OPENCV系列（一） 读取图像中任意点的像素值，并显示坐标

需求：在鼠标左键按下时，显示该位置的像素值和坐标。

在vs2010下新建了Win32控制台项目，在此只处理灰度图像，显示的像素值为灰度值

#include "iostream"
#include "cv.h"
#include "highgui.h"
#include "math.h"

using namespace std;

void mouseHandler(int event, int x, int y, int flags, void* param)
{
IplImage *img0, *img1;
img0 = (IplImage*)param;
img1 = cvCreateImage(cvSize(img0->width, img0->height), img0->depth, img0->nChannels);
cvCopy(img0, img1, NULL);

CvFont font;
uchar* ptr;
char label[20];
char label2[20];

cvInitFont(&font, CV_FONT_HERSHEY_PLAIN, 1, 1, 0, 1, 1);    //初始化字体

if(event == CV_EVENT_LBUTTONDOWN)
{
//读取像素
ptr = cvPtr2D(img0, y, x, NULL);

sprintf(label, "Grey Level:%d", ptr[0]);
sprintf(label2, "Pixel: (%d, %d)", x, y);
//调整显示位置
if(img0->width - x <= 180 || img0->height - y <= 20)
{
cvRectangle(img1, cvPoint(x-180, y-40), cvPoint(x-10, y-10), CV_RGB(255, 0, 0), CV_FILLED, 8, 0);
cvPutText(img1, label, cvPoint(x-180, y-30), &font, CV_RGB(255, 255, 255));
cvPutText(img1, label2, cvPoint(x-180, y-10), &font, CV_RGB(255, 255, 255));
}
else
{
cvRectangle(img1, cvPoint(x+10, y-12), cvPoint(x+180, y+20), CV_RGB(255, 0, 0), CV_FILLED, 8, 0);
cvPutText(img1, label, cvPoint(x+10, y), &font, CV_RGB(255, 255, 255));
cvPutText(img1, label2, cvPoint(x+10, y+20), &font, CV_RGB(255, 255, 255));
}
//以鼠标为中心画点
CvPoint centerPoint;
centerPoint.x = x;
centerPoint.y = y;
cvCircle(img1, centerPoint, 3, CV_RGB(0, 0, 0), 1, 8, 3);

cvShowImage("img", img1);
}
}
int main()
{
int exit = 0;
int c;
IplImage* img;
img = cvLoadImage("点云图.png", 1);
//img = cvLoadImage("hotel201.pgm", 1);
assert(img);

if(img->nChannels != 1) //判断是否为灰度图像，若不是，先转换为灰度图像
{
//转换为灰度图像
IplImage* gray = cvCreateImage(cvGetSize(img), img->depth, 1);
cvCvtColor(img, gray, CV_BGR2GRAY);
}
cvNamedWindow("img", 1);
cvSetMouseCallback("img", mouseHandler, (void*)img);
cvShowImage("img", img);
//检测键盘输入，按Q键退出程序
while(!exit)
{
c = cvWaitKey(0);
switch(c)
{
case 'q':
exit = 1;
break;
default:
continue;
}
}
cvDestroyAllWindows();
cvReleaseImage(&img);
return 0;
}

注：调整显示位置那部分代码理解为如果鼠标点击的位置太靠近边缘，显示的矩形框会在图片之外，用户无法看到，故设置了检测，如果靠近边缘，就在另一边显示内容。

效果见图：（采用例子为2D点云图）