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.

READ MORE - Color Contrast Optical Illusion

Photograph Optical Illusions

There are many ways to create an optical illusion. Digitally manipulating a photograph using software such as Photoshop or Gimp creates convincing images, but like special effects in the movies you know they are fake.

There are ways to setup true photographic optical illusions without altering or "faking" the image. Take the following actual photo as an example.


Chess Anyone?
(c)2002
Tim Jensen
Used w/permission

This modern photograph is reminiscent of Sandro Del Prete's famous illusion drawing "Impossible Chess Set" below.


Impossible Chess Set
Sandro Del Prete
(c) 1975


So how do you think the photo "Chess Anyone?" was accomplished?

One key to photographic illusions is the fact that photos are 2 dimensional images of 3 dimensional objects. This means most photo illusions would fall apart if you saw them first hand. If you wish to see the Chess Anyone illusion from an angle that will reveal how it was accomplished place your mouse over the below reveal screen.


Chess Anyone? Revealed
(c)2002
Tim Jensen
Used w/permission

For a complete tutorial on how this photographic optical illusion was done read Tim Jensen's explanation here.

READ MORE - Photograph Optical Illusions

Muller-Lyer Optical Illusion

The Muller-Lyer illusion is a size constancy illusion. In this illusion, the red and the blue lines below are the same length, but due to the effects of the arrows the red line appears longer.


The red and blues lines are both 170 pixels long


The illusion has been well studied since it was described by German psychiatrist Franz Carl Muller-Lyer in 1889. However, there is no certain explanation for the apparent difference in the perception of the lengths.


Muller-Lyer
1889

Muller-Lyer attempted to explain the illusion he had discovered as follows: "the judgment not only takes the lines themselves, but also, unintentionally, some part of the space on either side."

One of the better explanations I've read comes in the form of a PDF file from Catherine Q. Howe and Dale Purves of the Center for Cognitive Neuroscience, Duke University.

Below is an amazingly strong illusion that combines both the Ponzo and Muller-Lyer optical illusions.


Source
The two red vertical lines are the same length.
Placing your pointer over the image will aid you in exposing this illusion.

In the tickets image above the perspective of distance lends itself to the Ponzo optical illusion, the angles at the end of each line add to this the Muller-Lyer illusion, combined they create a very effective optical illusion.


Project: Create your own illusion. See how the following variations might effect the relative strength of this illusion.

Does changing the color of the background change the effect?
Does changing the color of the arrows change the effect?
Try changing the color of the equal lines,
is there any combination of colors that is stronger then the others?
Try fat lines. Try skinny lines. Does the thickness of the lines affect this illusion?
Does the distance from which you view the illusion change the illusion?

What can you conclude, if anything, about how we perceive things from this project?

READ MORE - Muller-Lyer Optical Illusion

Ambiguous Rabbit or Duck Optical Illusion

There is a whole section of illusions that are ambiguous. This means that the image is open to more than one interpretation.

One of the oldest ambiguous figures is the "Duck or Rabbit" This illusion first appeared in the October 23rd issue of Fliegende Blatter (a German humor magazine) in 1892. source.


The interesting thing about this illusion is that it is frequently credited to Joseph Jastrow 1899. Joseph Jastrow is an American psychologist who was the first to note this image in his work. He used the duck-rabbit figure to make the point that perception is not just a product of the stimulus, but also of mental activity – that we see with the mind as well as the eye - source.

Jastrow's Cartoon (1899)

The truth though is that while Jastrow used his image in 1899 it had appeared in print at least twice before both times in 1892.

Jastrow's 1899 cartoon version was based on one originally published in Harper’s Weekly (November 19, 1892, p. 1114). The Harper's cartoon, in turn, was based on the original in Fliegende Blatter.

Below is a new version of this old favorite...

The photographer found this version during a visit to the Ripley's Believe It or Not! museum in Branson, Missouri.

What do you see a duck (looking left) or a rabbit (looking right). If you slide your mouse over the image the photo will rotate giving you a slightly differ perspective.


Flickr Artist: Dropped_Stitch


So what did you see in this image a duck or a rabbit? Which version above is most effective for you?

There are an endless variety of this type of illusion. What other ambiguous optical illusions have you seen?

READ MORE - Ambiguous Rabbit or Duck Optical Illusion

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.

READ MORE - Watercolor Optical Illusion

Ponzo Optical Illusion

The Ponzo illusion is an optical illusion that was first demonstrated by the Italian psychologist Mario Ponzo (1882-1960) in 1913. He suggested that the human mind judges an object's size based on its background.

The typical example of this is the figure below. This is the typical railroad track scheme usually used to represent this illusion. The vertical lines appear to go off into the distance like train tracks. This gives us the impression that the line in the distance is larger then the line that appears to be nearer to the viewer.

Mario Ponzo
1913

Seeing this illusion against a great real photo backdrop can be amazing. Most of the time people pick train tracks. Below is an outstanding photo that presents this optical illusion slightly different...

The two red lines (or three if you move your mouse over the image) below are duplicates, they are the exact same size. Which image is more convincing the one with two lines or the one with three lines?

Ponzo Illusion
(c) 2012 Walt Anthony

Project: Create your own illusion. Here is a suitable image of train tracks (right click and select "save target as" or "save link as" depending on your browser). You can use Windows Picture and Fax viewer to print it out.

Now that you have it printed try and create your own illusion.

Use 2 Popsicle sticks painted red or just draw red lines with a marker.
Does changing the color change the effect?
Does using two different colors alter the illusion?
Try fat and skinny lines. Does the thickness of the lines affect this illusion?
Vary the distance between the lines, does this change the effect?
Is a three dimensional Popsicle stick as effective as 2 dimensional red line?
Does the distance from which you view the illusion change the illusion?

What can you conclude, if anything, about how we perceive things from this project?

READ MORE - Ponzo Optical Illusion

Hering Optical Illusion

This optical illusion was discovered by the German physiologist Ewald Hering in 1861. The two blue lines are both straight and parallel to each other. If you are like most folks you may see things differently. The lines in fact may look as if they are bowed outward.


Ewald Hering
1861

The distortion is produced by the lined pattern on the background, that simulates a perspective design, and creates a false impression of depth. If you pass your mouse over the image the background lines will be removed and you can see for yourself that the blues lines are definitely straight.

Project: Create your own illusion. Select a sheet of paper and place a dot in the center of the sheet. Now draw 10 lines through the center, mimicking as close as you can the background of the above illusion. Now on a sheet of clear document protector draw your two vertical lines.

Increase the amount of background lines to 18. Does that affect the illusion?
Does changing the color of the background change the effect?
Does changing the color of the background lines change the effect?
Does using two different colors for the vertical lines alter the illusion?
Try fat lines. Try skinny lines. Does the thickness of the lines affect this illusion?
Vary the distance between the vertical lines, does this change the effect?
Does the distance from which you view the illusion change the illusion?

What can you conclude, if anything, about how we perceive things from this project?

READ MORE - Hering Optical Illusion

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.

READ MORE - Checker Shadow Optical Illusion