[sane-devel] genesys Canon Lide 210 aspect-ratio-problem at 600 dpi

[M G Berberich]

Hello,

Am Montag, den 05. Mai schrieb Stef:
> On 25/04/2014 02:55, Andrew Kanaber wrote:
> >I hit the same problem with a Canon LiDE 110. I tried measuring the
> >distortion by scanning a sheet of graph paper in various modes.
> >
> >With sane 1.0.24 in 600dpi lineart and gray modes the scan is
> >stretched vertically by about 30%. Color mode scans are actually
> >also stretched at 600dpi, but much less noticeably by about 2%. The
> >stretching is still visible though if you compare the scanned
> >images side-by-side. With version 1.0.22 the lineart and gray scans
> >are correct at 600dpi but the 2%-ish stretching is still present in
> >600dpi color mode.
> >
> >In case it helps I've put some of the scans up at
> >http://www.chiark.greenend.org.uk/~akanaber/lide110/
> >
> >Let me know if there's something else I can do that might help,
> >
> >Andrew
> >
> >M G Berberich wrote:
> >>Hello,
> >>
> >>Canon LiDE 210 with sane-backends 1.0.24 (libsane:amd64 1.0.24-1.1+b1
> >>from debian testing) has problems with 600 dpi gray and lineart.
> >>
> >>In 600 dpi gray and lineart the scan is partial and aspect-ratio is
> >>not correct. Vertically only about ? of the area is scanned and then
> >>scaled to the area, horizontally all is fine. (So probably the driver
> >>sets the wrong scanline-skip (to small)).
> >>
> >>This worked in older versions, at least 1.0.22.
> >>
> >>600 dpi Color-scanning works fine, so do preview, 300dpi and 1200 dpi
> >>in all modes.
> >>
> >>2400 dpi and 4800 dpi do not work at all, but never did.
> >>
> >>	MfG
> >>	bmg
>
>     Hello,
> 
>     the vertical resolution is given by the motor speed which is eventually
> an int. So rounding errors may give ~2% distortion:
>     target=((exposure * dpi) / base_dpi)>>step_type;
>     Maybe by decreasing or increasing slightly exposure time rounding errors
> could be mitigated, but changing exposure may raise other problems. If the
> windows driver can do it, I'll manage to find something.
> 
>     I'll check how the gray scan beahves. The change between 1.022 and
> 1.0.24 is to use the LINESEL function when we try to scan below the minimal
> scanning speed of the motor. This should affect scans below 600 dpi, but not
> 600 dpi which is the minimal scanning speed.
> 
>     2400 and 4800 dpi scans works on my LiDE 210. So I'd need some logs or
> better information on what is not working for you.

Made some logs and images. Please see http://www.m-berberich.de/sane/
Details are in Readme.txt

>     I'm currently working on shading calibration problems for gl646 based
> scanners (HP2400 and HP3670). I'll look into this issues when I have
> finished it. If you have time for it, you can open a bug in the bug tracker
> (https://alioth.debian.org/tracker/?group_id=30186) and assigned it to me.
> 
> Regards,
>     Stef


	MfG
	bmg

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„Des is völlig wurscht, was heut beschlos- | M G Berberich
 sen wird: I bin sowieso dagegn!“          | berberic at fmi.uni-passau.de
(SPD-Stadtrat Kurt Schindler; Regensburg)  | www.fmi.uni-passau.de/~berberic