[argyllcms] Re: More direct method of measuring FWA?

  • From: Ernst Dinkla <info@xxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 29 Jul 2010 13:26:32 +0200

Graeme Gill schreef:
Ernst Dinkla wrote:
I think that the straight line from the high point in the 650-700 nm through the lowest point between 450-520 nm may stay too high and straight beyond that lowest point at the short waves side, papers without FBA tend to curve more downwards there. It may be a range with less practical value for profile creation though. Where you verified the FBA compensation with different illuminants it could be interesting to measure an FBA free paper with a UV measuring spectrometer and apply the algorithm in that case too and see what is altered where no change should happen. Creating that curve from a third value between 450 and 700 nm will not work, papers vary too much on that range and I see no relation between that range and the lower than 450 nm range.

The current code has been tuned slightly from the algorithm presented
in the paper, although the gist of it is the same. There is no doubt
that the details are influenced by the characteristics of the paper
I was able to test. If you have any examples of papers where you think
that the current code isn't doing a good job, by all means send me
the spectral .ti3 files so that I can take a look at it.


Graeme Gill.

Comparing the spectral data of papers with a high/bright white paper color with their natural white equivalents in the SpectrumViz application on my site I see that the FBA effect often stretches to 550 nm and a straight line from 700 nm through that point equals the warmer white of the non-FBA paper better then. It still doesn't fit the downwards bending curve in non-FBA papers from 450 to 380 nm. Both papers measured with an Eye 1 basic without a UV filter. It is correct that it isn't the same paper and the difference is not between a spectrometer with and without a UV meter but I suspect that the paper base + coating is very identical in the two versions and the FBA is added to the high/bright white version in addition to existing coating and base whitening agents. The back side reading can be identical in some cases. If the FBAs add to white reflectance even without UV light falling on them then I shouldn't compare the two versions. The practical value of FBA compensation is the main thing to consider.

Better at 550 nm
Matt Photo-Fine Art Smooth: Lumijet Photo Art versus Lumijet Photo White
Matt Photo-Fine Art Smooth: Moab Entrada Rag Natural versus Moab Entrada Rag Bright Matt Photo-Fine Art Smooth: Innova IFA14 Photo Smooth Cotton High White versus Innova IFA 11 Smooth Cotton Natural White
Fibre Matt papers: Harman Matt FB Mp Warmtone versus Harman Matt FB Mp.
Fibre Satin: Hahnemühle PhotoRag Pearl versus HM FineArt Pearl
Fibre Satin: Hahnemühle PhotoRag Satin (low FBA) versus HM FineArt Baryta (high FBA)

Better at 520 nm
Matt Photo-Fine Art Smooth: Hahnemühle Photorag Bright White (high FBA) versus HM Photorag (low FBA)
Fibre Satin: Lumijet Natural Pearl versus Lumijet Photo White Pearl

The Canson Matt Photo-Fine Art papers without FBA show the straightest spectral plots followed by the Moab qualities in that category. The rest drop more progressively towards the short waves.

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm

--
Met vriendelijke groeten,      Ernst


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