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Effect of gamma on printed images

We present the results of experiments in which we investigate how the physical gamma maps onto the perceived gamma, and how the subjective quality of a printed image may be influenced by the grey scale mapping that is used to print the image. The grey scale is altered by changing the gamma, the exponent relating the input to the output luminance. Five natural images, widely different in content, have been printed with 16 different values of gamma. First the printer gamma is measured. In general, this gamma differs from 1. In the printer a gamma transform is performed as well. The selected gamma values are corrected using the directly gamma function. The aim of the first experiment is to find out what the relation is between physical gamma and perceived gamma. The stimulus response function derived from our data is found to be quite linear over the range investigated. The aim of the second experiment is to test the subjective preference for a particular gamma. We have found that these gammas are not independent of image content. The mean preference averaged over the subjects for the various images ranges form 1.6 to 2.2.