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Thread: Why use CYMK?

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    tommyworksheets is offline Junior Member
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    Default Why use CYMK?

    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

  2. #2
    Sherbert's Avatar
    Sherbert is offline Senior Member
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    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.
    Prepress Monkey

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    Erik Nikkanen is offline Senior Member
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    Quote Originally Posted by tommyworksheets View Post
    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.

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    prepresscolor is offline Member
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    oxburger's Avatar
    oxburger is offline Senior Member
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    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.
    By the time I walk out of here, I'm going to be a lean, mean, prepress machine...

  6. #6
    oxburger's Avatar
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    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.
    By the time I walk out of here, I'm going to be a lean, mean, prepress machine...

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    gordo is offline Senior Member
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    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

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    Lukas Engqvist's Avatar
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    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.
    Last edited by Lukas Engqvist; 05-18-2010 at 01:28 PM. Reason: parsing for clarity

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    TerryWyse's Avatar
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    Quote Originally Posted by tommyworksheets View Post
    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
    Terence Wyse, WyseConsul
    Color Management Consulting, G7 Certified Expert

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    Luc St-Pierre is offline Senior Member
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    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.


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