Update README.md

better explanation.

Author: rafaelpadilla

README.md

@@ -254,7 +254,7 @@ The following table shows the bounding boxes with their corresponding confidence
 | Image 7 |	Y	| 95% | FP |
 --->
 
-In some images there are more than one detection overlapping a ground truth (Images 2, 3, 4, 5, 6 and 7). For those cases the first detection is considered TP while the others are FP. This rule is applied by the PASCAL VOC 2012 metric: "e.g. 5 detections (TP) of a single object is counted as 1 correct detection and 4 false detections”.
+In some images there are more than one detection overlapping a ground truth (Images 2, 3, 4, 5, 6 and 7). For those cases, the predicted box with the highest IOU is considered TP (e.g. in image 1 "E" is TP while "D" is FP because IOU between E and the groundtruth is greater than the IOU between D and the groundtruth). This rule is applied by the PASCAL VOC 2012 metric: "e.g. 5 detections (TP) of a single object is counted as 1 correct detection and 4 false detections”.
 
 The Precision x Recall curve is plotted by calculating the precision and recall values of the accumulated TP or FP detections.  For this, first we need to order the detections by their confidences, then we calculate the precision and recall for each accumulated detection as shown in the table below (Note that for recall computation, the denominator term ("Acc TP + Acc FN" or "All ground truths") is constant at 15 since GT boxes are constant irrespective of detections).: