On the Design of Quantizers for DPCM Coders: Influence of the Subjective Testing Methodology

In the Candy design procedure for DPCM quantizers, the subject is given a specific task to perform. We test the hypothesis that the form of this task influences the results that are obtained. In one experiment the viewers were permitted unlimited time to evaluate noise visibility; in another test using a different testing procedure viewing time was reduced to one second. Visibility functions were obtained from these tests, and quantizers were designed and then evaluated on the basis of impairment ratings of coded pictures. Our results indicate that the design procedure is indeed sensitive to the viewing conditions.