Constrained position dependent intra prediction combination (PDPC)
A second level intra prediction mode can be combined with one or more of sixty-seven JVET intra prediction modes during encoding of a coding unit in a video bitstream. Embodiments include making a position dependent intra prediction combination (PDPC) mode available as the second level intra prediction mode. In embodiments, when a PDPC (position dependent intra prediction combination) mode is enabled, the second level intra prediction is combined with one of the 67 selected intra predictor modes. In embodiments, the PDPC mode is only enabled or available for a predetermined subset of intra prediction modes (out of 67 possible modes), in order to reduce encoder complexity and potentially improve coding efficiency. The PDPC mode may be identifies as enabled or available by a list of modes or signaling in the video bitstream.
1. A method for coding a video bitstream, the method comprising:
(a) receiving the video bitstream including at least one rectangular coding unit;
(b) generating a first predictor for a pixel within said at least one coding unit based on neighboring pixels and an intra prediction mode selected from a plurality of prediction modes during encoding of said pixel;
(c) determining if a second prediction mode was combined with the at least one of the plurality of intra prediction modes selected during encoding of the pixel in the at least one coding unit;
(d) if the second prediction mode was combined with the at least one of the plurality of intra prediction modes selected during encoding, deriving the pixel in the at least one coding unit using the first predictor generated based on a selected at least one intra prediction mode and a second prediction process based on the second prediction mode, else deriving the pixel using the generated first predictor;
(e) decoding the at least one coding unit based on the derived pixel values within the coding unit;
(f) wherein determining if the second intra prediction mode was combined with the at least one of the plurality of intra prediction modes is determined based on a list of first prediction modes for which the second intra prediction mode is enabled and/or disabled;
(g) wherein the list identifies constrained first prediction modes, wherein constrained first prediction modes are excluded from combination with the second intra prediction mode;
(h) when the list indicates that a mode is disabled for the selected at least one of the plurality of intra prediction modes used to generate the first predictor, only the first predictor is used for intra prediction of the pixel.
2. The method of claim 1 wherein the second level prediction mode is a position dependent intra prediction combination (PDPC).
3. The method claim 1 wherein planar mode and DC mode are first intra prediction modes included in the list of constrained modes.
4. The method of claim 2 wherein the position dependent intra prediction combination (PDPC) mode is further constrained for decoding I slices and excluded for P and/or B slices.