HUE031186T2

HUE031186T2 - Eljárás intra predikciók dekódolására

Info

Publication number: HUE031186T2
Application number: HUE11818362A
Authority: HU
Inventors: Soo Mi Oh; Moonock Yang
Original assignee: M&K Holdings Inc
Priority date: 2010-08-17
Filing date: 2011-08-12
Publication date: 2017-07-28
Also published as: CN104602005A; PL3125560T3; JP2016213852A; PL3125557T3; KR20140075020A; EP3125557B1; WO2012023762A2; KR20130051443A; PL3125556T3; DK3125561T3; JP6322231B2; CN106851284A; JP6371801B2; JP2016213853A; PT3125552T; US20160301929A1; EP3125557A1; CN107071426B; US9924186B2; SMT201600449B

Description

(12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: H04N 191463 <201401> H04N 191176 <201401> 12.10.2016 Bulletin 2016/41 H04N 19I159<201401> H04N 19144<201401> H04N 19111 <201401> (21) Application number: 11818362.3 (86) International application number: (22) Date of filing: 12.08.2011 PCT/KR2011/005941 (87) International publication number: WO 2012/023762 (23.02.2012 Gazette 2012/08)

(54) METHOD FOR DECODING INTRA-PREDICTIONS

VERFAHREN ZUR DEKODIERUNG VON INTRAPRÁDIKTIONEN PROCÉDÉ DE DÉCODAGE D’INTRA-PRÉDICTIONS (84) Designated Contracting States: (72) Inventors: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB · OH, Soo Mi GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO Gyeonggi-do 463-887 (KR) PL PT RO RS SE SI SK SM TR · YANG, Moonock

Singapore 460405 (SG) (30) Priority: 30.06.2011 KR 20110064301 17.08.2010 KR 20100079529 (74) Representative: Griinecker Patent- und

Rechtsanwálte

(43) Date of publication of application: PartG mbB 26.06.2013 Bulletin 2013/26 LeopoldstraSe 4 80802 München (DE) (60) Divisional application: 16184557.3 (56) References cited: 16184568.0 WO-A1-03/105070 WO-A1-2009/080133 16184569.8 KR-A-20070 037 532 KR-A-20090 067 176 16184572.2 KR-A-20100 027 096 US-A1-2009 310 678 16184574.8 16184577.1 · TAKESHI TSUKUBA ET AL: "Adaptive 16184578.9 Multidirectional Intra Prediction", ITU-T SG16Q6

16184582.1 VIDEO CODING EXPERTS GROUP, 33. VCEG 16184586.2 MEETING, DOCUMENTVCEG-AG05, SHENZHEN, 16184616.7 CHINA, no. VCEG-AG05, 20 October 2007 (2007-10-20), pages 1-6, XP002501810, (73) Proprietor: M&K Holdings Inc.

Seoul 06586 (KR)

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).

Description of intra prediction modes wherein the first group consists of the most probable intra prediction modes and the sec-[Technical Field] ond group consists of the remaining intra prediction modes. The probability of each intra prediction mode is [0001] The present invention relates to a method for 5 determined adaptively according to intra prediction decoding intra prediction mode, and more particularly, to modes of neighbouring blocks. It is then signalled wheth- a method for restoring intra prediction mode, generating er the selected intra prediction mode belongs to the first a prediction block very similar to an original block, de- or second group of intra prediction modes. coding a residual block, and generating a reconstructed block using the prediction block and residual block. 10 [Technical Problem] [Background Art] [0009] The present invention is directed to a method forgenerating a prediction blockvery similarto an original [0002] In image compression methods such as Motion block according to an intra prediction mode, generating

Picture Experts Group (MPEG)-1, MPEG-2, MPEG-4 15 a residual block by decoding a residual signal, and gen- and H.264/MPEG-4 Advanced Video Coding (AVC), one erating a reconstructed block using the prediction block picture is divided into macroblocks to encode an image. and the residual block.

Then, the respective macroblocks are encoded using inter prediction or intra prediction. [Technical Solution] [0003] In intra prediction, a current block of a picture 20 is encoded not using a reference picture, but using values [0010] One aspect of the present invention provides a of pixels spatially adjacent to the current block. An intra method for decoding an intra prediction, comprising: deprediction mode with little distortion is selected by com- multiplexing intra prediction information and a residual paring a prediction block generated using the adjacent signal, restoring an intra prediction mode of a current pixel values with an original macroblock. Then, using the 25 prediction unit using the intra prediction information and selected intra prediction mode and the adjacent pixel val- intra prediction modes of prediction units adjacent to the ues, prediction values of the current block are calculated. current prediction unit, generating reference pixels using

Differences between the prediction values and pixels val- one or more available reference pixel if there exist una- ues of the original current block are calculated and then vailable reference pixels of the prediction unit, adaptively encoded through transform coding, quantization and en- 30 filtering the reference pixels based on the restored intra tropy coding. The intra prediction mode is also encoded. prediction mode, generating a prediction block using the [0004] In 4X4 conventional intra prediction, there are restored intra prediction mode and the reference pixels, nine modes of a vertical mode, a horizontal mode, a DC decoding the residual signal de-multiplexed to generatmode, a diagonal down-left mode, a diagonal down-right ing a residual block, and generating a reconstructed mode, a vertical right mode, a vertical left mode, a hori- 35 block using the prediction block and the residual block, zontal-up mode and a horizontal-down mode.

[0005] According to H.264 standard, one mode is se- [Advantageous Effects] lected among the nine modes to generate a prediction block of the current block. According to HEVC standard [0011] A method according to the present invention re- under development, there are 17 or 34 intra prediction 40 stores intra prediction mode of the current prediction unit, modes. and adaptively filters reference pixels according to the [0006] However, when some or all values of pixels ad- restored intra prediction mode in order to generate a pre- jacent to current block do not exist or are not already diction block minimizing the difference between a predic- encoded, it is impossible to apply some or all of the intra tion block and an original block. The residual block is prediction modes to the current block. In this case, if intra 45 generated by adaptively decoding the residual signal ac- prediction is performed by selecting an intra prediction cording to the intra prediction mode. And, restored block mode from available intra prediction modes, distortion is generated by combining the prediction block very sim- between a prediction block and an original block be- ilar to an original block and the residual block. Therefore, comes large. Therefore, the coding efficiency is degrad- it can be possible to provide a method for decoding pre- ed. 50 diction mode corresponding to a method for encoding [0007] Also, as the number of intra prediction modes prediction mode which can effectively decrease addition- increases, a more effective new method of encoding the al amount of bits according to increased number of intra intra prediction mode than the conventional method, and prediction modes and required to encode the residual a more effective method of decoding the intra prediction block is minimized. Also, it can be possible to obtain high mode and generating a reconstructed block are required. 55 performance of compression and high reproducing effi- [0008] WO 03/105070 discloses such an effective ciency by providing a decoding method corresponding method of encoding the intra prediction mode.WO to an encoding method which can decrease amount of 03/105070 specifically discloses to generate two groups bits required to encode by generating a prediction block similar to an original image. a picture into one or more coding units each of which has a predetermined size, determine prediction mode of each [Description of Drawings] coding unit, and determines size of prediction unit per each coding unit. The picture division unit 110 sends the [0012] 5 prediction unit to be encoded to the intra prediction unit 150 or the inter prediction unit 160 according to the pre-FIG. 1 is a block diagram of a moving picture coding diction mode. Also, the picture division unit 110 sends apparatus according to the present invention. the prediction units to be encoded to the subtracter 190. FIG. 2 is a block diagram of an intra prediction unit [0017] The transform unit 120 transforms residual of a moving picture coding apparatus according to 10 blocks between an original block of a prediction unit and the present invention. a prediction block generated by the intra prediction unit FIG. 3 is a conceptual diagram showing positions of 150 or the inter prediction unit 160. The residual block is reference pixels used for intra prediction according composed of a coding unit. The residual block may be

to the present invention. divided into optimal transform units and transformed. A FIG. 4 is a conceptual diagram illustrating directional 15 transform matrix type may be adaptively determined ac-intra prediction modes according to the present in- cording to a prediction mode (intra or inter). As residual vention. signals of a intra prediction mode have directivities ac- FIG. 5 is a block diagram of a moving picture decod- cording to intra prediction modes, the transform matrix ing apparatus according to the present invention. type may be adaptively determined according to an intra FIG. 6 is a block diagram of an intra prediction unit 20 prediction mode. The transform unit may be transformed of a moving picture decoding apparatus according by horizontal and vertical one-dimensional (1D) trans- to the present invention. form matrices. In inter prediction, one predetermined FIG. 7 is a flow chart illustrating a decoding proce- transform matrix type is applied. In intra prediction, there dure in intra prediction mode according to the is a high possibility that the residual blocks will have ver- present invention. 25 tical directivity when the intra prediction mode of the cur- FIG. 8 is a flow chart illustrating a procedure for re- rent prediction unit is horizontal. Thus, a discrete cosine storing intra prediction mode according to the transform (DCT)-based integer matrix is applied to the present invention when number of prediction modes vertical direction, and a discrete sine transform (DST) or in a first group of intra prediction mode is variable. Karhunen Loéve transform (KLT)-based integer matrix FIG. 9 is a flow chart illustrating another procedure 30 is applied to the horizontal direction. When the intra prefer restoring intra prediction mode according to the diction mode is vertical, a DST or KLT-based integer ma- present invention when number of prediction modes trix is applied to the vertical direction, and a DCT-based in a first group of intra prediction mode is fixed. integer matrix is applied to the horizontal direction. Also, in intra prediction, the transform matrix may be adaptively [Mode for Invention] 35 determined according to a size of the transform units.

