The blue and the green

By Phil Plait | June 24, 2009 10:34 am

Via my evil twin Richard Wiseman comes one of the best color optical illusions I have ever seen. The original was apparently posted on Buzzhunt Akiyoshi Kitaoka’s incredible optical illusion website:

Blue green spiral illusion

You see embedded spirals, right, of green, pinkish-orange, and blue? Incredibly, the green and the blue spirals are the same color. At first I thought Richard was pulling our collective legs, being a trickster of high magnitude. So I loaded the image in Photoshop and examined the two spirals. In the two squares displayed below, the one on the left is colored using the same color from the blue spiral, and on the right using the green spiral.

green and blue squares

Like I said, incredible! For pedantry sake, the RGB colors in both spirals are 0, 255, 150. So they are mostly green with a solid splash of blue.

The reason they look different colors is because our brain judges the color of an object by comparing it to surrounding colors. In this case, the stripes are not continuous as they appear at first glance. The orange stripes don’t go through the "blue" spiral, and the magenta ones don’t go through the "green" one. Here’s a zoom to make this more clear:

Blue green spirals zoom

See? The orange stripes go through the "green" spiral but not the "blue" one. So without us even knowing it, our brains compare that spiral to the orange stripes, forcing it to think the spiral is green. The magenta stripes make the other part of the spiral look blue, even though they are exactly the same color. If you still don’t believe me, concentrate on the edges of the colored spirals. Where the green hits the magenta it looks bluer to me, and where the blue hits the orange it looks greener. Amazing.

The overall pattern is a spiral shape because our brain likes to fill in missing bits to a pattern. Even though the stripes are not the same color all the way around the spiral , the overlapping spirals makes our brain think they are. The very fact that you have to examine the picture closely to figure out any of this at all shows just how easily we can be fooled.

This is why I tell people over and over again: you cannot trust what you see even with your own eyes. Your eyes are not cameras faithfully taking pictures of absolute truth of all that surrounds you. They have filters, and your brain has to interpret the jangled mess it gets fed. Colors are not what they appear, shapes are not what they appear (that zoomed image above is square, believe it or not), objects are not what they appear.

So the next time someone swears they saw Jesus, or a UFO, or a ghost, show them this picture. What you see in life is absolutely and provably not what you get.

Edit to add: if you like this illusion, then you might want to check out this audio illusion, and this one of a spinning woman’s sillhouette which is one of my all-time favorites.

CATEGORIZED UNDER: Antiscience, Cool stuff, Skepticism

Comments (419)

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  1. John Baxter

    My grandfather, head of the psychology department at U Michigan for years (through the depression and beyond both ways, I believe) loved this sort of thing. He would have been delighted with this one.

    Wow! (Off topic: he also loved multi-lingual puns, which kept the family “amused.”)

  2. That is extremely trippy, but wicked cool.

    If you really get your nose to the monitor, you can start to see that the blue-green spirals are the same color.

  3. Just in case anyone is wondering, wordpress image uploader adjusts images in a way that causes colors to change slightly. If you want to truly examine the image in photoshop use the one from the original post.

  4. This is way cool. In my non-majors biology course I spend a great deal of time discussing color vision and color processing as an example of sensory perception, and this will be a fun illusion to bookmark. Students are always astounded that perception of chroma, tonal value, and even hue are vastly influenced by context, but it makes perfect sense from an evolutionary standpoint. So does trichromatic vision, and the wavelengths of light our photoreceptors favor. Thanks for posting this!

  5. Stickend

    Try as I might, I can’t see Jesus, a UFO or a ghost in this picture. What am I missing?

  6. rob

    even at the very center of the spiral, where the two arms meet and are close together, they *still* look differently colored. cool.

  7. Charles Boyer

    These are tricks a good artist learns very quickly. Even in photography they work well.

  8. wright

    My late stepfather wrote a book on optical illusions; he was fond of saying “We make up reality as we go along.” This is a great example of that. Not only do we make assumptions and play fill-in-the-blanks at the cognitive level, but apparently at the autonomic level too!

    And we have to, in order to comprehend the vast amount of input our senses provide. Otherwise we would be overwhelmed, as some autistics are. The price is that our perceptions are not completely reliable, and we need to recognize that.

  9. I’m an amateur artist. One trick I learned was to always color the background first, even if I just gave it a flat color and didn’t worry about the details yet, for precisely this reason. If the background was dark, I’d start to pick darker colors by eye to paint in the foreground, and give it the look of a low-light painting. If I didn’t color the background, I’d paint things as if they were brightly lit, and then have to go back and change everything around. (Similarly, if I knew the scene should be tinted — say, a sunset — I should get the sky or surrounding colors first, so everything else would look right.

  10. Lorax

    Funny, my image program says something else. If I use the color picker to sample from each spiral, and then paste blocks of them side by side in a new image, there’s a visible contrast line (and the RGB values are not the same). They seem not to be the same color.

    Tried it a different way, and used flood fill to replace all the orange and pink with black. The two spirals appear to be somewhat different colors.

    With the pink and orange gone they look a lot more similar, but it seems not correct to say they are identical.

  11. BJN

    It’s not the eyes you can’t trust, it’s mostly the brain’s wetware image processing that leads us astray. We can’t believe our own brains, at least not without a big dollop of skepticism.

  12. Very cool. I was just revising this kind of concept for a Remote Sensing class on color theory. Excellent example!

  13. SteveG

    This is very cool and I love optical illusions.

    However to be fair, I noticed upon closer inspection that the green stripes that are surrounded by purple are outlined with a dark blue.

    The brain naturally blends these two colors into one. (The brain can only blend light, unlike sound where we can “hear” the different frequencies; you can’t “see” the different colors once they are blended together).

    So IMHO the two strips ARE different colors.

    I suspect the effect is similar without the dark blue outlines but I’d have to see it to be sure. You know, evidence.

  14. Jenn

    I love science!

    /sighs happily once again

  15. ak

    If I shrink the image to the size of a small fingernail and move a meter away from it, I can still see the illusion perfectly clearly, even though I cannot (consciously) see any cross-lines in the spirals. Unbelievable! What resolution for lines and color the eye must have.

    Never trust your brain. As a matter of fact, avoid using it at all costs…

  16. @Steve,Your brain is fooling you re: blue outline. Zoom in and you will see that “blue outline” remains the same size even as you zoom in deeper and deeper.

  17. Verified! The colors in both areas show a hex value of 00FF8A according to the color selection tool on my computer.

  18. Carla

    @SteveG – Actually, they’re not. that blue ‘outline’ is also being assumed by your brain, since right there the blue/green color is touching the magenta. Open it up in an image-editing program, and zoom in really close.

  19. Steve

    Using “Colorzilla”, a firefox HTML color plugin, I can verify that both of those colors are exactly the same. They both have the hexadecimal value of #00FF97. Really cool!

  20. Mike

    The illusion becomes more interesting when SteveG ‘sees’ the green stripes being surrounded by dark blue.

    Using the eyedropper in Photoshop there are only three colors :-
    R 0 G 255 B 150 – Green
    R 255 G 0 B 255 – Purple
    R 255 G 150 B 0 – Orange

    SteveG must be ‘seeing’ a dark blue i.e R 0 G 0 B 255 by subracting the red and green components. Is this evidence of some red/green defect in his vision?

  21. Dungheap

    “However to be fair, I noticed upon closer inspection that the green stripes that are surrounded by purple are outlined with a dark blue.”

    Do you perchance have glasses? I thought the same thing, but it turned out to be refraction from my glasses lenses. Try turning your head from side to side and see if the dark stripes change size. Also, look at the embiggened section and note that the dark blue stripes are smaller than the expanded pixels.

  22. jaroslav hasek

    wow, that is crazy. that reminds me of the time i was watching a color television set and it turns out that explosion of seemingly varied colors were all made of just 3 differently colored pixels!!! somehow my brain compared each of the thousands of tiny pixels against each other and fooled istelf into thinking i was watching an episode of law and order!

    sorry brain, but youre not a camera, better luck next time!

    what a fantastic optical illusion!!!! YEAH!!!!!

