> If the brightness cap of the HDR image is full SDR brightness, what value remains in HDR?
If you set #ffffff to be a comfortable max, then that would be the brightness cap for HDR flares that fill the entire screen.
But filling the entire screen like that rarely happens. Smaller flares would have a higher cap.
For example, let's say an HDR scene has an average brightness that's 55% of #ffffff, but a tenth of the screen is up at 200% of #ffffff. That should give you a visually impressive boosted range without blinding you.
Oh.
I don't want the ability for 10% of the screen to be so bright it hurts my eyes. That's the exact thing I want to avoid. I don't understand why you think your suggestion would help. I want SDR FFFFFF to be the brightest any part of my screen goes to, because that's what I've configured to be at a comfortable value using my OS brightness controls.