Method and apparatus for intra prediction with interpolation
An improved method of performing intra prediction for encoding or decoding uses interpolation such that substitute samples are found for samples to be used in the interpolation calculation that lie outside a normal reference range. The substitute samples can be repeated end samples from the bottom of a reference portion to the left of the target block, or right samples of a reference portion above the target block. An encoder can signal to a decoder whether to use intra prediction or interpolation prediction.
1. A method, comprising:
determining whether to encode a block in a video image using intra prediction or intra prediction with pixel interpolation, wherein intra prediction with pixel interpolation comprises using a linear interpolation of a neighboring reference pixel from a top reference section above the block and a neighboring reference pixel from a left reference section left of the block;
on condition it is determined to use intra prediction with pixel interpolation:
identifying a prediction mode for the block, the prediction mode having a particular direction of prediction;
determining, for the identified prediction mode, whether a reference sample to be used for the interpolation is excluded from the left reference section for performing the intra prediction with pixel interpolation in the particular direction;
on condition it is determined that the reference sample is excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using a substitute reference sample;
on condition it is determined that the reference sample is not excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using the reference sample,
wherein the substitute reference sample is determined from a first reference sample corresponding to a width of the block in the top reference section and a second reference sample corresponding to a sum of the width and a height of the block in the left reference section.
2. The method of claim 1 ,
wherein said substitute reference sample is determined from an estimate of the first reference sample and the second reference sample.
3. The method of claim 1 , wherein said determination of either intra prediction or intra prediction with pixel interpolation is signaled using a 1-bit flag.
4. The method of claim 1 , wherein the intra prediction with pixel interpolation is performed for a direct coding mode or a DM_CHROMA if the prediction mode is positive.
5. The method of claim 1 , wherein the substitute reference sample is determined from a weighted average of the first reference sample corresponding and the second reference sample.
6. A method, comprising:
determining whether to decode a block in a video image using intra prediction or intra prediction with pixel interpolation, wherein intra prediction with pixel interpolation comprises using a linear interpolation of a neighboring reference pixel from a top reference section above the block and a neighboring reference pixel from a left reference section left of the block;
on condition it is determined to use intra prediction with pixel interpolation:
identifying a prediction mode for the block, the prediction mode having a particular direction of prediction;
determining, for the identified prediction mode, whether a reference sample to be used for the interpolation is excluded from the left reference section for performing the intra prediction with pixel interpolation in the particular direction;
on condition it is determined that the reference sample is excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using a substitute reference samples;
on condition it is determined that the reference sample is not excluded in from the let reference section, performing the intra prediction with pixel interpolation in the particular direction using the reference sample,
wherein the substitute reference sample is determined from a first reference sample corresponding to a width of the block in the top reference section and a second reference sample corresponding to a sum of the width and a height of the block in the left reference section.
7. The method of claim 6 , wherein said substitute reference sample is determined from an estimate of the first reference sample and the second reference sample.
8. The method of claim 6 , wherein said determination of either intra prediction or intra prediction with pixel interpolation is based on a 1-bit flag.
9. The method of claim 6 , wherein the intra prediction with pixel interpolation is performed for a direct coding mode or a DM_CHROMA if the prediction mode is positive.
10. The method of claim 6 , wherein the substitute reference sample is determined from a weighted average of the first reference sample corresponding and the second reference sample.
11. An apparatus, comprising:
a memory, and
a processor, configured to:
determine whether to encode a block in a video image using intra prediction or intra prediction with pixel interpolation, wherein intra prediction with pixel interpolation comprises using a linear combination of a neighboring reference pixel from a top reference section above the block and a neighboring reference pixel from a left reference section left of the block;
on condition it is determined to use intra prediction with pixel interpolation:
identify a prediction mode for the block, the prediction mode having a particular direction of prediction;
determine, for the identified prediction mode, whether a reference sample to be used for the interpolation is excluded from the left reference section for performing the intra prediction with pixel interpolation in the particular direction;
on condition it is determined that the reference sample is excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using a substitute reference sample;
on condition it is determined that the reference sample is not excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using the reference sample,
wherein the substitute reference sample is determined from a first reference sample corresponding to a width of the block in the top reference section and a second reference sample corresponding to a sum of the width and a height of the block in the left reference section.
12. The apparatus of claim 11 , wherein said substitute reference sample is determined from an estimate of the first reference sample and the second reference sample.
13. The apparatus of claim 11 , wherein said determination of either intra prediction or intra prediction with pixel interpolation is signaled using a 1-bit flag.
14. The apparatus of claim 11 , wherein the intra prediction with pixel interpolation is performed for a direct coding mode or a DM_CHROMA if the prediction mode is positive.
15. The apparatus of claim 11 , wherein the substitute reference sample is determined from a weighted average of the first reference sample corresponding and the second reference sample.
16. An apparatus, comprising:
a memory, and
a processor, configured to:
determine whether to decode a block in a video image using intra prediction or intra prediction with pixel interpolation, wherein intra prediction with pixel interpolation comprises using a linear interpolation of a neighboring reference pixel from a top reference section above the block and a neighboring reference pixel from a left reference section left of the block;
on condition it is determined to use intra prediction with pixel interpolation:
identify a prediction mode for the block, the prediction mode having a particular direction of prediction;
determine, for the identified prediction mode, whether a reference sample to be used for the interpolation is excluded from the left reference section for performing the intra prediction with pixel interpolation in the particular direction;
on condition it is determined that the reference sample is excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using a substitute reference sample;
on condition it is determined that the reference sample is not excluded from the left reference section, performing the intra prediction with pixel interpolation in the particular direction using the reference sample,
wherein the substitute reference sample is determined from a first reference sample corresponding to a width of the block in the top reference section and a second reference sample corresponding to a sum of the width and a height of the block in the left reference section.
17. The apparatus of claim 16 , wherein said substitute reference sample is determined from an estimate of the first reference sample and the second reference sample.
18. The apparatus of claim 16 , wherein said determination of either intra prediction or intra prediction with pixel interpolation is based on a 1-bit flag.
19. The apparatus of claim 16 , wherein the intra prediction with pixel interpolation is performed for a direct coding mode or a DM_CHROMA if the prediction mode is positive.
20. The apparatus of claim 16 , wherein the substitute reference sample is determined from a weighted average of the first reference sample corresponding and the second reference sample.