Method for encoding/decoding video signal, and apparatus therefor

An apparatus for encoding an image, comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor being configured to:
• generate prediction samples of a current block based on an intra prediction mode,
• derive residual samples of the current block based on the prediction samples,
• perform a primary transform on the residual samples to obtain primary-transformed coefficients of the current block,
• determine a secondary transform set among a pre-determined number of secondary transform sets based on the intra prediction mode,
• generate a first syntax element related to a secondary transform matrix to be applied to the current block among secondary transform matrices included in the determined secondary transform set, and
• perform a secondary transform on the primary-transformed coefficients based on the secondary transform matrix, the secondary transform being a non-separable transform,
• wherein a number of input coefficients of the secondary transform and a number of output coefficients of the secondary transform are respectively determined as 16 and 8 based on the current block having a 4×4 size, and
• wherein the number of the input coefficients of the secondary transform for the current block having the 4×4 size is equal to a number of the input coefficients of the secondary transform for the current block having a 4×8 size or an 8×4 size, while the number of the output coefficients of the secondary transform for the current block having the 4×4 size is not equal to the number of a output coefficients of the secondary transform for the current block having the 4×8 size or the 8×4 size.

A transmission apparatus of data for an image, comprising:

• at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on generating prediction samples of a current block based on an intra prediction mode, deriving residual samples of the current block based on the prediction samples, performing a primary transform on the residual samples to obtain primary-transformed coefficients of the current block, determining a secondary transform set among a pre-determined number of secondary transform sets based on the intra prediction mode, generating a first syntax element related to a secondary transform matrix to be applied to the current block among secondary transform matrices included in the determined secondary transform set, and performing a secondary transform on the primary-transformed coefficients based on the secondary transform matrix, the secondary transform being a non-separable transform;
• and
• a transmitter configured to transmit the data comprising the bitstream,
• wherein a number of input coefficients of the secondary transform and a number of output coefficients of the secondary transform are respectively determined as 16 and 8 based on the current block having a 4×4 size, and
• wherein the number of the input coefficients of the secondary transform for the current block having the 4×4 size is equal to a number of the input coefficients of the secondary transform for the current block having a 4×8 size or an 8×4 size, while the number of the output coefficients of the secondary transform for the current block having the 4×4 size is not equal to a number of the output coefficients of the secondary transform for the current block having the 4×8 size or the 8×4 size.