OpenCV convert Mat Object to array in C++ - c++

Question

I am attempting to use OpenCV to grab frames from a webcam and convert it in to HSV(Hue,Saturation,Value) Mat object.
Now i need to convert HSV Mat object in to a array which store the values of pixels.
this is the far i got right now.
int main()
{
Mat imgOriginal;
VideoCapture cap(0); //capture the video from web cam
int camOpen = cap.open(CV_CAP_ANY);
if ( !cap.isOpened() ) // if not success, exit program
{
cout << "Cannot open the web cam" << endl;
return -1;
}
namedWindow("Control", CV_WINDOW_AUTOSIZE); //create a window called "Control"
int iLowH = 0;
int iHighH = 179;
int iLowS = 0;
int iHighS = 255;
int iLowV = 0;
int iHighV = 255;
//Create trackbars in "Control" window
cvCreateTrackbar("LowH", "Control", &iLowH, 179); //Hue (0 - 179)
cvCreateTrackbar("HighH", "Control", &iHighH, 179);
cvCreateTrackbar("LowS", "Control", &iLowS, 255); //Saturation (0 - 255)
cvCreateTrackbar("HighS", "Control", &iHighS, 255);
cvCreateTrackbar("LowV", "Control", &iLowV, 255); //Value (0 - 255)
cvCreateTrackbar("HighV", "Control", &iHighV, 255);
time_t start, end;
int counter = 0;
time(&start);
while (true)
{
time(&end);
counter++;
if(1<difftime (end, start))
{
cout<<"fps"<<counter<<endl;
counter=0;
time(&start);
cout<<"iHighH :"<<iLowH<<endl;
cout<<"iHighS :"<<iLowS<<endl;
cout<<"iHighV :"<<iLowV<<endl;
}
cap >> imgOriginal;
bool bSuccess = cap.read(imgOriginal); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read a frame from video stream" << endl;
break;
}
Mat imgHSV;
cvtColor(imgOriginal, imgHSV, COLOR_BGR2HSV); //Convert the captured frame from BGR to HSV
Mat imgThresholded;
inRange(imgHSV, Scalar(iLowH, iLowS, iLowV), Scalar(iHighH, iHighS, iHighV), imgThresholded); //Threshold the image
//morphological opening (remove small objects from the foreground)
erode(imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)) );
dilate( imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)) );
//morphological closing (fill small holes in the foreground)
dilate( imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)) );
erode(imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5)) );
//
// CONVERT imgHSV object in to an array
//
imshow("Thresholded Image", imgThresholded); //show the thresholded image
imshow("Original", imgOriginal); //show the original image
if (waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
system("pause");
return 0;
}

Answer 1

This will copy the image pixels into a vector. If you need a C like array just use &pixels[0].
std::vector<cv::Vec3b> pixels;
cv::MatIterator_<Vec3b> it, end;
for(it = imgHSV .begin<Vec3b>(), end = imgHSV.end<Vec3b>(); it != end; ++it)
{
pixels.push_back(*it);
}
This is a more efficient way to fill the pixels vector:
std::vector<cv::Vec3b> pixels(imgHSV.rows * imgHSV.cols);
cv::Mat m(imgHSV.rows, imgHSV.cols, CV_8UC3, &pixels[0]);
imgHSV.copyTo(m);