In message of 7 Jul, "arthur.thomson" <arthur.thomson(a)which.net> wrote:
Am I missing something? I find my, now ancient (bought in 1999) Fuji
MX-1700 Zoom camera with a mere 1.5 MegaPixels perfectly adequate for
anything from well-worn tombstones to microfiche-reader screens and
small-print documents. The essentials are a good lens, zoom, and ease
of over-riding automatic settings. Even at only 1.5M pixels the
computer storage space needed can become a problem needing back-up
onto CD-ROM or better DVD.
Let's do some sums. To start with I have more experience with scanning
and the first thing with that is the need to use at least 200 dots per
inch to get a good enough definition for text. With some documents I
have found it better to use 300 dots per inch.
A sheet of A4 has text that fills perhaps 7 inches wide and 10 high.
The number of dots horizontally is 1400 and vertically is 2000; that is
2.8 million dots at 200 dpi.
If I had to use 300 dpi, then the image takes up 6.3 million dots.
Dots are the same as much the same as pixels. So this looks like a
requirement for anything from 2.8 to 6.3 megapixels for a sheet of A4.
If you want to do anything larger than A4, then even more pixels are
required and this is the advantage of camera, that in principle you can
do the larger documents.
Storage space is another matter but it can rapidly account for a need
for 200+ Gigabyte disc drives - and drives because you need another one
for backup. Though you can scan- and photo - text in black and white,
enormously reducing the disc space required.
Tim Powys-Lybbe tim(a)powys.org
For a miscellany of bygones: http://powys.org/