Rainer> When I scan color images at resolutions of say 300dpi the
Rainer> scan process works right, but is very slow. This is because
Rainer> the scanner scans some line and then goes back (that's
Rainer> backtracking if I understood it right) and then scans the
Rainer> next lines. Looking at the scanner it seems the the way the
Rainer> scanner goes back is just a little smaller then the way it
Rainer> has scanned before. Scanning a paper of size DINA4 (~30cm at
Rainer> length, ~21cm wide) at 300dpi takes about 2min and 45
Rainer> sec. If I scan at 100 dpi the effect is basically still
Rainer> there but the sanner then scans a larger area in one step
Rainer> before going back only a little. So the whole thing works
Rainer> faster.
Rainer> What suprises me a lot, is that under windows doing the same
Rainer> scanprocess at the same resolution (via the mustec-twain
Rainer> driver) does not cause backtracking to occur and is
Rainer> completed much much faster (not even half the time).
What size scan-buffer are you using? If you're using the default size
of 32KB, could you try increasing it to 127.5KB? See sane-scsi(5) for
info on how to do that.
If increasing the scan buffer size to 127.5KB doesn't help, the
backtracking could be due to timing problems. If the scanner software
is too slow to issue the next "read data" command then backtracking
would occur. What kind of computer are you using and how much memory
does it have?
--david
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