Predictive Coding of Composite NTSC Color Television Signals

Abstract

A study is reported of intrafield predictive coding of composite NTSC television signals sampled at four times the color subcarrier frequency (14.3 MHz). The choice of predictor was found to be governed by three constraints, which are described. Of several predictors which satisfied these constraints, it was determined that one of them performed the best. A procedure for designing quantizers for composite signals was developed based on a three-parameter piecewise-linear approximation to the quantizer error threshold function. Observations of picture quality were made using real-time processing on a mixed hardware/software experimental facility, from which it was concluded that between 5 and 6 bits/pel were required for broadcast quality. Preliminary results were obtained on the effect of composite predictive coding on the vertical interval test signals (VITS). Our observations indicate that the waveform distortion criteria applied to VITS give some indication of granular noise visibility (in the SNR measurements); these criteria, however, are too severe in their requirements for slope overload distortion and do not consider edge busyness, an important temporal impairment in predictive coding.