Talk:Checker shadow illusion

Physics Stub‑class

This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics articles Stub This article has been rated as Stub-class on Wikipedia's content assessment scale. ??? This article has not yet received a rating on the project's importance scale.

This article definitely needs a different picture, in the one showing at the moment square A is obviously darker than square B. —Preceding unsigned comment added by 129.240.146.29 (talk) 13:28, 7 December 2009 (UTC)[reply]

Sigh. -- 98.108.219.226 (talk) 05:49, 24 February 2010 (UTC)[reply]

Maybe I didn't get the whole thing, but are those squares really supposed to have the same color? Because any 'pick color' tool will tell you this is nothing but a joke: there's a gradient from #b9b9b9 to #6c6c6c between those 2 squares.

Are YOU joking? It's #787878 all the way. What image are you looking at exactly? This one [1] from A to B? It's #78. Try moving your hands on either side of the "gradient", and you'll see it. Herd of Swine 03:23, 14 June 2007 (UTC)[reply]

Sorry. I was using a modified pick color tool with average sample over a 20px radius. It obviously didnt show the right pixel values. Shall I delete what I said?

No, others might make the same mistake. It really does LOOK like there is a gradient, and it's hard to believe it's not. Herd of Swine 22:15, 15 June 2007 (UTC)[reply]

At the size in the article, it looks like there's a gradient, but this becomes less apparent the further in you zoom. When the bridged A-B shape is about 15mm tall, it almost appears to be the solid grey it is. I zoomed the full-size image to 400% on a 1280*1024 17" 4:3 monitor. boffy_b (talk) 11:19, 15 March 2008 (UTC)[reply]

I put it to you that when you think you are sampling square B and getting the #787878 reading you are in fact sampling the shadow cast over the square, not the square itself - or at least a combination of the two. The shadow is a distinct entity, not to be confused with the square. It comes and goes according to the light source and that green thing. The real illusion here is in seeing your colour picker as perfectly objective.
Andrew van der Merwe, calligrapher, --Beachscriber (talk) 19:36, 6 October 2009 (UTC)[reply]

It helps if you just put your fingers on boths sides of the "bridge" if you look on the proof picture, then it's immediately obvious. It's a pretty cool illusion. :) Altairantares (talk) 02:24, 10 November 2009 (UTC)[reply]

There is no "square itself", there are merely pixels -- and people misperceive the relationships between the colors of those pixels. And that (properly working) color pickers are perfectly objective about the color of pixels is no illusion. -- 98.108.219.226 (talk) 08:16, 24 February 2010 (UTC)[reply]

I think this page should be titled Same color illusion. NickelShoe 14:57, 16 December 2005 (UTC)[reply]

• I agree with you. --StevenL 04:00, 5 January 2006 (UTC)[reply]
  • Guys, everybody else in the world calls this the checker shadow illusion. There are many, many other brightness illusions that also result in two patches appearing to be different colors, when in fact they are the same; thus, the name "Same color illusion" is hardly descriptive. 128.197.81.69 15:00, 28 March 2007 (UTC)[reply]
    • Can I point out that the actual letter B is darker than the letter A, lending to the illusion of the patch difference?
      • You're wrong and it's off topic. -- 98.108.219.226 (talk) 05:53, 24 February 2010 (UTC)[reply]
    • So why was this incorrectly moved? -- 98.108.219.226 (talk) 05:53, 24 February 2010 (UTC)[reply]

If I squint, and cover the green cylinder with my hand, I can see the identity! Try it! DS 14:55, 21 January 2006 (UTC)[reply]

You are a liar, sir. They are not the same color. This might work in a real-life example, but the picture is a mock-up to show the effect. —Preceding unsigned comment added by 138.163.0.43 (talk) 18:46, 15 January 2008 (UTC)[reply]

It works to me. I don't have to squint deliberately as I have a slight squint anyway, but if I put my finger between squares A and B they appear the same colour to me. Wouldnt that be the best way to invite people to test it?130.88.123.189 (talk) 12:04, 20 April 2009 (UTC)[reply]

Sigh. It's not a mock-up, they are the same color. -- 98.108.219.226 (talk) 05:54, 24 February 2010 (UTC)[reply]

