Converting a custom LUT into Cineon LOG format

Hello there every one.

I'm having an issue that I can't for the love of me figure out. I have created some looks that I would like to reuse for some upcoming projects. I'm working with BMP4k B-RAW footage. The problem I face with my looks is, that I lose a lot of "realestate" when I export them as a 3D cube. I know I could apply it as a powergrade, but my idea is, that if I can somehow make the LUT work with the Cineon LOG, it will be easier to match it with every exposure and different cameras (since all the footage I'll be working with will be transformed into the same LOG curve).
The way I try to make it work was to create 2 CST nodes, each at the start and end, do my LUT correction in between those CST nodes and then to remove the CSTs and simply use what's left on the inside. So after I export the LUT, I can simply do the same on a different video, create 2 CST nodes and convert the footage to Cineon FIlm LOG, put the LUT between them and start grading from there. But when I do that even on the same video I graded it on, the results are completely different and for some reason the contrast just doesn't apply at all.
It sucks that I can't simply export the information of the CST into the .Cube.
I just want the LOG curve to be mathematically correct, so I don't have to "guess" the curve. Would make my life a lot easier for the look creation as well.

Am I approaching this the wrong way? If so, do let me know please.

Thanks for the answers in advance,
Dawid


P.s. If any one does have a Cineon to Rec.709 LUT or an alternative to the CST, do let me know please.

Your approach sounds correct. Are you perhaps working in a colormanaged workflow? Maybe that messes the data up a bit? I did create a few luts myself both including and without CSTs to go from log to 709 or just apply certain looks in log space and never really found unexpected results outside the default inaccuracies you can get by saving as a cube.

On the other hand, if the created lut is purely living inside your workflow and inside Resolve why not save it as a grade instead. You could just create a compound node from it with or without the CSTs so it's virtually the same as a lut as it's only taking up 1 single node in the tree.

Your approach sounds correct. Are you perhaps working in a colormanaged workflow? Maybe that messes the data up a bit? I did create a few luts myself both including and without CSTs to go from log to 709 or just apply certain looks in log space and never really found unexpected results outside the default inaccuracies you can get by saving as a cube.

On the other hand, if the created lut is purely living inside your workflow and inside Resolve why not save it as a grade instead. You could just create a compound node from it with or without the CSTs so it's virtually the same as a lut as it's only taking up 1 single node in the tree.

Hey Shebanja,

the main reason I want to have the LUT fit a LOG file is for consistency. It requires a lot less tweaking, because the transformation is always going to be same, no matter the input. So if I have a scene which is a bit darker and then a scene which has more dynamic range, when converted to the same LOG, the LUT will have the same effect on both the images without having to do major rework. The point of the LUT is also duo to the fact that some of the looks are just ridiculously big, meaning there are around 5-7 compound nodes with each having around 10 parrallel nodes. And if I were to have to go back and retweak each and every one of them for every shot that is exopsed differently, that would just be really inefficient and to be quite frank I don't remember all of them by heart
And having a mathematically corect LUT will simply mean that all colors and luminance values will be transformed correctly into Rec.709 so I won't have any nasty surprises.
And to answer the question I'm working in Davinci YRGBCM but most of my grading is done in Cineon Film LOG.