# Explain this 3D optical illusion I see with green/red text **URL:** \ **Category:** Factual Questions\ **Created:** [January 8, 2014, 10:45pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322 "2014-01-08T22:45:45Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [January 8, 2014, 10:45pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/1 "2014-01-08T22:45:45Z")
I got a Christmas email where someone used green and red fonts. To my surprise, it didn’t just look like flat text to me. It looked like the green text was floating a bit above the screen and the red text a bit below it. In addition, with my glasses I see red sharp and green blurry, but without my glasses it’s reversed: With glasses: Green is sharp, red is blurry Without glasses: Red is sharp, green is blurry 3D effect close to the screen (1 foot): red is above the screen, green is below 3D effect far from the screen (3 feet): green is above, red is below 3D effect remains the same with or without glasses. The below text demonstrates the effect. green red green red green red green red green red red green red green red green red green red green green red green red green red green red green red What could cause this? ---
**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\ **Post date:** [January 8, 2014, 11:06pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/2 "2014-01-08T23:06:31Z")
If it works, it must have something to do with binocular vision, because I have only one functioning eye, and it looks like normal flat text to me. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [January 8, 2014, 11:15pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/3 "2014-01-08T23:15:37Z")
I have sight in both eyes, but it looks flat to me, too. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [January 8, 2014, 11:19pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/4 "2014-01-08T23:19:03Z")
I can’t explain the psychological reasons behind it, but yes, creating 3D effects with colour is a thing. I’m working my way through [this here](http://www.wired.com/design/2013/08/josef-albers-classic-interaction-of-color-gets-a-21st-century-upgrade/) to beef up (well, acquire in the first place) my skills with colour. Several of the exercises are devoted to making things look closer/farther than others through juxtaposition of colours. A basic trick of painting is that colour intensity is correlated with distance from the viewer. So close things in the painting tend to have higher intensity, far things less intensity. [This](http://www.ago.net/the-west-wind) may be relevant - see the mix of the intense reds in the foreground rocks and even the bark of the tree compared to the relatively less intense greens and blues of the far shore? (See it for real, and it just jumps at you!) So in your text - I’m guessing the intensity of the red creates the illusion of closeness; the lack of intensity of the green the illusion of distance. ---
**Author:** ![sitchensis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sitchensis/32/4892_2.png) [@sitchensis](https://boards.straightdope.com/u/sitchensis)\ **Post date:** [January 8, 2014, 11:19pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/5 "2014-01-08T23:19:34Z")
I can switch between the Green “floating” or the red “floating” by minutely changing my eyes focus. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 8, 2014, 11:39pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/6 "2014-01-08T23:39:06Z")
I haven’t fully worked out how these apply to your observations, but there are at least two related physical effects which I suspect contribute. First, your eyes can really only focus on one wavelength at a time. If you focus on a pure red object, green and blue objects will be slightly blurry (blue more so). Colors near each other on the rainbow will be in similar focus while ones farther apart will be relatively out of focus. Second, your glasses will slightly displace objects in different colors. You can see this on the edges of high-contrast objects near the rims of your glasses: you’ll see color fringing. This could easily cause a 3D effect. Your brain sees 3D via parallax, which in essence figures out how displaced objects are relative to each other in each eye. Objects with large displacements are close (your nose is in totally different sides of your left vs right eyes), while far away objects don’t move at all (stars stay fixed in place no matter which eye you use). There may be more going on, but these two effects (both related to index of refraction) almost certainly play a big part. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [January 9, 2014, 12:05am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/7 "2014-01-09T00:05:05Z")
I don’t see 3d, but as the area covered by both is equal, I suspect that you can switch the foreground and background at will. The way we see things as a coherent object is a part of [Gestalt psychology](http://en.wikipedia.org/wiki/Gestalt_psychology). Might you be seeing them as more like two objects, a red and a green field, maybe with windows. I see no big reason why it has to be text (and if you switch the text, you get the Stroop effect). If you get really close, it could become pointillism. > [@D18](#): > > A basic trick of painting is that colour intensity is correlated with distance from the viewer. So close things in the painting tend to have higher intensity, far things less intensity. [This](http://www.ago.net/the-west-wind) may be relevant - see the mix of the intense reds in the foreground rocks and even the bark of the tree compared to the relatively less intense greens and blues of the far shore? (See it for real, and it just jumps at you!) Also, we “expect” colors at a certain distance. Blues will either be the far away sky or a variable distance ocean. More importantly, we can see blue/green