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At the heart of this challenge remains the ability to retain customers and improve ROI with limited investment. Customers are constantly looking for signmakers to produce the “perfect sign,” which features the highest level of efficiency and image quality. Although a basic concept, color management is one of the most critical and commonly misunderstood aspects to creating this perfect application.

Employing proper color management techniques can become a headache. There are literally hundreds of varieties of devices that possess very significant color differences. As a result, signmakers are constantly seeking advice on ensuring that files will retain their essential integrity when sent to different devices.

The following article will provide a ground-up approach to color management, including an overview of the science behind the process, discussion of how ICC profiles for consumables, such as media and ink, can contribute to a fully color-managed workflow, as well as provide advice on ways to employ color management techniques for success.

The Basics: Color Theory and Beyond
Light is the visible part of the electromagnetic spectrum, which consists of vibrations called waves. Measured in nanometers, the frequency of waves is called wavelengths. Our eyes have sensors (cones) that sense the visible spectrums wavelengths. When stimulated, the sensors in our eyes send signals to our brain, which are in turn perceived as color. If sensors detect equal amounts of these wavelengths, white is perceived, and if no wavelengths are detected, black is perceived.

Light emission, reflection or transmission can alter or modify the wavelengths, and in turn how color is perceived. Since different objects can absorb different wavelengths, the wavelengths reflected from an object are sensed by our eyes and ultimately perceived as color.

Our visual system processes wavelengths down to dominate regions; red, green and blue. These dominate regions are referred to as additive primary colors, which can be mixed to produce subtractive primary colors: red and green light produce yellow, red and blue light produce magenta, and blue and green light produce cyan. Equal amounts of subtractive primary colors can make the additive primary colors: magenta and yellow produce red, cyan and yellow produce green, and cyan and magenta produce blue.

While devices such as cameras, monitors and scanners are classified as RGB because they add red, green and blue light to darkness, printers and paintings conversely are classified as CMYK since they are applied on a white substrate, hence subtracting light. Lastly, L*a*b* is a device independent color space because it is used to communicate colors from device dependant color spaces such as RGB (monitors, cameras, scanners) and CMYK (printers). Among these color spaces, there are varying differences in gamut size between the input profile and output profile.

ICC Profiles: The Keys to Color Management Success
The goal of color management is to reproduce the colors that are specified in ICC profiles. Since the output profile attempts to reproduce colors that the input profile has specified, the final result will not be accurate if the either of the profiles’ color specifications are inaccurate.

The output ICC profile is built upon predetermined conditions. These conditions are the building blocks or foundation for the quality and accuracy of the final output. If the foundation is poorly built or altered, then the ICC profile is rendered useless and quality output is impossible.

Checklist for ICC profile success

Checklist for ICC Profiling Success
The key to ensuring the accuracy of an ICC profile rests in checking that all of the steps that occurred below the profile do not vary drastically. The figure below outlines the seven steps required for this process, which include ambient /environmental conditions, calibrating a media to the printer, print settings, primary ink restrictions, linearization, total area coverage and lastly ICC profile. By keeping these steps, as well as the corresponding implications in mind, signmakers can optimize the color management process.

The following is a checklist for signmakers to use as a guide in managing the color management process:

Step One: Ambient & Environmental Conditions
There are several factors that may affect this step, including temperature, humidity, static electricity, bad electrical grounding, dust, dirt, etc. As it relates to temperature and humidity, signmakers must understand that these factors directly affect how ink penetrates the ink receptive coating of a substrate as well as dry time. For example a low RH may evaporate humectants too fast and clog print heads, as well as cause irregular dot patterns and banding. Similarly, static and bad grounding can affect the dispersion of ink (off angle ink lay down), nozzle deflection and misfire. This is often demonstrated by irregular dot pattern and banding. Another prime yet often overlooked example is the ability of dust and dirt to obstruct ink penetration and cause clogging of print heads.

