Effective way to automatically set NoiseSigma in BackgroundSubtractorMOG?

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Hey there, I'm trying to make a program that detects people in CCTV footage and I've made a lot of progress. Unfortunately, the amount of noise in the videos varies a lot between different cameras and time of day, so with each of the sample videos. This means that the NoiseSigma needed varies from 1-25.

I've used a fastNlMeansDenoisingColored function and that helped a bit, but the NoiseSigma is still an issue.

Would it be effective to maybe loop through the video once, and somehow get an idea for how noisy the video is and make a relationship for noise vs NoiseSigma? Any ideas would be welcome.