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Re: Current dpi standard for scanning photographs



At 01:46 PM 4/23/2002 -0500, Maribeth Betton wrote:
I'm looking for information regarding the current archival standard for
scanning photographs, both color and black & white.
What is the acceptable dpi for archival preservation?  What is the
current preferred minimum?

There is no archival standard for scanning photographs.  The "acceptable
dpi for archival preservation" depends on what you want to preserve.  See
Digital Imaging for Photographic Collections: Foundations for Technical
Standards, by Franziska S. Frey and James M. Reilly
<http://www.rit.edu/~661www1/sub_pages/page3a.htm#7>.

Steve Puglia in the Handbook for Digital Projects notes that for
preservation scans, the actual desired digital resolution will vary
depending on the photographic film, the original camera lens, the
significant feature size that is desired to be reproduced, and the quality
of the scanner used for digitizing.  (On the latter, I would add that
objective measurements such as MTF must be used).  Steve suggest that for a
preservation-quality scan, you would need to capture at 20,000 to 32,000
lines for an 8x10 print, and that the file size for a 16 bit gray scale
scan of an 8 x 10 print would be a minimum of 640 MB. See
<http://www.nedcc.org/pubs/dighand.htm>.  And discussion of resolution
doesn't begin to touch on other issues associated with accurate
preservation capture of photographs such as tonal depth and the long-term
maintenance of the digital files.  For a discussion of some of these latter
issues, see Guides to Quality in Visual Resource Imaging
<http://www.rlg.org/visguides/>.

You need to decide if you want to produce digital images that are of use on
today's display and printing technologies or are likely to be of longer
value (while recognizing that none of your scans are likely to be
"archival.")  Display and printing technologies are changing rapidly; 3
years ago we thought a 4 MB file compressed as a JPEG was a huge file; now
we routinely deliver 140 MB files over the Internet, and some people are
delivering images up to 2 GB in size.  My staff is in the process now of
rescanning photographs that had been scanned by others just two years ago
because the work was not done to the highest technical specifications.  The
final decision is as much a business decision as a standards decision,
however - how often can you afford to rescan, and is it cheaper to rescan
every couple of years than it is to do it better once.





---------------------------------------------------------------
Peter B. Hirtle
Director                                pbh6@cornell.edu
Cornell Institute for Digital Collections     607/255-4033 (ph)
2B Kroch Library                                   607/255-9524 (fax)
Cornell University                <http://cidc.library.cornell.edu/>
Ithaca, NY  14853
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