Step Two: Calibrating a Media to a Printer
Calibrating media to a printer is a critical element that must be considered when producing any output. The most critical elements that signmakers should check include ensuring that nozzles are firing properly, the heater is set correctly, head height has been adjusted, media feed is set correctly, as well as the proper alignment of uni and bi directional print heads. All of these factors are directly responsible for the quality of the dot pattern and banding.

Step Three: Print Settings
Printer settings are directly responsible for the printing quality, speed, gamut size, and dry time. As a result, signmakers must pay close attention to numerous variables when evaluating their print settings. Among the most critical factors include dither or dot pattern, print head pass count, print head speed, overprint or 2nd strike, variable dot settings (piezo print heads) and light ink transitions.

Step Four: Primary Ink Restrictions
Primary ink restrictions are directly responsible for gamut size, and if set incorrectly, over inking artifacts may occur. When evaluating this facet, signmakers should consider the primary ink restrictions, cyan, magenta, yellow, black, and spot colors (R,G,B,Vi,Or,Gr, etc.), as each channel can expense up to 100% of ink. In the high resolution printing conducted by sign shops, 100% per channel is unnecessary. Too much ink may cause unwanted hue shift, inverted densities, or over inking artifacts (bleed, coalescence, mottle, etc.), while too little ink results in a small color gamut.

Step Five: Linearization
Calibration/linearization is directly responsible for smoothness of transitions, shadow and highlight detail, accuracy/consistency, and gray balance or neutrality. To ensure these attributes, signmakers should be aware that the percentage of primary ink dispersion is correlated to density. The correlation is then altered so increasing amounts of ink dispersed appears to produce increased density. As a result, a linear correlation (1:1) between ink volume and density is the primary goal. Re-linearizing an output profile is suggested monthly or whenever an ink with a different lot number or a media with a different lot number is changed.

These graphs show the effects of linearization, the relationship between ink volume percentage and density are correlated to react linearly (1:1).

Step Six: T.A.C. (Total Area Coverage or Total Ink Limit)
T.A.C. represents the total amount of ink available to print. If the T.A.C. is set too high, it may produce over inking artifacts such as mottle, bleed, coalescence. In contrast, if the T.A.C. is set too low, it may restrict the color gamut. To calculate the maximum T.A.C., signmakers should multiply 100% ink per channel by the number of channels C,M,Y,K.

Step Seven: ICC Profile
When used properly, ICC profiles determine the accuracy of printed colors; however, it is important for signmakers to understand that the ICC profile does not have the ability to fix over inking artifacts such as bleed, coalescence, mottle, etc, banding, or to make a pretty print or dot pattern. Its main function is to provide a reasonable idea of what colors a device (printer, ink, substrate) can reproduce.

It’s also important to note that colorcasts can be present in an ICC profile due to limitations of technology and false readings caused by optical brighteners. Additionally, no matter how great the quality control is from any manufacturer, minor differences will still occur. The minor differences between inks, media, printers, and ambient environmental fluctuations can add up. This statement also applies to using a “canned” profile (a profile created on one printer and shared with another). These subtle differences can be minimized if accounted for properly.

Signmakers may also be able to correct these subtle differences with re-linearization of output. Re-linearization can accommodate subtle density changes; however, it cannot correct drastic changes like changes in print speed, pass count, resolution, changes in ink restrictions, or changing the total ink limit. When re-linearization is not an option, a new custom profile must be generated.

Conclusion
In the volatile economy of today, a re-focus on the color management process is a simple exercise to ensure optimal output without the need to invest significant resources or money. Although the factors discussed in this article may seem insignificant independently, making minor changes throughout the color management process can have dramatic effects on the overall quality and efficiency of output.

About the Author
As a digital imaging specialist for InteliCoat Technologies, Jonathan Read works with customers, employees and industry professionals to provide technical support in the areas of color management, printing, imaging, graphic arts software and hardware.