In case it is useful for anyone here, I created a Nuke implementation of the ACES Output Transforms matching the ACES 1.2 AMPAS CTL.
There are presets for most of the aces 1.2 view transforms, and each “module” of the output transform is customization so you can poke around and see how each piece works.
While I had my hands deep in the innards of the CTL code, I came across a question I have been wondering about - perhaps someone here would have an answer / clarification / or more information:
The older ACES 1.0.3 SDR view transforms use two steps for the tonescale / tonemapping component of the output transform: Step 1 is to transform from scene linear to OCES using the segmented_spline_c5 algorithm. Step 2 is to modify the knee and shoulder with the segmented_spline_c9 algorithm, then map to display linear.
For the newer HDR view transforms, these two steps are combined into one step: RRT+ODT, also referred to as an OutputTransform. This uses the newer Single Stage Tonescale (SSTS) algorithm.
While developing this tool I was trying to match the older segmented_spline_c5 + segmented_spline_c9 tonescale using the newer SSTS algorithm but I was not able to find parameters that exactly matched new to old. I got pretty close but not exact. Using the SSTS tonescale, the default values give you an image that has a slightly softer highlight rolloff in the shoulder. (which I personally actually prefer the look of, as it looks closer aesthetically to many film show luts that I have seen over the years)
With all that info layed out, my question… First: is it possible to exactly match the older tonescale using the SSTS algorithm, if you override the SSTS parameters in just the right way? And two: is it part of the plan for the future to use the SSTS algorithm for the SDR output transforms?
Just too curious for my own good Thanks for your help!