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. A decoding method using intra prediction, by a decoding apparatus, the method comprising:
determining an intra prediction mode of a current block, wherein the intra prediction mode is determined as a directional prediction mode from intra prediction modes including 33 directional prediction modes and at least one non-directional prediction mode;
deriving neighboring reference samples of the current block;
performing filtering on at least one of the reference samples; and
generating a prediction sample of the current block based on a filtered reference sample,
wherein the filtered reference sample is filtered by using a first reference sample located in a prediction direction of the intra prediction mode with regard to a location of the prediction sample and reference samples adjacent to the first reference sample.
2. The method of claim 1 , wherein a filtering coefficient for the first reference sample is greater than filtering coefficients for the reference samples adjacent to the first reference sample.
3. The method of claim 1 , wherein the filtered reference sample is filtered by applying a 3-tap filter with a filtering coefficient of [1 2 1] to the first reference sample.
4. The method of claim 1 , wherein the filtered reference sample is filtered by applying a filtering using a 3-tap filter to the first reference sample, a second reference sample located on the left side of the first reference sample, and a third reference sample located on the right side of the first reference sample to generate the filtered reference sample at the position of the first reference sample.
5. The method of claim 1 , wherein the intra prediction mode is a prediction mode having an eighth prediction direction on the right side of a vertical prediction mode.
6. The method of claim 1 , wherein the intra prediction mode is a prediction mode having an eighth prediction direction on the left side of a vertical prediction mode.
7. The method of claim 1 , wherein the intra prediction mode is a prediction mode having an eighth prediction direction on the bottom side of a horizontal prediction mode.
8. The method of claim 1 , wherein the first reference sample is filtered by using only the reference samples usable in the intra prediction mode.
9. The method of claim 8 , wherein when the intra prediction mode has a right side prediction direction of a vertical prediction mode, only the reference samples on the top side and the top-right side of the current block and the reference sample neighboring the top-left corner of the current block are filtered.
10. The method of claim 8 , wherein when the intra prediction mode has a left side prediction direction of a vertical prediction mode or an upward prediction direction of a horizontal prediction mode, the reference samples on the top side and the left side of the current block and the reference sample neighboring the top-left corner of the current block are filtered.
11. The method of claim 8 , wherein when the intra prediction mode has a downward prediction direction of a horizontal prediction mode, the reference samples on the left side and the left-bottom side of the current block and the reference sample neighboring the top-left corner of the current block are filtered.
12. The method of claim 1 , wherein it is determined whether the filtering is performed depending on the size and the current prediction mode of the current block.
13. The method of claim 12 , wherein when it is determined that the filtering is not performed, the prediction sample is generated based on the first reference sample, and
wherein a smoothing process using 2-tap coefficients is performed on the first reference sample.