In Part 1 of this series, we discussed color-managing files and monitors. We noted that the goal of monitor calibration and profiling is to see the true color of the file, which should have an embedded standard working space profile. The standard working space profile shows how the file looked on the last computer on which it was viewed.
In Part 2, we discussed color managing the input (scanner, digital camera) to get files that match the original photograph or scene.

Part 3 discusses color management for the printer. There are four possible goals in color managing your printer:

• Get the print to match the original file
• Get the best looking, most colorful (widest-gamut) print possible
• Get multiple printers to match
• Make proofs on one printer that match another.

Note that the first goal is to get the print to match the original file, not the monitor. Both the printer and monitor are output devices. The original file is the color benchmark to be matched, not the monitor.

The correct way to think of color management is not getting the printer to match the monitor, but the other way around—the monitor to match the printer using a proofing work flow. This involves the so-called “proofing scenario” and requires a color profile for both the monitor and printer.

If you output RGB files, you realize that the original file is bright and beautiful; the printer cannot help but tone it down. Using a printer profile helps you get the most color possible out of your printer’s color gamut.

Sometimes you may want to get one or more printers to match. If each one has a profile, it will match the original file to the best of its ability. However, if you need the closest possible color match from two or more printers, you’ll have to set the one with the smallest color gamut as the benchmark. By treating the other printers as proofers, you can get them to match the key printer.

The real objective of proofing, though, is to make prints on a low-cost, easy-to-use printer that will match a more-expensive, difficult-to-use, or high-production volume printer. You can also set up your monitor to match the printer.

WHAT YOU’LL NEED
Printer profiling is the most expensive operation in color management. It requires the most sophisticated hardware and software. To profile a printer, you will need:

• a color measurement instrument, generally a spectrophotometer (see Figure 1);
• a color management application capable of profiling printers.
Figure 1: To profile a printer, you’ll need a color measurement instrument, such as this X-Rite i1 iSis spectrophotometer. Fully automated instruments, such as the iSis, can read an entire chart without operator intervention. Lower-cost semi-automated instruments, such as the i1 Pro, read patches in strips, but require the operator to guide the instrument over each strip.

Software and instruments are commonly sold as bundles by the manufacturers, but can also be purchased separately. Since color management is now a mature technology, older instruments and software packages may be available on the aftermarket, such as on eBay. When considering such a system, be careful that the software is upgradeable to the latest version and works with the instrument. For example, most color management software is copy-protected with a USB dongle, which may also be built in to the instrument. Make sure the dongle is included in the sale package.

Another distinction to make when purchasing a color management program is whether your printer operates in RGB or CMYK mode. Of course, all printers use CMYK (and possibly other colors) of ink. However, so-called RGB printers are set up to receive RGB files. If sent CMYK files, the print driver converts them back to RGB, then to the printer’s colors of CMYK, CMYKcm, CMYKcmk, etc. (lower-case letters represent light inks). RGB printers generally operate with a driver, a non-PostScript software that sends data to the printer.

A CMYK printer is set up to receive images in CMYK mode. When sent CMYK images, it passes them through as CMYK, without conversion back to RGB. This type of printer can also accept RGB files, which is the preferred mode for the biggest-gamut color. CMYK printers generally operate with a PostScript raster image processor (RIP)—either a built-in hardware RIP or a separate third-party software RIP.

PRINTER PROFILING PROCEDURE
Color managing a printer can be divided into four steps, known as the “4 Cs” of color management.

Consistency. The first step ensures that the printer is set up to output the best color it can reproduce. On an inkjet printer, consistency refers to setting the ink density to achieve the biggest possible color gamut, but without printing too much ink. Excess ink is wasteful, delays drying, and causes artifacts such as mottling, banding, and cracking. If your printer operates with a driver, the manufacturer has already determined the optimum ink density and programmed that into the driver settings. If you use a RIP, however, you’ll need to determine the optimum ink density by printing an ink-restriction target (see Figure 2). This target consists of CMYK ink percentages from 0-100. Note the percentage point where density levels off, in spite of more ink being printed. This point is the optimum density. Program that into the RIP in the ink limit settings for each channel.

