Finn Jäger has spent some time in making a sleeker tool for all you VFX nerds out there, it takes a HEIC iPhone still and exports a Multichannel EXR – the cool thing is it also converts it to acesCG and it merges the SDR base image with the gain map according to apples math hdr_rgb = sdr_rgb * (1.0 + (headroom – 1.0) * gainmap)

https://github.com/finnschi/heic-shenanigans