Re: VueScan: (was: Re: Measuring DMAX

[Ryuji Suzuki <rs@silvergrain.org>]

While Vuescan may profile the particular scanner and make
correction for the density reading, beware of the limitations
of the technique. Don't assume any accuracy for the reading
values unless you do your own calibration. This is
particularly serious in the dark/dense area. I've measured the
scanner response (the raw sensor output) for Epson Perfection
V700, which is a very nice scanner for both prints and film.
The response is not even constant-gamma (linear on log-density
plot).

http://silvergrain.org/wiki/Perfection_V700

Another weakness of flatbed scanners for density reading is a
high level of flare affecting the reading of dense/dark
areas. Maybe I should've measured V750 vis-à-vis, which claims
to have different coating on the lens to reduce flare. One
thing I can tell is that most other flatbed scanners,
especially older or cheaper ones, suffer from poor reliability
of dark/dense area reading, with almost no hope for older and
cheaper ones.

These things are rarely problematic for most intended
applications, but if you want to use a consumer grade $500
device for scientific measurements, you'd expect all sorts of
issue to arise.

--
Ryuji Suzuki
"Make something religious and people don't have to deal with it, they
can say it's irrelevant." (Bob Dylan, Biograph booklet, 1985)