This is a great version of an old illusion – I came across it as the Edinburgh International Science Festival – amazing to think that these lines are actually straight…..


  1. Good one! I had to put a piece of paper up by the screen to check. BTW, those questions about your video were blimmin’ impossible!

    1. Actually none of the lines are straight. They’ve all got knobbly bits at the corners. Odd that no one’s noticed that yet

  2. That’s an excellent illusion, thanks, Richard; perhaps the best version of that particular illusion I’ve seen. The image seems to move when scrolling up and down, too (noticed it as I was scrolling to comment here). As always, thanks for these delightful illusions and snippets of food for thought 🙂

  3. I wonder if there is some process which detects that something is going wrong, even though it is not clear what – the picture is not comfortable to look at, it has a certain “dissonance”. Although, given that it “moves” when you tilt your head, that may be enough to account for the feeling (micro movement of the head).

  4. Save as and zoom in, and it’s clear that it’s a regular checkerboard with mini-checkerboards at 45 degrees. It would be interesting to know the optimum ratio between the sizes of the big and small squares for the best effect, is this it?

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