This video illusion will destroy your brain

By Phil Plait | August 17, 2011 6:00 am

I love love love optical illusions, and it’s been a while since I posted one. So here’s one of the greatest and most brain-eatingly pernicious illusions of them all… and this time, via my friend Richard Wiseman’s blog, it’s brought to life!

Now, if you’re like me, your first thought is "Baloney!" except perhaps with stronger language.

However, I promise you, this is real. It’s not a trick, it’s not Photoshop, nothing like that*. It’s an honest to goodness optical illusion completely inside your head. I can prove it, and you can prove it for yourself.

I took a screen grab from the video:

I then opened it in Photoshop and created two squares. I filled the first one with the color sampled from the "dark" square in the screengrab, the one next to the woman’s right hand. I then did the same thing using the color sampled from the "light" square just to the right of the cylinder. Here is the result:

How flipping awesome is that? And you don’t have to trust me: go do it yourself. Make a screen grab, or use a template the video maker put together. Heck, just grab the screengrab I already made and look for yourself!

You may note the two squares above aren’t exactly the same color; getting a screen grab and compressing the file and all that mucked with the coloring a bit. But clearly, those two squares are very close in shade and color, nowhere near as different as your brain thinks they are in the checkerboard. This classic illusion is due to the way you interpret color (or shading): it’s not done independently; your brain is always comparing things. In one case, the square is surrounded by lighter squares which make it look darker, and in the other case it’s surrounded by darker squares, making it look lighter. The shadow going across the squares messes with your perception as well, amplifying the effect.

These kinds of illusions are maddening and overwhelming that I expect that despite my clear demo and urging of people to try this for themselves, there will be quite the spirited discussion in this post’s comments (just as there was for this one, one of my all-time favorites) . But there you go. We humans are convinced that we see the world as it really is, but that’s complete rubbish. We don’t. We see things filtered not just through our fallible senses, but also then interpreted by our ridiculously pliable minds.

The Universe is not trying to fool us. It doesn’t need to; we do an astonishingly good job of that ourselves. But as long as you’re aware of it you can see through the illusion, and, if you’re sufficiently willing to, you might see everything a bit more clearly.

Tip o’ the Necker cube to Richard Wiseman; go subscribe to his blog. Trust me. You’ll love it.


* I noticed an edit in the video at 50 seconds in. I imagine they just had to do another take, and not work any trickery; as you’ll see in my demo, it doesn’t matter! The effect is real. In that it’s an illusion. Um. You know what I mean.


Related posts:

The blue and the green (one of the single best illusions of all time)
The illusion will drive you mad
Why does the Moon look so huge on the horizon?
Square circle spiral

Comments (101)

  1. Chris

    You can also just focus your eyes on the two squares in question and force your brain to ignore everything else and you will see they are the same color. Kind of like a magic eye type thing.

  2. Carey

    I wonder how the checkerboard looks without the pillar and its shadow.

  3. The original illusion is easy to understand – alternate squares of 25% grey and 50% grey look like 50% and 75% under 25% shadow – 50 = 50

    However, in this video, some jiggery-pokery is going on, as the girl is seemingly moving a 50% grey tile into shadow and it’s still only 50% grey. If you pause it in mid-move you will see the shade of the moved tile doesn’t quite match either shade.

  4. Erik

    Thank you – I was trying to make this point not too long ago, that we don’t experience the world the way we think we do.

  5. Georg

    “”We humans are convinced that we see the world as it really is, but that’s complete rubbish. We don’t. “”

    Of course we do! But on a much more sophisticated level. The effect behind this illusion is basis
    of our ability, to see “objective” body colors, almost independent from ilumination.
    Its not primitive physical reality (in the sense of the light entering our eyes)
    it is the reality of the checkerboard we see, in spite of the shadow cast over it.
    And in general: our sucess from hunter/gatherers up to today science shows that
    the view of world we have is not totally rubbish.
    Georg

  6. Bigfoot

    This is a live video created on the checker shadow illusion, which has always been my favorite still image illusion. Seeing it in motion brings a whole new dynamic to it (pun intended). Nice to see someone animate it in real life.

    Wikipedia has a great page showing the original still version of this illusion, which has always blown me away.

    http://en.wikipedia.org/wiki/Checker_shadow_illusion

  7. Tom K

    Whenever I see illusions like this I’m always reminded of this scene from the classic X-Files episode, “Jose Chung’s, ‘From Outer Space'”. Jesse Ventura plays a Man In Black, attempting to intimidate someone who believes he saw an alien spacecraft. (The second Man In Black is played by Alex Trebek.)