  23. Mark

    @SteveG

    Your “HO” is wrong. The strips are the same color. The “dark blue” outline effect is another optical illusion. Grab any basic image program and zoom into the image without scaling or smoothing turned on. The pixels are one of 3 colors in the image. The gif image data has a 4 color palette:

    JASC-PAL
    0100
    16
    0 0 0 (black)
    255 150 0 (orange)
    255 0 255 (purple)
    0 255 150 (teal)

  24. Dan I.

    Pretty cool. Looking at it again I noticed that when I look at the very ends of the blue bands (where they leave the frame) they ALMOST look their true color.

    Very cool, definitely saving this one.

  25. Very cool stuff. But I don’t think this explains UFO sightings.

  26. Where I work, we do image manipulation for publishing. I passed this around the staff. Loved it.

  27. Kyle

    Using the same trick as finding the image in those “magic picture” books I could get both strips the same….I think.

  28. Dzipi

    This is actually my favorite illusion although I encountered it in different shape (color :) ):

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

  29. That’s fabulous!
    Do I get points for spotting the T.P. reference?

  30. John Baxter

    Hmmm…it’s quite different when printed (on my printer at least, but as expected). The green spiral arms and the two small square green samples are light blue; the blue spiral arms are dark blue.

    Note: if you print, select the desired pages (IE 8 gave me 7 pages of scratch paper and two relevant pages when I carelessly let the machine print all pages).

  31. Karen

    Brody, it’s not meant to “explain” UFO sightings, it’s an illustration that what you think you see can be a lie, and that general rule is part of what allows people to think that mundane terrestrial objects are spaceships. Or, to rephrase the summary, once you have it proven to you beyond a doubt that the blue and green are actually the same colour, *and* even after knowing this when you look at the picture again, they *still* look like two different colours, how can you say with absolute certainty that the UFO you think you saw (at night, in the middle of the woods, with nobody else around) absolutely had to be visitors from another planet?

    Really, this illusion doesn’t need to “explain” UFO sightings, as such sightings tend to get explained on a regular basis.

  32. Hmm, interesting. I have trouble with seeing reds and greens, and when I saw that image I had to strain to see the effect that Phil is talking about. The green looked the same to me in both areas!

  33. John Swindle

    Fooled me, and fooled my computer,too! I copied the image to my desktop, and my system made an icon, using a reduced version of the picture. On close examination, the “blue” and “green” spirals in the icon actually ARE blue and green. This may provide a hint as to why Lorax, and maybe some others, saw differing shades of blue/green instead of exactly identical colors. Instead of making an exact copy, the computer may have made an approximation.

  34. rpsms

    Using photoshop:

    bottom layer: green
    top layer: orange or magenta, “overlay” “50% opacity.

    Arrives at virtually the same color(s).

  35. Jeffersonian

    I see Phil’s shower curtain.

    I’ve enjoyed these since Psych101 when our prof showed us tons. BTW, there are lots of great on-monitor optical illusions like this.
    tinyurl.com/dgs64g

  36. Oh, this is just full of win…

    I just linked to this entry on my blog… very cool.

  37. Arnold Martin

    Oddly enough, cameras are not “faithfully taking pictures of absolute truth of all that surrounds you” either. Simple issues like who points the camera, at what, with how wide or narrow a lens and why as well as what is going on behind the camera make the “truths” told by photographic imagery fully lacking in any factual kind of truth. Layer on photographic manipulation, be it analog or digital, and not only does the idea of “truth” dissolve completely but so does the idea of “objectivity.” This is why critical thinking is so crucial, perhaps more than ever. Thanks Dr. Plait for nurturing and promoting this kind of thought. Maybe your effort is a drop in the bucket, but if enough people learn to think and question like this we could fill an ocean with the results.

  38. TheBlackCat

    Simple issues like who points the camera, at what, with how wide or narrow a lens and why as well as what is going on behind the camera make the “truths” told by photographic imagery fully lacking in any factual kind of truth.

    Add to that the fact that cameras, both analog and digital, are designed to emphasize greens to better match the way our eyes work.

  39. Aaron S.

    I just went into Photoshop and removed the purple and orange lines.
    This is what I came up with.
    http://imgur.com/FFxtB.jpg

    Pretty neat illusion.

  40. T_U_T

    Be careful people. Don’t overgeneralize. The fact that our visual processing fails while processing an completely artificial pattern does not mean that it is worthless, or even very unreliable under normal circumstances under which it has evolved. Otherwise it is just a matter of time before some postmodern loon pops in and declares every empirical evidence and every reasoning faulty and worthless.
    And you surely don’t mean “We can’t believe our own brains” literally, because then you would have to dismiss every and each of your thoughts ( including the thought that you have to dismiss each and every thought you have ) yielding a complete does not compute paralysis of thought.

  41. Torbjörn Larsson, OM

    The price is that our perceptions are not completely reliable,

    If it’s any consolation, odds are that machine perceptions will end up skewed as well, not only from inherent processing problems. Just read about object recognition, where scientists made an order of magnitude compression just by mimicking how eyes work. (In this case, how we locate and track objects.)

    Our perceptions are highly adapted for low rate, noisy, biological signal pathways. Technology can benefit, and be corrupted, from that. (That said, I do think a decent color imager could sort out the true color above even in such cases. But they may make other mistakes.)

  42. Blind Squirrel FCD

    There is a much easier way to demonstrate that the colors are the same. Enlarge Phil’s enlarged image. cut two holes in a couple of unpaid bills and mask out everything except for a “blue and a “green” area. Bingo! Works for the shadow illusion @29 also.

  43. Tim G

    Now that’s a good illusion. That’s something to keep in mind when doing some interior decorating, I suppose.

  44. boris

    very cool!
    try looking at it from a distance and then getting closer slowly….
    not with the original image, with the zoomed one.

  45. I normally (but infrequently) reply only about astronomy issues – but color illusions have always tickled my fancy. Indeed all the “blue” and “green” segments are identically (R,G,B) = 0, 255, 150 ala Photoshop eyedropper. But here is a prescription also via Photoshop to convince you.

    1. Save the image to a JPG (or TIFF) file and Open it in Photoshop.
    2. Select the “Magic Wand” tool.
    3. Set the Tolerance to zero (numerically 0), so the color match to be found is exact only.
    4. Make sure the “contiguous” box is not checked
    5. Put the Magic Wand cursor (central hot-spot) dead center in one
    of the “blue-green” arcs.
    6. Click. This will select all identically colored pixels in the image
    7. Do a COPY
    8. From the file menu select NEW (to open a new identically sized window)
    9. Click in the newly opened window (to make it active)
    10. Do a Paste.
    11. QED.

  46. James

    Freaky stuff.

  47. Hans Henrik Krohn

    Even for those of us who are Windows (XP) users and don’t have Photoshop installed, there is a way to show that the blue and greens are the same. Save the image to a .gif file, and open it in Windows Paint, and zoom in to 800 %. You will now be able to recognize that the two different colours are actually the same; but of course you can try moving an area of previos “green” to “blue”, and thus convince yourself further.

    Re comment 13 above, it appears you need to zoom precisely to 100, 200, 400 or 800 (or so onwards) %; tools that don’t allow you to be this precise, will show non-existent “border colours” that aren’t actually there.

  48. Aldis Ozolins

    Neat Illusion. This reminds me of the Albers studies we had to do a couple semesters ago at art center. It’s basically the same principle that the ground color can be manipulated by core color and vice versa. Its pretty hard to get the correct color combination to accomplish this.

  49. Keith

    Or alternatively just do ‘color replacement’ on the orange and blend it to purple. Voila, same colour spirals.

  50. Another good demonstration of the effect of context on color and why you should develop your whole painting from simple to complex, rather than polishing one area and moving on.

    http://www.digitalartform.com/archives/2005/06/color_judgement.html

  51. David

    “Where the green hits the magenta it looks bluer to me, and where the blue hits the orange it looks greener”

    “However to be fair, I noticed upon closer inspection that the green stripes that are surrounded by purple are outlined with a dark blue.”

    “@Steve,Your brain is fooling you re: blue outline. Zoom in and you will see that “blue outline” remains the same size even as you zoom in deeper and deeper.”

    Because of the way subpixels are arranged on monitors, there really is a blue stripe between each magenta/(greenish)cyan transition.

