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 a neighboring intra prediction mode associated with a neighboring block, the neighboring block being adjacent to a current block;
determining a current intra prediction mode associated with the current block based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not;
performing intra-prediction based on the current intra prediction mode associated with the current block to generate a prediction block associated with the current block;
obtaining transform coefficients;
dequantizing the transform coefficients to generate dequantized transform coefficients;
transforming the dequantized transform coefficients to generate a residual block associated with the current block; and
reconstructing the current block based on the prediction block and the residual block,
wherein determining the current intra prediction mode associated with the current block comprises:
determining the current intra prediction mode associated with the current block according to a first set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has no directionality, and
determining the current intra prediction mode associated with the current block according to a second set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has directionality,
wherein the second set of two or more mathematical expressions is different from the first set of two or more mathematical expressions.
2. The video decoding method of claim 1 ,
wherein an intra prediction mode having no directionality includes a DC mode.
3. The video decoding method of claim 1 ,
wherein the second set of two or more mathematical expressions use the neighboring intra prediction mode associated with the neighboring block.
4. The video decoding method of claim 1 ,
wherein determining the current intra prediction mode associated with the current block comprises:
determining candidate intra prediction modes based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not; and
selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes.
5. The video decoding method of claim 4 ,
wherein the candidate intra prediction modes are determined by using the first set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has no directionality, and
wherein the candidate intra prediction modes are determined by using the second set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has directionality.
6. The video decoding method of claim 5 , wherein selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes comprises:
obtaining information for selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes; and
selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes based on the obtained information.
7. The video decoding method of claim 1 , wherein obtaining the transform coefficients comprises:
decoding the input bitstream to obtain the transform coefficients.
8. The video decoding method of claim 7 , wherein decoding the input bitstream comprises:
losslessly decoding the input bitstream to obtain the transform coefficients.
9. The video decoding method of claim 1 , wherein reconstructing the current block comprises:
reconstructing the current block by adding the prediction block and the residual block.
10. A video encoding method performed by a video encoding apparatus, the method comprising:
determining a neighboring intra prediction mode associated with a neighboring block, the neighboring block being adjacent to a current block;
determining a current intra prediction mode associated with the current block based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not;
performing intra-prediction according to the current intra prediction mode associated with the current block to generate a prediction block associated with the current block;
obtaining a residual block associated with the current block by using the prediction block and the current block;
transforming the residual block to generate transform coefficients;
quantizing the transform coefficients to generate quantized transform coefficients;
encoding the quantized transform coefficients,
wherein determining the current intra prediction mode associated with the current block comprises:
determining the current intra prediction mode associated with the current block according to a first set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has no directionality,
determining the current intra prediction mode associated with the current block according to a second set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has directionality,
wherein the second set of two or more mathematical expressions is different from the first set of two or more mathematical expressions.
11. The video encoding method of claim 10 ,
wherein an intra prediction mode having no directionality includes a DC mode.
12. The video encoding method of claim 10 ,
wherein the second set of two or more mathematical expressions use the neighboring intra prediction mode associated with the neighboring block.
13. The video encoding method of claim 10 ,
wherein determining the current intra prediction mode associated with the current block comprises:
determining candidate intra prediction modes based on whether the neighboring intra prediction mode associated with the neighboring block has directionality or not; and
selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes.
14. The video encoding method of claim 13 ,
wherein the candidate intra prediction modes are determined by using the first set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has no directionality, and
wherein the candidate intra prediction modes are determined by using a second set of two or more mathematical expressions, when the neighboring intra prediction mode associated with the neighboring block has directionality.
15. The video encoding method of claim 14 , wherein selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes comprises:
obtaining information for selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes; and
selecting the current intra prediction mode associated with the current block among the candidate intra prediction modes based on the obtained information.
16. The video encoding method of claim 10 , wherein encoding the quantized transform coefficients comprises:
encoding the quantized transform coefficients to generate an input bitstream.
17. The video encoding method of claim 16 , wherein encoding the quantized transform coefficients comprises:
losslessly encoding the quantized transform coefficients to generate the input bitstream.
18. The video encoding method of claim 10 , wherein obtaining the residual block comprises:
subtracting the prediction block from the current block to obtain a residual block associated with the current block.