ws wrote:
> At 08:06 PM 3/14/2009, Chuck wrote:
>
>> <snip> I'm wondering what happens to this image if you scan it at, say,
>> 1000-1200 ppi or just enough to avoid aliasing. Does it look just as good?
>>
Unfortunately, "That depends." Scanning 2 1/4 x 3 1/4 B&W negs my dad
made in the 1940s, anything over about 600 dpi seems to be simply wasted
effort. Slow film meant often slow shutter speeds. combine that with
softish lens, not quite precise scissors brace holding the lens, softish
lens, focus by scale and guess and there just isn't enoguht detail
captured to make resolving the grain precisely worthwhile. Move forward
from the Kodak folder to a Kodak TLR and different films and at least
1200 dpi is needed to get what's there on the film.
>
> Please ignore, technical engineer brain talking... Just a note on sampling
> and aliasing. To avoid aliasing when sampling the rule of thumb is to sample
> higher than twice the frequency of anything in the image. Which
> means noise, grain, etc. and is not related to the resolution. ...
> It just may be that with finer grain film and under-sampling that the grain
> will actually look more pronounced.
>
I found when I upgraded to the 4000 dpi 35mm film scanner that scans of
some 35mm slides had apparently smaller, less obtrusive grain @ 4000 dpi
than at 2700 dpi. I could strain and say detail resolution and tonal
resolution were maybe a tiny bit better, but the change in grain
appearance was the major change - with this particular film.
> But the important thing to remember is that the scanner sampling required is
> more related to the grain structure of the film than the image resolution. So
> I always sample as high as possible and use post processing to down sample to
> avoid enhancing the grain, especially if the grain is very fine. It may be
> that some scanners have less of a problem, and that is probably due to the
> optics in the scanner providing some anti-aliasing.
>
As above, practical experience has shown me that such is not always the
case with older MF films.
Moose
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