    The Magenta is made of
    255 Red 0 Green and 255 blue
    and the Cyan is made of
    0 Red 255 Green 150 Blue

    put them together and you get
    255 0 255 0 255 150

    The 2nd 255 is surrounded by two black subpixels.
    In other words, there is a blue subpixel with no subpixels directly by it to blend into.

    You get a similar effect by transitioning from cyan to orange, but instead there is a “pixel” made from 4 sub pixels.

    0 255 150 255 150 0

    The green subpixels here are as intense as the red and blue subpixels combined, so you get a bit of green in this area, though it is not as intense as the magenta/cyan transition.

    (None of this as has anything to do with how the primary illusion works)

  52. justin

    magenta and turquoise = deep blue.

    If you try and zoom in on the gif with some applications such as the default I am using in Ubuntu. The computer will create a thick blue outline around the green. Blending the two colors of the pixles.

    Your monitor does this too, hint hint…

    I wouldn’t be surprised if your photo receptors also are blending the colors at the edges. I’m not sure that supports the author’s claim.

    I don’t think it is as much context that is creating the illusion. Just some food for thought.

    I hope who ever is doing the study, considers alternate solutions.

  53. I learned this trickster phenomenon from my freshman 2 dimensional design art class, which was based on Josef Albers’ study of human perception of color. We had to do a lot of exercises creating effects like this. It was a great course.

  54. Claud

    Our minds play color tricks on us forever. We see reflected light; therefore if we are holding a piece of paper in a room with incandescent lights it is physically impossible to see a white sheet because incandescent light is more orange/red.

  55. Matteo

    “This is why I tell people over and over again: you cannot trust what you see even with your own eyes. Your eyes are not cameras faithfully taking pictures of absolute truth of all that surrounds you. ”

    Yes, but somehow you were still able to figure out how and why the blue and the green were the same color, and it is something you did with your own eyes. In order to make a sweeping general statement that our senses deceive us, we would have to know (via our senses) what the “real” situation is and compare it to the illusory situation. So our senses are plenty good enough to know that they can be deceived *sometimes*.

    But really, what a cool illusion!

  56. However much it may be that the RGB composition and even the wavelength of the light are the same, nevertheless, the two colors are different, as one can see by looking at them.

    Understand, I’m not trying to put the matter to rest. It was already at rest, and undeservedly so.

  57. RamblinDude

    Wow. I opened it in “Paint” and cut out a square and moved it over and…sure enough, it magically turned into the same color. It would have really freaked me out if I hadn’t been prepared for it! No wonder the real world is so hard to figure out.

  58. MadScientist

    Oooo! Pretty! I think I’ll plagiarize and make a PostScript version.

  59. The ‘outline’ is not an optical illusion. It’s simple chromatic aberration in the eye’s focusing ability being somewhat exacerbated by the fact that a monitor is an artifical tristimulus that is itself not perfectly aligned (and this is why ‘subpixel antialiasing’ drives me nuts). Those of us who use lenses for correction (contacts/glasses) have it even worse.

    Also, the color perception illusion is not so much your brain being ‘fooled’ or ‘overthinking’; it’s simply that color perception (and visual perception in general) is a system of power integrals. Many aspects of hearing work the same way.

  60. StevoR

    Well it seems that like Shroedingers dead/alive cat (Bingo! Hattrick!*) a colour can be BOTH blue and green depending on surrounding colours /patterns. Awesome! 8)

    Actually, in astronomical history there’s an even better example of what you’re seeing NOT being an accurate reflection of Reality : Percy Lowell’s non-existent but famous “Martian Canals.”

    Lowell straining to view Mars at the limits of his vision mapped a whole series of straight and curving lines then considered to be canals created by a dying, drying out Martian civilisation but now known to be nothing more than another sort of optical illusion.

    ——

    * See my comments on the ‘Quantum Entanglement’ (5) & ‘Enceladus Ocean or not’(29) articles.

  61. Simmo

    Well, I’m red-green colourblind and the illusion still works for me (I also feel slightly ill now). It is supposed to be moving about, right ?

  62. yy2bggggs

    “The original was apparently posted on Buzzhunt”

    FYI, I suspect the original is here:
    http://www.psy.ritsumei.ac.jp/~akitaoka/color-e.html

  63. Tom

    Great illusion.

    #58 David: Great comment, and a great point about not jumping to conclusions. Just as the eye attempts to reproduce the environment, so does the monitor. Both produce artifacts. (I think your comment is only correct for CRTs, not LCDs, though. #13 SteveG are you on a CRT?)

    It also seems that the explanation given does not sufficiently account for the phenomenon. Move away from the monitor until you can no longer see the small lines. Then keep going until you can barely see the spiral. The still appear blue and green, but there’s no contrasting color visible at this point, it’s just a blur.

  64. dude

    2 funny. this is simply wrong! the colors are not even remotely the same. interestingly enough though, the two words that i began my post with… yeah, you see them… 2 and funny…well, first off, they aren’t both words but, if they were both words they would be the same word and second off, even if 2 and funny aren’t both really words, if you were to paint them green, i mean from the exact same can of paint, well, they would be the same color!!!! i’m not kidding. they would be.

  65. (Color) blinded me with SCIENCE!

    J/P=?

  66. Jim B

    Let me get this straight. Phil says, “This is why I tell people over and over again: you cannot trust what you see even with your own eyes” and “What you see in life is absolutely and provably not what you get.” So what did Phil do when presented with this optical illusion? “So I loaded the image in Photoshop and examined the two spirals.” What?! How did he examine them? With his eyes! Later Phil says, “Here’s a zoom to make this more clear: See? The orange stripes go through the ‘green’ spiral but not the ‘blue’ one.” But Phil, with what are we supposed to see? Our eyes? Why bother trying to see if “you cannot trust what you see even with your own eyes”?

    So the next time someone swears they say saw Jesus, or a UFO, or a ghost—or for that matter saw Photoshop, or an automobile, or an apple, or an ink pen—show them this picture. What you see in life is absolutely and provably not what you get.

  67. Jack

    Doesn’t work too well if you are colorblind. I don’t see any real trick… maybe I’m not as smart as you say.

  68. Neosis

    This happens because, as the article says, our eyes (and in turn our brain) are not faithfully representing the world around us – and they can’t. Our brain creates a simulation of what our eyes take in. We begin to model everything in our mind from the time we first see anything at all. These models serve as interpretive shortcuts.

    Take for example, the Necker Cube. The reason that, from a solid image, we can see two entirely different orientations of a cube is because, based on the way the cube is drawn, there are two distinct models of a cube that we have inside of our brain that the picture satisfies, while our brain ignores certain pieces of information in order to fit the picture in either case.

    That the human brain simulates its reality means it can simulate anything, even things that are not there. This serves as my most important skeptical objection to those who have paranormal stories that they claim have “absolutely no explanation.” I’m not calling these people crazy, as their hallucinations have not persisted, merely the victim of the fact that sometimes, without any real cause besides an unfortunate chemical imbalance possibly brought on by fear or other extreme emotions, we can simulate something that does not exist. The human brain is not perfect and infallible to dysfunction.

  69. that’s the best illusion i’ve seen in a while – freaky

  70. The scientist

    Take photoshop, go to replace color, select orange, set hue to -94 (the pink interspiral color) and see the green does indeed disappear, it’s quite amazing.

  71. Dennis Bladergroen

    But if “everyone” sees the colours as green and blue, we all have the same perception although it is not strictly correct. So Einstein proves to be right again: perception is reality.

  72. Jimmy Mayo

    If you print this image on a color printer (hp laser jet 5550 dn) you see two diffrent green colors and no blue. Why?

  73. Dave

    Fascinating stuff. The greens do look the same when zoomed in at 1000% at the edge (two stripes) but sliding the 1000% view window over towards the center causes the rings to appear bluer.

    Not only that, but resizing to a 50×50 pixel thumbnail preserves the effect!

  74. Deborah

    Seurat…pointillisme

  75. Ian Michael

    Any art school student taking a proper color theory class will have learned to do this (often referred to as “one as two colors”). Unfortunately, I have taken such a class, so I don’t get the joy of being hoodwinked any more.

    Another more challenging optical illusion using similar principles is to make two different colors look like one color.

    Color theory for the win.

