[sane-devel] genesys 600 dpi Gray and Lineart distorted by factor 1.5 in y-direction

Stef stef.dev at free.fr
Sat Sep 26 13:02:14 UTC 2015

On 21/09/2015 21:04, M G Berberich wrote:
> Hello,
> Am Mittwoch, den 16. September schrieb Stef:
>> On 15/09/2015 15:57, M G Berberich wrote:
>>> on a Canon LiDE 210, the 600 dpi Gray and Lineart scans are distorted
>>> by a factor of 1.5 in y-direction (the scanner seems to scans with
>>> 600×900 dpi).
>>> Example:
>>> The image at http://m-berberich.de/Diverses/genesys-600dpi-Gray.png
>>> shows a 600 dpi Gray scan from a 5×5mm grid-paper, done with
>>>    scanimage -l 20mm -t 20mm -x 45mm -y 45mm --resolution 600 --mode Gray
>>      it is a known bug, see
>> https://alioth.debian.org/tracker/index.php?group_id=30186&atid=410366 .
> The bug must have been introduced between 2013-07-02 (bd0f989) and
> 2013-07-17 (1c3ec28) probably in commit
>     define specific LIDE210 sensor and motor instead of using LIDE110
>     ones
> from 2013-07-04 (730a2ba and 599f3ed).
> Anybody able to (re)fix this?
> 	MfG
> 	bmg

     previous code did gave the right number of lines. But those were of 
a higher resolution, giving improper aspect ratio. It cannot be fixed by 
reverted some changes.

     There are 3 options:
     - don't pretend the backend can do scan at these low resolution, 
and set 600 dpi as the lowest resolution in color, and 900 in gray, and 
let the user crop the picture.
     - do a 900x600 dpi scan (don't set yres = xres), which frontends 
rarely (if any) handle correctly
     - introduce yet another transformation stage in scan and do 
cropping into the backend.

     I personally consider the latter. However the "data pipeline" from 
raw data to sane compliant data has grown to the point it deserves some 
rewrite. This will take time.


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