[0018] The quantization unit 130 determines a quanti- [0013] Hereinafter, various embodiments of the zation step size for quantizing transform coefficients of present invention will be described in detail with refer- the residual block for each coding unit. The quantization ence to the accompanying drawings. However, the step size is determined per coding unit having a size present invention is not limited to the exemplary embod- 40 equal to or larger than a predetermined size. The prede-iments disclosed below, but can be implemented in var- termined size may be 8X8 or 16x16. Using the deter-ious types. Therefore, many other modifications and var- mined quantization step size and a quantization matrix iations of the present invention are possible, and it is to determined according to a prediction mode, the transform be understood that within the scope of the disclosed con- coefficients are quantized. The quantization unit 130 us-cept, the present invention may be practiced otherwise 45 es quantization step sizes of one or more coding units than as has been specifically described. adjacent to the current coding unit to generate a quanti- [0014] FIG. 1 is a block diagram of a moving picture zation step size predictor of the current coding unit, coding apparatus according to the present invention. [0019] The quantization unit 130 sequentially retrieves [0015] Referring to FIG. 1, a moving picture coding ap- coding units in the following scan order; 1) a left coding paratus 100 according to the present invention includes 50 unit of the current coding unit, 2) an above coding unit of a picture division unit 110, a transform unit 120, a quan- the current coding unit, and 3) an above left coding unit tization unit 130, a scanning unit 131, an entropy coding of the current coding unit. And the quantization unit gen- unit 140, an intra prediction unit 150, an inter prediction erates the quantization step size predictor of the current unit 160, an inverse quantization unit 135, an inverse coding unit using one ortwo valid quantization step sizes, transform unit 125, a post-processing unit 170, a picture 55 For example, thefirstvalid quantization step size encoun-storing unit 180, a subtracter 190 and an adder 195. tered in the scan order may be determined as the quan- [0016] The picture division unit 110 analyzes an input tization step size predictor. An average of the first two video signal to divide each largest coding unit (LCU) of valid quantization step sizes retrieved in the scan order may be determined as the quantization step size predic- verse transform unit 125 restores residual blocks of the tor, and one valid quantization step size is determined spatial domain from the inversely quantized transform as the quantization step size predictor when only one coefficients. The adder 195 generates a reconstructed quantization step size is valid. When the quantization block by adding the residual block reconstructed by the step size predictor is determined, a difference between 5 inverse transform unit 125 and the prediction block from the quantization step size and the quantization step size the intra prediction unit 150 or the inter prediction unit predictor is transmitted to the entropy coding unit 140. 160.

[0020] There may be none of a left coding unit, an [0025] The post-processing unit 170 performs a de- above coding unit and an above left coding unit of the blocking filtering process for removing blocking artifact current coding unit. On the other hand, there may be a 10 generated in a reconstructed picture, an adaptive offset previous coding unit of the current coding unit in coding application process for complementing a difference be- order of the LCU. Thus, for coding units adjacent to the tween the reconstructed picture and the original image current coding unit and the LCU, the previous coding unit per pixel, and an adaptive loop filter process for comple- of the current coding unit in coding order may be candi- menting a difference between the reconstructed picture dates. In this case, the above scanning order may be 15 and the original image in a coding unit. changed to the following scan order; 1) the left coding [0026] The deblocking filtering process may be applied unit of the current coding unit, 2) the above coding unit to a boundary between prediction units having a prede- of the current coding unit, 3) the above left coding unit of termined size or more and between transform units. The the current coding unit and 4) the previous coding unit of predetermined size may be 8x8. The deblocking filtering the current coding unit. The scan order may vary, or the 20 process includes a step of determining a boundary to be above left coding unit may be omitted in scan order. The filtered, a step of determining boundary filtering strength quantized transform block is provided to the inverse to be applied to the boundary, a step of determining quantization unit 135 and the scanning unit 131. whether or not to apply a deblocking filter, and a step of [0021] The scanning unit 131 scans the quantized selecting a filter to be applied to the boundary when it is transform coefficients of the quantized transform block, 25 determined to apply the deblocking filter. thereby converting the quantized transform coefficients [0027] Whether or not to apply the deblocking filter is into 1D quantized transform coefficients. A scan pattern determined according to i) whether or not the boundary is determined according to the intra prediction mode be- filtering strength is greater than 0 and ii) whether or not cause the distribution of the quantized transform coeffi- a value indicating the difference between boundary pixels cients depends on the intra prediction mode. The scan 30 ofPblockandQblockwhichareadjacenttotheboundary pattern may also be determined according to the size of to be filtered is smaller than a first reference value deter- the transform unit. The scan pattern may be determined mined according to a quantization parameter, depending on the directional intra prediction mode. The [0028] Two or more filters may exist. When an absolute quantized transform coefficients are scanned in a reverse value of a difference between two pixels adjacent to the direction. 35 block boundary is equal to or larger than a second refer- [0022] When the quantized transform coefficients are ence value, a weak filter is selected. The second refer- divided into a plurality of subsets, same scan pattern is ence value is determined by the quantization parameter applied to each subset. The plurality of subsets consist and the boundary filtering strength. of one main subset and one or more remaining subsets. [0029] The adaptive offset application process is in-

