Methods and apparatuses for processing video signal

A method of decoding a video signal by an apparatus, comprising:

• obtaining transform coefficients by performing entropy decoding and inverse quantization for a current block;
• obtaining residual data through an inverse transform for the transform coefficients;
• and
• reconstructing an image based on the residual data and prediction data,
• wherein performing the inverse transform includes:
• obtaining a secondary transform index based on a non-zero transform coefficient not positioned in a specific region,
• wherein the specific region represents a region other than a position where the non-zero transform coefficient exists when a reduced secondary transform is applied and transform coefficients are arranged according to a scan order;
• and
• performing an inverse secondary transform on the transform coefficients based on an inverse secondary transform matrix derived based on the secondary transform index;
• and
• performing an inverse primary transform on the transform coefficients to which the inverse secondary transform is applied,
• wherein the secondary transform index represents that one of 2 transform kernels in a transform set is used, and the transform set is determined based on an intra prediction mode.

A non-transitory computer-readable medium storing video information generated by an encoding method, the encoding method comprising:

• generating residual data except prediction data from an image of the video signal;
• generating transform coefficients through a transform for the residual data;
• and
• performing quantization and entropy coding for the transform coefficients,
• wherein generating the transform coefficients includes:
• performing a primary transform on the residual data to obtain transform coefficients;
• deriving a secondary transform matrix to be applied to the transform coefficients;
• performing a secondary transform on the transform coefficients based on the secondary transform matrix;
• and
• generating a secondary transform index based on a non-zero transform coefficient not positioned in a specific region,
• wherein the specific region represents a region other than a position where non-zero transform coefficient exists when a reduced secondary transform is applied and transform coefficients are arranged according to a scan order, and
• wherein the secondary transform index represents that one of 2 transform kernels in a transform set is used, and the transform set is determined based on an intra prediction mode.