7 mode 30 5 -7 mode 31 4 -3 Mode 0 is a vertical mode, mode 1 is a horizontal mode, mode 2 is a DC mode, mode 3 is a plane mode, and mode 32 is a bi-linear mode.
As described above with reference to Table 1, each of the intra prediction modes according to exemplary embodiments may have directionality of tan.sup.-1(dy/dx) by using a plurality of (dx, dy) parameters.
Referring to FIG. 16A, neighboring pixels A and B on a line 160 that extends from a current pixel P in a current luminance component coding unit, which is to be predicted, at an angle of tan.sup.-1(dy/dx) determined by a value of a (dx, dy) parameter according to a mode, as shown in Table 1, may be used as predictors of the current pixel P. In this case, the neighboring pixels A and B may be pixels that have been encoded and restored, and belong to previous coding units located above and to the left side of the current coding unit. Also, when the line 160 does not pass along neighboring pixels on locations each having an integral value but passes between these neighboring pixels, neighboring pixels closer to the line 160 may be used as predictors of the current pixel P. Also, a weighted average value considering a distance between an intersection of the line 160 and neighboring pixels close to the line 160 may be used as a predictor for the current pixel P. If two pixels that meet the line 160, e.g., the neighboring pixel A located above the current pixel P and the neighboring pixel B located to the left side of the current pixel P, are present, an average of pixel values of the neighboring pixels A and B may be used as a predictor of the current pixel P. Otherwise, if a product of values of the `dx` and `dy` parameters is a positive value, the neighboring pixel A may be used, and if the product of the values of the `dx` and `dy` parameters is a negative value, the neighboring pixel B may be used.
Referring to FIG. 16B, if the line 160 having an angle of tan.sup.-1(dy/dx) that is determined according to (dx, dy) of each mode passes between a neighboring pixel A 161 and a neighboring pixel B 162 of integer locations, a weighted average value considering a distance between an intersection of the extended line 160 and the neighboring pixels A 161 and B 162 close to the extended line 160 may be used as a predictor as described above. For example, if a distance between the neighboring pixel A 161 and the intersection of the extended line 160 having the angle of tan.sup.-1(dy/dx) is f, and a distance between the neighboring pixel B 162 and the intersection of the extended line 160 is g, a predictor for the current pixel P may be obtained as (A*g+B*f)/(f+g). Here, f and g may be each a normalized distance using an integer. If software or hardware is used, the predictor for the current pixel P may be obtained by shift operation as (g*A+f*B+2)>>2. As shown in FIG. 16B, if the extended line 160 passes through a first quarter close to the neighboring pixel A 161 from among four parts obtained by quartering a distance between the neighboring pixel A 161 and the neighboring pixel B 162 of the integer locations, the predictor for the current pixel P may be acquired as (3*A+B)/4. Such operation may be performed by shift operation considering rounding-off to a nearest integer like (3*A+B+2)>>2.
Meanwhile, if the extended line 160 having the angle of tan.sup.-1(dy/dx) that is determined according to (dx, dy) of each mode passes between the neighboring pixel A 161 and the neighboring pixel B 162 of the integer locations, a section between the neighboring pixel A 161 and the neighboring pixel B 162 may be divided into a predetermined number of areas, and a weighted average value considering a distance between an intersection and the neighboring pixel A 161 and the neighboring pixel B 162 in each divided area may be used as a prediction value. For example, referring to FIG. 16C, a section between the neighboring pixel A 161 and the neighboring pixel B 162 may be divided into five sections P1 through P5 as shown in FIG. 16C, a representative weighted average value considering a distance between an intersection and the neighboring pixel A 161 and the neighboring pixel B 162 in each section may be determined, and the representative weighted average value may be used as a predictor for the current pixel P. In detail, if the extended line 160 passes through the section P1, a value of the neighboring pixel A may be determined as a predictor for the current pixel P. If the extended line 160 passes through the section P2, a weighted average value (3*A+1*B+2)>>2 considering a distance between the neighboring pixels A and B and a middle point of the section P2 may be determined as a predictor for the current pixel P. If the extended line 160 passes through the section P3, a weighted average value (2*A+2*B+2)>>2 considering a distance between the neighboring pixels A and B and a middle point of the section P3 may be determined as a predictor for the current pixel P. If the extended line 160 passes through the section P4, a weighted average value (1*A+3*B+2)>>2 considering a distance between the neighboring pixels A and B and a middle point of the section P4 may be determined as a predictor for the current pixel P. If the extended line 160 passes through the section P5, a value of the neighboring pixel B may be determined as a predictor for the current pixel P.
