Design of DPCM Quantizers for Video Signals Using Subjective Tests

The application of differential pulse code modulation (DPCM) for broadcast color television signals requires a design which produces no visible impairments under normal viewing conditions. This paper describes a quantizer design which is based on measured visibility thresholds of the various kinds of DPCM impairments such as granular noise, edge busyness, and slope overload. The visibility thresholds are determined by subjective tests based on comparisons of DPCM and PCM encoded pictures. Constructions of quantizers are carried out such that the number of levels is minimized without exceeding the measured visibility thresholds. Besides nonadaptive quantizers, adaptive quantizers are also constructed which are controlled by the signal changes of surrounding picture elements. These investigations show that for component coding of color video signals with two-dimensional prediction, a transmission rate of 31.7 Mbits/s is possible for natural types of test pictures without visible impairments using constant word length coding.