[sane-devel] Epson Perfection 3490 -> included bugfix makes it work

[Bauke Jan Douma]

On Mon, Sep 19, 2005 at 09:07:22PM +0200, Julien BLACHE wrote:
> "Belgabor" <belgabor at gmx.de> wrote:
> 
> > I also have to thank for this patch (it came on the day I boght the scanner
> > without knowing about the issues). It is almost perfect as it works nice for
> > resolutions up to 1200 dpi. At 2400 and 3200 I get a combing effect. Every
> > other pixel column is offset by several pixels. It looks a bit like an
> > interlaced PAL TV picture (only the combing is vertical rather than
> > horizontal). 
> > Hints appreciated (also if someone could confirm this. The error isn't there
> > in windoze, so it doesn't seem to be a hardware problem).
> 
> The backend needs to perform line distance correction on the image as
> for the 2480/2580 and an increasing number of scanners.
> 
> The high resolution are obtained by combining the data from 2 slightly
> offset sensors (lower resolution, cheaper), hence the offset you see.
> 
> JB.

Here is an image showing the effect we're talking about.
This is a scan of a 5x5mm area at 2400 in Lineart mode.
Note that the ratio is also wrong -- the x dimension off
by a factor of approx. 1.333333.

The combing also shows up in res. 3200.  Ratio at that res.
is correct.

bjd
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