Visual fidelity criterion and modeling

Fidelity measures and criteria for visual communications are discussed. It is recognized that the basis of visual fidelity assessment is subjective judgement of reproduced pictures. However, in design and elsewhere there is also need for explicit evaluation of visual communication waveforms. The rate distortion theory model for such evaluations is brought out and two existing evaluations of limited scope, viz., weighted noise measurement and K rating, are reviewed in relation to that theory. It is suggested that video distortion can largely be identified with visibility of errors in reproduction. Relevant findings on luminance vision are examined. It is found that a comprehensive model of visibility would incorporate excitation, inhibition, and masking, and that considerable quantitative knowledge of these factors already exists. Looking ahead, a block schematic is given of a meter which might measure distortion produced by quantization noise in a video feed back quantizer.