Chromatic adaptation in a 2D photograph demonstrated by a D‐up viewer

It is said that we cannot have color constancy in a photograph. The concept of recognized visual space of illumination (RVSI) asserts that chromatic adaptation occurs when one perceives the illumination that is filling a space and not the objects in the space. It predicts then that if one perceives a 3D scene in a photograph, then color constancy will occur in the photograph. In this work, a dimension‐up (D‐up) viewer was developed to perceive a 3D scene on a 2D photograph, and the effect of chromatic adaptation was measured by the color appearance of a gray patch placed at the center of the photograph. Subjects saw the patch as a vivid color when they saw a photograph that had been taken under colored illumination, which is a normal experience in a real space observation. When the color appearance was measured by the elementary color naming method, the amount of chromaticness of the patch in percentage and the apparent hue were very similar to those observed in the 2‐room technique, thus confirming the prediction by the RVSI theory.     

Chromatic adaptation to illumination investigated with adapting and adapted color

The state of chromatic adaptation was investigated by using the two‐room technique. This technique involves a subject in a room who looks a white board in a separate test room through a window and judges the color of the window using the elementary color naming method. When the subject room is illuminated with a colored light and the test room with a white light, the window appears to be a very vivid color, for which the apparent hue depends on the color of the subject room. The color is referred to as the adapted color. The subject also evaluated the appearance of the illumination color of the subject room, which is called the adapting color. Two types of illuminating light in the subject room, fluorescent lamps with 7 colors and LED lamps with 19 colors, were employed. The adapting and the adapted colors were plotted on a polar diagram that was used in the opponent color theory, from which the hue angles were obtained. The hue angle difference between the two colors did not appear to be 180° except for one pair of adapting and the adapted colors, which implies that chromatic adaptation does not follow the opponent color concept. An improvement was achieved to explain the results by introducing complementary colors relation between the adapting and adapted color.     

Color appearance of afterimages compared to the chromatic adaptation to illumination

The color appearance of negative afterimages was measured by the elementary color naming method, and the results were compared with those obtained by the two‐room technique. Twenty adapting stimuli were presented on a display sequentially. Subjects first assessed the color appearance of the stimuli. After looking at the adapting stimulus for 10 seconds, the subjects assessed color of the afterimage. Apparent hue of the afterimage was in general not opponent color to the adapting color. The relation between the adapting stimuli and the afterimages was analyzed by the angle difference Δθ, when apparent hues are expressed by the angles of the points on the polar diagram of the opponent color theory. The relation relationship of Δθ to the angle of the adapting color θ_ing was quite similar to the results obtained by the two‐room technique, implying that the chromatic adaptation shown by the afterimage also occurs in the brain rather than in the retina.     

Strong effect of the simultaneous color contrast in an afterimage

The color appearance of the afterimage of the simultaneous color contrast pattern was investigated by the elementary color naming method. The color appearances of the surrounding, an afterimage of the surrounding, and the test patch were measured, and the results were shown on the polar diagram of the opponent colors theory. The colors of both the surrounding and the afterimage of the test patch were the same. The relationship between the afterimage color of the test patch and the afterimage of the surrounding was found to be the same as the relationship between the illumination color and the test patch color in the two‐rooms technique, implying that the same visual mechanism works for both situations, that is, eyes chromatically adapt to the afterimage color of the surroundings, and the afterimage color of the test patch is determined with the eyes so adapted.     

Simultaneous brightness contrast with three different stimuli: 2D, 3D,and D-up

In this study, simultaneous brightness contrast was investigated using three different devices: 2D (paper), 3D (space), and D-up. The paper stimuli were made by printing papers, the space stimuli were produced by illumination in a two-rooms experimental booth, and the D-up stimuli were shown to subjects using a D-up viewer. The brightness of test patches was judged by the amounts of whiteness and blackness. The results were different among the devices; however, if the whiteness of the test patches was plotted for the luminance contrast of the test patch versus the surround, all the data points were expressed by nonlinear equations. Data from the space stimuli were expressed by only one equation; those from the paper stimuli were also expressed by the nonlinear equation but with different coefficients for each test patch. The results from D-up were between those of the space and paper experiments. All the results were explained in relation to the hypothesized illuminated space over the surrounds. The difference among devices was explained by the whiteness of the surround being transferred to the illumination.