Assertion Error when using Contour Area-OpenCV

I get this error whenever I use the contourArea function in openCV Here is my code while (true) { Mat 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 (removes 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 (removes small holes from the foreground) dilate(imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5))); erode(imgThresholded, imgThresholded, getStructuringElement(MORPH_ELLIPSE, Size(5, 5))); int thresh = 100; Mat canny_output; vector<Vec4i> hierarchy; vector<vector<Point> > contours; RNG rng(12345); Canny(imgThresholded, canny_output, thresh, thresh * 2, 3); /// Find contours findContours(canny_output, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, Point(0, 0)); /// Draw contours Mat drawing = Mat::zeros(canny_output.size(), CV_8UC3); for (int i = 0; i< contours.size(); i++) { Scalar color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255)); drawContours(drawing, contours, i, color, 2, 8, hierarchy, 0, Point()); } double area = contourArea(contours); std::cout << area; imshow("contours", drawing); My code was working mostly fine before this, but it is very important that i grab the contour Area, but it keeps giving me this error. Any help is greatly appreciated