There used to be links to Flash files and other animations that show the truth of the same-colorness much better than the animated gif does. Where did those links go??? 70.20.147.17 12:33, 7 August 2006 (UTC)[reply]

It seems like most other optical illusions stubs are classified as psychology stubs. Is there any particular reason why this one is called an optics stub instead? Stebbins 06:59, 8 November 2006 (UTC)[reply]

Wouldn't joining squares A and B with line of the same color (in the green cylinder image) make the simmilarity more obvious ? I mean something like this---- Xil/talk 17:01, 7 May 2007 (UTC)[reply]

Yes, i agree, your image does make the similarity more obvious Rombust 09:20, 14 June 2007 (UTC)[reply]

Not entirely - To me it looks like the current bridge of the "same color" is actually a gradient of shades, lighter on one end than on the other. (Certainly I believe you that the bridge is just one color - There just isn't that "aha!" moment where I can see for myself it is.) -- 128.104.112.147 (talk) 14:36, 2 June 2008 (UTC)[reply]

(Should have clicked on Xil's link instead of assuming it was the same as the current image ([2])) To me, the wider band of Xil's image does a better job than the narrow one currently used. -- 128.104.112.147 (talk) 14:41, 2 June 2008 (UTC)[reply]

Best way to do is to use paint take the sample color tool and a make solid square with it. When u move the square between the 2 the shade changes. It wired i get he same effect by putting that same color square on one and a 2nd one on the opposite side and they will appear different.Kirbyroth (talk) 18:43, 5 November 2008 (UTC)[reply]

I feel that the animated gif on this article is not helpful at all. For one thing it animates way too fast, and it changes so much that it doesn't prove the illusion in my own personal opinion. Oh and what's that circle thing that comes into view on the far right on a few frames!?

When the article says the squares are the same color, it is making the same mistake it is trying to educate readers about.

It is only the physical parallelogram-shaped regions in the image that are the same color. There are no actual squares in the image.

The squares are in the perceived scene. Since the image has shading representing a cylinder and its shadow, you can't say that the squares are not the same color. —Preceding unsigned comment added by 216.1.16.126 (talk) 23:18, 3 February 2009 (UTC)[reply]

That's pointlessly pedantic -- and incorrect. This article is not about 2D representations of 3D objects. -- 98.108.219.226 (talk) 05:58, 24 February 2010 (UTC)[reply]

It seems to me that this article is missing something rather important. Does anyone know if this illusion has been explained and, if so, what the explanation is? This is what I came here to find. —Preceding unsigned comment added by 86.142.90.162 (talk) 12:19, 4 October 2009 (UTC)[reply]

I just noticed the "Explanation of the effect" reference but it still seems that some of the information from the reference should be added to the article. —Preceding unsigned comment added by 86.142.90.162 (talk) 12:23, 4 October 2009 (UTC)[reply]

This is not an optical illusion but an error of logic - an equivocation to be precise. The human eye makes no mistake here whatsoever. The squares are not the same colour and they are not "mistaken" to be different. It's all quite silly really. Obviously, any object, whatever its colour, is affected by its lighting conditions. The lighting conditions do not change its colour any more than an absence of light would make it black! We see and remember objects under different lighting conditions and are thus able to judge their colour more objectively. By objectively, I mean that we are usually able to judge, with reasonable accuracy, their colour, regardless of how they are lit at any particular time.

Observe that, apart from the light source, there are in fact 3 objects at play here, not just the As and Bs. We have A, B, and that green thing. The shadow is part of the green thing, not part of B. If you take the green thing away the shadow goes with it and, walla! - you will notice that your eye was right all along. (See my comment under Bad Joke)

The equivocation sneaks in where one switches between referring to the colour of the object and the colour per se, that is, between the colour and a colour. The squares represent themselves, while the grey strip running from A to B represents a colour. Obviously a colour can be the same across the differently coloured objects. How else would the off-white object B show shade? The equivocation is more easily fallen into if you have reductionist inclinations and Adelson was probably a typical scientist in this regard, tending to forget the object and its context, while considering only its parts. ;-)

