This week the blog is turning into a bit of an illusion fest. Last week I posted a wonderful contrast illusion. I wondered whether it might be possible to use the concept to create a more concrete image. Something that might enhance the effect by fitting in with people’s expectations about colour. A few nights ago I woke-up from a dream with this image of a world map fully formed in my head…..


The ‘green’ of the land is the same colour as the ‘blue’ of the sea. What do you think? Any other ideas?

Update: The people who read and comment on this blog never cease to amaze me! Matthew Wilkes (tonicblue) has just posted this much improved version….Genius!ย  Not sure the colours are right in the re-sized image below – go to the original here.



  1. Je JPEG format skews a lot of the original colors and messes up both part of the illusion and clean verification. Both the compression ringing and the anti-aliasing introduce a lot of improper hues and blur the image detail.

    Please create a properly-scaled PNG file, and post that.

  2. It’s not exactly the sam color … very close, but not the same green. Perhaps the downsize and compression made that.

    Source file, maybe?

  3. Yeah, they look like different colors to me, but if I let my eyes go out of focus, I can see that they are the same color. So it’s just a bunch of bars of the same color blocking a world map in the background.

  4. I’m not seeing the same effect of the green itself appearing a different colour. Instead, the dithering effect of mixing colours seems to dominate to create the map effect-eg magenta includes blue, where as orange doesn’t; I believe this is more an effect of the eyes rather than brain?

    I used to use such colour dithering many years ago on computers with only 8 colours to simulate a much larger pallet. The old game “Citadel” on the BBC micro used it very well throughout as an example.

    The perception that the green stripes are actually using different colours is still there but only very slightly, but the stronger dithering effect dominates the image.

  5. Im so naive! I didn’t believe you at first, not until I looked at the image in close up. Clever effect

  6. Hello,

    I had a look in MS Paint and I was well impressed ๐Ÿ™‚ I think docpi may have a point about jpg/png as there was some distortion in the colours, otherwise I thought it was a great start to the day.


  7. Would it be more effective if you broke the continuity of the green by changing which lines are that colour? So purple turns into green, and green turns into orange on going from sea to land?
    As it is the illusion really isn’t working for me, I’m afraid to say.

  8. The ringing on the edges of the continents is not a compression artefact, it is a 1 pixel stroke around the country borders. Check out the white lines inside Europe.

  9. Richard

    I just made a couple of Photoshop Patterns to make this effect really easily. It’s cool when you adjust the Hue on the end result.

    Have a look at these, they took literally seconds to make.

    You will need to click on the full size version to see them properly. Each line is just one pixel. I think it improves the effect. I have a head ache now after making them though.

  10. 2 illusions in one !

    I found that if you star at the picture close up, blur your eyes, thrn move your head slowly away from the screen, the bars disappear leaving you with a clear image of the map.

    Oh, and yeah the colorings good but i feel its a bit too similer to start with so you dont get as much of the ‘wow’ factor…… maybe compression to blame?……..

  11. Yes. We don’t see colors, but a small radius of colors as a color. All the background is light green, but the purple line on sea make it feels like cyan and the yellow line contrast with purple line strengthening green.

  12. “The โ€˜greenโ€™ of the land is the same colour as the โ€˜blueโ€™ of the sea.”

    No. The land is orange and the sea is purple.

    I don’t get it.

  13. Yes I understand how the image was made, but this has no impact on analysis, the focus is on why we see it different.

  14. I can’t acclaim this highly enough. The original illusion was good but the added psychological twist really adds a kicker. People are so familiar with the world map image, so when they’re told of the colour difference it’s even more amazing. GREAT IDEA Richard.

  15. I’m going to make a large, PNG (and SVG) version of this if you don’t mind (I’ll post it here)

  16. JPG does add compression artifacts, which could be avoided by using a 24-bit PNG in this case.

    FYI if you want to look at this image close up, in Firefox, just hold CTRL and use the mousewheel to zoom in, or hold CTRL and press “+” a bunch of times. CTRL 0 resets zoom to normal.

  17. Why thank you very much Richard ๐Ÿ™‚ A guy from Scientific American just tweeted me and asked if it could go up on the SA Gallery. Quite a good day so far I would say

  18. I don’t get it really – if the land and the sea are the same colour, then why when I convert to greyscale do they still look separate?

  19. I worry that we might be drifting away from true contrast illusions here.

    The illusion is that specifically the turquoise stripes should look blue in some places and green in others. I think what we might be looking at in some of these is simply the fact that the average of turquoise and orange (land) is green and the average of turquoise and magenta (sea) is blue.

    In the map image I have difficulty focussing specifically on the blurred turquoise stripes. In the butterfly image they’re just too small to resolve. Certainly the resampled version shown on this page is simply blurring the image and showing you the true average colours, and I suspect that if the full-size version linked from tonicblue’s page looks any different then that means your monitor gamma is set incorrectly.

