Understanding Exposure for Reverse Tone Mapping

High dynamic range (HDR) displays are capable of providing a rich visual experience by boosting both luminance and contrast beyond what conventional displays can offer. We envision that HDR capture and display hardware will soon reach the mass market and become mainstream in most fields, from entertainment to scientific visualization. This will necessarily lead to an extensive redesign of the imaging pipeline. However, a vast amount of legacy content is available, captured and stored using the traditional, low dynamic range (LDR) pipeline. The immediate question that arises is: will our current LDR digital material be properly visualized on an HDR display? The answer to this question involves the process known as reverse tone mapping (the expansion of luminance and contrast to match those of the HDR display) for which no definite solution exists. This paper studies the specific problem of reverse tone mapping for imperfect legacy still images, where some regions are underor overexposed. First, we show the results of a psychophysical study compared with first-order image statistics, in an attempt to gain some understanding in what makes an image be perceived as incorrectly exposed; second, we propose a methodology to evaluate existing reverse tone mapping algorithms in the case of imperfect legacy content.