I work on a number of TV shows, most shot on the Alexa and a few shot on the RED. The footage comes to me in some form of gamma color space and I need to color correct the footage to linearize it. Basically this involves setting new white and black points and adjusting the gamma. This increases the contrast and makes it look similar to what the final color will be. What’s important is that I am not the colorist and can’t know the future–that is to say, what color choices the producers will land on. Therefore, I need to work with a neutral color correction of my own design, (because one should never do color operations on gamma or log color space images) and then pass my finished, approved comp back to editorial, matching the exact color of the original footage.
In Nuke, there is a “reverse” checkbox in the grade node which makes this simple. It is there because this is a common practice. Reversing a color correction doesn’t seem to exist in Blender’s compositor and it looks like I will have to manufacture it myself with a custom node group using math (which I can do but am not the best with) and would welcome any help.
I was told by Ton himself that the nodes have an input color space to do color management, but after some investigation, this doesn’t work in common VFX compositing workflows. The LUTS used by the DIT on set do not travel with the prores 4444 Quicktime files I often get. In other words, the Quicktime was recorded in log color space but loads as sRGB. This cannot be avoided. If using a RED camera, blender doesn’t even support .R3D files (AFAIK), which can embed LUTs, so the .R3D files must be converted to a file Blender can read and will lose the color correction they were looking at on set. (Unless I convert them with the LUT applied in Red CineX as float .exr files). Not to mention, I want control over how the file looks when linearized. I don’t wan’t Blander making that decision for me.
Here is the pipeline:
Receive the footage from the client and import it into the comp.
Linearize it. That is to say apply a color correction taking it from milky, log color to higher contrast, proper white and black levels.
Execute the comp. This is where you would put in your CG elements, key your green screens, do color corrections to elements that are not your BG plate, etc.
Reverse the color correction of your entire comp to match the original look of your BG footage in step 1.
Return comp with the original milky, gamma color to client to be cut into the edit and eventually colored in DaVinci or whatever grading software they are using.
Final note: It is critical that the entire color pipeline be executed in 32 bit float. Otherwise you will clip your whites and blacks at step 2 and never get back to the original.