CMYK - subtrractive color model - gimp manual

[veek]

Hi, I'm reading the GIMP manual and it says:

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GIMP does not currently support the CMYK model. (An experimental plug-in providing rudimen-

tary CMYK support can be found [PLUGIN-SEPARATE].)

This is the mode used in printing. These are the colors in the ink cartridges in your printer. It is

the mode used in painting and in all the objects around us, where light is reflected, not emmitted.

Objects absorb part of the light waves and we see only the reflected part. Note that the cones in

our eyes see this reflected light in RGB mode. An object appears Red because Green and Blue have

been absorbed. Since the combination of Green and Blue is Cyan, Cyan is absorbed when you

add Red. Conversely, if you add Cyan, its complementary color, Red, is absorbed. This system is

subtractive. If you add Yellow, you decrease Blue, and if you add Magenta, you decrease Green.

It would be logical to think that by mixing Cyan, Magenta and Yellow, you would subtract Red,

Green and Blue, and the eye would see no light at all, that is, Black. But the question is more

complex. In fact, you would see a dark brown. That is why this mode also has a Black value, and

why your printer has a Black cartridge. It is less expensive that way. The printer doesn’t have to

mix the other three colors to create an imperfect Black, it just has to add Black.

Color depth

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I did not follow the 'add Red' bit. White light is incident on paper and the ink-pigments absorb certain colors and reflect certain other colors - therefore our eyes only receive certain wavelengths - this is subtractive. In a computer monitor, RGB is generated by phosphor excitation and mixed and goes straight into our eye.

Green + Blue = Cyan #got it.
Cyan falls on paper+pigment and is absorbed #got it
left over wavelengths are now travelling to my eye..
so how is Red 'added'???? He does 'adding' of colors and I don't get that.. Could someone explain it clearly.

[rich2005]

That section is really about why it is difficult to print black using the subtractive colours C M Y.

Quote:Green + Blue = Cyan #got it.
Cyan falls on paper+pigment and is absorbed #got it

It is white light (R + G + B) that falls on paper + pigment.

   

You have a splodge of 'cyan' ink on a sheet of 'white' paper
Red is absorbed (subtracted), the eye RGB (additive) sees G+B = cyan.

   

If the same paper is in a room illuminated by red light, then the 'cyan' splodge subtracts any red and the eye sees nothing (black), The eye (RGB) has nothing to add to the red reflected from the paper. 


At least that is the way I understand it.

[veek]

thanks and after reading your post I did some google and also got this link which is useful - has some other color models:
https://www.quora.com/What-color-does-blue-and-red-make