Comercial printing and color change

[Klaus Nordby]

Marcus: "A major myth is that all printers use CMYK inks. Actually, MANY desktop inkjets use RGB. Professional print houses use CMYK, so I guess that's why people think all printers use these inks."

As usual, my friend, you're dead wrong. :-)

ALL physical printers MUST use the CMY inks: it is quite impossible to print with the RGB colors and get anything like a full-color image. What actually is the case with ink-jet printers - and the source of your confusion - is that they internally, in the software driver - *receive* RGB information from the host application. But the driver must then translate this internal RGB information into the physical CMYK colors used by the printer. This is in contrast to PostScript printers, which can receive CMYK color specs from the host application.

The only kind of "printers" which CAN use actual RGB color on outputting are film recorders - but they don't spray physical inks on a paper, but expose a photographic film. Hence, they both can and must use RGB colored lights: the additive process of mixing colors. All ink-spraying deviced must use the subtractive method, i.e., CMY(K).

And you're a graphics teacher??? Sheesh . . ..


K
www.xaraxone.com/FeaturedArt/kn/
www.klausnordby.com/xara

[This message was edited by Klaus Nordby on January 16, 2002 at 14:54.]

[raffon]

is this:

CMYK
Short for Cyan-Magenta-Yellow-Black, and pronounced as separate letters. CMYK is a color model in which all colors are described as a mixture of these four process colors. CMYK is the standard color model used in offset printing for full-color documents. Because such printing uses inks of these four basic colors, it is often called four-color printing.

In contrast, display devices generally use a different color model called RGB, which stands for Red-Green-Blue. One of the most difficult aspects of desktop publishing in color is color matching -- properly converting the RGB colors into CMYK colors so that what gets printed looks the same as what appears on the monitor.

http://www.webopedia.com/TERM/C/CMYK.html

Ich bin ein New Yorker

[gwpriester]

<BLOCKQUOTE><font size="-1">quote:</font><HR> What exactly do you mean by that? Do you mean you draw it in RGB then hold up a colour match card to the screen and say to the printer that shape there should be ABCD in CMYK? <HR></BLOCKQUOTE>

Turan

Pantone and Trumatch have books and fan books with printed examples of CMYK colors along with the CMYK percentages. Pantone makes a pile of different swatchbooks with both CMYK colors and spot colors (colors intended to be printed as specially mixed inks). These are available both in swatch books with tear out color swatches and fan books.

Trumatch makes a fan book of CMYK colors. I prefer Trumatch's approach although either will work.

In addition to Trumatch and Pantone, there are about a dozen other color matching systems including Toyo, Focoltone, Spectra Master Colors and more.

Pantone has the most extensive collection of color matching system including metalic, and pastel colors and many more.

Gary

Gary Priester

Moderator Person

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XaraXone

[mgeduld]

I stand corrected, Klaus. I knew many ink-jets used RGB, but I didn't know it was in their brains, not in their bodies.

Marcus Geduld
{ email me } { visit me }

[Turan]

I know of the fan charts, but if I'm correct, your saying you go to the printer with something like that below. I've exagurated as I guess you do use an RGB shade of Blue and Pink, but when you approach the printer your restating what you want in pantone (or other) having picked the colours form a fan/book.

yes?

Turan

[Erik Heyninck]

That depends.

The advantage of the system is that you can go to any printer anywhere and say I want this square in this specific Pantone colour, and he will be able to mix it "exactly" as you saw it. The brackets are there because of the paper. There are Pantone guidebooks for glossy and matte paper, but not for any existing paper type and brand. And a little more grey or cream, a little more or less absorbing can make a world of difference.
Of course your printer can also buy the already prepared Pantone colour of your fancy.
Take for example 1935, a red that we often use.
Very often manufacturers mix some drying agents in the ink so it (don't know the English expression) "rolls up" on the press and requires a different liquid setting and mixture. When we mix it ourselves, this problem is far less prominent.

Because the CMYK colourspace is very limited but not fully included in the RGB (most often sRGB for the web), usually in the background the LAB mode is used.
And don't think you'll ever see CMYK on your monitor as it is always some kind of RGB (the phosphortriplets react to the primary light colours red, green and blue, and not to the pigment colours cyan, magenta and yellow).

Indeed, there are several RGB colourspaces, and they are all, in fact, conventions.
The cathode ray gun can emit any values between off and full power. It's just the convention that's accepted to make things manageable (question of memory and calculation time) that limits it to for example 256 different values.

But to give the impression of photographs etc, you need the basic CMYK inks on halftone screens.
Screening was a highly respected craft, with a lot of tricks and little secrets untill Mac and Photoshop took over and destroyed all knowledge.

Addendum:
When you have to reproduce art (paintings) in CMYK, it's a real disaster. Just imagine how many pigments a painter can use, and that no two brands produce the same hue of, let's say Venetian Red. Think of the different hues of all the blacks and whites...

If you don't work against time, time often works for you.

[gwpriester]

Turan

Pantone has two color matching systems, CMYK and spot colors. Pantone spot colors are specially mixed inks and used for reproducing a specific color or colors, such as a company logo. Each color has a speciific formular so that theoretically, any printer, anywhere in the world, can match the same color (if he/she mixes the inks correctly).

While Xara, and all graphics products have a Pantone spot color palette, only half these colors can be reproduced in CMYK. About 1/4 come close and the remaining 1/4 are not even close. Many people make the mistake of thinking because there is a Pantone spot color palette in their application, they can select one of these colors and it will print the same in CMYK.

Pantone CMYK color swatches should be used for reference when you are printing in four colors (CMYK). I'm not sure about Pantone's CMYK colors, but Trumatch includes the CMYK percentages on their fan book, so you can enter these percentages and be assured of a reasonable match when you go on press.

Does this make sense?

Gary

Gary Priester

Moderator Person

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XaraXone

[Erik Heyninck]

A fish cannot know the water. Chinese proverb


Indeed Gary, you actually write what I forget to write because i'm so inside and also no moderator.

Good lesson in taking things for granted and jumping over necessary steps.

If you don't work against time, time often works for you.