Re: Scanner Replies
Re: Scanner Replies
- Subject: Re: Scanner Replies
- From: Martin Orpen <email@hidden>
- Date: Wed, 17 Sep 2008 23:19:27 +0100
On 17 Sep 2008, at 21:31, Michael Papet wrote:
Mark said, "I put "raw" in quotation marks, because I don't believe
the term raw means the same thing for this process as it does for
cameras"
The term raw in a scanner is very different than a camera. Each
scanner manufacturer has a different implementation of "raw". Yes,
they are all whatever the claimed max bit-depth is, but how they get
there varies. Marketing loves the term raw because it can be abused
so easily.
"Raw" has two meanings with Scanview scanners - depending on which
models/type you are using. On some it just means disabling the colour
management features and the tagging of the scan with a profile. On
others it means getting a linear 16 bit RGB scan rather than the gamma-
corrected version that most of us would expect. Contrary to my earlier
claim, it is the PMT-based 11000 lpi drum scanner that gives the
linear data not the F10 CCD scanner.
Mark also said, "in the case of colour negs, the most "pristine"
state in which they can be rendered is as a negative and linear.i.e.
a negative colour image unreversed, the possible advantage being
that I can "reverse" it to taste using some published techniques
with Curves (usually in Lab mode)."
Mark, I used to work for a scanner manufacturer and directly with
hardware/software Engineering. Scanning a negative is not ideal.
There are so few CCD's with the sensitivity to pick up all of the
data hiding in the negative and fewer still being used in a
scanner. There are legions of other issues that Silverfast has sort
of solved, Using negatives is really more for corner-cases and
should be avoided. A good generalization is the best scans come
from medium format or larger transparencies.
I prefer scanning negatives for critical images because, although the
colour is easier to manage, so much detail is lost or softened during
the printing process.
CCD scanners like the F10 can get a lot of information from negative
-- here's a sample from mine:
<http://www.idea-digital.com/content/view/27/37/>
The original was liquid mounted on the flatbed, scanned in high-bit as
a positive without colour or tonal corrections -- the same way that we
scan everything else -- and then the image was reversed and colour
corrected with curves in Photoshop.
I don't normally use the flatbed for this sort of work because the
first generation Kodak CCD in the F10 has a tendency to reveal its
wiring in the scans when you work them hard with big curves :-(
Scanview put a lot of effort in to the negative scanning features for
version 4 of ColorQuartet. This included a negative module that
allowed you to build, edit and store custom reversal curves. But it
was never successful. The colour variation in negative is so great
that even the most minor over or underexposure will render your curves
useless :-(
And most scanner operators wanted simplicity rather than complex
features from the software. Many of us preferred using the forerunner
to CQ, called ColorTrio which was also used to control Scanview's
camera backs. But as the Mac OS developed ColorTrio became more and
more unstable until it wasn't worth risking using it.
If you have more questions, please email me directly.
Eldon said, "Is it applying auto exposure to each new scan, or does
it always set a single exposure? If the former, I don't see how it's
possible to profile with any degree of certainty."
It's possible to profile with a great deal of precision regardless
of exposure functions. This remark will inspire sudden thoughtless
replies, but it is a simple point of fact, the sensor gets itself
into a calibrated state before a slow scan. Preview, or quick scans
rely on stored calibration states. Those are close enough in most
instances as what happens after the capture as the image data passes
through several processing black boxes before appearing on your
monitor.
Higher-end scanners tend to have an option to put them in "ICC mode"
where the exposure range is fixed -- only leaving you with the option
of screwing up the white balance :-)
Profiling works well -- except for negs of course -- we've used
Hutchcolor targets for many years and sometimes build custom
reflection targets using Profilemaker too.
--
Martin Orpen
Idea Digital Imaging Ltd
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