Specifically, first, a value of a virtual pixel C 173 on a lower rightmost point of the current luminance component coding unit is calculated by calculating an average of values of a neighboring pixel (right-up pixel) 174 on an upper rightmost point of the current luminance component coding unit and a neighboring pixel (left-down pixel) 175 on a lower leftmost point of the current luminance component coding unit, as expressed in Equation 1 below: C=0.5(LeftDownPixel+RightUpPixel) [Equation 1]
Next, a value of the virtual pixel A 171 located on a lowermost boundary of the current luminance component coding unit when the current pixel P 170 is extended downward by considering the distance W1 between the current pixel P 170 and the left boundary of the current luminance component coding unit and the distance W2 between the current pixel P 170 and the right boundary of the current luminance component coding unit, is calculated by using Equation 2 below: A=(C*W1+LeftDownPixel*W2)/(W1+W2); [Equation 2]
A=(C*W1+LeftDownPixel*W2+((W1+W2)/2))/(W1+W2) When a value of W1+W2 in Equation 2 is a power of 2, like 2^n, A=(C*W1+LeftDownPixel*W2+((W1+W2)/2))/(W1+W2) may be calculated by shift operation as A=(C*W1+LeftDownPixel*W2+2^(n-1))>>n without division.
Similarly, a value of the virtual pixel B 172 located on a rightmost boundary of the current luminance component coding unit when the current pixel P 170 is extended in the right direction by considering the distance h1 between the current pixel P 170 and the upper boundary of the current luminance component coding unit and the distance h2 between the current pixel P 170 and the lower boundary of the current luminance component coding unit, is calculated by using Equation 3 below: B=(C*h1+RightUpPixel*h2)/(h1+h2) B=(C*h1+RightUpPixel*h2+((h1+h2)/2))/(h1+h2) [Equation 3]
Once the values of the virtual pixel B 172 on the right border and the virtual pixel A 171 on the down border of the current pixel P 170 are determined by using Equations 1 through 3, a predictor for the current pixel P 170 may be determined by using an average value of A+B+D+E. In detail, a weighted average value considering a distance between the current pixel P 170 and the virtual pixel A 171, the virtual pixel B 172, the pixel D 176, and the pixel E 177 or an average value of A+B+D+E may be used as a predictor for the current pixel P 170. For example, if a weighted average value is used and the size of block is 16.times.16, a predictor for the current pixel P may be obtained as (h1*A+h2*D+W1*B+W2*E+16)>>5. Such bilinear prediction is applied to all pixels in the current coding unit, and a prediction coding unit of the current coding unit in a bilinear prediction mode is generated.
Since a greater number of intra prediction modes than intra prediction modes used in a conventional codec are used according to a size of a coding unit according to an exemplary embodiment, compatibility with the conventional codec may become a problem. In a conventional art, 9 intra prediction modes at the most may be used as shown in FIGS. 14A and 14B. Accordingly, it is necessary to map intra prediction modes having various directions selected according to an exemplary embodiment to one of a smaller number of intra prediction modes. That is, when a number of available intra prediction modes of a current coding unit is N1 (N1 is an integer), in order to make the available intra prediction modes of the current coding unit compatible with a coding unit of a predetermined size including N2 (N2 is an integer different from N1) intra prediction modes, the intra prediction modes of the current coding unit may be mapped to an intra prediction mode having a most similar direction from among the N2 intra prediction modes. For example, a total of 33 intra prediction modes are available as shown in Table 1 in the current coding unit, and it is assumed that an intra prediction mode finally applied to the current coding unit is the mode 14, that is, (dx,dy)=(4,3), having a directivity of tan.sup.-1(3/4).apprxeq.36.87 (degrees). In this case, in order to match the intra prediction mode applied to the current block to one of 9 intra prediction modes as shown in FIGS. 14A and 14B, the mode 4 (down_right) mode having a most similar directivity to the directivity of 36.87 (degrees) may be selected. That is, the mode 14 of Table 1 may be mapped to the mode 4 shown in FIG. 14B. Likewise, if an intra prediction mode applied to the current coding unit is selected to be the mode 15, that is, (dx,dy)=(1,11), from among the 33 available intra prediction modes of Table 1, since a directivity of the intra prediction mode applied to the current coding unit is tan.sup.-1(11).apprxeq.84.80 (degrees), the mode 0 (vertical) of FIG. 14B having a most similar directivity to the directivity 84.80 (degrees) may be mapped to the mode 15.
