RGB v CMYK

[Boz]

Two questions here:

1. I understand that CMYK is used for commercial printing, but can anyone tell me why. Is it something to do with the ink materials available today? A hyperlink to another site/thread is more than sufficient.

2. I've read an article or two that says I should create my art using RGB then convert to CMYK for printing. I understand this. However, the last time I did this (online business card order) and I converted to CMYK, the colors were less than what I had originally wanted. Took me 3 orders to get it right. I ended up reworking the business card in Photoshop and worked with CMYK anyway. Is the "work with RGB, convert to CMYK" suggestion a good one?

Thanks

[mahuti]

1. MOST printing machines use 4-color process. If they are going to print a "full-color" image, they lazily and cheaply use only 4 colors to reproduce ALL of the colors of the rainbow. Sometimes this provides mixed results. So, in short; "YES" to #1.

CMYK is a subtractive system. As you add more color, it subtracts light... taking you to black. RGB is an additive system as you add color, it adds light... taking you to white. IF you put equal parts of CMYK printing ink together you (roughly) get black. If you add equal parts of RGB light together you get white... that's how the 2 mediums of print versus computer screen work.

Anymore, RGB can be used for printing, but most printers have to convert your colors to CMYK to output them anyway, because they are using 4 ink colors (Cyan, Magenta, Yellow Blac(k)) rather than Red, Blue and Green. If your colors are very vivid with RGB, they will not reproduce as well with actual 4-color printing ink, which can't reproduce vivid colors as well as an RGB photon gun in your monitor (or whatever the technology is).

2. In short; NO to #2. If you are going to print in CMYK, ALWAYS start with CMYK. Keep as few kinks out of your color process as possible. CMYK will never produce high range colors, so if you start with the CMYK color space, it will force you to stay away from those colors that won't output well.

There are, as always, many caveats to this, some "direct to plate" or digital output imagesetters don't seem to be very bothered by bright colors... course, some of them also use a hexachrome process or other 6-12 color process, rather than the traditional 4. If a company isn't outputting to film plates, then they can get away with using more ink colors, and consequently get a more accurate and vivid color output.

[RayB]

Here's the deal... RGB means: Red Green Blue, which is how televisions (and PC monitors) display images. They use light when mixed together to create an image. So, combined all three colors and you get WHITE. No colors gives you black. That's how light coloring works.

CMYK stands for Cyan, Magenta, Yellow, blacK. This is the format for print because print uses pigments. It's kind of the opposite of RGB, since with pigments, NO colors will give you white (assuming printing on white paper, which is the norm). Mixing ALL colors gives you a dark grey or even black. But to make sure blacks and greys are pure, they also use black ink, hence the "K" in the acronym. (By the way, Cyan is not quite blue. It's almost like an aqua. Magenta is not quite red. It's close to purple.)

So, if you create something in RGB, some colors are impossible to reproduce with standard inks. The most notable differences will be bright reds and blues.

**BUT** Before making your choices of using CMYK, I suggest contacting your intended print-house. Scott of MameMarquees for example informed me that his equipment gives better results if you stick to RGB.

[mahuti]

The MOST notable differences will be purples. Deep blues and vivid purples get really screwed by CMYK.

As I mentioned... one caveat is that digital imagesetters or direct to plate / print machines may use more / different inks. I'm sure Scott is not doing CMYK printing... he's probably using some sort of direct to print machine. You'll have better luck with marquees and cpos with that type of technology. Those types of machines cost more for high runs, and have less flexibility for normal printing needs, and effects (varnishes, etc.) They're definitely better for out purposes, though. If you're creating for 4-color process, work in CMYK. It's good advice to ask your outputter (printer, etc) what format works best for them, as RayB mentioned.

[Boz]

Very cool. Thanks guys. Probably saved me a ton of wasted time working with something that I'd have to convert anyway. I'll check with some of the printers around to see what they are using.

[Felsir]

very insightful answers guys! Added to the FAQ.

[Boz]

very insightful answers guys! Added to the FAQ.

While working as a systems administrator for a Fortune 500 company, I actually called Micro$oft for a server issue that resulted in creating a new MS knowledge base article. I feel special now, for asking a good question. Being a novice pays I tell you, it pays!  (tongue in cheek)

[J.P. Patches]

I used to work in a digital pre-press shop. 

I can say one thing to your colors not coming out as you expected them...

It's VERY likely that your monitor is not calibrated correctly.  The same with your any printer you have at home to make a proof from. 

It's amazing how off some monitors and printers are. 

If you can make a proof with colors you like you can very likely take that in to a local shop and have the shop do a bit of color correction (for a fee) so that you can get the colors you want. 

Also, I wouldn't call printing places "lazy" or "cheap" because they use process color (CMYK) to print full color stuff.  That's like saying that monitor manufacturers are cheap because they only use three electron guns.  They use four colors because three of those colors are the primary colors.  All the colors in the world (theoretically) can be made from those three colors.  Don't let anyone tell you that the primary colors are Red, Yellow and Blue.  That's a crock. 

Black is added to the CMY mixture because it reduces the amount of ink required to make darker colors.  Instead of putting 100% of CMY on there you can put 100%K and it'll be 1/3 the amount.  This, again, is not done because places are cheap, but because different printed surfaces react differently to the amount of ink put on them.  I know I've printed out something on my home printer that warped the paper when it put too much ink onto it.

If you need a darker black, you can always use "process black" which is 100%CMY and usually 50% or 100% black.  (Shades of black...  I sound like a Goth)  Just make sure that what you're printing on can handle it.

Anyway...  If you want to know 'bout things like linescreens or printing film or stuff like that, let me know.   