  76. Installed color tiles on kitchen counter with some of them- I thought, blue. When I placed what was a green mug on the tile, they were the same color. I told my family my new canister set will be green, everyone said it will clash with your colors. When the set was on the counter, we were surprised to see they matched, but were still blue and green. Thought again perhaps they are each shades of turquoise to explain it. Never understood it till now. Figured it had to be about context.

  77. I see a sailboat!

  78. LINDSAY

    COOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL

  79. Stone Age Scientist

    Very true, Phil, as I have no Photoshop, I used the very simple MSPaint to isolate the distracting colors, and voila!

    bluegreenzoom

    The resulting edges appear fuzzy, as can be expected from a very basic program that comes with Windows. I should have used the more powerful Gimp (a free software) but I find that a bit hard to manipulate through (a bit time-consuming).

  80. Xavier

    I don’t see any blue in this picture at all, only green, orange, and magenta. This optical illusion must only work for those without any sort of color deficiency. I am RGB color blind and when I saw no optical illusion in something all other people were excited about, I was confused. Now, I am just a little disappointed because I won’t be able to experience the wonder of this beautiful illusion!

  81. searching the 72. Comment. Can’t find it. Maybe counting is only illusion too?

  82. Andre

    If you scroll the first image up and down fast a magnetic field will be drawn.

  83. Gary Ansorge

    108. Stone Age Scientist:

    Gee, so much high tech,,,I just covered the distracting bars with my fingers and observed the same thing,,,

    Cool illusion though.

    Gary 7

  84. Suzie

    “Incredibly, the green and the blue spirals are the same color.”

    No they are not. And that’s the crux of the illusion.

    The blue-green WITHIN the green and the blue spirals is the same color.
    But the green and the blue spirals themselves are not.

    As you said:
    The green spiral is blue-green and orange.
    The blue spiral is blue-green and pink.
    And it’s the interaction of the blue-green with the pink and orange that produce the illusion.

  85. You should have asked an artist, the proper term for this is called simultaneous contrast. Most portrait paintings use grey to appear like blue because of the contrast next to the warmer skin tone.

  86. Joe Meils

    All I know is… now I have a headache.

  87. Stone Age Scientist

    No, Gary 7 @ #113, unfortunately, that method did not work for me.

  88. Wow! That is one of the best optical illusions I’ve seen. This just goes to show why we need skepticism, right? Our minds see patterns that don’t exist, according to Michael Shermer.
    I once saw an awesome optical illusion online: a spirally thing that really did look like it rotated. Freaky.

  89. Scven

    Yea, i did the same thing and the poster and they are diff colors. LRN2PHOTOSHOP

  90. Jesse

    I’d like to point out that this doesn’t work for hue blind people :P Those colors totally looked the same to me from the get-go.

  91. dart

    I, too, copied and opened the image in Photoshop and can confirm that there are only three colors in the entire image: magenta, orange, and the blue/green.

    I became curious if the spirals had any important effect on the illusion, and, surprisingly, they don’t…so I don’t know why this complex design was used. I created a “straightened out” version with horizontal stripes of the orange and magenta with vertical bars of the green/blue. The illusion holds up completely that way. The vertical bars alternate between looking green and blue.

    An earlier commenter was correct that art school students do color studies with the goal of creating the same illusion, and that the effect is called simultaneous contrast. I did many of those in art school.

  92. The original belongs to http://www.ritsumei.ac.jp/~akitaoka/index-e.html and should be properly attributed to him.

  93. brntoki

    Funny how it’s “the other guy” who could be making that big mistake and not YOU!

  94. We all know about after-images etc so illusions involving colour are interesting but
    expected. I really like this non-colour optical illusion:

    http://illusioncontest.neuralcorrelate.com/2009/the-break-of-the-curveball/

  95. poodle

    Lorax, your problem is the sample size your program is using. If it isn’t set to 1px it will be averaging the sample from multiple colors, just as your brain is.

  96. Rod

    Funny, But for a color blind person (me) they both appear the same color which is very wierd. What no it isn’t

  97. Most of the “blue outline” I am seeing is caused by the browser. The HTML on the page resizes the image to fit the article. The browser resizing blends adjacent colors. Green and purple blend into blue. The two colors that are supposed to look the same actually look slightly different because the browser’s blending algorithm makes them different.

    There is a *small* amount of “blue outline” I get from viewing the image on an LCD. I can exaggerate this by turning my head right, which combines with the chromatic aberration from my glasses. I can make the blue outline disappear by turning my head right, which causes the chromatic aberration in the other direction, and they cancel each other out.

    If you look at the original size image (right click, with View Image), you’ll get the version without adjacent pixels blended together, and the illusion remains, without any of the debate about blue outlines or whether the two colors are the same. If you then use the “zoom” functionality in your browser or operating system to try to get a better look at the blue outline, and the system blends pixels, you’ll see the blue outline generated by zooming. On Mac, use System Preferences → Universal Access → Zoom Options → Smooth images; turn this off to avoid blending. I don’t know of a way to turn blending off for browser zooming.

  98. bad Astronomer: “So the next time someone swears they saw Jesus, or a UFO, or a ghost, show them this picture. What you see in life is absolutely and provably not what you get.”

    That conclusion is just as poorly motivated as believing in ghosts. The BA should have stated, “What you see in life is not **necessarily** a close facsimile of what you get.”

  99. bleij

    Quote: “What you see in life is absolutely and provably not what you get.”

    With all due respect, this is a questionable conclusion to say the least. Quantum-mechanically speaking, there is required to have been some ‘collective perception’ – and thus value – of the color green before we evolved from the oceans, let alone before we were able to digitally represent this particular shade as RGB 0/255/150… So in that respect, I could just as easily argue that RGB 0/255/150 is some digital illusion of a certain quantum state of ‘green’…

    Then there is the problem of at what level of zoom you’re working… If you were to zoom out on the color combiation used above, you would see these colors disappear and blend to make place for a new one… You state it yourself in your article:

    “Like I said, incredible! For pedantry sake, the RGB colors in both spirals are 0, 255, 150. So they are mostly green with a solid splash of blue.”

    The very fact that it’s RGB 0/255/150 states exactly the same. This means that the green your cameras and software are “capturing faithfully”, are actually the same idea as the image above…

    Of course, in this respect, all of reality is an illusion…

  100. Daniel Barkalow

    If you take a blue-and-white striped object and a green-and-white striped object, and put the blue one under a magenta light, and the green one under an orange light, and the colors are adjusted such that exactly the same spectral distribution comes off of the colored parts of both objects, your eyes will still give you the perception of the spectral response of the two objects correctly (that is, in keeping with the measurements when both objects were under white light). The human eye and brain do this far better than any current artificial system (assuming, of course, that it can’t simply put each object under the system’s choice of illumination). And if you take a photograph of this setup, you can still pick out the (white-illuminated) colors of the original objects correctly, but Photoshop can’t. And, of course, you can’t pick out the colors of the ink on the paper correctly, because it conflicts with your other color perception.

    You can’t turn off your brain’s experience of this illusion for the simple reason that if you did, you wouldn’t be able to see shadows as something separate from the coloration of the objects they fall on, and you’d be unable to make sense of the world around you.

  101. Steve

    Also, if you copy the image over to Photoshop or similar and grey-scale it, the ‘blue’ spirals disappear completely, leaving only the ‘green’.

  102. Hoopz

    “that zoomed image above is square, believe it or not”

    Are you seriously saying that it does not look square to you? Wow, some people’s vision must be more frakked up than mine. Cos that seems like a perfect square to me… I imagine the diagonals: they are clearly at a nice 45 deg angle.

  103. Tom Allen

    The motion illusions on Kitaoka’s website are even more amazing. Everyone should go to his main index page and check them out.

  104. Seth

    Try this… Copy the pic into a photo editing program. Use the eyedropper to select the “blue” or the “green”. Draw a thick line across the picture. Look at it zoomed all the way in and the colors ARE the same. Zoom back out and it appears as if there is yet a third “color” that does not match either of the first two.

  105. I think this is probably the most impressive illusion I’ve seen so far :)

  106. Come on, who doesn’t know. Read some Josef Albers and you’ll start to get the hang of color illusions.

  107. Aaron

    Interaction of Color by Josef Albers. Pick it up.

