Backlight Brightness Fun

GNOME Power Manager trunk now does more with your backlight:


You'll notice the interactions are both subtle and complex.

Three significant new features:

  • Actually using the ambient light sensor on the Macbook Pro
  • Optionally using an integrated laptop webcam to sense ambient brightness
  • Learning when to dim on idle.

Using the webcam is more sane that you think. Using gstreamer, the webcam is turned on for about 300ms every minute, and a picture is taken. The luminance is used to find the ambient brightness. This means we can dim the screen when walking into a dark room, and also make the screen brighter when the sun comes out of the clouds. This uses about 5mW extra power, but saves many times that if we can automatically reduce the panel brightness by 15%.

Also in trunk we listen to GNOME Screensaver for the SessionPowerSave message which only fires when the session is momentarily idle. If on battery we reduce the brightness of the backlight and the split-second the session become non-idle (when the user touches the mouse or presses a key) the brightness comes back to what it was before. By default this timeout is 30 seconds, but if the backlight dims, and you immediately make the session non-idle, g-p-m learns that it should make the timeout longer.

Also, I'm now working for Red Hat UK for a couple of months during the summer. Without the help of Red Hat, and the flexibility to sometimes work on upstream stuff, none of this new coolness would be possible. Thanks.

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Richard has over 10 years of experience developing open source software. He is the maintainer of GNOME Software, PackageKit, GNOME Packagekit, GNOME Power Manager, GNOME Color Manager, colord, and UPower and also contributes to many other projects and opensource standards. Richard has three main areas of interest on the free desktop, color management, package management, and power management. Richard graduated a few years ago from the University of Surrey with a Masters in Electronics Engineering. He now works for Red Hat in the desktop group, and also manages a company selling open source calibration equipment. Richard's outside interests include taking photos and eating good food.

One thought on “Backlight Brightness Fun”

  1. > Optionally using an integrated laptop webcam to sense ambient brightness Huh. Don't they all do automatic exposure/brightness correction, and wouldn't that confound your test? – Chris.

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