Method for performing transform index coding on basis of intra prediction mode, and device therefor
The present disclosure, in a method of decoding a video signal, provides a method including checking whether a transform skip is applied to a current block; acquiring a transform index indicating transform types applied to a horizontal direction and a vertical direction of the current block from among a plurality of predefined transform types from the video signal when the transform skip is not applied to the current block; and performing an inverse primary transform on the current block using the transform types indicated by the transform index, wherein the transform types applied to the horizontal direction and the vertical direction of the current block are determined from among transform types defined according to an intra prediction mode of the current block based on the transform index.
1. A method of decoding a video signal by an apparatus, comprising:
checking whether a transform skip is applied to a current block;
acquiring a transform index indicating transform types applied to a horizontal direction and a vertical direction of the current block from among a plurality of predefined transform types when the transform skip is not applied to the current block; and
performing an inverse transform on the current block using the transform types indicated by the transform index,
wherein the transform index is binarized using a truncated unary method.
2. The method of claim 1 , wherein the transform types applied to the horizontal direction and the vertical direction of the current block are determined from among transform types defined according to an intra prediction mode of the current block based on the transform index,
wherein the method further comprises:
grouping intra prediction modes into a plurality of groups based on a prediction direction; and
mapping the transform types applied to the horizontal direction and the vertical direction to the transform index for each of the plurality of groups.
3. The method of claim 2 , wherein the transform types applied to the horizontal direction and the vertical direction of the current block are determined as the transform types indicated by the transform index from among transform types defined in a group to which the intra prediction mode of the current block belongs.
4. The method of claim 3 , wherein the mapping the transform types to the transform index is performed by mapping the transform types applied to the horizontal direction and the vertical direction to the transform index based on available values of the transform index for each of the plurality of groups.
5. The method of claim 2 , wherein the performing the inverse transform comprises:
determining a region where a transform has been applied to the current block based on the transform types indicated by the transform index and a size of the current block; and
performing the inverse transform on the region where the transform has been applied using the transform types indicated by the transform index.
6. A method of encoding a video signal by an apparatus, comprising:
determining whether to skip a transform on a current block;
generating a transform index indicating transform types applied to a horizontal direction and a vertical direction of the current block from among a plurality of predefined transform types when it is determined that the transform is not skipped to the current block;
performing the transform on the current block using the transform types indicated by the transform index; and
binarizing the transform index using a truncated unary method.
7. The method of claim 6 , wherein the transform types applied to the horizontal direction and the vertical direction of the current block are determined from among transform types defined according to an intra prediction mode of the current block based on the transform index,
wherein the method further comprises:
grouping intra prediction modes into a plurality of groups based on a prediction direction; and
mapping the transform types applied to the horizontal direction and the vertical direction to the transform index for each of the plurality of groups.
8. The method of claim 7 , wherein the transform types applied to the horizontal direction and the vertical direction of the current block are determined as the transform types indicated by the transform index from among transform types defined in a group to which the intra prediction mode of the current block belongs.
9. The method of claim 8 , wherein the mapping the transform types to the transform index is performed by mapping the transform types applied to the horizontal direction and the vertical direction to the transform index based on available values of the transform index for each of the plurality of groups.
10. The method of claim 7 , wherein the performing the transform comprises:
determining a region where the transform is to be applied to the current block based on the transform types indicated by the transform index and a size of the current block; and
performing the transform on the region using the transform types indicated by the transform index.
11. A non-transitory computer-readable storage medium storing encoded picture data generated by performing the steps of:
determining whether to skip a transform on a current block;
generating a transform index indicating transform types applied to a horizontal direction and a vertical direction of the current block from among a plurality of predefined transform types when it is determined that the transform is not skipped to the current block;
performing the transform on the current block using the transform types indicated by the transform index; and
binarizing the transform index using a truncated unary method.