[sane-devel] Canon N 650U Calibration step...

[Pierre Dumuid]

Hi,
I've got a quick question... I've got a canon N 650U, scanner which is 
working perfectly with sane.

The problem is, each time I scan, it appears the scanner does a 
calibration before each scan.

Under windows, the scanner gui interface has a button that you press to 
perform the calibration.  After this, the scanner never needs 
calibrating for a fair while. Before performing the calibration, the 
windows gui asks you to "make sure the lid is closed before performing 
calibration",

If the linux scanner calibrates each time it scans, then when I want to 
scan a thick book, the scanner is forced to have the lid open during 
calibration (since there's no pause between calibration and actually 
scanning). The result is that calibration is poor, and I have streaks 
running down the page (I haven't tried but I assume that no calibration 
may be better.)


Programming questions:
----------------------
I haven't really browsed through the code for sane at all yet, but I 
have a few questions I thought might be interesting (if they're out of 
place, I'm terribly sorry)

I can see that sane has a back-end and a front end, that makes all 
scanners very modular and have the same basic interface, but is it 
possible for extra special requests such as calibration to be requested 
from the client to the back-end to perform calibration (i.e. we could 
then calibrate only once).  Also does the backend provide any 
functionality for the frontend to query the backend to see what extra 
functionality the scanner provides?

i.e. a scanner query might return that:
   1. the scanner can perform some 3 types of internal image filtering; 

      specifically "descreening", "sharpening", and "normal".
   2. the scanner has a calibration procedure with a pop-up warning of
      "Please Close Lid while calibration is being performed"

(along with each property, there may be a description when the mouse is 
dragged over the button)

The front-end could then create a widget as a result of this query, with 
a pull down menu with these three values to select from, along with a 
button to press which calls the calibration procedure...

Sorry for a long email,
Pierre