Learn how to communicate color, achieve accurate color results and control color effectively within your organization and throughout your supply chain, which translates to better quality and reduced costs.
Editor’s note: X-Rite Color Services partnered with Fabric Graphics on a two-part series about the challenges involved in communicating color, the human aspect of viewing and perceiving color, and how to overcome these obstacles to achieve accurate color in your workflow. Some of the following information comes from X-Rite’s Fundamentals of Color and Appearance (FOCA) seminar, which introduces the basics of color management and explains the human factors that are involved in judging color. This one-day seminar is built for quality control and assurance professionals, lab technicians, parts suppliers, manufacturing specifiers, or anyone who evaluates and approves color.
How it works—the four Cs
There are a number of standards surrounding each aspect of color management, all guided and managed by the International Color Consortium (ICC). However, color management is a bit more complicated than profiling devices. It requires the steps known as the “Four Cs” of color management.
Consistency. You need to be sure each device in your workflow, like monitors and printers, is able to reproduce consistent color over time and across the device. Some flaws can be corrected with calibration, but if your devices aren’t capable of capturing or producing repeatable and uniform color, they cannot be reliable members of a color-managed workflow. ICC profiles cannot correct for inconsistent devices.
Calibration. Calibration brings a device back to standard settings. For a monitor, this includes white point, luminance, gamma, black point, gray balance, and tonal response. Calibration is important so that you are not making edits based on false information from your display. For a printer, calibration involves bringing it back to a predictable state where ink densities and tonal values are known and stable.
Characterization. For printers and monitors, the process involves using a colorimeter or spectrophotometer to measure the actual colors produced by the device, then comparing them to the RGB or CMYK values that were used to create the output to determine the device’s color reproduction characteristics. This information is used to build an ICC profile that is specific to that device. This ICC profile will represent this device through the workflow conversion.
Conversion. Once all of your devices are set up, it’s time to help them speak the same language through a successful conversion in your creative applications, such as Adobe® Photoshop®, or in the printer software.
Color management tools
Color management technology has evolved from the expensive print-edit-print cycle to the ability to achieve accurate color right from the start. Today, most companies that rely on accurate color utilize color measurement instruments and software. These color quality assurance systems store standard data and the rules (tolerances) that define a pass/fail characterization of each measured sample. There are two instruments used to measure color samples: colorimeters and spectrophotometers.
The human brain requires three components to see color: light, an object and an observer. A colorimeter works the same way by measuring color through red, blue and green filters. It is able to simulate the eye/brain sensitivity to color by simultaneously using specialized glass color filters and light detectors. The human eye can detect up to 10 million different shades of color and a colorimeter can quantify all of them into a three-dimensional color space. Currently colorimeters are only used for profiling displays.
Like the colorimeter, a spectrophotometer measures true color but uses a somewhat different measurement principal for even more precise results. It measures the entire visible spectrum of light that is reflected from a sample, and then uses mathematical tables representing human eye color sensitivity and mathematical tables representing the color output of different light sources to calculate the result. A spectrophotometer cannot take into account variances in weave and texture.
Colorimetry is a way of measuring and quantifying the color of an object based on a standard light source and a standard model of human vision. There are many software packages available for capturing, storing and analyzing this color measurement data. X-Rite has just launched its new i1Profiler software, which lets users create custom profiles for monitors, RGB, CMYK and multicolor printers, plus digital projectors.
When using a color management system, it’s crucial to establish and follow repeatable measurement techniques. Sample size, thickness, pattern and position can contribute to variations in measurement data. Also, it’s important to judge your prints under standard viewing conditions. Lighting should be color-balanced, bright and even. It is also important to consider surrounding objects. You must also consider metamerism, a phenomenon that occurs when two colors match under one lighting condition, but not another. To meet viewing standards, consider using a viewing booth and following the lighting standards set forth by the ISO.
A RIP-based color managed workflow
Setting up a color managed workflow takes a bit of time, but the predictable and consistent results are worth the effort in the long run.
