Quality versus color saturation and noise

A softcopy quality ruler study involving 12 scenes and 34 observers was performed to quantify the dependence of quality on color saturation, in the absence of noise, with saturation measured using Imatest software. It was found that quality falls off symmetrically with deviation of color saturation from the preferred value of about 110%, with a 20% change in saturation reducing quality by about two just noticeable differences (JNDs). Optimization of noise versus color saturation was investigated using (1) the aforementioned transform of color saturation to JNDs of quality; (2) a previously published objective metric and JND transform for isotropic noise; and (3) the multivariate formalism, for combining JNDs from independent attributes into an overall quality JNDs. As noise increases and signal to noise ratio (SNR) decreases, the optimal color saturation decreases from the 110% position, so that there is less noise amplification by the color correction matrix. A quality contour plot is presented, showing a region of plausible color saturation values, as a function of SNR, for a representative use case. One example of a reasonable strategy is to provide 80% color saturation at SNR = 5, 90% at SNR = 10, 100% at SNR = 20, and 110% at SNR 50 and above.