B.S.T.J. Briefs: Interframe Picturephone Coding Using Unconditional Verticaland Temporal Subsampling Techniques

A number of articles 1-4 have described the use of horizontal redundancy removal techniques to reduce the transmission rate required for coded Picturephone® signals to 6.312 Mb/s. Here an extension of this work is given which uses unconditional vertical and temporal subsampling techniques to reduce the required transmission capacity to 3 Mb/s. This type of processing is unique in that it does not employ the complex conditional replenishment techniques which typically have been used to reduce the digital transmission rate to either 2 Mb/s 5 or 1.5 Mb/s. 6 The analog Picturephone signal has an interlaced frame format 7 as illustrated in Fig. 1. Two adjacent fields, each containing 125? alternating lines, combine to form a complete 251-line frame of video information. In the experimental system being described, two adjacent fields are "averaged" together at the coder; this averaged 125^ line field is processed using variable-length coding techniques 3 and sent to the decoder at a 30-Hz rate. The decoder processes the received averaged field to form a two-field, 251-line frame for transmission to the station set receiver. Hence, unconditional vertical and temporal subsampling is being used to reduce the digital transmission rate from 6 M b / s to 3 M b / s ; vertical subsampling because only 125£ lines per frame are transmitted and temporal subsampling because averaged 395