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

1. A method for decoding a video signal by an apparatus, the method comprising:

obtaining an intra prediction mode of a current block from the video signal;

determining a modified intra prediction mode from the intra prediction mode for the current block based on a width and a height of the current block and the intra prediction mode;

determining a non-separable transform set index based on the modified intra prediction mode;

deriving a non-separable transform matrix based on the non-separable transform set index and a non-separable transform index; and

applying the non-separable transform matrix to the current block,

wherein when (i) the width is larger than the height, (ii) the intra prediction mode is equal to or larger than 2, and (iii) the intra prediction mode is smaller than a first reference value, the modified intra prediction mode is determined by adding 65 to the intra prediction mode,

wherein when (i) the height is larger than the width, (ii) the intra prediction mode is larger than a second reference value, and (iii) the intra prediction mode is equal to or smaller than 66, the modified intra prediction mode is determined by subtracting 67 from the intra prediction mode, and

wherein when the modified intra prediction mode is smaller than 0, the non-separable transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 0 and equal to or smaller than 1, the non-separable transform set index is determined as 0, when the modified intra prediction mode is equal to or larger than 2 and equal to or smaller than 12, the non-separable transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 13 and equal to or smaller than 23, the non-separable transform set index is determined as 2, when the modified intra prediction mode is equal to or larger than 24 and equal to or smaller than 44, the non-separable transform set index is determined as 3, when the modified intra prediction mode is equal to or larger than 45 and equal to or smaller than 55, the non-separable transform set index is determined as 2, and when the modified intra prediction mode is equal to or larger than 56 and equal to or smaller than 80, the non-separable transform set index is determined as 1.

2. The method of claim 1 , wherein the first reference value and the second reference value are determined based on an absolute value of a log for a value obtained by dividing the width by the height.

3. The method of claim 1 , wherein when the obtained intra prediction mode corresponds to a non-directional prediction mode or the width is equal to the height, the intra prediction mode is not modified.

4. The method of claim 1 , wherein the applying of the non-separable transform matrix includes applying the non-separable transform matrix to a top-left region of the current block, and

wherein the top-left region is determined based on the width and the height.

5. The method of claim 1 , wherein when both the width and the height are equal to or larger than 8, the non-separable transform matrix is applied to a top-left 8×8 region of the current block, and

wherein when both the width and the height are equal to or larger than 4 and the width or the height is smaller than 8, the non-separable transform matrix is applied to a top-left 4×4 region of the current block.

6. The method of claim 1 , wherein when both the width and the height are equal to or larger than 8, the secondary transform matrix is applied to a top-left 8×8 region of the primary-transformed block, and

wherein when both the width and the height are equal to or larger than 4 and the width or the height is smaller than 8, the secondary transform matrix is applied to a top-left 4×4 region of the primary-transformed block.

7. A method of encoding a video signal by an apparatus, 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;

determining a secondary transform set index based on the modified intra prediction mode;

performing primary transform on a residual block of the current block to generate a primary-transformed block of the current block;

selecting a secondary transform matrix in a secondary transform set specified by the secondary transform set index;

performing secondary transform on the primary-transformed block based on the secondary transform matrix; and

generating a secondary transform index related to the secondary transform matrix,

wherein when (i) the width is larger than the height, (ii) the intra prediction mode is equal to or larger than 2, and (iii) the intra prediction mode is smaller than a first reference value, the modified intra prediction mode is determined by adding 65 to the intra prediction mode,

wherein when (i) the height is larger than the width, (ii) the intra prediction mode is larger than a second reference value, and (iii) the intra prediction mode is equal to or smaller than 66, the modified intra prediction mode is determined by subtracting 67 from the intra prediction mode, and

wherein when the modified intra prediction mode is smaller than 0, the secondary transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 0 and equal to or smaller than 1, the secondary transform set index is determined as 0, when the modified intra prediction mode is equal to or larger than 2 and equal to or smaller than 12, the secondary transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 13 and equal to or smaller than 23, the secondary transform set index is determined as 2, when the modified intra prediction mode is equal to or larger than 24 and equal to or smaller than 44, the secondary transform set index is determined as 3, when the modified intra prediction mode is equal to or larger than 45 and equal to or smaller than 55, the secondary transform set index is determined as 2, and when the modified intra prediction mode is equal to or larger than 56 and equal to or smaller than 80, the secondary transform set index is determined as 1.

8. The method of claim 7 , wherein the first reference value and the second reference value are determined based on an absolute value of a log for a value obtained by dividing the width by the height.

9. The method of claim 7 , wherein when the determined intra prediction mode corresponds to a non-directional prediction mode or the width is equal to the height, the intra prediction mode is not modified.

10. The method of claim 7 , wherein the performing of the secondary transform includes applying the secondary transform matrix to a top-left region of the primary-transformed block, and

wherein the top-left region is determined based on the width and the height.

11. A non-transitory computer-readable medium for storing 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;

determining a secondary transform set index based on the modified intra prediction mode;

performing primary transform on a residual block of the current block to generate a primary-transformed block of the current block;

selecting a secondary transform matrix in a secondary transform set specified by the secondary transform set index;

performing secondary transform on the primary-transformed block based on the secondary transform matrix; and

generating a secondary transform index related to the secondary transform matrix,

wherein when (i) the width is larger than the height, (ii) the intra prediction mode is equal to or larger than 2, and (iii) the intra prediction mode is smaller than a first reference value, the modified intra prediction mode is determined by adding 65 to the intra prediction mode,

wherein when (i) the height is larger than the width, (ii) the intra prediction mode is larger than a second reference value, and (iii) the intra prediction mode is equal to or smaller than 66, the modified intra prediction mode is determined by subtracting 67 from the intra prediction mode, and

wherein when the modified intra prediction mode is smaller than 0, the secondary transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 0 and equal to or smaller than 1, the secondary transform set index is determined as 0, when the modified intra prediction mode is equal to or larger than 2 and equal to or smaller than 12, the secondary transform set index is determined as 1, when the modified intra prediction mode is equal to or larger than 13 and equal to or smaller than 23, the secondary transform set index is determined as 2, when the modified intra prediction mode is equal to or larger than 24 and equal to or smaller than 44, the secondary transform set index is determined as 3, when the modified intra prediction mode is equal to or larger than 45 and equal to or smaller than 55, the secondary transform set index is determined as 2, and when the modified intra prediction mode is equal to or larger than 56 and equal to or smaller than 80, the secondary transform set index is determined as 1.