Method and apparatus for processing video signal by applying secondary transform to partitioned block

A method for encoding a video signal, the method comprising:

• generating prediction data for a current block;
• generating residual data based on the prediction data;
• performing a primary transform for a transform block related to the residual data;
• deriving a secondary transform matrix for a specific area in the transform block, wherein the specific area represents an area including a top-left area of the transform block, and wherein a secondary transform matrix is denoted based on an input length and an output length of a secondary transform;
• performing the secondary transform for the specific area based on the secondary transform matrix;
• generating a secondary transform index related to the secondary transform;
• and
• performing a quantization and an entropy encoding for the transform block,
• wherein the input length of the secondary transform is determined as 48, and the output length of the secondary transform is determined as 16, based on that each of the height and the width of the transform block is equal to 8 or 16.

A non-transitory computer-readable medium storing encoded video information generated by performing the steps of:

• generating prediction data for a current block;
• generating residual data based on the prediction data;
• performing a primary transform for a transform block related to the residual data;
• deriving a secondary transform matrix for a specific area in the transform block, wherein the specific area represents an area including a top-left area of the transform block, and wherein a secondary transform matrix is denoted based on an input length and an output length of a secondary transform;
• performing the secondary transform for the specific area based on the secondary transform matrix;
• generating a secondary transform index related to the secondary transform;
• and
• performing a quantization and an entropy encoding for the transform block,
• wherein the input length of the secondary transform is determined as 48, and the output length of the secondary transform is determined as 16, based on that each of the height and the width of the transform block is equal to 8 or 16.