Color Management for Screen Printers

SGIA's Johnny Shell goes into the laboratory to find out whether color management systems are just for digital printing — and gets some surprising results.
June 4, 2007

By Johnny Shell

When garment decorators hear the term "color management," they usually think the subject doesn't apply to them. Color management — which helps control variability when transferring color information among devices that capture, display and print images — is known for its extensive use in wide-format digital printing, where several output devices using several ink sets may be used on several dozen types of media.

The question is, can it be used to help garment screen printers? I conducted some tests in the SGIA Digital Lab that applied color management practices to screen printing on a T-shirt. Here's what I found out.

Color Management Basics

Without a standard color management system, color results vary widely across applications and devices. As a result, color consistency is achieved largely through trial and error. A color management system helps to overcome these limitations by providing a communication framework for software, and input, display and output devices (Figure 1).



FIGURE 1. A color management system provides a communication framework for software, and input, display and output devices.

Color matching technology is used to calibrate an imaging system and allow it to accurately transfer the "meaning" of color from one device to another. Each device in the system uses an ICC profile to make this happen. These profiles make color calibration easier and help create better color reproductions when scanning, viewing and printing images. They're used in graphic applications such as Adobe Photoshop to accurately transfer and convert image data.

Working with Limitations

An ICC profile preserves the intended meaning of the original color based on the device's limitations. For example, computer monitors can display many more colors than you can print.

Using a printer profile, the monitor displays only colors you can get on press. I'm sure many decorators have set up a four-color process job only to be disappointed when it didn't look like it did on the monitor. Working together. ICC profiles work in pairs; one profile is the source and the other is the destination. The source profile describes colors of a particular device and then the meaning of the source's colors are transferred to a destination.

For example, say you're scanning an image to view on a monitor. The scanned image has a profile applied as the source, and the monitor's working space profile is applied as the destination. Producing a quality ICC profile is necessary to achieve good results; this usually means purchasing hardware and software for measuring color targets and producing profiles from the measurements.

Profiling applications and hardware range from $300 to more than $15,000. Also, profiling services can create a profile for a fee. Matching colors in a color management system won't always be exact. ICC profiles aren't perfect, and some find that using them in certain workflows can be difficult. Also, profiles must be updated or regenerated when any change occurs within the system, such as changing manufacturers for ink or shirts.

Printing a Test Target

The first step in creating a profile is to print a test target. The test target contains hundreds of color patches that will ultimately provide data to create an ICC profile. ProfileMaker5 from Gretag Macbeth is a software application that helps create and edit color profiles by working in conjunction with color measurement tools. I chose the IT8.7-3 target file that's included with ProfileMaker5; it contains 1,120 color patches. I opened the file in Photoshop CS2 and generated films using an Epson 4000 inkjet printer.

Software Settings

Before printing films, I first needed to turn off any color management options. I chose File>Print with Preview and chose Color Management from the pop-up menu below the preview thumbnail. If you don't see the pop-up window, expand the dialog box by clicking the More Options button on the right side. Select No Color Management from the Color Handling pop-up menu in the Options section. I also set Rendering Intent to Relative Colorimetric. (Rendering intents are standard ways of applying profiles.)

Printing Details
I set the line screen for the separations to 45 lpi and output all channels at 61 degrees using a round dot. I used retensionable frames and a 305.34/in. (120.34/cm) mesh tensioned to 30 N/cm. The mesh was coated with a dual-cure emulsion using a 0.25 mm radius trough edge (sharp), and a 1:2 coating was applied (1 coat to print side, 2 coats to squeegee side) using an automatic screen coater.

Proper exposure was calculated to be 88 units on a 5Kw exposure unit. I set up the four screens on our manual textile press and printed them using four-color process ink on a white heavyweight T-shirt. After achieving consistent prints, I flash cured the ink and removed the press platen with the shirt still in place. Leaving the shirt on the platen enabled me to keep it flat and adhered to the platen surface for proper measurement.

Measuring Color Info

The next step in creating a profile involves measuring the color information in the test target using a spectrophotometer. This device measures light intensity as a function of the color — or more specifically, the wavelength — of light. Basically, it illuminates the sample with white light and calculates the amount of light reflected by the sample at varying wavelength intervals.

For this test, I used Gretag Macbeth's Eye-One portable spectrophotometer. The ProfileMaker5 software is in constant communication with the Eye-One and provides user prompts while the target is being measured. The instrument passes over each row of the printed test target and measures the reflected light it receives from each color patch.

From this information, the software calculates the difference in color from the known value in the original test target. After reading the color patches, the software calculates and creates a profile. It saves an ICC file (.icc) to the appropriate location on your hard drive so that it can be accessed in graphic applications.

Generating New Films

The next step is to generate new films using the profile. Assign the profile to the image by selecting Edit>Convert to Profile, select your unique profile name from the list and select OK. This converts the colors in the image to the color space of the custom profile selected. If you select Edit>Assign Profile, color numbers in the image remain the same, but the new profile may dramatically change the appearance of the colors displayed on your monitor.

After converting the image to the new profile, I placed it and the original, unadjusted image into a vector document. This way, I could have both images represented in one print. I generated new films using the line count and angles previously stated, and I made screens exactly as before.

Test Conclusions

Take a look at Figure 2; it speaks volumes as to the improvement in the printed image. Notice the skin tones, which are tough to reproduce with screen printing.



FIGURE 2. We tested a direct-to-garment digital printer in the SGIA Digital Lab and used the color management techniques discussed in this article to produce a very decent print. I think we were in shock as we compared the digitally printed shirts that day. The photo on the left shows the print results from a digital direct-to-garment printer using no color management; the photo on the right shows the results with color management.


I was impressed with how little effort it took to make such a huge difference. After only two sets of screens, my image looked pretty good. I didn't have to spend any time at the press trying to match color by changing squeegees, making new film, basing the ink down, adjusting off contact, rearranging print order or battling muddy shadow details. There was no trial and error in adjusting curves and dot gain options, pulling back the Cyan curve in Photoshop, or employing any of the tricks so often used to achieve acceptable print results.

With this profile created, I could convert all images using this profile, and — as long as everything else in my system remained constant — my prints would look great each time. Several of my colleagues were equally impressed by the results of this test. Given these results, screen printers should sit up and take notice of the potential capabilities color-management technology offers.

This article appears courtesy of SGIA and the SGIA Journal and is reprinted from the May 2006 issue of High Volume Decorator.
Author's bio: Johnny Shell is the vice president of technical services for the Specialty Graphic Imaging Association (SGIA). His primary duties include directing and coordinating the activities of the Technical Services department and the Screen Printing Technical Foundation. He also writes technical articles for industry publications and conducts seminars at industry events.

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