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Grey square illusion

Posted: Tue Dec 17, 2013 4:13 pm
by SamKR
In this image do you think the the squares A and B are of different shades of grey (is the square B is lighter than the square A) ?
Or, are A and B of the same shade?

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:28 pm
by Babadhari
well i put my thumb between them and they appear to be the same shade.
like most things , the apparrent difference between them is an illusion

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:28 pm
by SamKR

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:32 pm
by Babadhari
the original one i saw had two grey cubes stacked upon each other, :jumping:

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:36 pm
by kmath
Wow that is insane!

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:39 pm
by purple planet
cool stuff

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:40 pm
by daverupa
Why does the illusion work?

The visual system needs to determine the color of objects in the world. In this case the problem is to determine the gray shade of the checks on the floor. Just measuring the light coming from a surface (the luminance) is not enough: a cast shadow will dim a surface, so that a white surface in shadow may be reflecting less light than a black surface in full light. The visual system uses several tricks to determine where the shadows are and how to compensate for them, in order to determine the shade of gray "paint" that belongs to the surface.

The first trick is based on local contrast. In shadow or not, a check that is lighter than its neighboring checks is probably lighter than average, and vice versa. In the figure, the light check in shadow is surrounded by darker checks. Thus, even though the check is physically dark, it is light when compared to its neighbors. The dark checks outside the shadow, conversely, are surrounded by lighter checks, so they look dark by comparison.

A second trick is based on the fact that shadows often have soft edges, while paint boundaries (like the checks) often have sharp edges. The visual system tends to ignore gradual changes in light level, so that it can determine the color of the surfaces without being misled by shadows. In this figure, the shadow looks like a shadow, both because it is fuzzy and because the shadow casting object is visible.

The "paintness" of the checks is aided by the form of the "X-junctions" formed by 4 abutting checks. This type of junction is usually a signal that all the edges should be interpreted as changes in surface color rather than in terms of shadows or lighting.

As with many so-called illusions, this effect really demonstrates the success rather than the failure of the visual system. The visual system is not very good at being a physical light meter, but that is not its purpose. The important task is to break the image information down into meaningful components, and thereby perceive the nature of the objects in view.

source

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:45 pm
by SamKR
SamKR wrote:In this image do you think the the squares A and B are of different shades of grey (is the square B is lighter than the square A) ?
Or, are A and B of the same shade?
In my opinion the square A and B have different shades in the image (of the first post). My question to those who think they are of the same shade, why do you think that is the case?
:stirthepot:

Re: Grey square illusion

Posted: Tue Dec 17, 2013 4:54 pm
by kmath
SamKR wrote:
SamKR wrote:In this image do you think the the squares A and B are of different shades of grey (is the square B is lighter than the square A) ?
Or, are A and B of the same shade?
In my opinion the square A and B have different shades in the image (of the first post). My question to those who think they are of the same shade, why do you think that is the case?
:stirthepot:
They are the same shade. Cover up all the other squares and you'll see.

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:02 pm
by SamKR
daverupa wrote:Why does the illusion work?
...
source
kmath wrote:
SamKr wrote:In my opinion the square A and B have different shades in the image (of the first post). My question to those who think they are of the same shade, why do you think that is the case?
:stirthepot:
They are the same shade. Cover up all the other squares and you'll see.
I think that to say the squares are of the same shade (as an objective reality), is a bigger and more significant illusion.
And, why does this bigger illusion work? Because of not giving attention to the things as they really are (or as they arise, or as they are experienced) but to give attention to a conceived "objective reality". I wonder if you agree.

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:14 pm
by kmath
SamKR wrote: I think that to say the squares are of the same shade (as an objective reality), is a bigger and more significant illusion. And, why does this bigger illusion work? Because of not giving attention to the things as they really are but to give attention to a conceived "objective reality". I wonder if you agree.
I disagree completely. You are not giving attention to things as they are in this case. You're giving attention to things as they seem. With a bit of investigation, you see things as they are.

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:15 pm
by kmath
SamKR wrote: I think that to say the squares are of the same shade (as an objective reality), is a bigger and more significant illusion. And, why does this bigger illusion work? Because of not giving attention to the things as they really are but to give attention to a conceived "objective reality". I wonder if you agree.
I disagree completely. You are not giving attention to things as they are in this case. You're giving attention to things as they seem. With a bit of investigation, you see things as they are.

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:21 pm
by SamKR
kmath wrote:
SamKR wrote: I think that to say the squares are of the same shade (as an objective reality), is a bigger and more significant illusion. And, why does this bigger illusion work? Because of not giving attention to the things as they really are but to give attention to a conceived "objective reality". I wonder if you agree.
I disagree completely. You are not giving attention to things as they are in this case. You're giving attention to things as they seem. With a bit of investigation, you see things as they are.
What kind of investigation would change the vivid experience of seeing different shades to anything else? How the things really could be other than the direct experience?

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:36 pm
by Mkoll
For more visual trickery, see this TED talk by Beau Lotto:

http://www.youtube.com/watch?v=mf5otGNbkuc

PS

I don't think arguing about this gets anywhere but to a mind of ill will and delusion...

Re: Grey square illusion

Posted: Tue Dec 17, 2013 5:53 pm
by SDC
Madness!!!!!