[sane-devel] SANE2 standard revisited: image data format

[Michael Herder]

Henning Meier-Geinitz, Donnerstag, 5. Dezember 2002 22:10:
...
> | # SANE_PFLAG_MORE_IMAGES (bit 1, bitvalue 2) is set to 1 to indicate
> | further pending images. It is permissible to set that value to 1 "in
> | good faith", as it has to be determined at a very early time, where it
> | might not be detectable, if there actually are more images to
> | transfer. E.g. you will usually not know if the document feeder
> | contains further pages when starting to scan the current one. Thus you
> | are allowed to set that bit but later fail at sane_start().
>
> So this flag is intended to flag the availability of some sort of ADF,
> or film holder? I didn't understand this on my first read. Maybe
> rewrite like this:
>
> "# SANE_PFLAG_MORE_IMAGES (bit 1, bitvalue 2) is set to 1 to indicate
>    further pending images. The frontend is expected to call sane_start
>    again after the end of the current scan to get more images, e.g. from an
>    automatic document feeder. It is permissible to set that value to 1
>    "in ..."
>
> | # SANE_PFLAG_NEW_PAGE (bit 2, bitvalue 4) is set to 1 to indicate that
> | the current frame comes from a new physical page. This bit is of
> | informational character only to help frontends to group multi-image
> | scans.
>
> As far as I know there is no way yet to specify multi-image scans on
> one page. Do we need this feature at all? Can't this be done easier in
> the frontend by selecting a big eough scan area to get all the images?

I think, that you are misinterpreting something here:
It's not the intention to support "multi-selection" of images on one page 
(i.e. more then one scan-area). Those proposals are probably based on the 
thread "Writing Fujitsu M3091 backend" 
(see http://panda.mostang.com/mail-archive/sane-devel/2001-02/ )
where someone asked how to implement support for a duplex scanner.
When you start a scan in duplex-mode with such a scanner, you can inform the 
frontend, that the next scan comes from the same physical page (the back page)
A frontend could use this information for filename generation, e.g.
image_front_001.png
image_back_001.png

bb
Michael