Hi Everybody,
In the beginning (1931), the CIE invented the present system of assigning numbers to colors.
If you're interested, here is a short synopsis.
To be accurate, the CIE did not "invent" the present numbering system. Rather, it was obtained experimentally as follows.
They set up three reference lights (RGB) and one target light as shown in the following diagram.
The wave lengths of the three target lights were known with super precision. Their wave lengths corresponded to "lines" of light emitted by a mercury vapor gas tube. This never changes.
The wave length of the target light was measured to a far greater precision than human vision.
The three reference lights and the target light were projected on a split image translucent screen
Then the observers were asked to vary the light power in each reference light until the color and brightness on the screen matched the color of the target light. The color scientists recorded the light power of the RGB reference lights for each wavelength and the light power of the target light.
THAT'S ALL THERE IS TO IT.
You can reproduce this experiment if you ever want to know precisely what RGB (67, 125, 201) looks like.
The precision is light years ahead of using sample inks, paints or any other way of identifying color.
Of course, sheets of paper with pencil notations are not the handiest way of looking up a color. It's certainly not a convenient way of matching clothing and gloves for the ladies or for matching automobile colors.
Color scientists are very smart people. They noticed that colors whose numbers were close to each other looked almost alike. Colors that were obtained by adding two different numbers and averaging looked like the average of the numbers assigned to them.
That's exactly what happens if you put numbers on the axis of a graph. You need a three dimensional graph for RGB but it's still a graph. It's just like real space if you were to use feet as the numbering system.
So now we have a color "space".
Subsequent "spaces" were just mathematical transformations of this original "space". So if you want to know exactly what sRGB (67, 125, 201) looks like, you only have to trace back through the math to get the original RGB numbers which correspond to it. Then set the light power of the three reference lights.
It's nice to know where all this color stuff comes from. You get used to it.
Phil
Today, they read the target with a spectrophotometer.
No I meant spectrophotometer, great one are about $3,000 but the good part is that decent ones can be found with $400 packages today. The read reflective and transmissible sources.
The good part as I said is that decent ones are getting cheaper.