title: What is the minimum size object I can detect using OpenCV train_cascade?
body: <p>I'm in the process of creating a classifier for an electrical outlet (specifically the three open holes that occur twice on standard outlet panels, not the entire panel itself).</p>
  
  <p><a href="https://i.stack.imgur.com/5oz3U.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5oz3U.jpg" alt="enter image description here"></a></p>
  
  <p>My question is, what are the ideal traits of positive images and what width and height should I pass to train_cascade to enable my object detector to detect the smallest possible outlets? I.e. to detect them from the farthest possible distance?  I also care about accuracy, and am fine with a classifier that takes weeks to train (assuming it is actually making progress).</p>
  
  <p>And a question to increase my understanding of this: is the width and height I pass to <code>train_cascade</code> the dimensions of the search box that will be passed over each image?  If so, and I want my detector to detect very small objects, than I should pass a small width and height, correct?</p>
  
  <p>I would like to be able to detect very large and very small instances of outlets.  From very close up (the camera is literally 3 inches away from the outlet) to at least a few feet away.</p>