overnits

Why

The display of a 14” or 16” MacBook Pro peaks at 1600 nits, but macOS caps ordinary content at 600. The rest is reserved for HDR video. Outdoors, or simply with a window behind the screen, that headroom is missed. Paid apps know how to unlock it. I wanted to understand how, and to see whether it fitted in a single file.

How

Two stages.

First, a one-pixel window in the corner of the screen displays HDR content. macOS then raises the backlight, whatever the size of the content.

The display gamma table is then read back, multiplied by the chosen factor and written again. While the panel is in HDR mode, values above 1 address the range beyond SDR white. Gamma acts at the very end of the display: everything is brightened the same way, video, cursor, full screen. Public APIs only, no permission to grant.

The method comes from BrightIntosh, by Niklas Rousset. That is the one to use for multi-display, sleep and battery. overnits is an independent rewrite, deliberately minimal, under the same licence (GPL v3).