Echo... Echo...  Ok.  didn't think so. 

Sorry to ramble. 

[mahuti]

I wouldn't refer to PRINTERS as "cheap" because they use CMYK. Purchasers are cheap because they use CMYK. CMYK makes the world go round, but for anything with complex colors, it can sometimes cause problems.

I don't think it's fair to chalk it all up to a bad monitor or a home printer, just like it's not fair to chalk up mistakes to a printers machinery. Having worked in a non-digital pre-press shop... I know what a huge mess color can be, regardless of a printer or a purchaser's intentions. Getting good color is complex. Working with your printer and letting him know what is really important to you is the best plan.

[Felsir]

Don't let anyone tell you that the primary colors are Red, Yellow and Blue.

[mahuti]

Most painters that I know, use much more than RGB for their canvases. I used to use about 6-8 colors....

cool yellow, warm yellow, cool red, warm red, thalo blue, ultramarine blue, thalo green, violet, black, white. I guess that's 10. Printers would use something similar if it wasn't so expensive.

If anybody wants to get into color theory, just read a few books by Johannes Itten

The elements of color

The art of color

Required reading for any serious student of color mixing, regardless of the medium, be it print, tv, or paint.

[mahuti]

Oh, and I forgot Josef Albers book;

Interaction of Color

[J.P. Patches]

It appears that CYM is concidered the right model in theory for the abstractive model 

In other words saying that RYB are the primary colors is a crock. 

Most painters that I know, use much more than RGB for their canvases. I used to use about 6-8 colors....

cool yellow, warm yellow, cool red, warm red, thalo blue, ultramarine blue, thalo green, violet, black, white. I guess that's 10. Printers would use something similar if it wasn't so expensive.

When I got out of the prepress buisness the eight color process was only used by one shop I knew of, but really that is just CMYK and lighter versions of those colors...   It didn't really give them that better of colors, but it allowed them to have a more uniform amount of ink on the paper, which was important for the posters they were printing.

[mahuti]

Yeah. I only rarely saw anything more than a 4 color job come through any of the places that I worked at.

Usually just CMYK + spot colors here and there, or effects. Did know a shop that occaisionally printed art books with 8-12 colors, but that's a pretty specific market.

Anyway, with our hobby, it's somewhat moot. We rarely get anything done in a true press.... 's all direct to print.

[jopenner]

What happens if you utilize a variety of image sources for a Photoshop image such as some logos with RGB colour and others with CMYK?  Mame Marquees has asked for an RGB file, but I am not sure if that is what I provided.
If my image file is a mixture of the two, can I convert the entire image to be an RGB file or CMYK file?  If so, how is this done in Photoshop or does it even matter?

John

[mahuti]

In Photoshop, you work in 1 colorspace at a time. If you are working in RGB, and add a CMYK image, it will automatically convert to RGB.

You can check or change your color space by going to Image>mode>

Mamemarquees is smart enough to convert the image if they need to... if you've already submitted it, I wouldn't worry about it.

[Crowquill]

One basic rule is this: Design it in CMYK if it will be printed in CMYK.

The industry standard for both commercial printing and even home printers is CMYK. However, one change in recent years is the introduction of home and professional photo printers. They typically use 6 colors (cyan, magenta, yellow, black,light cyan, light magenta). I've seen many examples where they can reproduce artwork outside of the limits of CMYK. For these types of devices it's usually better to send an RGB image and let the printer figure out how to print it with 6 inks. If you send a CMYK image, you are already limiting the prints you will get since the last two inks will not be utilized.

I use an HP DesignJet 5500 at the Kinko's I work at. This is the oversize printer that most Kinkos have and what they would use to print out your marquees, sideart, etc. I've tried printing an RGB image, convert it to CMYK, and print it again for comparison. The CMYK images are printed way too dark and saturated. The RGB file was reproduced much more faithfully. I'm guessing Mamemarquees or emdkay use similar types of printers.

On the other hand, if anyone's printing something 11x17 or smaller, then I want a CMYK image to send to the color copier as it prints using CMYK toner. RGB images that I send are typically really washed out. Like Mahuti said, if you know that you're going to be printing in CMYK, it's better to put together your design using those limitations. If you've designed it in RGB, converting it to CMYK will still get you more consistant printing as Photoshop is much more effective at converting RGB to CMYK than the printer is.

Commercial print companies are aware of the limitations of CMYK too. If I needed to print a bright purple in a document they could use a premixed purple ink to compensate for the shortcomings of CMYK. This is called a spot color. Spot colors are also used many times to make sure that a logo is consistantly the same color. The most commonly used system for spot colors is the Pantone color-matching system. Most people on this board will never have any use for a commercial printer.

Despite all the talk of the shortcomings of CMYK, most images will print/reproduce quite well.

There are many different color models. Every one has their own "primary colors" or elements. Each one has it's preferred usage. I was a little shocked the first time I was editing a character in a Playstation game and had to create the colors using hue, saturation, and brightness. HSB is a commonly accepted color model despite the fact that most people don't use it. It's not a matter of right-and-wrong, it's a matter of apples and oranges.

[acejas]

This aint a plug www.opaltone.com has some great easy to understand colour theory

this system uses cmyk +RGB ...pretty nifty and increases teh colour gammut significantly

also an aussie invention hehe

[mahuti]

Cheating. Anybody can add extra colors and get better results.

[CrispyXUK2]

CMYK has a lower gamut (colour space) of colour compared to RGB, you should do your artwork in RGB with the CMYK preview turned on, you printer will have their own colour workflow that will fit RGB to their CMYK gamut