Figure 2: Color profiling merely characterizes a printer’s color reproduction characteristics. Before profiling, the printer should be set up for optimum color reproduction by setting ink limits and linearizing the halftone scale. This illustration simulates the appearance of optimum and overinked printer density, and linear and nonlinear tone scales.

Calibration. The second “C” on inkjet printers refers to linearization. Once you have determined the upper ink limit, or density, the next step is to ensure that all tones between 0-100% are spaced evenly. This ensures that the printer outputs color the same from day-to-day, week-to-week, and so on. It produces the most even contrast. If you use a printer with a driver, the manufacturer has already linearized the printer to the recommended media. If you use a software RIP, this provides more flexibility in using third-party media. To linearize the media, first print a linearization target (included with the RIP’s color management routine) of tint patches from 0-100% in, say, 5% increments. Let the target dry, then measure it with a spectrophotometer. (RIPs support the most popular spectrophotometers.) If you compare images before and after linearizing, you’ll notice that the linearized printer produces better highlight and shadow detail.

Characterization. This refers to the profiling process itself. Profiling merely captures the printer’s current state of color reproduction. Before profiling, it’s important to set up the printer properly by setting ink limits (consistency) and linearizing (calibration).

Conversion. The fourth “C” of color management refers to applying the printer profile.

MAKING A PROFILE
To profile, first output a profiling target on the printer. When doing so, make sure that your ink limits and linearization are activated, but that color management is turned off. (You want to profile the printer in its raw state, not its profiled state.)

Your color management program may have a choice of different targets to print. You may need to select from RGB and CMYK targets. Use an RGB target for an RGB-type printer, such as one operated by a driver (see above). Use a CMYK target if you operate your printer with a software RIP that runs in CMYK mode.

The program may also have a choice of target size, from 200 patches to over 1,500. More patches will require more media and longer printing and measurement times. But, using more patches may make a smoother profile, especially if the printer is non-linear, or if the media is rough.

After printing the target, allow it to dry, preferably for an hour or longer. (Inkjet prints are notorious for changing color as the ink dries.) After drying, measure the target with your spectrophotometer, and make the profile. Before you save the profile consider using a naming convention to help sort out your profiles. For example, Epson Proofing Semi-Gloss media on an Epson 4800 printer with the ColorBurst RIP at 720 spots per inch resolution might be called “EP4800_CB_EPPrfSemi_720.icc.”

To install the profile on a Windows computer, place it in the folder Windows > WINNT > System 32 > Spool > Drivers > Color.

To install on a Mac, place in one of the Library > Color > Profiles folders. If you use a RIP, the RIP may have its own profiles folder or installation routine.

USING THE PROFILE
When using the profile to print a color image, the image should have an embedded standard working space profile, such as Adobe RGB. Applying the printer profile is known as “conversion,” the fourth “C” in the “4 Cs” of color management.

Conversion can be done by applications (e.g, InDesign, Photoshop, CorelDRAW), the host computer (Apple ColorSync, Windows ICM), the print driver, or by the RIP. Just use one to avoid double conversions. The most common conversion engines are applications and RIPs.

The most convenient way to convert color in an application is at the time of printing. For example, to convert an RGB image using the printer’s CMYK profile in Photoshop, select File > Print. In the Print dialog box (see Figure 3), select Color Handling > Photoshop Manages Colors, then select the printer profile. Use perceptual rendering for images and relative colorimetric for line art.
Figure 3: If you are not using a RIP, an efficient way to use a printer profile for output is to specify it in the application’s Print dialog box, as in this example from Photoshop.

You will get the same look by first converting color within the application (in Photoshop, Edit > Convert to Profile) and then printing with no color management, or with the same profile selected at print time. In Photoshop, remember that Edit > Assign Profile refers to the source profile (where the color came from), not the destination profile (the printer).

To convert with color management in the RIP (see Figure 4 above), transmit files in your standard working space by opening them in the RIP, dragging them to a hot folder, or printing to the RIP from an application. When printing from an application, turn off color management by selecting “No color management”.

Making your own color profiles will give you a higher degree of color control and more versatility for achieving demanding color on a variety of third-party media.

The complete color managed workflow described in parts 1, 2, and 3 of this series is diagrammed in Figure 5, (above).

(Click here to read Part 1 of this article series.)

(Click here to read Part 2 of this article series.)