opencv_contrib/modules/ml/samples/introduction_to_svm.cpp

#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/ml.hpp>

using namespace cv;
using namespace cv::ml;

int main(int, char**)
{
    // Set up training data
    //! [setup1]
    int labels[4] = {1, -1, -1, -1};
    float trainingData[4][2] = { {501, 10}, {255, 10}, {501, 255}, {10, 501} };
    //! [setup1]
    //! [setup2]
    Mat trainingDataMat(4, 2, CV_32F, trainingData);
    Mat labelsMat(4, 1, CV_32SC1, labels);
    //! [setup2]

    // Train the SVM
    //! [init]
    Ptr<SVM> svm = SVM::create();
    svm->setType(SVM::C_SVC);
    svm->setKernel(SVM::LINEAR);
    svm->setTermCriteria(TermCriteria(TermCriteria::MAX_ITER, 100, 1e-6));
    //! [init]
    //! [train]
    svm->train(trainingDataMat, ROW_SAMPLE, labelsMat);
    //! [train]

    // Data for visual representation
    int width = 512, height = 512;
    Mat image = Mat::zeros(height, width, CV_8UC3);

    // Show the decision regions given by the SVM
    //! [show]
    Vec3b green(0,255,0), blue(255,0,0);
    for (int i = 0; i < image.rows; i++)
    {
        for (int j = 0; j < image.cols; j++)
        {
            Mat sampleMat = (Mat_<float>(1,2) << j,i);
            float response = svm->predict(sampleMat);

            if (response == 1)
                image.at<Vec3b>(i,j)  = green;
            else if (response == -1)
                image.at<Vec3b>(i,j)  = blue;
        }
    }
    //! [show]

    // Show the training data
    //! [show_data]
    int thickness = -1;
    circle( image, Point(501,  10), 5, Scalar(  0,   0,   0), thickness );
    circle( image, Point(255,  10), 5, Scalar(255, 255, 255), thickness );
    circle( image, Point(501, 255), 5, Scalar(255, 255, 255), thickness );
    circle( image, Point( 10, 501), 5, Scalar(255, 255, 255), thickness );
    //! [show_data]

    // Show support vectors
    //! [show_vectors]
    thickness = 2;
    Mat sv = svm->getUncompressedSupportVectors();

    for (int i = 0; i < sv.rows; i++)
    {
        const float* v = sv.ptr<float>(i);
        circle(image,  Point( (int) v[0], (int) v[1]), 6, Scalar(128, 128, 128), thickness);
    }
    //! [show_vectors]

    imwrite("result.png", image);        // save the image

    imshow("SVM Simple Example", image); // show it to the user
    waitKey();
    return 0;
}