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The Basics of Color Management

A great deal of interest, confusion and misunderstanding surrounds the concept of color management. In simplest terms, it is the measurement and control of each and every step in your graphics reproduction process. The goal is to closely approximate what your output is going to look like before you commit precious resources to print. Rather than a cost, it is an investment that will save time, money and materials.

The process begins with the proper calibration and profiling of each input and output step in your reproduction chain. Calibration is a process that brings a device to known operational state. In and of itself, calibration doesnt improve your process, but it is fundamental to the success of color management because it brings us to a known, repeatable starting point. Profiling is the process where we determine the operational limits of a device, such as a digital camera or a scanner. We are determining how the device interprets a known range of colors. In the case of output, we are learning how known colors are actually reproduced. These profiles become maps that can be used by color management software to manipulate digital data.

The profiled capabilities of digital cameras, scanners and printers result in what is commonly called device-dependent data. "Device-dependent" is something of a misnomer because the profile data doesnt just depend on the device, but also on the media and operating conditions. A printer profile, for example, is only valid for a given substrate using a single inkset, in the environmental conditions that existed at the time. A change of ink cartridges, or an increase in humidity can invalidate your profile. Similarly, a change in ambient viewing conditions will alter your monitor profile.

Color is reproduced by adding together differing levels of red, green and blue (RGB) light, the additive color theory; or by subtracting various levels of yellow, magenta and cyan (CMY or CMYK) from white light, the subtractive color theory. The method used by a particular device is known as its Color Model. The color models commonly (but not always) used for these device dependent profiles are RGB for input and monitor output, and CMYK for physical output. A typical color management program will handle data in a "device-independent" color space, such as CIE XYZ, translating to and from color-dependent data as needed. Doing so frees the data from the gamut limitations any particular device may impose.

The way we reach our goal of saving time and resources is to simulate our output device with our proofing device, matching them within the limits of the different color models. This is accomplished by fitting the data into a gamut that accounts for the limitations imposed by each of our devices.

In this extremely simple workflow that consists of nothing more than a monitor for proofing, and a printer for final output we have two gamuts to contend with. By constraining our data to the colors that fall within the overlap area of the two, both devices are able to reproduce the same image.

The example shown here is very basic, designed to illustrate the concept. And while the concept as described here sounds easy enough, there are literally hundreds of different possible workflows and dozens of software packages available. Real differences exist in the manner in which various software packages and "color-management engines" transform the data. The choice of color-management software and tools to adopt for a particular workflow is not to be taken lightly.

A major obstacle preventing many presses from being profiled is the amount of real estate consumed by profiling targets. Unfortunately without this critical profile your color managed workflow in incomplete. Adding to this dilemma is the fact that most printing processes are relatively unstable.

Many factors contribute to this lack of stability, among them are variations in ink, substrate, press conditions, image carrier, operator, etc. There are literally hundreds, if not thousands, of factors that affect the end result. This lack of stability requires frequent profiling to capture the fluctuation. The goal on press needs to be; control those factors that you can, and profile frequently to account for those you cannot.

When conventional profiling targets are included on production print orders, a great deal of waste is produced due to their size. Running special "finger printing" trials to print the targets can also be very costly, and does not necessarily represent real life print conditions. Add to this the fact that your press conditions are constantly changing, and what your fingerprint produces is a snapshot that most likely does not represent your current operating conditions. The ideal solution is to profile every job, so that film or plate output for your next order reflects your current conditions. Until now, this simply has not been a realistic option.

A scanning spectrophotometer with an available micro-spot head can read targets as small as 1.6mm. This allows tiny profiling targets to be included on every production order. The targets can be included along with your color bar, or if need be, in place of a small section. This advancement in color scanning technology allows color management to truly move forward into the pressroom.

Open architecture prepress systems are a blessing in that they allow increased flexibility in workflow options. This increased flexibility requires careful planning to assure accurate color communication between devices. There are many ways in which a color managed workflow can break down. For those new to color management, you may wish to invest in the guidance of a knowledge-able consultant who can help you set up a system that works for your particular situation. For more information on instruments used in color management, a listing of third-party software products, and a list of recommended consultants, please visit our website at www.xrite.com.

By Bob Binder, X-Rite, Incorporated

X-Rite is a member if PICA's Associate Committee