Backtracking in color scanning

Rainer krienke (krienke@mailhost.uni-koblenz.de)
Fri, 29 Aug 1997 17:04:01 +0200

Hello,

I use sane0.62 with my mustek 1200spro (connected to an ADAPTEC 2940
scsi adapter). I have a question about backtracking.

When I scan color images at resolutions of say 300dpi the scan process
works right, but is very slow. This is because the scanner scans some
line and then goes back (that=B4s backtracking if I understood it right)
and then scans the next lines. Looking at the scanner it seems the the
way the scanner goes back is just a little smaller then the way it has
scanned before. Scanning a paper of size DINA4 (~30cm at length, ~21cm
wide) at 300dpi takes about 2min and 45 sec. If I scan at 100 dpi the
effect is basically still there but the sanner then scans a larger area
in one step before going back only a little. So the whole thing works
faster.

What suprises me a lot, is that under windows doing the same scanprocess
at the same resolution (via the mustec-twain driver) does not cause
backtracking to occur and is completed much much faster (not even half
the time).

So is this backtracking really needed, can scan speed be increased even
with backtracking? What I tried is to call scanimage with the option
--speed Fastest and I commented out the option -- option strip-height
in my mustek.conf file and set the buffersize SG_BIG_BUFF to the value
documented in sane-scsi (130560), recompiled kernel and sane.

Can someone try to explain this difference between twain-windows and
sane-linux to me ?

Thanks a lot,

Rainer

-- 
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Rainer Krienke                      krienke@informatik.uni-koblenz.de
Universitaet Koblenz, 		    http://www.uni-koblenz.de/~krienke
Rechenzentrum,                      Voice: +49 261 9119-641
Rheinau 3-4, 56075 Koblenz, Germany Fax:   +49 261 9119-499
----------------------------------------------------------------------

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