    1ST MAN IN BLACK: Venus was at its peak brilliance last night. You probably thought you saw something up in the sky other than Venus, but I assure you, it was Venus.
    ROKY CRIKENSON: I know…
    (Roky sits up, but the man in black pushes him back to where he was.)
    What I saw.
    (The man in black leans in as he talks, basically scaring the hell out of Roky.)
    1ST MAN IN BLACK: Your scientists have yet to discover how neural networks create self-consciousness, let alone how the human brain processes two-dimensional retinal images into the three-dimensional phenomenon known as perception.
    (The man in black stands and holds his arms in disbelief.)
    Yet you somehow brazenly declare seeing is believing?
    (The second man in black walks over to Roky, his face shaded to all but Roky.)
    Mister Crikenson, your scientific illiteracy makes me shudder, and I wouldn’t flaunt your ignorance by telling anyone that you saw anything last night other than the planet Venus, because if you do, you’re a dead man.

  8. Christopher

    Wow! This is the coolest optical illusion I have seen. Thanks!

  9. I don’t have time for your tricks, GOB.

    You don’t have time for my ILLUSIONS, dad. ILLUSIONS.

  10. Robert

    The only trick in this video is that the checkerboard is actually evenly lit by the large, shadowless lamp on the upper right. The smaller lamp to the left is just for show, and too small to actually create a shadow.

    The ‘shadow’ on the checkerboard is actually painted on, so the ‘light’ square in the center is actually the same color as the ‘dark’ square on the outside. Nice demonstration.

  11. DanVeteran

    Wow. My brain is destroyed. Will have to leave work and go home to drink beer. Thanks for posting.

  12. Ryan H

    This has long been one of my favorite illusions, but watching the square “magically” transform from light to dark absolutely blew me away. That is CRAZY.

  13. I’ve had an illustration of this illusion for a few years. The kids still have trouble believing it.

    Seeing a video of it is amazing, however.

    And, I’d also love to see the “checkerboard” without the cylinder in place. What does it “really” look like, when evenly lighted?

    http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html

  14. OtherRob

    My brain hurts…

  15. If you’re on an LCD screen that you can tip, just tip it till you see false colors. The two squares are obviously the same, in false color. (That works, somehow..)

  16. Mark Ormandy

    Here’s the illusion illustrated by removing the other colours;

    http://imageupload.org/?d=0A2B729B1

  17. I tried this myself, using the template in the description of the video. It works, and is amazing. It’s one thing seeing it on the video, wondering if there’s some digital trickery going on, but totally mind-blowing to print out the template, cut out the square and do it yourself at your own kitchen table.

  18. Very, very cool. I could watch that a thousand times and be fascinated each time. Thanks for sharing this one!

  19. Dan Zee

    I don’t think this an illusion, it’s more of a trick, especially if the shadow is painted onto the squares. I think of an illusion as a thing that your brain misconstrues rather than the trick playing a trick on you.

  20. Diane

    Held some bits of paper against the monitor to cover everything but the two squares, and yes, they are the same shade in the screen shot. Still hard to convince my brain that it’s true though.

  21. andyo

    I wonder how the checkerboard looks without the pillar and its shadow.

    It has the shadow painted on. The left lamp is there only to fool you. (Click on “a template” in Phil’s post to see it). And of course because everyone likes to appear smart, I will say I got it before looking at the description in the youtube video, when Evil Twin Wiseman put it up on his blog. You can see in the video when the woman puts his hands in what would be the “shadow”, that it’s not a shadow, but it’s actually evenly lit.

  22. andyo

    I don’t think this an illusion, it’s more of a trick,

    The illusion is that the squares seem different shades, not the shadow itself.

  23. Chris A.

    But, but…

    I accept that the two squares appear to be the same shade on the finished video. However, there must be some trickery here, simply because if the “dark” square is moved from a region of full illumination into the cylinder’s shadow, it should appear to get _darker_. Perhaps the problem here lies in what your definition of “is” is (i.e. “the light square _is_ the same color as the dark square”).

    For example, a square painted pure white would appear the same color as a square painted pure black in a windowless room with all the lights turned off. Does that make them the same color? It’s the optical equivalent of “If a tree falls in the forest…”

    @andyo (#19):
    “It has the shadow painted on.”

    If so, why can we see the shadow’s edge on the moveable square as it’s moved into and out of the shadow? I suspect that it is painted on, but that a real shadow overlies the painted one.

