Thursday, 25 June 2009

Awesome Illusion

This illusion has been doing the rounds this week (see Bad Astronomy and Richard Wiseman for a couple of science blogs I like that picked it up), but it's so good I thought it needed to be posted here also.

Look carefully at the image below. Do you see a couple of spirals, one blue and one green? Well, take a closer look - in actual fact, the blue and green are actually the same colour!


Don't believe me? Copy the image and open it up in PhotoShop or Paint and take a closer look....

You will notice that the orange curves move through the "green" spirals, but not the blue. And the purple curves don't move through the green.

If we blow this picture up even more, we can see that the colours are becoming more and more similar.

The blue and green appear to be different colours because our brain works out colours by comparing them to other surrounding colours and it does a bit of mixing. When we look at the "blue" spiral, we also take in the purple curves moving through it. This makes it look more blue. When we look at the "green" spiral, we take in the orange curves, which makes it look more green.

I know that's not a great explanation, so I'd be happy to hear a better one!

Edit by westius 2/7/09: If you doubt this illusion, check out this image - I've replaced some of the colours - you can clearly see now that the 'blue' and 'green' are the same:

42 comments:

  1. The actual explanation had to do with the principles of gestalt. yes, as in psychology, they also apply heavily to art. But as far as the way you said it, you are correct. The human brain sees things in comparison to other things, by manipulating the surrounding it is possible to change the appearance of something.

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  2. When you look at the "blue" areas there is actually a bit of blue on the purple lines going through it. This bit of 'real' blue along with the purple is what is causing the illusion.

    Look at the closeup and you'll see it. You take that blue outline out and the illusion wont be as strong.

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  3. I'm analyzing it in photoshop and I think you're theory about how this works is wrong. Its not so much a function of the brain as it is the eyes. Things far away blend together. Magazines are printed with only 4 colors but we see a full range because the dots are so dang tiny or far away. This is the same effect, there's no comparative brain functions at play here, its just the limitations of the optics in the eye, outputting averaged signals to the brain. Like what Muad'Dib commented on "ders wittle bwue aweas in da middle!", although stated cutely he's hinting at something very profound. Even photoshop took the liberty of interpolating the interfering color data to produce average tones towards the middle where the data is too dense to be represented accurately on a monitor. There is real blue in the middle. this illusion is a LIE. thanks internet for lying to me more.

    ...so I'm going to post a magazine picture with some benday dots and claim that some kind of illusion is taking place. lichtenstein is a pop artist not an op artist.

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  4. I'm ColorBlind!!! All the colors look the same to me so I wasn't tricked!!! finally paying off to be colorblind!!!

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  5. I don't know about your photoshop... but mine shows differing RGB values on the two colors. Especially the difference in the top image.

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  6. That's not 100% true. The further the spiral goes, the more green it gets. Near the center, the green is green and the blue is blue. People focus on the center making the illusion appear more valid. Even at the ends of the spirals, the colors are similar, but a few shades different.

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  7. It looks like there is some bleeding on this image - part of the upload to blogger I guess - but check out the image on this site - there is no mixing of colours here:
    http://www.psy.ritsumei.ac.jp/~akitaoka/color-e.html

    the effect is exactly the same - if not stronger. The illusion is definitely real, so don't be disillusioned with the internet Stewart!

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  8. So why does the orange always look orange?

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  9. Wicked! I didn't even believe that at first because the colors looked so different. But when I look at it very closely I can definitely see the trick how you make them look different. Very nice!

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  10. Awesome - I've heard that the Japanese don't have different words for green and blue - now that I've seen this, I can understand why. - It's all relative.

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  11. Muad' Dib--that little bit of blue isn't in the actual image. It is present because the image is stretched slightly on the page. Click the image to see it in its original form.

    John--You are a troll. The RGB values are the same for the "blue" and "green" (0R,255G,150B).

    Brambley--I'm guessing the orange always looks orange because you can see it connected to itself even against its two backgrounds.

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  12. This is absolutely valid. Upon closer inspection the colors that appear green & blue are both 00FF96.

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  13. Well, this is not the entire true.
    If you keep on zooming the picture, you ll find the blue spirale is indeed of the same green as the other.
    But, there is a thin border of blue around the green on the "blue" spirale wich is not present on the "green" spirale. This border plays a major role in the illusion.

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  14. I'm not sure about you guys but like some else said earlier that the RGB on both the colors are diffrent....but close enough that and "normal" person wouldn't see the diffrence

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  15. Freesoul, this thin border of blue around the green is an illusion. zoom and measure (with the eyedropper set to 1 pixel and not having the picture re-rendered to prevent anti-aliasing by the software you use.)

