title: OpenCV: What methods or binarization techniques can be used to generally extract foregrounds on low quality and low contrast images?
body: <p>Below are just 2 of the few cropped images that I wanted to binarize. As you can see, I just want to get the circular things from the images. Just from looking at it, one can clearly distuingished the circular objects as the foreground. I thought it was as easy to binarize it. I tried adaptice thresholding, Otsu's, Sauvola, Niblack and Wolf binarization technique. I've also tried improving their contrast before binarization but none of them works perfectly. Can anyone suggest a way or a step-by-step procedure to extract the circular things on the images below?</p>
  
  <p><a href="https://i.stack.imgur.com/HCeC9.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HCeC9.jpg" alt="sample01.jpg"></a></p>
  
  <p><a href="https://i.stack.imgur.com/GD9rB.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GD9rB.jpg" alt="sample02.jpg"></a></p>