【练习4.2】使用鼠标事件获取图片像素值

《学习OpenCV》中文版第4章第2题

题目要求：

点击图片是获取该点的颜色值，并在图像上点击鼠标处用文本将颜色值显示出来。

程序代码：

#include "stdafx.h"
#include <cv.h>
#include <highgui.h>
using namespace std;
using namespace cv;

void MouseCallBack(int event, int x, int y, int flags, void *param);

int _tmain(int argc, _TCHAR* argv[])
{
    const char * fileName = "D:\Work\Work_Programming\Source\Image\lena.jpg"; 
    cvNamedWindow("MouseEvent", CV_WINDOW_AUTOSIZE);
    IplImage * img = cvLoadImage(fileName,1);
    assert(img);

    cvSetMouseCallback("MouseEvent", MouseCallBack, img);

    while (true)
    {
        cvShowImage("MouseEvent", img);

        if (waitKey(15) == 27)
        {
            break;
        }
    }    
    
    cvWaitKey(0);

    cvReleaseImage(&img);
    cvDestroyWindow("MouseEvent"); 
 
    //system("pause");
 
    return 0;
}

void MouseCallBack(int event, int x, int y, int flags, void *param)
{
    IplImage * img = (IplImage *)param;

    CvFont font;
    cvInitFont(&font, CV_FONT_HERSHEY_SIMPLEX, 0.5, 0.5, 0, 2, 8);

    CvScalar scl;
    char * str = (char *)malloc(30 * sizeof(char));

    if (event == CV_EVENT_LBUTTONDOWN)
    {
        scl = cvGet2D(img, x, y);

        double b = scl.val[0];
        double g = scl.val[1];
        double r = scl.val[2];
        
        sprintf(str, "B:%.0f,G:%.0f,R:%.0f", b, g, r);

        cvPutText(img, str, cvPoint(x, y), &font, cvScalar(255, 0, 0));
    }

    free(str);
}