Encoding/decoding method for video signal and device therefor

1. A method for decoding a video signal, comprising:

checking whether a transform skip is applied to a current block;

obtaining, from the video signal, a transform index indicating which transform kernel are applied along horizontal and vertical directions of the current block based on that the transform skip is not applied to the current block;

determining a region to which a transform is applied based on the transform kernels indicated by the transform index, wherein the transform kernels correspond to at least one of predefined transform types including DCT2, DST7 and DCT8;

deriving, as zero, coefficients within a remaining region other than the region to which the transform is applied; and

performing an inverse transform on the region to which the transform is applied based on the transform kernels indicated by the transform index.

2. The method of claim 1 , wherein, based on that the transform kernels correspond to DCT2, a width of the region to which the primary transform is applied is determined as a smaller value between a width of the current block and 32, and a height of the region to which the transform is applied is determined as a smaller value between a height of the current block and 32.

3. The method of claim 1 , wherein, based on that the transform kernels correspond to one of a plurality of transform combinations of DST7 and/or DCT8, the width of the region to which the transform is applied is determined as a smaller value between the width of the current block and 16 and the height of the region to which the transform is applied is determined as a smaller value between the height of the current block and 16.

4. The method of claim 1 , further comprising obtaining a syntax element indicating a position of a last significant coefficient in scan order within the current block,

wherein coefficients to which the inverse transform is applied are obtained from the video signal based on the position of the last significant coefficient.

5. The method of claim 4 , wherein the syntax element is binarized according to a truncated unary method, and a maximum length of code for the syntax element is determined based on the remaining region.

6. A method for encoding a video signal, comprising:

deriving transform kernels being applied to a current block, wherein the transform kernels include a horizontal transform kernel and a vertical transform kernel;

determining a region in which a transform is applied to the current block based on the transform kernels and a width and/or a height of the current block;

deriving, as zero, coefficients of a remaining region other than the region to which the transform is applied;

performing a transform on the current block based on the transform kernels;

generating a transform index indicating which transform kernels are applied along horizontal and vertical directions of the current block based on that a transform skip is not applied to the current block, wherein the transform kernels correspond to at least one of predefined transform types including DCT2, DST7 and DCT8; and

generating an syntax element representing whether the transform skip is applied to the current block.

7. The method of claim 6 , wherein, based on that the transform kernels correspond to DCT2, a width of the region to which the transform is applied is determined as a smaller value between a width of the current block and 32, and a height of the region to which the transform is applied is determined as a smaller value between a height of the current block and 32.

8. The method of claim 6 , wherein, based on that the transform kernels correspond to one of a plurality of transform combinations of DST7 and/or DCT8, the width of the region to which the transform is applied is determined as a smaller value between the width of the current block and 16 and the height of the region to which the transform is applied is determined as a smaller value between the height of the current block and 16.

9. The method of claim 6 , further comprising obtaining a syntax element indicating a position of a last significant coefficient in scan order within the current block,

wherein coefficients to which an inverse transform is applied are obtained from the video signal based on the position of the last significant coefficient.

10. The method of claim 9 , wherein the syntax element is binarized according to a truncated unary method, and a maximum length of code for the syntax element is determined based on the remaining region.

11. A non-transitory computer-readable medium storing a bitstream causing an image decoding apparatus to perform an image decoding method, the image decoding method comprising:

checking whether a transform skip is applied to a current block;

obtaining, from a video signal, a transform index indicating which transform kernels are applied along horizontal and vertical directions of the current block based on that the transform skip is not applied to the current block;

determining a region to which a transform is applied based on the transform kernels indicated by the transform index, wherein the transform kernels correspond to at least one of predefined transform types including DCT2, DST7 and DCT8;

deriving, as zero, coefficients within a remaining region other than the region to which the transform is applied; and

performing an inverse transform on the region to which the transform is applied based on the transform kernels indicated by the transform index.