title: Circle detection from gray level image in MATLAB
body: <p>I have the image shown below. My aim is to detect the circle which shown in the second image. I used <code>[centers,radii] = imfindcircles(IM,[100 300]);</code> but it found nothing.</p>
  
  <p>Is there any other way to detect the circle? How can I do that?</p>
  
  <p>Original image:
  <img src="https://i.stack.imgur.com/YvIJd.jpg" alt="enter image description here"></p>
  
  <p>The circle:I drew it with paint.
  <img src="https://i.stack.imgur.com/DyEwT.jpg" alt="enter image description here"></p>