opencv实践::对象提取与测量

问题描述 
照片是来自太空望远镜的星云图像，科学家想知道它的面 积与周长。 

解决思路 
方法一： 通过二值分割+图像形态学+轮廓提取

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

using namespace cv;
using namespace std;

int main(int argc, char** argv) {
    Mat src = imread("D:/case7.png");
    if (src.empty()) {
        printf("could not load image...
");
        return -1;
    }
    namedWindow("input image", CV_WINDOW_AUTOSIZE);
    imshow("input image", src);

    Mat blurImage;
    //高斯模糊
    GaussianBlur(src, blurImage, Size(15, 15), 0, 0);
    //imshow("blur", blurImage);

    Mat gray_src, binary;
    cvtColor(blurImage, gray_src, COLOR_BGR2GRAY);
    threshold(gray_src, binary, 0, 255, THRESH_BINARY | THRESH_TRIANGLE);
    //imshow("binary", binary);

    // 形态学操作
    Mat morphImage;
    Mat kernel = getStructuringElement(MORPH_RECT, Size(3, 3), Point(-1, -1));
    morphologyEx(binary, morphImage, MORPH_CLOSE, kernel, Point(-1, -1), 2);
    //imshow("morphology", morphImage);

    // 获取最大轮廓
    vector<vector<Point>> contours;
    vector<Vec4i> hireachy;
    findContours(morphImage, contours, hireachy, CV_RETR_EXTERNAL, CHAIN_APPROX_SIMPLE, Point());
    Mat connImage = Mat::zeros(src.size(), CV_8UC3);
    for (size_t t = 0; t < contours.size(); t++) {
        Rect rect = boundingRect(contours[t]);
        if (rect.width < src.cols / 2) continue;
        if (rect.width > (src.cols - 20)) continue;
        //计算面积
        double area = contourArea(contours[t]);
        //计算长度
        double len = arcLength(contours[t], true);
        drawContours(connImage, contours, static_cast<int>(t), Scalar(0, 0, 255), 1, 8, hireachy);
        printf("area  of star could : %f
", area);
        printf("length  of star could : %f
", len);
    }
    imshow("result", connImage);

    waitKey(0);
    return 0;
}