XDR upscaling brightness decreases somewhat when bright content appears - why?

[sm1therz]

Hi, I'm having the following issue when XDR Brightness Scaling is set to on. All my settings are default.

Issue:

If I do something on a page that causes it's background-color, or contrast to change abruptly — eg, opening a menu, or opening chrome devtools — the XDR Brightness dims slightly.

Then, when I close the menu/devtools (and the page goes back to completely white) the XDR brightness goes back to normal.

These are very faint bumps/dips in brightness. But they are there.

Steps to reproduce:

• Open chrome,
• Go to google.com (or any page with a #ffffff background)
• Open chrome devtools
• If not set already, change the background/theme of devtools to dark
• Repeatedly open and close the devtools
• The page background (that's white) should darken (slightly) when you open devtools. It should then lighten (slightly) when you close devtools.

Machine:

• 2021 Macbook Pro
• M1 Max, 64gb
• macOS Sonoma 14.5

Settings in BetterDisplay:

• all my settings are default

[waydabber]

Hi there, this is because at certain brightness levels the panel uses a technique called ABL (automatic brightness limiter) to limit brightness - when the screen reaches its defined power limit, the controller automatically decreases its brightness to compensate. When XDR upscaling is used and the screen contains mostly bright elements and all mini-LEDS output at full power, this limitation kicks in on M1 and M2 MBPs (and to certain extent M3 MBPs as well even though these have more energy efficient LEDs).

If you are using a mostly bright/white desktop, you might not want to crank up XDR upscaling all the way to max. If you use native XDR upscaling, you can limit max slider brightness to around 1200 nits on the M1 MBP to avoid this issue.