Re: Writing Fujitsu M3091 backend

From: mh (crapsite@gmx.net)
Date: Tue Feb 27 2001 - 22:25:54 PST

  • Next message: Christoph Knauer: "xsane 0.72 win crashes"

    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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