Intra-prediction method, and encoder and decoder using same
The present invention relates to an intra-prediction method and to an encoder and decoder using same. The intra-prediction method according to one embodiment of the present invention comprises the steps of: deriving a prediction mode of a current block; and generating a prediction block with respect to the current block on the basis of the prediction mode of the current block. When the prediction mode of the current block is an intra-angular prediction mode, values of boundary samples from among left boundary samples and upper boundary samples of the prediction block, which are not positioned in a prediction direction of the intra-angular prediction mode, are derived on the basis of reference samples positioned in the prediction direction of the intra-angular prediction mode, and on the basis of adjacent reference samples.
1. A method for decoding a picture by a decoding apparatus, the method comprising:
determining an intra prediction mode for a current block based on prediction mode information obtained from a bitstream;
deriving a predicted block of the current block based on the intra prediction mode; and
generating a reconstructed picture based on the predicted block,
wherein when the intra prediction mode is a vertical prediction mode, prediction samples of the predicted block are derived based on a vertical prediction direction and a prediction sample adjacent to a left boundary of the current block is filtered,
wherein the prediction sample adjacent to the left boundary of the current block is filtered by applying filtering on the prediction sample derived based on a first reference sample which is located along the vertical prediction direction with regard to a location of the prediction sample, wherein the first reference sample is located outside of the current block and is adjacent to a top boundary of the current block, wherein the filtering is based on a second reference sample, and
wherein for the filtering, a filtering coefficient applied to a value of the prediction sample derived based on a value of the first reference sample is larger than a filtering coefficient applied to a value of the second reference sample which is located along a horizontal direction with regard to the location of the prediction sample, wherein the second reference sample is located outside of the current block and is adjacent to the left boundary of the current block.
2. The method of claim 1 , wherein the intra prediction mode for the current block is determined from intra prediction mode candidates including 33 directional prediction modes and at least one non-directional prediction mode.
3. The method of claim 1 , wherein the filtering is further based on a third reference sample, and
wherein the third reference sample is located outside of the current block and is located at a top-left corner side of the current block.
4. The method of claim 3 , wherein the filtering is performed based on the following equation,
predSamples[ x,y ]=Clip1 y ( p [ x,− 1]+(( p [−1, y ]− p [−1,−1])/2)), with x= 0, y= 0 . . . nS− 1
where predSample[x, y] represents the filtered prediction sample located at a position [x, y] in the predicted block, p[x, −1] represents the value of the prediction sample derived based on the value of the first reference sample, p[−1, y] represent a value of the second reference sample, and p[−1, −1] represents a value of the third reference sample.
5. A method for encoding a picture by an encoding apparatus, the method comprising:
determining an intra prediction mode for a current block;
deriving a predicted block of the current block based on the intra prediction mode;
generating information on the predicted block, wherein the information on the predicted block includes prediction mode information on the determined intra prediction mode; and
encoding image information including the information on the predicted block to generate a bitstream,
wherein when the intra prediction mode is a vertical prediction mode, prediction samples of the predicted block are derived based on a vertical prediction direction and a prediction sample adjacent to a left boundary of the current block is filtered,
wherein the prediction sample adjacent to the left boundary of the current block is filtered by applying filtering on the prediction sample derived based on a first reference sample which is located along the vertical prediction direction with regard to a location of the prediction sample, wherein the first reference sample is located outside of the current block and is adjacent to a top boundary of the current block, wherein the filtering is based on a second reference sample, and
wherein for the filtering, a filtering coefficient applied to a value of the prediction sample derived based on a value of the first reference sample is larger than a filtering coefficient applied to a value of the second reference sample which is located along a horizontal direction with regard to the location of the prediction sample, wherein the second reference sample is located outside of the current block and is adjacent to the left boundary of the current block.
6. The method of claim 5 , wherein the intra prediction mode for the current block is determined from intra prediction mode candidates including 33 directional prediction modes and at least one non-directional prediction mode.
7. The method of claim 5 , wherein the filtered prediction sample is derived by applying the filtering further based on a third reference sample, and
wherein the third reference sample is located outside of the current block and is located at a top-left corner side of the current block.
8. The method of claim 7 , wherein the filtering is performed based on the following equation,
predSamples[ x,y ]=Clip1 y ( p [ x,− 1]+(( p [−1, y ]− p [−1,−1])/2)), with x= 0, y= 0 . . . nS− 1
where predSample[x, y] represents the filtered prediction sample located at a position [x, y] in the predicted block, p[x, −1] represents the value of the prediction sample derived based on the value of the first reference sample, p[−1, y] represent a value of the second reference sample, and p[−1, −1] represents a value of the third reference sample.
9. A non-transitory decoder-readable storage medium storing a bitstream comprising: encoded image information generated by determining an intra prediction mode for a current block, by deriving a predicted block of the current block based on the intra prediction mode, by generating information on the predicted block, wherein the information on the predicted block includes prediction mode information on the determined intra prediction mode, and by encoding image information including the information on the predicted block to generate the bitstream, wherein when the intra prediction mode is a vertical prediction mode prediction samples of the predicted block are derived based on a vertical prediction direction and a prediction sample adjacent to a left boundary of the current block is filtered, wherein the prediction sample adjacent to the left boundary of the current block is filtered by applying filtering on the prediction sample derived based on a first reference sample which is located along the vertical prediction direction with regard to a location of the prediction sample, wherein the first reference sample is located outside of the current block and is adjacent to a top boundary of the current block, wherein the filtering is based on a second reference sample, wherein for the filtering, a filtering coefficient applied to a value of the prediction sample derived based on a value of the first reference sample is larger than a filtering coefficient applied to a value of the second reference sample which is located along a horizontal direction with regard to the location of the prediction sample, wherein the second reference sample is located outside of the current block and is adjacent to the left boundary of the current block.
10. The non-transitory decoder-readable storage medium of claim 9 , wherein the intra prediction mode for the current block is determined from intra prediction mode candidates including 33 directional prediction modes and at least one non-directional prediction mode.
11. The non-transitory decoder-readable storage medium of claim 9 , wherein the filtered prediction sample is derived by applying the filtering further based on a third reference sample, and
wherein the third reference sample is located outside of the current block and is located at a top-left corner side of the current block.
12. The non-transitory decoder-readable storage medium of claim 11 , wherein the filtering is performed based on the following equation,
predSamples[ x,y ]=Clip1 y ( p [ x,− 1]+(( p [−1, y ]− p [−1,−1])/2)), with x= 0, y= 0 . . . nS− 1
where predSample[x, y] represents the filtered prediction sample located at a position [x, y] in the predicted block, p[x, −1] represents the value of the prediction sample derived based on the value of the first reference sample, p[−1, y] represent a value of the second reference sample, and p[−1, −1] represents a value of the third reference sample.