Hi Gerald,
Of course what you write sounds plausible. I actually believe film
manufacturers do optimize films for scanning. I was more or less reacting
to the tone of the original claims. :-) Now let me see if I can
understand the details in what you wrote.
Tom C.
----- Original Message -----
From: "Gerald Cermak" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, February 27, 2001 2:42 PM
Subject: Films can be optimized for scanning (was Re: Scanning Fuji Superia
400?)
> aimcompute writes:
>
> > As for Kodak's assertion that their films are specially formulated for
> > scanning... I'm not sure I believe it, nor do I think that if true, it
> would
> > necessarily be more desirable than having a film that is specially
> > formulated for faithfully and accurately recording the image. I think
> all
> > films are formulated for scanning by virtue of the fact they can all be
> > scanned.
>
> Let me explain how I understand scanning works, and try to offer a theory
as
> to why some films can be optimized for scanning.
>
> Basically, all film scanners shoot a whitish light through the film, and
> record the results in some fixed amount of resolution (8, 10, 12, 16-bits,
> etc.). The scanner CCD is calibrated to this white light in hardware
using
> the scanners' particular calibration method, but not for each scan. In
> addition, the scanner itself has a characteristic response curve to the
> different colors at different levels. (Using an ICM color profile file
for
> you scanner is important). I don't think it is possible for the scanner
to
> change the hardware gain values on each color based upon readings from the
> film base edges, as mounted slides don't have this film based edge to
read,
> and doing so would also change the color profile of the CCD output for
every
> scan, so it relies upon software to correct for film based differences, of
> which some programs are better than others.
>
> When a film is scanned, particularly negative film that has an strong
orange
> base, the range of available colors is shifted, and compressed. Because
of
> this compression of the range as captured by the scanners limited pixel
> depth, you further reduce the range of pixel depth by a few bits or more.
> When correcting for the color shifts, it is not simply a matter of raising
> the high & low ends of each color a particular amount, but also a matter
of
> raising each color level a particular amount based on it's existing (raw)
> value (a full correction curve). This is what Vuescan does well (and also
> what ICM files provide).
>
> As an aside, I think there is a market for ICM files for particular films.
> Does anyone know if these can be bought on the web anywhere?
>
> Now, I will continue with my theory. When a film such as Superia 400 is
> scanned, the high amount of variability of correction leads to a loss of
> information. Once a scanned image is edited and saved, you can never go
> backwards completely and recreate the original file from the edited file.
> Essentially, all of the major transforms done during image editing are
> one-way streets, and result in the loss of a slight amount of information.
> The more corrections that need done, the more loss in information.
>
> A film could be designed to be optimized for scanning by normalizing and
> flattening the inherent characteristic color response curves. In this
way,
> the most information is captured in the raw scan. Users of sRGB monitor
> profiles might understand this as a film calibrated closely to sRGB.
(This
> is also where an film ICC profile will come into play.) So, a film
> optimized for scanning is also probably a film optimized to "faithfully
and
> accurately" capture the image.
>
> Does this seem plausible?
>
> Cheers,
> Gerald
>
>
>
>
>
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