GoKawiilAs an exception to my usual posts, this time I’ll write about a feature that’s already released. Since Plasma 6.6, you can enable automatic brightness in the display settings… let’s take a look at how it works, and why it took so long to make it happen.
The hardware
This is where the problems start - most laptops unfortunately don’t come with a brightness sensor, and there’s effectively no monitors that have a built-in sensor either (let alone one that can be accessed by the connected PC).
While it’s possible to buy or build a brightness sensor that connects via USB, brightness control for external monitors usually has limitations in how often we can safely adjust the brightness… So for quite some time, there was noone working on Plasma that had the combination of hardware, motivation and knowledge to do something about it.
Luckily, the Framework Laptop 13 comes with a brightness sensor, so on the hardware side I was all set:
The software
Making automatic brightness do something is easy, but making it work well enough that you actually want to use it is a very different story.
My first approach was to assume brightness of the display should scale linearly with environmental brightness. I tried this, and it was sort of usable, but just not good enough. There’s three problems with it:
the brightness setting sadly does not linearly control display luminance. 0% is generally not “off”, and sometimes firmware or drivers make the curve non-linear to make the brightness more “intuitive” in order for automatic brightness to be easy to use, we can’t expect the end user to configure an equation for their system. We need to automatically detect what they’re doing, and configuring two parameters based off one brightness slider is a challenge the best brightness curve isn’t necessarily linear. Depending on your personal preferences and how reflective your display is, you might want to keep brightness a lot higher in bright environments than in dark ones, or vice versa.
So a different approach was needed. I looked a bit at other operating systems for inspiration, and from the UX side I definitely wanted to copy Android: You use the brightness slider however you want, and the system should try to replicate what you do on its own. On the implemtation side however, I only saw claims that it uses machine learning, so that wasn’t exactly helpful.
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