Slow speed in stream webcam to do "detectMultiScale" - c++

Question

I'm new using OpenCV. I'm doing a sample face detector application console. I'm using haarcascade to detect the face from the webcam.
I did next code:
int main(int, char**)
{
CascadeClassifier face_cascade;
face_cascade.load("haarcascade_frontalface_alt2.xml");
vector<Rect> faces;
Mat frame_gray;
const double scale_factor = 1.1;
const int min_neighbours = 2;
const int flags = 0 | CV_HAAR_SCALE_IMAGE;
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
Mat frame;
for (;;)
{
cvtColor(frame, frame_gray, CV_BGR2GRAY);
equalizeHist(frame_gray, frame_gray);
face_cascade.detectMultiScale(frame_gray, faces, scale_factor, min_neighbours, flags, Size(30, 30));
if (faces.size() == 0)
{
cout << "No face detected" << endl;
}
else
{
for (unsigned int i = 0; i<faces.size(); i++)
{
Point pt1(faces[i].x, faces[i].y);
Point pt2(faces[i].x + faces[i].width, faces[i].y + faces[i].height);
rectangle(frame, pt1, pt2, Scalar(0, 255, 0), 1.5, 8, 0);
}
}
if (waitKey(30) >= 0) break;
}
return 0;
}
I tested the speed from the webcam is slow. I imagine that could be by the resolution from the image (640x480). I want to know if there are any way to keep the resolution and improving the speed between every frame to do the detection.
Thanks!

Answer 1

You can:
Increase minimal face size from Size(30, 30) to Size(50, 50) (it improves performance in 2-3 times).
Change value of scale_factor from 1.1 to 1.2; (it improves performance in 2 times).
Use LBP detector instead of Haar detector (it is faster in 2-3 times).
Check compiler options (may be you use Debug mode).