A perceptual evaluation of 3D unsharp masking

Much research has gone into developing methods for enhancing the contrast of displayed 3D scenes. In the current study, we investigated the perceptual impact of an algorithm recently proposed by Ritschel et al.1 that provides a general technique for enhancing the perceived contrast in synthesized scenes. Their algorithm extends traditional image-based Unsharp Masking to a 3D scene, achieving a scene-coherent enhancement. We conducted a standardized perceptual experiment to test the proposition that a 3D unsharp enhanced scene was superior to the original scene in terms of perceived contrast and preference. Furthermore, the impact of different settings of the algorithm's main parameters enhancement-strength (λ) and gradient size (σ) were studied in order to provide an estimate of a reasonable parameter space for the method. All participants preferred a clearly visible enhancement over the original, non-enhanced scenes and the setting for objectionable enhancement was far above the preferred settings. The effect of the gradient size σ was negligible. The general pattern found for the parameters provides a useful guideline for designers when making use of 3D Unsharp Masking: as a rule of thumb they can easily determine the strength for which they start to perceive an enhancement and use twice this value for a good effect. Since the value for objectionable results was twice as large again, artifacts should not impose restrictions on the applicability of this rule.