*Fourth in a series of blog entries about color theory with live help from the ColorTheory (Step 4) .
First_post,
Prev_post,
Next_post*

The RBG model is a simple one. There are three lights, R, G, and B. There are three numbers, each ranging from 0 to 255, each saying how bright that light should be. The lights could be the three phosphers in a cathode ray monitory, or three laser diodes in an LED display.

But that is also the difficulty with RGB from a scientific viewpoint. Each new set of lights represent a new set of colors. There was the NTSC standard for TV in 1953, with PAL for the Europeans. Adobe has one, as does Apple. Wikipeida lists a sample of thirteen different RGB standards. CYMK is even worse, as every new printer has its own CYMK color separation model.

From a scientific viewpoint, a more stable viewpoint is to base the color model by matching the cone receptors of the eye. And the most venerable of these is the CIE XYZ model (with the 1931 two degree observer), developed in 1931 on the basis of color observation experiments. So venerable that even though CIE itself has offered alternate definitions based on more recent research , the one that all current popular non-proprietary color models, including the RGB models and the CYMK models, and the CIE’s own CIELAB and CIECAM02 color appearance models, all remain based on the 1931 version.

Of particular note is the standard color model for HTML color, the sRGB model, defined in 2002. It is defined by starting with XYZ with a matrix transformation plus a nonlinear luminance function .

And now let’s show off some of the math.

(more…)