MadSci Network: Engineering

Re: Why sixteen million colors?

Date: Thu Oct 14 23:05:42 1999
Posted By: Matthew B. Weyerich, Technical Coordinator,ES&R Dept., CPI Corp.
Area of science: Engineering
ID: 939160578.Eg

Hi, Brent!

Can our eyes do better than the 16 million colors of "true color"? You bet, 
but not for the reasons you may think!

First of all, your screen isn't really working with 16 million colors. It's 
using THREE: red, green, and blue. If you perceive yellow on your screen, 
you're actually looking at red and green phosphor dots. This is an example 
of the principle of additive color. (There's no "yellow-wavelength" light 
entering your eye.) 

The "16 million figure" has more to do with your computer than your 
monitor, or, your eye. Computers only understand "on" and "off", or, 1 and 
0. If you want a computer to work with an advanced concept like "yellow", 
you have to describe this in terms of ones and zeros, or "bits". How best 
to do this?

We know our monitor works with three colors, red, green, and blue. If we 
represent each color with eight bits (one byte), we'd be working with a 
total of 24 bits. Each bit can be on or off, so we have 256 possible 
combinations of on/off for each byte/color (8 bits) and a grand total of 
16,777,216 possible combinations of 1's and 0's. There's nothing "magic" 
about this number. It's just a binary convenience. For monitors, we use it 
to divvy up the visible spectrum, using additive color and different 
saturations and intensities of red, green, and blue. (In other words, there 
should be 16.7 million different shadings and intensities in 24-bit color. 
There aren't that many actual wavelengths used.)

16.7 million is a pretty good sampling of anything, but it turns out not to 
be good enough. Your monitor simply can't display some colors. The color 
gamut of most monitors is smaller than that of photographic film, and 
certainly smaller than that of the human visual system. (A color gamut is 
often plotted on a CIE color diagram. The CIE colorspace was developed from 
human descriptions of perception of color, so we see all the colors.) So, 
the human eye DOES do much better than 24-bit color.

The visible electromagnetic spectrum is usually considered continuous, so 
there should be an infinite number of possible wavelengths and colors. 
However, I've seen good argument for 300 trillion as a ballpark figure for 
the number of possible colors.

There's still a great deal to learn about the perception of color, because 
no one knows exactly what happens after the light strikes the back of your 
eye. We have some idea of the mechanics, but we're a long way from figuring 
out how we get "yellow" (as a concept) out of this.

I've placed some links you may find useful below. They'll teach you more 
about all of this. (There are more. E-mail me if you need references.)

I hope I've helped with your questions!

Your MadSci,


True Color definition

How many colors?

(I  very lucky to get to work with those good folks all the time! Learn 
from the true masters, my friend!)

See EVERY link on this page to learn the whole story!

Color "slides"

A colorful site

Wanna get technical about perceptions?

What the journalists are saying

Links to links

Links to Books you should read

MadSci Ref.

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