Abstract: Video conferencing, wherein the outputs of a plurality of television cameras at one location are transmitted to a second location so that parties at the first location are perceived as present by parties at the second location, has received some attention directed toward bandwidth reduction. The subject invention relates to an improved video conferencing system for reducing bandwidth by advantageously applying temporal resolution and spatial reduction to a video picture provided by each camera. The temporal resolution of a picture from one or more of the cameras can be automatically adapted to a control signal, for example, to a speech level control signal so as to advantageously interleave and to give priority to a picture from one camera over a picture from other television cameras. The spatial reduction of each picture obtains by transmitting and displaying less than the total picture, illustratively the middle two-thirds of the picture from each camera.

Abstract: A pulse code modulator utilizes a predetermined bit, which is the least significant bit in each code group, to indicate the polarity of the signal amplitude sample whose magnitude is represented by the immediately succeeding code group. Since variations in magnitude change the value of the predetermined bit in a more or less random fashion and the same is true of the polarity of the samples to be encoded, in the course of the encoding process there is a relatively high probability of occasions when the magnitude and polarity will call for the same value of bit. When there is a disagreement in bit value for the magnitude and polarity, the predetermined bit in each code group is forced to indicate the correct polarity. Additional bits in each of these code groups may also be changed to provide the most accurate magnitude information with the corrected polarity information.

Abstract: Alternate lines of a 526 line video signal are time-stretched and transmitted over a transmission channel of limited bandwidth. At the receiver, the lines are compressed back to their original duration and displayed in an interlaced manner on a conventional receiver by blanking alternate lines in each field. In another embodiment of the invention, adjacent transmitted lines of the video signal are averaged at the receiver and the resultant signals are substituted for the non-transmitted lines of the video signal.