The perception and measurement of contrast: the influence of gaps between display elements

Abstract

The influence of the luminance of the gap between display elements of flat panel displays (FPDs) on perceived contrast was investigated. Twelve black-on-white FPDs, differing systematically with respect to foreground, background, and gap luminance, were simulated in an experiment. Twelve subjects rated each simulation on u scale, measuring several aspects of image quality, and performed a search task with each simulated FPD. The aims of the research were (a) to validate and assess the reliability of the rating scale items concerning contrast; (b) to relate subjective to objective measures; (c) to find out if ratings improve if raters perform a task with the rated objects; and (d) to evaluate a metric for expressing FPD contrast that we recently proposed. It is concluded that (a) the scale items are reliable if the rated objects vary on the property under concern; several items consistently measured subjective contrast; (b) subjective and objective contrast were strongly related in a linear fashion; (c) without actually using the stimuli in a working task, raters were capable of producing reliable and valid ratings; and (d) the proposed effective luminance modulation (M_r ) metric did, but ordinary luminance modulation did not correspond to perceived contrast. Based on this latter finding we recommend that an alternative contrast measurement procedure based on the (M_r ) metric is further validated for wide gaps and negative polarity displays.