Takuma Morimoto

Color Constancy in Two-Dimensional and Three-Dimensional Scenes: Effects of Viewing Methods and Surface Texture

There has been debate about how and why color constancy may be better in three-dimensional (3-D) scenes than in two-dimensional (2-D) scenes. Although some studies have shown better color constancy for 3-D conditions, the role of specific cues remains unclear. In this study, we compared color constancy for a 3-D miniature room (a real scene consisting of actual objects) and 2-D still images of that room presented on a monitor using three viewing methods: binocular viewing, monocular viewing, and head movement. We found that color constancy was better for the 3-D room; however, color constancy for the 2-D image improved when the viewing method caused the scene to be perceived more like a 3-D scene. Separate measurements of the perceptual 3-D effect of each viewing method also supported these results. An additional experiment comparing a miniature room and its image with and without texture suggested that surface texture of scene objects contributes to color constancy.

Effects of surrounding stimulus properties on color constancy based on luminance balance

The visual system needs to discount the influence of an illuminant to achieve color constancy. Uchikawa et al. [J. Opt. Soc. Am. A29, A133 (2012) showed that the luminance-balance change of surfaces in a scene contributes to illuminant estimation; however, its effect was substantially less than the chromaticity change. We conduct three experiments to reinforce the previous findings and investigate possible factors that can influence the effect of luminance balance. Experimental results replicate the previous finding; i.e., luminance balance makes a small, but significant, contribution to illuminant estimation. We find that stimulus dimensionality affects neither the degree of color constancy nor the effect of luminance balance. Unlike chromaticity-based color constancy, chromatic variation does not influence the effect of luminance balance. It is shown that luminance-balance-based estimation of an illuminant performs better for scenes with reddish or bluish surfaces. This suggests that the visual system exploits the optimal color distribution for illuminant estimation [J. Opt. Soc. Am. A 29, A133(2012)].

No effects of surround complexity on brown induction

A yellow stimulus turns brown when it is made sufficiently darker than its surroundings. Most previous studies have used simple contiguous surround stimuli to induce brown, so we know little about how brown induction may be controlled by more distant and more complex surround features. We begin to address this issue by varying the complexity of two configurations of achromatic surround stimuli. It was shown that the area most immediately contiguous to the test stimulus has strong effects on brown induction. More importantly, we found that neither the number of surround features nor the distribution of light in the surround region had an effect on brown induction, as long as the overall size of the surround region remained constant. Instead, we found that brown induction depended on the total amount of light in the constant-size surround region, regardless of how that light was distributed. This potentially distinguishes the mechanisms of brown induction from those of brightness induction.

Dichoptic perception of brown.

Two experiments assessed mechanisms underlying brown induction by presenting a foveal target disk and concentric annular surround stimuli that varied in contrast relative to larger backgrounds. Stimuli were presented under monocular, binocular, and dichoptic viewing conditions. Observers adjusted the luminance of the target disk to a criterion brown level. We found evidence for at least two separate mechanisms for brown induction: one mechanism that is dependent on physically contiguous contrast and operates in monocular pathways and another mechanism that responds to high luminance contrast anywhere in the visual field and can operate after convergence of signals from the two eyes.