The main subset is located at an upper left side and in- 40 tended to reduce a difference (distortion) between a pixel cludesaDCcoefficient.Theoneormoreresidualsubsets subjected to the deblocking filter and the original pixel, cover region other than the main subset. Whether or not to perform the adaptive offset application [0023] Zigzag scan may be applied to scan the sub- process in the unit of a picture or a slice can be deter- sets. The subsets may be scanned beginning with the mined. A picture or slice may be divided into a plurality main subset to the residual subsets in a forward direction, 45 of offset regions, and an offset mode may be determined orcán be scanned in a reverse direction. A scan pattern per the offset region. There may be predetermined for scanning the subsets may be set the same as a scan number of edge offset modes (for example, four edge pattern for scanning the quantized transform coefficients offset modes), two band offset modes. In case of edge in the subsets. In this case, the scan pattern for scanning offset mode, an edge mode to which each pixel is be- the subsets is determined according to the intra predic- so longed is determined and an offset corresponding to the tion mode. The encoder transmits information capable determined edge mode is applied. The edge mode is of indicating a position of the last non-zero quantized determined based on a distribution of pixel values of two coefficient of the transform unittoadecoder.Theencoder pixels adjacent to the current pixel. also transmits information capableof indicating a position [0030] The adaptive loop filter process may be per- ofthe last non-zero quantized coefficient of each subset 55 formed on the basis of a value obtained by comparing to the decoder. an original image and a reconstructed image to which [0024] The inverse quantization unit 135 inversely the deblocking filtering process or the adaptive offset ap-quantizes the quantized transform coefficients. The in- plication process is applied. The determined ALF can be applied to all pixels included in a 4X4 block or an 8X8 prediction unit 150 adaptively filters reference pixels to block. Whether or not to apply an ALF may be determined generate the intra prediction block. When some of refer- for each coding unit. A size and coefficients of a loop filter ence pixels are not available, it is possible to generate may vary according to each coding unit. Information in- the reference pixels at the unavailable positions using dicating whether ALF is applied to each coding unit may 5 available reference pixels. be included in slice header. In the case of a chrominance [0036] The entropy coding unit 140 entropy-codes the signal, whether or not to apply the ALF may be deter- quantized transform coefficients quantized by the quan- mined for each picture unit. Unlike luminance, the loop tization unit 130, intra prediction information received filter may have a rectangular shape. from the intra prediction unit 150, motion information re- [0031] The adaptive loop filter process is performed on 10 ceived from the inter prediction unit 160, and so on. the basis of slice. Therefore, the information indicating [0037] FIG. 2 is a block diagram of the intra prediction whether the adaptive loop filter process is applied to a unit 150 of a moving picture coding unit 100 according current slice or not is included in a slice header or a picture to the present invention. header. If the adaptive loop filter process is applied to [0038] Referring to FIG. 2, the intra prediction unit 150 the current slice, the slice header or the picture includes 15 includes a reference pixel generating unit 151, a refer- information indicating a horizontal filter length and/or a ence pixel filtering unit 152, a prediction block generating vertical filter length of luminance components which is unit 153, a prediction mode determining unit 154 and a used in the adaptive loop filter process. In case of using prediction mode coding unit 155. a prediction method, the slice header or the picture in- [0039] The reference pixel generating unit 151 deter- cludes predicted filter coefficients. 20 mines that it is necessary to generate reference pixels [0032] Chrominance components may also be filtered for intra prediction, and generates reference pixels if it is adaptively. The slice header or the picture header may necessary to generate the reference pixels. include information whether each chrominance compo- [0040] FIG. 3 is a conceptual diagram showing posi- nent is filtered or not. To reduce the amount of bits, the tions of reference pixels used for intra prediction accord- information indicating whether the Cr component is fil- 25 ing to the present invention. As shown in FIG. 3, the ref- tered and information indicating whether the Cb compo- erence pixels of the current prediction consist of above nent is filtered may be coded jointly. A lowest index is reference pixels, left reference pixels and a corner refer- assigned to the case that none of Cr and Cb components ence pixel. The above reference pixels of the current pre- are not filtered because the probability that none of Cr diction unit are pixels (regions C and D) present over and Cb components are not filtered in order to reduce 30 double the width of the current prediction unit, and the complexity is high and entropy encoding is performed. A left reference pixels of the current prediction unit are pix- highest index is assigned to the case that the both of Cr els (regions A and B) present over double the height of and Cb components are filtered. the current prediction unit. The corner reference pixel is [0033] The picture storing unit 180 receives post-proc- located at (x=-1, y=-1). essed image from the post-processing unit 170, and 35 [0041] The reference pixel generating unit 151 deter- stores the restored image in picture units. A picture may mines whether the reference pixels are available or not. be an image in a frame or a field. The picture storing unit If one or more reference pixels are not available, the ref- 180 hasa buffer (not shown) capable of storing a plurality erence pixel generation unit 151 generates reference pix- of pictures. els at the unavailable positions using available reference [0034] The inter prediction unit 160 performs motion 40 pixel. estimation using one or more reference pictures stored [0042] When the current prediction unit is located at in the picture storing unit 180, and determines one or the upper boundary of a picture or a slice, the above more reference picture indexes indicating the reference reference pixels (regions C and D) and the corner refer- pictures and one or more motion vectors. According to ence pixel ofthe current prediction unit do not exist. When the reference picture index and motion vector, the inter 45 the current prediction unit is located at the left boundary prediction unit 160 extracts a prediction block corre- of a picture or a slice, the left reference pixels (regions sponding to a prediction unit to be encoded from a ref- A and B) and the corner reference pixel do not exist. In erence picture selected among a plurality of reference those cases, reference pixels are generated by copying pictures stored in the picture storing unit 180 and outputs the value of an available pixel closest to the unavailable the extracted prediction block. 50 pixel. That is, when the current prediction unit is located [0035] The intra prediction unit 150 performs intra pre- at the upper boundary of a picture or a slice, the above diction using reconstructed reference pixels in a picture reference pixels can be generated by copying the upper- including a current prediction unit. The intra prediction most left reference pixel (that is, a reference pixel located unit 150 receives the current prediction unit to be predic- in the uppermost position of region A). When the current tively encoded, selects one of a predetermined number 55 prediction unit is located at the left boundary of a picture of intra prediction modes, and performs intra prediction. or a slice, the left reference pixels can be generated by

The predetermined number of intra prediction modes de- copying the leftmost above reference pixel (that is, a ref- pends on a size ofthe current prediction unit. The intra erence pixel located in the leftmost position of region C).

[0043] Next, a case in which some of reference pixels cause difference between values of the above-men- in an above or left reference pixels of a current prediction tioned reference pixels may be large. To be specific, it unit to be encoded are unavailable will be described. can be possible to generate unavailable reference pixels

There are two cases in which 1) available reference pixels of the current location by considering location against the are present in only one direction with respect to the un- 5 two available reference pixels. available reference pixels, and 2) available reference pix- [0051] The reference pixel filtering unit 152 filters adap- els are present in both directions with respect to the un- tively reference pixels of the current prediction unit, available reference pixels. [0052] Referring to the FIG. 4, the operation of the ref- [0044] First, a case in which available reference pixels erence pixel filtering unit 152 is described. FIG. 4 is a are present in only one direction with respect to the un- 10 conceptual diagram illustrating directional intra predic-available reference pixels will be described. tion modes according to the present invention.

[0045] It can be possible that the reference pixels ad- [0053] The reference pixel filtering unit 152 filters ref- jacent to the above boundary of the current prediction erence pixels adaptively according to the intra prediction unit(regionC)are available, buttheaboverightreference mode and position of the reference pixel. pixels (region D) may not be available. When the current 15 [0054] In the vertical mode (mode 0), the horizontal prediction unit is located at the right boundary of a slice mode (mode 1) and the DC mode (mode 2), the reference or an LCU, the reference pixels in region D are not avail- pixels are not filtered. But, in directional intra prediction able. In this case, the above right reference pixels (region modes other than the modes 0, 1 and 2, the reference D) are generated using one or more available above ref- pixels are adaptively filtered. The rightmost pixel of the erence pixels. The above right reference pixels are gen- 20 above reference pixels located at (x=2N-1, y=-1) and the erated by copying an above rightmost pixel or using two lowest pixel of the left reference pixels located at (x=-1, or more available above reference pixels. y=2N-1) are not filtered. The other reference pixels are [0046] When the reference pixels (region A) adjacent filtered using two adjacent reference pixels. to the left side of the current prediction unit are available, [0055] A low-pass filter is applied to smooth the differ-but the below left reference pixels (region B) may not be 25 ences between the adjacent reference pixels. The low-available. When the current prediction unit is located at pass filter may be a 3-tap filter [1,2,1] or a 5-tap filter [1, the below boundary of a slice or an LCU, the reference 2, 4, 2,1], pixels in region B are not available. In this case, the below [0056] The application of the low-pass filter is deter-left reference pixels (region B) are generated using one mined by a size of the current prediction unit and intra or more available left reference pixels. The below left 30 prediction mode. reference pixels are generated by copying a left lowest [0057] A filter is adaptively applied to the reference pix- pixel or using two or more available left reference pixels. els in the directional intra prediction modes 3, 6 and 9 [0047] As described above, if the available reference having a direction of 45° with reference to the horizontal pixel exists in only one direction from the unavailable or vertical direction according to the size of the prediction pixels, the reference pixel is generated by copying the 35 unit. If the size of the prediction unit is smaller than a valueofan available pixel closesttothe unavailable pixel. predetermined size, a first filter is applied. If the size of

Alternatively, the reference pixels may be generated us- the prediction unit is equal to or larger than the predeter-ing two or more available pixels closesttothe unavailable mined size, a second filter stronger than the first filter pixel. may be applied. The predetermined size may be 16x16.

[0048] Next, a case in which available reference pixels 40 [0058] In directional intra prediction modes existing be- are present in both directions with respect to the unavail- tween the intra prediction mode 3, 6 or 9 and the hori- able reference pixels will be described. zontal or vertical intra prediction mode, the filter can be [0049] For example, when the current prediction unit adaptively applied to reference pixels according to the is located at the upper boundary of a slice and the above size of the prediction unit. The filter may be applied in a right prediction unit of the current prediction unit is avail- 45 predetermined number of intra prediction modes adja-able, the reference pixels corresponding to region C of cent to the mode 3, 6 or 9. For the prediction units having the current prediction unit are not available, but the ref- same number of directional intra prediction mode, the erence pixels located at regions A and D are available. predetermined number may be increase as the size of

