I am using SVM algorithm to recognize Facial Expression using opencv library. I want to get prediction confidence of my test image but the syntax of predict is something like float response = svm->predict(TestDataMat). How can get the confidence value?? Thanks in advance!
Add the second parameter to return the prediction value
decision = svm.predict(testData, true);
confidence = 1.0 / (1.0 + exp(-decision));The distance itself is pretty ok, but if you want to have a confidence value in a range (0, 1), you can apply a sigmoidal function to the result, which could be a logistic function.
ABOVE WORKS FOR 2.4
THIS WORKS FOR 3.x
svm->predict(data_test, labels_SVM, ml::StatModel::RAW_OUTPUT);
Thanks a lot!
You are welcome!
Does this work in OpenCV 3.x? The StatModel docs suggest that the signature of predict() has changed, and I can't find whether it's still possible to get the confidence for SVM.
Actually, you might be on to something ... just tried float conf = svm.predict(data_test, labels_SVM, true); cerr << conf << endl; and the value is always 0 ... because the function with parameters described above is indeed missing ...
Just added a solution for 3.x ;)
Thanks, you are correct. Also, it's worth noting that the distance is only returned in the case of 2-class classification, and only when the SVM type is C_SVC or NU_SVC. (This limitation is the same in 2.4 and 3.x.) Otherwise, just the classification is returned.
@berak might be able to hop in here, been some time since I worked on this
Asked: Dec 2 '16
Seen: 2,882 times
Last updated: Dec 20 '16
