凸包

凸包在一个多变形边缘或者内部任意两个点的连线都包含在多边形边界或者内部。
首先把图像从RGB转为灰度
然后再转为二值图像
在通过发现轮廓得到候选点
凸包API调用
绘制显示。

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>
#include <opencv2\imgproc\types_c.h>

using namespace std;
using namespace cv;
Mat src, src_gray, dst;
int threshold_value = 100;
int threshold_max = 255;
const char* output_win = "convex hull demo";
void Threshold_Callback(int, void*);
RNG rng(12345);
int main(int argc, char** argv) {
	src = imread("D:\\lena.jpg");
	if (!src.data) {
		printf("could not load image...\n");
		return -1;
	}
	const char* input_win = "input image";
	namedWindow(input_win, WINDOW_AUTOSIZE);
	namedWindow(output_win, WINDOW_NORMAL);
	const char* trackbar_label = "Threshold : ";

	cvtColor(src, src_gray, CV_BGR2GRAY);//从RGB转为灰度
	blur(src_gray, src_gray, Size(3, 3), Point(-1, -1), BORDER_DEFAULT);
	imshow(input_win, src_gray);

	createTrackbar(trackbar_label, output_win, &threshold_value, threshold_max, Threshold_Callback);
	Threshold_Callback(0, 0);
	waitKey(0);
	return 0;
}

void Threshold_Callback(int, void*) {
	Mat bin_output;
	vector<vector<Point>> contours;
	vector<Vec4i> hierachy;

	threshold(src_gray, bin_output, threshold_value, threshold_max, THRESH_BINARY);//二值图像
	findContours(bin_output, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));//发现轮廓
	/*
	convexHull(
		InputArray points,// 输入候选点，来自findContours
		OutputArray hull,// 凸包
		bool clockwise,// default true, 顺时针方向
		bool returnPoints）// true 表示返回点个数，如果第二个参数是vector<Point>则自动忽略
	*/
	vector<vector<Point>> convexs(contours.size());
	for (size_t i = 0; i < contours.size(); i++) {
		convexHull(contours[i], convexs[i], false, true);
	}

	// 绘制显示
	dst = Mat::zeros(src.size(), CV_8UC3);
	vector<Vec4i> empty(0);
	for (size_t k = 0; k < contours.size(); k++) {
		Scalar color = Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));
		drawContours(dst, contours, k, color, 2, LINE_8, hierachy, 0, Point(0, 0));//l轮廓
		drawContours(dst, convexs, k, color, 2, LINE_8, empty, 0, Point(0, 0));//t凸包
	}
	imshow(output_win, dst);

	return;
}