[sane-devel] Scan quality enhancements/processing (vs Windows with Fujitsu ScanSnap S1500)

[Matt Garman]

Hi Allan,

Thank you for taking the time to provide some feedback and look into this!

More commentary inline below:

On Fri, Jul 7, 2017 at 12:06 PM, m. allan noah <kitno455 at gmail.com> wrote:
> In general, if you are using swdeskew, it is probably better to scan
> at full width, and use the swcrop option too. Also, some fujitsu
> machines support the overscan option, which will cause the scanner to
> output some extra background rows before the paper is ingested. This
> can significantly improve the swdeskew performance. The S1500 does not
> have a black background option, but the larger scanners do, and this
> will also help.
>
> If you have a document that consistently reproduces poor deskewing,
> even with those additional options, I'd like to see a .pnm file of the
> scan with and without swdeskew enabled.

Most of my documents have far too much personal info on them to
publish publicly... but we'll try to make due with some generic
documents.

Here's a link to the output of "scanimage -h", just for reference for
what default settings are.  I included the PDF as scanned under
Windows, and the PNM files from a Linux scan, both with and without
the --swdeskew option enabled.  (There are two files for each of the
Linux/PNM, because it was a duplex scan, i.e. front and back.  Windows
scan was also duplex, but the software concatenates all scans into one
file.)

    http://raw-sewage.net/images/linux_scansnap_s1500/

At any rate - this one doesn't demonstrate skew very well.  But it
does sort of answer my previous question: you can see that when I used
the swdeskew option, it actually cut off part of the document.  I
previously assumed the scanner was mis-judging the actual scan
area/document size, but from this simple experiment, it appears the
swdeskew can get confused and cutoff parts of the document.

Under Linux, you can see I scanned at 300dpi.  I have it set to "auto"
under Windows, but I'm quite sure it scanned at 300dpi or less.  If I
specify anything over 300dpi (under either platform) the scanning is
noticeably slower.  Not a precision measurement I know, but it's
something.

> All the options you list here are values which we send to the
> hardware. Frankly, I have little documentation about what they do, but
> it is certainly possible that some of these only have effect in binary
> mode, and they may not even work on the S1500. I'll see if I can track
> that down, and disable them in cases where they cannot be used.
> ( ... )
> I'm willing to guess that much of what you are seeing is the windows
> software making a larger, potentially higher resolution or color mode
> scan, and then cleaning it up in software.

I'm assuming similar open source tools exist for Linux; i.e.
scanimage/sane doesn't have to do all the work... I just want to get a
good, comprehensive scan out of sane.  Then I can script a pipeline of
post-processing tools.

I'll continue to look for non-personal documents to present more
examples.  I created a Windows virtual machine so now I can quickly
test the two without having to turn on my old PC and switch the
keyboard/video/mouse cables over!

Thanks again, let me know if I can provide any more info.

-Matt