Intra prediction in image processing
An intra prediction method and a device using the intra prediction method are provided. The intra prediction method includes the steps of: deriving a current prediction mode as a prediction mode of a current block; constructing neighboring samples of the current block with available reference samples; filtering the available reference samples; and generating predicted samples of the current block on the basis of the filtered available reference samples. The filtering step includes performing the filtering using the available reference sample located in the prediction direction of the current prediction mode and a predetermined number of available reference samples neighboring to the prediction direction of the current prediction mode.
1. An intra prediction method comprising the steps of:
deriving a current prediction mode as a prediction mode of a current block;
constructing neighboring samples of the current block with available reference samples;
filtering the available reference samples; and
generating predicted samples of the current block on the basis of the filtered available reference samples,
wherein the filtering step includes performing the filtering using the available reference sample located in a prediction direction of the current prediction mode and a predetermined number of available reference samples neighboring to the prediction direction of the current prediction mode.
2. The intra prediction method according to claim 1 , wherein the filtering step includes applying a 3-tap filter with a filtering coefficient of [1 2 1] to the available reference sample.
3. The intra prediction method according to claim 1 , wherein the filtering step includes applying a filtering using a 3-tap filter to a first available reference sample located in the prediction direction of the current prediction mode, a second available reference sample located on the left side of the first available reference sample, and a third available reference sample located on the right side of the first available reference sample to generate a modified reference sample at the position of the first available reference sample.
4. The intra prediction method according to claim 1 , wherein the current prediction mode is a prediction mode having an eighth prediction direction on the right side of a vertical prediction mode.
5. The intra prediction method according to claim 1 , wherein the current prediction mode is a prediction mode having an eighth prediction direction on the left side of a vertical prediction mode.
6. The intra prediction method according to claim 1 , wherein the current prediction mode is a prediction mode having an eighth prediction direction on the bottom side of a horizontal prediction mode.
7. The intra prediction method according to claim 1 , wherein the filtering step includes filtering only the available reference sample usable in the current prediction mode.
8. The intra prediction method according to claim 7 , wherein when the current prediction mode has a right side prediction direction of a vertical prediction mode, only the available reference samples on the top side and the top-right side of the current block and the available reference sample neighboring the top-left corner of the current block are filtered.
9. The intra prediction method according to claim 7 , wherein when the current prediction mode has a left side prediction direction of a vertical prediction mode or an upward prediction direction of a horizontal prediction mode, the available reference samples on the top side and the left side of the current block and the available reference sample neighboring the top-left corner of the current block are filtered.
10. The intra prediction method according to claim 7 , wherein when the current prediction mode has a downward prediction direction of a horizontal prediction mode, the available reference samples on the left side and the left-bottom side of the current block and the available reference sample neighboring the top-left corner of the current block are filtered.
11. The intra prediction method according to claim 1 , wherein it is determined whether the filtering step is performed depending on the size and the current prediction mode of the current block.
12. The intra prediction method according to claim 11 , wherein when it is determined that the filtering step is not performed, the predicted samples are generated on the basis of the available reference sample, and
wherein a smoothing process using a 2-tap filter is performed on the available reference sample and the predicted sample neighboring the available reference sample out of the predicted samples.