Convert video to 10 bit images
To preserve as much detail as possible, convert it to a 16-bit TIFF, eg:
ffmpeg -i "DF HDR Sampler.mp4" -pix_fmt rgb48 _Frames/out%05d.tiff

Example from Digital Foundry's GT Sport HEVC 10-bit H.265 video at https://www.digitalfoundry.net/2017-10-17-free-download-gran-turismo-sport-hdr-sampler

Before (16-bit TIFF framedump, untouched, to 8-bit ProPhoto RGB)  



After (16-bit TIFF framedump, HDR to SDR in Photoshop(eg. Curves and Vibrance adjustments), 8-bit ProPhoto RGB)