The Wikipedia Optical Illusion entry is full of this reductionist, Cartesian, ghost-in-the-machine nonsense. It is quite astounding in its archaic quality: "An optical illusion (also called a visual illusion) is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a percept that does not tally with a physical measurement of the stimulus source." So, the "objective reality" is presumed to be only what can be measured by some instrument. The exact opposite is true: humans can perceive correctly where instruments are usually fooled. Any instrument measuring the squares in this diagram would be fooled into thinking that A and B were the same colour, because, like the typical scientist who uses it, it is, shall we say, not inclined to distinguish between the colour of the object and the colour per se, i.e. the colour and a colour. Not so, an ordinary human being with a good pair of eyes.

If I had to concede anything here, it would have to be the power of the diagram. It shows how wrong we can be about a colour when we attempt to imagine it outside of its context. We are more likely to get a colour wrong than we are likely to get the colour of an object wrong. Of course, this is less of a problem for an experienced artist who will easily be able to mix an appropriate colour for the object's context. This lesson was learned a long time ago and there are even miniatures in Gothic manuscripts from the "naive" 1400's which show some sense of shading.

- Andrew van der Merwe, calligrapher --Beachscriber (talk) 05:18, 7 October 2009 (UTC)[reply]

Umm, sorry, but you don't get it. It's the same color, same shade, same everything. As I said above try blocking everything but the two squares and it's immediately obvious that it's true. Altairantares (talk) 02:26, 10 November 2009 (UTC)[reply]

"If I had to concede anything here, it would have to be the power of the diagram. It shows how wrong we can be about a colour when we attempt to imagine it outside of its context." -- in which you have "conceded" everything, as this article, and the illusion, is all about "the diagram" and people's mistaken perception of it -- there are no objects here! -- 98.108.219.226 (talk) 08:11, 24 February 2010 (UTC)[reply]

What you are saying about the colour in question is already obvious to me. I'm sorry I didn't make that clearer. Let me state it outright:
1.) the colour is the same,
2.) but the squares in question are not the same colour,
3.) and this is not a contradiction. There is therefore no optical illusion.

1 and 2 are demonstrable, even obvious. 1 can be demonstrated by blocking out other parts of the scene or by using a colour picker. 2 can be demonstrated by removing the green thing, and thus the shadow. As for 3, in order to see why it is not a contradiction, you have to first see the equivocation.

Read the Wikipedia entry on equivocation [3] and then ask yourself what you are referring to by the word "it" in "It's the same colour." Are you referring to the objects or are you referring to the shadow? Or are you referring to the colour independently of either (the colour per se / that colour as it may be applied to any object / that colour as it may be measured by a colour picker)? Are you able to make the distinction between the colour of an object and the colour per se (in and of itself)? The distinction is there to be made and as long as you do not make it, you will equivocate, and ironically, try to avoid a contradiction which is not there by doing things like "blocking out everything but the two squares".

Ask yourself, are the whitish square and the shadow distinct entities or not? Once you have answered that question, ask yourself what colour is the shadow and what colour is the square? (I'm hoping you will see that you can't rely on your colour picker or blocking out of things for this.) You might also ask yourself if the square can be a different colour because of the shadow? The answer is no. It may be painted grey to represent the presence of the shadow on it's surface but it cannot suddenly be grey itself - no more than it can be black because of an absence of light.

The whitish square and the shadow are distinct entities which a colour picker cannot distinguish between. You, and others here, are able, but refuse to make the distinction, and I suspect it is because you fear the contradiction. If you make the distinction you will have to admit that the whitish square and the shadow are different colours and will have to deal with the fact that your colour picker tells you otherwise. This is a problem, because for some reason you trust your colour picker more than your eye! What you don't realise is that your eye and your colour picker are measuring different things. The eye sees through the shadow and correctly assesses the colour of the square as whitish. The colour picker has a sharp eye, but no brain, so it measures pixels but cannot see the squares and cannot therefore give you the colour of any square.

In fact, the whitish square in shade and the shadow cast over it would have to be different colours in order for the whitish square to be measured the same by a colour picker. That whitish square has to be whitish in order to end up measuring grey #787878 in the shade. If the whitish square in shade was actually grey #787878, the shadow would not leave it grey #787878. It would be measured darker.

