On 4 Aug 99, at 17:46, raymond kornele <[log in to unmask]> wrote:

> >From: Uzi Paz <[log in to unmask]>
>
> >I guess: Negative Scheme : due to the fact that in printings the
> >          background (i.e. no color) is white while in monitor the
> >          background (i.e. no color) is black.
> >
> >Am I right?
> ===============
> Actually, it has to do with the difference between transmitted color
> (additive- red, blue, green) and reflected colors (subtractive, cyan,
> magenta, yellow)- physics of light. =====Korny=====

I think that this has no direct connection with whether the light is
transmitted or reflected.

In a sense, the monitor's Yellow+Blue gives gray (choice of other yellow
and blue frequencies may give Green), Magenta+Green gives gray, and
Red +Cyan gives also gray.

(You can check it by using RGB=(255,255,255) on your screen to get
white (bright gray for our "calculation"), then set green color to zero
(255,0,255) and see that the resulted color is magenta. Thus
Magenta+Green will give white. On monitors, gray is just less intensive
white.
You can do the same for the other couples to see that their sum (with
some definition of unity) is white (or gray if you wish).

Now, since gray is colorless, one can say that Magenta is equivalent to
minus Green, because their sum is colorless.

So that intead of using Red Green and Blue, we use on printers, minus
Red (which is Cyan), minus Green (which is Magenta) and minus Blue
(which is Yellow).
So that instead of adding the Red, Green and Blue colors to the dark
screen, we add "minus Red", "minus Green", and "minus Blue" to the
white paper. In other words, we substract RGB from the white instead of
adding them to the black.

Uzi

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