Scanning with a samsung 4600 in ubuntu

My trusty old Samsung SCX-4600 scanner/printer refused to be recognized anymore by my laptop running Ubuntu 18.04. Trying to initiate a scan failed both from SimpleScan, XSane and the command line:

$ scanimage -L              
 
No scanners were identified. If you were expecting something different, 
check that the scanner is plugged in, turned on and detected by the 
sane-find-scanner tool (if appropriate). Please read the documentation 
which came with this software (README, FAQ, manpages).

A longish google quest led me to a suggestion that fixed it for me. The mysterious SANE_USB_WORKAROUND setting resolved the issue. The scanner is recognized again:

$ export SANE_USB_WORKAROUND=1 
$ scanimage -L 
device 'xerox_mfp:libusb:002:004' is a Samsung Samsung SCX-4600 Series multi-function peripheral

And scanning works like a charm:

$ scanimage --format=png > /tmp/some_document.png

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