Improving the ROC curve

It turns out that the ROC curve posted in the previous post was incorrect. I accidentally tested on my training data. Oooops! Once I fixed this bug, my ROC curve became very ugly. In fact, this is what it looked like:



Uh oh! This scared me. I started tweaking the algorithm by changing the number of haar features from 1,000 to 5,000, and changed the number of weak classifiers from 25 to 100. This barely made any difference. I then thought that maybe my 24 by 24 pixel character images simply weren't sufficient so I generated new training data and made the images slightly bigger - 40 by 40 pixels. This also didn't make a difference.

What did make a difference was centering each of the images and getting rid of the extra white space. This changed the ROC curve to this: