Question: Is it possible to use EDID to spoof a reference display mode

[AndrewKeYanzhe]

I am using an MSI MP273U HDR monitor and the macOS 15.6 system tone mapping for HDR videos makes it darker by one stop as compared to the internal display.

This only happens for videos, but not UI.

With the MBP 16 internal display's reference mode, HDR videos in QuickTime will track the EOTF correctly.

So I'm wondering if it's possible to spoof the EDID so that macOS think that this MSI display supports a reference mode.
Here are the screenshots. Note that the screenshots appear dark due to tonemapping of the screenshots. But the relative brightness between SDR UI white and QuickTime is still visible.

MSI

MBP 16 internal

This is the test pattern, feel free to download and view in QuickTime:

100 203 nit.zip

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Additional notes, evaluated on MBP 16 internal screen:

1. Interestingly, when I embed the video in the Github issue, it becomes darker by 1 stop (203 nits PQ [media] = SDR white) in Chrome
2. But when I play the file using Chrome directly (rename to mp4), it does not become darker by 1 stop (so 100 nits PQ [media] = SDR white).

100.203.nit.mov

[waydabber]

No, if by reference mode you mean an Apple preset reference mode, that won't work for third party displays. You can however edit the display's EDID and change some luminance related stuff. There are also (undocumented) configuration override options to edit these - I might add these in a future app update.

An example with AW Edit Editor for a display:

[waydabber]

note: these are the related display override options:

DisplayMaxFullScreenWhite
DisplayMaxLuminance
DisplayMinUsableWhite

[AndrewKeYanzhe]

Thanks. I have tried using AW Edit Editor to set maximum luminance and maximum fullscreen luminance to 4000 nits.

I observed that the system tonemapping for HDR videos still reduces exposure by 1 stop.

[AndrewKeYanzhe]

@waydabber do you know if it's possible to create a virtual display that acts as a pro display XDR? I'm hoping that this will enable a reference mode.

I can then mirror my other displays for this virtual reference display

[waydabber]

No, this is not possible. Apple presets require specialized hardware (or display controller) support to work. For the Pro Display XDR preset data is known to be transferred to the display and is carried out by the display itself using specialized hardware and firmware. Later Apple adapted this technology to the MacBook Pro's XDR displays (using different implementation) and then the Studio Displays. No other displays support Apple presets.

[AndrewKeYanzhe]

@waydabber I see, thanks for the info. I'm wondering if it is possible to change the MBP 16's resolution from 1728x1117 (HiDPI) to 1920x1080 (HiDPI)?

Also, I'm curious to learn about the XDR implementation, so if you can provide the links to online sources that would be very helpful

[waydabber]

Yes, you can create a 1920x1080 custom scaled resolution, that should work with the 16" MBP. There are no sources afaik. I reverse engineered some of the undocumented APIs to manage presets. It would be great to have these documented properly indeed, but I don't think Apple designed all these to be tinkered with.

[AndrewKeYanzhe]

Thanks so much, I was able to create a 1080p (HiDPI) mode using this setting:

[waydabber]

Right. But I think you should specify 1920x1080, that should create both the LoDPI and HiDPI variant automatically.