Taking average of live webcam frames - c++

Question

I first used this code to capture webcam frames:
int main(int argc, char** argv)
{
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
cap.set(CV_CAP_PROP_FPS, 15);
std::vector<cv::Mat> images(100);
for (framenumb = 0; framenumb < 100; ++framenumb)
{
// this is optional, preallocation so there's no allocation
// during capture
images[framenumb].create(480, 640, CV_32FC3);
}
for (framenumb = 0; framenumb < 100; ++framenumb)
{
Mat frame;
cap >> frame;
if (frame.empty()) break; // end of video stream
imshow("webcam", frame);
if (waitKey(1) == 27) break; // stop capturing by pressing ESC
frame.copyTo(images[framenumb]);
}
and then tried to use the following code to average the captured frames:
Mat avgImg;
Mat capturedImg;
for (framenumb = 0; framenumb < 100; ++framenumb)
{
avgImg.create(480, 640, CV_32FC3);
capturedImg = images[framenumb];
cv::accumulate(capturedImg, avgImg);
}
avgImg = avgImg / 100;
avgImg.convertTo(avgImg, CV_8UC3);
imshow("averaged", avgImg);
But then it just broke the programme and gave me a black image. Can anyone help me to identify where the error is? Thank you very much

Answer 1

You need to:
Create a zero initialized accumulation image
Add every image to it
Divide the accumulated image by the number of images
You instead re-create an empty accumulation image at every frame.
The code should be changed as:
Mat avgImg(480, 640, CV_32FC3, Scalar()); // Create and zero initialize
Mat capturedImg;
for (framenumb = 0; framenumb < 100; ++framenumb)
{
// avgImg.create(480, 640, CV_32FC3); // Don't create each time!
capturedImg = images[framenumb];
cv::accumulate(capturedImg, avgImg);
}
You probably can simplify your code as:
Mat avgImg(480, 640, CV_32FC3, Scalar()); // Create and zero initialize
for (framenumb = 0; framenumb < 100; ++framenumb)
{
avgImg += images[framenumb];
}