Overview
ISO 446:2004 - Micrographics - ISO character and ISO test chart No. 1 - Description and use - defines the format, physical characteristics and procedures for using the ISO character and ISO test chart No. 1 for quality control of microimages. The standard supports assessment of the potential legibility of documents recorded by micrographic systems (microfilm, microfiche, digital microforms) and establishes measurable acceptance criteria for production and inspection.
Key topics and technical requirements
- ISO character design: a conventional character formed by a regular octagon of height c with two internal parallel lines; line and space widths = c/7. Four orientations: vertical, horizontal, 45° right and 45° left.
- Groups and layout: groups contain four characters (one of each orientation) arranged in a square; minimum spacing rules (2c/7) apply between characters and groups.
- Standard character sizes (c, µm): 450, 500, 560, 630, 710, 800, 900, 1000, 1120, 1250, 1400, 1600, 1800, 2000, 2250, 2500, 2800 (based on ISO 3 preferred numbers).
- Tolerances: line widths tolerance ±7 µm per segment; maximum tolerance on c/7 is ±2%.
- Base materials and densities:
- Opaque (paper) base: white, diffuse reflection density ≤ 0.08; opacity > 85%; positive-appearing.
- Transparent base: non-coloured, base + fog transmission density ≤ 0.08; may be positive or negative.
- Contrast: minimum visual diffuse density difference between base and characters - 3.0 for film, 1.6 for paper. White lines should be within 0.02 density of paper.
- Density of microimages: for positive-appearing test charts the background visual diffuse transmission density of microimages shall be 1.60 ± 0.10 (measured per ISO 6200).
- Legibility criterion: examine microimages at ×30 to ×50 magnification with lens NA ≥ 0.1. A group is “read” when all black and white lines within each character are discernible and continuous.
- Certification & identification: only charts verified by a qualified laboratory can be designated “ISO No. 1”; charts must display “ISO test chart No. 1”, reference to the standard and certifying source.
Applications and users
- Quality control of microform production (microfilm, microfiche), microform scanning and reprography
- Lab technicians, imaging QA personnel, archives and records managers, preservation specialists, and equipment manufacturers using micrographic systems
- Testing viewing, printing, and digitization workflows to ensure legibility and reproduction fidelity
Related standards
ISO 446 references and complements standards used for measurement and vocabulary, including:
Keywords: ISO 446:2004, micrographics, ISO test chart No. 1, ISO character, legibility, microimages, quality control, microfilm, microfiche.
