Message-Id: <mailto:199505051830.NAA13862@library.wustl.edu> Date: Fri, 5 May 1995 14:28:43 +0100 From: Mary Ellen Chijioke <mailto:mchijio1@CC.SWARTHMORE.EDU> Subject: Re: Microfilm To: Multiple recipients of list IMAGELIB
One reason why discussions if imaging vs. microfilm seldom get very
far is that people commonly conflate the two variables involved:
information format and medium. In brief, microfilm is an analog format
stored on a silver halide (for preservation purposes) film medium.
"Imaging" stores digitally formated information on magnetic or optical
storage media.
Digital files have the advantage that one can create several
succeeding generations of copy without loss of information from the
original. It is also more reliable for transmission, since the faintest
signal of a 1 or 0 will register the same as if it came through loud and
clear.
There are two disadvantages to digital files, however: the current
storage media for digital information are very unstable and/or untested for
durability; and one needs a method of decoding the digital surrogate to
recreate a visible image. Theoretically one could, for example, scan an
image, create a print-out of visual symbols of the binary code, then store
the file on microfilm. (Does anyone remember the days of punched paper
tapes?) Presuming that one has maintained an intelligible key for the
binary code used to create the file, one could program any later generation
computer to convert the file back into an image. Of course, the amount of
digital information required to an image at the same level of resolution
possible on decent microfilm is so large that the data file for one image
might fill a reel of microfilm, which is why we are using those highly
unsatisfactory magnetic and storage media.
Basically, anyone who wants to use digital files as the primary
means of storing preservation files for information has to be able and
willing to make a long-term commitment to the constant tending of the files
-- both in terms of the integrity of the physical storage and the
conversion of interpretation software as standards change. And, of course,
we shall always need hardwarIt is our healthy scepticism about our ability
to keep this up on a massive scale that makes many hesitate to leap quickly
into digitization. There is also the reassurance that, even after the
collapse of technology, a microfilm image will need only a light source and
a magnifier to reproduce a visible image.
It is also possible, in theory, either to shoot an analog picture
from which a digital file is created or scan a picture and create an analog
picture from the digital file. Until recently, the resolution of the
analog film picture was so much higher than even the best scans that the
latter option would be nonsensical. That gap, however, has been closing
rapidly, so that, even if one wants the security of the analog microfilm
images, we may soon be creating them from our digital files. The choice
may then be made on the basis of economics and work flows, not image
resolution and permanence.
Sorry to be so long-winded, that's what happens when one gets
theoretical about an issue!
Mary Ellen C.