Image:Grey square optical illusion.PNG

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Feast your eyes on the A and B squares and then cover up all the other squares and see what you find =)

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Prepared for Wikipedia by Adrian Pingstone in January 2004, based on the original created by Edward H. Adelson. See also same color.

This is possibly one of the most uncanny optical illusions in existence. No matter how hard you look, you may not be able to convince yourself that the two squares are the identical shade of grey. To check, try one of these methods:

  1. Right click the large picture, save it to your hard drive, put it into your image editor, "select" square A and then pull it down onto square B. There will be an exact match in colour! An example of this proof can be seen at de:Bild:Optical greysquares proof.png
  2. The presentation of this illusion here is linked to an animated GIF that demonstrates the color match. That animation demonstrates that B is also an exact match to the two "dark" squares straddling the corners closest to and farthest from the viewer (A is one of the latter two). Furthermore, it makes it clear that none of the "light" colored squares matches B (though the one diagonally touching B to the left comes close).
  3. As above but use the Color Sampler Tool or whatever means you have of sampling the RGB values of a point on the picture. Both squares produce the same RGB values. JPEG artifacts may cause slight variation.
  4. There is also a Flash animation of this illusion here.
  5. Another animation in WMV, AVI_DIVX, SWF (flash) formats, and EXE file are available to download from this page
  6. Right click the picture, choose Print, then cut out square A and position it on square B.
  7. Easiest of all, get a piece of paper and cut windows in it so that only squares A and B are showing through!
  8. Perhaps even easier than the above, if you place your finger covering the two to three squares that separate A and B, it can clearly be seen that they are the same color. In other words, forcefully ignoring the borders between the squares.
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"©1995, Edward H. Adelson. These checkershadow images may be reproduced and distributed freely."

http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html

Explanations and other animated examples of "lightness perception and lightness illusions" can be found in a paper by Adelson.

See also its APOD page

File history

Click on a date/time to view the file as it appeared at that time.

Date/TimeDimensionsUserComment
current21:13, 13 January 20081,087×844 (159 KB)Mahahahaneapneap (pngcrushed)
03:54, 24 April 20071,087×844 (214 KB)Jrockley (much larger version)
00:41, 9 April 2007522×408 (70 KB)Jrockley (Prepared for Wikipedia by Adrian Pingstone in January 2004, based on the [http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html original] created by Edward H. Adelson. See also [http://en.wikipedia.org/wiki/Same_color)