Issues in developing a very low bit rate videophone coder

The issues of a suitable transmission image size, general behaviour, and buffer control of a very low bitrate videophone video signal coder to be used in future mobile and public switched telephone networks are addressed. A software simulator of the coder was built so that the performance of the coder and the various alternative methods under consideration could be tested by subjective evaluation. In the case of transmission image size a clear choice between the two alternatives, QCIF and NCIF. is achieved: QCIF. The behaviour of the coder is explained on the basis of some statistical parameters extracted from it. With head-and-shoulders sequences without buffer regulation the coder is succesfiil in allocating bits to those regions in the image containing the most important information. Finally, the buffer control scheme of the coder is analyzed and an alternative method, based on framewise analysis of the bits created for that frame, is developed which is shown to be better than the original.