This image was previously a featured picture, but community consensus determined that it no longer meets our featured-picture criteria. If you have a high-quality image that you believe meets the criteria, be sure to upload it, using the proper free-license tag, then add it to a relevant article and nominate it.

• This image has been superseded by Image:Grey square optical illusion.PNG.

This image was selected as picture of the day on the English Wikipedia for November 5, 2004, February 19, 2005, and December 16, 2005.

File:Checker shadow illusion.svg is a vector version of this file. It should be used in place of this JPG file when not inferior. File:Optical.greysquares.arp.jpg → File:Checker shadow illusion.svg For more information, see Help:SVG. In other languages Alemannisch ∙ العربية ∙ беларуская (тарашкевіца) ∙ български ∙ বাংলা ∙ català ∙ нохчийн ∙ čeština ∙ dansk ∙ Deutsch ∙ Ελληνικά ∙ English ∙ British English ∙ Esperanto ∙ español ∙ eesti ∙ euskara ∙ فارسی ∙ suomi ∙ français ∙ Frysk ∙ galego ∙ Alemannisch ∙ עברית ∙ hrvatski ∙ magyar ∙ հայերեն ∙ Bahasa Indonesia ∙ Ido ∙ italiano ∙ 日本語 ∙ ქართული ∙ 한국어 ∙ lietuvių ∙ македонски ∙ മലയാളം ∙ Bahasa Melayu ∙ norsk bokmål ∙ Plattdüütsch ∙ Nederlands ∙ norsk nynorsk ∙ norsk ∙ occitan ∙ polski ∙ português ∙ português do Brasil ∙ română ∙ русский ∙ sicilianu ∙ Scots ∙ slovenčina ∙ slovenščina ∙ српски / srpski ∙ svenska ∙ தமிழ் ∙ ไทย ∙ Türkçe ∙ татарча / tatarça ∙ українська ∙ vèneto ∙ Tiếng Việt ∙ 中文 ∙ 中文（中国大陆） ∙ 中文（简体） ∙ 中文（繁體） ∙ 中文（马来西亚） ∙ 中文（新加坡） ∙ 中文（臺灣） ∙ +/−

 

Prepared for Wikipedia by Adrian Pingstone in January 2004, based on the original archive copy at the Wayback Machine 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.

The copyright holder of this work allows anyone to use it for any purpose including unrestricted redistribution, commercial use, and modification. Please check the source to verify that this is correct. In particular, note that publication on the Internet, like publication by any other means, does not in itself imply permission to redistribute. Files without valid permission should be tagged with {{subst:npd}}. Usage notes: If the work requires attribution, use {{Attribution}} instead. If this is your own work, please use {{Cc-zero}} instead. Copyrighted free useCopyrighted free usefalsefalse

"©1995, Edward H. Adelson. These checkershadow images may be reproduced and distributed freely."

http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html archive copy at the Wayback Machine

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