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It is both a technical and an artistic challenge to depict three-dimensional content using stereo equipment and a flat two-dimensional screen. On the one hand, the content needs to fit within the limits of a given display technology and at the same time achieve a comfortable viewing experience. Given the technological advances of 3D equipment, especially the latter increases in importance. Modifications to stereo content become necessary that aim at flattening or even removing binocular disparity to adjust the 3D content to match the comfort zone in which the clash between accommodation and vergence stays acceptable. However, applying such modifications can lead to a reduction of crucial depth details. One promising direction is backwardcompatible stereo, for which the disparity is low enough that overlaid stereo pairs seem almost identical. It builds upon the Craik-O'Brien-Cornsweet effect, a visual illusion, which uses so-called Cornsweet profiles to produce a local contrast that leads to a perceived brightness increase. Similarly, Cornsweet profiles in disparity can lead to an illusion of depth. Applying them skilfully at depth discontinuities allows for a reduction of the overall disparity range to ensure a comfortable yet convincing stereo experience. The present work extends the previous idea by showing that Cornsweet profiles can also be used to enhance the 3D impression. This operation can help in regions where the disparity range was compressed, but also to emphasize parts of a scene. A user study measures the performance of backward-compatible stereo and our disparity enhancement.

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.