For detection, a common way to determine if one object proposal was right is Intersection over Union (IoU, IU). This takes the set $A$ of proposed object pixels and the set of true object pixels $B$ and calculates: $$IoU(A, B) = \frac{A \cap B}{A \cup B}$$ Commonly, IoU > 0.5 means that it was a hit, otherwise it was a fail. For each class, one can calculate the True Positive ($TP(c)$): a proposal
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