Adaptive quantization for enhancement layer video coding

In a computer system that implements a video encoder, a method comprising:

• encoding a picture organized in multiple channels, thereby producing encoded data for the picture, the multiple channels including two chroma channels, wherein the encoding the picture includes varying quantization spatially and between the multiple channels for the picture, and wherein the encoding the picture further includes, for a current unit of the picture:
• determining a unit-level quantization parameter (“QP”) of a spatially neighboring unit, including:
• determining whether an actual QP of the spatially neighboring unit is available;
• and
• depending on whether the actual QP of the spatially neighboring unit is available, assigning the actual QP of the spatially neighboring unit to be the unit-level QP of the spatially neighboring unit or substituting another QP as the unit-level QP of the spatially neighboring unit;
• determining a predicted QP based at least in part on the unit-level QP of the spatially neighboring unit;
• and
• encoding a unit-level QP for a given chroma channel among the two chroma channels for the current unit based at least in part on the predicted QP and an index for the given chroma channel for the current unit;
• 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, the QP information including the index for the given chroma channel for the current unit.

One or more non-transitory computer-readable media having stored thereon encoded data in a bitstream for a picture organized in multiple channels, the multiple channels including two chroma channels, the encoded data including quantization parameter (“QP”) information that indicates multiple QPs that at least in part parameterize inverse quantization for the picture, the QP information including an index for a given chroma channel among the two chroma channels for a current unit of the picture, wherein the encoded data is produced by encoding the picture by operations that include varying quantization spatially and between the multiple channels for the picture, the operations further including, for the current unit:

• determining a unit-level quantization parameter (“QP”) of a spatially neighboring unit, including:
• determining whether an actual QP of the spatially neighboring unit is available;
• and
• depending on whether the actual QP of the spatially neighboring unit is available, assigning the actual QP of the spatially neighboring unit to be the unit-level QP of the spatially neighboring unit or substituting another QP as the unit-level QP of the spatially neighboring unit;
• determining a predicted QP based at least in part on the unit-level QP of the spatially neighboring unit;
• and
• encoding a unit-level QP for a given chroma channel among the two chroma channels for the current unit based at least in part on the predicted QP and an index for the given chroma channel for the current unit.