[sane-devel] hp5590 driver and ADF

[m. allan noah]

The backend should do its best to provide reasonable, clean images,
including removing padding, flipping images, and providing valid size
information. This might require buffering the image in the backend.
Unfortunately, the sane protocol does not have a good way for the
backend to signal the front-end that buffering is ongoing. You
basically have to block during sane_start, and read/clean the image.
Then return from sane_start. The frontend's subsequent call to
get_parameters will then have valid size data. The fujitsu backend
does that sort of thing when we are doing deskew and crop operations,
so you might look there for inspiration.

allan

On Wed, Sep 16, 2015 at 12:23 PM, Joel <hashbang at gmail.com> wrote:
> Hello,
> I found a discussion a while back about the ADF scans having extra
> lines and spilling to the next page. Someone discovered that there is
> a line on the right, with a blue dot signalling the end of the page.
> Also, the end of the document is signaled by alternating white and
> black pixels.
>
> I recently acquired a ScanJet 7650, and was planning on scanning a
> large amount of documents I have. For some reason, using PDFxchange to
> scan in windows won't duplex at all, so that's useless for me. The
> SANE driver appears to work well, but when I use the ADF, the pages
> get out of sync quickly.
>
> I've played around with it a little, and dug around in the backend
> code. I've also turned on hp5590 debugging and simple-scan debugging.
> It appears as if the length of the document should not be assumed/used
> when using the ADF, and the in-band "blue dot" should be used.
>
> Does it make sense for the backend to return EOF when in ADF mode and
> detects the blue dot? Should it remove the line on the right, as well
> as the alternating white and black? Should it also flip the even
> number page 180 degrees? My thought is that these are not frontend
> sort of tasks, as they are specific to this group of scanners.
>
> I could try to implement something, but certainly need some direction.
> I'm unsure of the right way to go about it.
>
> Cheers
> Joel
>
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