Hello community,
am working on a project involving realtime image processing of several consumer cameras on a normal computer.
Since normal webcams can be problematic, I'm using an USB Video grabber with four channels: https://www.aliexpress.com/item/4CH-USB-2-0-CCTV-Security-Camera-Video-Audio-Capture-DVR-Card-For-PC-Laptop/462961676.html with PAL/NTSC camera modules.
Now I have the following code in OpenCV 3.1 to read all the video streams:
#include "stdafx.h"
#include
#include "opencv2/opencv.hpp"
using namespace cv;
using namespace std;
int main(int, char**)
{
const String windows[] = { "Cam 0", "Cam 1", "Cam 2", "Cam 3" };
const int camera = 1; // Which camera to use
const int channelsOfCam = 4; // How many channels are uspposed to be available
VideoCapture capture = VideoCapture(camera); // Open the cam
if (!capture.isOpened()) // If not opened successfully
return(0); // Quit
printf("Camera has been started.\n");
// Create and move the four windows into a rectangle
for (int ch = 0; ch < channelsOfCam; ch++)
{
namedWindow(windows[ch], 1);
moveWindow(windows[ch], 100 + ch*150, 100);
}
Mat chFrame[channelsOfCam];
for (;;) // Endless loop
{
if (capture.isOpened())
{
capture.grab(); // Grab the frame
for (int ch = 0; ch < channelsOfCam; ch++)
{
capture.retrieve(chFrame[ch], ch); // Retrieve the different channels
imshow(windows[ch], chFrame[ch]); // Show in correct window
}
}
// Perform screen update
if (waitKey(1) >= 0) break;
}
return 0;
}
Despite using the "grab" and "retrieve" functions like described in the doc for "multi head cameras", the result is that I always get the input from the third physical channel (the cable has the number written on it) in all four image data-structures.
No matter what I do, it never displays any of the other channels (have even tried returning to Opencv 2.3 where it cannot read any stream at all unfortunately).
Anyone having a suggestion what the cause could be?
Do I have to use any of the camera parameters enable any of the other streams? Or can't the second argument of the retrieve function be used the way I did?
Huge thanks in advance!
Greetings,
Alex
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