Accessing the webcam

To access a computer's webcam or camera device, you can simply call the open() function on a cv::VideoCapture object (OpenCV's method of accessing your camera device), and pass 0 as the default camera ID number. Some computers have multiple cameras attached, or they do not work with a default camera of 0, so it is common practice to allow the user to pass the desired camera number as a command-line argument, in case they want to try camera 1, 2, or -1, for example. We will also try to set the camera resolution to 640 x 480 using cv::VideoCapture::set() to run faster on high-resolution cameras.

You can put this code in the main() function of your main.cpp file:

auto cameraNumber = 0; 
if (argc> 1) 
cameraNumber = atoi(argv[1]); 

// Get access to the camera. 
cv::VideoCapture camera; 
camera.open(cameraNumber); 
if (!camera.isOpened()) { 
   std::cerr<<"ERROR: Could not access the camera or video!"<< std::endl; 
   exit(1); 
} 

// Try to set the camera resolution. 
camera.set(cv::CV_CAP_PROP_FRAME_WIDTH, 640); 
camera.set(cv::CV_CAP_PROP_FRAME_HEIGHT, 480);

After the webcam has been initialized, you can grab the current camera image as a cv::Mat object (OpenCV's image container). You can grab each camera frame by using the C++ streaming operator from your cv::VideoCapture object in a cv::Mat object, just like if you were getting input from a console.