  24. Dan I

    My favorite thing about this illusion is even that knowing about it I can’t make it “right.” In most optical illusions if I know the trick or what the “truth” is you can force yourself to see past the illusion. Not here, when that square is in the shadow it looks lighter no matter how hard I try.

    Also obligatory:

    “Obviously photoshopped. I can tell by the pixels and having seen a lot of shops in my time.” :-P

  25. In case you might wanna blow your mind further BBC Horizon did a nice show about illusions, not just optical but all senses (title: Is seeing believing?), here is part one:
    http://www.youtube.com/watch?v=o3g66FRUYww

  26. Tom

    Bob Berman wrote a good column about similar illusions with regard to celestial bodies in the August Astronomy mag. I am not going to link it because it is behind a paywall. Also, apologies if even mentioning this on another magazine’s blog is considered bad form.

  27. CharonPDX

    Carey,

    The cylinder is a distraction. The light to the left is a distraction. I bet it’s set up so that the cylinder COMPLETELY blocks the light to the left, and the light stand you see to the right is providing all the light to the actual ‘checkerboard’. There is really no shadow. The shadow itself is an illusion, the checkerboard is painted to LOOK like there is a shadow when there really isn’t. The light to the left and the cylinder are there to complete the illusion. I bet if you turned off the light to the left, it would look nearly identical (except the left side of the cylinder wouldn’t be lit.)

  28. Marina Stern

    Brains don’t like to be told what to think/see. I once painted the interior of a shed pink. My brain insisted on seeing it as white. I added white trim, in order to force my brain to see the pink as pink. Instead, my brain still saw the pink as white, and saw the white as aqua. Oh, well. I stopped using that shed. It made me dizzy.

  29. Wow. Now that is just a neat demonstration! You may, however, be more accurate to call it a perceptual illusion (because it is entirely dependent on a heuristic employed by your perceptual system called colour constancy) rather than an optical illusion (dependent on optics, like light bending over a hot roadway to make it look wet). Fun video, thanks!

  30. Lars

    The only trick in this video is that the checkerboard is actually evenly lit by the large, shadowless lamp on the upper right. The smaller lamp to the left is just for show, and too small to actually create a shadow.

    The ‘shadow’ on the checkerboard is actually painted on, so the ‘light’ square in the center is actually the same color as the ‘dark’ square on the outside. Nice demonstration.

    Thank you! I thought I was going nuts.

    “Obviously photoshopped. I can tell by the pixels and having seen a lot of shops in my time.”

    True, apparently … ;D

  31. vader

    i find your lack of faith disturbing.

  32. Lorena

    I don’t get it, if the board is checkered and those two squares are the same color, then the checkered pattern is not regular, one light gray- one dark gray, because according to the pattern the one she moves has to be light gray. I want to see the board without that dustbin that’s blocking the light.

  33. It’s easy to see how this is accomplished by observing the shadows on the floor cast by both the raised checkerboard and the woman.

  34. panini

    In fact you can see a slight shadow cast by the cylinder, and the tiles aren’t exactly matching. Nice demonstration anyway, but I have to say I prefer the still drawing, where you can really measure that RGB values are precisely the same.

  35. Georg

    To several posters:

    “The shadow is painted on ”

    Oh yes?
    Or is a “true” checkerboard photographed with the
    ilumination setup? If You want to see the “original setup”,
    You have to take a checkerboard and a drum and a lamp.
    But both will lead to the same picture on Your retina!
    Either “reality” or the “photo” or the painted thing look
    the same as far as the light entering Your eye is concerned.
    This “illusion” is a big thing, allowing You to see reality of
    colored objects independent from ilumination and shadows.

    This “illusion” makes that our ancestors could see a deer in bright
    sunlight in a green meadow, but also in the shadow between bushes.
    In short, it makes that “things” look the same in daylight, when
    sky is overcast or when sunset creates a very red ilumination.

  36. Dr.Sid

    My brain is not destroyed .. I want my money back !

  37. John Wilson

    I have a laminated printed copy of this with a second page that masks out eveything but the two squares. It is a great skeptical tool to illustrate how we can feel certain about something and be completely wrong. I show it to everyone who is interested and I have yet to find someone who isn’t blown away by it.

  38. Dragonchild

    I don’t disagree that it’s an optical illusion; but I strongly disagree with this:

    “We see things filtered not just through our fallible senses, but also then interpreted by our ridiculously pliable minds. The Universe is not trying to fool us. It doesn’t need to; we do an astonishingly good job of that ourselves.”

