'Detect \'good features to track\' (corners) in the current frame
using sub-pixel accuracy.'

def detect_points(self):

    self.image = cv2.imread(self.imnames[self.current_frame])
    self.gray = cv2.cvtColor(self.image, cv2.COLOR_BGR2GRAY)
    features = cv2.goodFeaturesToTrack(self.gray, **feature_params)
    cv2.cornerSubPix(self.gray, features, **subpix_params)
    self.features = features
    self.tracks = [[p] for p in features.reshape(((-1), 2))]
    self.prev_gray = self.gray
