学步园

     首先介绍今天主角：void
convexityDefects(InputArray contour, InputArray
convexhull, OutputArray convexityDefects)

     使用时注意，最后一个参数 convexityDefects 是存储 Vec4i 的向量(vector<varname>)，函数计算成功后向量的大小是轮廓凸缺陷的数量，向量每个元素Vec4i存储了4个整型数据，因为Vec4i对[]实现了重载，所以可以使用 _vectername[i][0] 来访问向量 _vactername
的第i个元素的第一个分量。再说 Vec4i 中存储的四个整形数据，Opencv 使用这四个元素表示凸缺陷，第一个名字叫做 
start_index,表示缺陷在轮廓上的开始处，他的值是开始点在函数第一个参数 contour 中的下标索引；Vec4i 第二个元素的名字叫
end_index， 顾名思义其对应的值就是缺陷结束处在 contour 中的下标索引； Vec4i 第三个元素 
farthest_pt_index 是缺陷上距离 轮廓凸包(convexhull)最远的点；Vec4i最后的元素叫
fixpt_depth，fixpt_depth/256  表示了
轮廓上以 farthest_pt_index 为下标的点到 轮廓凸包的(convexhull)的距离,以像素为单位。

     All is so easy!下面就是简单的代码示例（首先计算两个轮廓的凸包，然后计算两个轮廓的凸缺陷）:

// 计算凸缺陷 convexityDefect
//

#include "stdafx.h"
#include <opencv.hpp>
#include <iostream>

using namespace std;
using namespace cv;

int _tmain(int argc, _TCHAR* argv[])
{
	Mat *img_01 = new Mat(400, 400, CV_8UC3);
	Mat *img_02 = new Mat(400, 400, CV_8UC3);
	*img_01 = Scalar::all(0);
	*img_02 = Scalar::all(0);
	// 轮廓点组成的数组
	vector<Point> points_01,points_02;


	// 给轮廓组赋值
	points_01.push_back(Point(10, 10));points_01.push_back(Point(10,390));
	points_01.push_back(Point(390, 390));points_01.push_back(Point(150, 250));
	points_02.push_back(Point(10, 10));points_02.push_back(Point(10,390));
	points_02.push_back(Point(390, 390));points_02.push_back(Point(250, 150));

	vector<int> hull_01,hull_02;
	// 计算凸包
	convexHull(points_01, hull_01, true);
	convexHull(points_02, hull_02, true);

	// 绘制轮廓
	for(int i=0;i < 4;++i)
	{
		circle(*img_01, points_01[i], 3, Scalar(0,255,255), CV_FILLED, CV_AA);
		circle(*img_02, points_02[i], 3, Scalar(0,255,255), CV_FILLED, CV_AA);
	}
	// 绘制凸包轮廓
	CvPoint poi_01 = points_01[hull_01[hull_01.size()-1]];
	for(int i=0;i < hull_01.size();++i)
	{
		line(*img_01, poi_01, points_01[i], Scalar(255,255,0), 1, CV_AA);
		poi_01 = points_01[i];
	}
	CvPoint poi_02 = points_02[hull_02[hull_02.size()-1]];
	for(int i=0;i < hull_02.size();++i)
	{
		line(*img_02, poi_02, points_02[i], Scalar(255,255,0), 1, CV_AA);
		poi_02 = points_02[i];
	}
	
	vector<Vec4i> defects;
	// 如果有凸缺陷就把它画出来
	if( isContourConvex(points_01) )
	{
		cout<<"img_01的轮廓是凸包"<<endl;
	}else{
		cout<<"img_01的轮廓不是凸包"<<endl;
		convexityDefects(
			points_01,
			Mat(hull_01),
			defects
			);
		// 绘制缺陷
		cout<<"共"<<defects.size()<<"处缺陷"<<endl;
		for(int i=0;i < defects.size();++i)
		{
			circle(*img_01, points_01[defects[i][0]], 6, Scalar(255,0,0), 2, CV_AA);
			circle(*img_01, points_01[defects[i][1]], 6, Scalar(255,0,0), 2, CV_AA);
			circle(*img_01, points_01[defects[i][2]], 6, Scalar(255,0,0), 2, CV_AA);
			line(*img_01, points_01[defects[i][0]], points_01[defects[i][1]], Scalar(255,0,0), 1, CV_AA);
			line(*img_01, points_01[defects[i][1]], points_01[defects[i][2]], Scalar(255,0,0), 1, CV_AA);
			line(*img_01, points_01[defects[i][2]], points_01[defects[i][0]], Scalar(255,0,0), 1, CV_AA);
			cout<<"第"<<i<<"缺陷<"<<points_01[defects[i][0]].x<<","<<points_01[defects[i][0]].y
				<<">,<"<<points_01[defects[i][1]].x<<","<<points_01[defects[i][1]].y
				<<">,<"<<points_01[defects[i][2]].x<<","<<points_01[defects[i][2]].y<<">到轮廓的距离为："<<defects[i][3]/256<<"px"<<endl;
		}
		defects.clear();
	}
	if( isContourConvex( points_02 ) )
	{
		cout<<"img_02的轮廓是凸包"<<endl;
	}else{
		cout<<"img_02的轮廓不是凸包"<<endl;
		vector<Vec4i> defects;
		convexityDefects(
			points_01,
			Mat(hull_01),
			defects
			);
		// 绘制出缺陷的轮廓
		for(int i=0;i < defects.size();++i)
		{
			circle(*img_02, points_01[defects[i][0]], 6, Scalar(255,0,0), 2, CV_AA);
			circle(*img_02, points_01[defects[i][1]], 6, Scalar(255,0,0), 2, CV_AA);
			circle(*img_02, points_01[defects[i][2]], 6, Scalar(255,0,0), 2, CV_AA);
			line(*img_02, points_01[defects[i][0]], points_01[defects[i][1]], Scalar(255,0,0), 1, CV_AA);
			line(*img_02, points_01[defects[i][1]], points_01[defects[i][2]], Scalar(255,0,0), 1, CV_AA);
			line(*img_02, points_01[defects[i][2]], points_01[defects[i][0]], Scalar(255,0,0), 1, CV_AA);
			// 因为 img_02 没有缺陷所以就懒的写那些输出代码了
		}
		defects.clear();
	}

	imshow("img_01 的轮廓和凸包：", *img_01);
	imshow("img_02 的轮廓和凸包：", *img_02);
	cvWaitKey();
	
	return 0;
}