    THE MIND ISN’T “RIDICULOUSLY PLIABLE” OR “FOOLING US” BECAUSE OF OPTICAL ILLUSIONS; IT’S DOING EXACTLY WHAT IT’S EVOLVED TO DO, and the illusion actually demonstrates how hard-wired these features are! The brain exaggerates contrast because that’s what helps it identify objects. It allows us to spot prey and predators, as most animals evolved camouflage. Even today, if you use contact lenses and drop one, good effin’ luck trying to find a small transparent lens without exaggerated contrast. And for that matter, you wouldn’t be able to even study fine details in pictures of planetary nebulae without your brain running these complex processes to help you pick out every minute change in texture or color!!

    Yes, we should acknowledge their existence and limitations — no disagreement there. No, we do not see the world as it truly is — I agree 100%. But please, for FSM’s sake, stop portraying optical illusions as a flaw. They are precisely the opposite. These are highly developed survival traits. What we have is best described as very advanced vision enhancements that, unfortunately for objectivity, cannot be turned off.

  39. I did this with cut outs of Barack Obama and Rick Perry – my photoshop tells me they are both vomit green.

  40. Pepijn

    I thought this was a pretty well known illusion, I’ve seen it several times. It’s a fantastic illusion though, one of best ones I’ve ever seen. It’s so simple, so convincing, and so cool to prove to yourself (or others).

    I am able to see the two squares as the same colour, by looking *between* the two squares and relaxing my eyes instead of focussing my eyes on either square. Then I can convince my brains that the two squares in my peripheral vision really are the same shade of grey.

  41. Matt Moore

    I don’t understand why people think the shadow is painted on. I can see the shadow on the moving square quite clearly during the overhead shot at around the 1 minute mark.

  42. andyo

    @andyo (#19):
    “It has the shadow painted on.”

    If so, why can we see the shadow’s edge on the moveable square as it’s moved into and out of the shadow? I suspect that it is painted on, but that a real shadow overlies the painted one.

    There is still a slight real shadow that’s a bit wider than the painted one, but it’s completely negligible when the square is in its two key positions. (BTW, you don’t have to take our word for it, just look at the video’s description on youtube.)

  43. noen

    There is no trickery involved. No secrets. The lamp is not misdirection. The shadow is not painted on. This is a large box with painted squares in a dark room lit by a spotlight.

    The only trickery is when she moves the light square in shadow over on top of the dark square not in shadow. The video is edited so the square in shadow keeps the same value it has when moved into the light. A real square piece of paper would brighten when moved but then we couldn’t visually compare the apparent values of the two squares.

  44. len222

    At 1:06, the partially moved “dark” square is clearly a different color than the square from which it’s being moved. There’s an unmistakable color difference on the border where they touch.

  45. evinfuilt

    I use this illusion at work quite often, I find it very powerful in demonstrations to show people how surrounding colours effect the colour you perceive.

  46. noen

    I think this video also illuminates a second cognitive error we humans are prone to, conspiracy theories. Notice how many people think there is some kind of deliberate trickery being perpetrated even though they are given an honest account of how the video was constructed. People prefer to believe what they *think* they saw rather than what their reason tells them.

  47. andyo

    I think this video also illuminates a second cognitive error we humans are prone to, conspiracy theories. Notice how many people think there is some kind of deliberate trickery being perpetrated even though they are given an honest account of how the video was constructed. People prefer to believe what they *think* they saw rather than what their reason tells them.

    So you’re saying that this “conspiracy theory” in which the author openly tells us (with drawings!) how the “conspiracy” was done is more of a conspiracy than “the video is edited so the square in shadow keeps the same value it has when moved into the light”, which doesn’t fit with careful observation (like the hands of the woman when they go into the “shadow”?

    Also, given your post in #44 (unless #45 was about yourself and not others) I don’t know what you mean by “even though they are given an honest account of how the video was constructed”. Which “honest account” are you referring to? Cause the only one I can think of is that of the one who made the video, which does say the shadow is painted on.

  48. Terry (#3) has hit the nail on the head!
    See my image:
    http://www.flickr.com/photos/24473498@N02/6053648648/in/photostream
    You can’t have it both ways! The square is being moved from the shadowed light square to an unshadowed dark square. We can clearly see it’s approximately the same shade as the dark square, but it’s clearly lighter than the dark square that is in the shadow area. So which is it?

    Clearly some digital effects is going on here. I suspect that the square is actually bright green and the grey colors are chroma-keyed into place. A background image with a wash of grey colors at the same location on-screen as the edge of the shadow would do the trick.

    This is a real illusion, though, that is being illustrated using trickery. This is a BAD way to go. Lying to tell the truth? Nope. Bad idea!

