reduce backlight brightness sets brightness level incorrectly

[Nicolay Doytchev]

Binary package hint: gnome-power-manager

Hello everyone,

Long Bug Description:

If you turn on Reduce Backlight Brightness in g-p-m the laptop's brightness is supposed to be dimmed by certain amount. That is:
TOTAL_BRIGHTNESS - AMOUNT_TO_DIM = REDUCED_BRIGHTNESS_ON_BATT (1)
This is not how it behaves on this system with Karmic RC + latest updates. Instead the behaviour is as follows:
CURRENT_BRIGHTNESS - AMOUNT_TO_DIM = REDUCED_BRIGHTNESS_ON_BATT (2)
Inherently if we reduce the brightness by MANUALLY_REDUCED_AMOUNT which makes it less than TOTAL_BRIGHTNESS then the new REDUCED_BRIGHTNESS_ON_BATT will be what it is supposed to be minus MANUALLY_REDUCED_AMOUNT.
The actual brightness reduction happens at certain events such as right clicking the g-p-m icon and then Preferences. Also if we disable then enable Reduce Backlight Brightness. It also gets triggered incosistently when resuming from suspend.

Steps to reproduce:

1. Open g-p-m preferences.
2. Go to On Battery Power tab.
3. Increase you screen brightness to maximum.
4. If Reduce backlight brightness is enabled - disable and then enable it.
Else enable Reduce backlight brightness.
5. Decrease your screen brightness by any amount.
6. Disable and re-enable Reduce backlight brightness. This should result in even lower brightness than the current.
7. Repeat steps 5 and 6.

ProblemType: Bug
Architecture: i386
Date: Mon Oct 26 15:28:45 2009
DistroRelease: Ubuntu 9.10
NonfreeKernelModules: nvidia
Package: gnome-power-manager 2.28.1-0ubuntu1
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-14.48-generic
SourcePackage: gnome-power-manager
Uname: Linux 2.6.31-14-generic i686

[Don Cristóbal (doncristobal)]

I can confirm this on Xubuntu Karmic (9.10, final, up to date on 2009-11-16).
Additionally to the procedure that lightrush describes:

A. When the brightness gets reduced after the specified idle time and is reactivated by mouse or keyboard activity, it invariably switches back to a medium brightness - even if before it was on maximum brightness.

B. Sometimes (I don't yet see the logic) this even means that touching the computer after some idle time makes the screen dim down.

I played around with the checkbox "Monitor power management control" and with the slider "Reduce screen brightness when computer is inactive ...", but these symptoms do not disappear. Anything I should test?

[Don Cristóbal (doncristobal)]

Funny. Today it constantly switches to /minimum/ brightness when I touch it after the specified time. And turning off the feature (sliding the appropriate slider to the very left) does not stop this... The logic of these algorythms should be thoroughly checked.

[Fabio Marconi (fabiomarconi)]

Hello
Is this issue reproducible with the latest updates of Karmic
Lucid or Maverick
Thanks
Fabio

[Launchpad Janitor (janitor)]

[Expired for gnome-power-manager (Ubuntu) because there has been no activity for 60 days.]