Seeking explanation for why imfindcircles() misses circles within tight radius constraint

Background:

I am working through a digital imaging processing tutorial. I have been using

imfindcircles() on the built-in demo image 'coins.png'

When I run

[centers,radii] = imfindcircles(F,[15 30]) %find circles with radius: 15px<radius<30px

imfindcircles() outputs:

 radii =

   24.6209
   24.3789
   24.2560
   28.1686
   28.6433
   24.4247
   29.4611
   28.8647
   29.0494
   29.0979

So, apparently, all the circles in this image have radii: 24<radius<30 However, when I run imfindcircles() constrained to that range

 [centers,radii] = imfindcircles(F,[24 30]) %find circles with radius: 24px<radius<30px

imfindcircles() find only a single circle:

    radii =

   29.2412

Question: What is it about the way the function imfindcircles() works that makes it miss some circles within the radius constraint when that constraint is tighter?

Answer 1

[Jayanti]

Hi Hayden,

I found a similar Matlab answer related to your query. Please refer to the below MATLAB Answer thread which addresses this behavior:

https://www.mathworks.com/matlabcentral/answers/1934150-imfindcircles-doesn-t-find-circle-although-radius-is-within-the-specified-range-and-circle-was-suc