Is there a preference for linearity when viewing natural images?

Abstract

The system gamma of the imaging pipeline, defined as the product of the encoding and decoding gammas, is typically greater than one and is stronger for images viewed with a dark background (e.g. cinema) than those viewed in lighter conditions (e.g. office displays). 1-3 However, for high dynamic range (HDR) images reproduced on a low dynamic range (LDR) monitor, subjects often prefer a system gamma of less than one, 4 presumably reflecting the greater need for histogram equalization in HDR images. In this study we ask subjects to rate the perceived quality of images presented on a LDR monitor using various levels of system gamma. We reveal that the optimal system gamma is below one for images with a HDR and approaches or exceeds one for images with a LDR. Additionally, the highest quality scores occur for images where a system gamma of one is optimal, suggesting a preference for linearity (where possible). We find that subjective image quality scores can be predicted by computing the degree of histogram equalization of the lightness distribution. Accordingly, an optimal, image dependent system gamma can be computed that maximizes perceived image quality.

Learning Preferential Perceptual Exposure for HDR Displays

“…This used LDR content on an LDR device, and did not find a significant effect of ambient illumination by itself, but had an effect when considering image content. Kane and Bertamío [23] investigated the preference of gamma when viewing HDR content on LDR displays with dark and light backgrounds. Similar to previous work [24], [25], they found that both the background and image content had an impact on chosen gamma values, with users preferring a linear gamma where image content permits it.…”