So How Does Conversion Benchmarking Work?
Consider a printed page that contains characters measuring 2 mm high or greater. If the page were scanned at 300 dpi, what level of quality would you expect to obtain? By plugging in the dpi and the character height and solving for QI, you would discover that you can expect a QI of 8, or excellent rendering.
You can also solve the equation for the other variables. Consider, for example, a scanner with a maximum of 400 dpi. You can benchmark the size of the smallest character that you could capture with medium quality (a QI of 5), which would be .96 mm high. Or you can calculate the input scanning resolution required to achieve excellent rendering of a character that is 3 mm high (200 dpi).
With this formula and an understanding of the nature of your source documents, you can benchmark the scanning resolution needs for printed material. We took this knowledge and applied it to the types of documents we were scanning- brittle books published from 1850 to 1950. We reviewed printers' type sizes commonly used by publishers during this period and discovered that virtually none utilized type fonts smaller than I mm in height, which, according to our benchmarking formula, could be captured with excellent quality using 600 dpi bitonal scanning. We then tested these benchmarks by conducting an extensive on-screen and in-print examination of digital facsimiles for the smallest font-sized Roman and non-Roman type scripts used during this period. This verification process confirmed that an input scanning resolution of 600 dpi was indeed sufficient to capture the monochrome text-based information contained in virtually all books published during the period of paper's greatest brittleness. Although many of those books do not contain text that is as small as I mm in height, a sufficient number of them do. To avoid the labor and expense of performing item-by-item review, we currently scan all books at 600 dpi resolution.