Microfiche scanning

[Scott Stevens]

On Thu, 21 Apr 2005 10:43:16 -0500
Jim Leonard <trixter at oldskool.org> wrote:

> Jim Leonard wrote:
> > Depends on the scanner.  Mine is optical 1200x2400 and cost $200, it
> > 
> > handles fiche just fine.  I just put a white sheet of paper behind
> > it before I start scanning.
> 
> CORRECTION:  Filmstrip, not microfiche.  My apologies.
> 
> So what *is* enough?  The last microfiche I read at my local library
> was 12 pages by 16 pages on a 4"x6" film, so we have roughly
> (12/4)*(16/6)=8 pages per inch of film.  150 DPI is the absolute bare
> minimum for a readable page, so a scanner would need a minimum
> resolution of (150*8)=1200 DPI just to get something discernable.  A
> better bet is 2400 DPI for easily readable text, and 4800 DPI if you
> want to be able to make out line drawings.  So it *is* possible with a
> consumer scanner of 2400 DPI optical or greater -- just make sure, as 
> someone else earlier already wrote, that it is a true 2400, and not
> 1200x4800 (ie rectangular pixels).

I spent years of my youth working in a COM Shop (Computer Output to
Microfilm).  Basically mounting 1/2" tapes (mostly 1200 and 2400 bpi)
and the camera would flash the data to a CRT inside the camera which
would shoot the frames of fiche.

Microfiche are shot, and the readers come in 3 common magnifications,
24x, 42x, and 48x.  Most likely for high density fiche, you're looking
at 42x.  That means 42 times a conventional dpi, like, say 300 dpi,
which would mean 12,600 dpi.

It's NOT feasible to use a conventional page scanner.  I suspect it's
not even realistic to use a conventional slide scanner.  (which is far
better than a 'slide adapter' on a conventional page scanner.

As an aside, another microfilm technolgy that is interesting is
'aperture cards.'  Those are 'conventional' IBM Punched Cards, with a
slotted window in them that you slide a piece of microfilm into. 
Generally used for archival document retrieval systems.  The film would
contain an engineering drawing, and part of the card has a field
containing punched index information.  Yet another technology that's
mostly gone.