In article , Don
writes
This sounds like grain aliasing. The mathematics of this are rather complex
because it involves the MTF of the scanner spot and lens, the line spacing
of the scanner, and the grain size distribution of the film being scanned.
It occurs when the grain size is small enought that it exceeds the Nyquist
limit of the sampling process. It results in the high frequency portions of
the grain being duplicated as lower frequency noise, and adds to the normal
low frequency component of the granularity. The result is an apparent
increase in granularity.

There are only two solutions to this that I know of. The first is to
introduce an anti-aliasing filter in the optical path of the scanner. This
almost has to be done by the manufacturer of the scanner, as it must be
carefully matched to the MTF of the spot and optics. The second solution is
to scan with a higher lpi and a smaller spot size (and better lens MTF). If
that can be done with the scanner that you are currently using, you're in
business. Otherwise, you will need to find a scanner that can handle film
with the small grain size that you have.

With a drum scanner the spot size (and it's shape) *is* the anti-alias
filter, and the only one that is needed. One of the most useful
features of most drum scanners is that the spot size can be adjusted
independently of the sampling density to obtain the optimum trade-off
between resolution and aliasing to suit the media being used, but there
is usually an automatic option which will achieve a compromise at least
as good as any CCD device.

I doubt that this is just aliasing though, especially if both were
scanned at 4000ppi or more. Remember that negative images are
compressed on film (the corollary being that negative film has more
exposure latitude and the ability to capture a wider tonal range).
Consequently, when producing a positive from the film image, whether by
scanning or by conventional chemical printing techniques, the image must
be contrast stretched. So, even if the grain on the film has the same
amplitude as the same as in slide film (a reasonable assumption for
similar speed films of the same generation from the same manufacturer,
the resulting image from the negative will always appear more grainy
than the image from the slide film.

There is a lot of truth in what the drum operator told Jytzel. Whether
its the truth, the whole truth and nothing but the truth is another
story. ;-) However, when viewed at 100% scaling, the size of the
original has little bearing on the results so I would expect to see more
grain on the 6x6cm negative image than from the 35mm slide under those
conditions.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)