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