Comment by jeroenhd

I don't think any OS exposes an API for this. There's a Linux tool I sometimes use to control the brightness of my screen that works by basically talking directly to the hardware over the GPU.

Unfortunately, EDID isn't always reliable, either: you need to know the screen's orientation as well or rotated screens are going to look awful. You're probably going to need administrator access on computers to even access the hardware to get the necessary data, which can also be a problem for security and ease-of-use reasons.

Plus, some vendors just seem to lie in the EDID. Like with other information tables (ACPI comes to mind), it looks almost like they just copy the config from another product and adjust whatever metadata they remember to update before shipping.