Dimming SDR white for an external HDR display?

[gregbenz]

One of the native features of Windows for external HDR monitors is an "SDR brightness slider", which modifies the EOTF from PQ to allow the user to adapt the SDR brightness. This is very helpful for a number of reasons, especially when trying to dim the display down to a level suitable for productivity work in a darker room.

MacOS only supports control of the brightness for Apple displays, and 3rd-party monitors do not have brightness controls on the monitor when in an HDR mode.

Does BetterDisplay have any mechanism to help control SDR brightness while still using an external monitor in HDR mode?

[waydabber]

Brightness control in HDR is display dependent. Some HDR displays allow DDC brightness control (for example my GP27U mini-LED display) in HDR mode, others don't (reference displays certainly shouldn't). The app can't easily move the around the SDR peak brightness around on a third party HDR display like Windows can or the way macOS can do on Apple XDR displays (where the SDR can be anywhere between 100 and 500/600 nits and the EDR range will adapt to that baseline). What it can do is to extend the SDR range up until peak HDR via various techniques (this is platform dependent) or apply dimming. Some techniques will clip HDR when this is happening, others leave HDR content alone (this is also platform dependent). There is some info about this here (focusing more on the extra brightness side of things, not dimming).

https://github.com/waydabber/BetterDisplay/wiki/XDR-and-HDR-brightness-upscaling

[modest]

Is the 500 nit SDR limit derived from the display metadata (EDID) or is it hard-coded in the OS? Sequoia's handling of non-Apple displays is better than before, but SDR content in HDR mode is still much dimmer than SDR-only mode (Samsung QN90B).

It seems like Apple continues to restrict SDR brightness upscaling as part of the "strategy tax" to make HDR look better.

[waydabber]

Seems to be hardcoded. 500 nits should be reasonable for a computer monitor (matches most MacBooks and Apple Displays). Some TVs and mini-LED displays depending on how they are set up can produce higher peak brightness in SDR than this though.

[modest]

Hm. Apple stuck to 500 nits SDR for their own displays for a while, but it's becoming clear that this was just was a point-in-time thing.

• The mini-LED M3 MacBook Pro raised its SDR limit to 600 nits (but capable of sustained 1000 nits HDR at 100% window)
• The dual-OLED iPad Pro raised its SDR limit to 1000 nits (equal to its sustained HDR 100% window)
• The OLED iPhone 13 Pro and later raised its SDR limit to 1000 nits (though capable of sustained 1600+ nits HDR at 100% window)

For Apple's own displays, there are some charitable explanations for limiting SDR brightness:

• (1) Power consumption on portables (at 1000+ nits with BetterDisplay's XDR upscaling, the 16" MBP can easily consume 30 W+)
• (2) Limiting the effects of full-array blooming & color distortion artifacts that appear at higher contrast levels
• (3) Reserving headroom for predictive uniformity compensation (i.e. preventing burn-in)

But there's also a fourth "strategy tax" motivation:

• (4) Restricting the highest brightness levels to HDR only so that stretched SDR content doesn't look "better and brighter" than HDR content

The shady thing is that that, for this Sequoia feature with third-party external displays, this 4th motivation for limiting SDR brightness to 500 nits is the only one that is applicable.

The concern is real; consumer TVs have been stretching the hell out of SDR brightness (from 100 nit SDR reference to their 1000+ nit limits) and gamut (from BT709 reference to their native gamuts) for years. This leads to an oversaturated SDR image that has brighter midtones and shadows than correctly-rendered HDR content... and many users like that, so much that they complain about HDR content looking worse.

As a user, though? I use an external 4K mini-LED display @ 1x native res in a well-lit room with giant windows. I need my 700+ nits to achieve appropriate visual contrast. I also want to be able to view HDR content with accurate color and luminance. It's a shame that macOS still won't let both of those happen. So, I hope that you figure something out :)

Please like and subscribe.

[waydabber]

Right. It might be possible to change the SDR brightness level for third party displays - honestly I did not investigate this angle at all (all mini-LED displays I have simply allow full brightness in SDR anyway + do some constant adjustment in HDR mode to "enhance the image" which is annoying for desktop use so I really put the display into HDR only when I watch HDR content full screen). You can use HDR upscaling with the app, but as you mention, this will clip HDR content so it is not ideal when you want to have HDR content on screen as well.

[gregbenz]

A brighter SDR will certainly deviate from creative intent of content, adversely affect battery life, and may (I don't know) affect longevity of the display.

However, I would find it occasionally helpful to have brighter SDR for productivity work on a laptop - as I occasionally find myself in bright shaded environments or with lights reflected on the display and find that 500-600 nits SDR can be somewhat hard to read. Most often this is when traveling and using the laptop outdoors (in shade, but the ambient light is still quite bright and I might even be wearing sunglasses). I do not see this being something I would personally use for an external monitor, just for a laptop where my ambient light is much more variable and harder to control - but I imagine others may have brighter ambient conditions around an external monitor.