Re: filmscanners: Film grain vs 2700 DPI scan resolution

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

"Frank Nichols" <frank@theNichols.net> wrote:
> 1. With 200 film, is the grain "large" enough for the 2700 DPI to record
it?
> If so could some one describe it (or email me a couple scan clips showing
> examples?)

Colour neg films have a random mixture of different sized dye clouds.  The
only C41 film I've scanned which showed no appreciable apparent grain in
mid-tones and highlights  was T400CN B&W film exposed at EI250.
All other C41 films *seem* to show "grain".  I don't think anyone one the
list has the exact figures to show the comparison between dye cloud size
and the area of a pixel at 2700dpi but from what I've read here, some are
approaching the same size.  Errors occur when the CCD elements see the
boundaries between different coloured dye clouds and these errors create
a random pattern resulting from the random pattern of dye clouds in the
film.  So what you see *isn't* actually the grain, but an interference
pattern based on the grain.

> 2. Would you expect 1 stop down to be enough to see serious increase in
> grain in 200 film in these conditions?

Yes.  Referring back to the scans of T400 I see a serious increase in the
apparent grain in shadow areas of the same frame.  So I'd expect any
change in exposure with a C41 film to demonstrate a change in apparent
grain.  Define "serious" however. :)

> This weekend I am going to repeat the tests with a couple rolls of FUGI
> Provia 100F to see if the "noise" I am seeing FUGI 200 goes away.

With low contrast images in Provia 100F and a 2700 dpi scanner you
shouldn't see any significant artifacts caused by grain.  Higher contrast
images will probably start to generate problems with scanner noise in
the shadows but this is *not* anything to do with film grain aliasing.

For a more meaningful comparison of grain in C41 it probably makes
more sense to compare a 10x8 enlargement with a 2700dpi scan than
to look at a 6"x4" print.

Rob