FIGS. 19A and 19B are a reference diagrams for explaining a mapping process of intra prediction modes between luminance component coding units having different sizes, according to an exemplary embodiment.
Referring to FIG. 19A, a current luminance component coding unit A 190 has a size of 16.times.16, a left luminance component coding unit B 191 has a size of 8.times.8, and an upper luminance component coding unit C 192 has a size of 4.times.4. Also, as described with reference to FIG. 13, numbers of intra prediction modes usable in luminance component coding units respectively having sizes of 4.times.4, 8.times.8, and 16.times.16 are respectively 9, 9, and 33. Here, since the intra prediction modes usable in the left luminance component coding unit B 191 and the upper luminance component coding unit C 192 are different from the intra prediction modes usable in the current luminance component coding unit A 190, an intra prediction mode predicted from the left and upper luminance component coding units B and C 191 and 192 may not be suitable for use as a prediction value of the intra prediction mode of the current luminance component coding unit A 190. Accordingly in the current exemplary embodiment, the intra prediction modes of the left and upper luminance component coding units B and C 191 and 192 are respectively changed to first and second representative intra prediction modes in the most similar direction from among a predetermined number of representative intra prediction modes, and one of the first and second representative intra prediction modes, which has a smaller mode value, is selected as a final representative intra prediction mode. Then, an intra prediction mode having the most similar direction as the final representative intra prediction mode is selected from among the intra prediction modes usable in the current luminance component coding unit A 190 as an intra prediction mode of the current luminance component coding unit A 190.
Alternatively, referring to FIG. 19B, it is assumed that a current luminance component coding unit A has a size of 16.times.16, a left luminance component coding unit B has a size of 32.times.32, and an up luminance component coding unit C has a size of 8.times.8. Also, it is assumed that numbers of available intra prediction modes of the luminance component coding units having the sizes of 8.times.8, 16.times.16, and 32.times.32 are respectively 9, 9, and 33. Also, it is assumed that an intra prediction mode of the left luminance component coding unit B is a mode 4, and an intra prediction mode of the up luminance component coding unit C is a mode 31. In this case, since the intra prediction modes of the left luminance component coding unit B and the up luminance component coding unit C are not compatible with each other, each of the intra prediction modes of the left luminance component coding unit B and the up luminance component coding unit C is mapped to one of representative intra prediction modes shown in FIG. 20. Since the mode 31 that is the intra prediction mode of the left luminance component coding unit B has a directivity of (dx,dy)=(4, -3) as shown in Table 1, a mode 5 having a most similar directivity to tan.sup.-1(-3/4) from among the representative intra prediction modes of FIG. 20 is mapped, and since the intra prediction mode mode 4 of the up luminance component coding unit C has the same directivity as that of the mode 4 from among the representative intra prediction modes of FIG. 20, the mode 4 is mapped.
FIG. 20 is a reference diagram for explaining a process of mapping an intra prediction mode of a neighboring luminance component coding unit to one of representative intra prediction modes. In FIG. 20, a vertical mode 0, a horizontal mode 1, a DC mode 2, a diagonal-left mode 3, a diagonal-right mode 4, a vertical-right mode 5, a horizontal-down mode 6, a vertical-left mode 7, and a horizontal-up mode 8 are shown as representative intra prediction modes. However, the representative intra prediction modes are not limited thereto, and may be set to have various directionalities.
Meanwhile, as described with reference to FIGS. 16 A through 16C, if a predictor for the current pixel P is generated by using neighboring pixels on or close to the extended line 160, the extended line 160 has actually a directivity of tan.sup.-1(dy/dx). In order to calculate the directivity, since division (dy/dx) is necessary, calculation is made down to decimal places when hardware or software is used, thereby increasing the amount of calculation. Accordingly, a process of setting dx and dy is used in order to reduce the amount of calculation when a prediction direction for selecting neighboring pixels to be used as reference pixels about a pixel in a coding unit is set by using dx, and dy parameters in a similar manner to that described with reference to Table 1.
