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)2007

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.

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Watercolor Optical Illusion

This is an example of the watercolor effect. This effect was first demonstrated by Baingio Pinna in 1987.

Simply put The watercolor effect is perceived when a dark (e.g., purple) contour is flanked by a lighter chromatic contour (e.g., orange). Under these conditions, the lighter color will assimilate over the entire enclosed area.

What does that mean? Take a look at the below image. You see 9 distinct squares. The center of each square looks white but the outer area of each square has taken on a watercolor shade, pink, green, yellow, blue etc...

Tic-Tac-Toe Board
(c)Walt Anthony
Created from samples
provided by Akiyoshi Kitaoka

The truth is that aside from the squiggly lines the only color here is white. The outer ring and the inner square are pure white.

Prove It: You can prove this by using the eye dropper tool in either of the following free graphics programs Paint.Net or Gimp or you can use the eye dropper tool in the free Colorzilla extension for Firefox browser. When you use these tools you will find that RGB value of everywhere on this image that is not a squiggly line is R:255 G:255 B:255 or #FFFFFF.

Print out this image and slide it into a plastic document protector. Now use an earasable marker and you have a reusable optical illusion Tic-Tac-Toe board.

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Checker Shadow Optical Illusion

This is the Checker Shadow Optical Illusion. It was developed by Edward H. Adelson of the Perceptual Science Group at MIT. The interesting thing about the below optical illusion is that square A is the exact same shade of gray as square B.

One way to identify a color is by it's Red, Green, Blue values or RGB for short. When written for 24 bit truecolor R:0 G:0 B:0 is black and at the other end of the spectrum R:255 G:255 B:255 is white. The other 16 million or so colors fall somewhere in between. Squares A and B below each have the same RGB value of R:120 G:120 B:120.

So now that I said it is true you have all obviously accepted the fact that square A and square B are indeed the exact same shade of gray, right? I mean if it is on the internet it must be true. Would it be easier if you could prove it to yourself and any skeptics you might run into (like Mom and Dad or that annoying sibling). Continue on and we'll get around to proving my statements correct.

Project: Proving square "A" is the same shade of gray as square "B".

There are a few ways you can prove that the 2 squares are the same shade.

Before we continue, right click on the image and open it in a new window. Now you have a giant 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 grays in both square A and square B are 120-120-120.
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 two 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 squares.

This is another way to isolate the patches from their surrounding context. Cut out each square along the edges. Remove them. Hold them side by side. Overlap the cut out
squares. Yup they're the same shade of gray. 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 values of gray. I haven't run into one of these printers yet where the overlapped squares didn't look identical, but your mileage may vary.

WHY you ask? You might have come to terms with the fact that the two squares are the same shade of gray, but how does this optical illusion work? The creator of the illusion has an explanation here.

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