precision recall curve from Bag of Visual words classifier

I have trained model using Bag of Visual words classifier for multi-class classification purpose. Though model produced confusion matrix for training and test phases. I want to produce precision-recall curve from these confusion matrix in matlab. I have saved workspace of my model as well. But dont know where to get points for precsion-recall plot? I need curve shown in given figure. Your help will be highy appreciated.

Answer 1

[Bernhard Suhm]

You need to systematically vary the threshold (or related parameter) determining whether you accept or reject the detection. You can watch at 1:45 of this video explaining ROC curves.