title: Grayscale segmentation/feature extraction/blob detection?
body: <p>I'm trying to find a starting point, but I can't seem to find the right answer. I'd be very grateful for some guidance. I also don't know the proper terminology, hence the title. </p>
  
  <ol>
  <li>I took an image of a bag with a black background behind it.</li>
  <li>And I want to extract the bag, similar to <a href="http://i60.tinypic.com/2gwck90.png" rel="nofollow">this</a>.</li>
  <li>And if possible, find the center, like <a href="http://www.societyofrobots.com/images/programming_computer_vision_fire2.jpg" rel="nofollow">this</a>.</li>
  </ol>
  
  <p>Essentially, I want to be able to extract the blob of pixels and then find the center point.</p>
  
  <p>I know these are two separate questions, but I figured if someone can do the latter, then they can do the first. I am using MATLAB, but would like to write my own code and not use their image processing functions, like edge(). What methods/algorithms can I use? Any papers/links would be nice (:</p>