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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by JimRaffel on October 18, 2005
I am often asked by customers one of two questions; 1. Which instrument that I already own should I use with my Colormetrix product; 2. Which instrument should I purchase to use with my ColorMetrix product? While my good friends who work for brand X and brand G will tell you the answer is simple (one of the ones they sell of course!) I find it to be one of the most difficult questions to answer.
The answer to this question begins with one word; application. Your application of the instrument implies several more questions:
What will be measured? – When I ask this question I am trying to determine if a scanning instrument like an EyeOne or PULSE can be used. Or it a hand-held instrument like a 528 or SpectroEye will be more appropriate. If press sheets with small color bars are what will be measured, a scanning instrument (of the type mentioned above) will not be appropriate. If, however, proofs with a large control strip (which we can set-up to be scanned by the EyeOne or PULSE) will be measured, then the speed of input and decreased opportunity for measuring the wrong patch makes the scanners more appropriate.
What is the spectral response of the colorants & instrument? – This one gets a bit technical, but is important. I visited with a customer last week who was testing out a new instrument. He is concerned that he will not be able to use this instrument to measure his proofs for color management purposes. This is because some spectrophotometers are built with spectral response every 20 nanometers while others respond every 10 nanometers. In the case of this customer’s application, the yellow ink he is using has a sharp fall off in the spectral response curve between two of the 20 nanometer points being measured by the instrument in question. Please do not read this section to mean that 20 nanometer spectrophotometers are bad and 10 nanometer instruments are good. It is a matter of application. There are many other factors that determine the overall quality of an instrument. In the case I just sited, however, this was an overriding factor.
Will you use the instrument stand-alone? – If this instrument will always be plugged into a computer running a ColorMetrix product in general a less expensive instrument can be purchased. If on the other hand, the same instrument will be connected to ColorMetrix, and stand-alone, then you will need an instrument with a display and battery operation. Just think of the price difference between a PULSE and a 528 or an EyeOne and a SpectroEye. That difference will pay for the ColorMetrix software and a computer to run it on.
Who else will be measuring the same samples? – If your customer or someone else in the production cycle will be measuring the same samples and expecting the same results you will both need to use the same instrument. It would be even more helpful if you also looked at Gretagmacbeth’s new netprofiler product. This allows two instruments to measure virtually the same (or so the manufacturer claims – I have not yet had the opportunity to test this exciting product).
There are many more questions that one could ask, but hopefully those listed above will get you going in the right direction. Always feel free to give me a call or send me and e-mail and I would be happy to assist with the process.
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