[sane-devel] bug with Canon N1240U in Lineart mode at 75 dpi?

[Eric Ding]

Gerhard,

This picks up from a conversation almost a year old (from Nov/Dec 2004),
but I hope it's not completely inscrutable as a result.  The issue I was
looking at involved a problem with scanning in Lineart mode at low
resolutions (75dpi or less) on a Canon n1240u scanner on my Gentoo Linux
box.

When we corresponded back and forth (see below), you suggested some
tweaking of some values in plustek-usbdevs.c, and I responded that
certain values seemed to do the trick.  I thought that would be the end
of the conversation.

However, since then, I've had problems... I'm using sane-backends
1.0.16rc2 on Gentoo (seems to be the same in this area as the release
version), and I am now having problems (again?) scanning in Lineart mode
at 75dpi.  Here's the table:

    /* Gray mode MCLK settings */
    { 7.0, 7.0, 6.0, 6.0, 6.0, 6.0, 6.0,  6.0,  6.0,  6.0 },
    { 6.5, 6.5, 6.0, 6.0, 6.0, 6.0, 8.0, 12.0, 12.0, 12.0 }

If I change the first value to 7.5, i.e.,

    /* Gray mode MCLK settings */
    { 7.5, 7.0, 6.0, 6.0, 6.0, 6.0, 6.0,  6.0,  6.0,  6.0 },
    { 6.5, 6.5, 6.0, 6.0, 6.0, 6.0, 8.0, 12.0, 12.0, 12.0 }

then my scanner happily scans in a Lineart image at 75 dpi.  Can/should
this be tweaked in the official source?

Thanks,
Eric

Gerhard Jaeger <gerhard at gjaeger.de> wrote:

> On Sunday 05 December 2004 01:37, Eric Ding wrote:
> > Gerhard Jaeger <gerhard at gjaeger.de> wrote:
> > > you might wanna try and tweak the motor settings, checkout file
> > > plustek-usbdevs.c and search for MODEL_CANON1200, you will find something
> > > like:
> >
> > [snip]
> >
> > >   /* Gray mode MCLK settings */
> > >   { 6.0, 6.0, XXX.0, 6.0, 6.0, 6.0, 6.0,  6.0,  6.0,  6.0 },
> > >   { 6.5, 6.5, 6.0, 6.0, 6.0, 6.0, 8.0, 12.0, 12.0, 12.0 }
> > >  },
> > >
> > > tweak the settings for "Gray mode" and <= 150dpi (where the XXX is
> > > located), you may increase the value to 7 or 8...
> >
> > Well, that certainly improved things!  If I change the value to 7.0 or
> > 8.0, scanning at 75dpi in Lineart now works. It does *not* work if the
> > value is changed to 6.5.
> >
> Ah, okay I see. I'll add 7.0 to the source with the next update. Thanx for
> testing.
> 
> Gerhard
>