title: What does mask r-cnn's AP, AP50, AP70 mean?
body: <p>I'm novice on r-cnn.</p>
  
  <p>There are term AP, AP50, AP75 on mask r-cnn paper.
  50, 75 is small postfix, but I can't make it small, sorry.
  Anyway the paper says it is averaged over IOU thresholds.
  For AP50, only candidates over 50% region comparing ground truth are counted,
  and for AP75 only candidate over 75% are counted. Then what is empty AP? I knew AP use 70% IoU threshold, but it wouldn't. Because just AP is lower then AP75.</p>
  
  <p>And additionally, there are another terms I don't understand well.
  They are APs, m, L. I know they mean small, medium, large. Then is there any criteria how big they are. Just saying small, medium, large makes me little bit confused.</p>
  
  <p>Thanks in advance!</p>