Open remia opened 6 years ago
@remia good catch! Nobody else caught this is the beta testing phase but it should definitely be done in a consistent space.
Like the "surround" module, the "white point sim" module is also very much a "placeholder" right now and will definitely need updating with a more robust algorithm to allow for simulation of any white point from any other white point (not just the few hard-coded options currently in there). There are comments noting this in ACESlib.OutputTransforms.ctl
. This is on the work items for a future release of ACES that more fully utilizes the parameterized output transforms.
I will review the options and push a fix to the hotfixes branch. We will then determine whether to issue a patch release or carry the fix along on the hotfixes branch for now.
Thanks @scottdyer, yes I saw the comments in the code and there is still some work to do as you say to support other whitepoint than D65 / DCI. I think there were also discussions on wether or not this adaptation needs to be dependent on the peak white luminance (current coefficients were derived for SDRs content I think ?).
I guess the compatibility issues are relatively minors because none of the existing HDR ODTs seems to be using the white point simulation transform yet.
Not that it really matter at the moment, because every HDR ODT target a D65 calibrated display, but I also noticed that in case we don't want to use the D60 simulation, a CAT from D60 to D65 is hardcoded : https://github.com/ampas/aces-dev/blob/master/transforms/ctl/lib/ACESlib.OutputTransforms.ctl#L138
I noticed that the standard cinema range output transforms perform the scale / rolloff highlight (as part of the white point simulation) in the rendering space (AP1, not pre-compensated) but the new HDR ODTs do this in the display primary space (not pre-compensated). Is there a reason behind this ?
I'm not really sure what happens exactly yet but when using the SSTS methods to design new HDR ODTs using Gamma EOTF, the results seems a bit off. When I move the D60 Sim to be done in AP1, things start to look better.
Hope this make sense.