Predicting a quantization parameter for a current unit using quantization parameters of spatially neighboring units
Techniques and tools for encoding enhancement layer video with quantization that varies spatially and/or between color channels are presented, along with corresponding decoding techniques and tools. For example, an encoding tool determines whether quantization varies spatially over a picture, and the tool also determines whether quantization varies between color channels in the picture. The tool signals quantization parameters for macroblocks in the picture in an encoded bit stream. In some implementations, to signal the quantization parameters, the tool predicts the quantization parameters, and the quantization parameters are signaled with reference to the predicted quantization parameters. A decoding tool receives the encoded bit stream, predicts the quantization parameters, and uses the signaled information to determine the quantization parameters for the macroblocks of the enhancement layer video. The decoding tool performs inverse quantization that can vary spatially and/or between color channels.
1. In a computer system that implements a video encoder, a method comprising:
receiving a picture organized in multiple channels, the multiple channels including a luma channel and two chroma channels;
encoding the picture, thereby producing encoded data for the picture, wherein the encoding includes varying quantization spatially and between the multiple channels of the picture, and wherein the encoding further includes, for a current unit of the picture:
predicting a unit-level quantization parameter (“QP”) for the current unit using multiple unit-level QPs for spatially neighboring units;
determining a differential QP between the unit-level QP for the current unit and the predicted unit-level QP for the current unit; and
encoding the differential QP; and
outputting, as part of a bitstream, the encoded data for the picture, the encoded data for the picture including QP information that indicates multiple QPs that at least in part parameterize the varied quantization of the picture, the QP information including the unit-level QP for the current unit signaled, relative to the predicted unit-level QP for the current unit, as the encoded differential QP.
2. The method of claim 1 , wherein the encoding the picture further includes determining whether to use spatial quantization variation for the picture based at least in part on a user setting that controls speed and complexity of the encoding.
3. The method of claim 1 , wherein the encoding the picture further includes determining whether to use spatial quantization variation for the picture based at least in part on analysis of complexity and spatial variance of the picture.
4. The method of claim 1 , wherein the encoding the picture further includes performing the quantization on transform coefficients of units of the picture.
5. The method of claim 1 , wherein the QP information further comprises picture-level information that indicates one or more picture-level QPs for the picture or respective channels of the picture.
6. The method of claim 1 , wherein the spatially neighboring units include a left unit that is to the left of the current unit and an above unit that is above the current unit, and wherein the predicting the unit-level QP for the current unit uses one or more prediction rules based upon QP for the left unit and QP for the above unit.
7. The method of claim 6 , wherein, according to the one or more prediction rules, when the QP for the left unit equals the QP for the above unit, then the predicted unit-level QP for the current unit is the QP for the left unit.
8. The method of claim 6 , wherein, according to the one or more prediction rules:
when the QP for the left unit is not available, another QP is substituted for the QP for the left unit; and
when the QP for the above unit is not available, another QP is substituted for the QP for the above unit.
9. The method of claim 1 , wherein the encoding the picture further includes:
determining whether to use spatial quantization variation for the picture; and
determining whether to use quantization variation between channels; and
wherein the encoded data further includes:
information that indicates whether the spatial quantization variation is used; and
information that indicates whether the quantization variation between channels is used.
10. One or more non-transitory computer-readable media having stored thereon computer-executable instructions for causing one or more processors, when programmed thereby, to perform operations of a video decoder, the operations comprising:
receiving, from a bitstream, encoded data for a picture organized in multiple channels, the multiple channels including a luma channel and two chroma channels, the encoded data including quantization parameter (“QP”) information that indicates multiple QPs that at least in part parameterize inverse quantization of the picture, the QP information including an encoded differential QP for a unit-level QP for a current unit of the picture; and
decoding the encoded data to reconstruct the picture, wherein the decoding the encoded data includes varying inverse quantization spatially and between the multiple channels of the picture, and wherein the decoding the encoded data further includes, for the current unit:
decoding the encoded differential QP;
predicting the unit-level QP for the current unit using multiple unit-level QPs for spatially neighboring units; and
combining the predicted unit-level QP for the current unit with the decoded differential QP.
11. The one or more computer-readable media of claim 10 , wherein the decoding the encoded data further includes performing the inverse quantization on quantized transform coefficients of units of the picture.
12. The one or more computer-readable media of claim 10 , wherein the QP information further comprises picture-level information that indicates one or more picture-level QPs for the picture or respective channels of the picture.
13. The one or more computer-readable media of claim 10 , wherein the spatially neighboring units include a left unit that is to the left of the current unit and an above unit that is above the current unit, and wherein the predicting the unit-level QP for the current unit uses one or more prediction rules based upon QP for the left unit and QP for the above unit.
14. The one or more computer-readable media of claim 13 , wherein, according to the one or more prediction rules, when the QP for the left unit equals the QP for the above unit, then the predicted unit-level QP for the current unit is the QP for the left unit.
15. The one or more computer-readable media of claim 13 , wherein, according to the one or more prediction rules:
when the QP for the left unit is not available, another QP is substituted for the QP for the left unit; and
when the QP for the above unit is not available, another QP is substituted for the QP for the above unit.
16. The one or more computer-readable media of claim 10 , wherein the encoded data further includes information in the bitstream that indicates whether spatial quantization variation is used for the picture, and wherein the decoding further comprises determining whether to use the spatial quantization variation for the picture.
17. Computer-readable memory having stored therein encoded data in a bitstream for a picture organized in multiple channels, the multiple channels including a luma channel and two chroma channels, the encoded data including quantization parameter (“QP”) information that indicates multiple QPs that at least in part parameterize inverse quantization of the picture, the QP information including an encoded differential QP for a unit-level QP for a current unit of the picture, and the encoded data being used by a video decoder, executing computer-executable instructions in a computer system comprising one or more processing units, in operations including, for the current unit:
decoding the encoded differential QP;
predicting the unit-level QP for the current unit using multiple unit-level QPs for spatially neighboring units; and
combining the predicted unit-level QP for the current unit with the decoded differential QP.
18. The computer-readable memory of claim 17 , wherein the QP information further comprises picture-level information that indicates one or more picture-level QPs for the picture or respective channels of the picture.
19. The computer-readable memory of claim 17 , wherein the spatially neighboring units include a left unit that is to the left of the current unit and an above unit that is above the current unit, and wherein the predicting the unit-level QP for the current unit uses one or more prediction rules based upon QP for the left unit and QP for the above unit.
20. The computer-readable memory of claim 17 , wherein the encoded data further includes information in the bitstream that indicates whether spatial quantization variation is used for the picture.