There are countless optical illusions but I think this is one of the best.

The squares A and B are exactly the same shade of grey.

(I did actually have to copy and paste the image into Paint and use the colour picker in order to draw a line through the two squares just to prove it to myself)

Tweakie.

This video demonstrate the principle;  https://youtu.be/z9Sen1HTu5o

Tweakie.

       

Good one Tweakie! That's right up there with the beer goggles effect.

Ahhh, the Beer Goggles   

Tweakie.

Interesting that the illusion can be reproduced by laser etching.

Tweakie.

Nice Tweakie!

By way of proof, a good friend of mine in Hungary sent me this picture. He has copied a section of the A square and pasted it by the B square and done a similar thing with the B and A squares to prove that my laser etched shades of the two squares are indeed the same.

Tweakie.

That's great Tweakie! What did you use to generate the Gcode for the laser? Did he actually do the laser etching too?  If so, is he running your Gcode or generating his own?

My Hungarian friend just copied my posted picture and then used Photoshop (or similar) to do the copy and paste. He did say that he could not believe his eyes so all credit must go to E.H.Adelson for creating such an excellent and reproducible optical illusion.

(I have to admit to being a bit dis-loyal but the Gcode was generated and the image laser produced using the Auggie / 57CNC Tempest planner and motion controller).
 
Tweakie.

Very nice Tweakie, that is a good one.
I tore two small holes in a piece of paper and laid it over the screen .... dead nuts, identical.
Really cool !
(too blurred to recognize through my beer goggles)
Thanks,
Russ