arcLength函数[通俗易懂]

1、arcLength函数

函数的作用

主要是计算图像轮廓的周长、

2、函数调用形式

C++: double arcLength(InputArray curve, bool closed)

参数详解：

InputArray curve：表示图像的轮廓

bool closed：表示轮廓是否封闭的

3、一般图像轮廓矩也可以算出图像的周长和面积

opencv代码：

 
 
 
 #include “opencv2/highgui/highgui.hpp”
 
 
 
 #include “opencv2/imgproc/imgproc.hpp”
 
 
 
 #include <iostream>
 
 
 
 #include <stdio.h>
 
 
 
 #include <stdlib.h>
 
 
 

 
 
 
 using namespace cv;
 
 
 
 using namespace std;
 
 
 

 
 
 
 Mat src; Mat src_gray;
 
 
 
 int thresh = 100;
 
 
 
 int max_thresh = 255;
 
 
 
 RNG rng(12345);
 
 
 

 
 
 
 /// 函数声明
 
 
 
 void thresh_callback(int, void* );
 
 
 

 
 
 
 /** @主函数 */
 
 
 
 int main( int argc, char** argv )
 
 
 
 {
 
 
 
 /// 读入原图像, 返回3通道图像数据
 
 
 
 src = imread( argv[ 1], 1 );
 
 
 

 
 
 
 /// 把原图像转化成灰度图像并进行平滑
 
 
 
 cvtColor( src, src_gray, CV_BGR2GRAY );
 
 
 
 blur( src_gray, src_gray, Size( 3, 3) );
 
 
 

 
 
 
 /// 创建新窗口
 
 
 
 char* source_window = “Source”;
 
 
 
 namedWindow( source_window, CV_WINDOW_AUTOSIZE );
 
 
 
 imshow( source_window, src );
 
 
 

 
 
 
 createTrackbar( ” Canny thresh:”, “Source”, &thresh, max_thresh, thresh_callback );
 
 
 
 thresh_callback( 0, 0 );
 
 
 

 
 
 
 waitKey( 0);
 
 
 
 return( 0);
 
 
 
 }
 
 
 

 
 
 
 /** @thresh_callback 函数 */
 
 
 
 void thresh_callback(int, void* )
 
 
 
 {
 
 
 
 Mat canny_output;
 
 
 
 vector< vector<Point> > contours;
 
 
 
 vector<Vec4i> hierarchy;
 
 
 

 
 
 
 /// 使用Canndy检测边缘
 
 
 
 Canny( src_gray, canny_output, thresh, thresh* 2, 3 );
 
 
 
 /// 找到轮廓
 
 
 
 findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point( 0, 0) );
 
 
 

 
 
 
 /// 计算矩
 
 
 
 vector<Moments> mu(contours.size() );
 
 
 
 for( int i = 0; i < contours.size(); i++ )
 
 
 
 { mu[i] = moments( contours[i], false ); }
 
 
 

 
 
 
 /// 计算中心矩:
 
 
 
 vector<Point2f> mc( contours.size() );
 
 
 
 for( int i = 0; i < contours.size(); i++ )
 
 
 
 { mc[i] = Point2f( mu[i].m10/mu[i].m00 , mu[i].m01/mu[i].m00 ); }
 
 
 

 
 
 
 /// 绘制轮廓
 
 
 
 Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
 
 
 
 for( int i = 0; i< contours.size(); i++ )
 
 
 
 {
 
 
 
 Scalar color = Scalar( rng.uniform( 0, 255), rng.uniform( 0, 255), rng.uniform( 0, 255) );
 
 
 
 drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
 
 
 
 circle( drawing, mc[i], 4, color, -1, 8, 0 );
 
 
 
 }
 
 
 

 
 
 
 /// 显示到窗口中
 
 
 
 namedWindow( “Contours”, CV_WINDOW_AUTOSIZE );
 
 
 
 imshow( “Contours”, drawing );
 
 
 

 
 
 
 /// 通过m00计算轮廓面积并且和OpenCV函数比较
 
 
 
 printf( “\t Info: Area and Contour Length \n”);
 
 
 
 for( int i = 0; i< contours.size(); i++ )
 
 
 
 {
 
 
 
 printf( ” * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n”, i, mu[i].m00, contourArea(contours[i]), arcLength( contours[i], true ) );
 
 
 
 Scalar color = Scalar( rng.uniform( 0, 255), rng.uniform( 0, 255), rng.uniform( 0, 255) );
 
 
 
 drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
 
 
 
 circle( drawing, mc[i], 4, color, -1, 8, 0 );
 
 
 
 }
 
 
 
 }