OpenCV  4.10.0-dev
Open Source Computer Vision
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An example using Laplace transformations for edge detection

#include <ctype.h>
#include <stdio.h>
#include <iostream>
using namespace cv;
using namespace std;
static void help(char** argv)
cout <<
"\nThis program demonstrates Laplace point/edge detection using OpenCV function Laplacian()\n"
"It captures from the camera of your choice: 0, 1, ... default 0\n"
<< argv[0] << " -c=<camera #, default 0> -p=<index of the frame to be decoded/captured next>\n" << endl;
int sigma = 3;
int smoothType = GAUSSIAN;
int main( int argc, char** argv )
cv::CommandLineParser parser(argc, argv, "{ c | 0 | }{ p | | }");
string camera = parser.get<string>("c");
if (camera.size() == 1 && isdigit(camera[0]))<int>("c"));
if (!cap.isOpened())
cerr << "Can't open camera/video stream: " << camera << endl;
return 1;
cout << "Video " << parser.get<string>("c") <<
": width=" << cap.get(CAP_PROP_FRAME_WIDTH) <<
", height=" << cap.get(CAP_PROP_FRAME_HEIGHT) <<
", nframes=" << cap.get(CAP_PROP_FRAME_COUNT) << endl;
int pos = 0;
if (parser.has("p"))
pos = parser.get<int>("p");
if (!parser.check())
return -1;
if (pos != 0)
cout << "seeking to frame #" << pos << endl;
if (!cap.set(CAP_PROP_POS_FRAMES, pos))
cerr << "ERROR: seekeing is not supported" << endl;
namedWindow("Laplacian", WINDOW_AUTOSIZE);
createTrackbar("Sigma", "Laplacian", &sigma, 15, 0);
Mat smoothed, laplace, result;
Mat frame;
cap >> frame;
if( frame.empty() )
int ksize = (sigma*5)|1;
if(smoothType == GAUSSIAN)
GaussianBlur(frame, smoothed, Size(ksize, ksize), sigma, sigma);
else if(smoothType == BLUR)
blur(frame, smoothed, Size(ksize, ksize));
medianBlur(frame, smoothed, ksize);
Laplacian(smoothed, laplace, CV_16S, 5);
convertScaleAbs(laplace, result, (sigma+1)*0.25);
imshow("Laplacian", result);
char c = (char)waitKey(30);
if( c == ' ' )
smoothType = smoothType == GAUSSIAN ? BLUR : smoothType == BLUR ? MEDIAN : GAUSSIAN;
if( c == 'q' || c == 'Q' || c == 27 )
return 0;
Designed for command line parsing.
Definition utility.hpp:832
n-dimensional dense array class
Definition mat.hpp:812
bool empty() const
Returns true if the array has no elements.
Template class for specifying the size of an image or rectangle.
Definition types.hpp:335
Class for video capturing from video files, image sequences or cameras.
Definition videoio.hpp:731
virtual bool open(const String &filename, int apiPreference=CAP_ANY)
Opens a video file or a capturing device or an IP video stream for video capturing.
virtual bool set(int propId, double value)
Sets a property in the VideoCapture.
virtual bool isOpened() const
Returns true if video capturing has been initialized already.
virtual double get(int propId) const
Returns the specified VideoCapture property.
void convertScaleAbs(InputArray src, OutputArray dst, double alpha=1, double beta=0)
Scales, calculates absolute values, and converts the result to 8-bit.
#define CV_16S
Definition interface.h:76
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
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.
void medianBlur(InputArray src, OutputArray dst, int ksize)
Blurs an image using the median filter.
void blur(InputArray src, OutputArray dst, Size ksize, Point anchor=Point(-1,-1), int borderType=BORDER_DEFAULT)
Blurs an image using the normalized box filter.
void Laplacian(InputArray src, OutputArray dst, int ddepth, int ksize=1, double scale=1, double delta=0, int borderType=BORDER_DEFAULT)
Calculates the Laplacian of an image.
void GaussianBlur(InputArray src, OutputArray dst, Size ksize, double sigmaX, double sigmaY=0, int borderType=BORDER_DEFAULT, AlgorithmHint hint=cv::ALGO_HINT_DEFAULT)
Blurs an image using a Gaussian filter.
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.