Surround Effects on Color Constancy in Virtual Reality

The degree of color constancy can be influenced by the color of an object's surroundings. We used virtual reality (VR) to observe how different color surroundings affect a target object under different illuminations. VR technology allowed us to easily modify the illumination and the reflectance properties of objects in a photorealistic indoor scene. The scene was rendered with Unreal Engine under five illuminants: a neutral illuminant metameric to D65, two more illuminants also on the daylight locus and two orthogonal to it. A color calibrated HTC Vive Pro Eye headset was used for display. The target object was presented on top of a colored surround, whose color was chosen to lie in between two of the illuminant directions in CIELab color space: kaki, purple, rose and teal. We measured the degree of color constancy for each surround color under each one of the five illuminants. Participants were asked to select the target that best matched an achromatic one, from a set of five differently colored competitors present in the scene. These five were chosen to include one that represented perfect constancy (matching the achromatic reflectance), one that represented zero constancy (matching the tristimulus value), two that were sampled in between reflectance and tristimulus, and one that represented overconstancy. We found that surround and illumination color interacted in their effects on constancy. For example, the purple surround under a greenish or yellowish light source – surround and illumination color in nearly opposite directions – led to a decrease in CCI. Similar effects were observed for other combinations of illumination and surround. Our results indicate that illumination and surround jointly affect color constancy and appearance.