Closed Loop Color

CLOSED LOOP COLOR

Before digital color management became the rigorous science that we currently use, print professional all had a bag of tricks to get their desired color results from a given printer. They had experimented, suffered, worked around and generally gotten to know their print device, warts and all, in order to get what they wanted from. Things got considerably more complicated when another device, like a scanner, or wide format printer was part of the mix.

Then when they got a new device, they had to start over from scratch.

This was Closed Loop color management, a tight bond between user and device.

Open Loop color management, however uses the "Universal Translator" concept, going from the input color start point color space (usually RGB of some kind) to L*a*b* color space - which is based on human vision, and a larger color space than any digital device - then from L*a*b* to CMYK+, according to the device profile of the printer. This allows users to plug new equipment into the mix without having to change color management setting for any other device. Essentially, it takes the input of any color space, then translates that to the output gamut of the print device.

As a method of color management, closed loop color is usually considered a mistake. However, some higher end production printers use Close Loop Color Control (CLC) to ensure color fidelity throughout a print run. The two concepts are very different.

Closed loop color is essentially an on-press feedback system that scans and measures the color bar on the moving paper (web or sheetfed) -- while the press is in operation -- and then feeds this information back to the press console to make automatic adjustments. When the color information recorded across the sheet: the ink density (or ink film thickness, and amount of light reflected off the press sheet) and the spectrophotometric data (or measurement of the hue of the ink) deviate from the specified levels, the closed loop system automatically adjusts the press to bring the color back to its target.

Why is this important? More and more presses include such measuring devices to ensure that the color you specify within your design application (InDesign, Quark, Photoshop) can be carried consistently from your computer to the printer's proofing devices and then on to the pressroom. This is also called color management.

So, remember the difference - the closed loop color management system is archaic and inadequate to modern CM needs, while closed loop control control is a breakthrough of technology that allows a digital press to maintain color throughout a lengthy print run.

n addition to color fidelity, additional benefits of closed loop color include reduced make-ready times, reduced paper waste and ink consumption, and the ability to save ink-presets for later use (i.e., to record all color information in the press console for later replication in future jobs).

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Email me at reilley4color@gmail.com