Jason
Pluto
May all your hits be crits
Posts: 5,579
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Post by Jason on May 31, 2007 12:05:48 GMT -4
That's pretty neat. Optical illusions don't usually get me, but this one does. Try copying the picture into Paint or something and sampling the colors. You'll see they are in fact the same shade of gray.
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Post by JayUtah on May 31, 2007 12:24:36 GMT -4
No one is immune to unconscious perceptual bias. That's the basis of formal techniques in photographic interpretation. This is why I categorically refuse to accept "common sense" arguments in photographic interpretation and the physics the photographs purport to capture.
There's another optical illusion that catches a lot of people. I don't have it handy in a postable graphics form. But it involves a triangle that's decomposed into two smaller triangles and a rectangle. If you sum the areas of the two smaller triangles and the rectangle, they do not equate to the area of the large triangle they form. I've even had very astute mathematics majors stump themselves over this. The answer is that the "straight" line forming the hypotenuse of the triangle is not straight at all. The outer "triangle" isn't really a triangle and so its area is not the result of the straightforward triangle area formula. The illusion is completed by the figure having been drawn on a grid in order to facilitate measurements. Take away the grid and the hypotenuse is obviously not a single straight line.
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Post by Jason Thompson on May 31, 2007 12:24:47 GMT -4
It's true. I saved the picture, opened it in paint, then cut out the two squares and put them next to each other. They are indeed exactly the same shade of grey.
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Post by scooter on May 31, 2007 12:26:58 GMT -4
I just hole punched two holes in a piece of paper to expose just the two squares...same, though it sure doesn't "look like" they are.
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Post by Joe Durnavich on May 31, 2007 12:27:51 GMT -4
What I think is neat about optical illusions like this is the duality: You can see that:
(1) Square B is the same white shade as the non-shadowed white squares.
Or:
(2) Square B is a white square in shadow. A skilled artist asked to paint this scene would pick the same shade of gray for squares A and B.
Also interesting is the fact that this is how a real checkerboard with a shadow casted across its surface would look in real life, yet we don't find anything odd in that case.
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Post by Joe Durnavich on May 31, 2007 12:33:46 GMT -4
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Post by sts60 on May 31, 2007 13:03:43 GMT -4
Same thing upon inspection with PhotoImpact; the illusion persists even after adjusting the dark squares around B to the same color as A.
I believe it now, but my eyes are still holding out. :-) I've seen similar illusions before, but this is the best one by far.
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Post by BertL on May 31, 2007 13:04:10 GMT -4
2/5 does not equal 3/8.
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Post by JayUtah on May 31, 2007 13:18:24 GMT -4
...though it sure doesn't "look like" they are.
Because you unconsciously remembered what the scene looked like. You took reasonable pains to remove the overt context, but not the latent context you didn't realize existed.
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Post by JayUtah on May 31, 2007 13:20:28 GMT -4
That one is a dirty trick!
It is; and because such dirty tricks crop up all the time in real life, I do not accept arguments based solely on "common sense." Common sense is a euphemism for intuition -- the knee-jerk reaction to subjective perception. Where the answer is instead a matter of computation and investigation, common sense cannot be considered reliable.
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Post by Joe Durnavich on May 31, 2007 16:20:45 GMT -4
I believe it now, but my eyes are still holding out. I've seen similar illusions before, but this is the best one by far.
This feature of perception--yes it is a feature and not a bug--is simultaneous contrast. It one thing that allows you in normal situations to see an object as a constant color even when the illumination changes or a shadow falls across it. Your freshly painted white wall still looks solid white, even though the illumination varies across its surface. (And, yet, you can also see the shadows too.)
As Jay points out, these features which serve us so well in typical situations can get in the way of properly interpreting photographs.
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Post by Count Zero on May 31, 2007 18:56:32 GMT -4
For certain crowds, there is the Cheech and Chong presentation of the problem. Ah, yes. "Let's Make a Dope-Deal": Cheech (as Monty Hall): "Let's see what's behind the door you chose . . . [sound of a siren] It's Officer O'Malley of the FBI! Yoooou'rrre BUSTED!!!" Chong (as contestant): "Aw maaannn!"
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Post by Count Zero on May 31, 2007 19:03:12 GMT -4
Believe it or not, squares A and B are exactly the same shade of grey . . .
That (and the replies) illlustrate something else:
One person posted a photo, made a claim about it, and challenged people to "believe it or not." At least five people came up experiments to test the claim, and posted the results, even when (in some cases) it failed to conform to their own beliefs/expectations.
Have we ever seen this sort of behavior among HBs?
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Post by svector on May 31, 2007 19:34:05 GMT -4
The Gimp reports that A and B are both approximately 47% gray, within a fraction of a percent. This is actually an example of a well-known exercise in contextual perception, one that appears all the time in photographic interpretation textbooks. I imported the image into Corel Photopaint and sampled each area with the eye dropper. Dave's right. Each square showed an RGB value of 120,120,120. My eyes told me they couldn't be the same, but they are. Good one Dave.
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Post by gillianren on May 31, 2007 22:28:11 GMT -4
Have we ever seen this sort of behavior among HBs? Ooo, ooo! I know this one!
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