Gestalt in Isoluminance

from “Visual Phenomena & Optical Illusions”

Warning: this is somewhat subtle.

What to do & see

On the right there is a simplified version of the painting “Nu bleu II” by Henri Matisse. The original is a medium blue on a light yellow background. Here, the background brightness slowly oscillates and passes a point where the luminance of the background equals that of the figure.

When the brightness of fore- and background is identical, the gestalt is suddenly not well defined, it loses cohesion. The exact point of this so-called ‘isoluminance’ or ‘equiluminance’ depends strongly on your visual display unit and on your eyes.

You can narrow down the effect by clicking on the ‘Interactive’ button and manually adjusting the brightness with the slider.

Comment

I dimly recall the first demonstration of gestalt perception breaking down at isolumiance was by Richard Gregory.

Sources

Thanks to Geoff Arden for many inspirations, and namely pointing me to this picture to demonstrate the isoluminance effect.