Tom Martone, Mit, 28 Feb 2001 :
[...]
> As far as sending multiple pages to the front end(s), the current SANE
> standard supports this very well. I think that you should stay away
> >from your duplex=hack approach and stay with two separate pages. A
> single sheet scanned in duplex will look like two sheets scanned
> single sided with an ADF.
The current SANE Standard says absolutely nothing about sending multiple
pages to the frontends(IMHO). It's quite clear, that a frontend can call
sane_start() more than once, but in fact, the SANE Standard leaves this
decision to the frontend.
"... If the frontend expects additional frames...,it can call sane_start())
again."
There's no way for a backend to tell the frontend, that it actually wants
to send additional images. This, however, could easily be solved with a
simple flag in SANE_Parameters.
> As far as front-ends go, xsane supports ADF mode and can deal with
> multiple pages in a single scan operation. For a command line, I took
> scanimage and reworked it into scanadf, which will also work with ADF
> and duplex scanners. The backend needs to reliably and correctly
> return the SANE_STATUS_NO_DOCS status code when the scanner is out
> of paper in the hopper. Look at the read loop in xsane and scanadf
> for the call sequence.
In fact, scanning with an ADF doesn't mean that you can scan multiple
pages in a single scan operation; it just means that the frontend can
automatically proceed with the next scan operation(without user interaction).
IMHO, it would be better (and easier), to make a small change in the
SANE Standard instead of trying to "hack around" the obviously existing
insufficiencies in the current implementation.
Michael
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This archive was generated by hypermail 2b29 : Tue Feb 27 2001 - 23:00:23 PST