Astounding Optical Illusion

Who doesn't like optical illusions ? It's been a while since I have seen something new, and this is one of the best I have seen. (This is not a new illusion, it's a few years old. I saw it only recently).

Which square is the darker shade of gray ? A or B ?

Of course, since you know this is an illusion, let me just give you the answer. They both are same shades of gray ! Now that you know it, can you see it ?

That's what makes this such a great illusion. It's irritating, no matter how hard you try, your brain just refuses to accept that they are the same shade.

There are many ways to prove this.

1. Print the image. Cut a small piece from both the squares and lay them side by side.

2. Copy and paste the image into an image editor like PaintBrush. Cut a small piece from each and compare.

3. Use a color inspector utility : like the Digital Color Meter on Mac. Hover over the squares to make sure that the RGB values are the same for both.

4. See this interesting proof ! (Focus your eyes on B).

You have to take the colors out of the surrounding context to see the same shade. That's pretty much the only way.

This image is courtesy of Prof Edward Adelson. You can find many similar examples on his site.

Another equally astounding and my favorite from this collection is the Koffka Ring.