PALETTE CODING FOR SCREEN CONTENT CODING
Sketch copy mode may be used to code blocks comprising irregular lines, syntax redundancy may be removed from blocks with special characteristics, and/or run value coding may be simplified. The parsing dependencies in palette coding design may be removed. For example, the context modeling dependency of the syntax element palette_transpose_flag may be removed, for example, by simplifying the corresponding context model. The context modeling of the syntax element palette_mode may be removed, for example, by using run-length coding without using context. The syntax parsing dependencies and/or the syntax signaling dependencies that are related with escape color signaling may be removed. A palette table generation process may handle input screen content video with high bit depths, for example, at the encoder side.
1 . A method of performing palette decoding comprising:
parsing a palette index run value of a coding unit (CU), wherein the palette index run value indicates a length of consecutive palette indices for corresponding pixel positions in the CU, wherein at least one of the consecutive palette indices corresponds to an escape color index;
reconstructing the consecutive palette indices for the corresponding pixel positions of the CU according to the palette index run value; and
reconstructing color values for the corresponding pixel positions of the CU according to the consecutive palette indices and one or more palette_escape_val values.
2 . The method of claim 1 , wherein the palette index run value indicates an index run.
3 . The method of claim 1 , wherein the palette index run value indicates a copy run.
4 . The method of claim 1 , wherein the consecutive palette indices correspond to a first escape color index and a second escape color index.
5 . The method of claim 1 , wherein reconstructing the color values for the corresponding pixel positions of the CU further comprises:
parsing, during a first pass, palette syntax values sufficient to reconstruct all palette indices in the CU other than the one or more palette_escape_val values; and
parsing, during a second pass, the one or more palette_escape_val values for the corresponding pixel positions in the CU for which palette indices parsed from the first pass corresponds to the escape color index.
6 . A decoder comprising:
a processor configured to:
parse a palette index run value of a coding unit (CU), wherein the palette index run value indicates a length of consecutive palette indices for corresponding pixel positions in the CU, wherein at least one of the consecutive palette indices corresponds to an escape color index;
reconstruct the consecutive palette indices for the corresponding pixel positions of the CU according to the palette index run value; and
reconstruct color values for the corresponding pixel positions of the CU according to the consecutive palette indices and one or more palette_escape_val values.
7 . The decoder of claim 6 , wherein the run value indicates an index run.
8 . The decoder of claim 6 , wherein the run value indicates a copy run.
9 . The decoder of claim 6 , wherein the consecutive palette indices correspond to a first escape color index and a second escape color index.
10 . The decoder of claim 6 , wherein, to reconstruct the color values for the corresponding pixel positions of the CU, the processor is configured to:
parse, during a first pass, palette syntax values sufficient to reconstruct all palette indices in the CU other than the one or more palette_escape_val values; and
parse, during a second pass, the one or more palette_escape_val values for the corresponding pixel positions in the CU for which the palette indices parsed from the first pass corresponds to the escape color index.
11 . A method of performing palette decoding comprising:
determining a palette table size for a coding unit (CU) of a picture, wherein:
if the palette table size of the CU is zero, inferring that a palette_escape_val_present_flag for the CU is equal to one; and
if the palette table size of the CU is a value other than zero, parsing a palette_escape_val_present_flag for the CU; and
reconstructing palette indices for corresponding pixel positions of the CU based on a palette table for the CU and a value associated with the palette_escape_val_present_flag of the CU.
12 . The method of claim 11 , wherein the palette table size for the CU being equal to 0 indicates that all pixels of the CU are coded as escape colors.
13 . The method of claim 11 , wherein the palette_escape_val_present_flag is not received for the CU if the palette table size is zero.
14 . A decoder comprising:
a processor configured to:
determine a palette table size for a coding unit (CU) of a picture, wherein:
if the palette table size of the CU is zero, than infer that a palette_escape_val_present_flag for the CU is equal to one; and
if the palette table size of the CU is a value other than zero, than parse a palette_escape_val_present_flag for the CU; and
reconstruct palette indices for corresponding pixel positions of the CU based on a palette table for the CU and a value associated with the palette_escape_val_present_flag of the CU.
15 . The decoder of claim 14 , wherein the palette table size for the CU being equal to 0 indicates that all pixels of the CU are coded as escape colors.
16 . The decoder of claim 14 , wherein the palette_escape_val_present_flag is not received for the CU if the palette table size is zero.
17 . A method of performing palette decoding comprising:
determining that a coding unit (CU) of a picture comprises only escape colors;
determining that the CU is coded according to an index and a palette index mode based on not receiving a palette_mode for the CU; and
reconstructing color values for the corresponding pixel positions of the CU.
18 . The method of claim 17 , further comprising:
determining that a run value of the index mode for the CU is equal to a size of the CU minus one based on not receiving a syntax value indicative of a palette run value for the CU.
19 . The method of claim 17 , further comprising:
determining that a palette index value for the CU is equal to zero based on not receive a palette index value for the CU.
20 . The method of claim 17 , further comprising:
inferring the palette_mode of the CU to be equal to zero based on not receiving the palette_mode for the CU; and
receiving a palette_escape_val for each pixel position in the CU.