Scanned images are deteriorated by compression artifacts with Brother MFC-L2710DW

[Karl Kastner]

I have a Brother MFC-L2710DW printer with integrated flatbed scanner. There are two major problems when scanning with sane:

The first problem is that the quality of all scanned images is very poor due to 8x8 pixel JPG compression artefacts. The root coarse seems to be the backend, as the result is the same independently if the image is acquired through xsane or scanimage.

The second problem is that sane only scans up to 300 dpi. 1200 dpi is not offered at all and for 600 dpi the error message "Failed to start scanner: Invalid argument" is displayed. Interestingly the message is displayed after the scanner has completed the scan, but the data seems not to be received or understood by sane.

The scanner works fine in Ubuntu with the commercial software vuescan, which rules out a firmware bug or malfunctioning of the scanner itself.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: libsane 1.0.29-0ubuntu5.2
ProcVersionSignature: Ubuntu 5.11.0-16.17~20.04.5-generic 5.11.12
Uname: Linux 5.11.0-16-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sat Aug 21 23:00:21 2021
InstallationDate: Installed on 2015-11-05 (2116 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
SourcePackage: sane-backends
UpgradeStatus: Upgraded to focal on 2020-09-10 (345 days ago)
modified.conffile..etc.apport.crashdb.conf: [modified]
mtime.conffile..etc.apport.crashdb.conf: 2019-03-07T14:28:39.455024

[David Ward (dpward)]

What happens if you run "scanimage" from the command line, and use one of:
  --format=pnm
  --format=tiff
  --format=png

Does the image still have artifacts?

[Karl Kastner (kastner-karl)]

The problems has disappeared. xsane and scanimage work fine now:

- The xsane gui offers scan resolutions up to 9600 dpi
- No compression artefacts, tested with 1200 dpi
- No error messages are displayed by xsane

The reason is a mystery, neither any sane nor brscan related packages seem to have been updated in the meantime, but the options xsane offers and how it behaves are clearly different. I can't remember having touched any scanner related configuration since then.

However, even though there is only one device, which is connected via WLAN, xsane offers me two "devices" upon startup:

Brother *b20210821 MFC-L2710DW [brother4:net1;dev0]

and

ESCL Brother MFC-L271 flatbed scanner [escl:http://192.168.178.26:80]

With the first "device", "Brother *b20210821", scanning works fine, with the second device "ESCL Brother MFC-L271", the old problems occur.

[Karl Kastner (kastner-karl)]

Note that the bug is still effects 20.04 and 22.04. I coincidentally worked on my 18.04 partition when testing and responding to David and thus thought it was fixed, as scanning works fine in 18.04.