Adjustment of the Cornsweet model to perception of defocused symbols

ABSTRACT The IDS Summation model was used to explain the perception of defocused symbols. Twelve different computer-generated words were used as stimulus for sharpness evaluation by a group of observers and the result compared with themodel response. obtained by software implementation. The symbol luminance slope was used as parameter. The correlationcoefficient is greater than 0.99.1. INTRODUCTION The border definition of a visual object is an important parameter to characterise the performance of the visual system. The maximum slope of the border profile has proved to be an appropriate physical parameter to evaluate it. and hasbeen used to study the response of the visual sysleni to a set of defocused symbols' . In addition to other models2 based on the superposition of excitatory and inhibitory zones of the receptive field. the use of the Cornsweet &Yellot's "Intensity- dependent Spatial Summation (IDS)" model3 is proposed in this paper. The IDS model is based on a single assumption: the output image is the sum of the nonnegative point spreadfunction generated around each input point. whose height is directly proportional to image intensity. In spite of the