The Preferred System Gamma is Primarily Determined by the Ratio of Dynamic Range of the Original Scene and the Displayed Image

International audienceThe dynamic range of real world scenes may vary from around 10 2 to greater than 10 7 , whilst the dynamic range of monitors may vary from 10 2 to 10 5. In this paper, we investigate the impact of the dynamic range ratio (DR ratio) between the captured scene and the displayed image, upon the value of system gamma preferred by subjects (a simple global power law transformation applied to the image). To do so, we present an image dataset with a broad distribution of dynamic ranges upon various sub-ranges of a SIM2 monitor. The full dynamic range of the monitor is 10 5 and we present images using either the full range, 75% or 50% of this, while maintaining a fixed mid-luminance level. We find that the preferred system gamma is inversely correlated with the DR ratio and importantly, is one (linear) when the DR ratio is one. This strongly suggests that the visual system is optimized for processing images only when the dynamic range is presented correctly. The DR ratio is not the only factor. By using 50% of the monitor dynamic range and using either the lower, middle or upper portion of the monitor, we show that increasing the overall luminance level also increases the preferred system gamma, although to a lesser extent than the DR ratio