Check if camera feed is blank before using

src/cv.cpp

@@ -16,6 +16,19 @@ cv::dnn::Net dnnFaceDetector;
 cv::VideoCapture vid;
 cv::Mat frame, gray, small;
 
+bool checkBlankFrame(cv::Mat mat) {
+	float firstPixel = mat.at<float>(0);
+	for (int j = 0; j < mat.total(); j++) {
+		if (mat.at<float>(j) != firstPixel) {
+			// different pixel found
+			return false;
+		}
+	}
+
+	// all pixels are the same
+	return true;
+}
+
 void initCV() {
 	haarFaceDetector = cv::CascadeClassifier (resolvePath("cvdata/haarcascade_frontalface_alt2.xml"));
 	dnnFaceDetector = cv::dnn::readNetFromCaffe(
@@ -31,9 +44,18 @@ void initCV() {
 		vid = cv::VideoCapture (i);
 		if (vid.isOpened()) {
 			std::cout << "Camera " << i << " opened" << std::endl;
-			break;
-		}
 
+			// check if camera is giving solid colored frames
+			cv::Mat testFrame;
+			vid.read(testFrame);
+			if (checkBlankFrame(testFrame)) {
+				// reject if giving blank frames
+				std::cout << "Camera " << i << " feed blank!" << std::endl;
+			} else {
+				std::cout << "Using camera " << i << std::endl;
+				break;
+			}
+		}
 	}
 }