One night I lay on the couch and prepared to watch TV, the idea of changing the solid lines of Hermann Grid Illusion into dotted lines just came up to me, so here's the Sequin Illusion!
Sequin Illusion (Lightness Difference)
---Try to figure out the mechanism behind.
I tried to figure out whether this illusion is connected with lightness difference between the lines and the background, or else why is dotted line so special? So I did these experiments and proved my assumption.
As the lightness difference getting bigger, it's easier to see the illusion, especially in the pictures with lighter background.
So here's the conclusion: If you want the Sequin Illusion to work out, there are two necessary conditions. First, there needs to be lightness difference in the same line, or else it'll become a solid line, and turn to the Hermann Grid Illusion instead. Second, at least there should be some differences in lightness between parts of the line and the background will the Sequin Illusion emerge. So now you know the secrets! Come and make your own Sequin Illusion!
%---lightness
R---red
P---purple
B---blue
P.S. I chose purple was because I wanted to eliminate the influences from the hue of colors.
And some people say that they can still see the illusion in the pictures that shouldn't be seen (the first nine pictures). So maybe it's the problem of the display device or the lightness I adjusted was not that precise. Or maybe the hue of colors are still involved in a part of the illusion...you can check out the last picture!