Hi i am working on a project from with i receive EXR files in ACES linear and i need to add a LUT to match the Rec709 reference. my workflow is as folows bur i am nor being able to have a perfect match:
Working space: ACES2065-1
Plate IDT: ACES2065-1
Colorspace transform: from ACES2065-1 to S-Log3 S-Gamut3.cine
LUT in working space ACES2065-1
Colorspace transform: from ITU Rec 709 to ACES2065-1
Reference IDT: ITU Rec 709
What am i doing Wrong.
Not sure what you mean by “Reference IDT: Rec.709”. Do you mean you are using a Rec.709 Output Transform, and are therefore are trying to use an inverse Rec.709 Output Transform to get the Rec.709 output of your LUT back into ACES so it ends up back at the same Rec.709 after the Output Transform?
If so, you need to use an OCIO Display node with invert direction checked, rather than an OCIO ColorSpace node. In OCIOv1 you could use a colour space transform, but in v2 you need to use an actual Display node in inverse mode.
I just realised, you mean you are using the Rec.709 IDT for the reference image with the LUT applied. In fact you need to apply an inverse ODT to that one as well, so when the forward ODT is applied it looks the same as the original. That means not applying any transform in the read node by e.g. checking “Raw Data” and applying an OCIO Display node after it with “invert direction” checked.
Doing this in an OCIO File Transform node, when your working space is set to ACSE2065-1, will ensure that no unwanted transforms are applied either side of the LUT. But choosing Utility > Raw has the same effect, and may be more obvious to somebody else looking at your node tree.
Here is a simple node tree replicating what I think you are trying to do, but using a LogC4 image and ARRI LUT:
