Why use CYMK?

[tommyworksheets]

This might seem like a bit of a silly question, but why use CMYK for printing purposes at all?

Just to clarify, I understand the difference between additive and subtractive colour systems so thats not really what confuses me. What has never fully been explained to me is why we print with CMYK at all? If RGB has a larger gamut than CYMK, why dont we print with it? Is CMYK used because it is a more stable means of producing various other colours?

It seems like such an obvious question that a beginner may have, yet none of the online resourses I found addressed the issue.

Thanks

 

[Sherbert]

You answered your own question.

Additive color mixing begins with black and ends with white; as more color is added, the result is lighter and tends to white.

Subtractive color mixing means that one begins with white and ends with black; as one adds color, the result gets darker and tends to black.

Paper is white.

 

[Deleted member 16349]

This might seem like a bit of a silly question, but why use CMYK for printing purposes at all?

Just to clarify, I understand the difference between additive and subtractive colour systems so thats not really what confuses me. What has never fully been explained to me is why we print with CMYK at all? If RGB has a larger gamut than CYMK, why dont we print with it? Is CMYK used because it is a more stable means of producing various other colours?

It seems like such an obvious question that a beginner may have, yet none of the online resourses I found addressed the issue.

Thanks

Tommyws,

It can be confusing but it helps to think in the proper terms.

RGB implies different ranges in the visible spectrum that look like red, green and blue. Add these light components up in different combinations and you get the gamut of colours.

One should not think of CMY as colours. This is where some confusion comes in. CMY in printing are films of ink that are filters of light. They are not used as specific colours but as filters that result in combinations of RGB light.

So it is better to think of CMY as an RGB system.
If one overprints a Y on M then one tends to get an R.
If one overprints a Y on C then one tends to get a G.
If one overprints M on C then one tends to get a B.

The resulting limits of RGB plus the extended areas of CMY determine the gamut. The RGB gamut from the monitor is basically larger due to more saturated RGB light.

K is used because combinations of CMY do not make very good grays or blacks and therefore K takes that role.

RGB works fine for additive colours such as a monitor where RGB light is emitted. Printing combinations of RGB inks would just result in a dark muddy brown or other mess. The RGB inks would filter out too much light and it would be useless.

Hope this helps.

 

[prepresscolor]

CMYK color model - Wikipedia, the free encyclopedia

 

[oxburger]

Try to think of it this way. When you look at your monitor, the light is emitted from the screen as RGB. When you print with CMYK inks, the light is hitting the paper and reflecting light after the CMYK inks absorb different wavelengths and allow only certain colors to be reflected (a sort of reverse/mirror monitor if you will) If you were to lay down RGB inks, it would work in the opposite direction. As Erik says, they would look like a muddy brown.

 

[oxburger]

From Wikipedia:

The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks “subtract” brightness from white.

In additive color models such as RGB, white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta and yellow.

 

[gordo]

To: tommyworksheets

You originally wrote: "Just to clarify, I understand the difference between additive and subtractive colour systems so thats not really what confuses me."

So, my question to you is what would be your explanation for why CMYK is used to print rather than RGB?

best, gordon p

 

[Lukas Engqvist]

CMYK is essentially RGB in reverse.
Cyan has the function to block red, so it is not infact M and Y that produce Red, it is that all but the Red light is blocked in the absence of Cyan.

This is what is subtractive:

you start out with white (reflected) light and subtract all but the Red
by first subtacting the Green with Magenta
and then Subtracting the Blue from what is left, with Yellow.

M blocks Green
Y blocks Blue

and K is to Block all light, and to cover any imperfections.

Our Eyes can only see light.
And the light that reaches our eyes is allways addative, and calculated by our brains from the information collected from our sensory organs that respond to Red Green and Blue respectively, stimulate all equally and you will believe you are seeing something white or grey.

 

[TerryWyse]

If RGB has a larger gamut than CYMK, why dont we print with it?

RGB (which RGB?) does NOT inherently have a wider gamut than CMY/CMYK, it's just that were used to *press* CMYK as defining CMYK color gamuts.

For example, it can be shown that CMYK inkjet printing (on the right media) can have a fairly wide gamut, wider than sRGB and even wider than AdobeRGB in some cases. Even "press CMYK" can have a wider gamut than RGB in certain regions such as pure cyan colors.

Besides, I vote that we print using L*a*b* colorants so we print ALL the colors.

Terry

 

[Luc St-Pierre]

As far as the RGB-CMY gamut difference is concerned, other factorws are to be considered. C, M and Y filters are theorically correct. In real life, the correct ink pigments to create those exact filters do not really exist. They are produced as close as possible. In LCH Cyan and magenta, especially, are deviated from target by more than 10 degrees (polluted). Also, the transparency required to make them act as filters is achieved on behalf of density, therefore reducing gamut and forcing in Black ink to achieve contrasts.

 

[gordo]

This question was posted in a separate thread. I thought I'd include it here as well.

Thanks to replies that I recieved in another thread, I feel like I grasp the concept now.

We print with CMY because those colours function more effectively in a subtractive colour scheme. RGB is not used because those colours block too much of the light that we want to reflect. Therefore, many of the the colours that we want to produce using these three colours would appear muddy or brown, and not all like we had intended. CMYK on the other hand removes more appropriate levels of the colour wavelengths from any light that is reflected, and thus it results in better colour.

Hopefully I have grasped what it is the others where trying to say. If I have misunderstood, please let me know.

