Add LogC4 to CSC

[nick-shaw]

ARRI LogC4 has been added to the IDTs, but not to the CSCs. This PR adds it to the CSCs as well, for completeness.

[nick-shaw]

@scoopxyz it would be good to get your eyes on this.

The LogC4 to ACES is pretty much a copy of the IDT, except it uses the same CTL calculate_rgb_to_rgb_matrix function that the other CSCs use, rather than declaring matrix values in the code. The other is the same, but edited to invert things.

[nick-shaw]

In my testing, the use of calculate_rgb_to_rgb_matrix means that there are some very small differences in the lower decimal places between using the IDT and the CSC. But this is the case with all the CSCs. Arguably all the IDTs should use that same function too, so as not to limit the matrix to varying arbitrary precision, as the different manufacturer IDTs do.

[JoshkVFX]

Hi all,

We're currently facing this same thing on a project we're running right now and would love to see this get through

Thanks,
Josh

[scoopxyz]

Hi Nick, just acknowledging that I've seen this but haven't had the time to validate it myself. It sounds logical to continue using the derivation of matrices in the same fashion as the the other CSC spaces.

[CLAassistant]

All committers have signed the CLA.

[scoopxyz]

Just looping back here, although this specific PR may not be relevant now with the repo restructuring, that the implementation looks correct and matches the CTL code provided in the LogC4 white paper.

[scottdyer]

The LogC4 CSCs can be seen here https://github.com/ampas/aces-input-and-colorspaces/tree/main/arri