  108. Wow that is pretty cool. It’s good that we have photoshop so we can check our answers too.

    And the curveball someone posted was insane. I’ve always been a fan of these optical illusions. Good job.. now my eyes hurt ;)

  109. babis

    This is exactly what Raster is based uppon to make huge posters seem like having milions of colors while only using the basic ones

  110. kp

    meh,

    Think about, your television does the same thing. Get close enough and you will be able to see the different pixels, red, green, blue.

  111. v.dog

    You don’t need an image editor to see the truth.

    If your browser has an image zoom extention, it’s very cool to watch the bands seemingly change colour as you zoom in.

    Do it on the smaller image, tho’ as you’ve got to zoom in pretty close for the illusion to break.

  112. GMJH

    I find it quite amusing after reading both the article and the 159 comments that there is no definitive simple statement saying how many colors there actualy really are in the image. In fact reading the comments, people still say there are 2, 3, or 4

    which is it? 2?

  113. Patrick H.

    The spiral pattern has NOTHING to do with why these colors look off. They look different because of the bleeding effect of the interior stripe colors being different.
    BTW, there are three colors. One green, one orange and one pink.

  114. MJ

    Michael Jackson is DEAD! 06/25/09

  115. Semantic Nazi

    Green? Blue? Both?

    Actually, its neither!

    What it is is a separate colour again called aquamarine or turquoise which is half-way between blue & green! ;-)

    Has anyone else thought of and tried colour printing out the original tricolour spiral design, sticking it to a bit of carboard and spinning it at different speeds to see what happens? I so want to do this experiment but my printer’s dry of ink right now …

  116. C. Charles Caruso

    I’m not color-blind, but I do have a defect in the my optic color receptors–the frequencies for green are shifted for me. So I don’t see blue and green, but I do see the optical illusion of pale lime green and aqua. I see two different shades of green in the top image, and the same two shades of green in the second image. A very pale lime green coming in second up at the bottom left, and second from the top at the upper right. The other “blue” (second from the top left and second from the bottom right) is what I would call an “aqua” green (much more green with just a slight tilt to blue). The close-in image has the same tints as the top image for me.

    (My color defect sometimes causes me to mistake the green of a stop light at night for a blue-white street light–until a yellow light comes on above the “street light” and then the red light atop that.)

    It is interesting however that even though the colors are identical, I see two different shades, as those who have normal color vision.

  117. geez, try colorzilla plugin for your firefox and compare the hex values, you’ll get the truth.

  118. Milarepa

    He’s right, Micheal Jackson really IS dead…

  119. Brian

    “So the next time someone swears they saw Jesus…”

    …or that Krishna was blue?

  120. Iyanski said, “geez, try colorzilla plugin for your firefox and compare the hex values, you’ll get the truth.” I reply that the two colors, the third color seen in isolation, and the hex values seem to be parts or aspects of a complex truth.

  121. Ted

    My god, it’s full of stars…..

  122. Christ Tao

    One simple one to verify is to put your fingers over the blue spiral. Narrow the gap between your fingers to block out the magenta. As your fingesr get closer, you will notice that the blue is getting a bit greener.
    Really interesting.

  123. Calypte

    Well, I’m also red-green colorblind, and I don’t see the alleged “optical illusion.” I don’t see green anywhere in these spirals.

  124. Matriarch

    Most days I would find this incredibly interesting and fun and would post links like crazy. Today, I’m just refusing to believe anything but what my eyes see. This is a brain-stem sorta day if there ever was one.

  125. The thing is that the brain is just mixing colors together, because it doesn’t deal with colors in a pixel-precise manner. If you take the image and do a Gaussian blur on it, very similar perceived colors come about:

    The illusion isn’t terribly different from how halftoning or dithering works.

  126. Bob

    That’s really weird, if I stare intently long enough, the colors do look the same. It starts to change color after a few seconds.

  127. Colin Day

    I would say that the brain processes signals rather than interprets them. As for the reliability of our brains, they are physically quite reliable, as most of us agree that there was a visual discrepancy.

  128. BBB

    “So the next time someone swears they saw Jesus, or a UFO, or a ghost, show them this picture. What you see in life is absolutely and provably not what you get.”

    Uh, this kinda proves that the next time someone claims they saw a green Jesus he might really be a blue one. Unless you want to read waaaayyyy to much into this.

  129. karl

    This is a zoomed photo of the MONITOR ITSELF – now you can see the *actual pixels* that are being displayed. It’s quite clear that there’s not “just 3 colors.”

    non illusion

  130. harry

    here is an interest fact to this discussion….

    Actually many native cultures around the world don’t distinguish betweeblue and green in their languages, they use the same word for both colors.
    Also often lush green forested mountains are called the blue mountains because they can appear as such in the right conditions, or think about the seas different colours at different days everything from green to grey………
    actually a quite old thing then….

  131. Marc-Yves Tumin

    Nice anti-Christian swipe near the end, marring the piece beyond redemption and leaving one with no illusions about the petty viciousness of the scientist.

    Marc-Yves Tumin
    Manhattan

  132. Marc-Yves Rumin (#226), nice try at trying to foment a religious fervor there, but what I wrote was clearly not anti-Christian. It was a statement about people who claim to see Jesus everywhere, when it’s just as clearly a case of your brain finding patterns in random noise. Search this blog for the word pareidolia.

    And you might want to find out a little bit more about the author — me — before making such grand statements. It only reveals your ignorance.

  133. Dean G

    Well said Phil.

  134. adam

    move your browser window around and look at that picture and you’ll see some more optical movement illusions. now, explain that all you visual perception gurus.

  135. Holy crap. I think this picture just shows me that I can’t trust my brain or my eyes…which sucks.

  136. LD

    I cut out a paper mask to show only the colour of the spiral, they are two different colours. Nice trick, it just doesn’t work.

  137. I was skeptical at first, but it’s very easy to test it. Simply open in Photoshop CS4, then zoom in to 500%, then use the eye dropper to sample the color that appears to be green. It is hexidecimal #00ff96. Then sample the color that appears to be blue. It is hexidecimal #00ff96. Both are exactly the same colors.

    For those people who mention seeing blue halos, there are none. I can zoom in as far as 3200% (yes, more than 3 thousand percent), and each individual pixel is clearly visible.

    p.s. There is one solid black pixel at the very centre of the image. The optical illusion is fantastic. I teach Photoshop and will show this one to my students tomorrow.

    Cheers!

  138. Mike Caprio

    How many different color combinations can produce this kind of effect – or is it just a matter of shape and color blending in the brain? Is it more pronounced when reds and greens are involved? It seems like it would be relatively easy to algorithmically create many versions of slightly different patterns and variations of color to see if there are greater or lesser effects with varying combinations.

  139. Heather

    fantastic :)

    but the comment at the end… you ever think that maybe it’s things like that prove why most people CAN”T see jesus, ghosts, or ufo’s? Don’t be so skeptical, as you said, not everything is as it seems.

  140. @237: Since it’s a paletted .gif, all it takes is a paint program which allows you to modify the palette (which is most of them). The effect definitely occurs with lots of different combinations.

  141. Josie

    When you print the image, then scan it back in as a gif file, it turns into an image of an academic on a piece of toast. Just because our senses play tricks on us doesn’t mean that we need to walk around never actiing and never believing anything. Sometimes, you just need to believe what you see and enjoy the colors.

  142. ME

    While I take Phil at his word that no anti-religionism was meant at the end (I suspect he was referring to things like seeing the Virgin Mary in potato chips among other things), as T_U_T points out, there is a very big generalization at the end. The brains ability to process color in close proximity is a bit different from the ability to explain unusual visual phenomenon in general.

    This relates to a pet peeve of mine, how people apply Heisenburg’s Uncertainty Principle to pretty much anything they want to, ignoring that it is in actuality a very specific principle aimed at explaining the difficulty of measure atomic/subatomic particles.

    As someone with a BA in Art, the phenomenon on display does interest me, but the close up provided by Karl raises questions as well. Having tried the Photoshop eyedropper test (same color was the answer to that one) I have to wonder if Karl’s photo was saved in a format that altered the color (JPG saved at less than 24 bit or worse a GIF which will use adaptive color). Theoretically though, that should change the colors to the same alternative color, so that doesn’t explain it completely.

