Color perception and constancy of objects in three-dimensional complex scenes

Color perception is a fundamental problem in perception because it is an example of how the visual system extracts invariant information about objects based on an ambiguous retinal image. Previous research on color perception mostly used two-dimensional scenes that consist of small numbers of flat surfaces under a uniform light source. In three-dimensional scenes, however, light reflected from an object's surface depends on its shape, pose, orientation, surface material property, and spatial location. In the face of uncertainty introduced by so many variables, can the previous findings about color constancy in simple scenes be used to generate predictions for 3D scenes? My thesis focused on studying the color perception of objects in three-dimensional scenes. The first part of my thesis consists of two experiments examining how the color appearance of 3D objects is affected by changes in object material properties. The first experiment examines the color perception of objects across variation in surface gloss. I found that observers do not simply match the average light reflected from the object's surface. Instead, the visual system compensates for the physical effect of varying gloss. The second experiment studies how people perceive color across locations on an object. I found the effect is small in comparison with the physical shift caused by the change in location. The second part of my thesis focused on color constancy of objects in complex scenes. In particular, I studied the effect of material properties on constancy of 3D objects. I found that the mean constancy index for 3D objects is lower than for 2D objects reported previously, but similar to what we measured for 2D objects in the current experiments. Constancy indices were significantly decreased when the reflectance of the background wall was inconsistent with the illuminant change. I observed that glossy materials have better constancy than matte materials when the illuminant is changed from Neutral to Yellow; but this was not true when the illuminant is changed from Neutral to Blue. Finally, I report preliminary experiments that examine the effect of depth, shape and local contrast on color constancy of objects in complex scenes.