Grabbing multiple frames for marker detection in parallel

asked 2016-04-19 13:14:35 -0500

MarKS9 gravatar image

I have a marker detection code which runs fine with a video file and camera stream. I want to modify the code to grab frames from 2 videos in 2 different threads and then process marker detection accordingly. Here is a Psuedo code what i really want to do:

string camera[2] = {"test.avi","test1.avi"};
int main(){
VideoCapture cap();
while(1){
            int threads = get_num_threads(2);
            cap >> frame;
            marker_detection(frame);
            namedWindow(Camera[Thread], CV_WINDOW_NORMAL);
            imshow(Camera[Thread], frame);
            waitKey(1);
        }
}

It is just the pseudo code. I am completely new to multithreading. How do i grab a frame from both the files in parallel and then process marker detection for both the frames simultaneously? Note: i have gui functions like imshow() inside marker detection function.

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Comments

3

This really has nothing to do with OpenCV and everything to do with concurrency in C++. I suggest you start by reading C++ Concurrency In Action - Practical Multithreading by Anthony Williams. As a .pdf it is readily found on the web and will teach you everything you want to know and more.

Der Luftmensch gravatar imageDer Luftmensch ( 2016-04-19 19:02:00 -0500 )edit
2

multithreading should be absolutely forbiden for noobs.

berak gravatar imageberak ( 2016-04-20 01:18:58 -0500 )edit

@Der Luftmensch thank you very much for your suggestion will check it out.

MarKS9 gravatar imageMarKS9 ( 2016-04-20 04:37:57 -0500 )edit

@berak true! it is complex. But i have to start at some point. Thank you.

MarKS9 gravatar imageMarKS9 ( 2016-04-20 04:39:05 -0500 )edit

namedWindow() contains the message-loop for the window, you can't have that in a thread.

berak gravatar imageberak ( 2016-04-20 04:41:02 -0500 )edit

you should rather empower opencv's builtin multithreading with TBB, openMP, IPP, etc. , than knitting your own, naive threading code around your app.

berak gravatar imageberak ( 2016-04-20 04:43:56 -0500 )edit

@berak yes i agree handling GUI's in separate thread is dangerous. I have indeed compiled OpenCV with OpenMP, CUDA, OpenCL and TBB. I just wanted to accomplish this multiple frames capture for marker detection but it seems way too complex. i followed this well written article link text and i managed to implement it for small opencv programs but could'nt for marker detection.

MarKS9 gravatar imageMarKS9 ( 2016-04-20 04:58:54 -0500 )edit