Kazuho Fukuda

The dichoptiscope: an instrument for investigating cues to motion in depth.

A stereoscope displays 2-D images with binocular disparities (stereograms), which fuse to form a 3-D stereoscopic object. But a stereoscopic object creates a conflict between vergence and accommodation. Also, motion in depth of a stereoscopic object simulated solely from change in target vergence produces anomalous motion parallax and anomalous changes in perspective. We describe a new instrument, which overcomes these problems. We call it the dichoptiscope. It resembles a mirror stereoscope, but instead of stereograms, it displays identical 2-D or 3-D physical objects to each eye. When a pair of the physical, monocular objects is fused, they create a dichoptic object that is visually identical to a real object. There is no conflict between vergence and accommodation, and motion parallax is normal. When the monocular objects move in real depth, the dichoptic object also moves in depth. The instrument allows the experimenter to control independently each of several cues to motion in depth. These cues include changes in the size of the images, changes in the vergence of the eyes, changes in binocular disparity within the moving object, and changes in the relative disparity between the moving object and a stationary object.

Estimating illuminant color based on luminance balance of surfaces

To accomplish color constancy the illuminant color needs to be discounted from the light reflected from surfaces. Some strategies for discounting the illuminant color use statistics of luminance and chromaticity distribution in natural scenes. In this study we showed whether color constancy exploits the potential cue that was provided by the luminance balance of differently colored surfaces. In our experiments we used six colors: bright and dim red, green, and blue, as surrounding stimulus colors. In most cases, bright colors were set to be optimal colors. They were arranged among 60 hexagonal elements in close-packed structure. The center element served as the test stimulus. The observer adjusted the chromaticity of the test stimulus to obtain a perceptually achromatic surface. We used simulated black body radiations of 3000 (or 4000), 6500, and 20000 K as test illuminants. The results showed that the luminance balance of surfaces with no chromaticity shift had clear effects on the observers achromatic setting, which was consistent with our hypothesis on estimating the scene illuminant based on optimal colors.

75.3: Is Brighter Always Better? The Effects of Display and Ambient Luminance on Preferences for Digital Signage

Preferred brightness may depend on many variables including image luminance and ambient illumination. To better understand the effects of these variables we asked observers to rate natural images according to their preferred brightness. Surprisingly, ratings plateaued at moderate luminance levels, and were only weakly influenced by ambient lighting.

Vertical-size disparities are temporally integrated for slant perception

We investigated temporal properties of vertical-size and horizontal-size disparity processing for slant perception. Subjects indicated perceived slants for a stereoscopic stimulus in which the two magnitudes of vertical-size or horizontal-size disparities were oscillated stepwise with various frequencies (from 0.2 to 10 Hz). For the stimulus with vertical-size disparity oscillation, two slants corresponding to the two magnitudes of disparity were perceived for low-frequency conditions, whereas only a static mean slant of the two slants was perceived for high frequencies (5 and 10 Hz). For the stimulus with horizontal-size disparity oscillation, two slants were perceived for all the temporal frequency conditions. These results indicate that temporal properties of vertical- and horizontal-size disparity processing are clearly different and vertical-size disparities are temporally integrated over a period of around 500 ms for slant perception.

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)].

P1-29: Banding Detection Exceeds Spatial Frequency Limit of the Visual System by Single Frequency Grating and Jitter

The halftone screen with fine vertical gratings is often used to modulate images in the printing technology. When the halftone screen is disturbed by the jitter in horizontal direction we observe the lattice fringe (called banding) in the horizontal direction. Surprisingly, any frequency component does not exist in the spatial frequency domain of the banding. Also, the banding is detected even when the spatial frequency of the halftone screen exceeds the frequency limit of the visual sensitivity, where the gratings (carrier) are the longitudinal waves of the horizontal direction and the jitter (side band) are transversal waves of the vertical direction. A doubly periodic function takes place above as etiology, and then higher harmonics occur. This complicates an argument. We validated the banding appearance by the carrier grating of the single frequency (69 cpd) and jitter (5.2 cpd) as the side band that removed higher harmonics, to find a response curve by 2AFC in experiment. The correlation between the ...