Methods of handling escape pixel as a predictor in index map coding
Methods to overcome issues associated with predictors being an Escape pixel in palette coding using a copy mode are disclosed. According to one embodiment, if the predictor for a copy-above mode is an Escape pixel, the pixel value of the current Escape pixel is transmitted so that it can be reconstructed using the transmitted pixel value. In another embodiment, restriction is applied to the encoder side, where in the copy-above mode, the copy-above run is terminated or the copy-above mode is not selected for the current pixel whenever an above pixel located above a current pixel is an Escape pixel. In yet another embodiment, directly copying the Escape value is used, where both the Escape index and Escape value, or the reconstructed pixel value of the predictor is directly copied to reconstruct a current pixel when the predictor is an Escape pixel.
1. A method of palette mode coding using palette prediction for a picture, wherein the palette prediction includes a copy-above mode for predicting one or more first pixels based on one or more second pixels located above said one or more first pixels correspondingly, the method comprising:
receiving input data associated with a current block;
determining a current coding mode for one or more current pixels;
if the current coding mode is the copy-above mode, identifying one or more above pixels located above said one or more current pixels correspondingly for said one or more current pixels to copy from said one or more above pixels; and
if said one or more above pixels include one or more current Escape pixels, signaling one or more Escape values for said one or more current Escape pixels or terminating a copy-above run at a first above pixel being one Escape pixel.
2. The method of claim 1 , wherein if the current coding mode corresponds to the copy-above mode, one Escape value for each of color components of each current Escape pixel corresponding to said one or more current Escape pixels included in said one or more above pixels is signaled.
3. The method of claim 1 , wherein if the current coding mode corresponds to the copy-above mode, a first number of said one or more current pixels is signaled, derived or inferred.
4. The method of claim 3 , wherein when the first number of said one or more current pixels is signaled, the first number of said one or more current pixels is signaled before said one or more Escape values for said one or more current Escape pixels.
5. The method of claim 3 , wherein if said one or more above pixels include one or more Escape pixels, the copy-above run is terminated at a first pixel being the Escape pixel.
6. The method of claim 1 , wherein if the current coding mode corresponds to a copy-index mode and a corresponding signaled index is escape index, a second number of said one or more current pixels is signaled, derived or inferred.
7. The method of claim 6 , wherein when the second number of said one or more current pixels is signaled, the second number of said one or more current pixels is signaled before said one or more Escape values for said one or more current Escape pixels.
8. The method of claim 7 , wherein one Escape value for each of color components of each Escape pixel correspond to the second number of said one or more current pixels is signaled.
9. A method of palette mode decoding using palette prediction for a picture, wherein the palette prediction includes a copy-above mode for predicting one or more first pixels based on one or more second pixels located above said one or more first pixels correspondingly, the method comprising:
receiving an input coded bitstream including compressed data of a current block;
parsing a current coding mode for one or more current pixels from the input coded bitstream;
if the current coding mode corresponds to the copy-above mode, identifying one or more above pixels located above said one or more current pixels correspondingly; and
if said one or more above pixels include one or more current Escape pixels, parsing one or more Escape values from the input coded bitstream for reconstructing said one or more current Escape pixels of said one or more current pixels.
10. The method of claim 9 , wherein if the current coding mode corresponds to the copy-above mode, a first number of said one or more current pixels is parsed, derived or inferred.
11. The method of claim 10 , wherein if the above pixel located above a leading current pixel of said one or more current pixels is one Escape pixel, the first number of said one or more current pixels is inferred as zero.
12. The method of claim 10 , wherein if the current coding mode corresponds to a copy-index mode and a corresponding parsed index is escape index, a second number of said one or more current pixels is parsed, derived or inferred.
13. The method of claim 12 , wherein when the second number of said one or more current pixels is parsed, the second number of said one or more current pixels is parsed before one or more Escape values for said one or more current Escape pixels.
14. The method of claim 13 , wherein one Escape value for each of color components of each current Escape pixel correspond to the second number of said one or more current pixels is parsed.
15. The method of claim 9 , wherein if the current coding mode corresponds to a copy-index mode, an adjusted maximum palette index (AdjustedMaxPaletteIndex) is fixed to be equal to maximum palette index minus 1 (MaxPaletteIndex−1) except for a first sample in the CU.