Jamie's Blog

Tuesday, August 14, 2007

Shadows and Color


In the above picture both the A and the B squares are actually the same color. But because of the way they are drawn, they appear to be different colors. Don't believe they are the same color? Click this link to see a "proof" image.
The illusion is based on a study by Edward H. Adelson, a Professor of Vision Science at MIT. The study is of light perception and the human visual system. Our eyes actually see the correct colors, but our brains reinterpret them based on the surroundings.

I found the entire study fascinating, though his paper was pretty technical. Still worth reading even if like me you don't understand all of it. So check out his paper here: Lightness Perception and Lightness Illusions

And if you want a more simplified explanation of the above picture read this: Why does the illusion work?

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7 Comments:

  • I know this optical illusion just for years and I don't still want to believe it is true. Even with the grey bars aside - they will have scaled the colour. And isn't the contrast around the "A" less than around the "B"?!?
    My brain doesn't want to believe this! How can it be betrayed in such a manner?!
    There are so many optical illusions that aren't a problem for me - but this...

    P.S.: I "know" it is like they explain but...
    O.K., let's drop it.

    By Anonymous Alexander, at August 16, 2007 11:13 AM  

  • Even the one with the gray bars in it confuses your eyes if you look at it too long.

    By Blogger Jamie Barrows, at August 16, 2007 11:17 AM  

  • They simply are not the same color. Anyone who thinks they are would probably also believe in something as stupid as evolution.

    By Blogger Josh, at August 23, 2007 9:05 PM  

  • I'm not sure I understand your comment Josh.
    The colors are the same. You can dissect the image in your favorite image editor if you want. For an explanation of of why your brain "sees" them differently, I encourage you to read the research paper I linked to in the post.

    And what does this image have to do with evolution?

    By Blogger Jamie Barrows, at August 24, 2007 9:55 AM  

  • Aha! Emphatic proof! Open the Image in the GIMP. Use the color picker tool. On Tile A you will see that the tile is CONSISTENTLY Red:120, Green:120, Blue:120 (HEX:787878). Now, repeat on tile B. Tile B is indeed Red:120, Green:120, Blue:120 (HEX:787878) on SOME of its pixels, but also Red:121, Green:121, Blue:121 (HEX:797979) on OTHER of it's pixels. In other words, tile A is consistently the same color, but tile B alternates between that color and other of ever so slight a difference. Because it alternates between HEX:787878 and HEX:797979, Tile B looks different than tile A which is consistently HEX:787878. Tada! Proof! No illusion at all--they ARE different colors.

    By Blogger Josh, at August 25, 2007 2:06 AM  

  • on closer inspection, tile b also sometimes has rgb(119,119,119) or hex 777777. Tile A is still consistently the same color, rgb(120,120,120) or hex 787878.

    By Blogger Josh, at August 25, 2007 2:08 AM  

  • I'm not sure if I understand these "red-green-blue-HEX"s right.
    But on average it seems that the tiles proove to have really the same colour?!?

    Good to know now, that evolution is right!

    :-)

    By Anonymous Alexander, at August 26, 2007 12:25 PM  

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