Within each individual "view-finder" frame below, all of the pixels are the same shade of gray. Frames A, C, and E appear to be a darker gray while frames B and D appear to be lighter. However, based on the actual pixel values only one frame contains a different shade of gray.

Which single frame contains the different pixel value? And what is causing the difference between our perception and the measured pixel values?


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    $\begingroup$ I'm voting to close this question as off-topic because it is not a puzzle but simply an exercise in observation. $\endgroup$ – Rand al'Thor May 18 '15 at 19:04
  • $\begingroup$ I'm ambiguous about this "puzzle". I think it currently appears off-topic, because Len phrased it "non-puzzle-matic". The actual challenge (if just the question is asked) is rather cool - in particular as it is only tagged "visual". Given, it is a very different sort of puzzles as many others, but I think it indeed is a puzzle. You have to look closely, think through and test things to find a solution which is rather surprising and non-obvious. I very, very much like the accepted answer. This will get a "re-open" vote from me. (But Len, maybe you want to re-phrase it?) $\endgroup$ – BmyGuest May 19 '15 at 7:35
  • $\begingroup$ @BmyGuest - I appreciate your constructive feedback. I thought I would try something different and am happy to have received the answers and comments. I have rephrased the question but it is ok if it doesn't get reopened. $\endgroup$ – Len May 19 '15 at 8:24

enter image description here

Look what happens if you hide the frames between two consecutive areas! As you can see, B is the same colour of A and C!

Where is the trick? Of course in the frames! The dark grey rectangles have a slightly darker margin, while the light rectangles have a lighter shade of grey as margin. This generates the illusion that the whole content of the rectangles is different, when it's not!

Ah, and if you want a proof that the margins have different shades of grey, here is it: enter image description here

Small areas near the borders have been translated to show that difference.

As discussed in the comments, the reality is that A, B, D, E are the same shade of gray. The pixel values of C are slightly darker.

Thanks to BmyGuest, this horizontal "line profile" shows the pixel value gradients at the borders.


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  • $\begingroup$ C is actually slightly different from the other four - (168,168,168) vs (171,171,171). $\endgroup$ – Kevin May 18 '15 at 19:42
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    $\begingroup$ I'm not very proficient with color values, but I think that the difference between 168 and 171 is imperceptible. Also, did you measure the colors in the middle of the rectangles? If it was near the borders, the measure could result altered. $\endgroup$ – leoll2 May 18 '15 at 19:47
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    $\begingroup$ Perception of color distance by humans is a tricky subject, but the difference is just barely noticeable in good conditions (ex. good lighting, viewer is up close, colors are directly adjacent). Yes, I measured in the center of each rectangle. I suspect the OP's image has been doctored from its original form because the bottom of the C rectangle extends downwards a few more pixels than the others. $\endgroup$ – Kevin May 18 '15 at 19:50
  • $\begingroup$ I had the values for A, B, D, and E at (157,157,157) and for C at (155,154,155) - all were measured near the center and I moved it around to see if the results were consistent. $\endgroup$ – mdc32 May 18 '15 at 21:10
  • $\begingroup$ A horizontal "line profile" would be very useful to this answer. I've created such an image, but can't upload it right now as the question is currently closed. I've uploaded it here(i.stack.imgur.com/LFyrp.png). $\endgroup$ – BmyGuest May 19 '15 at 7:47

The question has totally changed now, but the answer below was for the original question.


They are all the same.


The gradients between each of the 5 cause your brain to perceive those colors on the darker sides of the gradients to be darker. Thus, A, C, and E look darker.

More cool gradient illusions here

I saw this type of thing on the Netflix show "Brain Games."

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