If SDR is 32bpp, why can't HDR just simply be 64bpp? Or, 128, if that somehow isn't enough? I'm sure I'm misunderstanding but it seems like the whole thing has become very complicated with a lot of competing standards and not a lot of working together towards something simple that works for everyone.
SDR is 24 bit and HDR is 30 bit. However there seems to be some brightness metadata required to specify how bright 1023 is. What baffles me is that there seem to be five or six different standards for this metadata.