Re: [Printing-architecture] [Printing-summit] Another Common Dialog

[Olaf Meeuwissen <olaf.meeuwissen@avasys.jp>]

Hin-Tak Leung <hintak_leung@yahoo.co.uk> writes:

> --- On Tue, 21/4/09, Suffield, David <david.suffield@hp.com> wrote:
>
>> > From: Johannes Meixner [mailto:jsmeix@suse.de] 
>> > 
>> > How does the scanner unit enumerate nowadays?
>> 
>> There is no change with scanner USB enumeration. As far as
>> I know there is no well defined "scanner" interface like the
>> "mass storage" interface.  
>
> [snip] ... just want to say that the USB specification has an imaging
> device class (I don't remember the precise name), besides printer and
> mass storage. The imaging device class is where many usb-capable
> digital camera/camcorder appears as. I think the class is called ptp
> but can't remember the name...

There was a scanner device class in a draft of the USB spec (ID = 6) but
that never made the cut for the final standard :-(  As a result the bulk
of the USB scanners now use the vendor specific class (ID = 255).  There
may be some that use something else but there is NO reliable way you can
identify a scanner device short of consulting a database (which needs to
be updated continuously to account for new devices hitting the shelves).

FWIW, SCSI devices are a little bit better off but even there all is not
well.  Although the bulk identify themselves as a SCANNER, there are a
number of (Epson and HP) devices that think they are a PROCESSOR.

There has been some discussion regarding SCSI scanner on the sane-devel
mailing list in the threads below:

  http://lists.alioth.debian.org/pipermail/sane-devel/2009-January/023456.html
  http://lists.alioth.debian.org/pipermail/sane-devel/2009-January/023507.html
  http://lists.alioth.debian.org/pipermail/sane-devel/2009-January/023528.html

Hope this helps,
-- 
Olaf Meeuwissen, LPIC-2           FLOSS Engineer -- AVASYS Corporation
FSF Associate Member #1962               Help support software freedom
                 http://www.fsf.org/jf?referrer=1962