Control Dailies VS Cortex - Noisy blue channel blacks

I’m on my 3rd day of dailies for my new season of a show. My DP for this job has always been very consistent with his shooting preferences. He shoots Alexa. I’ve been noticing my blacks have been a bit noisier than the last 2 years when I did the show on Control Dailies. I checked with a fellow colorist who was also working on a show shooting Alexa, and of course using Cortex. I noticed the identical problem in his room. Entirely different show / crew, even a different LUT, same exact issue. I wouldn’t call this problem terrible, I would categorize it as simply “noticeable” to a trained eye, probably not something that would normally get flagged. I only noticed it because I’ve been on this specific show for some time. I did a test with my final colorist using the exact same footage and applying the exact same LUT (AlexaV3_K1S1_LogC2Video_Rec709_EE_lustre3d.lut) and there’s definitely a noise difference. What I saw on his Lustre was closer to what I saw last year on Control Dailies. Since it’s not a problem on his end, I don’t think this is serious by any means, but worth at least inquiring about.

That’s interesting.

Here’s a shot in the dark:

My best guess at the moment is that this is caused by the fact that Cortex’s image processing pipeline does all of its computation in 32bit floating point, whereas Control Dailies did most of it in 10 bit integers.

So you may actually now just be seeing some of the noise that is really there, but which gets clipped when it gets processed with less precision.