as a larger object - a sea or a sky or a forest, and not individual water droplets or even trees. A red object is _more likely_ to be a small thing, and thus the foreground and not the background, usually. > [@Dr.Strangelove](#): > > First, your eyes can really only focus on one wavelength at a time. If you focus on a pure red object, green and blue objects will be slightly blurry (blue more so). Colors near each other on the rainbow will be in similar focus while ones farther apart will be relatively out of focus. Cite? Or are we sure this has anything to do with color? Our eyes can do lots of things, but it is further on down the line that we do more complex processing. In the retina, we can’t see things that we aren’t focusing on as well because there are little or no cones in the periphery of our vision, so we really don’t see color. But are brain can make assumptions and adjustments so that we rarely notice this. But this does not relate to the color. Glasses are a whole other filter that can mess with your vision in that way. Contacts could be a problem too, but they aren’t as problematic because they’re so close to your eye and there is less refraction. BTW: if you view something like this on an LCD montior (odds are that you are), it is harder to say that you are seeing the same colors as someone else compared to a CRT. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 9, 2014, 12:16am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/8 "2014-01-09T00:16:56Z")
> [@thelurkinghorror](#): > > Cite? Or are we sure this has anything to do with color? I haven’t read it in detail yet (it was the first one I could find that looked reasonable), but [this](http://www.telescope-optics.net/eye_chromatism.htm) page seems to go into great detail. The quick version is that all optical systems exhibit some degree of dispersion, which means that different colors get bent by varying amounts. It’s why you see rainbows–the different frequencies that make up white light get bent by varying amounts as they bounce around the water droplet, and so they exit at different angles. The human eye is no different, and hence only one color at a time can be in focus. The difference may be very small, especially in bright light when your pupil has contracted, but it’s still there. It also applies to the glasses themselves (although some materials have lower dispersion than others). ---
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [January 9, 2014, 2:04am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/9 "2014-01-09T02:04:26Z")
> [@D18](#): > > A basic trick of painting is that colour intensity is correlated with distance from the viewer. So close things in the painting tend to have higher intensity, far things less intensity. [This](http://www.ago.net/the-west-wind) may be relevant - see the mix of the intense reds in the foreground rocks and even the bark of the tree compared to the relatively less intense greens and blues of the far shore? (See it for real, and it just jumps at you!) I don’t really see the effect in the picture you linked, but sometimes I have this happen when I’m looking at a painting done in vivid colors. For example, at an art fair I saw a picture of a parrot on a blue background. The parrot looked like it was way above the painting. I asked the artist how she made it 3D, but she didn’t know what I was talking about. My wife and daughter didn’t see it in 3D either. > [@Dr. Strangelove](#): > > Second, your glasses will slightly displace objects in different colors. You can see this on the edges of high-contrast objects near the rims of your glasses: you’ll see color fringing. This could easily cause a 3D effect. Your brain sees 3D via parallax, which in essence figures out how displaced objects are relative to each other in each eye. Objects with large displacements are close (your nose is in totally different sides of your left vs right eyes), while far away objects don’t move at all (stars stay fixed in place no matter which eye you use). I can see the 3D effect with and without my glasses. My glasses just affect which color I see blurry. But maybe my eyes have this displacement effect for different colors. Like, the green is getting bent more than the red, so the parallax is creating the 3D effect. ---
**Author:** ![drewtwo99](https://avatars.discourse-cdn.com/v4/letter/d/d07c76/32.png) [@drewtwo99](https://boards.straightdope.com/u/drewtwo99)\ **Post date:** [January 9, 2014, 2:06am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/10 "2014-01-09T02:06:51Z")
I stared at the example and couldn’t see anything popping out/sinking in to me. I normally have no problem seeing optical illusions and such. ---
**Author:** ![DataX](https://avatars.discourse-cdn.com/v4/letter/d/e99b99/32.png) [@DataX](https://boards.straightdope.com/u/DataX)\ **Post date:** [January 9, 2014, 2:27am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/11 "2014-01-09T02:27:16Z")
I see it a little bit and like **sitchensis** I can control it my “focusing” at will. I’m a little bit tired - and I think that helps. I have noticed it before, and it is similar in believability as the fake 3d Apple uses on locked screens and such since I guess OS7 (only noticed it then). It helps if I shake the screen - I’m using an iPad - but i suspect moving my head would help too. When I used to have an LED alarm clock - I could make the numbers float by shaking my head. Also I sometime can get almost any LCD screen text to “float” (fairly regularly I believe) if I am taking Ambien (not currently /recently) on it - so it isn’t effecting me now). Not sure how much any of that would be of use, but there it is 🙂 I don’t think it is necessarily the color - I think it is my brain/eye is able to focus them as separate “layers”. I think if I did a big X O X alternating pattern it would/could have the same effect. I might have to concentrate harder, but I think I could force them to have the same effect that the green and red do somewhat more naturally. ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [January 9, 2014, 4:13am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/12 "2014-01-09T04:13:23Z")
