Welcome to Part 2 of our focus on printing. As we discussed in Part 1, time is money and do-overs are a drag. This time around, we’ll get into more detailed terminology and methodology for getting your files to look their best in print.
First, the most basic thing to understand is the difference between RGB (Red, Green Blue) and CMYK (Cyan, Magenta, Yellow, Black). I know, “Duh,” but a lack of understanding of these two color spaces can seriously impair your printed result. Very simply put, RGB = light, and CMYK = ink. When you’re working with your camera and your computer, you’re working with light. When you’re getting something printed, you’re dealing with ink. As you might imagine, the number of colors that can be reproduced with ink is a lot fewer than what can be produced by light.
A typical LCD monitor is capable of displaying 16.8 million colors. Since CMYK inks are created with pigments, they simply cannot reproduce all the colors in the spectrum. The range of colors that a system can display or print is called its gamut. In the diagram below, the rounded triangle represents the visible spectrum — all the colors the human eye can see. The colors inside the yellow line are the RGB Gamut; those inside the light blue line can be reproduced in CMYK.
If you’ve ever created an electric blue in Photoshop, then switched to CMYK, you’ve experienced the heartbreak of an out-of-gamut color. Photoshop has a way to alert you to these unprintable colors before you get your spirits dashed. Go to the View menu and select Proof Setup>Working CMYK. This will show you, based on your CMYK settings, what the file will look like when you convert it to CMYK. For a specific view of which colors are out of gamut, go to View>Gamut Warning. Ouch.
So what can you do about it? There are several color-correction techniques that can get you close, but that’s a whole ‘nother article. The best thing is to just be aware of the limitations of CMYK, and to talk to your printer about getting the best reproduction possible. Refrain from creating images with electric blue and green, if possible, if you know they’ll need to be printed.
NOTE: Converting to CMYK should be close to the last thing you do with your file before it’s printed. For one, RGB files are smaller and thus faster to work with, and take up less space on your hard drive. Also, if you’re putting a copy of the photo on the Web, you’ll want it in all its RGB glory. Once you convert to CMYK, Photoshop brings all colors into gamut (the smaller, CMYK one), and converting it back to RGB won’t get them back. Ever. It is always a good idea to keep an RGB backup. If you use InDesign, you can keep your options open by keeping the Photoshop file in RGB and choosing from the various Export to CMYK options in the final InDesign step. InDesign offers different CMYK export settings for a variety of different printers.
For more on color theory, check out this article.
Speaking of color gamuts: When an image is uploaded to iStock, the server automatically creates different versions for each of the different sizes it will be available at. These different sized version are also reprocessed into two specific color-profiles. Small and Extra-Small versions are in the sRGB color profile, in order to be the most effective in web uses. All Medium and larger files are converted to Adobe RGB for the best print reproduction. The images are not changed in any other way — there isn't any sharpening or anything like that done, just the new color profile.
(If you're using Internet Exporer or another browser which doesn't support color profiles, you may have noticed that the colors of an image shift when using the image zoom tool - at first you're looking at the Small version, but after zooming-in far enough you change over to the larger size, with its different profile.)
If you don’t have the budget for a full-color job, spot color may be the way to go. A spot color is simply a single, extra color applied in addition to the black plate. You can actually have as many spot colors as you want, but since each requires its own plate, the cost will rise accordingly. The process inks (Cyan, Magenta and Yellow) can be used as spots, but often, a premixed ink is used as the spot color. There are several ways of specifying these colors, the most common being Pantone®. You’ve probably seen the big, pinwheel swatch books, which contain chips of color and their corresponding Pantone numbers. These are used to ensure consistency across the industry. If you’re printing a company’s logo, for example, they might specify a particular Pantone color to use so that their logo looks the same no matter where it’s printed.
Spot colors are pretty easy to set up in a vector file, a little trickier in Photoshop. Again, talk to your printer if you need help. In illustrator, a spot color is indicated by a little dot inside a white box on the swatch. Some of the Pantone colors are already spots; To make a color a spot color, double-click its swatch and choose “Spot Color” in the pull-down menu.
In Photoshop, go the Channels palette, and click “New Spot Channel…” In the dialog box, click the color square to bring up the color picker, then click “Color Libraries” to choose a specific color.
Once you’ve placed a file containing a spot color in your layout program, it will show up as a color swatch in that program. You can then tell the printer to just print that plate, plus the black one.
With some forethought, you can get pretty colorful using just one spot together with black. For even more versatility, two spot colors can be combined to achieve a full-color look. In this example, the transparent green and red inks combine to make brown. The separated three plates are shown below.
Trapping refers to how inks relate to one another, and how they get laid down on paper. Basically, there are three ways ink can behave. It can knock out, overprint, or trap. Knockout simply means that there’s no ink at all. If you want white type on a blue background, for example, the white “knocks out” the blue. That doesn’t mean that you use white ink (but oh, I could tell you stories of customers insisting on it), it just means that nothing prints in that area, and the white paper shows through. (You can of course have different paper colors, which will show through, and you would knock out the type on these as well).
Ink can also “overprint,” meaning that just like it sounds, one color prints over another. This is usually desirable when you have a darker ink overprinting a lighter one, but not so much when the reverse is true. In the example below, the red is overprinting the blue, which results in a muddy purple. You can get a good idea of what the final printed piece will look like using Overprint Preview in Illustrator or InDesign.
The third option is to “trap” the colors. Also called “spread,” this is used to compensate for slight misalignments on the press. A very thin line of color is added to the top-most shape, which overprints the edges of the shape below, but lets the main shape print directly on the paper. This prevents the “ghosting” that occurs when a sliver of white shows through due to mis-registration. Trapping can be done manually in Illustrator and QuarkXPress, but nowadays it’s pretty much done automatically through the use of special software. Ask your printer.
A few more words about registration. While modern presses and printers are very good at getting the plates to line up perfectly, there are still a few things you should avoid when building your files. Remember that an ounce of prevention is worth a pound of rush charges.
•The fewer plates a printer needs to knock out, the happier they will be.
• Given the inevitability of slight mis-registration, you don’t want to reverse small type out of a four-color background. There’s just too much ink on the page for the white to show through. Even if one of the plates is mis-aligned ever so slightly, there goes your type. You may want to increase the point size and the leading (the space between the lines of type), and/or make it bold. You'll probably need to go sans-serif as well — serifs get lost too easily. Check with your printer for the best strategy.
• If you do need a solid patch of black, try to achieve it with a minimum of ink. For example, a nice rich black can be made with 58% Cyan, 50% Magenta, 53% Yellow and 100% Black. Never use 100% of all four colors — that just puts too much ink on the page and will make a mess. Illustrator allows you to preview and print so-called “Rich Blacks” accurately. Go to Preferences>Appearance of Black for a preview. Photoshop can display Total Ink coverage in the Info palette. On the Info palette, click the tiny triangle next to the eyedropper to choose what to display in each panel. Check with your printer to see how much total ink they can handle for a particular paper (maximum ink density is usually around 300%) and adjust your files accordingly.
If you’ve read this far I hope you’ve learned something new. Modern printing technology is ever-changing, but the concepts and the craft are as old as Herr Gutenberg himself.
With a basic understanding of some of the concepts, and a respect for the expertise of your printer, you’ll never be trapped or put on the spot. (Or use bad puns.)