Method and apparatus for intra prediction

An intra-prediction method in which an intra-prediction is performed on a current block, comprising:

• determining whether or not to perform smoothing on a reference pixel of the current block based on a size of a block and an intra-prediction mode for the current block, the size of the block being indicated by an encoder and transmitted to a decoder;
• and
• determining a smoothing method by comparing the size of the current block with the transmitted size of the block,
• wherein the determining of whether or not to perform smoothing on the reference pixel based on the transmitted size of the block and the intra-prediction mode for the current block comprises determining to perform smoothing only in response to each of:
• the size of the current block being 8×8 and the intra-prediction mode for the current block being a No. 2 intra-prediction mode,
• the size of the current block being 8×8 and the intra-prediction mode for the current block being a No. 18 intra-prediction mode,
• the size of the current block being 8×8 and the intra-prediction mode for the current block being a No. 34 intra-prediction mode,
• the size of the current block being 8×8 and the intra-prediction mode for the current block being a planar mode;
• the size of the current block being 16×16 and the intra-prediction mode for the current block being a No. 2 intra-prediction mode to a No. 8 intra-prediction mode,
• the size of the current block being 16×16 and the intra-prediction mode for the current block being a No. 12 intra-prediction mode to a No. 24 intra-prediction mode,
• the size of the current block being 16×16 and the intra-prediction mode for the current block being a No. 28 intra-prediction mode to a No. 34 intra-prediction mode, and
• the size of the current block being 16×16 and the intra-prediction mode for the current block being a planar mode;
• and
• the size of the current block being 32×32 and the intra-prediction mode for the current block being a No. 2 intra-prediction mode to a No. 34 intra-prediction mode, and
• the size of the current block being 32×32 and the intra-prediction mode for the current block being a planar mode other than a No. 10 intra-prediction mode and a No. 26 intra-prediction mode.

An image decoder in which an intra-prediction is performed on a current block, comprising:

• an intra-prediction unit configured to:
• determine whether or not to perform smoothing on a reference pixel of the current block based on a size of a block and an intra-prediction mode for the current block, the size of the block being indicated by an encoder and transmitted to the decoder,
• determine a smoothing filter by comparing the size of the current block with the transmitted size of the block,
• in response to the result of comparison between the size of the current block and the transmitted size of the block, determine the smoothing filter to be a bi-linear smoothing filter or a smoothing filter having predetermined filtering coefficients.

The image decoder of claim 10,

• wherein the smoothing filter having the filtering coefficients of [1,2,1] is a filter for calculating a filtered reference pixel, pF[x][y] (x=−1, y=−1 . . . nT*2−1, x=−1 . . . nT*2−1, y=−1),
• according to:
• pF[−1][nT*2−1]=p[−1][nT*2−1]
• pF[nT*2−1][−1]=p[nT*2−1][−1]
• pF[−1][y]=(p[−1][y+1]+2*p[−1][y]+p[−1][y−1]+2)>>2 for y=nT*2−2 . . . 0
• pF[−1][−1]=(p[−1][0]+2*p[−1][−1]+p[0][−1]+2)>>2
• pF[x][−1]=(p[x−1][−1]+2*p[x][−1]+p[x+1][−1]+2)>>2 for x=0 . . . nT*2−2
• wherein the current block is a current transform block and the size of the current block is a size of a current transform block, and wherein the size of the transform current block is nT, and a reference pixel of the transform block is
• p[x][y] (x=−1, y=−1 . . . nT*2−1, x=−1 . . . nT*2−1, y=−1).

The image decoder of claim 10

• wherein the bi-linear smoothing filter is a filter for calculating a filtered reference pixel, p[x][y] (x=−1, y=−1 . . . nT*2−1, x=−1 . . . nT*2−1, y=−1), according to:
• pF[−1][nT*2−1]=p[−1][nT*2−1]
• pF[nT*2−1][−1]=p[nT*2−1][−1]
• pF[−1][y]=((nT*2−1−y)*p[−1][−1]+(y+1)*p[−1][nT*2−1]+nT)>>(1+log2(nT)) for y=0 . . . nT*2−2
• pF[−1][−1]=p[−1][−1]
• pF[x][−1]=((nT*2−1−x)*p[−1][−1]+(x+1)*p[nT*2−1][−1]+nT)>>(1+log2(nT)) for x=0 . . . nT*2−2
• wherein the current block is a current transform block and the size of the current block is a size of a current transform block, and wherein the size of the transform block is nT, and a reference pixel of the transform block is p[x][y] (x=−1, y=−1 . . . nT*2−1, x=−1 . . . nT*2−1, y=−1).