I have an old Pi-3 running Stretch. I have what
apt-get install tells me is the latest version of everything installed. I plug in an old HP PSC 750xi All-In-One USB printer/scanner. The Pi recognizes the printer features of the device and I can successfully configure CUPS to use the printer. But I cannot get the Pi to recognize the device's scanner.
I have a separate laptop running Ubuntu 20. When I plug the USB device into that laptop, I can use hplip's
hp-scan tool to successfully scan. But none of the Pi's hplip tools (
scanimage, ...) recognize the USB scanner.
Clearly, as the Ubuntu test proves,
hplip does support scanning for this all-in-one printer/scanner. And
hplip documentation indicates that the device is supported both for the Pi
hplip version (3.16.11) and for the Ubuntu version (3.20).
I also have an HP 6978 Network printer/scanner that the Ubuntu system sees on the network and can manipulate with the hplip tools. The Pi's CUPS server sees and can use that network printer. But, like the USB device, the Pi fails to 'see' the network scanner.
My understanding is that these scanners are supported through use of the
libsane-hpaio backend. Yes, I have installed the
libsane-hpaio package on the Pi. I've run
scanimage on the Pi with
SANE_DEBUG_HPAIO=128 but the output simply reports no scanners found without indicating any errors of any kind. On the Ubuntu system, the same debug output shows successful discovery of both the network scanner and the USB-connected scanner.
I cannot find any missing packages or dependencies on the Pi. I have tried removing and re-installing hplip and a number of other packages. Clearly, there is some configuration difference between the Pi and the Ubuntu platforms. But after several days of struggle, I'm stumped.
Anyone have any ideas?