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  16. This is pretty cool. I disagree with Stewat claiming that this is a function of your eyes and not your brain. Your magazine analogy doesn't work because it's not as if we're seeing the purple and blue and interpreting it as one color; we can still differentiate very clearly between the two, hence it's not an issue of limited visibility (until you got very very tiny, then sure). I think the illusion is your brain just making relative judgments on colors, much like black and white illusions where it looks like two shades of grey are very different when they're the same.

    Lastly, there are absolutely different terms for blue and green in Japanese for whoever was claiming otherwise, that's nonsense.

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  17. Copy the picture and, in your favourite viewing software, zoom OUT (not in) until the individual lines are smaller than the pixels on your display. They still seem green and blue. What's that all about? I can easily tell they have the same RGB values otherwise.

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  18. If you do open this in Photoshop and get out the dropper tool you will see that the colors are different. You can look in the info pallet and see that the numbers are not the same.

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  19. An interesting thing to do is to cover up everything surrounding a section of the blue color with your fingers. The color shifts instantly to match the green. That was cool.

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  20. I was skeptical. I print/screened it and copied little spots of each color. Amazingly they are the same.

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  21. I just clicked on the picture and zoomed in with my browser and it is obvious that the part that looks blue has a blue border and the part that looks green has a green border. So FALSE, this is NOT an illusion.

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  22. Most definitely is real. If you want to test and don't have a photoshop program...just use the eyedropper on the blue and then fill in some orange and purple lines with it...they match both the 'blue' and 'green'. Not even a need to check the RGB, pure simple proof, no change whatsoever.

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  23. Totally Photoshopped. Just look at those pixels.

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  24. This is clearly shoooped. I can tell by looking at the pixels and from seeing a few shoops in my day.

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  25. 225 Green
    150 Blue

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  26. It's an illusion.

    Deconstruct it by selecting areas of similar colour (easily done in Photoshop or Gimp). You can see that there are only three colours in the image - green, orange, and magenta.

    If you take each of those colours and create a new layer of each individual colour and pattern you can enable and disable each layer to illustrate the illusion.

    With only the green layer you only see green spirals. When you add the orange layer you see a subtle difference in colours. When you add the magenta background the blue and green are very obvious.

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  27. Amazing. The are both #00FF96. Even up close it's rather hard to tell.

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  28. This effect is solely in the brain. Photo-receptors in the eye act exactly like (inefficient) photo-receptors in a camera.

    The brain is slow to process information from the eyes, so it takes shortcuts to give the appearance of higher speed, like motion-blur and mixing colors together. Most optical illusions result from these shortcuts, though some illusions, such as afterimages, result from the function of the eyes.

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  29. Oh dear, my eyes ache trying to figure out before you explain further. I am not good at photoshop so I cannot experiment further with this but I am always up for a nice illusion. This is fascinating.

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  30. EXACTLY THE SAME PROCESS AS A RGB TELEVISION. THE BRAIN UTILISES MINIMAL COLOURS WHEN THE COLOURS ARE IN TINY FRAGMENTS AND IT MIXES THEM INTO MULTI COLOURS. SAME WITH THIS ILLUSION. THE MIX OF COLOURS CREATES ANOTHER COLOUR.

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  31. Just had an eye exam, Dr. told me I have excellent color perception, yet all I see is distinctively green and blue patterns.
    What gives.

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  32. It's not "just the brain". The key is the thin orange and magenta spirals, which at first glance might appear to be one and the same. They are not and they greatly affect the perception of the broader spirals, as they're much thinner. At one level the eye/brain normalizes the colours within the broad spirals, but on another level the two contrasting colours exaggerate the difference.

    After opening the illusion in Photoshop, try blurring it (Filter->Blur->Gaussian Blur->4 pixels) and see what happens.

    Another helpful experiment enyailsto desaturating the illusion (Image->Mode->Grayscale), which reveals that the eye (or 'The Brain') still see some difference between the two spirals, while the grayscale value is of course the same. The grayscale value of the magenta and orange spirals are not.

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  33. FredWallace -- let's not call people names...

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  34. I love the colors green and blue together, but this illusion is awesome... i get it now, and in my pic., im not that old I'm much older now, that's from when I was around 5 years old. I'm actually not a science person, so excuse me!(or u!)
    Tehee!

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  35. Stewat, it is how your brain interprets it. How do you think your eyes see things? Without the brain?

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  36. keep writing, just wait new post

    Thanks for sharing, nice blog, i like it, wait for new post.


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  37. It's the Devil, is what it is. SATAN is confusing you!

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  38. My brain has a hard time trying to process this image.

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