Patent US 4,467,356

Two input pictures are each compressed horizontally, one to three-quarters width, the other to one-quarter width, and combined side-by-side to form a single picture suitable for transmission over a standard link. The two signals are interchanged on alternate fields. Bandwidth limiting in the transmission link results in the signal compressed to one-quarter width having a final bandwidth one-third that of the other signal. This applies to each picture on alternate fields. A one-field delay repeats the high-frequencies from the field having wider bandwidth on the subsequent field, so that fine detail will be present on both fields. Lower bandwidth information is separately transmitted every field preserving vertical detail and the reproduction of motion at field rate. At the receiving end, the pictures are separated and expanded to normal width.