Display images under high illumination may appear to have lower lightness and attenuated contrast. In this paper, we review the image degradation phenomenon in ambient light through photoreceptor physiology. The influence of different environmental parameters and their effects on various gray areas in images can be evaluated by the cone response difference. Based on this, we propose a fast global tone mapping method to minimize the cone response difference at different pixel intensity levels of images displayed at different illumination levels. This method has a superior computational efficiency and higher evaluation score than existing algorithms.