Color Compensation for Visibility Enhancement in Optical See-Through Displays across Ambient Light

Abstract

Optical see-through (OST) displays present digital imagery over a real scene. Because the light reaching the eye is an additive combination of displayed light and ambient light transmitted from the environment, changes in ambient luminance level and ambient chromaticity (summarized by correlated color temperature, CCT) can alter the appearance of overlaid content, including reduced contrast, reduced color strength, and shifts in overall color balance. Increasing SR is associated with compression of tone differences in low and mid levels and a reduction in CIELAB chroma (C*). Across SR levels, changes in ambient CCT are associated with hue-dependent deviations and chroma changes relative to a 6500 K darkroom reference condition. Based on these observations, an image visibility enhancement algorithm is formulated in the BT.709 YCbCr domain. SR-dependent processing adjusts Y(Luma) using a power-law tone parameter α expressed as a function of SR and image-mean luma Ȳ, and adjusts color magnitude using a power-law chroma parameter β that varies with SR within the tested range. In addition, CCT-dependent adjustments are organized as a lookup table of hue shift and chroma weight indexed by SR, CCT, and YCbCr hue, applied through rotation and scaling of the (Cb, Cr) vector while preserving Y(Luma). Pairwise preference evaluations with natural images on an OST display indicate that SR-dependent tone and chroma processing tends to improve visibility preference as SR increases under 6500 K ambient light. When ambient chromaticity differs from 6500 K, adding the CCT-dependent adjustment tends to provide additional preference gains. Qualitative analysis suggests that observer judgments reflect multiple criteria beyond shadow recovery alone, including highlight separation, texture preservation, scene impression in dark or backlit content, and the legibility of informative elements such as text and icons.