As for suggesting that I try "blocking everything but the two squares": its like I saw how you did your card trick, but now you want me to close my eyes so I can be fooled the next time! Sure, this will demonstrate to me what is already obvious: that the colour per se is the same ( I am an artist and would have mixed more or less the same colour in order to achieve the effect of the shadow), but it will not fool me into thinking that the squares in question are the same colour. If you had done all that blocking out before I had seen the whole scene, then sure I might have been fooled, but only because the colour per se happened to be the same and I would have had no visual cues to read what was being presented to me any differently.

The upshot of all this is that the failure to make the distinction between the colour of the squares and colour per se leaves you thinking you have an illusion. The real illusion here is of having an illusion!

I don't know if I can make this any clearer. It's all pretty obvious to me and sometimes that makes it harder to explain.

I think this entry and the Wikipedia entry on optical illusion need to totally rewritten. To start with, the definition needs to be exorcized of the ghost-in-the-machine nonsense that colour pickers or spectrometers are objective while the human eye is not.

- Andrew van der Merwe --Beachscriber (talk) 12:45, 13 November 2009 (UTC)[reply]

I'm sorry, but you're still not getting it. This is especially revealed by your statements like, "The whitish square and the shadow are distinct entities which a colour picker cannot distinguish between." Here's the key: There is no whitish square, and there is no shadow! It's a two-dimensional image! You are speaking of this as if we're considering the colors of an actual object struck by light. We are not. Rather, we are considering the colors of a REPRESENTATION of an object, so your entire explanation (and problems with calling it an optical illusion) is one massive category error. Unequivocally, the two colors in this image are precisely identical. The optical illusion occurs precisely because the human mind sometimes has to force itself to see visual representations AS representations, and - to be blunt - I can't recall a more spectacular failure in this regard as demonstrated by your comments above. —Preceding unsigned comment added by 65.51.248.100 (talk) 19:48, 26 January 2010 (UTC)[reply]

So basically what you're saying is: a) If you take away all the things that fool your eyes/brain, then they aren't fooled and you therefore don't think it counts as an illusion. b) You think a shadow is an actual, physical thing? and c) That even if this were real, the shadow would not actually change the colour of the square but would only make it appear darker, this would still not be an optical illusion... 213.31.180.126 (talk) 15:04, 2 February 2010 (UTC)[reply]

The equivocation and logic errors are all yours, Beachscriber. It's an optical illusion because two areas of the screen appear to be different colors when in fact they are the same color. This illusion -- this appearance that pixels of the same color are of different color -- is so strong that we have a number of people claiming here that they really are different, that this is just a mockup to show the effect, that people are lying when they say they are the same color ... and then there is you, seeing squares and shadows and cylinders when there are no such things here, only a rendering, and it is the properties of the rendering that are at issue.

You ask what you are referring to by the word "it" in "It's the same colour." Are you referring to the objects or are you referring to the shadow? Or are you referring to the colour independently of either -- we are of course referring to none of those. There are no objects or shadows, only a rendering. And it's nonsensical to talk about a color per se being the same color. No, we are talking about the color of the pixels -- or, if this illusion were presented on paper, the color of the ink at those spots on the paper. They appear to be different when they are actually the same -- hence, an illusion.

Also, you are inverting the meaning of the phrase "ghost in the machine". Humans do not have some magical ability to perceive correctly what instruments fail to register -- a charge that is particularly ridiculous in this case because the two areas of the image are the same color by design; we don't need a color picker to determine that they are the same, we can look at the image data. No, human visual processing is not magical, not ghostly, it is algorithmic, and that algorithm employs heuristics -- which produce illusions.

In any case, this discussion doesn't belong here; it's a violation of WP:NOR. The Wikipedia articles reflect the cited literature, so what you think about the matter is irrelevant. -- 98.108.219.226 (talk) 08:06, 24 February 2010 (UTC)[reply]

I feel sorry for all you people who think that A is different than B. It is an illusion. The point of an illusion is to make you think that something is different than it really is, and this is doing just that to you. Paperfork ♠ 01:44, 21 March 2010 (UTC)[reply]