System for encoding and decoding video signals

A system is described which makes use of the fact that in a raster scanned television system a high degree of correlation exists both in the luminance and in the chrominance signals of a pair of adjacent lines. Because of this correlation, the difference between the luminance signals of the two lines is usually much smaller than the luminance signal of either line alone, and requires less bandwidth. A luminance carrier is amplitude modulated by the average value of two adjacent lines, while the phase of the carrier is modulated by the difference of two adjacent lines. The bandwidth of the resulting signal is comparable to that of a carrier that is amplitude modulated by a single raster line. Since two lines of information are being transmitted, however, it would be possible to take twice as much time to transmit them as when only a single line is being transmitted. Stretching the time axis in this way results in a factor of about two reduction in bandwidth. Also, as the eye has very poor resolution for color, a simple average of the chrominance signal is used for both hue and saturation. A chrominance carrier is amplitude modulated by the average value of two adjacent hue lines, while the phase of the carrier is modulated by the average of two adjacent color saturation lines. After synchronous demodulation of the carriers, inverse operations are utilized to reconstitute the luminance and chrominance signals.