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

[Matt Garman]

TL;DR: for those of you who have migrated your document scanning
workflow from Windows to a Sane platform (e.g. Linux), what
settings/tools have you found to maintain or improve quality of
scanned documents (relative to Windows)?

Long version:

I have a Fujitsu ScanScan s1500 document scanner, and sane-1.0.27
running on Arch Linux.  So far it seems to just work.  I've had this
scanner for nearly a decade, and used it exclusively under Windows
until now (trying to move to a pure Linux desktop).

So while I can scan documents just fine, the results to me aren't as
good as what I get under Windows using the proprietary ScanSnap
software.  Specifically, they are too light/too dark, text not crisp
enough, straight lines not straight, colors a bit off, etc.

One example: de-skewing.  All the years I've had this scanner, I
didn't even realize this was a thing until now.  I can use scanimage's
software de-skewing (--swdeskew=yes), and it seems to *mostly* work,
but pages are often still somewhat skewed.  Excepting for
wacky/unusual documents, I don't recall ever seeing any skew under
Windows.

Despeckling (--swdespeck=n) does seem to be a major step in the right direction.

I'm also playing with all the enhancement options.  E.g.,
--brightness, --contrast, --emphasis, etc.  Brightness and contrast
are fairly intuitive, but I don't really understand what the other
options actually mean, or what I should expect from them.  I've been
taking the trial-and-error approach, but e.g. --variance doesn't seem
to do anything.  And I'm not sure how the options interact with each
other, so trial-and-error could take forever.

Having said all that, my one test document is maybe 90% as "good" as
the same scanned on Windows.  Probably good enough to live with, but:

(1) This seems to be a very popular scanner - has anyone been able to
back out the settings the proprietary ScanSnap software uses?
- and -
(2) I wonder if the Windows ScanSnap software settings are static or
dynamic?  E.g., is there some kind of pre-processing algorithm applied
to guess at the best enhancement settings?

As for 3rd party tools, I've read about unpaper, and played a bit with
scantailor, but (outside of OCR), they don't seem to offer more
enhancement features than sane itself (or I'm overlooking something).

Any other rules of thumb or general pointers for getting the best out
of my scanner with Sane?

Thanks!