OpenCV  4.10.0-dev
Open Source Computer Vision
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This program demonstrates usage of the Canny edge detector

Check the corresponding tutorial for more details

#include <stdio.h>
using namespace cv;
using namespace std;
int edgeThresh = 1;
int edgeThreshScharr=1;
Mat image, gray, blurImage, edge1, edge2, cedge;
const char* window_name1 = "Edge map : Canny default (Sobel gradient)";
const char* window_name2 = "Edge map : Canny with custom gradient (Scharr)";
// define a trackbar callback
static void onTrackbar(int, void*)
blur(gray, blurImage, Size(3,3));
// Run the edge detector on grayscale
Canny(blurImage, edge1, edgeThresh, edgeThresh*3, 3);
cedge = Scalar::all(0);
image.copyTo(cedge, edge1);
imshow(window_name1, cedge);
Mat dx,dy;
Canny( dx,dy, edge2, edgeThreshScharr, edgeThreshScharr*3 );
cedge = Scalar::all(0);
image.copyTo(cedge, edge2);
imshow(window_name2, cedge);
static void help(const char** argv)
printf("\nThis sample demonstrates Canny edge detection\n"
" %s [image_name -- Default is fruits.jpg]\n\n", argv[0]);
const char* keys =
"{help h||}{@image |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(samples::findFile(filename), IMREAD_COLOR);
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(window_name1, 1);
namedWindow(window_name2, 1);
// create a toolbar
createTrackbar("Canny threshold default", window_name1, &edgeThresh, 100, onTrackbar);
createTrackbar("Canny threshold Scharr", window_name2, &edgeThreshScharr, 400, onTrackbar);
// Show the image
onTrackbar(0, 0);
// Wait for a key stroke; the same function arranges events processing
return 0;
Designed for command line parsing.
Definition utility.hpp:832
n-dimensional dense array class
Definition mat.hpp:812
void copyTo(OutputArray m) const
Copies the matrix to another one.
void create(int rows, int cols, int type)
Allocates new array data if needed.
Template class for specifying the size of an image or rectangle.
Definition types.hpp:335
#define CV_16S
Definition interface.h:76
int waitKey(int delay=0)
Waits for a pressed key.
void namedWindow(const String &winname, int flags=WINDOW_AUTOSIZE)
Creates a window.
int createTrackbar(const String &trackbarname, const String &winname, int *value, int count, TrackbarCallback onChange=0, void *userdata=0)
Creates a trackbar and attaches it to the specified window.
CV_EXPORTS_W Mat imread(const String &filename, int flags=IMREAD_COLOR_BGR)
Loads an image from a file.
void cvtColor(InputArray src, OutputArray dst, int code, int dstCn=0)
Converts an image from one color space to another.
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
"black box" representation of the file storage associated with a file on disk.
Definition core.hpp:102
STL namespace.