  143. Thanks Sam,

    I really enjoy these things. You really need to look at them.

    Gramps

  144. Paz

    This is an impressive optical illusion, however it is actually fairly obvious.

    If I show you a purple coloured square and a yellow coloured square, they would still be the same colours. Because all colours are made up of different parts of red, green and blue light. Therefor everything you see on this site, even the text and the background is actually the “same colour”, namely red, green and blue (as you rightly pointed out when giving us the formula of the green spiral 0, 255, 150).

    Nothing else is happening here. Your brain mixes the greenish colour (0, 255, 150) of the spiral with the orange and magenta spirals respectively. Just like it does with every single colour on this page and in fact everywhere around you, just on a larger scale.

    Inspect your screen with a magnifying glass and you see what I mean.

    The illusion is so successful because it manages to convince you that the spirals are something like ‘pure’ colours.

  145. kevin

    The theory behind the illusion is sound, but some people’s monitors don’t support it properly.

  146. Off topic but…

    Did you really make a ‘Tomorrow People’ reference in the title of this blog?

  147. Uh… the explanation of what’s going on here is hogwash.

    The same effect occurs with a simple checkerboard pattern with the same colors. It’s got nothing to do with your brain being fooled into believing anything about what’s in front or back or how lines continue or don’t. The fundamental principle here is that when you put any two colors together in an alternating pattern they tend to be perceived as a solid color field that is between the two colors in the pattern. This is nothing more amazing here than what you see if you hold a magnifying glass up to a television screen or a piece of paper printed with two inks.

    I have a straightforward demonstration of why the explanation is nonsense here:

    http://www.facebook.com/album.php?aid=2024171&id=1534102452

  148. Another reason to use a trained artist who understands that corporate colors can chage in the viewer’s eye, no matter how precise the rgb colors are …

  149. Candace

    In reference to drawing false conclusions based on what you see, don’t you think it’s interesting how we see the world around us, and we come to the conclusion that the world began with a “Big Bang” or “on the backs of crystals” or “was seeded onto our planet by some Intelligent Life on another planet” and then it evolved and became more and more complex (even though this works against the Law of Entropy) and that is how we got here today?

  150. Jason G

    I’ve spent quite a bit of time inside and outside of Paintshop verifying that the illusion is true. Yes, the initial image does have different colored artifacts surrounding each spiral when you zoom the image up 4 or 5 hundred percent. Even when you remove then all so that only 4 colors exist (purple and orange stripes) and (green and blue spirals), the illusion is still there.

    Finally I created the images shown in the link below. It shows 2 black “cover” blocks side by side. There is a tiny sliver of space between the two boxes. In the first image I placed a slice from that spiral. It is the “blue” stripe surrounded by purple on either side. In the next image I moved the 2 black “cover” blocks closer together so that all the purple was covered by the 2 black “cover” blocks on either side of the center blue slice. When I did that, suddenly the “blue” slice turned “green”! Hence by using only 2 PURE colors (purple and green) we’re able to still demonstrate the effect. Amazing stuff. Greatest illusion I’ve ever seen. Hopefully somebody will clean up the original image so that all stray anti-aliased colors around the borders are eliminated.

    http://i44.tinypic.com/2dl3qlv.jpg

  151. Jennifer K.

    Quote: “Where the green hits the magenta it looks bluer to me, and where the blue hits the orange it looks greener. Amazing.”

    I noticed a different effect in the magnified image. It seems that the area of the ‘blue’ spiral which the eyes are focussing on seem more green than the surrounding areas of the same spiral, which appear to be more blue. This becomes more even more noticeable if I focus on a different area so that the colours shift. Anyone else notice this?

    Anyway it’s pretty difficult to amaze me, but this optical illusion is way cool! :)

  152. Jason G

    Here’s something else amazing. I REVERSED all the colors using Paintshop so that the spirals became magenta and orange as shown in the following image ..

    http://i44.tinypic.com/14kfw9h.png

    Needless to say, if you play around with that image you’ll see that both spirals are now magenta. You don’t really need a paint program to verify all this. Just use your browser to zoom the page up about 500%. The more you zoom in, the closer the colors become.

  153. Leah

    Our eyes are faithful cameras (when they are fully functional and in adequate light!). Our brains are not faithful interpreters :P That’s why one person might see a dragon in the clouds, but another person might see an elephant. Their eyes are processing exactly the same image, but their brains are interpreting them differently.

    Despite the nay-sayers, the above illusion is definitely correct. My first thought upon seeing the image and reading “these are the same colours” (on a different site) was “What complete and utter BS. There’s no way those are the same.” Then I stared at it a bit longer, back and forth between the two coloured arms. Then I had a look at the zoomed image. Definitely the same colour. Trippy. Waving around a pic taken of your monitor is lame, firstly because monitors are different, and cameras don’t take accurate photos of monitors, so combine those two inaccuracies and you’re bound for problems.

  154. Vince Clorso

    So! Your basically saying that since we all see the green and blue(ex-colorblind). Then, nothing we see can be truth? However; you should now utterly believe anyone who professed to see an UFO or Jesus. Since, if you were there you would have saw the same.

    LOL.
    What do you see? A couple of wavy lines. Wrong anwser. BUZZ.

  155. Jason G

    Nothing we see is truth? The short answer is “YES”. That great big blue thing we see up there every day with the birds and clouds in it? If you could get a little closer to it and observe it’s pixels , you’d see that it’s nothing more than a mixture of magenta and green enhanced with a subtle shade of mauve. Most traffic accidents in fact are caused by folks incorrectly thinking the light is green when in fact it’s an off-shade of orange and banana nut yellow. There’s more but I don’t feel like making it up right now

  156. Richard Kennaway

    “Your eyes … have filters, and your brain has to interpret the jangled mess it gets fed.”

    Not really. The filters are part of the interpretation. The eyes have their imperfections as cameras, but nearly all optical illusions work by tricking the brain’s image processing algorithms.

    I don’t know exactly what part of the process is being gamed by the spirals, but for some other examples, computing colour constancy leaves you subject to illusions like these, and a lot of the traditional optical illusions result from computing size constancy.

  157. Mark C

    **** In reference to drawing false conclusions based on what you see, don’t you think it’s interesting how we see the world around us, and we come to the conclusion that the world began with a “Big Bang” or “on the backs of crystals” or “was seeded onto our planet by some Intelligent Life on another planet” and then it evolved and became more and more complex (even though this works against the Law of Entropy) and that is how we got here today? ***

    I guess if I’d never taken a course in thermodynamics, and had no idea what the “Law of Entropy” (presumably you mean the second law of thermodynamics) says or the very well-defined limits to the situations to which is applies are, then I might agree with you. As it happens, I have had had more than one course in thermodynamics, though, and can confidently state that you have no idea what you’re talking about.

  158. Sharon

    For me, Computer Op Art is more about mathematics and percentages. It would be fascinating though to experiment with color perception formulas.
    The work of artist James Turrell comes to mind when referring to the shape or framework of light, which ultimately defines the perceived color. Artist James Irwin also worked with Optical cominations of color/light too. For some reason The Allegory of the Cave comes to mind…

  159. Annoyed

    Wow . . . nice of you to bring in Jesus. Good slam. Not.

  160. Textile artists are familiar with this phenomen. In trade jargon it is called “visual mix.” This is how textile mfg’s get different colorways and ever different patterns emerging on the same warp, just by manipulation color juxtaposition. It is both fascinating and can be vexing at times when unwanted surprises occur in production.

    Multi-color yarn painting is another way a good designer can put this to use, and get lots of different effects using a minimal number of hues simply by careful color placement.

  161. ThePutz

    Bollocks, they are different colours. I don’t care what the colour programme says.

  162. Dave

    Author, hold up. I find it fascinating that you are aware of the tricks our eyes play on us, but are oblivious to the many realms of the energy of light that we do NOT see at all. So, rather than smugly declaring that other people do not see Jesus and UFO’s etc., perhaps you should be investigating what it is that they are seeing that you are NOT.

