by JimRaffel on February 28, 2006
Part 4: TVI is not measured it is calculated from density which is king. All the other values our modern densitometers display are simply calculated values from the densities the instrument measures. In short, all a densitometer does is transmit a predetermined amount of light and then measure how much comes back to the instrument. This is done through Red, Green and Blue filters so the instrument can tell if the light was stopped by Cyan, Magenta, or Yellow ink.
One reader made a comment at JimRaffel.com that density is also a good indicator of ink film thickness on a printing press. Just remember that two inks with different pigment loads can record the same density and have different ink film thickness.
Coming next…Part 5 Measuring TVI of Inkjet proofs in meaningless
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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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