In this case that reference pixels present in both direc- the prediction block increases. For example, the filter is tions are available, the reference pixels are generated 50 applied to a first number of intra prediction modes adja-by selecting available reference pixels nearest to each cent to the mode 3, 6 or 9 for 8x8 prediction units, to a direction and using them (that is, utmost above reference second number of intra prediction modes adjacent to the pixel in region A and utmost left reference pixel in region mode 3, 6 or 9 for 16x16 prediction unit, and to a third D). number of intra prediction modes adjacent to the mode [0050] The reference pixels are generated by rounding 55 3, 6 or 9 for 32x32 prediction unit. The first number is average of the above-mentioned reference pixels (that equal toorsmallerthan the second number, andthesec-is, pixels nearest to each direction). But, linear interpo- ond number is equal toorsmallerthan the third number, lation may be used to generate the reference pixels be- [0059] The prediction block generating unit 153 gen- erates a prediction block corresponding to the intra pre- predetermined direction (e.g., from right to left) to deter- diction mode. mine the intra prediction mode of a first available predic- [0060] In the DC mode, the prediction block consists tion unit as an above intra prediction mode. Also, when of averages of reference pixels, and a step difference there exist a plurality of left prediction units of the current may occur between pixels in a prediction block adjacent 5 prediction unit, the plurality of left prediction units are to the reference pixels. Therefore, the prediction pixels scanned in a predetermined direction (e.g., from bottom of upper line and left line which are adjacent to the ref- to top) to determine the intra prediction mode of a first erence pixels are filtered using the reference pixels. The available prediction unit as a left intra prediction mode, upper left prediction pixel adjacent two reference pixels Alternatively, among a plurality of available prediction (the upper reference pixel and the left reference pixel) is 10 units, the intra prediction mode of an available prediction filtered by 3-tap filter. The other prediction pixels (pixels unit having the lowest intra prediction mode number may of upper line and pixels of left line in the prediction block) be set as an above intra prediction mode, and adjacent to one reference pixel are filtered by 2-tap [0067] Next, the derived intra prediction mode may be filter. converted into one of the permissible modes for the cur- 10061] In the planar mode, the prediction pixels are 15 rent prediction unit when the derived intra prediction generated using a comer reference pixel, left reference mode number is equal to or greater than the number of pixels and above reference pixels. A prediction pixel lo- intra prediction modes permissible for the current predicated at (a, b) is generated using a corner reference pixel tion unit. located at (x=-1, y=-1); an above reference pixel located [0068] Next, a first intra prediction mode group is con- at (x=a, y=-1) and a left reference pixel located at (x=-1, 20 structed using the derived or converted intra prediction y=b). In the planar mode, the prediction pixels are not mode. filtered by reference pixel. [0069] Thederived orconverted intra prediction modes [0062] The intra prediction mode determining unit 154 and one or more intra prediction mode candidates deter- determines the intra prediction mode of the current pre- mined in a predetermined order by the derived or con- diction unit. The intra prediction mode determining unit 25 verted intra prediction modes are used to construct the 154 selects one intra prediction mode in which the first intra prediction mode group. When the derived or amount of coding bits of a residual block is minimized for converted intra prediction mode is a directional mode, each intra prediction mode as the intra prediction mode the intra prediction mode candidates may be one or more of the current prediction unit. directional intra prediction modes closest to the derived [0063] The intra prediction mode coding unit 155 en- 30 or converted intra prediction mode. codes the intra prediction mode of the current prediction [0070] Next, it is determined whether the intra predic- unit determined by the intra prediction mode determining tion mode of the current prediction unit belongs to the unit 154. The intra prediction mode coding unit 155 may first intra prediction mode group or not. be integrated into the intra prediction unit 150 or into the [0071] When the intra prediction mode of the current entropy coding unit 140 35 prediction unit belongs to the first intra prediction mode [0064] The intra prediction mode coding unit 155 en- group, information indicating the first intra prediction codes the intra prediction mode of the current prediction mode group and an index corresponding to the intra preunit using intra prediction modes of the prediction units diction mode of the current prediction unit in the first intra adjacent to the current prediction unit. The intra predic- prediction mode group are encoded. tion mode coding unit 155 classifies intra prediction 40 [0072] But, when the intra prediction mode of the cur- modes (for example, 35 modes) permissible to the cur- rent prediction unit does not belong to the first intra prerent prediction unit into a plurality intra prediction mode diction mode group, information indicating a second intra group, encodes an index corresponding to a group to prediction mode group and an index corresponding to which the current intra prediction mode belongs and an the intra prediction mode of the current coding unit in the index corresponding to the intra prediction mode of the 45 second intra prediction mode group are encoded. The current prediction unit in the group to which the current second intra prediction mode group includes intra pre- intra prediction mode belongs. Each group includes at diction modes other than the intra prediction modes be- least one intra prediction mode. Preferably, the number longing to the first intra prediction mode group, of the intra prediction mode group is 2 or 3. [0073] When none of the above intra prediction mode [0065] Hereinafter, a case that the number of the intra so and the left intra prediction mode is available, one or more prediction mode groups is 2 will be described. intra prediction modes are added to the first intra predic- [0066] First, the intra prediction modesofthe prediction tion mode group. For example, DC mode or planar mode units adjacent to the current prediction unit are derived. may be added when one intra prediction mode is added.

The intra prediction modes may be intra prediction modes DC mode and planar or vertical mode may be added of a left prediction unit and an above prediction unit of 55 when two intra prediction modes are added. DC mode, the current prediction unit. When there exist a plurality planar mode and one of the vertical mode and the hori- of above prediction units of the current prediction unit, zontal mode may be added when three intra prediction the plurality of above prediction units are scanned in a modes are added.

[0074] When one of the above intra prediction mode diction mode of the current prediction unit is equal to one and the left intra prediction mode is available or when of the intra prediction mode of previous block adjacent the above intra prediction mode and the left intra predic- to the current prediction units, a flag indicating this tion mode are same, one or two intra prediction modes (pred_flag) is set to 1 and the intra prediction mode of may be added to the first intra prediction mode group. 5 the current prediction unit is encoded using the available

For example, DC mode or planar mode may be added left or the above intra prediction mode. Otherwise, the when one intra prediction mode is added. When two intra flag (pred_flag) is set to 0 and an index indicating the prediction modes are added, the intra prediction modes ordered numberofthe intra prediction mode of the current to be added vary according to whether the available intra coding unit among intra prediction modes other than the prediction mode is a directional intra prediction mode or 10 left and the above intra prediction modes is encoded, not. If the available intra prediction mode is one of non- [0078] Meanwhile, intra prediction modes of chromi- directional intra prediction modes (that is, DC mode and nance component may includes a mode using corre- planar mode), a vertical mode and a horizontal mode sponding intra prediction mode of luminance component, may be added or the other directional intra prediction In this case, such information may be included in a se- mode and a vertical mode may be added. If the available 15 quence parameter set (SPS), a picture parameter set intra prediction mode is a directional intra prediction (PPS) or a slice header. The number of intra prediction mode, two intra prediction modes closest to the direc- modes of chrominance component may vary according tional intra prediction mode in both sides may be added. to a size of the prediction unit. The intra prediction modes

But, if there exist the adjacent intra prediction mode in of chrominance component may be encoded using intra only one side of the available intra prediction mode (that 20 prediction modes of adjacent block. In this case, encod- is, the available intra prediction mode is mode 6 or 9), ing method is the same as described above. Otherwise, the one adjacent intra prediction mode (mode 25 or 33) the intra prediction modes of chrominance component and one of DC mode or planar mode may be added. may be encoded not using intra prediction mode infor- [0075] When the intra prediction mode of the current mation of adjacent block. In this case, VLC table can be prediction unit belongs to the second intra prediction 25 used. mode group, the index corresponds to a reordered [0079] The prediction block transmitting unit 156 transnumber of the intra prediction mode of the current coding mits the prediction block generated corresponding to the unit in the second intra prediction mode group. In this intra prediction mode to the subtracter 190. case, one VLC table may be used. [0080] FIG. 5 is a block diagram of a moving picture [0076] The case that the numberofthe intra prediction 30 decoding apparatus according to the present invention, mode group is 2 is presented, but the numberofthe intra [0081] The moving picture decoding apparatus ac- prediction mode groups may be 3. When the number of cording to the present invention includes an entropy de- the intra prediction mode groups is 3, if the intra prediction coding unit 210, an inverse scanning unit 220, an inverse mode of the current prediction unit does not belong to quantization unit 230, an inverse transform unit 240, an the first intra prediction mode group, it is determined 35 intra prediction unit 250, an inter prediction unit 260, a whether the intra prediction mode of the current predic- post-processing unit 270, a picture storing unit 280, an tion unit belongs to the second intra prediction mode adder 290 and an intra/inter changing switch 295. group. If the intra prediction mode of the current predic- [0082] The entropy decoding unit 210 extracts intra tion unit belongs to the second intra prediction mode prediction information, inter prediction information and group, information indicating the second intra prediction 40 quantized coefficients information from a received bit mode group and an index corresponding to the intra pre- stream. The entropy decoding unit210 transmits the inter diction mode of the current coding unit in the second intra prediction information to the inter prediction unit 260, the prediction mode group are encoded. If the intra prediction intra prediction information to the intra prediction unit250 mode of the current prediction unit does not belong to and the quantized coefficients information to the inverse the second intra prediction mode group, information in- 45 scanning unit 220. dicating the third intra prediction mode group and an in- [0083] The inverse scanning unit 220 converts the dex corresponding to the intra prediction mode of the quantized coefficients information into a two-dimensional currentcodingunitinthethirdintrapredictionmodegroup quantized transform block. One of a plurality of inverse are encoded. The second intra prediction mode group is scan patterns is selected for the conversion. The inverse generated based on the intra prediction modes of the left so scan pattern is selected based on the intra prediction prediction unit and the above prediction unit of the current mode. If a size of a transform unit to be decoded is larger prediction unit. than the predetermined reference size, a quantized [0077] Alternatively, the prediction mode coding unit transform unit is generated by inversely scanning the 155 may encode the intra prediction mode of the current quantized transform coefficients in the unit of a predeter- prediction mode as follows. First, it is determined whether 55 mined size of subset. If the size of a transform unit to be the intra prediction mode of the current prediction unit is decoded is equal to the predetermined reference size, equal to one of the intra prediction mode of previous block the quantized transform unit is generated by inversely adjacent to the current prediction units. If the intra pre- scanning the quantized transform coefficients in the unit of the transform unit. If the quantized transform coeffi- restored by the inverse transform unit 240 and a predic- cients are inversely scanned in the unit of the subset, a tion block generated by the intra prediction unit 250 or same inverse scan pattern is applied to the quantized the inter prediction unit 260 to generate a reconstructed transform coefficients in each subset. The plurality of image block. subsets consist of one main subset and one or more re- 5 [0089] The intra prediction unit 250 restores the intra maining subsets. The main subset is located at an upper prediction mode of the current block based on the intra left side and includes a DC coefficient, and the one or prediction information received from the entropy decod- more remaining subsets cover region otherthan the main ing unit 210, and generates a prediction block according subset. to the restored intra prediction mode.

