In Reply to: Re: 35mm slides to digital images posted by kd on August 31, 2005 at 15:24:14:

A 35mm slide is 36 mm x 24 mm. There are 25.4 mm in an inch.
So 4000 dpi would be (4000*36/25.4) * (4000*24/25.4) = 21,427,243
pixels, or 64,281,729 bytes at 8-bit color depth, or 128,563,457
bytes at 16-bit color depth. And you REALLY want to do the initial
scans at maximum color depth. If you scan at 8-bit, as you start
adjusting things, some of the adjacent values get combined, and
other values become unused, introducing "gaposis" in the
histogram.

It's also possible to make a case for film being a bit over
4000 dpi. The old Modern Photography lens tests used to routinely
resolve about 85 line pairs per mm. It takes two pixels to
resolve a line pair, so 2*85*25.4 = 4318 dpi. BUT the film "pixels"
aren't in fixed locations, so it can actually resolove a bit
better than that.

Digital photography is a wonderful thing for hard drive makers.

Chuck