Some embodiments further improve the selection of the chroma QP offsets of a current picture by examining its neighboring pictures. Specifically, some embodiments examine how these neighboring pictures have been coded or will be coded, as well as how these neighboring pictures temporally relate to the current picture and its regions. For example, if the current picture is to be coded as a “key” picture (e.g. as an intra or a “periodic” refresh picture), some embodiments would encode additional chroma QP offsets in order to improve the chroma quality of the current picture. Conversely, if the current picture is a disposable picture or a less important picture in the coding hierarchy, some embodiments would refrain from assigning additional chroma QP offsets in a way that results in higher bit rate (or not to use additional chroma QP offsets at all). For other types of pictures, some embodiments use a more moderate chroma QP offset change to achieve a better compromise between bit rate and quality.

In some embodiments, different chroma QP offset parameters are specified for different scalability layers such as for resolution, quality, bit-depth, etc. Some embodiments apply additional chroma QP offsets to 3D/Multi-view applications where different chroma QP offsets are assigned to different views. For example, stereo masking could be considered to allocate and predict the chroma QP offsets as to reduce overhead and maximize the subjective quality of such a system.

For some embodiments, FIG. 17 conceptually illustrates a process 1700 for analyzing different regions of an image and assigning chroma QP offsets accordingly. The process is performed by a video encoder in some embodiments.