凸殼(Convex Hull)是一個計算幾何中的概念，在給定二維平面上的點集合，凸殼就是將最外層的點連接起來的凸多邊型，
能包含點集合中的所有點，在影像處理中，通常是找到某個物件後，用來填補空隙，或者是進一步的進行物件辨識。
void convexHull(InputArray points, OutputArray hull, bool clockwise=false, bool returnPoints=true)
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>
using namespace cv ;
using namespace std ;
int main() {
Mat src_gray;
cv::Mat src = cv::imread("/Users/powenko/Desktop/1.png");
if(src.data!=NULL){
cvtColor( src, src_gray, CV_BGR2GRAY );
//Dilate
int erosion_size =10;
Mat element = getStructuringElement(cv::MORPH_ELLIPSE,
cv::Size(2 * erosion_size + 1, 2 * erosion_size + 1),
cv::Point(erosion_size, erosion_size) );
dilate(src_gray,src_gray,element);
imshow( "Source", src_gray );
// Convex Hull implementation
Mat src_copy = src_gray.clone();
Mat threshold_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
// Find contours
threshold( src_gray, threshold_output, 200, 255, THRESH_BINARY );
findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
// Find the convex hull object for each contour
vector<vector<Point> >hull( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{ convexHull( Mat(contours[i]), hull[i], false ); }
// Draw contours + hull results
RNG rng;
Mat drawing = Mat::zeros( threshold_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, 1, 8, vector<Vec4i>(), 0, Point() );
drawContours( drawing, hull, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
}
cv::namedWindow("Image") ;
cv::imshow("Image", src) ;
cv::imshow("result", src_gray) ;
cv::waitKey() ;
}
return 0;
}
