Method and device for processing video signal by using intra-prediction

A method of encoding a video signal, comprising:

• determining an intra prediction mode of a current block;
• determining a modified intra prediction mode from the intra prediction mode of the current block based on a width and a height of the current block and the intra prediction mode;
• performing primary transform on a residual block of the current block to generate a primary-transformed block of the current block;
• performing secondary transform on the primary-transformed block based on a secondary transform matrix;
• and
• generating a secondary transform index related to the secondary transform matrix,
• wherein the modified intra prediction mode is determined by adding 65 to the intra prediction mode based on (i) the width being larger than the height, (ii) the intra prediction mode being equal to or larger than 2, and (iii) the intra prediction mode being smaller than a first reference value,
• wherein the modified intra prediction mode is determined by subtracting 67 from the intra prediction mode based on (i) the height being larger than the width, (ii) the intra prediction mode being larger than a second reference value, and (iii) the intra prediction mode being equal to or smaller than 66,
• wherein the secondary transform matrix is determined based on a secondary transform set index, and
• wherein the secondary transform set index is determined based on the modified intra prediction mode.

A method for transmitting picture information generated by performing steps of:

• determining an intra prediction mode of a current block;
• determining a modified intra prediction mode from the intra prediction mode of the current block based on a width and a height of the current block and the intra prediction mode;
• performing primary transform on a residual block of the current block to generate a primary-transformed block of the current block;
• performing secondary transform on the primary-transformed block based on a secondary transform matrix;
• and
• generating a secondary transform index related to the secondary transform matrix,
• wherein the modified intra prediction mode is determined by adding 65 to the intra prediction mode based on (i) the width being larger than the height, (ii) the intra prediction mode being equal to or larger than 2, and (iii) the intra prediction mode being smaller than a first reference value,
• wherein the modified intra prediction mode is determined by subtracting 67 from the intra prediction mode based on (i) the height being larger than the width, (ii) the intra prediction mode being larger than a second reference value, and (iii) the intra prediction mode being equal to or smaller than 66,
• wherein the secondary transform matrix is determined based on a secondary transform set index, and
• wherein the secondary transform set index is determined based on the modified intra prediction mode.