Thursday, September 6, 2012

Canny Edge on Webcam

From StackOverflow

  1. Remember that OpenCV works with BGR, so when you convert, use the CV_BGR2GRAY
  2. Be careful with the threshold in Canny, they should be different and with a ratio of 2 or 3( recommended). Might try 100-200...
  3. Try to avoid printing in every loop, that slows down a little bit your code
  4. For filters, try not to use a big window. A size 3 0r 5 at most is usually fine (Depending on your application). A size 11 is probably not required.
  5. consider using cv::Mat. It is far more flexible than IplImage and in fact ( no more Release Image...)
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
using namespace cv;
int main(int, char**)
    namedWindow( "Edges", CV_WINDOW_NORMAL ); 
    CvCapture* capture = cvCaptureFromCAM(-1);

    cv::Mat frame; cv::Mat out; cv::Mat out2;

    while(1) {
        frame = cvQueryFrame( capture );

        GaussianBlur( frame, out, Size(5, 5), 0, 0 );
        cvtColor( out ,out2, CV_BGR2GRAY ); // produces out2, a one-channel image (CV_8UC1)
       Canny( out2, out2, 100, 200, 3 ); // the result goes to out2 again,but since it is still one channel it is fine

        if( ! ) break;
        imshow( "Edges", out2 );

        char c = cvWaitKey(33);
        if( c == 'c' ) break;
    return 0;

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