how to get photometric data from film

When shooting stars with film it should be possible to use known
magnitudes to calibrate film intensity to (better) photometric accuracy.
Thats why I ask in this group,in the hope that this has been done.

Does somebody know how to process a raw scan (Velvia on a Polaroid SS4000) so
that the intensity of the resulting image is photometricaly locally correct?
Lets also say I scan at 4000dpi and downsample it to 1000dpi so that individual
grains want be visible.
Is it possible to get some calibration-file from the manifacturer?
Does a films inherent unlinearity differ much between brands?

I need this calibration for successful deconvolution.

Per Sabelström www.quantimage.com