Re: Profiling film recorder
Re: Profiling film recorder
- Subject: Re: Profiling film recorder
- From: "Wolf Faust" <email@hidden>
- Date: Wed, 9 May 2001 09:42:25 +0200
- Priority: normal
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The CRT has no black matrix so
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the bright point doesn4t illuminate only one of the 8000x8000 possibly
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"pixels" but also "wastes" the field arround it because it has an
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unsharp corona. When You try to give out an TC2.0 RGB Testchart You will
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see that there are bright patches in the neighbourhood of dark patches
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and these dark patches get wasted by the corona of the bright ones. Even
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when the slide machine exposes correctly these "wasted" patches will be
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measured as too bright !
Just my rubbish on the issue:
1. Tests made here during the past months with Lasergraphics
Mark IIIDPM, CCG PCR8, Solitaire, Polariod 8000 and laser film
recorders do show that effects of these surrounding on a certain
patch are not much different between modern CRT and laser/LED
based recorders. I see no major advantages here for laser/LED
based recorders when it comes to the corona effect, at least not
large enough to justify the much higher costs.
2. The main advantage of laser based film recorders is the ability
to record much more "pure" colors. As you described, CRT
recorders use filters to produce the red/green/blue. Because of
various reasons, the spectrum of one of these filters is not really
sharp, wich means, you can't exposure "pure" colors with high
chrominance. Especialy when it comes to bright yellow and green,
CRT film recorders can be a real nightmare with nearly no
chrominance in the colors. (PS: LaserGraphics Mark III DPM was
best here in the tests with roughly 40% more chroma than the
worst case: CCG PCR8). The color gamut you do get with laser
film recoders on film is MUCH greater causing you even more
sleepness nights when it comes to profiling.
3. When it comes to profiling a film recorder, one needs to look at
the situation for RGB profiling software in general. I'm far from
impressed from the RGB profiling software I have seen so far. I
strongly doubt ColorTune or PrintOpen will be able to deal with the
huge color gamut of the film recoders in decent quality as they fail
to work on much simpler devices. Beside the large color gamut of
films (CRT or laser), as said, the surrounding of a color has a very
high influence on the actual color.
Example: take an IT 8.7/1 scanner target reference file and look at
the neutral DMax (L16) patch and compare it with DMax/GS23.
The effect is only rather mild here and things can be a lot worse for
other colors. But just as example take L16/GS23. On good film
targets you will get a luminance value of L 2-3 for L16 and roughly
L0.7 for DMax. Both are usualy pretty much neutral. The huge
difference is really caused by the brighter surrounding of L16.
Interestingly the effect is also pretty visible with the rather large
patches of a 4x5 film target. So it's not only a problem of small
dots getting influenced. The effect does cover a pretty large area.
Also the lab used to develop the film does play a major role here.
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The other problem is that the emulsion of analog films doesn4t react
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linear like other digital output systems. You cannot linearize it. When
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Your profile tries to correct the file for the slide machine You cannot
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be sure if the emulsion reacts like it should.
If you do ask the manufacturer, most better film recorders do come
with film tables that can be edited. Also, the software I saw so far
for adjusting the colors of film recorders is based on linearizing just
the channels... resulting in neutral grays to be reproduced. This
surely doesn't really solve adjusting the colors. Also, all the film
tables I have seen so far do not get to the limits in order to avoid
highly non linear exposure range near DMin.
I think the manufacturers of film recorders should feel ashamed.
After all those years they haven't even started providing decent
solutions to the color problem. I think with some months software
development the color quality of film recorders could be dramaticly
increased. But now that the market for film recorders is nearly dead
as other solutions take over, I see no customers for working
solutions...
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If anyone knows of SW (and the hardware...) to create ICC profiles of 35mm slides,
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I'd love to hear about it.
Typical ICC CMS systems are single pixel based... as you
indicated, this does not work to well with film recorders. One needs
to write special software and a special test target that allows you
do adjust a color of a pixel based on the surround. I think a decent
working solution wich has a dramatic effect on the output is
possible.... but as said, none of the manufacturers really seems to
care anymore...
--
Wolf Faust Tel: +49-69-5486556
mailto:email@hidden Fax: +49-69-95409598
http://www.coloraid.de Mobile: +49-179-6924769