title: How to not use a few pixels for anything in GrabCut
body: <p>Currently, in the grabcut function available, I have to mark all pixels one of the four variables - GC_BGD, GC_FGD, GC_PR_BGD and GC_PR_FGD. </p>
  
  <p>What should I do if I have a few pixels for which I can't decide any of the afore-mentioned labels. The problem is that if I mark them as GC_PR_FGD or GC_PR_BGD, they are being used to train the respective colour models and hence the grabcut is biased to mark them as the labels I provide them.</p>
  
  <p>Is there anyway I can bypass the assertion that the pixels should have any of the four values in the mask?</p>