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Believe Some of What You See

Posted by Cousin Ricky , 12 November 2013 · 5,461 views

color spectrum Wikipedia accuracy
Color is imaginary, by definition. It is what we perceive, and only that.

Saying that a yellow object is yellow because it reflects yellow light and absorbs the rest is an oversimplification. An object that reflects green and red, but absorbs yellow, still looks yellow! And what color is ultraviolet? Bees can see ultraviolet. Partially colorblind people perceive colors differently from trichromats. Optical illusions regularly show two patches of color with exactly the same light curve (and which therefore stimulate exactly the same cone cells) that we nevertheless perceive as different colors. And then there’s the problem of qualia: no one can say whether the color yellow looks the same to one fully trichromatic human as to another.

The bottom line is that colors, like gods, don’t exist until your brain creates them.

There are two universal laws of Wikipedia usage:
  • Wikipedia is a supremely convenient and useful information resource.
  • Wikipedia is never, ever to be used as a reference.
Some time ago, I looked in Wikipedia to get an idea of what wavelengths correspond to the spectral colors. But it wasn’t until late last year that I bothered to create a computer simulation of a spectrum for myself[1]. The simulation uses software created by “Ive.” These are the Wikipedia wavelength intervals plotted against my simulation:

Posted Image

(Note that in order to see this image properly, you must use a monitor calibrated to the HP/Microsoft sRGB standard. Most monitors are already built to this standard, but may be improperly calibrated.)

To my eyes, Wikipedia’s blue interval extends well into violet, and their orange interval incorporates quite a bit of deep red. In fact, the representative wavelength that they give for orange (620 nm) is actually on the purple side of an sRGB monitor’s red phosphor!

After viewing this disaster, I tried to draw my own intervals. (It’s all subjective, so I can do that.) The green area looks overly broad to me, so I took the liberty of splitting it up into chartreuse, green, and aqua. Ladies and gentlemen, meet Roy C. Gabiv:

Posted Image

It is tempting to draw the line between green and aqua at around 545 nm. This would be a mistake; the sharp dropoff in brightness in that area is an artifact of the RGB composition, and does not show up in a real spectrum. (The bright green band actually represents the green phosphor on your monitor.) If you look at a diagram of the sRGB gamut, you can see what is happening. The gumdrop shape represents all the colors we can perceive, and the triangle represents the colors that can be reproduced on your monitor. As you can see, the most vibrant greens and turquoises cannot be reproduced.

This last image reveals the deceptive subtlety of the green-to-aqua transition:

Posted Image

P.S. You will notice that magenta appears nowhere in the spectrum (i.e., there is no such thing as pure magenta light), yet we can perceive magenta. This is another indication that color is something that is conjured up by our brains, and is not a characteristic of the outside world.

 [1]Since it is impossible to reproduce the spectrum on a color monitor, I obviously had to fudge the colors. (It is similar to the problem of projecting the round Earth onto a flat map. Something has to be distorted.) Here are other mappings by myself, using Ive’s software, and by Andrew T. Young of San Diego State University.

  • Zeff likes this

I am partially colorblind, yet I was widely praised by customers in my TV repairman days for my ability to properly adjust the ancient tube-type color TVs of the late 60s and early 70s.


I also seem to be able to adjust digital photos in a way that does not come across as broken to people with full color vision.


in the color chart you produced I perceive what you label indigo as blue, and what you call blue I see as aqua.  I'm using an iMac with it's native color configuration.  I've perceived these color differences the same way on a MacBook Air set to factory color calibration also.

Jul 24 2014 05:34 PM

I see color bars on this thread.

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