Effect of Pictorial Depth Cues, Binocular Disparity Cues and Motion Parallax Depth Cues on Lightness Perception in Three-Dimensional Virtual Scenes

Surface lightness perception is affected by scene interpretation. There is some experimental evidence that perceived lightness under bi-ocular viewing conditions is different from perceived lightness in actual scenes but there are also reports that viewing conditions have little or no effect on perceived color. We investigated how mixes of depth cues affect perception of lightness in three-dimensional rendered scenes containing strong gradients of illumination in depth.Observers viewed a virtual room (4 m width x 5 m height x 17.5 m depth) with checkerboard walls and floor. In four conditions, the room was presented with or without binocular disparity (BD) depth cues and with or without motion parallax (MP) depth cues. In all conditions, observers were asked to adjust the luminance of a comparison surface to match the lightness of test surfaces placed at seven different depths (8.5-17.5 m) in the scene. We estimated lightness versus depth profiles in all four depth cue conditions. Even when observers had only pictorial depth cues (no MP, no BD), they partially but significantly discounted the illumination gradient in judging lightness. Adding either MP or BD led to significantly greater discounting and both cues together produced the greatest discounting. The effects of MP and BD were approximately additive. BD had greater influence at near distances than far.These results suggest the surface lightness perception is modulated by three-dimensional perception/interpretation using pictorial, binocular-disparity, and motion-parallax cues additively. We propose a two-stage (2D and 3D) processing model for lightness perception

Discounting effects across depth cue conditions.

<p>The logarithm of luminance is plotted versus depth for each of the depth cue conditions, pictorial cues only (black solid square), pictorial cues and binocular disparity (red solid circle), pictorial cues and motion parallax (blue circle), pictorial cues, binocular disparity and motion parallax (green cross). The conditions of test surface luminance were merged here. The negative slopes indicate discounting of lightness. Luminance profile of the floor is superimposed. See text.</p

Stereo example of the scene.

<p>An example of the scene with pictorial cues and binocular disparity cues (for crossed fusion). The test patch is 6 meters from the back wall, 11.5 meters from the observer.</p

Prior for lightness perception.

<p><i>(A)</i> Possible gradients of illumination indexed by a parameter <i>s</i>. <i>(B)</i> Prior distribution on the light field.</p

Lambertian bidirectional reflectance density function.

<p>The light field recorded at a point in a forest scene. The environment map for this illustration was obtained from <a href="http://www.debevec.org/Probes" target="_blank">http://www.debevec.org/Probes</a>.</p

Test patch and comparison patch.

<p>The observer adjusted the luminance of the comparison patch until the perceived albedo of the patches was the same.</p

The rendered scene.

<p><i>(A).</i> Top view of the rendered scene. The test patch (violet) could be at any of seven depths. <i>(B).</i> A plot of the actual intensity of light incident on the test patch as a function of depth, and a top view of rendered room.</p

Depth cue effect analyzed by regression slope.

<p>The value of regression slope for each depth condition was plotted against test-patch luminance. Paired t-tests were conducted to test difference between conditions (* <i>p</i><.05, **<i>p</i><.01).</p

Discounting effects across depth cue conditions for test-surface luminance conditions.

<p>The logarithm of luminance for each surface-luminance condition (4, 8, 16 cd/m2) is plotted versus depth for each of the depth cue conditions like in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003177#pone-0003177-g006" target="_blank">Figure 6</a>.</p