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! ^^

(Image 2 doesn’t open.)

If a measure on concentration is the portion of white pixels inside the circles, you can treshold() the circle images to make them totally black and white, and then countNonZero() to get the number of white pixels.