David Novick's Color Illusion Page: Color-Completion

This page presents a related color illusion, the color-completion illusion. In this illusion, lines of a main color result in a relate, ghosting color between them. Here are some examples:

Color completion illusions similar to the Sohmiya illusion can be created with straight lines rather than waves. For example, here are blue and green lines that produce a yellowish illusory color between the green lines.
Amazingly, a yellowish illusory color also comes from red lines in place of the green lines.
In the color completion illusion, some see completion of blue. To my eyes, this looks more like extra brightness ("whiter white") of the white background. Here's an uncropped image with the surround of background white.
Another way to assess this effect is by adding a background color. When I add a light yellow background, if blue color-completes then those areas should look greenish. Instead, to my eyes, those areas remain yellow and the red areas complete to a darker yellow.
And here's a similar treatment of blue and green on a background of light yellow.
More on weak blues in color-completion illusions: With this arrangement of blue and yellow, I see fairly strong completion of the yellow (even for such a light color) but weak or no completion in the blue.
Yet with the arrangement of blue and yellow areas reversed, I still see the yellow completion much more strongly than I do for the blue, which see as having interpolated color similar to that of the white background.
The illusion seems stronger with a background of light yellow. I think that the yellowish color-completion effect in the green area becomes less salient, and the color-completion effect in the violet area becomes redder and more salient.

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Department of Engineering Education and Leadership | The University of Texas at El Paso

December 12, 2017