[0084] A scan pattern to be applied to the subsets may 10 [0090] The inter prediction unit 260 restores reference be a zigzag scan. The subsets may be inversely scanned picture indexes and motion vectors based on the inter beginning with the main subset to the residual subsets prediction information received from the entropy decodin a forward direction, or can be scanned in the reverse ing unit 210, and generated a prediction block using the direction. An inverse scan pattern for scanning the sub- reference picture indexes and the motion vectors. When sets may be set the same as an inverse scan pattern for 15 motion compensation with fractional precision is applied, scanning the quantized transform coefficients. The in- the prediction block is generated using an interpolation verse scanning unit 220 performs inverse scanning pro- filter. cedure using information indicating a position of the last [0091] The post-processing unit 270 operates the non-zero quantized coefficient of the transform unit. same as the post-processing unit 160 of FIG. 3.

[0085] The inverse quantization unit 230 determines a 20 [0092] The picture storing unit 280 stores the postquantization step size predictor of a current coding unit. processed reconstructed image by the post-processing

The operation to determine the quantization step size unit 270. predictor is same as the procedure of the quantization [0093] FIG. 6 is a block diagram of the intra prediction unit 130 of FIG. 1. The inverse quantization unit adds the unit 250 of a moving picture decoding apparatus 200 ac- determined quantization step size predictor and a re- 25 cording to the present invention, ceived residual quantization step size to generate a [0094] The intra prediction unit 250 according to the quantization step size of the current coding unit. The in- present invention includes an intra prediction mode de- verse quantization unit 230 restores inverse quantized coding unit 251, a reference pixel generating unit 252, a coefficients using a quantization matrix determined by reference pixel filtering unit 253, a prediction block gen- the quantization step size. The quantization matrix varies 30 erating unit 254 and a prediction block transmitting unit according to the size of the current block to be restored. 255.

The quantization matrix may be selected for a block hav- [0095] The intra prediction mode decoding unit251 re- ing the same size on the basis of at least one of a pre- ceives the intra prediction information from the entropy diction mode and an intra prediction mode of the current decoding unit 210 and restores the intra prediction mode block. 35 of the current prediction unit. The intra prediction infor- [0086] The inverse quantization unit 230 determines a mation includes information indicating the intra prediction quantization step size predictor of a current coding unit. mode group to which the current prediction unit to be

The operation of determining the quantization step size decoded belongs and the intra prediction mode index, predictor is same as the operation of the quantization [0096] The intra prediction mode decoding unit251 deunit 130 of FIG. 1. The inverse quantization unit adds the 40 rjVes intra prediction modes of the prediction units adja- determined quantization step size predictor and a re- cent to the current prediction unit. The intra prediction ceived residual quantization step size to generate a modes may be the intra prediction mode of a left intra quantization step size of the current coding unit. The in- prediction unit and an above intra prediction unit of the verse quantization unit 230 restores inverse quantized current prediction unit. When there exist a plurality of coefficients using a quantization matrix determined by 45 above prediction units of the current prediction unit, the the quantization step size. The quantization matrix varies plurality of above prediction units are scanned in a preaccording to the size of the current block or the quanti- determined direction (e.g., from right to left) to determine zation matrix varies for a block according to at least one the intra prediction mode of a first available prediction of the prediction mode and the intra prediction mode. unit as an above intra prediction mode. Also, when there [0087] The inverse transform unit 240 inversely trans- 50 exist a plurality of left prediction units of the current preforms the inverse quantized block to restore a residual diction unit, the plurality of left prediction units are block. The inverse transform matrix to be applied to the scanned in a predetermined direction (e.g., from bottom inverse quantized block is adaptively determined accord- to top) to determine the intra prediction mode of a first ing to the prediction mode (intra or inter) and the intra available prediction unit as a left intra prediction mode, prediction mode. The determination procedure of the in- 55 Alternatively, among a plurality of available prediction verse transform matrix is the same as the procedure in units, the intra prediction mode of an available prediction the transform unit 120 of FIG. 1. unit having the lowest intra prediction mode number may [0088] The adder 290 adds the restored residual block be set as an above intra prediction mode.

[0097] The above intra prediction mode or the left intra tion mode are same, one or two intra prediction modes prediction mode is converted into one of the permissible may be added to the first intra prediction mode group, modes when the above intra prediction mode number or For example, DC mode or planar mode may be added the leftintra prediction mode number is equal to orgreater when one intra prediction mode is added. When two intra than the number of intra prediction modes permissible 5 prediction modes are added, the intra prediction modes for the current prediction unit. to be added vary according to whether the available intra [0098] A first intra prediction mode group is construct- prediction mode is a directional intra prediction mode or ed using the derived or converted intra prediction mode. not. If the available intra prediction mode is one of non-

The derived or converted intra prediction modes and one directional intra prediction modes (that is, DC mode or or more intra prediction mode candidates determined in 10 planar mode), a vertical mode and a horizontal mode a predetermined order by the derived or converted intra maybe added or the other non-directional intra prediction prediction modes may be included in the first intra pre- mode (that is, planar mode or DC mode) and a vertical diction mode group. When the derived or converted intra mode may be added. If the available intra prediction prediction mode is directional mode, the one or more mode is a directional intra prediction mode, two intra pre- intra prediction mode candidates may be at least one 15 diction modes closest to the available intra prediction directional intra prediction mode closest to the derived mode in both sides may be added. But, fora certain mode or converted intra prediction mode. (for example, the mode 6 or the mode 9) which has the [0099] The intra prediction mode decoding unit 251 de- adjacent intra prediction mode in only one side of the termines whether the information indicating the intra pre- available intra prediction mode, the adjacent intra pre diction mode group indicates the first intra prediction 20 diction mode (the mode 25 or the mode 33) and one of mode group or not. DC mode and planar mode may be added.

