Tech Talk: Perfect Prints with Profiled Printers
Monday, March 1, 2010
Digital Basics Part VI: Profiling the printer—the third major element of color management.
In Tech Talk’s last installment of “Digital Basics” we looked at color management for monitors. A color-managed monitor provides an accurate “window” onto the bits and bytes of a digital color file. The goal of monitor profiling is to get WYSIWIF color—what you see is what’s in the file.
Now, if you want to print a file after viewing it, the color will probably not match on the printer unless a printer profile is also used in the workflow. Seeing accurate color on-screen does not guarantee that WYSIWYG—what you see is what you get—at the printer.
The key to success when using a printer profile is to get the printer profile and the monitor profile to match the original file—not each other. Only when the printer profile is used in a proofing workflow will you get an on-screen simulation of the print. We will look at this in another installment.
HOW IT WORKS
Printer profiling became possible in the mid-1990s when several manufacturers developed comparatively low-cost spectrophotometers that many color shops could afford. At the same time, sophisticated profiling programs came to the mass market at a reasonable cost.
To make a printer profile, you first print a test chart that represents the printer’s color reproduction capabilities in CMYK. Reading the chart with a spectrophotometer measures the colors in device-independent LAB, a mathematical model of human vision. Printing a photo or other graphic in RGB space converts the photo to CMYK values that match the original RGB values as closely as possible. This conversion may not match the monitor, but the printed color will be as accurate as possible.
PROCEDURE
To profile a printer, you will need:
• A color spectrophotometer such as those made by X-Rite or Techkon
• A color profiling program such as X-Rite i1 Match, X-Rite ProfileMaker, X-Rite Monaco Profiler, Heidelberg PrintOpen, Agfa ColorTune, Kodak ProfileWizard, EFI Color Profiler, TGI PerfX, or comparable program
To make a profile:
1) Print a color test chart, preferably with 200 or more color patches, with Color Management turned off. (Failing to disable color profiles at this point will “profile the profile” and not the printer.)
2) .preview.jpg "Figure 1 To make a printer profile, you will need a profiling program and compatible spectrophotometer. First print a color test chart (preferably 200 or more patches), then read the chart and make the profile. Here Ryerson GCM graduate Evelyn To reads a")
Figure 1 To make a printer profile, you will need a profiling program and compatible spectrophotometer. First print a color test chart (preferably 200 or more patches), then read the chart and make the profile. Here Ryerson GCM graduate Evelyn To reads a Measure the test chart using a spectrophotometer connected to a profiling program. (See Figure 1) If possible, save the measurements in a text file for future reference or use, or in case something goes wrong with the profile.
Figure 1 To make a printer profile, you will need a profiling program and compatible spectrophotometer. First print a color test chart (preferably 200 or more patches), then read the chart and make the profile. Here Ryerson GCM graduate Evelyn To reads a Measure the test chart using a spectrophotometer connected to a profiling program. (See Figure 1) If possible, save the measurements in a text file for future reference or use, or in case something goes wrong with the profile.
3) Use the measurements to create an ICC printer profile. Entry-level programs have settings for the type of printer being profiled (e.g., inkjet printer, laser printer, offset press), which determine the settings for black generation. Advanced programs let you set black start, maximum black, and gray component replacement to minimize ink use and graininess in prints.
4) Give the profile a unique name so you can recognize it in software pop-up menus. It’s a good idea to include the printer, media and date. An example of a profile name for an HP 5550 color laser printer using plain paper, made on March 15, 2010 would be: “HP5550_PlainPaper_031510.icc”.
5) Save the profile in the appropriate folder (Mac: Library > ColorSync > Profiles; Windows: Windows > System 32 > Spool > Drivers > Color) where it can be read by ICC-compatible programs, or as directed by the manufacturer of the raster image processor (RIP) that drives the printer.
USING THE PROFILE
Now that you have a printer profile, here’s how you would use it in a workflow application like Adobe Illustrator, InDesign, or Photoshop (used here as an example).
1) Open a photo, preferably in RGB mode.
2) Select Print with Preview > Photoshop Manages Colors, and choose the profile you made.
(See Figure 2)
(See Figure 2)
Figure 2
.jpg)
To use an ICC printer profile in an ICC-compatible program such as Photoshop, open an image file (preferably RGB) and select Print with Preview. Select “Photoshop Manages Color” and select your profile from the pop-up menu.
3) The print should look as close as possible to the original file as shown in Figure 3.
Figure 3
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Profiling gives a very accurate picture of a printer’s color reproduction capabilities. Here third-year Ryerson GCM student Zigrida Mila checks an Epson 4800 print she made with an ICC profile. Next to the print are ink density and linearization targets used to optimize and calibrate the printer before profiling
CALIBRATING AND OPTIMIZING
The last article on monitor profiling discussed the “4 Cs” of color management, which include conversion, characterization (profiling), calibration, and consistency (optimization).
