[sane-devel] Scan slow to start on Canon N670U (plustek)

[Gerhard Jaeger]

On Thu, 7 Apr 2005 Jon Niehof wrote:
>I'm using scanimage in batch mode to scan books (at 300dpi, 8
>bit grey) on a Canon N670U (plustek backend, sane-backends
>1.0.15). Once the scan starts it's reasonably fast; however, the
>scan head spends quite a bit of time (maybe twenty seconds)
>futzing about before scanning.

Hmmm, this is normally the coarse calibration to find the correct
lamp settings. When using the cache calibration feature, this 
step should be skipped...

>I'm using the option to cache calibration and it doesn't seem to
>make much difference. Is the calibration cached to a file that I
>need to have write permission for, or just kept in RAM between
>scans for a particular process, or something else?

The file is kept in ~/.sane/ directory...

>Also, I understand only the coarse calibration data is cached,
>and fine calibration is redone for each page; is this correct?

Yes, that's true, as the fine calibration relies on the current 
scansettings and is not too slow.

>How disastrous is it to skip fine calibration?
Hmmm, try it, you might notice, that you get vertical stripes...

I've done some tests here on my N1240U and the coarse calibration
takes about 20 seconds and the whole scan about 50s. With 
cache calibration enabled the scantime decreases to 30s...
Could you please enable the debug-output of the backend and do
two or three scans with enabled cache calibration, so we might
can track down the problem?

Gerhard