[argyllcms] Re: [argyllcms] how many patches, profiling Epson printers
- From: "Gerhard Fuernkranz" <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 27 Jul 2005 12:28:08 +0200 (MEST)
> --- Ursprüngliche Nachricht ---
> Von: Jan-Peter Homann <homann@xxxxxxxxxxxxxxxxxx>
> Sometimes the compensation of optical brightners in
> Profilemaker or PrintOpen helps.
>
> **
> Is there a comparable function in Argyll ?
> **
Yes there is, if spectral measurements are available.
See the options -f of the "profile" command.
See also Graeme's paper
http://www.imaging.org/store/epub.cfm?abstrid=22190
which describes the principles of the implemented algorithm.
(Actually I'm wondering, whether the other professional profilers are
probably based on Graeme's algorithm as well?)
In addition to the measured spectral radiance factors, the algorithm
requires the spectrum of the instrument's light source as input paramter
(for instuments with a filter in the illumination path, of course the
filtered light spectrum hitting the paper needs to be used). My
understanding is, the algorithm eventually attempts to predict the spectral
radiance factors of the patches, as if the paper were illuminated by the
actual desired viewing illuminant (e.g. D50).
Argyll currently assumes an illuminant A light source for virtually all
instruments, which is probably a reasonable approximation for instruments
with tungsten lamps, but which if of course not correct, if an UV filter is
used, or if e.g. a Spectrolino is equipped with a D65 filter. Graeme was
also so kind to add on my request Spectrocam's Xenon flash spectrum to
spectro/inst.c and xicc/xspect.c, which can be selected for FWA compensation
by setting TARGET_INSTRUMENT to "Spectrocam" in the .ti3 file.
Regards,
Gerhard
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