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 prediction samples by performing an intra prediction on the current block based on intra prediction mode information of the current block and reference samples adjacent to the current block;
obtaining residual samples of the current block; and
reconstructing the current block by using the residual samples and the prediction samples,
wherein the obtaining the residual samples comprises:
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; and
obtaining, based on a transform skip flag, the residual samples of the current block by selectively performing an inverse-transform on the inverse-quantized coefficients of the current block, the transform skip flag specifying whether an inverse-transform is performed or skipped on the inverse-quantized coefficients of the current block,
wherein when the transform skip flag specifies that the inverse-transform is performed on the inverse-quantized coefficients of the current block, obtaining the residual samples further comprises:
determining, based on a size of a transform block relating to the current block, a transform type of the current block among 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 obtaining the quantized coefficients of the current block comprises:
determining a scan mode of the current block based on the size of the transform block relating to the current block and the intra prediction mode of the current block; and
obtaining the quantized coefficients of the current block by considering a scanning order of the determined scan mode.
4. The method of claim 3 , wherein the determined scan mode is representative of one of a diagonal scan, a vertical scan and a horizontal scan.