Threshold to outline cells vs background

Hello All,

I am new to ImageJ, Fiji, R, and QuPath but I am giving it my best shot. I am trying to do a basic cell count for this image that is a stacked image. The problem seems to be the threshold does not differentiate between the lightest cells and the darkest background.

I have attached a sample of the images I am trying to process…
Thoughts or a thread to check out?

Thank you!

Have you tried using Subtract Background? It seemed to help a bit when I ran it on the green channel of the image.