The Same Color Illusion
Edward H. Adelson, Wikipedia
Explanation: Are square A and B the same color? They are. Are too. To verify this,
click on the
above image to see them connected. The above illusion, called the
same color illusion, illustrates that purely human observations in science may be
ambiguous or inaccurate. Even such a seemingly direct perception as relative color.
Similar illusions exist on the sky, such as the
size of the Moon near the horizon, or
apparent shapes of astronomical objects. The advent of automated,
reproducible, measuring devices such as
CCDs have made science in general and
astronomy in particular less prone to, but not free of,
human-biased illusions.
Sci-Tech-Prod (Science-Technology-Products) Village: 科學技術產品村: 021
Same Color Illusion   
received from Mark Yang
----- Original Message -----
From: "Mark Yang" <>
To: Distribution
Sent: Tuesday, July 31, 2007 5:48 AM
Subject: Re: Fw:

Dear classmates,

This is one of the best optical illusions I have ever seen.

The Same Color Illusion
Same Color Illusion
Same color illusion
From Wikipedia, the free encyclopedia
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The same color illusion — also known as Adelson’s checker shadow illusion,
checker shadow illusion and checker shadow — is an
optical illusion published by
Edward H. Adelson in 1995.[1] The squares A and B on the illusion are of the same
color (or shade), although they seem to be different.

"When interpreted as a 3-dimensional scene, our visual system immediately
estimates a lighting vector and uses this to judge the property of the material."[2]

The left image below shows what appears to be a black and white checker-board
with a green cylinder resting on it that casts a shadow diagonally across the middle
of the board. The black and white squares are actually different shades of gray. The
image has been constructed so that "white" squares in the shadow, one of which is
labeled "B," are actually the exact same gray value as "black" squares outside the
shadow, one of which is labeled "A." The two squares A and B appear very different
as a result of the illusion. A second version of the same picture includes a
rectangular bridge connecting square A and B to show the are the same shade of

Second example
As a further example, the two "A"s in the animated image on the right are both the
same color and do not change. The shadow is removed in two frames, and the
colors of the chess board are reversed.

See also
Chubb illusion
Lilac chaser

^ Adelson, Edward H. (2005).
Checkershadow Illusion. Retrieved on 2007-04-21.
^ Retrieved on 2006-06-10.

External links
Explanation of the effect
Illusion of colours
Email from Mark Yang
Email from Shing Lin
Email from Mark Yang
----- Original Message -----
To: ;
Cc: Distribution
Sent: Tuesday, July 31, 2007 11:48 AM
Subject: (no subject)

Interesting stuff.  Image is image, it is the interpretation that counts.  Our eye is just
a kind of optical instrument, good but not perfect.  For example, the image hits on
retina, it is upside down, but our brain interprets right side up due to million years of
evolution.  The shade compensation is another trait that we adapt after the birth. The
checkered board pattern is the one that most likely to throw our interpretation off
base, especially in the adjacent corner or line.  Brain is the intrument to do the
compensation.  Most of them are due to evolution.  But some are not, it is called
"brain wash".  I am sure you have seen some painting with some random dot
pattern in your local shopping mall.  You think it is just a kind of modern art.  But
some one passes by and say it is "1234" on the painting.  This is another type of
optical illusion.  The trick is the focus of your eye.  I used to work on the printers and
some engineers often printed out some weird pattern that turns out to be something
with substance.  It is possible to create a dot pattern that contains multiple layers of
information.  You just have to adjust the focus of your eyes.  Since you have two
eyes, if you can adjust the focus in different depth for different eyes, now you turn the
2-dimensioned image into 3-dimensioned one with all bunch of interesting
variations.  Statistically, we may be able to work out some kind of formula that
calculates the max info we can get from this kind of print.  Since Mark Young is a
professor of statistics, he might be able to work out something meaningful.

ps1:  Current DVD has multiple layers of image.  With multple laser heads, we can
have all kind of final images we like to show on the screen.  What this really means
is that the image or data is there, but only the interpretation counts for the final result.

ps2:  Since different people interpret things differently even they see the same thing.
 No wonder our world is a mess.
----- Original Message -----
From: mark yang
To: ; ;
Cc: Distribution
Sent: Tuesday, July 31, 2007 2:37 PM
Subject: Re: Illusion


I am glad that you like that optic illusion. The best effect is to print two copies of that picture, cut the A, B squares from one and compare their hue levels. They are exact the

I enjoy your explanation. I have seen many those 3-D pictures. To a deeper level, some philosopher (also many physicists) says that the world exists only in our mind. There
is no real world without measurement. The nice thing about this is that the whole universe is created for me (and by me and of me), when I am gone the universe is gone.
Nobody can prove that this is incorrect to any individual. This is one thing we can discuss during the cruise. Amo cannot yell at our ignorance, because his idol Feyman said
"Nobody understands quantum mechanics."

To your comment on why the world is a mess: One reason is that in past (also now?)  there were not enough resources to feed all the people. As you said we were evolved
as survivors. It is surprising that nature demonstrates it is more efficient to rob than to till, if the robbers can get away with their action. We all realize this. So you see, even
the most civilized country becomes a robber if not checked. You talked about the peaceful life of the Norwegians we are going to see. Remember, these were pirates not
long ago. Again, we can argue during the cruise.

Click to go to companion website: