Dav

I was reading Slashdot at work today and came across an interesting thread about color, encoding of color, and the human perception of color (in an article tagged ’snakesonaplane’, no less). Here are some of the more interesting things I found.

1. Finding berries is exceedingly hard if you are red-green colorblind. To simulate what this might look like to a red-green colorblind person, I took an image containing some berries, split it into component RGB channels, and overwrote each of the red and green channels with the average of the two, then combined it all back into a master image. Here is the result. It is indeed hard to spot berries with no red-green information. Hooray for survival of the fittest. (You can click on the image for the original version.)

2. Most* display devices are unable to reproduce all colors. This almost certainly includes the monitor you’re looking at right now. CRT and LCD monitors show colors in the sRGB colorspace, which is some subset of the colors that the human eye can perceive (sRGB is an accepted standard). For a visual example of this, see the following image grabbed from Wikipedia.

I’m not sure I fully understand what is going on, but the outer curve encompasses the CIE 1931 color space**, which if I understand correctly is the most widely accepted approximation of the range of colors humans can see. The inner triangle encompasses the range of colors that can be expressed with sRGB. The big losers here are greens and cyans, though partcularly bright versions of other colors miss out as well. There are alternative RGB colorspaces that are used, though none as widely as sRGB. One popular such example is Adobe RGB, which is accepted to be much better than sRGB. RGB colorspaces need not even be used; there is also CMYK (Cyan-Magenta-Yellow-Key[black]) , HSV (Hue-Saturation-Brightness), and others, though each of these has shortcomings as well. For example, CMYK is much better at displaying Cyan, but worse at displaying Red, as you might expect. In the above picture with the curve and the triangle, imagine if the points of the triangle were rotated about 45 degrees and you can get an idea of the kinds of extra colors you’d get and ones that would go missing.

For a more interactive example of how your monitor is unable to produce cyan, here is an interesting picture. In case you were never 6 years old and don’t know how these work, put your face near your monitor and stare at the white dot in the center of the red circle for about a minute. You should notice a faint blue aura around the circle start to form. As this happens, slowly move your face back from the monitor and it will get bigger. This color you are seeing is “true” cyan and cannot be displayed by your monitor — the approximations in sRGB are showed on the right for contrast.