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

[m. allan noah]

On Sun, Jul 9, 2017 at 2:54 PM, Matt Garman <matthew.garman at gmail.com> wrote:
> 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.

Well, I got over my fear of clicking on 'raw sewage' and looked at a
couple of your images. I agree that this is a bug, the swdeskew should
not crop the top of the image in this case. I wonder- is that purple
stripe near the left margin actually on the page, or does your scanner
have a problem?

> 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.

I expect the sane driver to be equal or slightly faster than the
windows driver. If you find otherwise, let me know.

>
>> 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.

There are some tools like unpaper and leptonica which can do some of
these things. Perhaps they will be useful to you. Even still, I would
like to fix bugs in sane if I can. I'll take a crack at it using your
image.

> 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

allan

-- 
"well, I stand up next to a mountain- and I chop it down with the edge
of my hand"