[0100] If the information indicating the intra prediction [0104] Alternatively, the prediction mode decoding unit mode group indicates the first intra prediction mode 251 may decode the intra prediction mode of the current group, the intra prediction mode corresponding to the prediction mode as follows. First, a flag (pred_flag) indi- received intra prediction mode index is selected from the 25 eating whether the intra prediction mode of the current first intra prediction mode group, and the selected intra prediction unit is equal to one of the intra prediction prediction mode is set as the intra prediction mode of the modes of previous intra prediction units (for example, current prediction unit. above and left prediction units) is parsed. If the flag [0101] If the information indicating the intra prediction (pred_flag) is 1, the intra prediction mode of the current mode group indicates the second intra prediction mode 30 prediction unit is determined using the available left intra group, the intra prediction mode corresponding to the prediction mode and the available above intra prediction received intra prediction mode index is selected from the mode. Iftheflag (pred_flag) is 0, the intra prediction mode second intra prediction mode group, and the selected of the current prediction unit is determined using remain- intra prediction mode is set as the intra prediction mode ing prediction mode information (rem_pred_mode). The of the current prediction unit. The second intra prediction 35 remaining prediction mode information mode group includes intra prediction modes other than (rem_pred_mode) indicates the order of the intra predic- the intra prediction modes belonging to the first intra pre- tion modes of the current intra prediction unit among diction mode group. The intra prediction modes of the available intra predictions mode other than the available second intra prediction mode may be reordered with ref- left intra prediction mode and the available above intra erence to the intra prediction mode index. Also, the intra 40 prediction mode. prediction modes of the second intra prediction mode [0105] The reference pixel generating unit 252 gener- may be reordered with reference to the intra prediction ates reference pixels using the same method as de- mode of the above and the left prediction unit of the cur- scribed in the reference pixel generating unit 151 of the rent prediction unit as well as the intra prediction mode coding apparatus 100. But, the reference pixel generat- index. 45 ing unit 252 may adaptively generate reference pixels [0102] When none of the above intra prediction mode according to the restored intra prediction mode only when and the left intra prediction mode is available, one or more the reference pixels used for generating a prediction intra prediction modes are added to the first intra predic- block and determined by the intra prediction mode are tion mode group. For example, DC mode or planar mode not available. may be added when one intra prediction mode is added. 50 [0106] The reference pixel filtering unit 253 adaptively DC mode and planar or vertical mode may be added filters the reference pixels based on the restored intra when two intra prediction modes are added. DC mode, prediction mode and a size of the current prediction unit, planar mode, and one of the vertical mode and horizontal The filtering condition and method are same as those of mode may be added when three intra prediction modes the reference pixel filtering unit 152 of the coding appa- are added. 55 ratus 100.

[0103] When one of the above intra prediction mode [0107] The prediction block generating unit 254 gen- and the left intra prediction mode is available or when erates a prediction block using the reference pixels based the above intra prediction mode and the left intra predic- on the restored intra prediction mode. A method for gen- erating the prediction block is the same method as used of left prediction units are scanned in a predetermined in the prediction block generating unit 154 of the coding direction (e.g., from top to bottom) to determine the intra apparatus 100. prediction mode of a first available prediction unit as a [0108] The prediction block transmitting unit255 trans- left intra prediction mode. mits the prediction block received from the prediction 5 [0116] Ifthe available intra prediction mode is not equal block generator 254 to the adder 290. to one of permissible intra prediction modes of the current [0109] FIG. 7 is a flow chart illustrating a decoding pro- prediction unit, the available intra prediction mode iscon- cedure in intra prediction mode according to the present verted to one of permissible intra prediction modes of the invention. current prediction unit.

[0110] First, intra prediction information and residual 10 [0117] It is determined whether the intra prediction signals are de-multiplexed from a received bit stream in mode of the current prediction unit belongs to the first step S 100. The step S100 is performed in the unit of a intra prediction mode group or not based on the intra coding unit. The intra prediction information is extracted prediction mode group indicator in step S112. from a prediction unit syntax in the coding unit. The re- [0118] If the intra prediction mode of the current pre-sidual signals are extracted from a transform unit syntax 15 diction unit belongs to the first intra prediction mode in the coding unit. group, it is determined whether the intra prediction mode [0111] The intra prediction mode of a current prediction index exists or not in step S 113. unit is restored using the intra prediction information ob- [0119] Ifthe intra prediction mode index exists, the intra tained from the prediction unit syntax in step S110. The prediction mode of the first intra prediction mode group intra prediction information includes the intra prediction 20 corresponding to the intra prediction mode index is de-mode group indicator (pred_mode) and the intra predic- termined as the intra prediction mode of the current pre-tion mode index. Ifthe intra prediction information does diction unit in step S114. not include the intra prediction mode index, the intra pre- [0120] Ifthe intra prediction mode index does not exist, diction information is set to 0. The intra prediction mode the intra prediction mode index is set to 0 and the intra group indicator indicates the intra prediction mode group 25 prediction mode of the first intra prediction mode group which the intra prediction mode of the current prediction corresponding to the intra prediction mode index 0 is deunit belongs to. Ifthe number of the intra prediction mode termined as the intra prediction mode of the current pregroups is 2, the intra prediction mode group indicator diction unit in step S115. That is, ifthe intra prediction (pred_mode) may be a flag of one bit. The number of the mode index does not exist, only one intra prediction mode intra prediction mode groups may be 2 or 3. 30 is included in the first intra prediction mode group.

[0112] FIG. 8 is a flow chart illustrating a procedure for [0121] If the intra prediction mode of the current prerestoring intra prediction mode according to the present diction unit does not belong to the first intra prediction invention. The number of intra prediction modes belong- mode group, the intra prediction mode of the second intra ing to the first intra prediction mode group varies. A case prediction mode group corresponding to the intra predic- thatthe number of the intra prediction mode groups is 2 35 tion mode index is determined as the intra prediction will be described. mode of the current prediction unit in step S116. The [0113] First, a first intra prediction mode group is con- second intra prediction mode group includes all the intra structed using intra prediction modes of the prediction prediction modes other than the intra prediction modes units adjacent to the current prediction unit in step S111. belonging to the first intra prediction mode group. The [0114] For example, the first intra prediction mode 40 intra prediction mode index may be assigned in the order group is comprised of available intra prediction modes of the mode number of the intra prediction mode of the of the above and the left intra prediction units of the cur- second intra prediction mode group. rent prediction unit. If both of the intra prediction modes [0122] FIG. 9 is a flow chart illustrating another proce-of the above and the left intra prediction units are una- dure for restoring intra prediction mode according to the vailable, DC mode or planar mode may be added to the 45 present invention. The number of intra prediction modes first intra prediction mode group. The first intra prediction belonging to a first intra prediction mode group is fixed, mode group may include at least one additional intra pre- [0123] First, a first intra prediction mode group is con- diction mode which is a first available intra prediction structed using intra prediction modes of the prediction mode encountered when retrieving a right above intra units adjacent to the current prediction unit in step S211. prediction mode, a left below intra prediction mode, a left 50 [0124] When the first intra prediction mode group in- above intra prediction mode of the current prediction unit. eludes two intra prediction modes, the first intra prediction [0115] When there exist a plurality of above prediction mode group is constructed as follows. units of the current prediction unit, the plurality of above [0125] It is determined whether the intra prediction prediction units are scanned in a predetermined direction modes of the above and the left intra prediction units of (e.g., from left to right) to determine the intra prediction 55 the current prediction unit are available or not. Ifthe availmode of a first available prediction unit as an above intra able intra prediction mode is not one of the permissible prediction mode. Also, when there exist a plurality of left intra prediction modes of the current prediction unit, the prediction units of the current prediction unit, the plurality available intra prediction mode is converted to one of the permissible intra prediction modes. When both of the in- above and the left intra prediction units are unavailable, tra prediction modes of the above and the left intra pre- the first intra prediction mode group is comprised of three diction units are available and are not same, the first intra additional intra prediction modes. The three additional prediction mode group is comprised of the intra prediction intra prediction modes may be a DC mode, a vertical modes of the above and the left intra prediction units. 5 mode and a horizontal mode, or a DC mode, a planar

When one of the intra prediction modes of the above and mode and a vertical mode. left intra prediction units is only available or when the [0131] When there exista plurality of above prediction intra prediction modes of the above and the left intra pre- units of the current prediction unit, the plurality of above diction units are same, the first intra prediction mode prediction units are scanned in a predetermined direction group is comprised of the available intra prediction mode 10 (e.g., from left to right) to determine the intra prediction and one additional intra prediction mode. If the available mode of a first available prediction unit as an above intra intra prediction mode is not DC mode, the additional intra prediction mode. Also, when there exist a plurality of left prediction mode may be DC mode. If the available intra prediction units of the current prediction unit, the plurality prediction mode is DC mode, the additional intra predic- of left prediction units are scanned in a predetermined tion mode may be planar mode or vertical mode. 15 direction (e.g., from top to bottom) to determine the intra [0126] When the first intra prediction mode group in- prediction mode of a first available prediction unit as a eludes three intra prediction modes, the first intra predic- left intra prediction mode. tion mode group is constructed as follows. [0132] Next, it is determined whether the intra predic- [0127] It is determined whether the intra prediction tion mode of the current prediction unit belongs to the modes of the above and the left intra prediction units of 20 first intra prediction mode group or not based on the intra the current prediction unit are available or not. If the avail- prediction mode group indicator in step S212. able intra prediction mode is not one of the permissible [0133] If the intra prediction mode of the current pre- intra prediction modes of the current prediction unit, the diction unit belongs to the first intra prediction mode available intra prediction mode may be converted to one group, the intra prediction modeofthefirst intra prediction of the permissible intra prediction modes. 25 mode group corresponding to the intra prediction mode [0128] When both of the intra prediction modes of the index is determined as the intra prediction mode of the above and left intra prediction units are available and are current prediction unit in step S213. not same each other, the first intra prediction modegroup [0134] If the intra prediction mode of the current pre- is comprised of the two available intra prediction modes diction unit does not belong to the first intra prediction and one additional intra prediction mode. The additional 30 modegroup, the intra prediction mode of the second intra intra prediction mode is different from the two available prediction mode group corresponding to the intra predic- intra prediction modes and is one of a vertical mode, a tion mode index is determined as the intra prediction horizontal mode and a DC mode. The additional intra mode of the current prediction unit in step S214. The prediction mode is the first intra prediction mode able to second intra prediction mode group includes all the intra be added in the order of the DC mode, the vertical mode 35 prediction modes other than the intra prediction modes and the horizontal mode. belonging to the first intra prediction mode group.

