opencv：轮廓逼近与拟合

轮廓逼近，本质上是减少编码点

拟合圆，生成最相似的圆或椭圆

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

using namespace cv;
using namespace std;
RNG rng(12345);

void fit_circle_demo(Mat &image);

int main(int argc, char** argv)
{
    //Mat src = imread("f:/images/qq/jihe.png");
    Mat src = imread("f:/images/qq/stuff.png");
    if (src.empty())
    {
        printf("Could not find the image!\n");
        return -1;
    }

    namedWindow("input", WINDOW_AUTOSIZE);
    imshow("input", src);

    // 做一个高斯模糊，消除一些细微的东西
    GaussianBlur(src, src, Size(3, 3), 0);

    Mat gray, binary;
    cvtColor(src, gray, COLOR_BGR2GRAY);
    imshow("gray", gray);

    // 二值化
    threshold(gray, binary, 0, 255, THRESH_BINARY | THRESH_OTSU);
    imshow("binary", binary);

    vector<vector<Point>> contours;
    vector<Vec4i> hierarchy;
    //findContours(binary, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point());
    // 只绘制最外层的轮廓
    findContours(binary, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE, Point());

    fit_circle_demo(src);
    src = imread("f:/images/qq/stuff.png");

    //多边形逼近演示
    for (size_t t = 0; t < contours.size(); t++) {
        Moments mm = moments(contours[t]);
        // 计算每个轮廓的中心位置
        double cx = mm.m10 / mm.m00;
        double cy = mm.m01 / mm.m00;
        circle(src, Point(cx, cy), 3, Scalar(0, 255, 0), 2, 8, 0);

        double area = contourArea(contours[t]);
        double clen = arcLength(contours[t], true);

        Mat result;
        approxPolyDP(contours[t], result, 4, true);
        printf("corners: %d, colums: %d, contour area: %.2f, contour length: %.2f\n", result.rows, result.cols, area, clen);
        if (result.rows == 6) {
            putText(src, "poly", Point(cx, cy-10), FONT_HERSHEY_PLAIN, 1.0, Scalar(0, 255, 0), 1, 8);
        }
        if (result.rows == 4) {
            putText(src, "rectangle", Point(cx, cy - 10), FONT_HERSHEY_PLAIN, 1.0, Scalar(0, 255, 0), 1, 8);
        }
        if (result.rows == 3) {
            putText(src, "trangle", Point(cx, cy - 10), FONT_HERSHEY_PLAIN, 1.0, Scalar(0, 255, 0), 1, 8);
        }
        if (result.rows > 10) {
            putText(src, "circle", Point(cx, cy - 10), FONT_HERSHEY_PLAIN, 1.0, Scalar(0, 255, 0), 1, 8);
        }
    }

    imshow("result", src);

    waitKey(0);
    destroyAllWindows();

    return 0;
}

void fit_circle_demo(Mat& image) {
    Mat gray, binary;
    cvtColor(image, gray, COLOR_BGR2GRAY);
    // 二值化
    threshold(gray, binary, 0, 255, THRESH_BINARY | THRESH_OTSU);
    imshow("binary", binary);

    vector<vector<Point>> contours;
    vector<Vec4i> hierarchy;
    //findContours(binary, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point());
    // 只绘制最外层的轮廓
    findContours(binary, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE, Point());

    //拟合圆或者椭圆
    for (size_t t = 0; t < contours.size(); t++) {
        //drawContours(image, contours, t, Scalar(0, 0, 255), 2, 8);
        RotatedRect rrt = fitEllipse(contours[t]);
        float w = rrt.size.width;
        float h = rrt.size.height;
        Point center = rrt.center;
        circle(image, center, 3, Scalar(255, 0, 0), 2, 8, 0);
        ellipse(image, rrt, Scalar(0, 255, 0), 2, 8);
    }
    imshow("fit demo", image);
}