    Phil has gone about it much, much better, with the frame grab and PhotoShop analysis. No lying there! Always best to use your baloney detection kit when confronted with illusions.

    We need Captain Disillusion to deconstruct this one!
    Captain?
    Rich

  49. BJN

    As an artist, I create similar “illusions” all the time. The only difference between the checkerboard construction and any drawing (or even a photograph since it simulates light and shadow using tones too) is that its a 3D painting. Your brain makes assumptions and isn’t always reliable. That shouldn’t be a surprise these days.

  50. BJN

    @anddyo:

    “Careful observation” shows a shadow cast by the woman’s arm from a third light that’s not apparent in the wide view of the scene. That’s the way the shadow trick is done. There’s a spot light shining from the POV of the camera that makes the “shadow” lighting the same as the apparently brighter lighted area. There’s a bit of actual shadow that isn’t illuminated by the spotlight so you see the hands of the woman go into shadow.

  51. Chris A (#24):

    However, there must be some trickery here, simply because if the “dark” square is moved from a region of full illumination into the cylinder’s shadow, it should appear to get _darker_.

    Nope, the squares _are_ the same color. You’re thinking things backwards.

    If you take a piece of light-gray paper, and then move it into a real shadow, you are correct that it will appear to darken to a dark gray. Your brain knows this. Therefore, if you see a dark gray square within what appears to be a shadow, your brain _lightens_ it, because it “knows” it’s “really” light-gray, making it appear brighter than the same dark-gray square outside of the “shadow”.

    As you move the dark-gray square outside of the “shadow”, and it’s color doesn’t actually change, your brain darkens it as it moves, until it sees the same shade of gray as the one outside of the “shadow”.

    (At least, that’s how I understand things.)

  52. Keith Bowden

    Actually, the most fascinating thing about this is how many people are trying to work out how the squares are not the same, that this is a fake – or at least a fake version of a real effect. (For those supposing that the loose square is a slightly different shade to “help” the illusion, I submit that as a real object it is subject to the properties of reflected light. What I mean is, as the angle of the moveable square changes with movement, it reflects the overhead light more directly to (our) the camera’s eye.)

    This says a LOT about the nature of people to try to explain how our perceptions aren’t wrong, whether visual or conceptual, and resist explanations to the contrary. (I’m not saying that there’s anything sinister or “wrong” with any of the other commenters here specifically, just that this little exercise demonstrates remarkable similarities to arguments against change, and with political, philosophical or religious beliefs.)

    There’s a paper in this… :)

  53. Wait, I’m going to correct myself. The background graphic that is chroma-keyed onto the green square of paper is all one shade of color. (If chroma key is the way it’s done.) It’s not a gradient of colors. My mind got ahead of itself! (Wouldn’t it be NICE if creationists could self-correct? Yeah, like THAT’s gonna happen!)

    There, however, IS a shadow as she reaches in to pick up the square in the shadow zone. If you look at the left side of her arm you’ll see it easily. The right side of her arm is lit by the lamp on the right and is evenly lit all the while.

    I’m not sure exactly what the YouTuber brusspup meant when he says “But the trick is ..that when you move the square you are moving it WITH the shadow still printed on the square.” This might make you think that the shadow is painted (printed) onto the squares, and that the cylinder is added digitally, and is not really there. I suspect that chroma-keying is the easiest way to go to make this illusion stick. It might be better if she came in with a green shirt on afterward to expose the trickery. With the green square in either location it’d appear the correct grey shade…

    There does look like there’s a small shadow on the square of paper when she moves it through the shadow’s edge, though. This might be another addition to the fakery to aid in the illusion.

    Captain Disillusion? You out there? (Sure you are…)

  54. TheBlackCat

    @ Ken B: I think it is even simpler than that. You don’t really “see” color per se, what you see is contrast. That is, you eyes look for areas where the color changes and send that information to your brain. This is called opposition.

    The eye also subtracts out the average color and lightness over an area, roughly speaking. This is called “simultaneous color contrast”, and it happens right in the retina, long before the brain gets it. In fact, these two techniques are a form of image compression. If all the information from the retina was transferred to the brain, it would require an optic nerve the size of a donut.

    So what is happening here is not a high-level cogntivie task like knowing where there is and is not shadow, it is an extremely low-level contrast adjustment based roughly on the average color over an area.