[0129] When only one of the intra prediction modes of [0135] Index of the intra prediction mode candidate in the above and the left intra prediction units is available the second intra prediction mode group is assigned in or when the intra prediction modes of the above and the the orderofthe mode number of the intra prediction mode left intra prediction units are same, the first intra prediction 40 of the second intra prediction mode group. mode group is comprised of the one available intra pre- [0136] Next, reference pixels are adaptively generated diction mode and two additional intra prediction modes. based on the restored intra prediction mode of the current

The two additional intra prediction modes are adaptively prediction unit in step S120. determined according to the available intra prediction [0137] When there are available reference pixels in on- modes and a size of the prediction unit. If the size of the 45 |y one side of the position of the unavailable reference prediction unit is equal to or smaller than a predetermined pixel, the reference pixels are generated by copying the size and the available intra prediction mode is a direc- value ofan available pixel closest to the unavailable pixel, tional mode, two intra prediction modes having direction Alternatively, the reference pixels are generated using closest to the direction of the available intra prediction two available pixels closest to the unavailable pixel, mode are selected as the two additional intra prediction so when the unavailable reference pixel exists between the modes. But, ifthe available intra prediction mode is mode available pixels, the reference pixel is generated using 6 or 9, mode 6 or 9 is selected as the other additional two available reference pixels closest to the unavailable intra prediction mode. Ifthe available intra prediction pixel in both sides. The value of the generated reference mode is non-directional intra prediction mode, the two pixel may be average of the two available reference pixels additional intra prediction modes are a vertical mode and 55 closest to the unavailable pixel in both sides. Linear in- a horizontal mode, or the other non-directional intra pre- terpolation method may be used to generate the refer- diction mode and a vertical mode. ence pixels when a difference between the two available [0130] When all of the intra prediction modes of the reference pixels is large.

[0138] Next, the reference pixels are adaptively filtered verse scan pattern is selected among a plurality of in- based on the restored intra prediction mode (S130). verse scan patterns for this conversion. The inversescan

When the restored intra prediction mode is a vertical pattern is determined according to the intra prediction mode (mode 0), a horizontal mode (mode 1) or a DC mode. If the size of the transform unit is larger than a mode (mode 2), the reference pixels are not filtered. In 5 predetermined size, the residual signals are inversely directional intra prediction mode other than the vertical scanned in the unit of subset and a quantized transform mode and the horizontal mode, the reference pixels are block is generated. If the size of the transform unit is adaptively filtered. The rightmost reference pixel of the equal to the predetermined size, the residual signals are above reference pixels located at (x=2N-1, y=-1) and the inversely scanned in the unit of transform unit and aquan- lowest reference pixel of the left reference pixels located 10 tized transform block is generated. at (x=-1, y=2N-1) are not filtered. Remaining reference [0144] The two-dimensional quantized transform block pixels are filtered using two adjacent reference pixels. is inversely quantized in step S170. The quantization step [0139] Low-pass filter is applied to smooth the differ- size predictor of the current coding unit is determined for ence between adjacent reference pixels. The low-pass inversequantization.Thequantizationstepsizepredictor filter may be a 3-tap filter [1,2, 1] or a 5-tap filter [1,2, 4, 15 is determined using the same method as that of the in- 2, 1], verse quantization unit 230 of FIG. 5. The determined [0140] A filter is adaptively applied to the reference pix- quantization step size predictor and a received residual els according to the size of the prediction block in the quantization step size are added to generate a quantiza- directional intra prediction modes existing between a hor- tion step size to be applied to transform block. And in- izontal or vertical mode and the intra prediction mode 20 verse quantization coefficients are restored using the having a direction of 45° with reference to the horizontal quantization matrix determined by the quantization step or vertical direction. The filter may be adaptively applied size. to the modes existing between the horizontal mode and [0145] Next, the inverse-quantized block is inversely modes having a direction of 45° with reference to the transformed in step S180. An inverse transform matrix horizontal mode, or the modes existing between the ver- 25 may be adaptively determined according to the restored tical mode and modes having a direction of 45° with ref- intra prediction mode. The transform unit may beinverse- erence to the vertical mode according to the size of the ly transformed by horizontal and vertical one-dimension- prediction block. The predetermined number may be in- al (1D) transform matrices. In intra prediction, there is a crease as the size of the prediction block increases. For high possibility that the residual signals will have vertical example, the filter is applied to the prediction mode hav- 30 directivity when the intra prediction mode is horizontal, ing a direction of 45° with reference to the horizontal or Thus, the DCT-based integer matrix is applied to the ver- vertical direction and a first number of intra prediction tical direction, and the DST or KLT-based integer matrix modes closest to the prediction mode having a direction is applied to the horizontal direction. When the intra pre- of45° with reference to the horizontal orvertical direction diction mode is vertical, an inverse DST or KLT-based for 8x8 prediction block. And the filter is applied to the 35 integer matrix is applied to the vertical direction, and an prediction mode having a direction of 45° with reference inverse DCT-based integer matrix is applied to the hori-

to the horizontal or vertical direction and a second zontal direction. When the intra prediction mode is a DC number of intra prediction modes closet to the prediction mode, an inverse DCT-based integer matrix is applied in mode having a direction of 45° with reference to the hor- the both directions. izontal or vertical direction for 16x16 prediction block. 40 [0146] The generated prediction block and the inverse-

And the filter is applied to the prediction mode having a transformed block are added to generate a reconstructed direction of 45° with reference to the horizontal orvertical image in step S190. The restored residuals signals and direction and a third number of intra prediction modes the restored prediction signals may be added in the unit closet to the prediction mode having a direction of 45° of coding unit. with reference to the horizontal or vertical direction for 45 32x32 prediction block. The first number is equal to or smallerthan the second number, and the second number Claims is equal to or smaller than the third number.

