void setMouseCallback(const string& winname, MouseCallback onMouse, void* userdata = 0)
This may be helpful while you want to select a region on an image and perform certain task in that region only.
------------
Sources:
http://opencv-srf.blogspot.in/2011/11/mouse-events.html
http://stackoverflow.com/questions/14874449/opencv-set-mouse-callback
http://stackoverflow.com/questions/15570431/opencv-return-value-from-mouse-callback-function
This function sets a callback function to be called every time any mouse
events occurs in the specified window. Here is the detailed explanation
of the each parameters of the above OpenCV function.
- winname - Name of the OpenCV window. All mouse events related to this window will be registered
- onMouse - Name of the callback function. Whenever mouse events related to the above window occur, this callback function will be called. This function should have the signature like the following
- void FunctionName(int event, int x, int y, int flags, void* userdata)
- event - Type of the mouse event. These are the entire list of mouse events
- EVENT_MOUSEMOVE
- EVENT_LBUTTONDOWN
- EVENT_RBUTTONDOWN
- EVENT_MBUTTONDOWN
- EVENT_LBUTTONUP
- EVENT_RBUTTONUP
- EVENT_MBUTTONUP
- EVENT_LBUTTONDBLCLK
- EVENT_RBUTTONDBLCLK
- EVENT_MBUTTONDBLCLK
- x - x coordinate of the mouse event
- y - y coordinate of the mouse event
- flags - Specific condition whenever a mouse event occurs. See the next OpenCV example code for the usage of this parameter. Here is the entire list of enum values which will be possesed by "flags"
- EVENT_FLAG_LBUTTON
- EVENT_FLAG_RBUTTON
- EVENT_FLAG_MBUTTON
- EVENT_FLAG_CTRLKEY
- EVENT_FLAG_SHIFTKEY
- EVENT_FLAG_ALTKEY
- userdata - Any pointer passes to the "setMouseCallback" function as the 3rd parameter (see below)
- userdata - This pointer will be passed to the callback function
This may be helpful while you want to select a region on an image and perform certain task in that region only.
Example:
-----------#include "opencv2/highgui/highgui.hpp" #include <iostream> using namespace std; using namespace cv; void CallBackFunc(int event, int x, int y, int flags, void* userdata) { if ( event == EVENT_LBUTTONDOWN ) { cout << "Left button of the mouse is clicked - position (" << x << ", " << y << ")" << endl; } else if ( event == EVENT_RBUTTONDOWN ) { cout << "Right button of the mouse is clicked - position (" << x << ", " << y << ")" << endl; } else if ( event == EVENT_MBUTTONDOWN ) { cout << "Middle button of the mouse is clicked - position (" << x << ", " << y << ")" << endl; } else if ( event == EVENT_MOUSEMOVE ) { cout << "Mouse move over the window - position (" << x << ", " << y << ")" << endl; } } int main() { // Read image from file Mat img = imread("lena.JPG"); //if fail to read the image if ( img.empty() ) { cout << "Error loading the image" << endl; return -1; } //Create a window namedWindow("ImageDisplay", 1); //set the callback function for any mouse event setMouseCallback("ImageDisplay", CallBackFunc, NULL); //show the image imshow("ImageDisplay", img); // Wait until user press some key waitKey(0); return 0; }-----------
Example 2:
This code will detect left mouse clicks while
pressing the "CTRL" key , right mouse clicks while pressing the "SHIFT"
key and movements of the mouse over the OpenCV window while pressing the
"ALT" key.
