Experiments On Image Coding With Distortion Below Visual Threshold

Two quantization methods for high quality image coding are presented. The goal in both methods is to keep subjective distortion below visual threshold. The first method is a discrete cosine transform coding system. The coefficients of the transformed blocks are quantized with a set. of uniform quantizers with step sizes determine by a parametric function. Subjective experiments were carried out to determine the parameter values which minimize output entropy while keeping distortion at about the threshold of perceptibility. The second method is a vector quantizer on small image blocks. A structured quantizer defined by a few parameters is described, and approximate parameter values for transparent, coding are given.