c++ - Get SVM classification score in multiclass classification with OpenCV

Question

I'm working on a project where I'm doing multiclass classification with SVM in OpenCV.

My goal is to get the confidence score of the classification as well as the predicted class. How can I do that? Right now I'm doing something like

float result = mysvm.predict(sample);

Having a fairly high amount of classes I prefer to avoid doing a lot of one-vs-all classifications and then calculate the scores.

Since OpenCV SVM is implemented using LibSVM, I'm quite sure that there is a way to do this, but looking at http://docs.opencv.org/modules/ml/doc/support_vector_machines.html doesn't really help.

Thanks for any input provided.

Answer 1

In opencv/include/opencv2/ml/ml.hpp, there is a struct called CvSVMDecisionFunc.. It has been used in line 546 as a Protected Variable,

CvSVMDecisionFunc* decision_func;

What you need to do is to cut that line and paste it as Public and then do a complete rebuild of OpenCV.. This variable, decision_func contains all the data for specific support vectors (ie, the alpha and rho values)..