scanner profiling woes (WAS Minolta 5400...)
scanner profiling woes (WAS Minolta 5400...)
- Subject: scanner profiling woes (WAS Minolta 5400...)
- From: Armand Rosenberg <email@hidden>
- Date: Fri, 12 Dec 2003 18:35:56 -0500
A couple of helpful individuals have provided info on their profiled
scanner workflows, and I thank them. They have also helped me
organize my thoughts on the topic. So I have a follow-up question
that is hopefully of more general interest.
For scanning positive film, it seems the practice is to determine an
appropriate exposure setting for the target and "lock" it for future
scans. After scanning the target, one calculates a scanner profile.
Then future scans are done by:
- scan with that "locked" exposure setting
- set the white and black points (*)
- assign scanner profile
- convert to working space
It's that second step (*) that bothers me. Since the target already
contains the equivalent of a true shadow and a true highlight, why is
it necessary to set wp and bp for each individual image? If the image
has a correct exposure and the target is on the same type of film as
the image, it seems the wp and bp should be the same for both target
and image, even if the image contains a tonal distribution that
differs from "average." (I'm not addressing any "improved"
interpretations of the image here.)
This has been the cause of my concern: I find that I have to set wp
and bp for each image, even when the image is properly exposed.
Otherwise the scan is usually too dark (the histogram is compressed
to the lower range). If I do this step (*), then profiling results
are reasonable. But this step seems essential to the workflow, and it
involves operator decisions on an individual image basis, which seems
contrary to the ColorSync philosophy. Hence my dilemma.
And while I'm on the topic, does the order of steps 2 and 3 (above)
matter? IE, should wp and bp be set before assigning the scanner
profile or after (or does it not matter)?
I've read Ian Lyons' informative description of profiling. My
impression after reading this article was that indeed wp and bp
should not usually need to be set on an individual image basis in a
profiled workflow. But his "yes" and "no" answer assumes that
histogram settings in scanner software are applied during the scan,
and this assumption appears from what I gather to be incorrect... If
these settings are applied after the scan anyway, then there is no
advantage in doing them inside the scanner driver (as long as a
16-bit file is saved).
And as far as I can tell, the wp and bp settings are always applied
AFTER the scan. I think Ed Hamrick (VueScan's author) has also said
this, and supposedly this is true of all scanner software (I know
it's dangerous to over-generalize...) So it doesn't matter whether
those settings are done in the scanner driver or later in PS, as long
as there is a 16 bit data path up to that point. In fact, why isn't
it advantageous to archive a file without these settings but with the
scanner profile embedded? That way you can always go back and modify
the wp and bp later, so you don't have to rely on your (possibly
impaired...) judgment at the time of the scan... It seems like it's
just a matter of convenience to apply these settings in the driver --
the results should be the same if you do a Levels adjustment in PS
later. Is this true?
To summarize, I suppose I have 2 basic questions on this topic:
1) In a ColorSync profiled workflow, should it be necessary to set wp
and bp for each image, or should that information be determined from
the target once during profiling (and hence become part of the
profile)?
2) Is there any advantage in adjusting the wp and bp in the scanner
driver, or are those settings applied after the scan, in which case
they could just as well be applied in PS (in a 16-bit file)?
I hope I haven't made some critical error in arriving at these
questions (if I did, I would of course like to know what it is).
Any thoughts from the experts on this List?
Armand
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