    1. I think you might be trying to make a distinction where there isn’t one. As far as I’m concerned the fact that the average of the two colours is the same is how the illusion works. It’s just the fact that you can make the bars quite large and still retain the effect. That’s quite cool. But versions with bars that are too small to resolve are cool also. As far as I know however, they’re working on the same effect.

      PS. Disregard the resized tonicblue version in the post, it does not have correct colours, the blue and green are actually different colours.

    2. I’m pretty sure there is a distinction. The original illusion works by finding a colour that looks blue when seen against magenta and looks green when seen against orange, and presenting it in an intricate picture designed so you don’t consciously notice the background changing. You’d swear blind there were four colours in the image: blue, green, orange and purple. I think the version of the map someone posted with the magenta/orange border really helped with this.

      Printing three colours very small so it blurs into two is just dithering. You look at them and see two differently coloured regions and are vaguely aware of a load of high-frequency stripes you can’t really resolve, just like when you look at a printed photograph in a newspaper. You wouldn’t like to say either way whether the blue stripes in one region are the same as the blue stripes in another because you’d be only fairly sure that any of the stripes were blue at all.

      (PS. I do find it amusing that when you shrink these the stripes combine so they become really unimpressive attempts at themselves.)

    3. I take your point. The question is, is the effect played upon by dithering or colour merging in the high frequency versions the same physiological effect as achieved by finding a colour that appears different based on that what colour surrounds it. Although I cannot say for certain I think these effects are the same.

    4. I don’t think dithering uses a psychological effect. After all, dithering works even when the image is sufficiently blurred/far away that you can’t see the individual dots/stripes. It’s just that the reflected light from each area mixes to produce one colour.

    5. Psychological effects and physiological effects are different things ๐Ÿ™‚
      What you describe is indeed physiological (as I said). Both illusions work at any suitably distant distance anyway.

    6. Hang on, no, the contrast illusion doesn’t work at a distance where you can’t resolve the turquoise stripes. How can you say two stripes are different colours when they’re invisible?

    7. OK it doesn’t work from a distance where you can no longer resolve it because then you can’t see it! This is all beside the point.

  20. Ok, ok, don’t get carried away now. We’ve known this effect for ages. It’s used in TV screens from CRT to LCD. It’s amazing how people look at it every day and don’t even notice.

    Perhaps the only interesing aspect of this would be to explore how fat the lines can get until the effect disappears. Where is the boundary of this?

    1. David,
      You’ve misunderstood the point. The intention here is to create an illusion more akin to this one but for colours rather than greys. Like I said, though, I think you’re right about what effect some of these are actually exploiting.

  21. Tried it adding a border to see if it helped with the contrast, I think you lose the fidelity of the map though.

  22. Just to point out that if you are not seeing the illusion, you many not be alone. I’ve been trying to figure out why everyone is so amazed at these illusions for a week – it seems that due to my inability to distinguish various shades of greens, blues, pinks etc I don’t see any colour change. The two stripes are always the same colour.

    One of the few examples of how having a (minor) disability enables you to see thing clearer. Sort of. ๐Ÿ˜‰

  23. All I see is pink green and blue on the top one and green and blue on the bottom no matter how I look at them.

    Not colour blind.

  24. Loving the illusions, keep them coming.

    Saw this one on youtube, and thought of your site for some reason ๐Ÿ™‚

    Optical Illusion Girlfriend…


    P.S. Love the vanishing head illusion

  25. I loved the original illusion, it gave me a really strong sense of being deceived and many of the people I showed it to didn’t believe that the ‘green’ and the ‘blue’ were actually the same colour.

    These other versions are a lot less impressive to me.

    Don’t all colour magazine and newsprint printers use a very similar technique?

    Cyan, Magenta, Yellow and Black, four colours, are all you need to create a photo-realistic image. The colours aren’t mixed they’re just small dots placed near each other and taking advantage of this effect.

  26. I’ve created two smaller versions of the picture in GIF format:

    This really small version shows better the intended effect of the illusion:

  27. And stretching the image produces lovely moirรฉ patterns as the screen pixels interact with the coloured vertical bars.

  28. These seems a lot like like the Bezold Effect and using color vibrations to the extreme. Something you learn in Color & Comp class and other design related classes. We used just cut color stock to make the same color look different by just changing one color in the background to change the whole feel. The next was using the same materials to either get the colors to blend (using similar yet different hues in close proximity that are easily distinguished when not near each other) and then to make the colors work in a way as to cause “vibrations” which just means the colors play off of each other in a way that looks like they move or come forward and recede the longer you look. The amazing thing was some of them came out just as hard on the eyes as a computer generated image using similar techniques. It’s not just some trick of the eyes and the monitor causing things to look different, it’s the ways our eyes and brains translate the visual information.

    Anyway, sorry for the long post there! I just love it when I can go off on something that I learned in classes. Really cool work you are doing! Keep it up! Maybe I can look at a few that don’t make my eyes hurt lol.

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