OpenCV

Continued from the above discussion, I draft the following codes to form a Bow-based feature representation. I try to use three feature descriptors to extract the keypoints of characters. And then use Hog feature descriptors to describe these keypoints for the further training in Bow and SVM.

    vector<Point2f> pts1,pts2,pts3;

    ORB detector1;

    vector<KeyPoint> keypoints1;
    detector1.detect(src, keypoints1);
    keyPointsToPoints(keypoints1, pts1);

    GoodFeaturesToTrackDetector  detector2;
    vector<KeyPoint> keypoints2;
    detector2.detect(src, keypoints2);
    keyPointsToPoints(keypoints2, pts2);

    DenseFeatureDetector detector3;
    vector<KeyPoint> keypoints3;
    detector3.detect(src, keypoints3);
    keyPointsToPoints(keypoints3, pts3);

    vector<float> descriptors1,descriptors2,descriptors3;

    HOGDescriptor hog;

    hog.compute(src,descriptors1,Size(3,3),Size(1,1),pts1);
    hog.compute(src,descriptors2,Size(3,3),Size(1,1),pts2);
    hog.compute(src,descriptors3,Size(3,3),Size(1,1),pts3);