title: How to classify true negative from a video?
body: <p>For a performance measuring purpose I am trying to draw ROC curve. In ROC curve I have to plot False Positive Rate (FPR) in x-axis and True Positive Rate (TPR) in y-axis. As we know, </p>
  
  <blockquote>
    <p>FPR = FP/(FP+TN)</p>
  </blockquote>
  
  <p>So in the following picture how can i detect True Negative(TN) ? I have used HOG classifier to detect human. I marked with rectangle 1,2,3,4,5,6(or should be 7) to show the human objects that should be ignored and not to classify as human. and I think those are True Negative.</p>
  
  <p><a href="https://i.stack.imgur.com/CvJd5.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CvJd5.jpg" alt="True Negative detetion in this frame"></a></p>
  
  <p>In this picture i want to say my assumption,as we know,</p>
  
  <blockquote>
    <p>False negative: Result should have been positive, but is negative.</p>
    
    <p>False positive: Result should have been negative, but is positive.</p>
    
    <p>True positive: Result should have been positive and is positive.</p>
    
    <p>True negative: Result should have been negative and is negative</p>
  </blockquote>
  
  <p>So i think in this frame FP = 0, TP = 0, FN = 0 but not sure about TN, is it 6 or 7 or anything other? Please correct me also about FP, TP, and FN if i am wrong. I saw this question <a href="https://stackoverflow.com/questions/16271603/how-to-categorize-true-negatives-in-sliding-window-object-detection">How to categorize True Negatives in sliding window object detection?</a> which was really helpful but still i have to calculate FPR for this scenario.</p>