Detecting circles and concentration of pixels in cell plaques

Hello everyone!

Iḿ new to opencv and I have images of cell growth essays, such as these ones:
example 1
example 2

and I need to detect the concentrations of those “dots” that appear inside the circles from little to full.

To do this, my idea was to:

  1. Detect the 24 circles in the image
  2. Identify each of the circles by numbers and letters - such as A0, A1, to A6 then B0 to B6.
  3. Get different numbers for the concentrations inside the circles. → into the unknown here
  4. List the content such as A0: 0.23, A1: 0.52 (and probably export that to a csv).

Up to now I could detect the 24 circles using median blur + hough circle and it seems to be working. I’m moving up to 2, it is kinda fuzzy still - but I couldn’t find any good idea on 3, because people usually detect shades of colors or specific colors and my images are grayscale - also because they usually detect one part of the image and I need to detect a progression.

So, any ideas on number 3?

Also, if you have any suggestion on the 1 to 4 steps, it will also be very much appreciated - since I’ve never done this, that might not be the way to go about it.

thanks in advance! ^^