The effect of visual perception on the required performance of imaging systems

Current performance measures for infrared imagers are applicable to linear mechanically scanned systems but not to those with focal plane arrays of detector elements, because these are nonlinear due to aliasing. The performance of an imager affects the ability of an observer to perform perception tasks using it. Psychophysical trials have been undertaken in an attempt to identify more appropriate performance measures. Simple shapes degraded by various degrees of Gaussian blurring and pixelation were selected at random and displayed on a computer monitor. A correlation has been found between the probability of recognition of an image and a quantity called ‘recognition contrast’ (C R). This is related to the shape observed and a template of the equivalently degraded alternative shape most similar to it. This quantity C R was refined following trials in which spatial noise was added to Gaussian blurred images. C R is calculated from information about each of the two images and is directly proportional to the sensitivity index d' obtained from probability measurements. The results described are believed to have a wide range of applications such as in defining image quality and performance measures for imaging equipment.