Thanks again for your help, but I’m afraid I’m probably not explaining myself clearly enough.
The final grade on the film will be done in Resolve with Aces cct.
On set, we will be very limited in terms of DIT. We’ll have someone backing up cards, but no on set grading or anything. So what we want is a LUT we can load onto monitors (a SmallHD 502 in this case) that will give a reasonable (all things considered, especially the budget) approximation of the final ACES “look” whilst on set.
What I planned to do was create a LUT that would stack the effect of the camera IDT, the RRT and a REC.709 ODT into one 3D LUT, I’ve done this in the past with other cameras with OCIO. I understand that the RRT is somewhat subjectively designed, and by and large like how it looks. I just wanted something that would show how footage will look after ACES colour management, but without a custom grade.
Unfortunately, although Blackmagic have evidently created IDTs for all their cameras, they are hidden away inside Resolve, so I can’t access them. For whatever reason, they won’t publish them openly.
To get around this, I planned to load the OCIO LUT Image into Resolve, tell it it was Ursa footage, export it through the RRT and ODT, and use it to create a LUT. This has worked up to a point, but if I then apply that LUT to footage (in Resolve) it gives a different result to running the same clip through ACES colour management in Resolve; this is the tonal shift mentioned.
I tried creating the LUT as a 64x64x64 cube in case the shift was simply due to a lack of precision in a monitor sized LUT, but got the same result. Once I’ve got the LUT worked out, I’ll make one the appropriate size for the monitor.
So, does anyone have any idea what is causing the colour shift and how I can get round it? I’m assuming it’s some quirk of Resolve’s. Alternately, are there any decent home made IDTs out there for Blackmagic’s 4.6K sensor. Or does anyone have any contacts at Blackmagic who might be willing to discuss making the IDTs public?
We start shooting on Tuesday.