How to Achieve Great Color Every Time (1,549 words)
How to achieve great color every time
By Jim Chase and Ken Peterson
"Through informed use of digital technologies,
the catalog marketer
can achieve better color performance on press and greater control of the
final product than were possible using film."
— Tom O'Connor, Banta Catalog Group
Has this ever happened?
You're on a press check, trying to get the color you expected when you sent the job in. First, you work the mid-tones to get a good balance. Bam, your solids and solid overprints go south on you. The olives and plums are too blue, and the oranges are growing mold. The whole page looks flat and lifeless, and what you see on the printed sheet couldn't really be called "color." So, to get more color, you have them add more ink, and all three colors are added evenly. The mid-tones are completely off and detail is gone.
If you've ever had a print job come off press looking like gremlins had gone in and exchanged the bright, snappy inks you expected with dull, lifeless ones, you know that not all the results of the digital revolution in prepress have been wonderful.
There is hope. A skilled art director should be able, with a little effort, to understand and manage the color reproduction process successfully.
First Things First: The Printing Partnership
Printers still have a responsibility to communicate and assist in managing their end of the printing process to their customers. The printer must communicate his requirements for file and proof preparation, and be ready to explain how these affect the final product. Printers must also operate within established practices. They must print using standard process inks, print at standard densities and achieve standard color balances. Most printers use SWOP standards (Specifications for Web Offset Publications, a non-profit industry group that establishes and publishes standards for publications printing). By maintaining these targets, the printer establishes a basis for the entire print job. Customers know that if their file is prepared correctly, it will print as predicted.
Catalogers also have responsibilities within this partnership. For example, they must provide color proofs to ensure that these proofs are an accurate representation of how the job is likely to print. This presumes the customer is familiar with color web offset printing and its limitations; there are limits to the colors that can reproduce on a press. And the cataloger must be aware that their choice of paper has a major effect on the appearance of the finished job.
"That orange looks dull. Fix it!": The Basic Principles of Color Reproduction
Every device that perceives or reproduces color has a built-in "color space." This is the range of colors that the particular device can reproduce. The most important device is the human eye, because any "color" outside human perception is irrelevant. Where print jobs get into trouble is in the difference between the color space of the art director's computer monitor and that of the printing press.
A computer monitor is an "RGB" device. It reproduces color using dots of red, green and blue. The color space of a monitor is smaller than that of the human eye.
Because printed color is reflected off the paper, it is created by either absorbing or reflecting color, not by projecting light, as the monitor does. Printing presses therefore use the complementary colors of RGB, which are cyan, magenta and yellow. The CMYK color space is even smaller than the RGB. In other words, just because you can see a color on the monitor doesn't mean you can have it on press.
The cataloger's best tool for ensuring that the desired color comes off the press is a good color proof—a full-color representation of the page to be used on press to predict what the final printed page will look like. We say "predict" because there will always be differences. The proof is being printed on a device that also has its own color space, and this space, or "gamut," is much larger than that of a printing press. It is also printed on a substrate that may or may not resemble the paper on which the job is to be printed. The paper you use on press has a big effect on your color space.
Despite the challenges, it does mean you can get close enough to your proof make it worthwhile.
First, calibrate your monitor carefully. There are a number of ways to do this, including the built-in monitor calibration utility that comes bundled with your Macintosh system. You can also purchase separate calibration utilities.
In Adobe Photoshop, you can apply conversions of digital images to your monitor's color space. This can be useful because if it is done properly, it results in a fairly accurate rendition of your image on screen.
Get Your Images Right To Begin With
When you print color images, remember that it's garbage in, garbage out. Color must be balanced and corrected, the white points and shadow points of each image adjusted. These are the brightest and darkest parts of the image in which you still want to maintain detail. In Photoshop, this is done in either the Levels palette or the Curves palette using the highlight and shadow samplers. Since the average printing press needs at least a 3-percent dot to ensure detail, set your highlight sampler (the little white eyedropper in the palette) to a CMYK value of 4-3-3-0 (cyan saturation always has to be a bit higher), and then use it to select your white point. Set your shadow sampler to RGB values of 5-5-5 and then click it on the darkest point in which you want to see detail. (This will also keep your total ink coverage below 300 percent.) Balance your color.
Adjust the Proofer
Next, calibrate the printer that puts out your proofs to stay within the color space of the printing press. It's a bit more complex, but there are tools to accomplish it. The first—and it's a must-have for color proofing—is a SWOP Calibration Kit for Digital Press Proofs. It includes a digital file containing graphic images, and a color proof of that file. You print out the file on your proofing device. By comparing your output with SWOP's, you can get your proofer very close to press gamut.
SWOP recently announced a program that certifies proofing devices. All certified proofing devices have an application data sheet (ADS), which is submitted by the manufacturer upon certification. It states that by following the instructions on the data sheet, your proofing device should reproduce a SWOP-compliant proof. A list of SWOP-approved proofing devices and their ADSs can be found at www.swop.org.
An alternative is to place a color bar on your proof and analyze this using a color meter (spectrodensitometer). These results, compared to SWOP standards (refer to ASNI CGTATS TR001-1995) and your printer's color space should give you a good read on how accurate your proof will be on-press. A graphic representation appears above to the right. SWOP offers a good description of a color bar, or your printer may offer one.
Finally, print your proof using a substrate (paper) that is as close to what will be used on-press as possible in surface texture, brightness and gloss.
International Color Consortium (and other) Profiles
One emerging methodology for color matching and management is "embedded profiles" in your devices. Your printer probably uses computer-to-plate correction curves—profiles to adjust your color when they "RIP" your job to the plate. This is a system of values and transfer curves that takes into account a press' ink densities, dot gain and other color balancing characteristics, adjusted to the paper to be used on the job.
Similarly, you can apply color profiles to your proofer. Though some systems use their own format (a Fiery RIP station is one example), an increasing number of proofing systems accept standardized profiles, such as those based on the International Color Consortium (ICC) standard. Your printer may be able to supply you with a profile on a disk or via e-mail that you can load into your proofing system. If these are unavailable, the accepted ICC profile for printing is ANSI CGATS TR001-1995.
With the advent of digital imaging, four-color reproduction has undergone an overhaul in the way it goes to press. As design and prepress departments race to catch up, this has caused confusion and required changes in workflow.
However, the promise of digital prepress remains alive. Through informed use of digital technologies, the catalog marketer can achieve better color performance on press and greater control of the final product than were possible using film.
This requires several things. First, it necessitates a renewal of the cataloger/printer partnership, based on the new realities of digital color reproduction. Second, catalogers must educate key design personnel to understand and manage the color reproduction process as it relates to prepress. Finally, both printers and catalogers will have to make the continued investment in technologies that will give them the full benefits of this process.
Ken Peterson is quality technical control manager for Banta Catalog Group in St. Paul, MN. He can be reached at email@example.com. Jim Chase is prepress trainer for Banta Catalog Group in St. Paul, MN. He can be reached at firstname.lastname@example.org.