[sane-devel] new Backenddriver

Olaf Meeuwissen paddy-hack at member.fsf.org
Sat Oct 22 12:22:55 UTC 2016

Johannes Meixner writes:

> Hello,
> On Oct 19 21:51 Olaf Meeuwissen wrote (excerpt):
>> Michael Rall writes:
> ...
>>> So basically my SANE Backend needs to call a Webservice
>>> an will receive an Image as result.
> ...
>> ... I mentioned the pnm backend is because
>> it reads an image from file.
> I have a - perhaps stupid - generic question:
> What is the reason for a SANE backend when one already
> has an image as a file?

Testing or demoing your super-duper new SANE frontend, perhaps?  I for
one have used such an approach in the past where it was not feasible to
use a real scanner (because it was still on the drawing board or its
firmware was only in the early stages of development ;-).

> I assumed the reason for a SANE backend is to create
> an image file in a known image data format from whatever
> special bits of data that a scanner hardware can deliver.

That has been and probably still is the main reason but anything you can
come up with that is exposed via the SANE API is, by definition, a SANE
backend.  The dll and net backends are good examples. 

> For example when a network scanner can deliver an e-mail
> with the scanned image(s) e.g. as JPEG or PDF attachment,
> then I think there is no need for a SANE backend.
> In other words: When that Webservice cannot deliver
> known image data formats but only whatever special bits
> of data that need to be converted into a known image data
> format, then I would understand a SANE backend for it.

I have no idea what web service Michael needs/wants to capture in a SANE
backend and whether that makes sense to begin.  Trying to think up a not
completely ridiculous scenario, what about a computationally intensive
image rendering or post-processing service (i.e. SaaSS[1]).  The whole
system has been put somewhere on a VPC in the cloud and results are made
available piecemeal via a websocket over HTTPS.  Your old workflow used
to let you do everything via an existing SANE frontend but now the, eh,
"service" requires you pump the image into the cloud and pull results
out of it again.

 [1] https://www.gnu.org/philosophy/who-does-that-server-really-serve.en.html

Hope this helps,
Olaf Meeuwissen, LPIC-2            FSF Associate Member since 2004-01-27
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