Adaptive transform method based on in-screen prediction and apparatus using the method
Disclosed is an adaptive transform method based on an in-screen prediction, and an apparatus using the method. A method for encoding an image can comprise a step of determining in-screen prediction mode groups, and a step of transforming by using a different transform method according to the in-screen prediction mode group. As a result, transforming can be performed by applying the different transform method according to the in-screen prediction mode group.
1. A method of decoding a video signal having a current block to be decoded with a decoding apparatus, comprising:
obtaining quantized coefficients of the current block from the video signal;
obtaining inverse-quantized coefficients of the current block by inverse-quantizing the quantized coefficients;
obtaining, based on a transform skip flag specifying whether an inverse-transform is skipped for the current block, residual samples from the inverse-quantized coefficients of the current block, wherein when the transform skip flag is equal to 0, the residual samples are obtained by performing the inverse-transform for the inverse-quantized coefficients of the current block, and when the transform skip flag is equal to 1, the residual samples are obtained by skipping the inverse-transform for the inverse-quantized coefficients of the current block;
obtaining prediction samples of the current block based on prediction mode information of the current block, the prediction mode information indicating whether the current block is an inter-coded block or an intra-coded block; and
reconstructing the current block by using the residual samples and the prediction sample, wherein when the transform skip flag specifies that the inverse-transform is performed for the current block, the obtaining of the residual samples comprises:
determining, based on at least one of the prediction mode information of the current block or a size of a transform block relating to the current block, whether a transform type of the current block is a discrete cosine transform (DCT) or a discrete sine transform (DST); and
performing the inverse-transform for the inverse-quantized coefficients of the current block by using the determined transform type.
2. The method of claim 1 , wherein the inverse-transform includes a transform on rows of the current block and a transform on columns of the current block.
3. The method of claim 1 , wherein when the prediction mode information indicates that the current block is the intra-coded bock, the prediction samples of the current block is obtained based on an intra prediction mode of the current block and neighboring samples adjacent to the current block, and
wherein when the neighboring samples include an unavailable sample which is not used for intra prediction of the current block, the unavailable sample is replaced with at least one of available samples adjacent to the unavailable sample.
4. The method of claim 3 , wherein the unavailable sample corresponds to at least one sample in a neighboring block which is the inter-coded block, the neighboring block being adjacent to the current block.
5. An apparatus of decoding a video signal having a current block to be decoded, comprising:
a decoding apparatus configured to obtain quantized coefficients of the current block from the video signal, configured to obtain inverse-quantized coefficients of the current block by inverse-quantizing the quantized coefficients, configured to obtain, based on a transform skip flag specifying whether an inverse-transform is skipped for the current block, residual samples from the inverse-quantized coefficients of the current block, wherein when the transform skip flag is equal to 0, the residual samples are obtained by performing the inverse-transform for the inverse-quantized coefficients of the current block, and when the transform skip flag is equal to 1, the residual samples are obtained by skipping the inverse-transform for the inverse-quantized coefficients of the current block, configured to obtain prediction samples of the current block based on prediction mode information of the current block, the prediction mode information indicating whether the current block is an inter-coded block or an intra-coded block, and configured to reconstruct the current block by using the residual samples and the prediction samples,
wherein when the transform skip flag specifies that the inverse-transform is performed for the current block, the decoding apparatus is configured to obtain the residual samples by determining, based on at least one of the prediction mode information of the current block or a size of a transform block relating to the current block, whether a transform type of the current block is a discrete cosine transform (DCT) or a discrete sine transform (DST) and by performing the inverse-transform for the inverse-quantized coefficients of the current block by using the determined transform type.
6. The apparatus of claim 5 , wherein the inverse-transform includes a transform on rows of the current block and a transform on columns of the current block.
7. The apparatus of claim 5 , wherein when the prediction mode information indicates that the current block is the intra-coded block, the prediction samples of the current block is obtained based on intra prediction mode of the current block and neighboring samples adjacent to the current block, and
wherein when the neighboring samples include an unavailable sample which is not used for intra prediction of the current block, the unavailable sample is replaced with at least one of available samples adjacent to the unavailable sample.
8. The apparatus of claim 7 , wherein the unavailable sample corresponds to at least one sample in a neighboring block which is the inter-coded block, the neighboring block being adjacent to the current block.