filmscanners: ReSize, ReSample or ReScan ?

["Gordon Potter" <gordon-potter@home.com>]

 I have been told resampling is much more destructive to an image
then  resizing.  (I can reationalize that in my mind by saying
all the pixels are calculated rather then measured.)   Recently I
received a reply to a question which says in part that resampling
is preferable to scanning at less then full resolution.    In
fairness to the people trying to help me, these possibly
conflicting comments were to different questions on different
subjects.

So I will attempt to ask a clear question and I would really like
to know what people think/know.  Agreement between people would
be nice, but not necessary.  Also I may have my dpi, pixels and
lpi mixed up -- the issue I want to address is ReSample vs.
ReSize vs. ReScan.

Lets say I have a slide that is perfect - no dust, no blur, sharp
as a brand new tack.  Now I want to make a 4 by 4inch print from
a part of my slide which happens to be exactly 0.500 inches by
0.500 inches.   My calculator says, if I want to make the print
at exactly 200 dpi, I need am image that is 800 dots by 800 dots
(Let us assume my printer operates at only 200 dpi.)  To get 800
dots of data from the 0.500 inches of slide, I would need to scan
at 1600 dots per inch and crop.

Next part -   I push the scanner button without looking and I
make a scan at 2900  dots per inch.  Well I now have the
following options:

#1  Resize the scanned pixels so the image is 4 inches by 4
inches within photoshop keeping the 2900 dots of data from the
original scan.  (I am not at all certain how this works, but this
is what I got from  reading "A Few Scanning Tips" by Wayne Fulton
and Photoshop 6.0 seems to do it.)

#2  Resample in photoshop to "convert" the 2900 dots of data to
800 dots of data at 200 dpi  which I send to the printer.

#3  Stick the slide into the scanner and get the "desired" 800 by
800 bits of data from the selected portion of the slide.  i.e.
somehow use the Twain drivers to get the resolution I want.


I recognize in the real world the choices will never be this
clear, but can one generalize that resampling to a *lower*
resolutions is better/worse then resizing under certain
circumstances?

It seems to me scanner software would not even offer the option
of lower resolution scans if the quality were always better for
resampling and resizing.

Thanks for reading.

______________

Gordon Potter   <twocybers@home.com>
Nashville, TN 37215
USA