Relative effects of gaussian and poisson noise on subjective image quality.

Photographic transparencies were prepared with precisely determined quantities of gaussian (signal-independent) and Poisson (signal-dependent) noise and submitted to observers for subjective ranking of image quality. Average values of noise and signal-to-noise ratio, based upon the relative variance of the signal, were calculated for the imagery: (a) assuming equal a priori probabilities of allowed signal levels; (b) using a normalized probability density function for signal levels derived from scene statistics. Best correlation with the results of subjective quality ranking was obtained with an average signal-to-noise ratio based upon the normalized probability density function.