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// Example : query colour elements in an image
// usage: prog <image_name>
// Author : Toby Breckon, toby.breckon@cranfield.ac.uk
// Copyright (c) 2010 School of Engineering, Cranfield University
// License : LGPL - http://www.gnu.org/licenses/lgpl.html
#include <cv.h> // open cv general include file
#include <highgui.h> // open cv GUI include file
#include <iostream> // standard C++ I/O
using namespace cv; // OpenCV API is in the C++ "cv" namespace
/******************************************************************************/
void colourQueryMouseCallBack(int event, int x, int y, int flags, void* img)
{
int row = y; // y-axis is image rows (down the side)
int col = x; // x-axis is image columns (along the top)
switch (event)
{
case CV_EVENT_LBUTTONDOWN :
// left button prints colour information at click location to stdout
std::cout << "Colour information at image location (" << x << ","
<< y << "): ";
for(int channel = 0; channel < 3; channel++){ // three channels (B,G,R)
// note that variable img is now a pointer to the image object
// in this case (as it was passed by reference)
// IN GENERAL: pixel access is img.at<Vec3b>(row,col)[channel] for
// a 3 channel image (3 bytes per pixel) and img.at<uchar>(row,col) for
// a single channel image (1 byte per pixel)
std::cout <<
(unsigned int) ((Mat*) img)->at<Vec3b>(row,col)[channel] << " ";
}
std::cout << std::endl;
;
break;
case CV_EVENT_RBUTTONDOWN :
// right button sets colour information at click location to white
std::cout << "Colour information at image location (" << x << "," << y
<< ") set to white.";
for(int channel = 0; channel < 3; channel++){ // three channels (B,G,R)
((Mat*) img)->at<Vec3b>(row,col)[channel] = 255;
}
std::cout << std::endl;
;
break;
}
}
/******************************************************************************/
int main( int argc, char** argv )
{
Mat img; // image object
int key;
bool keepProcessing = true;
const string windowName = "OPENCV: colour query"; // window name
// check that command line arguments are provided and image reads in OK
if ((argc == 2) && !(img = imread( argv[1], CV_LOAD_IMAGE_COLOR)).empty())
{
// create window object
namedWindow(windowName, 0 );
// set function to be executed everytime the mouse is clicked/moved
// (note: this uses the older cvXXX function naming style from the
// OpenCV C interface)
cvSetMouseCallback("OPENCV: colour query",
(CvMouseCallback) colourQueryMouseCallBack, &img);
// print out some helpful information about the image
std::cout << "Image : (width x height) = (" << img.cols << " x "
<< img.rows << ")" << std::endl;
std::cout << " Colour channels = " << img.channels() << std::endl;
// loop so that events are processed and the image constantly redisplayed
while (keepProcessing){
// display image in window
imshow(windowName, img );
// start event processing loop (very important,in fact essential for GUI)
key=waitKey(20);
// get any keyboard input given by the user and process it
if (key == 'x'){
// if user presses "x" then exit
std::cout << "Keyboard exit requested : exiting now - bye!" << std::endl;
keepProcessing = false;
}
}
// all OK : main returns 0
return 0;
}
// not OK : main returns -1
return -1;
}
/***************************************************************************** |