  163. The other day I blogged about this and went a little further in several directions. My discussion ends up with Music and Gestalt theory of Perception. Hope you could enjoy. http://chemoton.wordpress.com/2009/07/05/can-you-trust-your-own-eyes-or-hears/ Regards, Vitorino

  164. Andy

    This is very tricky actually and can’t be fully examined by just looking at the original pic.

    The green and blue colours in the original pic in your blog post are different in the monitor already, because there is sub-pixel rendering in effect. Look at the first pic. It’s a high res pic of my TFT display that I just snapped. The pixels are different.

    hi res photo of tft monitor (zoom in to 100%):

    I zoomed the original in, so there aren’t pixels but surfaces. The effect is still there in our brains:

  165. The brain blends sounds too. The common example is two frequencies close to each other, blending to give “beats” with a blended frequency of the difference between the two frequencies. That beat frequency is what we use to perform simple tasks like tuning a guitar.

  166. I draged the GIF onto my desktop and OSX rendered a small preview image. I was surprised to see that even OSX got fooled by that effect and used green and blue instead. :-D

    Image and video hosting by TinyPic

  167. Andy

    Of course OSX didn’t got fooled. It’s caused by the blurring filter -> when sizing the picture down to icon size, the common values of surrounding pixels are used. Google for gaussian blur / neirest neighbor / convolution matrix.

  168. Incredible! I get picture in photoshop, because you try me to make fool. Thanx!

  169. Jason G

    I took the whole thing into Paintshop and completely removed all of those “Gaussian blurred” anti-aliased edges so that no extraneous colors existed around any of the edges .. nothing but pure green and purple. Still the illusion works.

    Good catch though. The image on this page does indeed have blue pixels surrounding the “blue” spiral. Perhaps that image could be cleaned up .. just so folks like you and me won’t think that those pixels (especially at small image sizes) are in fact bleeding over and causing the illusion.

    Below I removed all the complexity from the image and cleaned up all the pixels, leaving two PURE colors .. purple and “green”. As you’ll see, by surrounding the green with the purple, the green suddenly turns blue. Zoom this image by 700 percent or more to prove that there are no stray edge pixels or blurring of any kind around any edges. Meaning, no bleed-over effect. To duplicate these results yourself, import the 2 large purple and green blocks into a paint program, duplicate the purple block and surround the green one by the purple ones.
    That should prove beyond a shadow of doubt that the illusion is real.

    http://i26.tinypic.com/mhqdsn.png

  170. cdozo

    I found a low-tech way to see that the colors are the same. You can remove the noise that’s fooling your eyes by covering all but a tiny line along the bottom of the picture. Then you can see that the colors are the same.

  171. Henry Swanson

    Enjoyed reading the above comments more than the illusion itself. Particularly the mildly ontologically-flustered ones, semi-consciously worried about their particular invested reality-model.. but also the picture of a zoomed-in monitor screen. “In the grand hotel, it’s turtles all the way down.” After a while, I got bored of the illusion, and the phrase “[..] even though they are exactly the same color” reminded me of “[and if you reverse the words in god you get dog!” Deadpan wow. Yet there’s some kind of unintended irony at work here (indeed it’s only ever ironic if it’s unintended) – and (perhaps once again) an import issue to do with the nature of Language & description itself is being forgotten. I get the oblique, corner-of-the-eye sense that optical illusions tell us less about ‘reality’TM than we’d like to think – ie. despite the fairly minor psychological revelation that somehow we’ve been (allegedly) ‘fooled’, and that as a result we’re now ‘smarter’ and more-attuned-to-illusion (or so we think), we are in fact no less clued up about the nature of either Reality or Illusion, either before or after we ‘get’ the illusion presented.. As if the illusion were ‘merely’ a.nother (cryptic) symbol of truth about reality – ie. one that does not uncover an underlying reality-truth but perhaps is actually yet-another onion layer of truth andor illusion.. Sorry to get so deconstructively zizekian-reversal on yo azz – I mean I hardly know you – but I was wondering if anyone else had this sense of “Fool me once, shame on er..” ie. in fact we’re just constantly getting fooled / being foolish again.. and again.. Take it easy. Still confused, Henry Swanson

  172. Courtney F

    Actually, on my monitor, the zoomed in box is a rectangle, not a square.

  173. you can't see gamma rays but they are real

    Phil, I wish you would apply your logic in an more open minded fashion…i.e. not automatically assume that those who have seen Jesus or a UFO are simply not seeing correctly. For one, they usually feel something as well, thus it’s called an experience, not just a sighting. Is it possible to be a skeptic and open minded?

    If more scientists such as yourself actually studied the matter, I guarantee you would be impressed by the amount of evidence (over thousands of years, from all cultures) that exists. The evidence may be mostly anecdotal, but absolute truth does exist. For example, as in the color illusion, our perceptions can be fooled, but the absolute truth is that the colors do exist, and that they are the same (just presented in a different context).

    Scientific evidence overwhelmingly suggests that people are experiencing something real–the fact that they have given it a label of Jesus or UFO is irrelevant. So lets use our considerable brain power and find out what they are experiencing instead of assuming they are making it up or delusional. I want to see more open minded, intelligent scientists investigate this matter!

    End rant. Great illusion, btw.

    Signed,
    the open minded scientist

  174. Marcie

    Very interesting. But according to the author I provably didn’t really see that typo in the last sentence! Ha!

  175. oddiofile

    >I don’t see any blue in this picture at all, only green, orange, and magenta. This
    >optical illusion must only work for those without any sort of color deficiency. I am
    >RGB color blind and when I saw no optical illusion in something all other people
    >were excited about, I was confused. Now, I am just a little disappointed because I
    >won’t be able to experience the wonder of this beautiful illusion!

    blue-green color-blindness is quite common in the population, especially among men, and many people have a small degree of it without realizing. It does not surprise me that some of the previous commenters are failing to be fooled, as is the case with you, or getting fooled more (is that possible?) by this *moreso* because of that very deficiency.

  176. Jason G

    I know someone with color-blindness who also can’t see the illusion. Speaking of illusions .. variations on this one seem to be infinite .. as in the amazing ANIMATED
    fade-to-black-and-white version. All I did was ask the software to gradually fade that image to black and white. This it what it came up with ..

    Note how the “green” spiral is the only one left standing. What these results mean is anybody’s guess.

  177. I spotted the Blue disk in the May, 09 issue. I have several, original shots of this disc. I have some in red green and blue, large jelly beans, and some in R,G,and B, dots and dashes. I have one of the disk slightly deformed on one side. It’s easy to say that this is an illusion, but I and several others have photographed this item several times. I have one where the disk is nearly completly covered with three different layers, resembling clouds, Red, Blue, and Green. I discovered that I could sharpen each seperatly, and that each color required a different angle of motion. So what’s your take?

  178. TubeStuff

    Didn’t read ALL the comments so please forgive me if someone mentioned this. The phenomenon also exists when the image colors are reversed. Obvious…but fun.

  179. Przemek

    I actualy could see the green not blue, but i had to concentrate on that.

  180. Robert

    This is not an optical illusion, I see green and blue, exactly as intended. Everyone else sees green and blue (except those who are color blind). We see green and blue because this the way our Creator designed us. Since we are all the same, when our Lord returns we shall all see him!! The illusion itself is a fairly marginal effect and can not be compared with any of the miracles. Also, just what this has got to do with UFOs must be a figment of the author’s overactive imagination lol.

  181. In dutch there is a name for a color called “appelblauwzeegroen”, translated Apple-Blue-Sea-Green, and I found it always one of the strangest descriptions, it’s kinda applicable in this case.

    btw try this do a ” Select -> Color Range ” to that color in Photoshop, and see what happens ^_^

  182. eve

    that is soooo weird anyway i cant see that they are the colour

  183. betty

    hey! thanks for clearing things up mr. swanson. laughter truly is the best medicine!