    As others have said, this is necessary for survival, but I haven’t seen anyone describe it exactly right. The reason this is important becomes clear when you think about light sources. Ever notice how the sun is a lot redder at dusk than at noon? There is also a lot more red light falling on objects at dusk than at noon. Yet an apple still looks the same shade of red or green, a lion is still the same shade of tan. Simultaneous color contrast is why. It doesn’t matter whether we are under fairly yellow incadescent light, white flourescent, or colored neon lights, objects still look roughly the same color. Under all these conditions the actual frequencies of light hitting your eyes are totally different, yet we don’t even notice it.

    This is absolutely essential for survival. If we see an apple at noon, we need to know it is still the same, safe food to eat at dusk. If we learn that a lion is dangerous in the open, we have to know to run away when we see one in the shade.

  55. Black Cat:
    Good points. Our eyes are sensitive to a huge range of tonalities. They work in noontime sun and at night too. To some extent they even work with huge contrasts in the same image. I’m thinking of a strong sunlit beach with a girl under a dark beach umbrella. Both seem properly lit but there’s a hundred times more light on the sunlit sand than under the umbrella. Digital cameras struggle to achieve the same effect we naturally evolved millions of years ago.

    Keith:
    I’m with ya! I just wonder how the heck they did the illusion is all. True enough, at the outset the shades of grey are the same, Phil’s framegrab proved that. But what I wanna know is (subtle Max Headroom reference) how the heck did they pull this off?

  56. steve_cosmo

    What I’m most curious about is what would happen if you changed the labels on the two images. Right now the one on the left labeled “light” looks less dark than the one on the left. What would happen if they were relabeled. Is the labeling altering our perceptions as well.

  57. truthspeaker

    I agree with Dragonchild. It is a similar pliability that allows us to understand spoken language. Objectively, the sounds that make up speech are more similar than they are different. It is only by exaggerating the differences and making assumptions about what was heard that the brain can pick out different phonemes.

  58. andyo

    @anddyo:

    “Careful observation” shows a shadow cast by the woman’s arm from a third light that’s not apparent in the wide view of the scene. That’s the way the shadow trick is done. There’s a spot light shining from the POV of the camera that makes the “shadow” lighting the same as the apparently brighter lighted area. There’s a bit of actual shadow that isn’t illuminated by the spotlight so you see the hands of the woman go into shadow.

    There is no spotlight. There is no need for one. The dark shadows of the hands are from the softbox that you see there. Also, those shadows can’t be done by a spotlight, they are soft. There are weaker shadows coming from the light at the left, but that shadow is negligible. Do you see one more shadow that I’m missing, which would indicate a third light? What I meant with “careful observation” was the fact that the hands aren’t affected by the cylinder’s shadow, so that shadow (the shadow that matters) is not real.

    Also, are you saying that you think the shadow is not painted on? I can’t tell from your post. Cause, again, the authors themselves have said it.

  59. katwagner

    @40, mat noir: HAHAHAhahahaha! Vomit green, HAHAhaha! Ewwie. But thank you.

  60. noen

    I am pretty sure that this video was made in a studio at NASA and that the shadows pointing in different directions prove it is a fake.

  61. Chris A.

    @Ken B. (#53):

    “Nope, the squares _are_ the same color. You’re thinking things backwards.”

    I disagree. My point was: in order for the squares to be actually the same RGB color on the video (as demonstrated by Phil’s side-by-side comparison) something funny must be going on, since the square when not in shadow should have a different RGB value than the same square in shadow (i.e. the shadow is not really a shadow, but painted on, as the filmmaker admits).

    Note that my statement has absolutely nothing to do with how the two squares are perceived.

  62. anthony

    Take the screen capture into Photoshop and start erasing everything but the two squares. The lighter one will go darker right in front of your eyes.

  63. One Eyed Jack

    Do not try and bend the spoon. That’s impossible. Instead… only try to realize the truth.
    What truth?
    There is no spoon.
    There is no spoon?
    Then you’ll see, that it is not the spoon that bends, it is only yourself.

    In this illusion, there is no shadow.

  64. CB

    Ever notice how the sun is a lot redder at dusk than at noon? There is also a lot more red light falling on objects at dusk than at noon. Yet an apple still looks the same shade of red or green, a lion is still the same shade of tan. Simultaneous color contrast is why. It doesn’t matter whether we are under fairly yellow incadescent light, white flourescent, or colored neon lights, objects still look roughly the same color. Under all these conditions the actual frequencies of light hitting your eyes are totally different, yet we don’t even notice it.

