Finder patterns

Geometry

Each finder pattern is a 7 × 7-module square composed of an outer ring of dark modules (one module wide), an inner ring of light modules (one module wide), and a central 3 × 3 block of dark modules. The three patterns are located at the upper-left, upper-right, and lower-left corners of the symbol. The lower-right corner carries no finder pattern, permitting the scanner to disambiguate the symbol's orientation.

The 1:1:3:1:1 ratio

Traversed along any line passing through the center of a finder pattern, the sequence of dark and light modules occurs in the ratio 1:1:3:1:1 — one dark, one light, three dark, one light, one dark. Denso Wave selected this ratio after analyzing the frequency of module-ratio patterns occurring on printed matter, with the objective that the finder be unlikely to be mistaken for an incidental pattern appearing in surrounding artwork.

Separators

Each finder pattern is bordered on its inward edges by a one-module light separator, which isolates the finder from neighboring data modules and protects the integrity of the 1:1:3:1:1 ratio when scanned.