What can you see? This variation of the Hermann grid was first described by Schrauf et al. (1997). It is made up of black squares and mid-gray bars. At the intersections white dots are added. When you look at a white dot, at some intersections illusory dark dots seem to appear and disappear (if you do not see the effect immediately, enlarge the image by clicking on it). The effect is clearer if you do not fix a single point, but let your gaze wander around. It is reduced, if you tilt your head or your eyes are too close or too far from the picture.
What can you do? In this project you can change sq_size and gap as well as the dot_size. The HSV model is used to set the colors. Accordingly, you can specify the three values for the squares (sq_hue, sq_saturation, sq_brightness) and the gaps (gap_hue, gap_saturation, gap_brightness) separately. The color of the dots is coupled to the color of the gaps, but always with v = 1. Thereby you can test how how dependent is the effect of color and contrast differences.
Related topics: Hermann grid illusion, Ehrenstein illusion
Schrauf, M., Lingelbach, B. & Wist, E.R. (1997). The Scintillating Grid Illusion. Vision Research 37, 8, 1033-1038. Available as download.