Video signal processing method and apparatus using multiple transform kernels

A video encoding method, the method performed by an apparatus and comprising:

• obtaining a bitstream to be decoded by a decoder using a decoding method,
• wherein the decoding method comprises:
• obtaining flag information indicating whether index information indicating a horizontal transform kernel and a vertical transform kernel is signaled for an intra predicted block in the bitstream;
• obtaining prediction mode information indicating whether a current block is the intra predicted block;
• obtaining a plurality of transform coefficients for residual samples of the current block, wherein the plurality of transform coefficients are two-dimensionally arranged;
• based on the flag information indicating that the index information is not signaled for the intra predicted block in the bitstream and the prediction mode information indicating that the current block is the intra predicted block:
• determining, based on length information of a first side of the current block, the horizontal transform kernel for horizontal transformation of the plurality of transform coefficients, regardless of a length of a second side of the current block, wherein the second side is orthogonal to the first side, and
• determining, based on length information of the second side of the current block, the vertical transform kernel for vertical transformation of the plurality of transform coefficients, regardless of a length of the first side of the current block;
• obtaining the residual samples of the current block by performing, based on the plurality of transform coefficients, inverse transformation using the horizontal transform kernel and the vertical transform kernel;
• and
• reconstructing the current block based on the obtained residual samples,
• wherein, based on the length information of the first side having a value outside a preconfigured range and the length information of the second side having a value within the preconfigured range, the horizontal transform kernel is determined to be a first transform kernel and the vertical transform kernel is determined to be a second transform kernel, and
• wherein the first transform kernel is a discrete cosine transform type 2 (DCT-2)-based transform kernel, and the second transform kernel is not the DCT-2-based transform kernel.

A method for transmitting a bitstream, the method comprising:

• generating the bitstream being decoded by a decoding method;
• and
• transmitting the bitstream through a communication line,
• wherein the decoding method comprises:
• obtaining flag information indicating whether index information indicating a horizontal transform kernel and a vertical transform kernel is signaled for an intra predicted block in the bitstream;
• obtaining prediction mode information indicating whether a current block is the intra predicted block;
• obtaining a plurality of transform coefficients for residual samples of the current block, wherein the plurality of transform coefficients are two-dimensionally arranged;
• based on the flag information indicating that the index information is not signaled for the intra predicted block in the bitstream and the prediction mode information indicating that the current block is the intra predicted block:
• determining, based on length information of a first side of the current block, the horizontal transform kernel for horizontal transformation of the plurality of transform coefficients, regardless of a length of a second side of the current block, wherein the second side is orthogonal to the first side, and
• determining, based on length information of the second side of the current block, the vertical transform kernel for vertical transformation of the plurality of transform coefficients, regardless of a length of the first side of the current block;
• obtaining the residual samples of the current block by performing, based on the plurality of transform coefficients, inverse transformation using the horizontal transform kernel and the vertical transform kernel;
• and
• reconstructing the current block based on the obtained residual samples,
• wherein, based on the length information of the first side having a value outside a preconfigured range and the length information of the second side having a value within the preconfigured range, the horizontal transform kernel is determined to be a first transform kernel and the vertical transform kernel is determined to be a second transform kernel, and
• wherein the first transform kernel is a discrete cosine transform type 2 (DCT-2)-based transform kernel, and the second transform kernel is not the DCT-2-based transform kernel.