Is it possible to turn off EDR on Apple non-XDR displays?

[Vvorcun]

Hi! First of all - huge thanks for your work! This issue is related to displays like Apple Studio Display and built-in display on MacBook Air M1. On Intel Macs there's "Allow extended dynamic range" in settings, while on Apple Silicon there's no native way to disable EDR. As far as I understand, Apple's EDR gets turned on when app with wantsExtendedDynamicRangeContent set to true is started - as long as maximumPotentialExtendedDynamicRangeColorComponentValue is higher than 1.0 (on MacBook Air M1 it is set to 2.0). There's a setPotentialHeadroom symbol on SkyLight.framework, though my knowledge is kinda limiting me - I wasn't able to find a proper solution yet. So... Is there a way to use setPotentialHeadroom symbol from SkyLight.framework (or something else) to write maximumPotentialExtendedDynamicRangeColorComponentValue (since I believe that's how EDR gets turned off on Intel Macs)?

[alin23]

Hi @Ferbez thank you for the kind words!

Not sure if this would work, but you could try exploiting one of the macOS bugs that has been wasting weeks of my time in Lunar.

Basically, when any app that uses the Gamma API is running (e.g. CGSetDisplayTransferByFormula) then EDR doesn't work anymore.

Simplest way to try it is to use something like Black Light.

Open an EDR photo or video, then just launch Black Light and you should see the EDR highlights normalize. Here's a demo video where I point to a whiter than white region that becomes normal white after launching the app:

IMG_0715.mp4

If this works, then I can help you with a command line binary that will simply read the current gamma then do nothing for the rest of its runtime. Simply by having it running should stop EDR from functioning.

[Vvorcun]

Looks like macOS only disables actual HDR when Gamma API is running, since on my MacBook EDR is still present even when Black Light is running (I also tried f.lux - just in case).

IMG_6818.mp4

If only it was possible to just disable EDR via settings, just like on Intel Macs...

[alin23]

I looked into what that "Allow extended dynamic range" checkbox does which apparently is only available in Monterey. It seems to call CGSEnableHDR.

I've added a small utility here that you can use to try that API: 9f21d48

[Vvorcun]

I also thought that this "Allow extended dynamic range" may not be available on Sonoma, but it looks like it is only absent from Apple Silicon Macs - as seen on waydabber/BetterDisplay#2742. And about CGSEnableHDR - sadly it still doesn't disable EDR