Why use CYMK?

[gordo]

[SNIP]
RGB represents the spectrum of light. It's what our eyes perceive when it bounces off everything else.

Some people here may be getting over-technical with their explanations of CMYK as a 'filter'. Or with their explanations of Red/Green/Blue as printed hues. Everything we look at is a 'filter' by that definition.

Basically the INKS (CMYK or any other) are colored by the lights reflecting off them. Just like every other object in this world you see is.[SNIP]

That is not correct.

If the inks that printers used were completely opaque then you might have a valid point. However, the inks that printers use are transparent. The color you see is the result of light being filtered by the ink and being reflected from the substrate through the ink. That is an important distinction because it means that the substrate is part of the color equation. It also means that the efficiency and effectiveness of light filtering is an important criteria in selecting inks used for printing. It also helps to explain how things like optical dot gain as well as the homogeneity of ink film across the surface of the halftone dots affect the final color.

best, gordon p

 

[Lukas Engqvist]

Transparent inks are necessary for ABS screening to work. To some extent i suppose AM raster would be able to work with opaque ink, but then a prints would be tottaly intollerant to missregistration.

 

[Bret Hesler]

Transparent inks are necessary for ABS screening to work. To some extent i suppose AM raster would be able to work with opaque ink, but then a prints would be tottaly intollerant to missregistration.

Overprints would not be overprints. The last down color would overpower the first down color. Magenta on Cyan = Magenta not Blue.

Bret

 

[kyle]

...the inks that printers use are transparent. The color you see is the result of light being filtered by the ink and being reflected from the substrate through the ink.

Exactly. Spot inks (especially metallic, and "opaque" white) are more opaque, but CMYK inks are formulated to be transparent, so it is entirely appropriate to think of them as filters. If anyone suspects that process inks primarily reflect light instead of absorbing and transmitting it, try printing on black paper.

You could theoretically print with RGB - you would just need to alternate between red and green in a sort of checkerboard pattern to get yellow, rather than overprinting them (because if the inks are perfectly transparent, overprinting would yield something close to black, and if they're perfectly opaque, you'd just get whichever color was layed down last). That would, however, reduce the intensity by nearly half, so you would either get a very dark saturated yellow, or an unsaturated bright yellow depending upon how closely the non-overlapping dots were packed.

CMY is theoretically the perfect subtractive equivalent of RGB (start with white and selectively cut red, green or blue with cyan, magenta and yellow respectively, rather than start with black and selectively add red, green and blue). The fourth color (black) is added for three reasons: the imperfectness of the real-world inks (both in transparency and in filtering) requires it to make a decent black; ink consumption is reduced because black can be made with solid coverage of one ink instead of three; and misregistration (especially of black) is much less noticeable.

 

[gordo]

[SNIP} The fourth color (black) is added for three reasons: the imperfectness of the real-world inks (both in transparency and in filtering) requires it to make a decent black; ink consumption is reduced because black can be made with solid coverage of one ink instead of three; and misregistration (especially of black) is much less noticeable.

There's a 4th reason. Most 4/C printing contains black text. It would be very difficult, and more expensive, to print black text using CMY inks.

best, gordon p

 

[Polar Designer]

That is not correct.

If the inks that printers used were completely opaque then you might have a valid point. However, the inks that printers use are transparent. The color you see is the result of light being filtered by the ink and being reflected from the substrate through the ink. That is an important distinction because it means that the substrate is part of the color equation. It also means that the efficiency and effectiveness of light filtering is an important criteria in selecting inks used for printing. It also helps to explain how things like optical dot gain as well as the homogeneity of ink film across the surface of the halftone dots affect the final color.

best, gordon p

I was just covering the basic principle of 'reflective' vs 'produced light'.

Because it seemed the mix-up was happening with the concept of using 'red green blue' ink as opposed to 'cyan magenta yellow black' ink.

I understand this. ;}

 

[Polar Designer]

There's a 4th reason. Most 4/C printing contains black text. It would be very difficult, and more expensive, to print black text using CMY inks.

best, gordon p

I think he covered that with the concept of misregistration. :} Can you imagine how illegible small type would be?

 

[Johu]

I did not read all the answers but to give something to think for the Tommyworksheets: How much red green and blue would you mix on paper in order to get yellow color?