Ill. Admin. Code tit. 44, § 4500.60
d) The background photographic densities must be appropriate to the type of documents being filmed.
1) Background densities must be as follows:
| Classification | Description of Documents | Background Density |
| Group 1 | High-quality, high-contrast printed books and periodicals; black type face; fine-line originals; black opaque pencil writing; and documents with small, high-contrast print............................... | 1.00 to 1.30 |
| Group 2 | Pencil and ink drawings; faded and very small print (for example, footnotes at the bottom of a printed page); scenic checks; documents with printed pictorial images; and newspapers........ | 0.90 to 1.10 |
| Group 3 | Low-contrast manuscripts and drawings; graph paper with pale, fine-colored lines; letters typed with a worn ribbon; poorly printed, faint documents ........................................... | 0.80 to 1.00 (1:24 reduction or less) |
| Group 4 | Very low-contrast (worst case) documents can require extremely low background density............................. | 0.75 to 0.85 (1:24 reduction or less) |
| Group 5 | COM.................................................... | 1.50 to 2.00 |
(Source: Amended at 39 Ill. Reg. 3094, effective February 11, 2015)