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The Power of Neutral Gray

(March 2009) posted on Sun Mar 08, 2009

This article will explore how to harness neutral gray to benefit print production.


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By Mike Ruff

So with the neutral gray defined and my proof color target neutral, all I have to do is adjust my C, M, and Y press curves to attain neutral values. Adjustments will necessarily change based on the substrates and solid ink colors in use. But because I am now measuring and targeting neutral gray, I can set up a press with a clearly defined objective and know that the prepress work is clearly targeting neutral.

Setting the curves from a gray bar

If we define the L*a*b* gray value of each tonal area in a tonal ramp and ignore the highlight in honor of the different substrates on which we may print, we’ll see an amazing result. Images appear very similar, even when we print on different substrates and our solid colors have slightly different hues. The reason for this phenomenon is that the gray-bar curve requires us to adjust C, M, and Y separately to attain neutral gray. This adjusts for substrate and solid-ink-hue error. Dot-gain adjustment does not address this. Even absolute-density adjustments taken from pure color bars do not report the effect of color-on-color overprint. Taking the curve-value-adjustment numbers from a C, M, Y gray bar does. The G7 Color Calibration Specification uses a gray bar embedded in the P2P25X neutral-gray print target (Figure 7). Each tonal value is a gray built to neutral specification of L*a*b*. When converted to all densities, a neutral curve can easily be created that corrects for substrate and ink-hue differences.

Benefits to the client and the printer



The client who understands neutral gray wants to work with a printer who also understands neutral gray. The benefit here for both parties is that neutral gray eliminates subjective opinion about the visual appearance of the file. Neutral is neutral, and you cannot argue with the purity of a neutral specification. The press operator who understands this can quickly determine whether the print is out of balance and which color is out with a modern densitometer that has an All Density function. As neutral gray becomes the controlling factor in a production facility, clients and printers find that communication reverts back to the professional language of the scanner operator who spoke of accurate gray balance with assurance in his voice.

The simplicity of neutral-gray color control is an example of Ockham’s Razor, a principle attributed to a 14th century logician named William of Ockham. It is often expressed as the law of parsimony, law of succinctness, or entia non sunt multiplicanda praeter necessitatem, roughly translated as: entities must not be multiplied beyond necessity. In today’s language it would be: all other things being equal, the simplest solution is the best. I believe that neutral-gray balance is the Ockham’s Razor for the printing industry. It works for printing and proofing in screen, digital, flexo, and offset, and it’s one of the most powerful tools we have to ensure accuracy and quality.

 

Mike Ruff is chief technology officer for Nazdar Consulting Services, Kansas City, KS. His experience in the graphics-printing industry spans more than 37 years. Ruff is a certified G7 Color Calibration Expert and a regular instructor at the SPTF Graphics Four-Color Workshop in Fairfax, VA, and he has authored numerous articles published in trade publications domestically and internationally.


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