[sane-devel] I have achieved ADF duplex scan

[eagleskycloud]

Hi ,

With your help,I have achieved duplex ADF scan in our backend with
sane-backends 1.0.19 and XSane 0.995. Xsane could get front image and back
image of a paper at the same time while scanning with ADF.

   I save back image in a buffer allocated by my backends  then Xsane  read
a back image  after XSane have get a whole front image.

   Below suggestion is from m. allan noah:

1. from the frontend perspective, duplex is no different from simplex
adf, there are just more images.

2. i have never gotten xsane's multi-page mode to work, i use
'scanimage -b' or 'scanadf' command line tools

3. there are several other backends which support duplex scans.
fujitsu, avision, epjitsu come to mind. You could look at their code
for suggestions, but then your code becomes a derivative work, and you
must release it also under the GPL.

4. The way to write your code depends on the scanner. If the scanner
has enough memory to buffer the back side data until after the
front-side has been read, then you just read them sequentially. if the
scanner sends back the data interlaced, then you must buffer the back
side in memory until the front side has been sent to front-end, then
read back side from buffer. the fujitsu backend demonstrates both of
these.

5. be aware that a proper front-end in batch mode will call
sane_start() at the beginning of each page, but only call sane_cancel
after the last page returns SANE_STATUS_NO_DOCS.
...

Thank you.
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