filmscanners: Histograms

["Rob Geraghty" <harper@wordweb.com>]

OK, I had a go at scanning some slides on the SS4K at work and scanning the
same slides on my LS30 at home.  I had to recrop a photo to get a comparison
of the crop histograms because the brightness on the screen at work is
clearly utterly different to the one at home - which is why the brightness
adjustment in Vuescan suddenly seemed so different.  Cropping the SS4K raw
file again at home using a brightness of 1.4 gave a similar result to the
LS30, although the SS4K result still seems significantly brighter with more
shadow detail.

My apologies to those on the digest for using attachments. :(

The first gif is the raw histogram comparison for the USAF resolution target
and a colour target.  The second gif is the comparison between LS30 and SS4K
crops of a portrait slide.  All the photos were taken in natural light using
the same camera and Provia 100F.  I'm not going to try to analyse the
histograms because there's others much more qualified on the list to do it
than me.  I can supply small jpegs of the actual images to give you an idea
of what the histograms represent if need be.

It doesn't look to me like comparing raw scan histograms is hugely
meaningful, and comparing crop histograms is much less so because there's so
many differences in the scanner profiles.

Reducing the histograms to gifs makes the greyscales blocky but it doesn't
change the nature of the histograms themselves.  Just comparing the result
from the portrait scans, the SS4K does seem to get a lot more shadow detail
from darker slides.  On the downside the colour balance is quite different
to the LS30 so I'd need to experiment with Vuescan to get the same sort of
colour matching.  One thing I didn't like in my brief test of Insight was
that there didn't seem to be an undo for the tones tab.  The LS30 is
significantly quicker than the SS4K but to be fair it's not scanning at
4000ppi and the computer it was connected to was a little slower.

Anyway FWIW, comments welcome.

Rob

Attachment: raw_histograms.gif
Description: GIF image

Attachment: samred_histograms.gif
Description: GIF image