[SOLVED] Networking scanning broken above 300 DPI (600 DPI, 1200 DPI, 2400 DPI all broken) in Mint 20.1

[snook]

This is more a Public Service Announcement (of the "here be dragons" variety) than a request for help.

I recently upgraded from Mint 19.3, to 20.0, then straight away upgraded again to 20.1. I was trying to avoid a fresh install.

Everything seems to be working great, apart from scanning.

Previously in 19.3, I had scanning working fine, using the network printer/scanner & Simple Scan, at any resolution I liked. I had the Simple Scan preferences set to 600 DPI for text and 1200 DPI for photos, but I have no idea if these were the defaults or not.

Now in Mint 20.1, when I use Simple scan / Document scanner, it opens, showed "ESCL Brother HL-2395DW series" (there were no other options), then when I click "Scan", it starts the scanner (I can hear the scanner scanning the page), but on the computer the page stays white, and then it shows a dialog with this error: "Failed to scan: Unable to start scan".

I redid the scanner setup that I used in 19.3, which is as follows, to try and make sure I was using the latest drivers:

* Download brscan4 drivers from Brother's website: https://www.brother.com.au/en/products/ ... hl-l2395dw -> Downloads & Resources -> Software downloads -> Linux + linux (deb) -> click "Scanner driver 64bit (deb package)" -> agree to EULA & download
* sudo dpkg -i brscan4-0.4.10-1.amd64.deb
* sudo brsaneconfig4 -q
* Then run "Simple Scan".
* However it gave the same error: "Failed to scan: Unable to start scan".

Basically I assumed it was a hardware driver issue. But after a bunch of checking logs (and finding nothing), googling, reading forums, and dead ends, I found the problem here: https://gitlab.gnome.org/GNOME/simple-scan/-/issues/207

The problem is that this backend version just does not work above 300 DPI. So I reduced the resolution, and straight away it worked. I tried all the resolutions above this, and none of them worked. So it seemed to be that network scanning is broken above 300 DPI (i.e. at 600 DPI, 1200 DPI and 2400 DPI) in Mint 20.1 (and most likely Mint 20.0 too).

I was going to accept this as an very annoying regression, but after a bit more reading, I discovered it can be fixed! The proper fix is to do this:
* sudo aptitude install sane-airscan
* airscan-discover

This should add another SANE backend, which does not have the same 300 DPI limitation. Now when you start Simple Scan, you should get an option to use "eSCL Brother HL-2395DW series" - note that it's "eSCL" instead of "ESCL" before. The capitalisation of that one letter seems to be very important. Once you choose that option, which uses the different backend, you can now successfully scan at any resolution you like over the network, without errors. Problem solved.

[gittiest personITW]

Welcome to the forums snook.

That looks like it might help others. Didn't even realise this was 'a thing'.
This might be a good place to start when others have problems with network scans.

Nice one.