General Workflow before and during DCP-o-matic

[MartinL]

Good Morning,

I was a bit hesistant to register and actually ask here since it seems to be a beginners question.
But then on the other hand I'm not sure where to post it elsewhere and since everything looks fine
until I run it through DCP-o-matic, my mistakes could be just here and not in the steps before.

I am really new to the whole topic. I already have a DCP and I wanted to edit some parts of it.
Hence I opened the DCP in Da Vinci Resolve. Since I also require a ProRes 444 and can't export
this from Resolve I exported it as DNXHR 444 from Resolve, opened it in Scratch and exported it
as ProRes 4444 from Scratch again.

To my understanding I shouldn't have introduced too much compression in those steps.
Resolve handles everything in 32 bit float during the process, so exporting it as 12 bit 444
should be fine. The only change is that I get from XYZ or X'Y'Z' color coordinates to
BT709 color space. And to my understanding DNXHR 444 should be almost lossless as well.

One mistake I noticed before was that DCI spec seems to use a Gamma of 2.6 for DCP while
Resolve uses 2.4 with BT709. So I manually set my project timeline to Gamma = 2.6 which
also made the picture a bit brighter.

I imported the whole thing into DCP-o-matic Creator and wanted to turn it back into a DCP.
For color space conversion I set the import clip Gamma to 2.6 and exported the whole thing
as SMTPE. To my surprise however the resulting output seems to have a lot of compression in the
black levels. Anything that is really dark as hard borders now.

So I guess it was somehow compressed during the conversion process. My question is, where are the major
problems with my workflow? I'd like to keep the original colors but when I set my Resolve project
to XYZ before I start the colors are suddenly all off. So it would be nice to be able to export it
already as XYZ rather than BT709. But since most monitors only use BT709 I don't really care for the lost
colors in that case. Question is rather, does that final conversion back to XYZ in DCP-o-matic cause
any problems?

Sorry if this was answered or discussed before but it consists of many small parts that have to be right
I guess and I'm basically trying to teach all of that to myself without much experience.

Thank you in advance for any help and best regards,
Martin.

[Carsten]

Too much recompression, too many X'Y'Z' -> rec.709 -> X'Y'Z transforms. Probably wrong gamma/inverse gamma application/interpretation.
I guess you should stay within Resolve after you have imported the original DCP, and output to DCP from there (using Kakadu encoder). You can still use that DCP from Resolve in DCP-o-matic without further compression and gamma shift (pass through processing in DCP-o-matic).