ROC opencv

ROC opencv

namespace ROC {
    void curve(const Mat &probs, const Mat &truth, vector<Point2f> &roc, int N, const float eps=1e-1) {
        for (int i=0; i<N; i++) {
            float thresh = float(N-i) / N;
            float TP = countNonZero((probs >  thresh) & (truth >  eps));
            float TN = countNonZero((probs <= thresh) & (truth <= eps));
            float FP = countNonZero((probs >  thresh) & (truth <= eps));
            float FN = countNonZero((probs <= thresh) & (truth >  eps));
            float FPR = FP / (FP + TN);
            float TPR = TP / (TP + FN);
            roc.push_back(Point2f(FPR, TPR));
        }
    }

    float auc(vector<Point2f> &roc) {
        float _auc = 0.0f;
        for (int i=0; i<int(roc.size())-1; i++) {
            _auc += (roc[i+1].y + roc[i].y) * (roc[i+1].x - roc[i].x);
        }
        return _auc * 0.5f;
    }

    void draw(vector<Point2f> &roc, Mat &img, const Scalar &color) {
        int   N = roc.size();
        float S = float(img.rows) / N;
        Point2f prev;
        for (size_t i=0; i<roc.size(); i++) {
            Point2f cur(roc[i].x*N*S, (1.0-roc[i].y)*N*S); // opencv y axis points down
            if (i>0)
                line(img, prev, cur, color, 1);
            prev = cur;
        }
    }
} // ROC



/*
    svm->predict(vdata, results, ml::StatModel::RAW_OUTPUT);
    normalize(results, results, 1, 0, NORM_MINMAX);
    // svm gives distances, needed are probs
    results = 1.0f - results;
*/