-------- Original Message --------
Subject:        Aerial Photos Scanning Parameters Question
Date:   Fri, 22 Aug 2008 08:46:35 -0500
From:   Xiaohong Zhang <[log in to unmask]>
To:     <[log in to unmask]>
CC:     David C. Clark <[log in to unmask]>




Dear Colleagues,

We have a series of aerial photos (approximately 6,825) printed on
translucent sheets (mylar?) that we wish to archive using a large-format
scanner (Vidar HD3630). Our purposes are to:

   1. To create a digital archive of this unique resource;
   2. To have the digital files serve as the source of our prints so
      that we are no longer sending out the mylars; and
   3. To create a geo-referenced “mosaic” of each year’s imagery for use
      with GIS mapping software (i.e. ArcMap or ArcIMS).

The “problems” with these aerial photos include:

- Our agency has traditionally sent out the photos to a reproduction
company that would make prints using the diazo process. Some of these
images have been sent out numerous times for printing, and as a result
have scratches and creases.

- With the exception of some of our newer images (which are
continuous-tone), all of the images appear to be halftone, although I
don’t see the variation on dot size that I would expect. When looking at
them on a light table, there appear to be roughly 64 dots per inch. I do
not know if they are “true” half-tone, or if it is some other method
which is optimal for printing using the diazo process.

- The mylar sheets measure 34” x 34”. The photographic image area is 30”
x 30”, but we also need title and other information at the top and
bottom of each sheet.

- We do not possess the negatives from any of these sets; they were
retained by the various firms that conducted the flights.

My question:

Does anyone have experience with these types of aerial photos? If so, do
you have any recommendation on what would be the best parameters? (Our
proposal is TIFF, Greytone, 400 DPI)

Thanks a lot for your help!

Best regards,

Xiaohong

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XIAOHONG ZHANG

Data Librarian/Metadata Specialist

Chicago Metropolitan Agency for Planning (CMAP)

233 S Wacker Drive,

Suite 800, Sears Tower

Chicago, IL 60606

(312) 386-8719 (voice)

(312) 676-7453 (fax)

Email:[log in to unmask]

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