I am currentyl experiencing this in RV 4.0.12 but already encountered that problem with RV6+ at another company.
What I want to do is go from Linear to the Alexa standard 3D LUT (AlexaV3_EI0800_LogC2Video_Rec709_EE.cube) in one .csp LUT.
Therefore I am using a 10 bit ShaperLUT with the 3D LUT on top (32 res).
The LUT has been generated with OCIO (ociobakelut) but similar problems arised with other LUT sources as well.
The result looks fine in Nuke with either a OCIOFileTransform or Vectorfield node, but using this as a File LUT in RV crushes the blacks.
It seems like its working with a shaper LUT up to 8 bit but shadows fall apart with the attached 10 bit version.
Another workaround is to use 2 csp LUTs whereas the shaper LUT part is skipped and all transforms happen in the main part (lin 2 logC in LUT1 and logC to ARRI rec709 in LUT2). But this is only a workaround but no real solution to the problem I'm having.
Attached you can find:
- lut_compare.png => Shows the comparison between Nuke und RV
- darkexample.exr => stopped down Alexa sample footge, linear float
- linear_2_Alexa3D.csp => The LUT mentioned above
Thank you in advance for any feedback that might come.