Visibility of DCT basis functions: effects of display resolution

The authors have examined the variation in visibility of single DCT basis functions as a function of display visual resolution. They have shown that the existing model (Ahumada and Peterson, 1992; and Peterson et al., 1993) accommodates resolutions of 16, 32, and 64 pixels/degree, provided that one parameter, the peak sensitivity s0, is allowed to vary. Variations in this parameter are to some extent consistent with spatial summation, although sensitivity is lower at the lowest resolution than summation would predict. Practical DCT quantization matrices must take into account both the visibility of single basis functions, and the spatial pooling of artifacts from block to block. Peterson et al. (1993) showed that to a first approximation this pooling is consistent with probability summation. If one considers two images of equivalent size in degrees, but visual resolutions differing by a factor of two, then the sensitivity to individual artifacts would be lower by 4^1/4 in the higher resolution image due to the smaller block size in degrees, but higher by 4^1/4 in the same image due to the greater number of blocks. Thus the same matrix should be used with both. The point of the illustration is that the overall gain of the best quantization matrix must take into account both display resolution and image size