[filmscanners] Colour negatives, Vuescan, and an ICC worflow

["Tony Terlecki" <ajt@mrps.demon.co.uk>]

I have only recently started to scan colour negatives on my LS-4000 scanner.
Previously I had only been scanning transparancies and B&W films. For
transparancies I have been using the NikonScan software and have been
applying a device profile after the scan which I had created using Monaco
EZColor & a Kodak IT8 35mm target. All of that, along with output to
printers has been working within a completely profiled ICC workflow. So far
so good.

Moving on now to colour negative film. I am using Vuescan to scan this type
of film and I am having a hard time understanding how the ICC features of
Vuescan are being properly implemented.

Once the film has been scanned, Vuescan allows you to save the image as a
file or to print it. When saving there is an option to tag the file with the
ICC colourspace of your choice and when printing you can specify the printer
device profile so an output translation can be done to get a good print. I'm
OK with these features.

What I don't understand is how Vuescan can perform these later ICC
manipulations when it does not know the proper colour state of the image in
the first place. Usually to get a scanned image into a known ICC state one
applies an input scanner device profile whose purpose is to characterise the
input data and allow transformation into to Profile Connection Space (PCS).
This, in turn, is then translated into a common working colourspace.

As far as I can see there is no facility within VueScan to assign an input
devic e profile to a scanned image, nor to instruct VueScan to use an input
profile with one's particular scanner.

How then does Vuescan know the indivudual characteristics of your scanner to
manage all this accurate negative-positive translations using film
chracteristic curves for various brands/types of film? Surely all colour
translations based on film data are only going to work if the image data you
are acting upon is accurate in the first place? By not having a scanned
image which has been tagged with an input profile how can one succesfully
then go on and manage further colour mani pulations?

I'm asking all this, of course, because I am not getting satisfactory
colours from my negatives. I've gone through the advanced workflow
instructions for doing things like locking the exposure and film base colour
for my type of film but the colours I am getting using this method are not
very good and it requires some nifty curves moves to correct the colours.

Anyone have any ideas how Vuescan is managing the early part of this ICC
workflow or what I am doing wrong?

--
Tony Terlecki
ajt@mrps.demon.co.uk

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