[sane-devel] Fwd: verticle stripes in high res scans

[Henning Meier-Geinitz]

Hi,

On Mon, Mar 15, 2004 at 06:15:45AM -0800, Christopher Marshall wrote:
> > I have a CanoScan LiDE 80 that I have been happily using with SANE for a few months now.

I'd be very surprised if that was true. The Canon Lide 80 uses the
Genesys GL841 chips as far as I know. It's not supported by SANE.

Please show us the output of "sane-find-scanner -v -v", 
"scanimage --version" and "scanimage -L".

> > I have noticed verticle stripes or bands of brightness and darkness when I scan photos at high
> > res.

Usually the reason for vertical stripes is trouble with the
calibration. Each element of the CCD/CIS sensor has a different
sensitivity. This difference in sensitivity must be adjusted by doing
a calibration on white calibration target. That's usually a white
strip on top of the scan area.

If you still get stripes, the backend may accidently use the wrong
area for calibration (scanning part of the case) or there is just some
bug in the calibration routine.

> > I'm taking a small photo and scanning it at high res.

Can you put a small example somewhere on the web?

> > Is post-processing with a destriping filter the way a windows driver would handle this problem?

No. ANd neither the SANE backend :-)

> > Perhaps a better question would be: how much of the difference in quality between default SANE
> > scans and scans done with the windows driver (for the same scanner) are due to simple
> > post-processing steps that can be done with GIMP like programs?

Usually none. At least no stripes should occur. There may be
differences when sharpening or other filters are used in Windows
drivers but usually the effect is not that big.

You may get more specific information when we know which scanner you
actually have and which backend we are discussing :-)

Bye,
  Henning