[sane-devel] Epson perfection 660 usb - problem with lineart scanning - snapscan backend

[Frédéric Leroy]

Le mardi 05 septembre 2006 à 20:29 +0200, Oliver Schwartz a écrit :
> Hi,
> 
> > > When I try to scan in lineart mode, it makes garbage on output.
> > > The scan seems "misaligned".
> > > But if I first make a scan in gray or color mode, and then switch
> > > to lineart, it works !
> >
> > It works ... sometimes :(
> >
> > I acquire a scan in Lineart mode and make a log :
> > http://www.starox.org/pub/sane/snapscan/lineart.log
> > It makes dirty squares in the image :
> > http://www.starox.org/pub/sane/snapscan/lineart.pnm
> 
> So... is this the best result you can get or does it work ok (without 
> the dirty squares) if you scan in grayscale first?
It is the best result I can get with scanimage.
It always fails.
Whereas with xsane, sometimes it works after a real scan (not a preview,
but after a preview). Maybe a problem with preview ?

> Unfortunately it seems that lineart mode is less and less supported in 
> newer scanners. These scanners always scan in grayscale mode, the 
> conversion to lineart has to be done in the backend. I don't know if 
> this is the case for the Perfection 660, but on the other hand 
> there's not much that can fail on lineart mode.
So, it's possible to fallback to software conversion.
It seem's there is many scanner with this problem, maybe we can add a new option for this ?

> Maybe you can provide an USB trace of a lineart scan on windows. 
> You need to install an USB sniffer first. I prefer USBSnoop which is 
> available from http://benoit.papillault.free.fr/usbsnoop/ . The page 
> also gives basic instructions on how to use it.
> [...]
I'll do this tomorrow.