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The wide variety of large-format inkjet printers, inks, media, and RIPs has made color profiling a popular practice for users who want to get prints that match what they saw on the screen, or WYSIWYG (“what you see is what you get”). Profiling is also useful in getting a printer to print the same every day, and getting two printers to match each other.

To profile your printer, you’ll need:

• a color profiling program, either a third-party application or, if you’re using a software RIP, the RIP vendor’s standard or optional built-in profiling module.
• a spectrophotometer capable of interfacing with the profiling program. Popular models include GretagMacbeth’s Eye-One (Fig. 1), SpectroScan, and iCColor, and X-Rite’s DTP41.

To make printer profiles, you'll need a spectrophotometer like GretagMacbeth's i1. This manual scanning instruments reads rows of patches as you slide it across the targets. Fully automated instruments are also available that read charts unattended.

The Four “Cs” for Printers
In Part 1 we discussed the “Four Cs of Color Management” for monitors—consistency, calibration, characterization, and conversion. These four “Cs” also apply to printers. Profiling counts as the third “C” (characterization), but before profiling your printer should be linearized (second “C,” calibration) and optimized for ink density (first “C,” consistency).

Consistency
“Consistency” or “optimization” refers to setting the optimum ink density on the media. If you don’t have enough ink, the color gamut will be limited and prints will look too light and unsaturated. Too much ink, though, can also cause problems. Prints won’t dry, or ink may bleed or even puddle and run off.

Ink limits. If an inkjet printer puts too much ink on the page, the result may be bleeding, or seepage of ink from one area to another. To reduce bleed and drying time, individual CMYK ink limits must be reduced using the RIP.

If you’re using the printer with the manufacturer’s free driver or built-in RIP, the manufacturer has already determined the optimum ink density settings. For example, if you use an Epson 7600, the ink densities are determined by the media setting in the driver. If you use an HP 5500ps, they’re determined by the front panel setting for media.

If you want to use a third-party media, you’ll need to determine which of the manufacturer’s media most closely approximates it to get the necessary ink densities. If you use a third-party software RIP, however, most of these have settings for ink density. RIPs typically include a target that you print and use to determine the optimum ink density.

Calibration
After determining the optimum ink density for your printer, ink, and media, the next step is to calibrate the printer by performing a linearization. Linearization ensures your printer prints tone values evenly throughout the scale, from 0­100%. The result is consistent color and good tone reproduction—detail in highlights and shadows.

Linearization. After setting the printer's ink limits, you should linearize the printer, which spaces all of the tones evenly for good highlight and shadow detail. The linearization target is a series of tone scales from 0-100% for each ink. Compare the LAB color diagram at left of an unlinearized printer with the one at right of a linearized printer. Note how after linearization all of the tones are more evenly spaced.

Linearization may not be an option if you use the manufacturer’s driver, or it may be automatic. In our previous examples, you can’t linearize an Epson 7600 with the Epson driver, while the HP 5500ps’s linearization is done through the front panel Color Calibration function.

If you have a software RIP, however, it will undoubtedly have a linearization function. To linearize, print a linearization test chart on your printer after you’ve determined the optimum ink density settings. Then, read the chart with one of the supported densitometers or spectrophotometers. The RIP will calculate a linearization curve that makes tones evenly spaced from highlight to shadow.

Characterization
Profiling the printer involves making an ICC color profile using a profiling application. You can use a third-party profiling application like GretagMacbeth’s i1 Match or ProfileMaker or Monaco’s PROFILE. If you have a RIP, it may have a standard or optional built-in profiling module. In either case, to make a profile, print a profiling test chart and measure it with a supported spectrophotometer.

Some programs offer a choice of profiling targets with varying numbers of patches. The more patches you print, the more accurate the profile may be, but the longer it’ll take to read it. If the printer is linearized, a color target with 300­500 patches may be sufficient. If the printer is non-linear, a larger target of 1,000­2,000 patches may produce a more accurate profile.

GretagMacbeth ProfileMaker 5, a profiling application, offers numerous settings for color separation control, including the black start point, maximum black, total ink coverage, and GCR amount.

Profiling applications and modules have certain settings that are important for inkjet printers. Some of these settings are:

• Black start—Percent dot area of process color (usually cyan) at which black starts printing, generally 40­70% for inkjet. Increase if speckling is noticeable in highlights.
• Maximum black—Maximum black tone value printed. Set to maintain good shadows. Reduce if shadows plug and obscure detail.
• Total ink coverage—Sum of CMYK inks printed, 400% maximum. Set using a total ink coverage target. Lower if overprint colors bleed or don’t dry quickly.
• UCR—Undercolor removal, reduction of process colors in shadows and replacement with black to achieve total ink coverage limit.
• GCR—Gray component replacement, replacement of the “gray component” of CMY with black. Usually quantified as a percent or numerical value (1, 2, 3, 4, etc.). Generally 60% GCR or 3 on a scale of 1­4, produces good results for inkjet printing.

Conversion
To use your profile, select it in the RIP when printing with the printer, ink, media, and settings used to make the profile. When using a RIP, it’s important to note that different profiles may be required for different RIP settings, including printer resolution, screening type, number of print passes, and other settings.

Testing Your Profile
After making a profile, it’s a good idea to test it by printing a test photo. Sometimes users look for a way of quantitatively testing profiles, e.g., by measuring colorimetric values before and after profiling. Remember that the product of profiling is a visual color match, not a numerical match. So it’s best to evaluate your profile with an image that’s evaluated visually.

Your test photo should include:

• high-key (bright), low-key (dark), and flesh tone photos for checking color accuracy
• photos with memory colors—red, green, and blue, for checking colors that people “remember” how they should look, like fire-engine red, green grass, and blue sky
• a grayscale for checking neutrality
• adjacent or overlapping colors to check for bleed
• solid colors to check ink density, mottling, cracking, cockling, and other ink/paper problems

Print the test photo using your RIP and the same settings you used to make the profile. Check the test print in a standard viewing booth. Compare the photos with originals (if available) or with a standard print that you consider accurate.

If you have a program for viewing the color gamut of a profile, such as Chromix ColorThink (www.chromix.com), open your profile in the gamut checker and check the size of the gamut. After profiling different media, you’ll get an idea of how big the gamut should be on bond, matte, semigloss, and gloss photo media. If the gamut is too small, it could mean that ink limits were set too low. Also note whether the gamut has any inconsistencies or artifacts, which could indicate missing color patches, erroneous measurements, or defects in the profiling target.