Method and device for video coding using various transform techniques
The present invention relates to a method and a device for decoding an image, which improve encoding and decoding efficiency by performing various forms of transform and inverse transform during transform and inverse transform processes of a video coding technique.
1. A method of decoding a video, the method comprising:
obtaining, from a bitstream, first information indicating whether a first inverse transform is skipped for a current block;
obtaining, from the bitstream, second information on a horizontal transform type and a vertical transform type for the first inverse transform of the current block when the first information indicates that the first inverse transform is not skipped for the current block;
determining the horizontal transform type and the vertical transform type selectively from multiple inverse transform types by using the second information; and
performing the first inverse transform for the current block in horizontal and vertical directions by using the determined horizontal transform type and the determined vertical transform type,
wherein the second information indicates one of a plurality of transform type sets,
wherein each of the transform type sets includes a transform type of a horizontal direction and a transform type of a vertical direction, and
wherein the each of the transform type sets is defined based on a combination of two of the multiple inverse transform types.
2. The method of claim 1 , wherein the performing the first inverse transform for the current block in horizontal and vertical directions by using the determined horizontal transform type and the determined vertical transform type comprises:
performing the first inverse transform by using the horizontal transform type determined among the multiple inverse transform types; and
performing the first inverse transform by using the vertical transform type determined among the multiple inverse transform types.
3. The method of claim 1 , wherein a number of the multiple inverse transform types is 3.
4. The method of claim 1 , wherein the multiple inverse transform types include DCT-2, DCT-8 and DST-7 based transform kernels, and do not include a non-transform matrix.
5. The method of claim 1 , wherein the first information is encoded in units of blocks regardless of horizontal and vertical directions.
6. The method of claim 1 , further comprises:
obtaining, from the bitstream, a flag indicating whether the horizontal transform type and the vertical transform type is determined based on the multiple inverse transform types,
wherein when the flag indicates that the horizontal transform type and the vertical transform type is not determined based on the multiple inverse transform types, the horizontal transform type and the vertical transform type is determined based on a pre-defined default transform type.
7. The method of claim 6 , wherein the default transform type is a DCT-2 based transform kernel.
8. The method of claim 1 , further comprises:
obtaining, from the bitstream, third information indicating whether a second inverse transform is performed for the current block.
9. The method of claim 8 , wherein the second inverse transform has a non-separable form in horizontal and vertical directions.
10. A method of encoding a video, the method comprising:
determining whether a first transform is skipped for a current block;
determining a horizontal transform type and a vertical transform type selectively from multiple transform types;
encoding information on the horizontal transform type and the vertical transform type for the first transform of the current block when it is determined that first transform is not skipped for the current block; and
encoding a residual block of the current block, the residual block being encoded by performing the first transform for the current block in horizontal and vertical directions by using the horizontal transform type and the vertical transform type,
wherein the information indicates one of a plurality of transform type sets,
wherein each of the transform type sets includes a transform type of a horizontal direction and a transform type of a vertical direction, and
wherein the each of the transform type sets is defined based on a combination of two of the multiple inverse transform types.