------------#include "opencv2/highgui/highgui.hpp" #include <iostream> using namespace std; using namespace cv; void CallBackFunc(int event, int x, int y, int flags, void* userdata) { if ( flags == (EVENT_FLAG_CTRLKEY + EVENT_FLAG_LBUTTON) ) { cout << "Left mouse button is clicked while pressing CTRL key - position (" << x << ", " << y << ")" << endl; } else if ( flags == (EVENT_FLAG_RBUTTON + EVENT_FLAG_SHIFTKEY) ) { cout << "Right mouse button is clicked while pressing SHIFT key - position (" << x << ", " << y << ")" << endl; } else if ( event == EVENT_MOUSEMOVE && flags == EVENT_FLAG_ALTKEY) { cout << "Mouse is moved over the window while pressing ALT key - position (" << x << ", " << y << ")" << endl; } } int main(int argc, char** argv) { // Read image from file Mat img = imread("lena.JPG"); //if fail to read the image if ( img.empty() ) { cout << "Error loading the image" << endl; return -1; } //Create a window namedWindow("My Window", 1); //set the callback function for any mouse event setMouseCallback("My Window", CallBackFunc, NULL); //show the image imshow("My Window", img); // Wait until user press some key waitKey(0); return 0; }------------
Example 3:
This code will extract color information at a pixel location in an image.------------
#include "opencv2/highgui/highgui.hpp" #include <iostream> using namespace std; using namespace cv; void mouseEvent(int evt, int x, int y, int flags, void* param) { Mat* rgb = (Mat*) param; if (evt == CV_EVENT_LBUTTONDOWN) { printf("%d %d: %d, %d, %d\n", x, y, (int)(*rgb).at<Vec3b>(y, x)[0], (int)(*rgb).at<Vec3b>(y, x)[1], (int)(*rgb).at<Vec3b>(y, x)[2]); } } int main(int argc, char** argv) { // Read image from file Mat img = imread("lena.JPG"); //if fail to read the image if ( img.empty() ) { cout << "Error loading the image" << endl; return -1; } //Create a window namedWindow("My Window", 1); //set the callback function for any mouse event setMouseCallback("My Window", mouseEvent, &img); //show the image imshow("My Window", img); // Wait until user press some key waitKey(0); return 0; }------------
Example 4:
------------#include "opencv2/highgui/highgui.hpp" #include <iostream> using namespace std; using namespace cv; void on_mouse( int e, int x, int y, int d, void *ptr ) { Point*p = (Point*)ptr; p->x = x; p->y = y; cout<<*p; } int main(int argc, char** argv) { // Read image from file Mat img = imread("lena.JPG"); //if fail to read the image if ( img.empty() ) { cout << "Error loading the image" << endl; return -1; } //Create a window namedWindow("My Window", 1); //set the callback function for any mouse event Point p; setMouseCallback("My Window", on_mouse, &p ); //show the image imshow("My Window", img); // Wait until user press some key waitKey(0); return 0; }------------
Sources:
http://opencv-srf.blogspot.in/2011/11/mouse-events.html
http://stackoverflow.com/questions/14874449/opencv-set-mouse-callback
http://stackoverflow.com/questions/15570431/opencv-return-value-from-mouse-callback-function
What kind of user data can I pass to my mouse call back?
ReplyDeleteYou can pass pointers of any data type to the callBackFun.
DeleteFor example, you can pass pointers to Mat, or Point. You can get a hint from example 3 and 4.
no u cant u idiot
DeleteIf i want to return value x, y to main. How could i do ?
ReplyDeleteSorry but i just a newbie on opencv
See example 4. It will return the mouse coordinates to main function as pointer.
DeleteHI, thank you very much for your codes, I just have one question, why do you put first the y and then the x in these instructions:
ReplyDelete(int)(*rgb).at(y, x)[0],
(int)(*rgb).at(y, x)[1],
(int)(*rgb).at(y, x)[2]);
Is it the right order?
Image axis convention: x->columns, y->rows
DeleteHow can I blur faces by drawing a rectangle on them by opencv (c++) ?
ReplyDeleteThanks
Thanks
ReplyDeleteI tried to use the example 4, but I still cant access the x and y in main. How can I do it?
ReplyDeletebecause u are a fool
Deletein example 4,what's the meaning of "Point*p = (Point*)ptr;"?
ReplyDeleteThanks a lot man! You saved my day!
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thanks !
ReplyDeletehttps://imgur.com/Ps6pZJm
ReplyDeleteWhy does it will create 2 instances of window?
Its very strange...
I copy pasted from tutorial and still generating 2 windows...instead of one
just get lost from this blog u idiot
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