Abstract: A system and method for coding a digitized picture is described. The picture is divided into a plurality of regions and then each region is further divided into a plurality of subregions. Linear combinations of pixels in each subregion are then computed. A subregional adaptive quantisation parameter for each of the subregions is then determined based on the courseness tolerance of that subregion as established by processing the linear combinations. A regional quantisation parameter for each region is then determined as a function of the subregional adaptive quantisation parameters and then a quantisation level for each of the regions is determined based on the regional quantisation parameter. Once the regional quantisation level for a region has been determined, it is transform encoded. The transform encoded representations of the regions are concatenated to obtain an encoded representation of the entire picture which can then be decoded for display or storage.

Abstract: A system and methods for implementing a video encoder which for each picture guarantees that the number of bits produced will not exceed a limit. In a preferred embodiment, the system includes two cooperating components or subsystems that together with other components of a video encoder operate to encode the input video, detect when the limit on the number of bits produced so far is close to exceeding the limit on the number of bits that may be produced and reduce the bit rate when such a condition is detected. One aspect of the current invention embodies a macroblock (MB) bit stream generator that can operate in a "low bit rate mode" Another aspect embodies a subsystem for detecting when the number of bits in the picture is close to exceeding the limit.