    Huh? That has never been my experience. A red apple may look largely the same but that’s because it’s mostly only reflecting red light to begin with. A lion at sunset looks much more red-ish than it does at noon. My pale-blue room looks pale blue in sunlight or illuminated by 6000K bulbs, but looks slightly-orangey-white illuminated by 4000K bulbs. Colored neon? Yeah, that makes things look like they’re the color of the neon, or much darker if they absorb the color of the neon.

    I may be mentally aware that the lion is tan-colored-red-by-sunset or that the pink tabletop is actually white but the only light in the room is a neon sign, but the point is I actually perceive the “true” color of the photons coming off these things.

    The way evolution dealt with this is by not making our image-recognition of “lion” depend on it being exactly the specific shade of tan that a lion appears to be at noon, just like it also doesn’t have to be in a specific pose oriented in a specific way relative to us for us to recognize it. :P

    In this illusion, though, you do not perceive the “true” color correctly. It is a contrast trick, yes, one of the oldest in the book — things look brighter if next to dark objects, and darker if next to light.

  65. Maurice

    There is no need to do a convoluted effort to prove the illusion. Take some sticky notes and fold them to cover the dark squares around the supposedly light square onscreen. As you start covering the four dark squares you will see the light square appearing darker and darker. When you cover the four dark squares you will then see that the “light” square is the same shade as the “dark” square. QED.

  66. entropy

    Go to 52 seconds in the video. Hit the full screen button. Hit play, and then try to pause it just as she’s sliding the square over. If you pause it (in the 53rd second)at just the right time, you can see the square she is moving en route is touching both the place where it came from, and where it’s going to.

    It breaks the illusion from your color perception being relative, because it’s one solid color straight across, and it breaks up the pattern and the shadow line.

    Then it’s much easier to see, 3 colors on all the squares, and the shadow is painted on.

  67. noen

    How to reproduce this video

    1) Build a cardboard box and cylinder to match that in the illusion.

    2) Print out squares of 50% gray and 25% gray and cover the cardboard in a check pattern.

    3) In a darkened room illuminate the box and cylinder as seen in the video.

    4) Set up your camera on a tripod and take a screen capture.

    5) In photoshop sample the *apparent* value of the square not in shadow and print out a square of that precise value.

    6) If everything is correctly lit and you made sure that the *sampled* gray values for both the square in shadow and out of shadow are of the same value you will then be able to amaze your friends and confuse people on the internet.

    7) Enjoy the lulz

  68. Joseph G

    @25 Dan I: Are you a Farker? That last bit brings back memories… :)

  69. andyo

    Chris A. #65,

    My point was: in order for the squares to be actually the same RGB color on the video (as demonstrated by Phil’s side-by-side comparison) something funny must be going on, since the square when not in shadow should have a different RGB value than the same square in shadow (i.e. the shadow is not really a shadow, but painted on, as the filmmaker admits).

    I think you’re a bit confused here. “Not in shadow” doesn’t have any meaning here, since the shadow is fake! There is no (signficant) shadow, and that’s the trick that makes the illusion work. The two squares are the same shade in the video or live, cause they’re evenly illuminated at those two positions.

  70. noen

    The shadow is not fake andyo. It’s a real checkered box and cylinder lit with real lights and casting real shadows. The paper she moves from one square to the other is also real. There is no trickery at all. All of the squares are either 50% or 25% gray except for one. The square that she moves is whatever shade of gray a 50% gray square is when not in shadow (less than 50%) which als0 happens to be the same shade of gray a 25% square is when in shadow (greater than 25%).

  71. noen

    Wait, that’s wrong. The gray square that gets moved is also 50% gray. There’s no need to print out a special gray square at all. I’m an idiot.

  72. edwardv

    I like her matching outfit. I wonder if it was bought or made for the video.

  73. Random Excess

    I used to work as a research scientist in digital image processing so I am getting a kick out of these replies.

    Thanks guys, you are the greatest. And is has already been stated, there is a distinction between being a skeptic and being conspiratorial. Remember to lock your doors, wash your library books before reading them and beware, they are out to get you.

    Great effect, BTW. It is a real effect and the photography is not faked,

  74. Svlad Cjelli

    I used to misunderstand this and compare the real light tiles with the real dark tiles. Obviously, that didn’t go so well.
    When I found out I was supposed to compare the lighter dark ones and the darker light ones, I thought, “Oh. Yeah? Half-light stuff is as half-light as half-light stuff is half-light.”

  75. Svlad Cjelli

    My expectations were too high.

  76. Stephen

    I don’t think anyone’s brain was destroyed by this. Pretty meh, actually.

  77. TheBlackCat

    but the point is I actually perceive the “true” color of the photons coming off these things.

