Two-tier DPCM codec for videoconferencing

A two-tier differential pulse-code modulation (DPCM) codec for videoconference applications is described that utilizes the so-called masking effect of motion. In this approach, an image is separated into high-frequency and low-frequency components. The low-frequency signal is processed by an adaptive spatiotemporal DPCM codec. A motion indicator derived from the low-frequency signal is used to control the corresponding block of high-frequency component pixels. The system is aimed at adaptively removing the high-frequency component of an image in those areas which contain motion. Since less information is needed to be sent, the data rate is lower. Since the missing high-frequency information occurs only in moving areas, the human eyes are less likely to notice. In this way, the data rate is lowered without unduly giving up on the subjective image quality. Simulation results have shown that the amount of visible degradation in image quality is small while the reduction in data rate is substantial