D. The Scanning Process

Materials to be scanned are brought to the lab and stored. Digital Imaging Technicians evaluate the material to determine which scanning device will be needed - one of the flatbed scanners, the camera or the slide scanner.

For a given image, the earliest generation of the photograph, for instance, a glass plate negative, is removed from its sleeve and inspected.  If there is any question as to whether a later generation of the image, such as a print, would be superior for scanning, the two are compared and the best chosen by the imaging technician who is also a skilled darkroom technician. 

When production begins, dust is removed from the item to be scanned using an electrostatic film cleaner.  The item is placed on the scanner.  The imaging specialist makes several low-resolution preliminary scans to calibrate the scanner for the lightest and darkest tones found within the photograph.  Additionally, the operator chooses scanner settings that adjust the digital output from the scanner to the characteristics of the object being scanned. Black-and-white prints and negatives are scanned using a palette of 256 shades of gray. Color prints, transparencies, and negatives are scanned using a palette of 16 million colors. 

After the imaging technician calibrates the scanner for the characteristics of the photographic material and the required resolution, the final scan is made.  The resolution chosen for the scan varies with the size and quality of the negative or print to be scanned. 

Next, the imaging specialist performs quality control procedures.  The distribution of tonal values of the digital image is examined to determine if the lightest and darkest values of the photograph have been properly captured.  Intermediate values are examined to determine if unwanted compression or expansion of the middle tones of the photograph has occurred. Next the complete image is examined and alternative adjustments to the scanner settings are explored to see if the image quality can be improved.  If the image quality is judged unacceptable for any reason, the scanner settings are adjusted and the scan redone.

A principal objective of this project is to digitally capture the content of the historic photographs.  In line with this objective, digital manipulation or retouching of the content of an image is strictly forbidden.  Flaws inherent in the original photographs, such as tears and scratches, are left intact in the digital image.

After the photographs are scanned, the image specialist programs a computer to run unattended overnight to perform the slow, computationally intensive processing of the Archive files in order to derive additional image files to be used on the public access systems. (See Image File Specifications)

When sufficient image files have been produced, they are written to CD-ROMs.  Duplicate disks are made for all digital images  so that copies can be stored in separate locations.