[tig] This is very grey to me...

Robert Lund robert.lund
Fri Apr 23 00:28:20 BST 2004

jeffh wrote:

>Some of you may have seen this before, or other things
>like it; I just found this yesterday.  Look at box A, and 
>then box B.  They look like they are different shades?.
>but in fact they are not - they are identical. 
>So, my question is: why?  Why do both boxes appear 
>different when they are in fact the same?  What is making 
>my brain perceive the boxes as different ? and better yet: 
>how do I get my brain to stop doing that!?!??  <cough>  
>It is not the prescence of the letters ?A? and ?B? ? if I crop 
>each box, and paste both into a new image, they now look 
>the same, thus proving that the letters are not causing the 
>boxes to appear different in the original image. Nor is it the 
>prescence of the cylinder ? removing it, or altering it?s color 
>does not change anything.  Therefore, I am figuring it is not 
>the boxes themselves, but the SURROUNDING boxes ? but 
>what gives?  Why would the shade of any of the surrounding 
>boxes affect how others are perceived?
I've seen this before - and I was still startled and found it 
unbelievable that A & B were the same - but my Mac's Digital Color Meter 
utility revealed them both to be at level 107! The dark squares around 
B, which should be the same as A, are down at level 50, but that 
difference isn't so perceptible.

I think the effect is due to the shadow of the cylinder. Your brain 
"knows" the checkerboard is uniform, and applies a subconscious gradient 
to compensate for the darkening effect of the shadow, making squares A & 
B appear different.


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