by JimRaffel on February 16, 2007
Since #45 in December we have been discussing resolutions to improve the quality of your proofs. In order to gain the full benefit of this installment one should have read and implemented the suggestions in #46 & #47.
Proceeding forward it does not matter if you are utilizing a methodology like GRACoL G7, or a more traditional color management approach. In either case you will include a target on each print job with the same color bar swatches that you output on the proof (#46). This will allow you to measure the press ok sheets and compare them to the proofs, thus building even a larger statistical database to call upon.
When utilizing software like our ColorMetrix and ProofPass.com products for process control and print certification purposes it does not matter if you are using a methodology like G7 or traditional color management. While there are some new formulas out there to run the collected data through the tried and true colorimetric data (L*a*b* and derivatives along with some version of Delta E), do a great job comparing two similar or dissimilar imaging systems.
Unlike density and dot gain values which must be used with pigment sets designed for 4/color process printing, L*a*b* values allow the comparison of an inkjet proof and an offset press sheet. This is possible because we are looking at the actual colors, not values derived from a formula which assumes a certain pigment set.
Not only will you be comparing the measurements of the proof to the press sheet, but you will be building a history of what is a “normal” print condition of each press and paper combination. Some refer to this as finding the “sweet spot” of the printing press.
Overall, as your volume of collected data grows you will be able to refine the system in small steps by reviewing the proofing and press information both independently and together. Using numeric results, charts, and graphs you will be able to see small differences in color that can be adjusted for over time. No system is stable over time, so continuous monitoring is a must in order to maintain stable color.
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by JimRaffel on October 26, 2005
This post has be revised and reposted at ColorMetrix[dot]com as Color Conversations: Metamerism & Color Management.
There was a good comment in response to “Golden Nugget #15 Which Instrument Should I Use?” Adam made the following comment:
“This is because some spectrophotometers are built with spectral response every 20 nanometers while others respond every 10 nanometers.”
I believe this is referred to as the resolution on the device.
Adam’s comments got me thinking about the visual spectrum in general and all the different ways we work with the spectrum on an everyday basis in our industry.
So, for our discussion Matamerism is…
When two color samples appear to match under a particular light source, and then do not match under a different light source, this is an example of “sample metamerism.” One can conclude that the spectral reflectance distributions of the 2 samples differ, and their plotted reflectance curves cross in at least 2 regions.
The next image shows 3 examples of the GATF/RHEM Light Indicator which is printed with 2 magenta colorants which are a metameric pair. In this case when viewed under proper graphic arts lighting (5000K), the two colorants appear the same color. When viewed under other light sources you can see the two different colorants.
The RHEM indicator is a great tool, because it comes in rolls with self adhesive backing, so one can purchase them from GATF, and attach them to color proofs going out to a customer. If the customer is complaining about color a simple question about the appearance of the indicator will let you know if they are viewing the proof in 5000K lighting.
This brings me to the fun part of this week’s conversation. I happen to know the “Adam” who commented on last week’s Golden Nugget, and he is a graduate student at RIT. Adam and I had an interesting discussion yesterday about Color Management being the solution to the matamerism that exists between ink jet proofing ink and media combinations, and pressroom ink and paper combinations.
Color Management also solves the problem of soft proofing matamerism that exists because of the way displays (CRT or LCD) are illuminated. Without Color Management there would be virtually no way to match ink jet or soft proofing devices to ink on paper printing presses. Because these colorants are metameric it is increasingly important that all viewing of color occur under proper 5000K lighting.
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