This collection of American sheet music was scanned from 35mm roll microfilm originally produced by the Library of Congress Photoduplication Service to preserve these materials for the Library of Congress Music Division. The originals are still held by the Music Division, but they have been largely withdrawn from service. The entire microfilm collection consists of 441 reels which have been scanned and released as this online collection. This collection, representing the years 1870-1885, includes approximately 365,000 images or 47,000 items. The duplicate negative, or scanning microfilm, was produced both by the Photoduplication Service and the NDL microfilm scanning contractor, Preservation Resources, Inc. The "scanning negative" was printed directly from the master microfilm held by the Photoduplication Service and it was processed with the technical objective of maximizing the quality of the resulting digital images. All scanning of the microfilm was performed offsite by Preservation Resources in Bethlehem, Pennsylvania, under contract to the National Digital Library Program.
Typically the documents are four pages in length with a front and back cover. They are 2A position (cine) frames which were split for single image presentation as digital images. Most all of the sheet music material was scanned as bitonal TIFF (Tagged Image File Format) images initially at 300 dpi and later all at 400 dpi with Group IV compression. Mid-production test scanning completed by Preservation Resources demonstrated that an increase in the dpi to 400, for all of the bitonal images, consistently showed that increased resolution more accurately captured the music notation. Since there was tonality present in the covers, they were scanned as 200 dpi grayscale JPEG File Interchange Format (JFIF) images as were any images where the originals appeared soiled, damaged or deteriorated on the microfilm. The grayscale solution was also used for other problem pages or frames. Much like our experience in scanning handwritten manuscript materials, the tonal capture was able to suppress some of the print-through in the covers so that the text is able to be read. Similarly, stamps and markings on these covers were also enhanced and made legible by grayscale capture. The GIF images for access were created by the NDL Music Team staff.