OpenCV  4.10.0-pre
Open Source Computer Vision
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This program demonstrates using mouse events and how to make and use a mask image (black and white) .

* create_mask.cpp
* Author:
* Siddharth Kherada <siddharthkherada27[at]gmail[dot]com>
* This tutorial demonstrates how to make mask image (black and white).
* The program takes as input a source image and outputs its corresponding
* mask image.
#include <iostream>
using namespace std;
using namespace cv;
Mat src, img1, mask, final;
Point point;
vector<Point> pts;
int drag = 0;
int var = 0;
int flag = 0;
void mouseHandler(int, int, int, int, void*);
void mouseHandler(int event, int x, int y, int, void*)
if (event == EVENT_LBUTTONDOWN && !drag)
if (flag == 0)
if (var == 0)
img1 = src.clone();
point = Point(x, y);
circle(img1, point, 2, Scalar(0, 0, 255), -1, 8, 0);
drag = 1;
if (var > 1)
line(img1,pts[var-2], point, Scalar(0, 0, 255), 2, 8, 0);
imshow("Source", img1);
if (event == EVENT_LBUTTONUP && drag)
imshow("Source", img1);
drag = 0;
flag = 1;
img1 = src.clone();
if (var != 0)
polylines( img1, pts, 1, Scalar(0,0,0), 2, 8, 0);
imshow("Source", img1);
if (event == EVENT_RBUTTONUP)
flag = var;
final = Mat::zeros(src.size(), CV_8UC3);
mask = Mat::zeros(src.size(), CV_8UC1);
fillPoly(mask, pts, Scalar(255, 255, 255), 8, 0);
bitwise_and(src, src, final, mask);
imshow("Mask", mask);
imshow("Result", final);
imshow("Source", img1);
var = 0;
drag = 0;
flag = 0;
imshow("Source", src);
int main(int argc, char **argv)
CommandLineParser parser(argc, argv, "{@input | lena.jpg | input image}");
parser.about("This program demonstrates using mouse events\n");
cout << "\n\tleft mouse button - set a point to create mask shape\n"
"\tright mouse button - create mask from points\n"
"\tmiddle mouse button - reset\n";
String input_image = parser.get<String>("@input");
src = imread(samples::findFile(input_image));
if (src.empty())
printf("Error opening image: %s\n", input_image.c_str());
return 0;
namedWindow("Source", WINDOW_AUTOSIZE);
setMouseCallback("Source", mouseHandler, NULL);
imshow("Source", src);
return 0;
Designed for command line parsing.
Definition utility.hpp:820
n-dimensional dense array class
Definition mat.hpp:812
CV_NODISCARD_STD Mat clone() const
Creates a full copy of the array and the underlying data.
MatSize size
Definition mat.hpp:2160
void bitwise_and(InputArray src1, InputArray src2, OutputArray dst, InputArray mask=noArray())
computes bitwise conjunction of the two arrays (dst = src1 & src2) Calculates the per-element bit-wis...
std::string String
Definition cvstd.hpp:151
#define CV_8UC1
Definition interface.h:88
#define CV_8UC3
Definition interface.h:90
GMat mask(const GMat &src, const GMat &mask)
Applies a mask to a matrix.
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.
void setMouseCallback(const String &winname, MouseCallback onMouse, void *userdata=0)
Sets mouse handler for the specified window.
CV_EXPORTS_W Mat imread(const String &filename, int flags=IMREAD_COLOR)
Loads an image from a file.
void fillPoly(InputOutputArray img, InputArrayOfArrays pts, const Scalar &color, int lineType=LINE_8, int shift=0, Point offset=Point())
Fills the area bounded by one or more polygons.
void polylines(InputOutputArray img, InputArrayOfArrays pts, bool isClosed, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws several polygonal curves.
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.