4. Sample documents and initial image capture

Selecting samples. The opening round of discussions set the stage for selecting sample documents and and producing test images. The small number of responses from the library and archive survey led the committee to charge the consultants to be guided by the general trend of the committee's discussions and by their own technical experiences.

The Music Division curator worked with the consultants to select 35 documents from the Federal Theatre Project collection. The samples were intended to (1) represent the range of imaging difficulties present in the collection and (2) include the boundaries of that range. i.e., the more difficult items. In addition, the documents were selected to include typical small features in order to assist in the determination of levels of spatial and tonal resolution. The set included documents with some of the following characteristics:

Although the committee's discussions had provided the guideline that facsimiles need not reach a pinnacle of perfection, the samples suggested that high-quality grayscale or color images would be required to retain the information in these documents. But since the survey had indicated that bitonal images at a high spatial resolution were often proposed as a preferred approach (usually for printed matter), Picture Elements agreed that some test images of this type should also be produced.

Initial capture. Picture Elements began with "raw" capture, producing 35 uncompressed images to serve as image source for the various manipulations to come. Grayscale capture of 8-bits-per-pixel at 300 dpi was employed for 25 images. Color capture of 24-bits-per-pixel, also at 300 dpi, was used for 10 documents.

These images were then reprocessed in a series of experiments which compared varying spatial resolutions and varying levels of compression, using the JPEG (Joint Photographic Experts Group) compression algorithm. The processed samples would permit comparisons of grayscale and binary renditions of the images and would demonstrate the adequacy of deriving binary access images from JPEG-compressed preservation images as opposed to deriving them from the raw (uncompressed) original images. The actual digital files were delivered to the Library as digital image files on a recordable CD-ROM disk. The 24 images deemed to represent the most distinctive examples (10 of them also in color) accompany this report in Appendix A.

For the committee's deliberations, the digital image files were documented in a set of high quality printouts produced on a photographic-quality printer (Primera Pro from Fargo). Copies of these printouts are available in the offices of the National Digital Library Program at the Library of Congress.

The experiments, and the committee's reactions to them, formed the basis of the set of choices for the image formats for the Federal Theatre Project. The committee guided Picture Elements's work in this area through an iterative set of changes. These changes, and the pointed comparisons which resulted from them, led to the final recommendations, which were placed before the committee for approval.

Next Section | Previous Section | Contents