I don’t see the effect in your example, but I’ve seen the same thing many times before, usually when the two colors are on a black background. Usually, when I point it out to others they do not see it. I’ve always guessed that it must be due to chromatic aberration in my eyes, but I’ve never been able to pin down the mechanism, in spite of googling for an explanation. One public place in which the illusion is very pronounced is inside the Mapparium in Boston (where you walk inside a huge stained-glass globe). In addition to the great echo chamber effect, I see two strong optical illusions. The second one is that the spherical globe looks from the inside like a prolate spheroid (elongated along the axis from pole to pole). When I mentioned these two illusions to the tour guide, she had no idea what I was talking about. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [January 9, 2014, 4:22am UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/13 "2014-01-09T04:22:33Z")
> [@filmore](#): > > What could cause this? An obsession with Canadian sitcoms? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 9, 2014, 5:49pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/14 "2014-01-09T17:49:22Z")
I suspect that the cause is somehow related to the fact that our eyes have different resolutions in different color channels. This is also why, for instance, it’s hard to read yellow text on a white background, or blue on black: The colors only differ in the blue channel, which is the one with the lowest resolution. ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [January 9, 2014, 6:25pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/15 "2014-01-09T18:25:43Z")
Filmore, does the 3D effect happen when the colours and words are reversed, so that the brain has to work a tifle harder? If not, it could mean . . . well, I have no clue. red green red green red green red green red green red green red green red green red green red green red green red green red green red green red green red green ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [January 9, 2014, 7:12pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/16 "2014-01-09T19:12:32Z")
As a child I had a book which had the title printed in big blue letters on a red cover. I found that if I jiggled the book from side to side, the title appeared to wobble around on the cover. It was really quite an impressive effect. I wonder if this is related? [This](http://www.sapdesignguild.org/goodies/diagram_guidelines/textcolor_bk.html) design page says “Do not use blue text on a red background or vice versa - the colors are seen at different depths.” (As an aside, I don’t have proper binocular vision.) See this previous discussion: [Why Does Red Text On A Blue Background "Jump Out" At You? - Factual Questions - Straight Dope Message Board](http://boards.straightdope.com/sdmb/showthread.php?t=106992) ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [January 9, 2014, 7:25pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/17 "2014-01-09T19:25:27Z")
> [@Kenm](#): > > Filmore, does the 3D effect happen when the colours and words are reversed, so that the brain has to work a tifle harder? If not, it could mean . . . well, I have no clue. > > red green red green red green red green red green red green red green red green red green red green red green red green red green red green red green red green Oddly enough, which color is (slightly) in front switches for me with this configuration. It seems more to do with visual placement than which color is which. Also, I notice that I still see it with only one eye open. In fact, it’s easier to see that way. I suspect that, with both eyes open, I get more depth information via stereoscopy that overrides the slight misinformation I get from the colors. I do notice that I can only focus on one color at a time. The green is harder to see, so I have to focus on it more to read it. When I do so, the red goes slightly out of focus. ---
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [January 9, 2014, 7:29pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/18 "2014-01-09T19:29:02Z")
> [@Kenm](#): > > Filmore, does the 3D effect happen when the colours and words are reversed, so that the brain has to work a tifle harder? If not, it could mean . . . well, I have no clue. > > red green red green red green red I still see the text that is colored green floating above the page. I need both eyes to see the floating text. If I close one eye, then it looks flat. This would seem to mean that the effect is happening in my eye and not in how my brain is interpreting the image. If I change the background to be black, then the 3D effect is reversed. Red is above and green is below. However, the red doesn’t seem to be as far above the black page as the green was above the white page. ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [January 9, 2014, 7:49pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/19 "2014-01-09T19:49:04Z")
Works better with blue and red on a dark background ---
**Author:** ![UncleFred](https://avatars.discourse-cdn.com/v4/letter/u/f0a364/32.png) [@UncleFred](https://boards.straightdope.com/u/UncleFred)\ **Post date:** [January 9, 2014, 8:05pm UTC](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322/20 "2014-01-09T20:05:54Z")
> [@Bryan\_Ekers](#): > > An obsession with Canadian sitcoms? Keep your stick on the ice! [Next page](https://boards.straightdope.com/t/explain-this-3d-optical-illusion-i-see-with-green-red-text/678322.md?page=2)