Object size, spatial-frequency content and retinal contrast

Abstract

Recent interest in HDR scene capture and display has stimulated measurements of the usable range of contrast information for human vision. These experiments have led to a model that calculates the retinal contrast image. A fraction of the light from each scene pixel is scattered to all retinal pixels. The amount of scattered light decreases with distance from the other pixels. By summing the light falling on each retinal pixel from all the scene pixels we can calculate the retinal image contrast. As objects, such as text letters, get smaller, their retinal contrast gets lower, even though the scene contrast is constant. This paper studies the Landolt C data, a commonly used test targets for measuring visual acuity, using three frameworks. First, it compares the visual acuity measurements with the receptor mosaic dimension. Second, discusses the Campbell and Robson's experiments and the limits of the Contrast Sensitivity Function (CSF). Third, the paper reports the calculated retinal stimulus after intraocular scatter of both Landolt C and Campbell and Robson's stimuli. These three different frameworks are useful in understanding limits of human vision. Each approach gives only one piece of the puzzle. Retinal contrast, CSF, and retinal cone spacing all influence our understanding of human vision limits. We have analyzed Landolt C and CSF using retinal contrast. Glare effect on Landolt C shows that retinal images are significantly different from target images. Veiling glare of the sine-wave stimuli used by Campbell and Robson to measure CSF, results in a retinal contrast decrease. This, above 3-4 cpd, correlates well with the data reported by them.