Glad to see everyone’s efforts here!
I haven’t been able to experiment as much as I had liked to, but would anyway like to share my latest efforts towards the guard rail, especially the “high side” compensation. It’s in the format of a standalone Python script which can process linear EXR files. Hope someone finds this useful. Happy to answer your questions as well. The high side compensation equation I use has been found by experimentation, so unfortunately there’s no derivation for it from first principles at this point.
guard_rail.py (4.4 KB)
This has the low side compensation that has been introduced by Troy here a long time ago, without the “reflection” of negative luminance that was experimented here some time ago.
It has a tunable parameter for the high side compensation that you can give as the second command line argument. It controls the tradeoff between chrominance and luminance for values above the medium upper bound. Here are some examples with this parameter at 0.8, 1.0 and 1.2 in this order. This doesn’t have any image formation process, so this is just the guard rail.
This sweep is Rec.709.
