Why print with CMYK?

[tommyworksheets]

This must seem like a silly question, but I've got to ask it anyways.

Why do we print with CMYK? I understand that we have to have primary colours that mix to create other colours, but what stops us from printing with RGB inks? Im especially confused by this because RGB has a larger gamut than CMYK doesnt it? Wouldnt that make it more suitable for printing?

To clarify, I understand the difference between additive and subtractive colour spaces. The online resources I have been looking at have been thouroughly unhelpful because they often simply state "CMYK is subtractive and RGB is additive and produces white when mixed together". However this is like comparing apples to oranges, because they neglect the fact that this is only true when you are dealing with monitors. If i mix red, green and blue ink on a piece of paper I wont get white ink obviously. So what stops me from using RGB in a subtractive system.

I'm sorry to post such a seemingly obvious question, but I dont know where else to ask.

Thank you

 

[gordo]

To: tommyworksheets

You 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

 

[tommyworksheets]

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

 

[gordo]

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

 

[fullyboy]

Good question and excellent explanation

Thanks for both,
fullyboy

 

[Cold]

[snip]

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

Add on-

There is a developed system doing exactly that. It is a 7 color process called Opaltone. K,C,M,Y,R,G,B. It is actually a very good color gamut. I would have changed one color. Instead of Blue, I would have used carbazole violet. But otherwise, a very fun process that has excellent applications in packaging, both flexo and off-set.

 

[gordo]

Add on-

There is a developed system doing exactly that. It is a 7 color process called Opaltone. K,C,M,Y,R,G,B. [SNIP]

There are several developed systems that do exactly that. One from my former employer, others from Esko, Heptacromía from Tru Tone, FM6 from M.Y. Cartons, and I'm sure others.

best, gordon p