Digitizing the Panoramic Photographs Collection

Producing the collection images and the introductory video clips

The Collection Images
The panoramic photographs have been digitized from 35mm film produced by a contractor in 1992-93 using a modified motion picture camera. The full-frame exposures were made on color motion picture film stock. The contractor, Stokes Imaging, Inc., constructed a computer controlled table that moved the panorama under the camera, producing a sequence of exposures that represent overlapping segments of the original photograph. (Imagine a comic strip with overlaps.) The computer program tracked the number of segments and the amount of overlap to permit the "reassembly" of the panorama in digital postprocessing, where match lines were identified for each segment, the overlap cropped away, and the segments blended. The digital images were created at a resolution appropriate for video production, e.g., the individual segments were scanned at 560x480 pixels. In 1993, the resulting digital images (both the assembled whole views and all of the individual segments) were converted to analog video and copied to videodisc media.

In 1996, the 35mm film was rescanned for this digital presentation by another contractor, JJT, Inc., of Austin, Texas. Once again, the images for each segment were captured from the film in a computer controlled process that tracked the information needed for later assembly, with a base capture resolution of about 1000x700 pixels. Once again, the frames were assembled, this time to produce an archival or master digital image of the panoramic photograph. The archival images were next rescaled and processed to produce the thumbnail and reference images; the thumbnail appears with the bibliographic record and the reference image displays when a researcher clicks on the thumbnail.

The archival or master digital image is the image referred to as the "unsharpened high resolution image" on the bibliographic record. It is made available to researchers who wish to see a greater amount of detail than is shown in the smaller reference image. Minimal computer enhancements were applied to the archival image during the production process. The image is offered to researchers ready to be loaded into graphic arts software where user-selected enhancements may be applied. In contrast, the enhancement called sharpening has been applied to the reference image and, as a result, it may look better in some display settings than the archival master.

Specifications:

Initial segment capture:
Spatial resolution: about 1000x700 pixels
Tonal resolution: color, 24 bits per pixel
Compression: none
Enhancement: none

Archival (master) image:
Spatial resolution of short side (typically the vertical): about 700 pixels
Spatial resolution of long side (typically the horizontal): about 500 pixels times the number of original segments (approximate range: 1000-5000 pixels)
Tonal resolution: color, 24 bits per pixel
Compression: none
Enhancement: none

Reference image:
Spatial resolution of short side (typically the vertical): 420 pixels
Spatial resolution of long side (typically the horizontal): approximate range: 700-3000 pixels
Tonal resolution: color, 24 bits per pixel
Compression: JPEG
Enhancement: sharpening

Thumbnail image:
Spatial resolution of short side (typically the vertical): 150 pixels or less
Spatial resolution of long side (typically the horizontal): not to exceed about 600 pixels
Tonal resolution: 8 bits per pixel
Compression: native to GIF
Enhancement: color indexing, sharpening


The Introductory Video Clips
The video clips were produced by Buckaroo Associates of Washington, DC, during the winter of 1991-92 and first incorporated in the videodisc version of the collection. The original format was Betacam. The clips were digitized by Crawford Multimedia of Atlanta, Georgia, in 1997, in the following formats:

Moderate resolution files
Image size: 320x240 pixels
Frame rate: 30 fps
Data rate: ca. 1.2 megabits/second
Compression: MPEG-1
Format: mpg

Low resolution files
Image size: 160x120 pixels
Color depth: 24 bits/pixel
Data rate: ca. 100 kilobytes/second
Format: QuickTime

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