The images below involve the use of photographs in the contest of illusory contours. The project is a collaboration with my wife, Constance, and we reported on it at the 2008 meeting of the Vision Sciences Society. There are many ways to study the combinations, and the examples show different approaches. In the early example below the inducing pie figures were created in Photoshop and superimposed over a photograph.
Different inducing pie figures were created for the following, comparison pair. Illusory contours result in each photograph, but the comparison also points to a somewhat novel example of simultaneous contrast. Normally examples of contrast show how a figure seemingly changes color when different grounds are used. A blue figure will look different on a yellow and purple ground. Here the inducing figures affect the appearance of the photograph.
Different inducing figures were created for the four comparison below. Light and dark inducing stimuli were us for the top two. But for the bottom two, photographic inducing stimuli were used. Pie sections were copied for the bottom two photographs but then alternated in the two versions. The pies were flipped vertically in the bottom left, but they were flipped horizontally in the bottom right.
For the next three examples, the perspective of the inducing stimuli was varied.
In the following example the illusory contour effect is weak. The reason might result from the "noisy" photograph with many interfering lines. In addition the value of the inducing stimuli and the photograph is relatively similar.
So, as a check on these two, the photographic image was lightened and the illusory contour effect became more pronounced.
Another way of creating illusory contours is by creating the inducing stimuli by darkening the pie sections. Thus a photograph is used, but some sections are darkened a bit. A similar effect would result if sections were lightened.
More examples follow on the "More Photos" page.
Saved the best for last.