Test Results

The relative reflectance spectra shows that at longer wavelegths the contrast between the text and the background of carbonized papyri is somewhat better than in the shorter wavelengths. At visible wavelengths, or at the band of red-extended film materials, the differences are still quite small. Comparison between two negatives, one taken with an IR-filter and another without, shows no radical qualitative differences. A CCD camera, with sensitivity range extended to over 800 nm, produces somewhat better images at the longer wavelengths. Proper focusing and placement of light sources is also easier with CCD equipment than with conventional cameras; one can see the effect on a video screen immediately, even when recording in near-infrared band.

A near-infrared sensitive CCD camera with enough spatial resolution seems be a good choice for recording carbonized papyri. Unluckily, at the present, the resolution of the economically suitable cameras seem to be inadequate; recording a 4x3 inch fragment at 600 dpi would need 2400x1800 pixels, or several pictures, attached together like mosaic. Cooled HCCD cameras, with 2048x2048 resolution and 12 bits of dynamical range, cost from $17000 to $70000, while conventional video cameras (resolution about 700x500 pixels, 8 bit dynamical range) cost from $1500 to $12000 (Photometrics, Spring 1995).

For fine spatial resolution (1200x600dpi), economical price (less than $2000), and good dynamic range (10-12 bits), the flat scanners are one of the best current choices for recording carbonized papyri. Digital cameras are also very capable of obtaining good-quality pictures, but currently they are not economically priced.

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Antti Nurminen, 34044T, andy@cs.hut.fi