background-noise | A simple white noise app that plays in the background | Android library

I'm new to OpenCV and tried multiple things but still have some problems. I have images like this:

In the center there is a cluster (hard to see). I want to find those clusters and count them. I use cv2.findContours for this and this already works very good for images where this clusters have a good brightness and the background noise is not too strong.

With images like this, where the cluster is very dark or images where the background noise is very strong and looks very similar to the actual cluster, i have problems detecting them.

So what I would like to do now is remove the background noise, so that only the clusters are left. Then I could increase the brightness of the image and (I think) it should be easier to identify those clusters.

The background noise can very a lot! The image above is a sample, where there is not that much background noise, but it can be a lot worse. I have images where I know, that there are no clusters in it (negative control). Everything in there is just the background-noise. So my idea was to find the dominant color in this negative control: