Fiche scanning (was Re: [Simh] Listings of XXDP test and maindec'sfor 11/70)
Paul_Koning at Dell.com
Wed Apr 15 08:59:24 CDT 2009
> Jan-Benedict Glaw wrote:
> > On Tue, 2009-04-14 10:52:00 -0500, Jules Richardson
> <jules.richardson99 at gmail.com> wrote:
> >> The DEC ones I've seen are extremely high resolution - from memory,
> >> something like 11 x 13 A4 pages on a fiche around 1" x 1.5".
> > If this is right, then there's a scale factor of about 1:90 to 1:100
> > involved. That should tell everybody why even a good consumer-grade
> > scanner will not do the job. To get the equivalent of a 300dpi scan,
> > you'd need to have about 30000dpi. Nothing any el-cheapo scanner
> > handle. (Let alone the problem of getting the sheet properly into the
> > light's focus.)
> you are confusing linear pixel density with areal pixel density.
> the 11"x13" fitting in 1"x1.5" implies a 11:1 scaling in density, so
> dpi would be 3300 dpi. still very high for typical consumer grade
> scanners. I believe 2400 dpi actual (not interpolated) is available on
> decent models, though.
I think the confusion is in: 'on a fiche around 1" x 1.5"'
J-B read that as the size of the whole fiche (with lots of A4 images on it). I think you actually meant that each page image is that size.
The truth is most likely in between: page images (on DEC fiche at least) are a bit smaller than that, and also they are usually images of line printer size pages (A3, not A4). So a 2400 dpi scanner is about a factor 3x too low for acceptable quality. (And yes, that ignores other issues like ability to hold the fiche flat enough and focus well enough.)
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