The digital images were created by staff in the Geography and Map Division by scanning the original map on a large-format (24 x 34 inches) flatbed scanner using RGB (red- green-blue) color separation. The scanner was loaned to the Division by Tangent Color Systems.
Each raster image was produced by scanning the item at a resolution of 300 dots- per-inch and converting the resulting proprietary file format to TIFF format. These TIFF files, which average approximately 180Mb, are moved over a network to Surestore jukebox 1.3Gb magnetic optical platters for temporarily offline storage. The Surestore jukebox and the associated servers and workstations were donated by the Hewlett Packard Company.
Following scanning, the TIFF files were enhanced using the WindowsNT version of xRes, an image processing software, to rotate, crop, adjust brightness or contrast, and stitch together TIFF images for items requiring multiple scans. This software was donated by Macromedia.
The TIFF files were compressed, using a wavelet-based image compressing software called Multi-Resolution Seamless Image Database, or MrSID. This software integrates multiple resolutions of an image in a single file which enables Internet users to zoom in, getting more and more detail. Although MrSID is a "lossy" compressor, the images were compressed at a ratio of 22:1 without experiencing any loss of information. LizardTech donated the license for the compression software.
The final step was the creation of a small GIF file for use as the initial thumbnail display of the item.
After completing the scanning, the Archive TIFF file along with the SID and GIF files are stored on the Library's RS6000 World Wide Web server.
Master image:
Scanning resolution: 300 dpi
Tonal resolution: 24 bit color, RGB separation
File format: TIFF
Compression: none
Reference image:
Scanning resolution: 300 dpi
Tonal resolution: 24 bit color, RGB separation
File format: SID
Compression: Wavelet
Thumbnail image:
Viewing resolution: 72 dpi
Tonal resolution: 8 bit color, RGB separation
File format: GIF
Compression:none
am Nov-3-97