Foreground/background bit allocation for region-of-interest coding
Two bit allocation strategies, namely, maximum bit transfer (MET) and joint bit assignment (JBA) are proposed for region-of-interest coding. The MBT strategy uses a pair of quantizers to facilitate maximum bit transfer from the background to foreground image region. It assigns the highest quantization parameter to the background quantizer, and then determines the finest value of foreground quantizer that can be used without increasing the bit rate. In this approach, the background is always encoded with the coarsest quantization level, but this is not always desirable. Therefore, the JBA strategy can be used instead. It has two modes: user defined and automatic. In the user defined mode, the user can adjust bit consumption using a scale that ranges from "not coding foreground" to "coding foreground only". In the automatic mode, bit allocation is based on the characteristics of the image regions, which include size, motion and priority. The coding results showed that improved image quality was achieved at the same bit rate.