[sane-devel] snapscan & interpolation

[Bertrik Sikken]

Alexandre Abbes wrote:

> Hi I have a snapscan 310, which has an optical resolution at 300dpi.
> Thus the xsane button only proposes resolution up to 300dpi. But I
> know that with a good interpolation, one can scan with this scanner
> up to 1200dpi. Does anybody know how interpolation works? Is it a job
> done by the scanner itself, or a soft post-prossessing that can be
> done with gimp? Any comment welcome ! Alex

As far as I know, you can never get more than the optical resolution
(unless you do weird tricks like moving the scanner head sideways
in sub-pixel steps or something).

Creating a 1200 dpi from a 300 dpi scan is just fooling yourself.
It's like converting an mp3 from 64 kB/s to 256 kB/s, it takes
more hd space but the quality stays the same (or even gets a little
worse).

One case that I can imagine is that the scanners' CCD has a resolution
of 300 dpi (=horizontal resolution), but can do motor steps with a
higher resolution (=vertical resolution = e.g. 1200 dpi).(=vertical).
In that case I can imagine that it makes sense to interpolate to
300x1200 dpi.

I think that usually interpolation is done in software, to keep
the amount of data that the scanner has to send as small as possible.

Bertrik