## Tuesday, July 17, 2012

### Color Contrast Optical Illusion

The below two cubes share some things in common. The creator of this optical illusion states the following.
"Despite the fundamental difference in the apparent colour of the 'blue' tiles on top of the left cube, and the 'yellow' tiles on the top of the right cube, all the tiles are in fact physically identical (grey in both cases)."
I'll take this one step further and let you know that the RGB value for all 11 squares mentioned is exactly the same R:136 G:136 B:136. The blue and yellow squares mentioned are the exact same color as the gray block to the right.

Dale Purves M.D.
R. Beau Lotto
(c)2012

But they are not the only tiles on these cubes that look different but are exactly the same. Can you spot the other tiles that look different but are actually the same exact color?

The truth is that the optical illusion for tiles numbered 1 are the result of color contrast and the optical illusion for tiles numbered 2 and 3 are the result of brightness contrast.

With that said you must have no doubts that what I'm stating as fact is true. What's that you say? You don't believe it? Ok, OK already, quiet down. I guess we will just have to take the steps needed to prove that I am correct.

Project: Proving all the 1, 2, or 3 tiles are respectively all the same color.

There are a few ways you can prove that the tiles are the same color.

Before we continue, right click on the top image and open it in a new window. Now you have an image to work with.

1) You can use a graphics program like Photoshop, Paint.Net, Gimp or the Colorzilla extension for Firefox browser.

My choice is Colorzilla w/Firefox. Using the eyedropper tool you can determine that the RGB values of the respective tiles are the same, for number 1 tiles the RGB value is R:136 G:136 B:136, number 2 tiles have a RGB value of R:182 G:159 B:14, and number 3 tiles have a RGB value of R:75 G:45 B:138.

Not good enough for you, heh? Still not ready to trust that the computer is correct or you don't have an eyedropper tool? Either way you can move on to step 2 or 3 below.

2) Cut out a cardboard mask.

By viewing patches of the squares without the surrounding context, you can remove the effect of the illusion. A piece of cardboard with holes created in the right spots will work as a mask for a computer screen or as a mask for a the printed illusion. Holding up this mask to the image on the screen or printed paper should be enough to convince you. But if you were like my daughter nothing but this next step would do.

3) Print the image and cut out the respective tiles.

WARNING: Do Not use any specialty scissors your mother or wife uses for any kind of crafts, IE. quilting or fabric scissors. Doing this can be hazardous to your short term happiness. When in doubt get permission to use the scissors first.

This is another way to isolate the patches from their surrounding context. Cut out each tile along the edges. Remove them. Hold them side by side. Overlap the cut out tiles. Yup they're the same color. No denying it now, is there?

Please note that I have heard that some printers have "enhancement" processing that increases the contrast of edges. This can cause the printed squares to have slightly different RGB values. I haven't run into one of these printers yet where the overlapped squares didn't look identical, but your mileage may vary.

4) Of course you could just go to the interactive demo that the creator has up on his site. He shows both the color contrast and brightness contrast illusions, plus a few more that will make you think twice about believing what you see.