OpenCV - getting pixel data from camera device - c++

Question

I am using OpenCV 2.4.6. I have found over the Internet some example of getting frame from a camera. It works well (it displays my ugly face onto the screen). However, I absolutely cannot get pixel data from the frames. I've found some topic here: http://answers.opencv.org/question/1934/reading-pixel-values-from-a-frame-of-a-video/ but it doesn't work for me.
Here is the code - in the commented parts I pointed out what is wrong.
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
using namespace cv;
int main() {
int c;
IplImage* img;
CvCapture* capture = cvCaptureFromCAM(1);
cvNamedWindow("mainWin", CV_WINDOW_AUTOSIZE);
while(1) {
img = cvQueryFrame(capture);
uchar* data = (uchar*)img->imageData; // access violation
// this does not work either
//Mat m(img);
//uchar a = m.data[0]; // access violation
cvShowImage("mainWin", img);
c = cvWaitKey(10);
if(c == 27)
break;
}
}
Could you give me some suggestions, please?

Answer 1

I suggest using the newer Mat structure instead of IplImage since your question is tagged with C++ tag. For your task you can use a data member of Mat - it points to internal Mat storage. For example Mat img; uchar* data = img.data;. Here's a full example
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
using namespace cv;
int main() {
int c;
Mat img;
VideoCapture capture(0);
namedWindow("mainWin", CV_WINDOW_AUTOSIZE);
bool readOk = true;
while(capture.isOpened()) {
readOk = capture.read(img);
// make sure we grabbed the frame successfully
if (!readOk) {
std::cout << "No frame" << std::endl;
break;
}
uchar* data = img.data; // this should work
imshow("mainWin", img);
c = waitKey(10);
if(c == 27)
break;
}
}