[Lenovo ThinkPad T510] Backlight brightness control regressed from logarithmic scale to linear scale
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux (Ubuntu) |
Triaged
|
Low
|
Unassigned |
Bug Description
After upgrading from kernel 3.15.0-6 to kernel 3.16.0-3, the backlight became very difficult to control near the low end of the scale. The lowest setting now turns the backlight completely off, but the second-lowest setting is too bright. Meanwhile, the difference between the highest several settings is nearly imperceptible.
This happened because /sys/class/
I measured the exact relationship between the two scales on kernel 3.15 and plotted it with the intel_backlight values on a logarithmic scale (see attachment). You can see that the function intel_backlight = 60*(4/3)
It’s well known that perceived brightness varies logarithmically with physical intensity (Fechner’s law), so it’s no surprise that the acpi_video0 scale was more useful. Either the kernel or GNOME should adjust the intel_backlight scale to logarithmic.
(I’m running utopic on a Lenovo Thinkpad T510.)
ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: linux-image-
ProcVersionSign
Uname: Linux 3.16.0-3-generic x86_64
NonfreeKernelMo
ApportVersion: 2.14.4-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/
CurrentDesktop: GNOME
Date: Sat Jul 12 07:06:12 2014
EcryptfsInUse: Yes
HibernationDevice: RESUME=
InstallationDate: Installed on 2010-12-05 (1315 days ago)
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20101202)
MachineType: LENOVO 4313CTO
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=
RelatedPackageV
linux-
linux-
linux-firmware 1.132
SourcePackage: linux
UpgradeStatus: Upgraded to utopic on 2013-10-31 (254 days ago)
dmi.bios.date: 09/26/2012
dmi.bios.vendor: LENOVO
dmi.bios.version: 6MET92WW (1.52 )
dmi.board.name: 4313CTO
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.
dmi.modalias: dmi:bvnLENOVO:
dmi.product.name: 4313CTO
dmi.product.
dmi.sys.vendor: LENOVO
tags: | added: kernel-bug-exists-upstream kernel-bug-exists-upstream-3.16-rc6 |
Changed in linux (Ubuntu): | |
status: | Incomplete → Confirmed |
This change was made by a bot.