  184. David Edwards

    Actually, this illustrates a principle that is used in automatic white balancing in TV, video and digital cameras. The perceived colour is determined by performing a matrix scaling of the signal along numerous contours intersecting various boundaries. The Open University in the UK devoted a television programme to this, and used Mondrian images to illustrate the operating principle. it illustrated what happens when a camera without a white balancing feature is used to view the world, moving between different lighting conditions, and the resulting image shows colours changing on a more or less constant basis, because the raw unprocessed signal not only depends upon the reflection spectrum of the object being viewed, but upon the spectrum of the light illuminating it. So, a camera without white balance, taken from indoors with, say, tungsten illumination, will view a given object as possessing one set of RGB values, but when taken outdoors into brilliant sunshine, will view the same object as possessing a different set of RGB values. White balancing corrects for this effect by re-scaling the raw image data to what it would be if illuminated under a standard set of conditions. One white balancing model uses balancing based upon illumination conditions that preserve neutral greys without producing colour casts, and another model is based upon something known as ‘tristimulus values’ that are related to the sensitivity of the three different colour receptors in the human eye. Interesting that the visual cortex evolved to perform white balancing in order to correct for different illumination conditions a long time before humans began analysing colour perception and applying the knowledge to camera technology.

  185. This illussion works with metameric colors only, i.e. with colors, which are interpolated by our brain from three basic colors.

  186. actingcrazy
  187. Actually many native cultures around the world don’t distinguish betweeblue and green in their languages, they use the same word for both colors.
    Also often lush green forested mountains are called the blue mountains because they can appear as such in the right conditions, or think about the seas different colours at different days everything from green to grey

  188. The blue and green spirals are actually of the same colour. This is because the brain perceives the colour of an objects with respect to its surroundings. By zooming into the picture, you would realise that the orange stripe is not continuous

  189. Emma

    Wow, I had to get so close to the screen I was positive a joker guy was going to pop out and scare the boogers out of my nose right onto the screen!!!

  190. I think that this picture just shows me that I can’t trust my brain or my eyes

  191. dan

    it is pull it in to photoshop and make a box. or use MS paint even. eye dropper both colors and make a box over them too even. THEY ARE THE SAME!

  192. @scibuff—

    buzzhunt.co.uk also uses WordPress, so if its image up-loader corrupts images, then the image there would also be suspect — unless the author there did an end-run around that up-loader. (Someone here could likewise do an end-run.)

  193. Bobby

    I wish I could be impressed but I’m colorblind :(

  194. Tintin

    Although some of the proofs offered in the comments were resourceful and imaginative, there is NO need for Photoshop and the likes to demonstrate that is is just an optical illusion…

    1) Print the picture

    2) Take a pair of scissors

    3) Cut a strip of the “blue” and one of the “green,”" et VOILA!

    This reminds me of the simple and convincing “o” ring and ice water demonstration by Richard Feynman, during the Challenger disaster inquiry (although I certainly don’t pretend to ever match his genius)

  195. Andy

    its a fake, check out what i found inside it

    the main green is the same colour but the rings have lighter and darker shade pixels spread out inside them – like having a dirty carpet and hoovering one side.

    http://i.imgur.com/ItFbW.jpg

    and

    http://i.imgur.com/IrQ0D.jpg

  196. thisguywholikescolor

    its called a chromatic shift.
    in color theory anyway.

  197. Jeez

    It seriously disheartens me to see so many people missing the point of this trick.

    It does *not* come about by any trickery, or issues to do with how LCD/CRT screens manifest images.

    The trick comes about because the brain does not get high spatial frequencies of colour. So in effect what your brain is interpreting is a blurred version of the image so the interleaved colours in the spirals get mixed. You don’t notice how poor your colour acuity is in everyday life because it is pasted underneath the high frequency luminance (black and white) channel which *does* capture the high frequency details (the lines).

    You can prove this to yourselves by grabbing the true colour and then mixing it with the colour in the intercepting stripes. You will end up with colours close to the ones you perceive.

    I know how “strange” this is, but trying to disprove is makes you look silly.

  198. charles

    Seurat employed this to good effect.

  199. I just wrote an article on optical illusions where I attempt to explain the image above using lateral inhibition. Feel free to check it out as I’m sure it relates to many of your interests. the article covers: simultaneous contrast and hermann grids. The link is: http://www.goo.gl/IbNOk

    Cheers!

  200. Adam F

    I’ve got a bit of a problem with the idea that this image demonstrates that the pre-processing our brain does generally makes us see the world in a less accurate way. The problem here is that this image presents the eyes with an unnatural and intentionally confusing arrangement of colors. In real life, our brain processes the images so that objects which are _actually_ the same color appear to be the same color, despite different lighting conditions causing different wavelengths and intensities of photons to actually hit our eyes. If it didn’t do these sorts of things, you might, eg, have trouble finding your car if you parked it in the sun and came back looking for it in the shade, because it would falsely appear to be a different color.

    TL;DR
    In most instances, the same things which make you see this image inaccurately help you see the world more accurately.

  201. Devin

    Well, I took this .png file into paint AND into photoshop, and there are hundreds of colors in the image. There is a fuzzy but definitely real outline to both the blue and green sections, so I don’t know what image you guys are looking at. I’ve found versions of this spiral online which are legitimately composed of only three colors, and they’re convincing, but this version has been botched. Even using your inkdropper in paint will confirm it. Zoom in on the borders and try dropping the color onto the other spiral. Not even close.

  202. Anthony

    I’m with Devin here. This image appears to have been saved at least once, perhaps more times, as a jpeg and so is full of jpeg artifacts that are doing just what the eye does and what the description claims is illusory, distorting colour and brightness at tonal boundaries. It’s not too bad at the outside where the blocks of colour are large so the distorted values are a less significant part of the image, but towards the centre the distorted values become a large portion of each colour block. The RGB values near the centre are approx. 0.155.190 in the “green” blocks and from approx. 0.155.100 to 0.155.120 in the “blue” blocks. This image needs to be replaced with a clean version that hasn’t had lossy compression.

  203. Anthony

    Following-on from my last comment (June 13th, 2011), after more thought I’ve concluded that the errors in this image aren’t jpeg artifacts, but anti-aliasing errors.

    I’ve looked at this illusion on a couple of websites and both have a similar problem. Apparently, in 2009, most commenters remarked that the “blue” spirals and the “green” spirals were perfect matches. But now, in 2011, the image of the illusion is so full of anti-aliasing errors that these supposedly identical colours are in fact different. Try it yourself before you reflexively deny it. Copy the source file out to an editor and sample the “blues” and “greens” at a high magnification.

    Could the web-host have reprocessed the image files to reduce the page size, unwittingly introducing errors?

  204. Anthony

    (continued from last comment)
    There has been an ill-conceived attempt to smooth out the dithering at the tonal boundaries of the image, which in its original form was quite jagged (evidenced by the detailed view below the large image). This would have introduced anti-aliasing errors, bleeding in colours across tonal boundaries.
    The goal of digital image processing is to replicate human visual performance. In this instance it has also replicated a human visual anomoly, even when the author sought to illustrate the opposite.

  205. sam

    crazy, i played around with the image in photoshop (yes the same color) and it its the same with any color…using black makes one spiral look blue, using white, one looks yellow. You can try it by in the select color range and then adjusting lightness, saturation and hue..impressive

  206. Josh

    It’s interesting, but even when I look at this pattern from far away without my glasses (fuzzy!), the blue/green illusion remains..meaning it’s not the brain “assembling” the colors from the lines themselves, but just the collective mixed color reaching my retina from each general area of the image..meaning it’s a physical phenomenon, and not a neurological one

  207. edzonrapisora

    i always use this as an example when teaching color grading and correction.

    this is why i always tell people to never use their naked eye alone when color correcting photos and videos. always use visual reference for viewing color like the historgram, RGB parade, vector scope, etc. to judge your adjustments.

    even proud people who say that their “eyes are sensitive to color” should see this and know better after on.

  208. wow! illusions are sooo cool haha
    (: you should post how ton draw one!! haha thanks!!!!!!!!!!!!!!!!!!<3

  209. AWESOME CCRAZYYYYYYYYYYYYYYYYYY LOVE IT :]

  210. I and also my friends ended up checking out the best tricks located on your web blog and so quickly came up with a horrible feeling I had not thanked the website owner for them. Those women had been for this reason very interested to learn all of them and have in actuality been taking advantage of those things. Thank you for being very helpful and then for obtaining such notable issues millions of individuals are really wanting to discover. My personal honest regret for not expressing appreciation to you sooner.

  211. zeniden

    Really, all one has to do is put a pinhole in a card and examine the ” blue” and the “green” right on your screen and you will see they are the same. No need for software analysis.

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