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A series of three experiments has been performed to test both the preference and accuracy of high dynamic-range (HDR) rendering algorithms in digital photography application. The goal was to develop a methodology for testing a wide variety of previously published tone-mapping algorithms for overall preference and rendering accuracy. A number of algorithms were chosen and evaluated first in a paired-comparison experiment for overall image preference. A rating-scale experiment was then designed for further investigation of individual image attributes that make up overall image preference. This was designed to identify the correlations between image attributes and the overall preference results obtained from the first experiments. In a third experiment, three real-world scenes with a diversity of dynamic range and spatial configuration were designed and captured to evaluate seven HDR rendering algorithms for both of their preference and accuracy performance by comparing the appearance of the physical scenes and the corresponding tone-mapped images directly. In this series of experiments, a modified Durand and Dorsey's bilateral filter technique consistently performed well for both preference and accuracy, suggesting that it is a good candidate for a common algorithm that could be included in future HDR algorithm testing evaluations. The results of these experiments provide insight for understanding of perceptual HDR image rendering and should aid in design strategies for spatial processing and tone mapping. The results indicate ways to improve and design more robust rendering algorithms for general HDR scenes in the future. Moreover, the purpose of this research was not simply to find out the “best” algorithms, but rather to find a more general psychophysical experiment based methodology to evaluate HDR image-rendering algorithms. This paper provides an overview of the many issues involved in an experimental framework that can be used for these evaluations.

In recent years, new display technologies have emerged that are capable of producing colors that exceed the color gamut of broadcast standards. On the other hand, most video content currently remains compliant with the EBU standard and as such, there is a need for color mapping algorithms that make optimal use of the wider gamut of these new displays. To identify appropriate color mapping strategies, we have developed, implemented, and evaluated several approaches to gamut extension. The color rendering performance and robustness to different image content of these algorithms were evaluated against a reference (true-color) mapping. To this end, two psychophysical experiments were conducted using a simulated and actual wide-gamut display. Results show that the preferred algorithm had a dependency on image content, especially for images with skin tones. In both experiments, however, there was preference shown for the algorithm that balances chroma and lightness modulations as a function of the input lightness. The newly designed extension algorithms consistently outperformed true-color mapping, thus confirming the benefit of appropriate mapping on wide-gamut displays.

Current HDR display technology approaches the dynamic-range capabilities of the fully adapted human visual system. As such, this technology has potential for performing as a surrogate for real-world scenes in the perceptual evaluation of high-dynamic-range (HDR) image-reproduction algorithms that aim to map HDR scenes to the limited dynamic ranges available in typical display and print technology. Compared with direct image assessment in comparison with real-world scenes, it is clear that use of HDR display technology has the benefit of simplicity in experimental design while maintaining the HDR of the original scene. To evaluate this potential application of HDR display technology, seven published versions of well-known HDR tone-mapping algorithms were benchmarked for perceptual rendering accuracy against each of four real-world scenes constructed in the laboratory and against corresponding images on an HDR display. The results illustrate that visual assessments obtained from the HDR display and those obtained from real-world scenes are in good agreement, validating the potential for HDR display technology as an evaluation tool in this context.

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