Hi Pat,
Please refer to the following updated code that successfully detects circles in the provided image:
[centers, radii] = imfindcircles(rgb,[10 55],'ObjectPolarity','dark','Sensitivity',0.91)
In this case, the circular object appears darker than the background, so I set the 'ObjectPolarity' to 'dark'. The 'sensitivity' parameter in imfindcircles controls how aggressively the algorithm searches for circles. Increasing it from the default value of 0.85 to 0.91 improves detection in this image, though it may also increase the chance of false positives with very high value. With this adjustment, the circles are detected correctly.
Below is the output image I am getting:
To get more information on the name value arguments of this function please refer to the below link:
