Institute for Data Analysis and Visualization

The design of very low bit rate coders, below 64 kilobits per second, presents a number of new challenges. Such low bit rate coders are targeted to small size images, say 176 X 144, or below and are limited to head and shoulders scenes. In this paper, we compare and rate the performance of several still image encoding methods such as DCT: Subband and Wavelets, using a new quality scale based on properties of human vision. These still image coders are embedded into video coders such as the H261 coder. The relative importance of intraframe and interframe quality and contributions to the total bit rate provide an overall design framework for these low bit rate video coders. We discuss and illustrate, for the encoding of low bit rate video. the still image and motion impairments that are perceptually most important.