Video encoding apparatus, video decoding apparatus, and video decoding method for performing intra-prediction based on directionality of neighboring block
Provided are methods and apparatuses for improving compression efficiency in directional intra-prediction. A video encoding apparatus, which does not need to record intra mode information, includes a mode selector that selects one from among a plurality of intra modes on the basis of a directionality of at least one neighboring block that has already been reconstructed before a current block is reconstructed, an intra predictor that obtains a prediction block of the current block from the at least one neighboring block according to the directionality of the selected mode, and obtains a residual block by subtracting the prediction block from the current block, and a unit for encoding the obtained residual block.
1. A video decoding method performed by a video decoding apparatus, the method comprising:
determining an intra mode for a neighboring block of a current block;
determining an intra mode for the current block based on whether the intra mode for the neighboring block is a directional mode or a non-directional mode;
performing intra-prediction according to the intra mode for the current block to generate a prediction block for the current block;
obtaining quantization coefficients from an input bitstream;
dequantizing the quantization coefficients to generate transform coefficients;
transforming the transform coefficients to a residual block for the current block; and
adding the prediction block and the residual block to reconstruct the current block,
wherein the intra mode for the current block is determined by using a first set of one or more mathematical expressions, if the intra mode for the neighboring block is the non-directional mode,
wherein the intra mode for the current block is determined by using a second set of one or more mathematical expressions, if the intra mode for the neighboring block is the directional mode, and
wherein the second set of one or more mathematical expressions is different from the first set of one or more mathematical expressions.
2. The video decoding method of claim 1 ,
wherein the non-directional mode includes a DC mode.
3. The video decoding method of claim 1 ,
wherein the second set of one or more mathematical expressions use the intra mode for the neighboring block.
4. The video decoding method of claim 1 ,
wherein determining the intra mode for the current block comprises:
determining candidate intra modes based on whether the intra mode for the neighboring block is the directional mode or the non-directional mode; and
selecting the intra mode for the current block among the candidate intra modes.
5. The video decoding method of claim 4 ,
wherein the candidate intra modes are determined by using the first set of one or more mathematical expressions, if the intra mode for the neighboring block is the non-directional mode, and
wherein the candidate intra modes are determined by using the second set of one or more mathematical expressions, if the intra mode for the neighboring block is the directional mode.
6. The video decoding method of claim 5 , wherein selecting the intra mode for the current block from among the candidate intra modes comprises:
obtaining information for selecting the intra mode for the current block among the candidate intra modes; and
selecting the intra mode for the current block among the candidate intra modes based on the obtained information.
7. The video decoding method of claim 1 ,
wherein determining the intra mode for the current block comprises:
selecting the intra mode for the current block among a plurality of intra modes, based on whether the intra mode for the neighboring block is the directional mode or the non-directional mode,
wherein the number of the plurality of intra modes for a 32×32 block is equal to the number of intra modes for a 16×16 block, and the number of the plurality of intra modes for the 32×32 block is equal to the number of intra modes for an 8×8 block.
8. The video decoding method of claim 7 ,
wherein the number of the plurality of intra modes is greater than 9 corresponding to the number of a plurality of intra modes specified in the H.264 standard.
9. The video decoding method of claim 8 ,
wherein the plurality of intra modes includes a plurality of directional modes, each of the plurality of directional modes has a direction, the direction has a slope defined as dy in a vertical direction over dx in a horizontal direction, and dx and dy are integer numbers.
10. A video encoding method performed by a video encoding apparatus, the method comprising:
determining an intra mode for a neighboring block of a current block;
determining an intra mode for the current block based on whether the intra mode for the neighboring block is a directional mode or a non-directional mode;
performing intra-prediction according to the intra mode for the current block to generate a prediction block for the current block;
subtracting the prediction block from the current block to obtain a residual block for the current block;
transforming the residual block to transform coefficients;
quantizing the transform coefficients to generate quantization coefficients;
encoding the quantization coefficients to generate an input bitstream,
wherein the intra mode for the current block is determined by using a first set of one or more mathematical expressions, if the intra mode for the neighboring block is the non-directional mode,
wherein the intra mode for the current block is determined by using a second set of one or more mathematical expressions, if the intra mode for the neighboring block is the directional mode, and
wherein the second set of one or more mathematical expressions is different from the first set of one or more mathematical expressions.
11. The video encoding method of claim 10 ,
wherein the non-directional mode includes a DC mode.
12. The video encoding method of claim 10 ,
wherein the second set of one or more mathematical expressions use the intra mode for the neighboring block.
13. The video encoding method of claim 10 ,
wherein determining the intra mode for the current block comprises:
determining candidate intra modes based on whether the intra mode for the neighboring block is the directional mode or the non-directional mode; and
selecting the intra mode for the current block among the candidate intra modes.
14. The video encoding method of claim 13 ,
wherein the candidate intra modes are determined by using the first set of one or more mathematical expressions, if the intra mode for the neighboring block is the non-directional mode, and
wherein the candidate intra modes are determined by using the second set of one or more mathematical expressions, if the intra mode for the neighboring block is the directional mode.
15. The video encoding method of claim 14 , wherein selecting the intra mode for the current block from among the candidate intra modes comprises:
obtaining information for selecting the intra mode for the current block among the candidate intra modes; and
selecting the intra mode for the current block among the candidate intra modes based on the obtained information.
16. The video encoding method of claim 10 ,
wherein determining the intra mode for the current block comprises:
selecting the intra mode for the current block among a plurality of intra modes, based on whether the intra mode for the neighboring block is the directional mode or the non-directional mode,
wherein the number of the plurality of intra modes for a 32×32 block is equal to the number of intra modes for a 16×16 block, and the number of the plurality of intra modes for the 32×32 block is equal to the number of intra modes for an 8×8 block.
17. The video encoding method of claim 16 ,
wherein the number of the plurality of intra modes is greater than 9 corresponding to the number of a plurality of intra modes specified in the H.264 standard.
18. The video encoding method of claim 17 ,
wherein the plurality of intra modes includes a plurality of directional modes, each of the plurality of directional modes has a direction, the direction has a slope defined as dy in a vertical direction over dx in a horizontal direction, and dx and dy are integer numbers.