After installing Ubuntu 20.04 my scanner CANON TS3150 won't work anymore.
I use an usb cable and followed the steps as indicated in the answer to Stave Morris' question "Step by step instruction required to install Canon TS3150 Printer" and while completing those steps (downloading from the Canon official website) one of the messages was:

```
#========================================#
#  Register Printer
#========================================#
Enter the printer name.[TS3100USB]TS3150USB
Command executed = sudo /usr/sbin/lpadmin -p TS3150USB -P /usr/share/cups/model/canonts3100.ppd -v cnijbe2://Canon/?port=usb&serial=37C00F -E 
lpadmin: Printer drivers are deprecated and will stop working in a future version of CUPS.

```

However installation ended okay. Shortly after that, I did not test the printer already, Ubuntu asked me to install new available software. I did so and to my surprise the new package brought me again a printer driver for my Canon. I tested the printer and it worked fine.

But testing the scanner again, still did not work:
Document Scanner got 'Ready to Scan', found CANON Canon PIXMA TS3100 Series  

But pushing the green Scan button gives me the error:  

 Failed to scan  

 Unable to connect to scanner

So I proceeded to install the scanner driver from the official Canon website:
<https://www.canon-europe.com/support/consumer_products/products/fax__multifunctionals/inkjet/pixma_ts_series/pixma-ts3150.html?type=drivers&driverdetailid=tcm:13-1641020&os=linux%20%2864-bit%29&language=en>

This is what followed in my Terminal window:

```
jan@Lenovo-ideapad-100-15IBY:~/Downloads$ tar -zxvf scangearmp2-3.50-1-deb.tar.gz
scangearmp2-3.50-1-deb/
scangearmp2-3.50-1-deb/packages/
scangearmp2-3.50-1-deb/packages/scangearmp2_3.50-1_amd64.deb
scangearmp2-3.50-1-deb/packages/scangearmp2_3.50-1_i386.deb
scangearmp2-3.50-1-deb/resources/
scangearmp2-3.50-1-deb/resources/scanner_ja_utf8.lc
scangearmp2-3.50-1-deb/resources/scanner_fr_utf8.lc
scangearmp2-3.50-1-deb/resources/scanner_zh_utf8.lc
scangearmp2-3.50-1-deb/documents/
scangearmp2-3.50-1-deb/documents/LICENSE-scangearmp-3.50SC.txt
scangearmp2-3.50-1-deb/documents/LICENSE-scangearmp-3.50FR.txt
scangearmp2-3.50-1-deb/documents/LICENSE-scangearmp-3.50JP.txt
scangearmp2-3.50-1-deb/documents/LICENSE-scangearmp-3.50EN.txt
scangearmp2-3.50-1-deb/install.sh
jan@Lenovo-ideapad-100-15IBY:~/Downloads$ cd scangearmp2-3.50-1-deb
jan@Lenovo-ideapad-100-15IBY:~/Downloads/scangearmp2-3.50-1-deb$ sudo ./install.sh
[sudo] password for jan: 
==================================================

ScanGear MP
Version 3.50
Copyright CANON INC. 2007-2017

==================================================
Command executed = sudo dpkg -iG ./packages/scangearmp2_3.50-1_amd64.deb  
dpkg: will not downgrade scangearmp2 from 3.90-1+2004+1ubuntu1 to 3.50-1, skipping  
Installation has been completed.

```

This last line was obviously a lie because the installation was skipped.  

