Troubleshooting Color: Source Color Space

More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set

Part 1 - Source Color Space

Color files set up to be printed always use a color space, even when the exact color space is not known by the customer. In general, the source color space is either RGB or CMYK, and composed pages are often found to contain both. For most customers, RGB is preferred, since it offers a larger color gamut, and higher saturation levels.

RGB usually comes in one of two flavors: sRBG or AdobeRGB. The key difference is in the size of the gamut, with sRGB having a smaller gamut than AdobeRGB.

Any work produced on a Windows device will usually be in sRGB by default. RGB is usually preferred since most sources (scanners and digital cameras) generate RGB, and most display screens use RGB as a native representation.

Some customers use CMYK as a source color space, with many flavors possible; SWOP, GRACol, ISO, etc., each with multiple variants. (See the Definitions page for definitions of these and other terms) The CMYK color spaces are usually characterized by the achievable gamut of a certain printing technology (ink and press type) on a certain class of media. While designing in RGB offers more possibilities, designing in CMYK often assures the final output will be within gamut.

The CMYK source space may also be used to emulate the lowest common denominator of two or more digital printers/copiers when matching output between the multiple printers/copiers. 

In any case, the source color space and variant must be known for optimum output color. 

A tag or profile is frequently embedded into the source file to identify the color space being used. The tag may be directly read in the RIP's job parameters.  Embedded profiles, if present, should ALWAYS be honored.

If the source color space is not known or discernable, experimentation must be used to find the closest match.

Other parameters specified in the Source area of the RIP job setup pertaining to color are:

• Almost always leave at the Full Output GCR default, allowing GCR parameters in the output ICC profile to specify black channel generation. Setting this parameter to Full Source GCR5 may cause color translation problems and should be avoided.
• Rendering Intent : Usually set to Relative Colorimetric which assures maximum colorimetric accuracy of in‐gamut colors. The default Presentation designation increases chroma of many in‐gamut colors, often rendering them inaccurate. 
• Photographic (Perceptual) also changes many in‐gamut colors, but may be useful if the shadows tend to block‐up.

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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com

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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Do you have a color management question, horror story or event to share?

Email me at reilley4color@gmail.com