Collecting historical font metrics from Google Books

A system is presented for extracting key metrics from fonts used in historical documents. The system identifies important landmarks on a page, such as margins, paragraphs, and lines, and applies frequency analysis techniques to identify relevant sizes. The system was validated by comparing its measurements to the measurements of a human expert on randomly selected samples, and differed on average from the expert by less than 5% for x-height, body size, and line spacing metrics.