Fiche scanning (was Re: [Simh] Listings of XXDP test and maindec'sfor 11/70)

Paul Koning 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
> could
> > 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
> 300
> 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.)

	paul


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