> To me, HDR feels like the system is ignoring my screen brightness settings.
On both Android & iOS/MacOS it's not that HDR is ignoring your screen brightness, but rather the brightness slider is controlling the SDR range and then yes HDR can exceed that, that's the singular purpose of HDR to be honest. All the other purported benefits of HDR are at best just about HDR video profiles and at worst just nonsense bullshit. The only thing HDR actually does is allow for brighter colors vs. SDR. When used selectively this really enhances a scene. But restraint is hard, and most forms of HDR content production are shit. The HDR images that newer iPhones and Pixel phones are capturing are generally quite good because they are actually restrained, but then ironically both of them have horrible HDR video that's just obnoxiously bright.
>HDR can exceed that
It's not just the HDR content that gets brighter, but SDR content too. When I test it in Chrome on Android, if an HDR image shows up on screen the phone start overriding the brightness slider completely and making everything brighter, including the phone's system UI.
>The only thing HDR actually does is allow for brighter colors vs. SDR.
Not just brighter, but also darker, so it can preserve detail in dark areas rather than crushing them.
you are right but at least in my experience it's very easy for a modern iPhone to capture a bad HDR photo, usually because there is some small strong highlight (often a form of specular reflection from a metallic object) that causes everything to be HDR while the photo content wouldn't need it
It isn't just about the brightness (range).
In practice the 'HDR' standards are also about wider color gamuts (than sRGB), and (as mentioned in parallel) packed into more bits, in a different way, so as to minimise banding while keeping file sizes in check.
"On both Android & iOS/MacOS it's not that HDR is ignoring your screen brightness, but rather the brightness slider is controlling the SDR range and then yes HDR can exceed that"
Doesn't this mean HDR is ignoring my brightness setting? Looking at the Mac color profiles, the default HDR has some fixed max brightness regardless of the brightness slider. And it's very bright, 1600 nits vs the SDR max of 600 nits. At least I was able to pick another option capping HDR to 600, but that still allows HDR video to force my screen to its normal full brightness even if I dimmed it.