How to detect low contrast objects with varying intensity ?

I have an image with more or less circular objects. Majority of the objects are going to be low contrast. Intensity varies from dark to bright, against a noisy background. I can easily detect the comparatively high contrast ones using imfindcircles (separately running with bright and dark ObjectPolarity). However the ones in the center with pixel value very close to background go undetected. Any suggestions please?

Answer 1

[Arun Mathamkode]

Detecting circles or shapes rely on the quality of the image gradient we can get. When the circle pixels are close to the background the image gradients also will be weak. Maybe you can try an adaptive histogram equalization ( adapthisteq ) before detecting the circles.