After reading the manpage of apt-get, I decided to purge all versions of scangearmp2 and then install version 3.50 again:

```
jan@Lenovo-ideapad-100-15IBY:~$ sudo apt-get purge scangearmp2
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libcanon-proprio-bin
Use 'sudo apt autoremove' to remove it.
The following packages will be REMOVED:
  scangearmp2*
0 upgraded, 0 newly installed, 1 to remove and 9 not upgraded.
After this operation, 411 kB disk space will be freed.
Do you want to continue? [Y/n] Y
(Reading database ... 185663 files and directories currently installed.)
Removing scangearmp2 (3.90-1+2004+1ubuntu1) ...
(Reading database ... 185642 files and directories currently installed.)
Purging configuration files for scangearmp2 (3.90-1+2004+1ubuntu1) ...
jan@Lenovo-ideapad-100-15IBY:~$ sudo apt autoremove
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  libcanon-proprio-bin
0 upgraded, 0 newly installed, 1 to remove and 9 not upgraded.
After this operation, 317 kB disk space will be freed.
Do you want to continue? [Y/n] 
(Reading database ... 185640 files and directories currently installed.)
Removing libcanon-proprio-bin (0.2+3.90-2004ubuntu1) ...
jan@Lenovo-ideapad-100-15IBY:~$ cd ~/Downloads/scangearmp2-3.50-1-deb
jan@Lenovo-ideapad-100-15IBY:~/Downloads/scangearmp2-3.50-1-deb$ sudo ./install.sh
==================================================

ScanGear MP
Version 3.50
Copyright CANON INC. 2007-2017

==================================================
Command executed = sudo dpkg -iG ./packages/scangearmp2_3.50-1_amd64.deb
Selecting previously unselected package scangearmp2.
(Reading database ... 185622 files and directories currently installed.)
Preparing to unpack .../scangearmp2_3.50-1_amd64.deb ...
Unpacking scangearmp2 (3.50-1) ...
Setting up scangearmp2 (3.50-1) ...
Processing triggers for libc-bin (2.31-0ubuntu9) ...
Installation has been completed.

```

Unfortunately this did not help.  

Document Scanner got 'Ready to Scan', found CANON Canon PIXMA TS3100 Series  

But pushing the green Scan button gives me the error:  

 Failed to scan  

 Unable to connect to scanner 

What I think is really funny here, is that I have 3 printer drivers installed for my one and only Canon Pixma TS3150 (probably because of my different attempts) named: 'TS3100 Generic Text-Only Printer', 'TS3100\_series Canon Canon TS3100 series', and 'TS3150USB Canon TS3100 series Ver. 5.50' - but Document Scanner nevertheless knows the real name of my machine: 'CANON Canon PIXMA TS3100 Series'! How does he know this name without being able to connect to it?  

(selecting different drivers as preferred doesn't solve the problem) 

I tried to start scangearmp2 in the Terminal Window as I was used to do under Ubuntu 18.04, the command 'scangearmp2' works but ends up saying "Cannot find available scanners. Cable may be disconnected or scanner may be turned off, Check the scanner status, and then try again." As described above, the connection is fine, because I am able to print. 

For some reason scangearmp2 cannot find the scanner, while under Ubuntu 18.40 that was never a problem.

A few hours after writing the above, Software Update announced new updates  

for 'Libs for ScanGear MP for Linux'. I installed those but Document Scanner and scangearmp2 still show the same problem. I wonder what version of scangearmp2 I now have. 

Inspired by Janos' question at [Scanner part of USB multifunction printer/scanner not found](https://askubuntu.com/questions/998359/scanner-part-of-usb-multifunction-printer-scanner-not-found?rq=1)  

I tried the command sane-find-scanner and the answer was: 

```
(...)  
found USB scanner (vendor=0x04a9 [Canon], product=0x1827 [TS3100 series]) at libusb:001:010  
(...)  
 # Your USB scanner was (probably) detected. It may or may not be supported by  
 # SANE. Try scanimage -L and read the backend's manpage.  
(...)  

```

scanimage comes up with a memory insufficiency:

```
jan@Lenovo-ideapad-100-15IBY:~$ scanimage -L
Error my backend :  out of memory
device `pixma:04A91827' is a CANON Canon PIXMA TS3100 Series multi-function peripheral

```

I don't understand the 'my' in 'my backend' but anyway it seems that I have an insufficient RAM memory. Ubuntu 20.04 on my laptop indicates I have 3.7 GB RAM - that equals 4 GB as indicated on the hardware - which is the minimum necessary according to ubuntu.com.  

Might that be the problem?  

I am using a Lonovo laptop: Lenovo-ideapad-100-15IBY as you can see in the Terminal prompt but I tried to make a scan also on my Toshiba laptop, also using Ubuntu 20.04 fresh installed and 3.7 GB RAM available according to system settings 'About'. No luck here either, but no memory error reported:

```
jan@Toshiba:~$ scanimage -L
device `pixma:04A91827' is a CANON Canon PIXMA TS3100 Series multi-function peripheral

```

Reading the manpage of 'backend' the suggestion is that 'backend' is not implemented in the scangearmp2 software, or something. That would be a bug. How should I report this?