Steve Underwood wrote:
> What you need is not more bits. You need a spectral shift. Your stained documents
> might really come alive, if you look at them through a part of the spectrum we
> cannot see well. You may find colours (probably in the IR band) where the stains
> don't show at all, and the text is beautifully clear. If you try an IR filter you
> might get interesting results. Most glasses will pass the high end of the IR band,
> and I think the CCD in the scanner will respond OK when you do a black and white
> scan. If you can find a suitable filter, its worth a try.
The best way for a quick experiment would probably be to use one of
those old BW (handheld) scanners that have used red LEDs for
Just replace the red LEDs with IR ones. You can find IR LEDs with
dominant wavelengths between 800 and 950 nm. (TV remote stuff)
These scanners usually employ arrays of miniature SMD LEDs, so you'll
need a steady hand for soldering :-)
The CCD chips actually have their peak sensitivity in the near IR in the
same range, but it falls sharply below one micron, being quasi zero
at 1100 nm.
A color scanner won't be adequate, because those have special IR
blocking filters to prevent color falsification by the IR light.
(or else the RGB color separation filters themselves are IR blocking)
Selecting a BW scan on a color scanner doesn't change this.
Documents printed with old soot-containing inks should be nice in IR,
but I'm not sure if modern color-process inks have any contrast in IR?
A quick way to see this would be to use a night-vision device and your
TV remote as a torch in a dark room.
Enough crazy ideas -
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