DNN Face Detection Confidence — Part 2

Posted: November 21, 2019 at 5:39 pm

I ran a whole day (~8 hours) test when no one was home with a low threshold of confidence (0.1) for deep face detection. As I had previously seen, non-faces can be attributed with very high confidence values. Before the sunset (leading strangely high confidence in noise) the confidence wavers around quite a lot and the max confidence remains .96.

The following image shows the extreme wavering of confidence over time where no faces are present (blue) shown with the short face test (red). The horizontal lines show the means of face and noface sets. It seems that under certain (lighting) conditions, like the dip below, the DNN reports very low confidence values (0.36) that would be easily differentiated from the true positive faces. Since I’m working with example code, I have not been dumping the frames from the camera corresponding with these values. I may need this to determine under what conditions the DNN does perform well. Tomorrow I’ll run a test while I’m working (with face present) and see if I can make sure there are no false positives and collect more samples. Over this larger data-set I have determined that the bump of no face samples around 0.8 confidence does not happen in appropriate (bright) lighting conditions, see histogram below.

Without more information it’s unclear what confidence threshold would be appropriate or even whether the DNN face detector is indeed performing better than the haar-based detector. This reference showed a significant difference in performance between the DNN and Haar methods, so I’ll see what model they used and hope for better performance using that…