OpenCV Slow camera framerate - c++

Question

I just copied an program to detect faces through webcam but the video capture is really slow, and i dont know how to fix it!
Here is the code:
#include<stdio.h>
#include<math.h>
#include<opencv\cv.h>
#include<opencv\highgui.h>
#include<opencv2\objdetect\objdetect.hpp>
#include<opencv2\highgui\highgui.hpp>
#include<opencv2\imgproc\imgproc.hpp>
#include<vector>
using namespace cv;
using namespace std;
int main()
{
CascadeClassifier face_cascade;
if(!face_cascade.load("c:\\haar\\haarcascade_frontalface_alt2.xml")) {
printf("Error loading cascade file for the face");
return 1;
}
VideoCapture capture(0);
if(!capture.isOpened())
{
printf("Error trying to start the Camera");
return 1;
}
Mat cap_img,gray_img;
vector<Rect> faces;
while(1)
{
capture >> cap_img;
waitKey(10);
cvtColor(cap_img, gray_img, CV_BGR2GRAY);
cv::equalizeHist(gray_img,gray_img);
face_cascade.detectMultiScale(gray_img, faces, 1.1, 10, CV_HAAR_SCALE_IMAGE | CV_HAAR_DO_CANNY_PRUNING, cvSize(0,0), cvSize(300,300));
for(int i=0; i < faces.size();i++)
{
Point pt1(faces[i].x+faces[i].width, faces[i].y+faces[i].height);
Point pt2(faces[i].x,faces[i].y);
rectangle(cap_img, pt1, pt2, cvScalar(191,191,191), 2, 8, 0);
}
imshow("Result", cap_img);
waitKey(3);
char c = waitKey(3);
if(c == 27)
break;
}
return 0;
}
I am using Visual studio 2012 and this is the main.cpp file. Im using OpenCV 2.4.9!

Answer 1

OpenCV comes with prebuild libraries. When you use them in an application you actually want to deploy make sure you use the release libraries. In debug mode you have lots of additional checks in the form of asserts as well as debug symbols allowing you to step into the libraries with a debugger that are removed in release mode.
Another more specific advise regarding the code you posted: Avoid calls to cv::waitKey() as every single call, who would have guessed, makes your main thread wait the specified amount of time in milliseconds. Do not drop calls to it entirely as e.g. cv::imshow() will only work appropriately with these in place.
Edit:
Reduce your while loop to:
while ( true ) {
capture >> cap_img;
imshow("Result", cap_img);
if(waitKey(1) == 27)
break;
}
When you know how much time you need for capturing the image and just displaying it, then you can compare how much of an impact whatever algorithm you are running has on your performance.

Answer 2

Here is solution...everytime you read!!!..everytime you use vcap>>cap or cap.read(vcap)... you must set FPS ..25 is max..if i try to set 26 or higher it runs slow.
...this runs 30 fps for me
If you not set FPS...it runs slow too
if (cap.read(vcap)){
imshow("Cam Feed", vcap);
cap.set(CV_CAP_PROP_FPS, 25);
}

Answer 3

On top of the other answers, Multiprocessing is what fixed my issue. I split my program into 3 processes. One for grabbing the image, one for processing the image, and one for displaying the image. Referencing this page helped me a lot. I also followed the tips of the other answers here.