Method and apparatus for processing video signals using reduced transform

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 being configured to:
• derive transform kernels being applied to a current block,
• perform a primary transform on the current block based on the transform kernels,
• generate transform index information indicating the transform kernels applied to the current block, and
• encode a video signal including the transform index information,
• wherein a size of a non-zero region for the primary transform is determined based on the transform kernels and a size of the current block,
• wherein the non-zero region has a predetermined width and height and includes a top-left sample position within the current block, and non-zero coefficients are located within the non-zero region,
• wherein the transform kernels indicated by the transform index information include a pair of a horizontal transform kernel and a vertical transform kernel,
• wherein based on the size of the current block being 32×32 and the transform kernels applied to the current block belonging to a first transform group, the size of the non-zero region is determined as 32×32,
• wherein based on the size of the current block being 32×32 and the transform kernels applied to the current block belonging to a second transform group, the size of the non-zero region is determined as 16×16, and
• wherein the first transform group includes a DCT2 kernel, and the second transform group does not include the DCT2 kernel.

A transmission apparatus of transmitting data including a bitstream for an image, comprising:

• at least one processor configured to obtain the bitstream for the image, wherein the bitstream is generated based on deriving transform kernels being applied to a current block, performing a primary transform on the current block based on the transform kernels, generating transform index information indicating the transform kernels applied to the current block, and encoding a video signal including the transform index information;
• and
• a transmitter configured to transmit the data including the bitstream,
• wherein a size of a non-zero region for the primary transform is determined based on the transform kernels and a size of the current block,
• wherein the non-zero region has a predetermined width and height and includes a top-left sample position within the current block, and non-zero coefficients are located within the non-zero region,
• wherein the transform kernels indicated by the transform index information include a pair of a horizontal transform kernel and a vertical transform kernel,
• wherein based on the size of the current block being 32×32 and the transform kernels applied to the current block belonging to a first transform group, the size of the non-zero region is determined as 32×32,
• wherein based on the size of the current block being 32×32 and the transform kernels applied to the current block belonging to a second transform group, the size of the non-zero region is determined as 16×16, and
• wherein the first transform group includes a DCT2 kernel, and the second transform group does not include the DCT2 kernel.