Rules for intra-picture prediction modes when wavefront parallel processing is enabled
Various innovations facilitate the use of intra-picture prediction modes such as palette prediction mode, intra block copy mode, intra line copy mode and intra string copy mode by an encoder or decoder when wavefront parallel processing (“WPP”) is enabled. For example, for a palette coding/decoding mode, an encoder or decoder predicts a palette for an initial unit in a current WPP row of a picture using previous palette data from a previous unit in a previous WPP row of the picture. Or, as another example, for an intra copy mode (e.g., intra block copy mode, intra string copy mode, intra line copy mode), an encoder enforces one or more constraints attributable to the WPP, or a decoder receives and decodes encoded data that satisfies one or more constraints attributable to WPP.
1 . A computer system comprising one or more processing units and memory, wherein the computer system implements a video decoder configured to perform operations comprising:
receiving, as part of encoded data in a bitstream, a flag that indicates whether or not wavefront parallel processing (“WPP”) is enabled, the flag being part of a picture parameter set syntax structure or sequence parameter set syntax structure in the bitstream;
determining, based on the flag, that WPP is enabled;
receiving, as part of the encoded data in the bitstream, encoded data for a picture; and
decoding the encoded data for the picture with WPP enabled to reconstruct the picture, including, for a palette decoding mode, predicting a palette for an initial unit in a current WPP row of the picture using previous palette data from a previous unit in a previous WPP row of the picture, wherein the previous palette data from the previous unit in the previous WPP row includes, for each of C colors, one or more color component values, and wherein C is limited by a threshold count for the previous palette data from the previous unit in the previous WPP row.
2 . The computer system of claim 1 , wherein the palette for the initial unit in the current WPP row represents at least some colors used in the initial unit in the current WPP row.
3 . The computer system of claim 1 , wherein the previous palette data from the previous unit in the previous WPP row (a) represents at least some colors used in a palette for the previous unit in the previous WPP row or (b) was inherited by the previous unit in the previous WPP row.
4 . The computer system of claim 1 , wherein the previous unit in the previous WPP row is above the initial unit in the current WPP row or above and to the right of the initial unit in the current WPP row.
5 . The computer system of claim 1 , wherein the operations further comprise:
predicting a palette for a subsequent unit in the current WPP row of the picture using palette data from the palette for the initial unit in the current WPP row.
6 . The computer system of claim 1 , wherein the current WPP row and the previous WPP row are rows of coding tree units, and wherein the initial unit in the current WPP row and the previous unit in the previous WPP row are coding units.
7 . The computer system of claim 1 , wherein the predicting the palette for the initial unit in the current WPP row includes one or more of:
determining whether to reuse the previous palette data from the previous unit in the previous WPP row as the palette for the initial unit in the current WPP row; and
selecting one or more colors from the previous palette data from the previous unit in the previous WPP row to include in the palette for the initial unit in the current WPP row.
8 . The computer system of claim 1 , wherein the predicting the palette for the initial unit in the current WPP row does not use previous palette data from a last unit in the previous WPP row.
9 . The computer system of claim 1 , wherein the previous WPP row is immediately above the current WPP row, and the previous unit in the previous WPP row is immediately above the initial unit in the current WPP row or above and to the right of the initial unit in the current WPP row.
10 . One or more non-transitory computer-readable media having stored thereon computer-executable instructions for causing one or more processing units, when programmed thereby, to perform operations comprising:
determining that wavefront parallel processing (“WPP”) is enabled;
outputting, as part of encoded data in a bitstream, a flag that indicates whether or not WPP is enabled, the flag being part of a picture parameter set syntax structure or sequence parameter set syntax structure in the bitstream;
encoding a picture with WPP enabled, wherein the encoding produces encoded data for the picture, including, for a palette coding mode, predicting a palette for an initial unit in a current WPP row of the picture using previous palette data from a previous unit in a previous WPP row of the picture, wherein the previous palette data from the previous unit in the previous WPP row includes, for each of C colors, one or more color component values, and wherein C is limited by a threshold count for the previous palette data from the previous unit in the previous WPP row; and
outputting the encoded data for the picture as part of the encoded data in the bitstream.
11 . The one or more computer-readable media of claim 10 , wherein the palette for the initial unit in the current WPP row represents at least some colors used in the initial unit in the current WPP row.
12 . The one or more computer-readable media of claim 10 , wherein the previous palette data from the previous unit in the previous WPP row (a) represents at least some colors used in a palette for the previous unit in the previous WPP row or (b) was inherited by the previous unit in the previous WPP row.
13 . The one or more computer-readable media of claim 10 , wherein the previous unit in the previous WPP row is above the initial unit in the current WPP row or above and to the right of the initial unit in the current WPP row.
14 . The one or more computer-readable media of claim 10 , wherein the operations further comprise:
predicting a palette for a subsequent unit in the current WPP row of the picture using palette data from the palette for the initial unit in the current WPP row.
15 . The one or more computer-readable media of claim 10 , wherein the current WPP row and the previous WPP row are rows of coding tree units, and wherein the initial unit in the current WPP row and the previous unit in the previous WPP row are coding units.
16 . The one or more computer-readable media of claim 10 , wherein the predicting the palette for the initial unit in the current WPP row includes one or more of:
determining whether to reuse the previous palette data from the previous unit in the previous WPP row as the palette for the initial unit in the current WPP row; and
selecting one or more colors from the previous palette data from the previous unit in the previous WPP row to include in the palette for the initial unit in the current WPP row.
17 . The one or more computer-readable media of claim 10 , wherein the predicting the palette for the initial unit in the current WPP row does not depend on previous palette data from a last unit in the previous WPP row.
18 . The one or more computer-readable media of claim 10 , wherein the previous WPP row is immediately above the current WPP row, and the previous unit in the previous WPP row is immediately above the initial unit in the current WPP row or above and to the right of the initial unit in the current WPP row.
19 . In a computer system, a method comprising:
receiving encoded data in a bitstream, the encoded data including a flag that indicates whether or not wavefront parallel processing (“WPP”) is enabled, the flag being part of a picture parameter set syntax structure or sequence parameter set syntax structure in the bitstream, and the encoded data further including encoded data for a picture; and
storing the encoded data, wherein the encoded data is usable to cause a computer-implemented video decoder, when processing the encoded data, to perform operations comprising:
determining, based on the flag, that WPP is enabled; and
decoding the encoded data for the picture with WPP enabled to reconstruct the picture, including, for a palette decoding mode, predicting a palette for an initial unit in a current WPP row of the picture using previous palette data from a previous unit in a previous WPP row of the picture, wherein the previous palette data from the previous unit in the previous WPP row includes, for each of C colors, one or more color component values, and wherein C is limited by a threshold count for the previous palette data from the previous unit in the previous WPP row.
20 . The method of claim 19 , wherein the previous WPP row is immediately above the current WPP row, and the previous unit in the previous WPP row is immediately above the initial unit in the current WPP row or above and to the right of the initial unit in the current WPP row.