Method and apparatus for processing image signal

An apparatus for decoding an image signal, comprising:

• a memory for storing the image signal;
• and
• a processor coupled to the memory,
• wherein the processor is configured to:
• determine a non-separable transform set index indicating a non-separable transform set for a current block, based on an intra prediction mode of the current block, among predetermined non-separable transform sets;
• determine a transform kernel included in the non-separable transform set the current block as a non-separable transform matrix for the current block;
• and
• apply the non-separable transform matrix for the current block to a top-left region of the current block, the top-left region being determined based on a width and a height of the current block,
• wherein the non-separable transform set index has a value among 4 values, according to an intra prediction mode range to which the intra prediction mode of the current block belong,
• wherein the transform kernel for the current block is determined as one among two transform kernels included in the non-separable transform set for the current block, and
• wherein the non-separable transform matrix is applied to R coefficients included in the top-left region of the current block to generate N transformed coefficients, R being smaller than N, N being equal to a total number of coefficients included in the top-left region of the current block.

A method for encoding an image signal by an apparatus, comprising:

• determining a non-separable transform set for a current block, based on an intra prediction mode of the current block,
• determining a transform kernel included in the non-separable transform set as a non-separable transform matrix for the current block;
• and
• applying the non-separable transform matrix for the current block to a top-left region of the current block, the top-left region being determined based on a width and a height of the current block,
• wherein a non-separable transform set index indicating the non-separable transform set for the current block, among predetermined non-separable transform sets, is encoded,
• wherein the non-separable transform set index has one index value among 4 index values, according to an intra prediction mode range to which the intra prediction mode of the current block belong,
• wherein the transform kernel for the current block is determined as one among two transform kernels included in the non-separable transform set for the current block, and
• wherein the non-separable transform matrix is applied to N coefficients included in the top-left region of the current block to generate R transformed coefficients, R being smaller than N, N being equal to a total number of coefficients included in the top-left region of the current block.

A non-transitory decoder-readable storage medium for storing a bitstream, the bitstream comprising a decoder executable program, the decoder executable program, when executed, causing a decoder to perform the following steps:

• determining a non-separable transform set index indicating a non-separable transform set for a current block, based on an intra prediction mode of the current block, among predetermined non-separable transform sets;
• determining a transform kernel included in the non-separable transform set as a non-separable transform matrix for the current block;
• and
• applying the non-separable transform matrix for the current block to a top-left region of the current block, the top-left region being determined based on a width and a height of the current block,
• wherein the non-separable transform set index has one index value among 4 index values, according to an intra prediction mode range to which the intra prediction mode of the current block belong,
• wherein the transform kernel for the current block is determined as one among two transform kernels included in the non-separable transform set for the current block, and
• wherein the non-separable transform matrix is applied to R coefficients included in the top-left region of the current block to generate N transformed coefficients, R being smaller than N, N being equal to a total number of coefficients included in the top-left region of the current block.