Referring to FIG. 25, it is assumed that a location of the current pixel P is P(j,i), and an up neighboring pixel and a left neighboring pixel B located on an extended line 2510 having a directivity, that is, a gradient, of tan.sup.-1(dy/dx) and passing through the current pixel P are respectively A and B. When it is assumed that locations of up neighboring pixels correspond to an X-axis on a coordinate plane, and locations of left neighboring pixels correspond to a y-axis on the coordinate plate, the up neighboring pixel A is located at (j+i*dx/dy,0), and the left neighboring pixel B is located at (0,i+j*dy/dx). Accordingly, in order to determine any one of the up neighboring pixel A and the left neighboring pixel B for predicting the current pixel P, division, such as dx/dy or dy/dx, is required. Such division is very complex as described above, thereby reducing a calculation speed of software or hardware.
In detail, if dy has a fixed value of 2^m, an absolute value of dx may be set so that a distance between prediction directions close to a vertical direction is narrow, and a distance between prediction modes closer to a horizontal direction is wider. For example, referring to FIG. 27, if dy has a value of 2^4, that is, 16, a value of dx may be set to be 1, 2, 3, 4, 6, 9, 12, 16,0, -1, -2, -3, -4, -6, -9, -12, and -16 so that a distance between prediction directions close to a vertical direction is narrow and a distance between prediction modes closer to a horizontal direction is wider.
Likewise, if dx has a fixed value of 2^n, an absolute value of dy may be set so that a distance between prediction directions close to a horizontal direction is narrow and a distance between prediction modes closer to a vertical direction is wider. For example, referring to FIG. 28, if dx has a value of 2^4, that is, 16, a value of dy may be set to be 1, 2, 3, 4, 6, 9, 12, 16,0, -1, -2, -3, -4, -6, -9, -12, and -16 so that a distance between prediction directions close to a horizontal direction is narrow and a distance between prediction modes closer to a vertical direction is wider.
For example, prediction modes described with reference to FIGS. 25 through 28 may be defined as a prediction mode having a directivity of tan.sup.-1(dy/dx) by using (dx, dy) as shown in Tables 2 through 4.
TABLE-US-00002 TABLE 2 dx Dy -32 32 -26 32 -21 32 -17 32 -13 32 -9 32 -5 32 -2 32 0 32 2 32 5 32 9 32 13 32 17 32 21 32 26 32 32 32 32 -26 32 -21 32 -17 32 -13 32 -9 32 -5 32 -2 32 0 32 2 32 5 32 9 32 13 32 17 32 21 32 26 32 32
TABLE-US-00003 TABLE 3 dx Dy -32 32 -25 32 9 32 -14 32 -10 32 -6 32 -3 32 -1 32 0 32 1 32 3 32 6 32 10 32 14 32 19 32 25 32 32 32 32 -25 32 -19 32 -14 32 -10 32 -6 32 -3 32 -1 32 0 32 1 32 3 32 6 32 10 32 14 32 19 32 25 32 32
TABLE-US-00004 TABLE 4 dx Dy -32 32 -27 32 -23 32 -19 32 -15 32 -11 32 -7 32 -3 32 0 32 3 32 7 32 11 32 15 32 19 32 23 32 27 32 32 32 32 -27 32 -23 32 -19 32 -15 32 -11 32 -7 32 -3 32 0 32 3 32 7 32 11 32 15 32 19 32 23 32 27 32 32
For example, referring to Table 2, a prediction mode having a directionality of tan.sup.-1(dy/dx) by using (dx, dy) represented as one of (-32, 32), (-26, 32), (-21, 32), (-17, 32), (-13, 32), (-9, 32), (-5, 32), (-2, 32), (0.32), (2, 32), (5, 32), (9, 32), (13, 32), (17,32), (21, 32), (26, 32), (32, 32), (32, -26), (32, -21), (32, -17), (32, -13), (32, -9), (32, -5), (32, -2), (32, 0), (32, 2), (32, 5), (32, 9), (32, 13), (32, 17), (32, 21), (32, 26) and (32, 32).
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