While nearly all digital printers come ready to print with the required software, using a RIP (Raster Image Processor) will take your digital workflow to the next level. A RIP essentially becomes the “brain” of the printer, and provides more control than a standard print driver.
Color management is highly specific to industries, workflows and color needs. Although it is impossible to cover every aspect of color management as it relates to different industries, this section provides a brief overview of the main steps in a color managed inkjet print workflow. X-Rite Color Services can provide custom guidance to help you create your own based on your color needs, equipment and RIP software.
Prior to profiling: configure the printer
To ensure your printer is in optimal printing condition, always perform printer maintenance before you profile and each time you change media. Each printer has maintenance steps that can be found in the user manual that include printhead cleaning, media feed calibration, bidirectional calibration and other calibrations supported by the printer. All calibrations should be redone after loading a different substrate. These settings should remain constant while profiling.
- Tip: Make sure you select the proper resolution and speed in your RIP. Also, decide whether to use bidirectional or unidirectional. You will have to consider the print quality as well as the production speed. Slower speeds and unidirectional printing can provide superior print quality, but may be too slow for production. You may find that a combination of higher speed and/or bidirectional printing can provide adequate quality at a reasonable production speed.
- Tip: Each printer and each final substrate needs its own profile. This is because each printer behaves differently, and each media and coating will react differently with the inks and sublimation process. Keep in mind, this process should be done on the final substrate, not transfer papers.
Step one: set channel ink limits
More ink does not always give you more color. In some cases, when you lay down more ink the color will shift in hue. In other cases, you cannot see a density change, or even worse, it gets lighter with more ink.
The typical ink limit target will have patches in uniform steps from 0 to 100 percent ink. In the RIP, set all ink channels to 100 percent, then print out the steps from 0 to 100 percent. Visually or with software, judge where the ink channel limits should be. Look for the point where the density no longer goes up, while also looking for hue shifts. The goal is to achieve the most color without using excess ink.
- Tip: Some RIPs will graph each ink channel on a 2-D plot. This graph will help you see where colors start to shift hues, reach a chroma limit, or where the color will reach a density limit. See your RIP user manual for more information.
- Tip: It is helpful to use the Pantone guides and Process CMYK colors for guidance on selecting channel ink limits.
Step two: create a linearization
Linearization is a type of printer calibration that brings the device back to a known repeatable state. To create a linearization, print the steps from 0 to 100 percent for each of the ink channels. Next, read the values into the RIP software. The goal is to achieve smooth curves.
- Tip: Linearization should be done to bring the device back to a known state when you start to see color drift, or when you service or move the equipment, or change inks.
Step three: set the total ink limit
Without a RIP, the most control you have over ink limiting is probably selecting a different type of media, or using the included sliders to make minor tweaks across the board. With a RIP, you can specify ink percentages for each ink channel that is supported by the printer. The benefits include faster dry times, more accurate color mixing and fewer reprints due to overinking.
From the RIP software, print a total ink limit swatch, which includes various combinations of the ink in your printer. The purpose is to see how much ink the media can handle. Once it is printed, look for signs of over inking, such as puddles, bleeding, cockeling, mottling, ink offset and excessive dry time. Then, set the limits in the RIP software.
- Tip: Give the print the same time to dry as you would in your production workflow. For instance, if you are working on a printer with a rewind roll, then the print must be completely dry before it gets to the rewind roll to avoid offset and other issues.
Once you have ensured your printer is producing consistent color to the best of its ability, it is time to create your ICC profile. This profile will help achieve the most accurate color possible from the printer.
Make sure that all other steps have been applied and print the ICC profiling target. Using your measurement device, read the target values into the RIP, which will create the ICC profile that describes your specific printer, inks, media and settings.
There are many different settings, and every process is different, so we cannot make general recommendations. Contact X-Rite Color Services to learn about classes that can help you select the best settings for your specific scenario.
- Tip: If you have the ability, use presets for dye sublimation. Check your RIP and/or profiling software to see if there is a preset for sublimation.
Implementing a custom color management workflow will help you effectively control color, which will result in better quality and reduced costs. Don’t let the initial setup deter you. Your efforts will be rewarded with consistent, accurate prints.