Video coder for color signals

Abstract

The luminance and two chrominance signals generated in a color video system are all translated into pulse code modulation signals by a plurality of analog-to-digital encoders. The luminance signal is then differentially encoded into variable length digital words and applied to a buffer. The encoded differences of the luminance signal are between the values of successive picture elements along horizontal scan lines. At least one of the chrominance signals is encoded using differences between corresponding picture element values in alternate horizontal scan lines. When the differences are large, the value of the corresponding picture element of the intermediate horizontal scan line is classified. If half the difference between the large transition of alternate picture element values does not correspond to the value of the intermediate picture element, another code word indicative of both intermediate picture element and alternate picture element is used. This improves the coding accuracy of large transitions in the chrominance signal which is also applied to the buffer. The output of the buffer is then transmitted over a channel to receiver. The receiver decodes each signal component to produce an analog replica. The chrominance signal is decoded using an interpolation technique that is also responsive to the code words indicative of both intermediate and alternate picture element values. Accordingly, the analog replica of the chrominance signal is produced which faithfully reproduces sharp color edges in the video scene.