Classification | Description of document | Background density |
Group 1 | High-quality, high contrast printed book, periodicals, and black typing | 1.3-1.5 |
Group 2 | Fine-line originals, black opaque pencil writing, and documents with small high contrast printing | 1.15-1.4 |
Group 3 | Pencil and ink drawings, faded printing, and very small printing, such as footnotes at the bottom of a printed page | 1.0-1.2 |
Group 4 | Low-contrast manuscripts and drawing, graph paper with pale, fine-colored lines; letters typed with a worn ribbon; and poorly printed, faint documents | 0.8-1.0 |
Group 5 | Poor-contrast documents (special exception). | 0.7-0.85 |
Film type | Process | Density measurement method | Min. Dmax1 | Max. Dmin1 | Minimum density difference |
Silver gelatin | Conventional | Printing or diffuse | 0.75 | 0.15 | 0.60 |
Silver gelatin | Full reversal | Printing | 1.50 | 0.20 | 1.30 |
1 Character or line density, measured with a microdensitometer or by comparing the microfilm under a microscope with an image of a known density.
36 C.F.R. §1238.14