TRANSFORMATION-BASED METHOD FOR ENCODING IMAGES AND DEVICE FOR THE SAME

Abstract

A method for decoding an image according to the present document may comprise the steps of: obtaining a modified transformation coefficient; verifying whether the tree type for a current block is a dual-tree chroma; determining whether an MIP mode is applied to the current block on the basis that the current block is not the dual-tree chroma; determining whether an LFNST application width and LFNST application height corresponding to the current block are 16 or more, on the basis of the MIP mode being applied to the current block; and parsing an LFNST index on the basis that the LFNST application width and LFNST application height are 16 or more.

Claims

1. An image decoding method carried out by a decoding apparatus, wherein the method comprises: receiving residual information via a bit stream; deriving transform coefficients for a current block based on the residual information; deriving modified transform coefficients by applying an LFNST to the transform coefficients; deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients; and generating a reconstructed image based on the residual samples, wherein the derivation of the modified transform coefficients comprises: checking whether a tree type for the current block is a dual-tree chroma; determining whether a MIP mode is applied to the current block based on the current block not being the dual-tree chroma;Determine if an LFNST-applied width and LFNST-applied height corresponding to the current block 144 are 16 or more based on the MIP mode applied to the current block; and analyze an LFNST index based on the LFNST-applied width and LFNST-applied height being 16 or more.

2. The image decoding method according to claim 1, wherein the width applied by LFNST is set to the width of the current block divided by a number of split subdivisions when the current block is split vertically, and is set to the width of the current block when the current block is not split, and wherein the current block is an encoding block.

3. The image decoding method according to claim 1, wherein the height applied by LFNST is set to the height of the current block divided by a number of subdivisions when the current block is divided horizontally, and is set to the height of the current block when the current block is not divided, and wherein the current block is an encoding block.

4. The image decoding method according to claim 1, wherein when the tree type of the current block is dual tree chroma, the LFNST index is analyzed independently of whether a MIP mode 145 is applied to the current block.

5. The image decoding method according to claim 1, wherein when the tree type of the current block is dual tree chroma, the LFNST index is analyzed regardless of whether the LFNST applied width and LFNST applied height corresponding to the current block are 16 or more.

6. The image decoding method according to claim 1, wherein when the tree type of the current block is not dual tree chroma, the LFNST index is analyzed based on a MIP mode that is not applied to the current block.

7. An image coding method carried out by an image coding apparatus, wherein the method comprises: deriving prediction samples for a current block; deriving residual samples for the current block based on the prediction samples; deriving transformation coefficients for the current block based on a primary transformation of the residual samples; deriving modified transformation coefficients from the transformation coefficients by applying an LFNST; and encoding quantized residual information and an LFNST index indicating an LFNST matrix applied to the LFNST, wherein when a tree type of the current block is not a dual-tree chroma and a MIP mode is applied to the current block, the LFNST index is encoded based on an LFNST-applied width and an LFNST-applied height corresponding to the current block being 16 or more 8. The image encoding method according to claim 7, wherein the width applied by LFNST is set to the width of the current block divided by a number of split subdivisions when the current block is split vertically, and is set to the width of the current block when the current block is not split, and wherein the current block is an encoding block.

9. The image encoding method according to claim 7, wherein the height applied by LFNST is set to the height of the current block divided by a number of subdivisions when the current block is divided horizontally, and is set to the height of the current block when the current block is not divided, and wherein the current block is an encoding block.

10. The image encoding method of 147 according to claim 7, wherein when the tree type of the current block is dual tree chroma, the LFNST index is encoded regardless of whether an MIP mode is applied to the current block.

11. The image encoding method according to claim 7, wherein when the tree type of the current block is dual tree chroma, the LFNST index is encoded regardless of whether the LFNST applied width and LFNST applied height corresponding to the current block are 16 or more.

12. The image encoding method according to claim 7, wherein when the tree type of the current block is not dual tree chroma, the LFNST index is encoded based on a MIP mode that is not applied to the current block.

13. A computer-readable digital storage medium that stores indication information for carrying out an image decoding method, wherein the image decoding method comprises: receiving residual information via a bit stream; deriving transform coefficients for a current block based on the residual information; deriving modified transform coefficients by applying an LFNST to the transform coefficients; deriving residual samples for the target block based on an inverse primary transform for the modified transform coefficients; and generating a reconstructed image based on the residual samples, wherein the derivation of the modified transform coefficients comprises: checking whether a tree type for the current block is a dual-tree chroma;10 determine if an MIP mode is applied to the current block based on the current block not being the dual tree chroma; determine if an LFNST applied width and an LFNST applied height corresponding to the current block 15 are 16 or more based on the MIP mode applied to the current block; and analyze an LFNST index based on the LFNST applied width and LFNST applied height being 16 or more;

Images