A simple interframe coder for video telephony

The technique of exchanging resolution according to the amount of movement in a picture has been previously described; in stationary parts of the picture the temporal resolution is reduced while in moving parts of the picture the spatial resolution is reduced. Here, we describe a method of applying resolution exchange to a differentially quantized (DPCM) signal. The resulting channel capacity required for the subjectively satisfactory transmission of the differential signal is halved. The coder is simpler than most interframe coders and should not increase the sensitivity of the system to channel errors.