Visibility enhancement via optimal two-piece gamma tone mapping for optical see-through displays under ambient light

Abstract

Visibility of the overlaid virtual image is highly sensitive to surrounding illumination in optical see-through (OST) displays. Ambient light can especially deteriorate the visibility of low gray-levels of comparable luminance. Therefore, we first derive a luminance model based on actual measurements under varied ambient light and use it to extract low gray-level regions (LGR), which suffer from severe contrast loss. It was experimentally found that gamma tone mapping is the most appropriate method for LGR contrast enhancement of OST displays. Luminance boosting before gamma tone mapping allows better expression of very low value gray levels in the output AR image. The gamma values and luminance boosting parameter are optimally determined by cost minimization. Visibility enhancement is verified experimentally on a practical setup using a variety of ambient light levels and images. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)