Thanks very much

You're close.

Think of it this way. If you used red, green, and blue inks - what combination of those inks would give you Yellow?
The answer is that there is no combination of red, green, and blue inks that can give you a lighter color - like Yellow - than the colors that you start with.

Inks act as light filters. So when you cover paper with an ink, the ink reduces the light that would otherwise be reflected. Inks are subtractive because they “subtract” brightness from the white of the paper.
I can make Green appear by mixing Yellow and Cyan inks
I can make Red appear by mixing Yellow and Magenta inks
I can make Blue appear by mixing Magenta and Cyan inks

However, with Red, Green and Blue inks I cannot make a Yellow, Cyan, or Magenta color. Therefore I cannot make any of the colors that can be made with combinations of Yellow, Cyan, or Magenta inks. Printing combinations of RGB inks would therefore just result in a limited palette/gamut of dark muddy colors.

So you could use RGB inks, but you would be giving up a whole gamut of possible colors.

That being said, the CMY inks are not perfect light filters. As a result there are RGB hues that combinations of CMY inks cannot reproduce. In that case, it is possible for printers to add an extra press unit or more to print with R,G,B inks to expand the gamut in those specific areas where CMY combinations of ink are not so effective.

hope that's clear. gordon p

 

[prepresscolor]

You do not need to print in CMYK. This is why the Pantone Color Inks are made. Depending on the number of units on your press and the number of times you want to run the paper through the press you should be able to print just about anything without CMYK.
CMYK and the color separation process just make everything easier.

 

[vaithi47]

why print with cmyk

why print with cmyk

This might seem like a bit of a silly question, but why use CMYK for printing purposes at all?

Just to clarify, I understand the difference between additive and subtractive colour systems so thats not really what confuses me. What has never fully been explained to me is why we print with CMYK at all? If RGB has a larger gamut than CYMK, why dont we print with it? Is CMYK used because it is a more stable means of producing various other colours?

It seems like such an obvious question that a beginner may have, yet none of the online resourses I found addressed the issue.

Thanks

the answer is in your question itself.rgb is additive that is from nothing (black)by adding r+g+b you create white.this used in monitors.in priting you are using subtractive ,you are seeing colours from the surface you are printing on by reflection.white-red=cyan; white-green=magenta;white-blue=yellow.so so when you put cyan on paper you are removing the red light from the incident white light.when cyan and magenta are printed you are removing both red and green from the white light and you see only blue...and so on.so printing is a subtractive system and you print with cmyk

 

[Sherbert]

You do not need to print in CMYK. This is why the Pantone Color Inks are made. Depending on the number of units on your press and the number of times you want to run the paper through the press you should be able to print just about anything without CMYK.
CMYK and the color separation process just make everything easier.

Except Images.

 

[meddington]

the answer is in your question itself.rgb is additive that is from nothing (black)by adding r+g+b you create white.

There's Additive RGB (light) and then there's subtractive RGB (inks). Here's a interesting article, though its evident from the samples that Gordo's last post fully applies.

http://cias.rit.edu/~gravure/tt/pdf/gvi/TT8_Non-CMYK Pictorial Color Image Reproduction.pdf

 

[Mark Flanders]

Hiya Prepress,

I love the color talk, and printing in RGB would be ugly in additive, but I think the original post was asking a question which is more ordinary. As I understand it, the CMYK inks were arrived at over many years, as the primary printing colors because they cover the broadest range of colors, and which make skin tones appear most natural. It has it's shortcomings, such as oranges and violets, but is the long established compromise. Actually, I just like to sound smart and historicalistical. :>

Happy Thursday!

mf.

 

[Mark H]

Frankly, with today's computer controlled digital printers we certainly could create a system based on RGB inks. Similar to CMYK we would most likely need to add a dedicated black (K) ink in order to avoid muddy or washed-out black resulting in RGBK. However, RGB would create very poor bright colors, especially vibrant yellow (notice how some TV manufacturers are now adding a new yellow LED to their RGD based LCD panels?) and other bright non-red based colors.

At the end of the day, even if all of this could be done why do it? Why change the industry? What would the upside of abandoning CMYK for RGBK be?

Mark H

 

[Mark H]

Inks are subtractive because they “subtract” brightness from the white of the paper.

It might alter (or cover) the reflective properties of the paper but what is being changed is really the color of the reflected light coming back to the viewer.

Mark H

 

[usbox]

Can any one tell me where i get the all printing press information. I want to learning about printing press like stocks and others stuff.

Thanks,

 

[Polar Designer]

I think Erik, Ox and a few others stated it the simplest.

I also think 'additive and subtractive' can be confusing for some. As are some of the conversations about printing in Red/Green/Blue inks. And in this case, it's because you /can't/ print in RGB as a light spectrum. Even printers that 'print RGB' are /converting/ light values to solid reflective color when they assign values.

Scientifically Speaking:
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.

Monitors and televisions PRODUCE LIGHT for color. (what RGB represents)
Papers and flat solid surfaces REFLECT LIGHT for color. So we use inks and pigments that we know will reflect the colors we want (CMYK)

There are several other printing methods/inks out there....none of them will be /LIGHT/ RGB unless they PRODUCE spectrums of light for their color.

And light has a MUCH larger gamut than reflective values do because the more you add, the less it may reflect.


As a random scientific fact: it is also why black heats up faster in the sun (it's not reflecting light, it's absorbing it).