This following questions framed the Preservation Office/Picture Elements demonstration project: What types of tonal images might be suitable for preservation-copying of a large manuscript collection? Would these images also serve to provide efficient online access for researchers? If not, what type of images might serve this function? The project is described in more detail in a final report.
A project steering committee determined that the Federal Theatre Project documents selected for this activity were typical of large twentieth century manuscript collections at the Library of Congress. (This may be contrasted with the IBM project, for which pictorial items and exceptional documents were selected.) The normal preservation actions that would be applied to collections of routine documents include (1) rehousing the original documents to conserve them and (2) creating a preservation microfilm copy. The importance of this class of manuscript, the committee said, lies in their information value. The preservation microfilm would be judged successful if the documents were legible and if a researcher could derive some sense of layout and look. But there would be no expectation that the microfilm image would offer a museum quality rendering of the original.
After viewing a number of sample images, a project steering committee of Library staff members selected two image types for testing. Grayscale and color images were selected for the highest quality reproduction--called preservation-quality in this project--for all of the reasons noted above. The committee agreed to tolerate some unaesthetic degradation of the images so long as legibility was not impaired and agreed that "lossy" JPEG compression could be applied to the preservation-quality images. For the access images, the model of microfilming projects influenced the outcome and bitonal images were deemed appropriate for access. Such images resemble the high contrast images familiar to microfilm users and offer small file size (for ease of use in a computer network environment) and print with good results from a laser printer.
The next step was to produce a test bed of 20,000 images representing two versions of each of 10,000 pages. The image specifications are:
The second reason for dissatisfaction with the bitonal documents applied to the entire set and reflects the exigencies of access in the World Wide Web environment. World Wide Web browsers and related software are not set up to accommodate TIFF-format, ITU Group IV compressed images. The Picture Elements project began in 1994 and thus coexisted with the Library's increasing use of the Web and the corollary growth in Web software tools, but failed to anticipate the impact of these two factors. Thus the Library produced a second set of access images to supplement the bitonal images produced by Picture Elements. These images are employed in the collection's "page turning" display.