什么是轮廓？

轮廓是一系列相连的点组成的曲线，代表了物体的基本外形。

轮廓与边缘好像挺像的？

是的，确实挺像，那么区别是什么呢？简而言之，轮廓是连续的，而边缘并不全都连续（见下图示例）。其实边缘主要是作为图像的特征使用，比如可以用边缘特征可以区分脸和手，而轮廓主要用来分析物体的形态，比如物体的周长和面积等，可以说边缘包括轮廓。

边缘和轮廓的区别（图片来源：）

寻找轮廓的操作一般用于二值化图，所以通常会使用阈值分割或Canny边缘检测先得到二值图。

【注：寻找轮廓是针对白色物体的，一定要保证物体是白色，而背景是黑色，不然很多人在寻找轮廓时会找到图片最外面的一个框】

 

OpenCV4.1.0 C++ Sample Code:

/** * @function findContours_Demo.cpp * @brief Demo code to find contours in an image * @author OpenCV team */#include "opencv2/imgcodecs.hpp"#include "opencv2/highgui.hpp"#include "opencv2/imgproc.hpp"#include 
     
      using namespace cv;using namespace std;Mat src_gray;int thresh = 100;RNG rng(12345);/// Function headervoid thresh_callback(int, void* );/** * @function main */int main( int argc, char** argv ){    /// Load source image    CommandLineParser parser( argc, argv, "{@input | ../data/HappyFish.jpg | input image}" );    Mat src = imread( parser.get
      
       ( "@input" ) );    if( src.empty() )    {      cout << "Could not open or find the image!\n" << endl;      cout << "Usage: " << argv[0] << " 
       " << endl;      return -1;    }    /// Convert image to gray and blur it    cvtColor( src, src_gray, COLOR_BGR2GRAY );    blur( src_gray, src_gray, Size(3,3) );    /// Create Window    const char* source_window = "Source";    namedWindow( source_window );    imshow( source_window, src );    const int max_thresh = 255;    createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );    thresh_callback( 0, 0 );    waitKey();    return 0;}/** * @function thresh_callback */void thresh_callback(int, void* ){    /// Detect edges using Canny    Mat canny_output;    Canny( src_gray, canny_output, thresh, thresh*2 );    /// Find contours    vector
       
        
          > contours;    vector
         
           hierarchy;    findContours( canny_output, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE );    /// Draw contours    Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );    for( size_t i = 0; i< contours.size(); i++ )    {        Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );        drawContours( drawing, contours, (int)i, color, 2, LINE_8, hierarchy, 0 );    }    /// Show in a window    imshow( "Contours", drawing );}
         
        
       
      
     

Result: