OpenCV  3.0.0-dev
Open Source Computer Vision

An example on using the canny edge detector

#include <stdio.h>
using namespace cv;
using namespace std;
int edgeThresh = 1;
Mat image, gray, edge, cedge;
// define a trackbar callback
static void onTrackbar(int, void*)
blur(gray, edge, Size(3,3));
// Run the edge detector on grayscale
Canny(edge, edge, edgeThresh, edgeThresh*3, 3);
cedge = Scalar::all(0);
image.copyTo(cedge, edge);
imshow("Edge map", cedge);
static void help()
printf("\nThis sample demonstrates Canny edge detection\n"
" /.edge [image_name -- Default is ../data/fruits.jpg]\n\n");
const char* keys =
"{@image |../data/fruits.jpg|input image name}"
int main( int argc, const char** argv )
CommandLineParser parser(argc, argv, keys);
string filename = parser.get<string>(0);
image = imread(filename, 1);
printf("Cannot read image file: %s\n", filename.c_str());
return -1;
cedge.create(image.size(), image.type());
cvtColor(image, gray, COLOR_BGR2GRAY);
// Create a window
namedWindow("Edge map", 1);
// create a toolbar
createTrackbar("Canny threshold", "Edge map", &edgeThresh, 100, onTrackbar);
// Show the image
onTrackbar(0, 0);
// Wait for a key stroke; the same function arranges events processing
return 0;