TRANSFORM-BASED IMAGE CODING METHOD AND TRANSMISSION METHOD THEREFOR
An image decoding method according to the present document comprises a step of deriving a corrected transform coefficient, wherein the step of deriving the corrected transform coefficient comprises the steps of: determining whether LFNST can be applied to the height and width of a divided sub-partition block when an ISP is applied to a current block; parsing a LFNST index when the LFNST can be applied; and deriving the corrected transform coefficient on the basis of the LFNST index and a LFNST matrix.
1 . A decoding apparatus for image decoding, the decoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
obtain residual information from a bitstream;
derive quantized transform coefficients for a current block based on the residual information;
derive transform coefficients for the current block by performing dequantization on the quantized transform coefficients;
derive modified transform coefficients by applying a non-separable transform to the transform coefficients;
derive residual samples for the current block by applying a separable transform to the modified transform coefficients; and
generate a reconstructed picture based on the residual samples,
wherein the at least one processor is further configured to:
determine a height and a width of a subpartition block based on an intra sub partitions (ISP) being applied to the current block;
parse a non-separable transform index based on the height and the width of the subpartition block; and
derive the modified transform coefficients by applying the non-separable transform based on a non-separable transform matrix related to the non-separable transform index to the transform coefficients,
wherein the non-separable transform matrix is selected based on the non-separable transform index in a non-separable transform set, and the non-separable transform set is selected based on an intra prediction mode of the current block, and
wherein in case a tree-type of the current block is a dual-tree luma or single-tree, based on the height and the width of the subpartition block corresponding to a luma component block for the current block being equal to 4 or more, the non-separable transform index is parsed.
2 . An encoding apparatus for image encoding, the encoding apparatus comprising:
a memory; and
at least one processor connected to the memory, the at least one processor configured to:
derive prediction samples for a current block;
derive residual samples for the current block based on the prediction samples;
derive transform coefficients for the current block by applying a separable transform to the residual samples;
derive modified transform coefficients by applying a non-separable transform based on a non-separable transform matrix to the transform coefficients;
derive quantized transform coefficients by performing quantization on the modified transform coefficients; and
encode residual information on the quantized transform coefficients, and a non-separable transform index related to the non-separable transform matrix to output a bitstream,
wherein the at least one processor is further configured to:
determine a height and a width of a subpartition block based on an intra sub partitions (ISP) being applied to the current block,
wherein the non-separable transform index is encoded based on the height and the width of the subpartition block, and
wherein the non-separable transform matrix is included in a non-separable transform set, and the non-separable transform set is derived based on an intra prediction mode of the current block, and
wherein in case a tree-type of the current block is a dual-tree luma or single-tree, based on the height and the width of the subpartition block corresponding to a luma component block for the current block being equal to 4 or more, the non-separable transform index is encoded.
3 . An apparatus for transmitting data for an image, the apparatus comprising:
at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on deriving prediction samples for a current block, deriving residual samples for the current block based on the prediction samples, deriving transform coefficients for the current block by applying a separable transform to the residual samples, deriving modified transform coefficients by applying a non-separable transform based on a non-separable transform matrix to the transform coefficients, deriving quantized transform coefficients by performing quantization on the modified transform coefficients, and encoding residual information on the quantized transform coefficients, and a non-separable transform index related to the non-separable transform matrix; and
a transmitter configured to transmit the data comprising the bitstream,
wherein the deriving the modified transform coefficients comprises:
determining a height and a width of a subpartition block based on an intra sub partitions (ISP) being applied to the current block,
wherein the non-separable transform index is encoded based on the height and the width of the subpartition block, and
wherein the non-separable transform matrix is included in a non-separable transform set, and the non-separable transform set is derived based on an intra prediction mode of the current block, and
wherein in case a tree-type of the current block is a dual-tree luma or single-tree, based on the height and the width of the subpartition block corresponding to a luma component block for the current block being equal to 4 or more, the non-separable transform index is encoded.