OpenCV C++開發 第二節：圖像處理（十二、凸包）

一、凸包

代碼：

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.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) {
	// 待檢測圖像
	src = imread("C:\\Users\\Administrator\\Desktop\\test.png");
	if (!src.data) {
		printf("could not load image...\n");
		return -1;
	}
	const char* input_win = "input image";
	namedWindow(input_win, CV_WINDOW_AUTOSIZE);
	namedWindow(output_win, CV_WINDOW_NORMAL);
	const char* trackbar_label = "Threshold : ";

	cvtColor(src, src_gray, CV_BGR2GRAY);
	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);
	findContours(bin_output, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0));

	vector<vector<Point>> convexs(contours.size());
	for (size_t i = 0; i < contours.size(); i++) {
		convexHull(contours[i], convexs[i], false, true);
	}

	// 繪製
	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));
		drawContours(dst, convexs, k, color, 2, LINE_8, empty, 0, Point(0, 0));
	}
	imshow(output_win, dst);

	return;
}

以上代碼中主要的幾個知識點解釋下：

1.threshold(src_gray, bin_output, threshold_value, threshold_max, THRESH_BINARY);

之前的課程有講過閥值操作。點擊跳轉

2.convexHull(contours[i], convexs[i], false, true);

什麼是凸包(Convex Hull)，在一個多變形邊緣或者內部任意兩個點的連線都包含在多邊形邊界或者內部。

convexHull (

InputArray points,// 輸入候選點，來自findContours

OutputArray hull,// 凸包

bool clockwise,// default true, 順時針方向

bool returnPoints）// true 表示返回點個數，如果第二個參數是  vector<Point>則自動忽略

）

效果圖如下