    Then you are some sort of strange mutant. Everyone else on the planet does not and cannot perceive the “true” color of the photons coming off something because our retinas are not constructed that way. That information isn’t even carried by the optic nerve. This is a well-known perceptual phenomenon going back over 150 years with a fairly decently-understood neural basis.

    Of course the system isn’t perfect, it is based on averaging particular areas and it cannot include light frequencies that aren’t present (so it won’t work if there is only red light, for instance), but is much more powerful than what most people think. And it is the reason for this illusion.

  78. Christos

    The square in its original location A , which is in the shade, is the same colour as the stationary square B. That I can understand.

    When it moves out of the shade to B, it is still the same colour. That is more than just an illusion.

  79. @26. lacalaca:

    I watched the first 6 minutes of that first video of the BBC documentary and freeze-framed it at the 6 minute mark.

    http://www.youtube.com/watch?v=o3g66FRUYww

    There is clearly a ball leaving the hand of the person playing with the ball and it is edited out of the frame at 6:00. I stopped watching the show at that point.

    It’s shows like this that make people argue about optical illusions. When the magician in your show can’s portray the illusion good enough and you are forced to edit your material in post because you feel that you need the footage otherwise your documentary falls apart, then you are getting into the territory of fraud. And it’s no wonder that people think that they aren’t fooled but rather betrayed when you publish videos like this one.

  80. Thanks for a very thought-provoking video. Chilean biologists Humberto Maturana and Francisco Varela deal with this phenomenon elegantly and profoundly in their book “The Tree of Knowledge — the roots of the biology of human cognition”. The book is much more encompassing than just the “optical illusion” aspect, but in one of the early chapters they devote some space to similar experiments and conclude by saying “…neuronal activations which are primed by external stimulation are determined by what is inside the person and not only by the perturbing agent, and are therefore different from person to person. For this reason we do not “see the world” but we “live our visual field”. We do not see the colors of the world but we live our chromatic space: every experience involves the experiencer and it is deeply rooted in his/her individual biological structure.”

  81. Jackie

    It’s just color theory in action- not a big deal.

  82. Matt

    I don’t understand what all the fuss is about. One is a dark square in the light, the other a light square in the dark. Of course they’d match or at least be close in tone. I’d be surprised if they didn’t match.

  83. Jim1138

    The shadow from the woman’s arms and hands do not match the shadow of the cylinder. The shadow of her arms and hands appear to be from a light overhead. Her hands do alter in brightness from a light to the viewer’s left. I would conclude that there is trickery involved in illumination and that the “illusion” is from a checkerboard with a painted shadow, not the shadow from the cylinder.

    Such shadow anomalies are often indicative of photoshopping when two images with different illumination are combined.

  84. Carl

    If you ever have to sit through a powerpoint show, ask the person next to you how they project blackness onto the screen (the Perception). Reality: no point in the image is actually darker than the surface it’s projected onto. At least the discussion might be more interesting than the powerpoint.

  85. Michael Rochler

    Surely this IS a TRICK, not an optical illusion? If a dark square in brighter illumination is exchanged for a lighter square in shadow, and this is supposedly a bona-fide standard checkerboard, then how come the same square/tile in the shadow abuts four squares that are darker still?

    The people asking how the checkerboard looks without the pillar/bucket in even, softer illumination are IMO on the right track. I agree with them there’s an airbrushed shadow where it appears to be, but possibly not on the single moveable tile itself.

    If this is NOT a trick, and really an optical illusion as purported, then it should be possible to:

    1. Create a checkerboard pattern using only TWO shades of grey – no fake shadows, thank you.

    2. Illuminate as shown, and PLACE the MOVEABLE pillar/bucket as shown.

    3. Refilm in one continous take, but this time lift and replace the bucket at the beginning and, after the several exchanges of the tile, towards the end of the video to show/prove that there is no fake airbrushed shadow (if there isn’t).

    Good luck with this, if you can. I’m waiting ;-)

    This trick – not an optical illusion – shows that one can fake something that looks like a normal checkerboard pattern to recreate an amazing effect. As 49. Richard Drumm says, a real illusion illustrated through trickery.

    This is also partly a terminology issue; I notice Phil Plait only claims that there’s a physical arrangement which can be videoed in one take as shown; and that the two squares are pretty much the same shade of grey. He doesn’t actually claim that the checkerboard is really what it appears to be.

    I would also suggest that rather than our senses being be unreliable and feeding us false information, it’s exactly the contradiction between the supposed standard checkerboard pattern and the noticing that the tile shade’s unchanged that makes one wonder about a painted shadow.

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