In previous articles on color management, built a foundation, exploring the factors that affect color output and how to manage them. In this, the seventh in a series on color management, we’ll describe what a “profile” is in digital printing, how they’re used and how to create a profile.
A profile is a set of data that characterizes a color device. The purpose of a profile is to facilitate translation between devices, to accurately communicate color between disparate devices. A profile describes the color attributes of a device by defining a mapping between the device and a PCS, or Profile Connection Space. The range of colors that can be defined in the PCS is broad enough to encompass any devices mapped to it.
Each device that captures, displays or prints color can have its own profile associated with the device. Profiles for some devices may be provided by the hardware / device manufacturer. Many devices allow you to create your own profile with a color spectrophotometer such as
XRite’s I1Xtreme.
The spectrophotometer is key to profiling devices. The remainder of this article will use the I1Xtreme in profile creation and assumes accompanying software has been installed and configured appropriately.
Monitor Profiles
The purpose of a monitor profile is to ensure colors are more accurately displayed during the design and review process. Profile creation is accomplished by selecting the appropriate wizard, the software walks you through the process.
Prior to profiling a monitor, it is recommended that the monitor be turned on at least 30 minutes prior and the display area should be clean. The first step is to select the device type to be profiled. When “Monitor” is selected, you are prompted for the type of monitor, e.g. LCD, CRT, etc. Next you are prompted to calibrate the spectrophotometer. The device is placed in a cradle that contains a white target used for calibration. Once calibration has been completed, the scanning device is mounted to a base used for monitor calibration. This base has a rubber strap attached to a counter weight. The based is placed flat against the monitor. The rubber strap is looped over the top with the counter weight hanging on the back side of the monitor.
Once the scanner is in place, the software “finds” the location of the scanner by displaying a series of patterns on the monitor while the scanner senses the changes in the display. Each subsequent pattern further narrows the search area until the precise location of the scanner resting against the monitor’s surface is located in software.
Once the position of the scanner is known, the software displays a series of about 80 colors in front of the scanner’s discovered location on the monitor. The scanner reads each of the displayed colors and builds a look-up table of expected and actual (displayed) color. Once completed, an .ICC profile for your monitor is created and activated on your system. Prior to exiting the software, you’re given the opportunity to see the display “before” and “after” application of the profile. Your monitor should be profiled periodically for best results. It is recommended that an LCD monitor be profiled monthly, a CRT should be profiled weekly.
Scanner Profiles
The I1Extreme includes a scanning target that is used in scanner profile creation. The scanning target is placed in tray guide that’s included with the product. You then scan each color on the target, one row at a time. You are then prompted to select an image on your file system, the target as scanned by your scanner. The software then generates a profile by comparing the expected colors (as scanned by the spectrophotometer) to those in the image file from your scanner.
Media Profiles
The actual process of creating a media profile will vary depending on the software used, so the description below is generic and assumes familiarity with your RIP or other software. The general information is based on an internal process utilizing Roland’s Versaworks driving an Eco-Sol printer, and XRite I1Extreme color management system.
Determine the maximum ink limit for each color / channel, CMYK. We use a prepared ink limit file that prints small swatches of each color, increasing in ink percentage from 0 to 100% in 2% increments. This ink limit test must be printed using Density Control – essentially disabling any color management. This is necessary because we don’t want any color adjustment, and because we want the percentages of ink to be actual, not adjusted by an embedded profile.
In viewing the printed ink limit chart, at lower percentages, the increase of ink at 2% increments is quite noticeable. As the percent of ink increases, the difference becomes less apparent. For each channel, find the percentage where the difference is all but imperceptible. Make note of the percent for each channel. Depending on the media, printer and ink, and color, these percentages will commonly be in the range of 72% – 90%.
Once the ink limit per channel is known, a color ramp is printed using these percentages. The ramp is then measured with a color spectrophotometer. This measures the density changes in the ink ramps for incorporation in the profile.
We’ve already determined the individual channel limits and measured the ink ramp. The next step is to determine the ink limit of all 4 channels combined. A combined ink limits test is printed to allow visual and tactile evaluation. As the total combined ink percentage increases, at some point the media will become completely saturated with ink. Additional ink added beyond saturation at some point will appear raised above the media and will not dry promptly. The total ink limit chart is checked immediately after being printed to determine at what percentage the ink does not appear raised, and is mostly dry. The ink may be partly tacky, but should not smear easily. The combined total ink percentage is then added to the media profile.
The next step is to use the new media profile to print a color scan chart. This chart is then measured using the I1Extreme, which will generate an .ICC profile for incorporation in the RIP’s media profile. If your printer supports multiple resolutions, this media profiling process should be followed for each supported resolution.
Though the process may vary with your hardware and software, the concepts are fairly common in media profile creation. To ensure that color can be produced predictably, media profile creation is critical component of a color managed work flow.
For more information, contact:
Spectrum Signs
23382 Madero Suite L
Mission Viejo, CA 92691
(949) 297-3800
