[sane-devel] Re Canon LiDE 120 calibration

[Robert A. Schmied]

Marshall Jose

i'm using a Canon LiDE 200 (genesys_gl847 backend) and i've found two
ways to do what you want; one or both might work for you.

please note will your scanner is using the genesys_gl124 backend so
the rest of this might just be inapplicable to your situation.

first is brute force -- find and remove any existing calibration file.
not on a network and not using saned, mine is at $HOME/.sane/canon-lide-200.cal
yours will likely be called canon-lide-120.cal or similar.

second is likely part of the backend enabled options for scanimage.
in my situation --clear-calibration forces a new calibration without
any regard for the time-stamp on .sane/canon-lide-200.cal.

i've been accused of being overly verbose, and so i am:  you might find
with your scanner plugged in a command line like

    $   scanimage --help --all-options

of some beneficial use.

finally as an aside i also experience the same issue with the lide200
images having an uneven background across the width of a scan line.
my solution so far is a horrible hack i don't yet understand why the
built-in calibration system values are failing, but they do seem to.
it might be the under-glass calibration image is missing, damaged or
different than that defined and implemented by the backend calibration
routines.

anyway in file backend/gensys_devices.c the struct the scanner models
defines in the last two entries "count of lines used in shading calibration"
and "count of lines to search start position".

for the lide_200 these were originally 50 and 400 respectively.
i found that changing 50 (lines in shading calibration) to 200 it
remarkably improved the uneven background across the width of a scan.

the problem it causes however is this: the calibration seems to
move the sensor head into the document window area -- why i'm thinking
the under-glass calibration image is missing, etc.  as a consequence
when a new calibration is performed one must remember to do it on
a blank white sheet first and then run the actual image scan. like
i wrote "... a horrible hack...".

for the genesys_gl847 there is an option --expiration-time <integer>
that sets the minutes a calibration file lasts before it expires.
default is 60 minutes.  a negative value never expires the file.
your backend might have something similar.

hope this helps

aloha

ras