Method and device for encoding/decoding images
A method and a device for encoding/decoding images are disclosed. The method for encoding images comprises the steps of: deriving a scan type of a residual signal for a current block according to whether or not the current block is a transform skip block; and applying the scan type to the residual signal for the current block, wherein the transform skip block is a block to which transform for the current block is not applied and is specified on the basis of information indicating whether or not transform for the current block is to be applied.
1. A video decoding method, comprising:
obtaining first information indicating whether a residual signal is present in a current block;
determining a transform type of the current block, based on second information indicating whether or not an inverse-transform based on discrete cosine transform (DCT) or discrete sine transform (DST) is allowed;
acquiring transform coefficients from the residual signal of the current block based on a scanning direction for the residual signal of the current block, if the first information indicates that the residual signal is present in the current block;
performing the inverse-transform on the transform coefficients based on the determined transform type to obtain residual samples;
deriving an intra prediction mode of the current block;
obtaining prediction samples of the current block based on the intra prediction mode of the current block; and
reconstructing the current block based on the residual samples and the prediction samples,
wherein the scanning direction is determined based on the second information.
2. The video decoding method of claim 1 , wherein the scanning direction is determined based on the intra prediction mode of the current block, if the second information indicates that the inverse-transform based on DCT or DST is allowed.
3. The video decoding method of claim 2 , wherein the scanning direction is determined independently to the intra prediction mode of the current block, if the second information indicates that the inverse-transform based on DCT or DST is not allowed.
4. The video decoding method of claim 1 , wherein the scanning direction is determined to be one of a first direction, a second direction and a third direction, based on the intra prediction mode of the current block, if the second information indicates that the inverse-transform based on DCT or DST is allowed.
5. The video decoding method of claim 4 , wherein the second direction is a direction of columns of the current block, and the third direction is a direction of rows of the current block.
6. The video decoding method of claim 5 , wherein the scanning direction is determined to be the first direction, independently to the intra prediction mode of the current block, if the second information indicates that the inverse-transform based on the DCT or the DST is not allowed.
7. The video decoding method of claim 6 , wherein the second direction is more vertical than the first direction, and the third direction is more horizontal than the first direction.
8. The video decoding method of claim 1 , wherein the transform type of the current block is determined further based on a size of the current block.
9. A video encoding method, comprising:
deriving an intra prediction mode of a current block;
performing an intra prediction based on the intra prediction mode of the current block to generate prediction samples for the current block;
determining whether a residual signal is present in the current block;
generating residual samples based on the prediction samples;
determining a transform type of the current block, based on whether or not an inverse-transform based on discrete cosine transform (DCT) or discrete sine transform (DST) is allowed;
transforming the residual samples based on the transform type of the current block to generate transform coefficients;
applying a scanning direction to the transform coefficients;
generating a bitstream comprising the residual signal if the residual signal is present in the current block,
wherein the scanning direction is determined based on whether or not an inverse-transform based on discrete cosine transform (DCT) or discrete sine transform (DST) is allowed.
10. A non-transitory computer-readable recording medium storing a bitstream which is decoded by a decoding method, the video decoding method comprising:
obtaining first information indicating whether a residual signal is present in a current block;
determining a transform type of the current block, based on second information indicating whether or not an inverse-transform based on discrete cosine transform (DCT) or discrete sine transform (DST) is allowed;
acquiring transform coefficients from the residual signal of the current block based on a scanning direction for the residual signal of the current block, if the first information indicates that the residual signal is present in the current block;
performing the inverse-transform on the transform coefficients based on the determined transform type to obtain residual samples;
deriving an intra prediction mode of the current block;
obtaining prediction samples of the current block based on the intra prediction mode of the current block; and
reconstructing the current block based on the residual samples and the prediction samples,
wherein the scanning direction is determined based on the second information.