[sane-devel] Scanning produces black images

Gerhard Jaeger gerhard at gjaeger.de
Mon Apr 16 12:50:01 UTC 2007

On Montag, 16. April 2007, JKD wrote:
> > This is also an issue with the Plustek backend, reported by various
> > Ubuntu and Gentoo users. As already stated by PhobosK, the problem is
> > the kernel option CONFIG_USB_SUSPEND. This in deed is needed for laptop
> > users. It is currently marked as "experimental" but already used by various
> > distros. 
> > 
> That was my first thought. But if it's a kernel problem neither xsane
> nor scanimage would scan successfully. And in two different compilations of
> hp3900, ubuntu's one fails and my last compilation works.
> > I think the problem really is, that libusb does not know anything about that
> > suspend stuff and therefore we have more or less no possibility to wakeup
> > the port, where the scanner is connected to.
> I think you're right. But may be libusb is already updated in debian
> unstable. That would explain that my compilation works in ubuntu and
> library provided by ubuntu in libsane-extras package doesn't. So my
> conclusion would be the same. Backends need to be compiled against
> current version of libusb.

Could you please check which version of the libusb you/they use?

> > One thing that could be observed: In all cases, scanimage works fine - guess
> > this is because it never closes the port until the scan process is done.
> I'm confused. Why should exist any difference between scanimage and xsane when
> both frontends use the same SANE API to access usb scanners?

Guess it's the workflow. When you call scanimage, then the scanner is openend,
detected, configured, scanning is done, closed.
XSane tries to open and detect, then closes a device. Then then scan is done
upon request. And I think after the first close, the device (or the port) will
be suspended.

- Gerhard

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