The point of the “4 Cs” is that profiling, which enables you to get a very accurate picture of a device’s color reproduction capabilities, raises two questions:
• What could you do to get this printer to look its best? That means to have the biggest possible color gamut, meaning the highest contrast and most saturated colors for artwork and photos. That’s “optimization,” or consistency, the first “C.”
• And, once the printer is optimized, how can you keep it printing the same? This means that you don’t have to re-profile the device every week, or whenever a system variable changes. This is the second “C,” calibration.
To illustrate, let’s look at the “4 Cs” for inkjet printers, toner-based laser printers and conventional presses. Calibration and optimization steps for these printers or processes are listed in Table 1.
Table 1
| Inkjet Printer | Laser Printer | Conventional Press | |
| Calibration | Using the RIP, print a linearization target, read it using a spectrophotometer, and let the RIP calculate a linearization curve. This ensures accurate halftone dots and smooth gradients. | Most toner-based laser printers are self-calibrating. The printer uses a built-in densitometer to linearize halftone dot area by reading toner on the drum. | Linearize the platesetter to ensure accurate halftone dot size and smooth blends and gradients |
| Consistency | Using the RIP, set ink density limits for each color and determine total ink coverage limits for the sum of all colors. | Most laser printers have toner density optimized for manufacturer-approved papers. | Choose a printing specification such as SWOP, GRACoL (G7), or FIRST. Use a color-control bar to set ink density and gray balance. |
Calibration and Consistency for Different Printer Types
“4 Cs” FOR INKJET PRINTERS
Unlike printing presses, inkjet printers shoot tiny drops of ink onto media and can achieve much higher ink densities. Also, a wide range of inks and media are available, not to mention RIP programs that drive the printers. Therefore, a customized approach is required to optimizing an inkjet printer.
“Consistency” for an inkjet printer means setting the ink density. (See Figure 4) If ink density is set too high, ink could actually puddle and run off the print, and certainly take too long to dry. If set too low, colors will look weak, and prints will lack contrast. You want to find the optimal amount of ink that gives the highest density and the fastest drying time and print performance.
Figure 4
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Optimization of inkjet printers includes setting ink density through the RIP, as shown in this dialog box from the ColorBurst RIP. Unlike lithographic presses, these printers “spit” ink onto the sheet. They can actually depsit enough ink that it runs off the page. Optimum ink is the level that has the largest color gamut but dries quickly.
“Calibration” for an inkjet printer is similar to printing presses. You also want to standardize all the tones from light to dark. To do this, you print a tone scale, or graded sequence of values, then measure it with a densitometer. The RIP calculates a linearization curve that spaces the tone values evenly.
“4 Cs” FOR LASER PRINTERS
Toner-based laser printers are the easiest to set up for consistency and calibration—they do it themselves! Most laser printers are optimized for toner density on manufacturer-approved papers, so that takes care of “consistency”. Most also have built-in densitometers that measure color tones and keep them calibrated. So “calibration” is automatic too.
“4 Cs” FOR PRESSES
Since conventional printing presses have been around for the longest time, they have the largest number of printing specifications. The first specification, SWOP (Specifications for Web Offset Publications, www.swop.org), was developed for lithographic web presses that use large rolls of paper to print magazines, catalogs and newspapers.
Due to the larger number of papers, inks, and coatings used, it was harder to develop a specification for higher-quality sheetfed printing that’s used for annual reports, brochures, posters and artist’s prints. Sheetfed lithographic printing is covered by the GRACoL specification (General Requirements for Applications in Commercial Offset Lithography, www.gracol.org)
Flexographic printing, which uses raised rubber plates for printing packages like freezer bags, bread wrappers, and labels, is covered by FIRST (Flexographic Image Reproduction Specifications and Tolerances).
The “consistency” part of color management for conventional presses involves printing to a specification. This requires including a color-control bar at the trailing edge of the press sheet. Color patches are measured with a densitometer to ensure that they have the correct density. Ink density and paper brightness determine the contrast range of the prints.
The “calibration” part of presses involves adjusting the tone values of the printing plates. This standardizes all the tones from light to dark (that is, from maximum density to white paper) to keep them consistent and repeatable.
USING MANUFACTURER PROFILES
Understanding the high value of good color reproduction, many inkjet media manufacturers offer pre-made, or “canned,” ICC profiles for their substrates. These are most commonly downloaded from Web sites, according to the printer, RIP, resolution, and media used.
High-quality canned profiles are made on printers that have been optimized and calibrated. You can download and use these profiles if you have the matching RIP. But it may be necessary to calibrate your printer so it will perform like the printer that was used to make the profiles.
Profiling only captures the color reproduction capabilities of the output device. Calibration ensures accurate, repeatable results by bringing devices to known specifications. Optimization involves setting ink density and related variables to create the largest color gamut with minimum ink usage and fastest drying time.
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