[0141] Next, a prediction block is generated using the 1. A method for decoding an intra prediction mode, reference pixels according to the restored intra prediction 50 comprising: mode in step S140. The method of generating a prediction block is the same as that of the intra prediction block restoring an intra prediction mode group indica- generating unit 254 of FIG.6 tor and a prediction mode index of a current pre- [0142] The residual signals are entropy-decoded in diction unit; step S150. 55 generating a first intra prediction mode group [0143] The residual signals are inversely scanned in using available intra prediction modes of a left step S160. That is, the residual signals are converted to prediction unit and an above prediction unit of a two-dimensional quantized transform block. One in- the current prediction unit, wherein the number of intra prediction modes belonging to the first travorhersagemodi einer linken Vorhersageein- intra prediction mode group is fixed to three; heit und einer oberhalb gelegenen Vorhersage- determining an intra prediction mode which is einheit der momentanen Vorhersageeinheit, included in the first intra prediction mode group wobeidieAnzahlvon Intravorhersagemodi, wel- and indicated by the intra prediction mode index 5 chezuderersten Intravorhersagemodusgruppe as the intra prediction mode of the current pre- gehören, auf drei festgelegt ist; diction unitwhen the intra prediction mode group Bestimmen eines Intravorhersagemodus, wel- indicator indicates the first intra prediction mode cher in der ersten Intra-vorhersagemodusgrup- group; and pe enthalten und durch den Intravorhersagemo- determining an intra prediction mode which is 10 dusgruppenindex als der Intravorhersagemo- included in a second intra prediction mode group dus der momentanen Vorhersageeinheit ange- and indicated by the intra prediction mode index zeigt ist, wenn der Intravorhersagemodusgrup- as the intra prediction mode of the current pre- penindikator die erste Intravorhersagemodus- diction unitwhen the intra prediction mode group gruppé anzeigt; und indicator indicates the second intra prediction 15 Bestimmen eines Intravorhersagemodus, wel- mode group, cher in einer zweiten Intravorhersagemodus gruppe enthalten und durch den Intravorhersa-wherein, when only one intra prediction mode out of gemodusindex als der Intravorhersagemodus the left intra prediction mode and the above intra der momentanen Vorhersageeinheit angezeigt prediction mode is available, the first intra prediction 20 ist, wenn der Intravorhersagemodusgruppenin- mode group is composed of the available intra pre- dikator die zweite Intravorhersagemodusgrup- diction mode and two additional intra prediction pe anzeigt, modes that are added to the first intra prediction mode group, wherein the two additional intra predic- wobei sich die erste Intravorhersagemodusgruppe tion modes are determined according to the available 25 aus dem verfiigbaren Intravorhersagemodus und intra prediction mode, and zwei zusátzlichen Intravorhersagemodi zusammen- wherein, when the available intra prediction mode is setzt, welche zu der ersten Intravorhersagemodus- a non-directional intra prediction mode, the two ad- gruppé hinzugefügtwerden, wenn nurentwederder ditional intra prediction modes are another non-di- linké Intravorhersagemodus oder der oberhalb ge- rectional intra prediction mode and a vertical mode. 30 legenene Intravorhersagemodus verfiigbar ist, wo bei die zwei zusátzlichen Intravorhersagemodi ent- 2. The method of claim 1, wherein, when the available sprechend des verfiigbaren Intravorhersagemodus intra prediction mode is a DC mode, the two addi- bestimmt sind, und tional intra prediction modes are a planar mode and wobei die zwei zusátzlichen Intravorhersagemodi the vertical mode. 35 ein anderer nichtgerichteter Intravorhersagemodus und ein vertikaler Modus sind, wenn der verfiigbare 3. The method of claim 1, wherein, when the available Intravorhersagemodus ein nichtgerichteter Intravo- intra prediction mode is a planar mode, the two ad- rhersagemodus ist. ditional intra prediction modes are a DC mode and the vertical mode. 40 2. Verfahren nach Anspruch 1, wobei die zwei zusátz lichen Intravorhersagemodi ein planarer Modus und 4. The method of claim 1, wherein the second intra pre- der vertikale Modus sind, wenn der verfiigbare Indiction mode group is composed of intra prediction travorhersagemodus ein DC-Modus ist. modes other than the intra prediction modes belonging to the first intra prediction mode group. 45 3. Verfahren nach Anspruch 1, wobei die zwei zusátz lichen Intravorhersagemodi ein DC-Modus und der vertikale Modus sind, wenn der verfiigbare Intravo-

Patentanspriiche rhersagemodus ein planarer Modus ist. 1. Verfahren zum Dekodieren eines Intravorhersage- 50 4. Verfahren nach Anspruch 1, wobei die zweite Intramodus, umfassend: vorhersagemodusgruppe aus anderen Intravorher sagemodi zusammengesetzt ist, als die Intravorher-Wiederherstellen eines Intravorhersagemodus- sagemodi, welche zur ersten Intravorhersagemo- gruppenindikators und eines Vorhersagemodu- dusgruppe gehören. sindexes einer momentanen Vorhersageein- 55 heit;

Erzeugen einer ersten Intravorhersagemodusgruppe unter Verwendung von verfiigbaren In-

Revendications 4. Procédéselonlarevendication1,oCi,lesecondgrou- pe de modes d’intra-prédiction est composé de mo- 1. Procédé de décodage un mode d’intra-prédiction, des d’intra-prédiction différents des modes d’intra- comprenant les étapes consistant á : prédictions appartenant au premier groupe de mo des d’intra-prédiction. restaurer un indicateurde groupe de mode d’intra-prédiction et un index de mode de prédiction d’une unité de prédiction actuelle ; générer un premier groupe de mode d’intra-prédiction en utilisant des modes d’intraprédiction disponibles d’une unité de prédiction gauche et d’une unité de prédiction supérieurede l’une unité de prédiction actuelle, oü le nombrede modes d’intraprédiction appartenant au premier groupe de modes d’intra-prédiction est fixé á trois ; déterminer un mode d’intra-prédiction qui est indus dans le premier groupe de modes d’intraprédiction et désigné par l’index de modes d’in-tra-prédictions comme étant le mode d’intra-prédiction de l’unité de prédiction actuelle lorsque l’indicateur de groupe de modes d’intra-prédiction indique le premier groupe de modes d’intraprédiction ; et déterminer un mode d’intra-prédiction qui est indus dans un second groupe de modes d’intraprédiction et désigné par l’index de modes d’in-tra-prédictions comme étant le mode d’intra-prédiction de l’unité de prédiction actuelle lorsque l’indicateur de groupe de modes d’intra-prédiction indique le second groupe de modes d’intraprédiction, oü, lorsque seul un des modes d’intra-prédiction par-mi le mode d’intra-prédiction gauche et le mode d’intra-prédiction supérieur est disponible, le premier groupe de modes d’intra-prédiction est composé du mode d’intra-prédiction disponible et de deux modes d’intra-prédiction additionnels qui sont ajoutés au premier groupe de modes d’intra-prédiction, oü les deux modes d’intra-prédiction additionnels sont dé-terminés selon le mode d’intra-prédiction disponible, et oü, lorsque le mode d’intra-prédiction disponible est un mode d’intra-prédiction non directionnel, les deux modes d’intra-prédiction additionnels sont un autre mode d’intra-prédiction non directionnel et un mode vertical. 2. Procédé selon la revendication 1, oü, lorsque le mode d’intra-prédiction disponible est un mode DC, les deux modes d’intra-prédiction additionnels sont un mode planaire et un mode vertical. 3. Procédé selon la revendication 1, oü, lorsque le mode d’intra-prédiction disponible est un mode planaire, les deux modes d’intra-prédiction additionnels sont un mode DC et un mode vertical. FIG. 1

FIG. 2

FIG. 5

FIG. 6

FIG. 7

FIG. 8

FIG. 9

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • WO 03105070 A [0008]

Claims

I, EIJébís kmsoreőikaó mód dekódoláaka, smkymrmhrmom femsfóMSBi atellisisréitie!# egység prcdlfenö i«M mdmémák tlú&Mttd prcdsMl mód csoport generálásán amely bal predikdé egysé|álÉ%Pö IktlprtkíkeíŐ médiák ás a?, aktuális predikció egység fend predikck» egységéi: MáíMt^Mé m inim pmékaó módok sréma, amelyek a? ehó mtm pmdikoió· mád caoportltms tartosmíkj hámmra ven tó|ki:tyéi. lóim pmdikmó mód meghatározását, amdysl ae első intra prediMé. mó#eáoport - wíntra pmákclómód indes. által jaime, miat &* akínális predrktíó js|pgg intra prcdikac módpo ha aginÉ$gftt8kei& mód csoport Indikátor jelzi az •élá# irdre peáikdó wM is mtrs prsdikeii mód.^^aiiá^án.sm:<ipl:másiíd)k kim preáítóó pó# c§oprt iÉjsÉnsz ds s>- hm predikeiómod imiex álM vgs jelezve, n#i gg skkáii fiédikmó egység ímraptodtkctó módja* ha a* mtra predtkdó mód csoport indikátor jekj a második »m predikció mM csoportot, ahol, ha csak egy iatra predikeíó htod «léitek a hál & a kall ihlm prédikáló módbólrák alsó Ikra prssIlkeiS médíesegort dsszc v»n léve na slérhetó rabra predikeió módból és kóiánváMs ktra predikeió módból, amelyek hozzá vannak adva az első kim predikció isodeaeponte, ahol a kél további mtr.a pródlkoll módok meg'vanaak hst&rorvn az elérhető intm predíkek mód szerint, és ahói la M elérhető istire pmdikeuS mód nem dlrckdonáks intra prédikáló mód, 3 két kim gsédikeió stódok egy másik nsm dirakeionáiis kim predikdo mód és vertikális mód. :L Az 1, igénypont satónil eljárisv shol.
Is aa akrbek intra predikdó méá 1X1 mód, a kát iovibhi;imiitj|riahk^mMok,fl«l8Mi kód ás s vertikális »ktk
3, Az Mg&ygftft sacrligiep^Sí,· ahol, ha sa dókat# tóba prcdikckV mód p keim kód, & két tev ábbl mit* pt«dikc»ó módok DC mód és a vertikális mód.
4. Air. 1. igénypont szerinti átjárás, ahol a másodsk >rm predikvíó mód csoport bura predikeió módokból van összeiévt. «melyek mások, mint as km pmiikoié módok, amelyek &z alsó irnra predikeió mód csoporthoz tartoznak.