花老湿学习OpenCV：distanceTransform()的使用

引言：

Opencv中distanceTransform方法用于计算图像中每一个非零点距离离自己最近的零点的距离，distanceTransform的第二个Mat矩阵参数dst保存了每一个点与最近的零点的距离信息，图像上越亮的点，代表了离零点的距离越远。

可以根据距离变换的这个性质，经过简单的运算，用于细化字符的轮廓和查找物体质心（中心）。

API：

 

 代码示例：

 1.细化字符的轮廓：

#include "pch.h"
#include 
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


int main()
{
	Mat src = imread("F:\\visual studio\\Image\\number.jpg");
	if (src.empty())
	{
		cout << "Can't load the image" << endl;
	}
	
	//转化为灰度图
	Mat graysrc;
	cvtColor(src, graysrc, COLOR_BGR2GRAY);
	
	//高斯模糊
	Mat blursrc;
	GaussianBlur(graysrc, blursrc, Size(3, 3), 0, 0);

	//转化为二值图像
	Mat bin;
	threshold(~blursrc, bin,CV_THRESH_TRIANGLE, 255, CV_THRESH_BINARY);
	imshow("bin", bin);
	
	//距离变换
	Mat dist = Mat::zeros(src.size(), CV_32FC1);
	distanceTransform(bin, dist, CV_DIST_L1, 3);
	

	//求取距离的最大值
	double maxVal;
	minMaxLoc(dist, 0, &maxVal, 0, 0, Mat()); 

	//距离图像
	Mat temp;
	dist.convertTo(temp, CV_8UC1);
	imshow("dist", temp/maxVal*255);

	//细化字符的轮廓
	Mat dst = Mat::zeros(src.size(), CV_8UC1);
	for (int i = 0; i < dist.rows; i++)
	{
		for (int j = 0; j < dist.cols; j++)
		{
			if (dist.at(i, j) > maxVal / 2)
				dst.at(i, j) = 255;
		}
	}
	imshow("dst", dst);

	waitKey(0);
}

效果展示： 

 

 2.寻找物体的中心：

#include "pch.h"
#include 
#include "opencv2/opencv.hpp"

using namespace std;
using namespace cv;


int main()
{
	Mat src = imread("F:\\visual studio\\Image\\liujiao.jpg");
	if (src.empty())
	{
		cout << "Can't load the image" << endl;
	}

	//转化为灰度图
	Mat graysrc;
	cvtColor(src, graysrc, COLOR_BGR2GRAY);

	//高斯模糊
	Mat blursrc;
	GaussianBlur(graysrc, blursrc, Size(3, 3), 0, 0);

	//转化为二值图像
	Mat bin;
	threshold(~blursrc, bin, CV_THRESH_TRIANGLE, 255, CV_THRESH_BINARY);
	imshow("bin", bin);

	//距离变换
	Mat dist = Mat::zeros(src.size(), CV_32FC1);
	distanceTransform(bin, dist, CV_DIST_L1, 3);

	//求取距离的最大值
	double maxVal;
	Point Pt;
	minMaxLoc(dist, 0, &maxVal, 0, &Pt, Mat());
	
	//距离图像 
	dist.convertTo(dist, CV_8UC1);
	normalize(dist, dist, 0, 255, CV_MINMAX);
	imshow("dist", dist);

	//绘制物体的中心
	Mat dst;
	src.copyTo(dst);
	circle(dst, Pt, 2, Scalar(255, 0, 0), 2, LINE_AA);
	circle(dst, Pt, maxVal, Scalar(0, 0, 255), 2, LINE_AA);
	imshow("dst", dst);
	
	waitKey(0);
}