Scanning and interpolation

Ole W. Saastad (o.w.saastad@kjemi.uio.no)
Fri, 23 Apr 1999 09:59:11 +0200 (MET DST)

I have played some time with scanning software (AGFA and HP) and
especially tested the best way of scanning, 100, 200, 300 dpi, and
1200 dpi (interpolated). The file size differ a lot but they are reduced
afterwards to equal with jpg compression. Apparently it looks like the
interpolation routines (HP) do a good job. It looks like the picture
scanned with 1200 dpi have higher resolution than the one scanned with
only 300 dpi, which is the optical resolution of the scanner.
The best result is obtained by scanning in 1200 dpi and reducing the
file with jpg compression, even though I had expected scanning in 300
dpi to as good as 1200 dpi.

SANE does no interpolation and will only deliver the optical resolution
of the scanner. Is the apparent enhancement of the picture only an
illusion?
It seems that the resolution is higher also when blowing the picture up
to see each individual pixel. Even if the illusion is only apparent to the
eye it could in many cases make the pictures look better.

It might be a good idea to introduce interpolation into SANE ? Is the
algorithms behind this free ? Or are these routines known for all ?
How is the interpolation done ? Close to the hardware or on the picture
after scanning ? E.g. could it be done in GIMP ? - Or must it be a driver
routine ?

None of the companies that make scanners have introduced Linux software
yet. Agfa has stated that it newer will. The other say they will wait
and see. With 10 million Linux users growing 25% a annum Linux support
will emerge.

Ole W Saastad 

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