opencv学习之路（39）、PCA

一、PCA理论介绍

网上已经有许多介绍pca原理的博客，这里就不重复介绍了。详情可参考

http://blog.csdn.net/zhongkelee/article/details/44064401

计算过程

数据互换

二、opencv代码

#include<opencv2/opencv.hpp>
using namespace cv;
using namespace std;

void calcPCAOrientation(vector<Point>&pts, Mat &image){
    int size = static_cast<int>(pts.size());//static_cast强制类型转换
    Mat data_pts = Mat(size,,CV_64FC1);//size个对象，2个维度(即平面坐标x，y)
    for (int i = ; i < size; i++)
    {
        data_pts.at<double>(i, ) = pts[i].x;
        data_pts.at<double>(i, ) = pts[i].y;
    }
    //执行PCA的一系列步骤：样本数据-均值，算协方差，算特征值和特征向量……
    PCA pca(data_pts, Mat(), CV_PCA_DATA_AS_ROW);
    //获取均值（中心）位置
    Point cnt = Point(static_cast<int>(pca.mean.at<double>(, )),
                      static_cast<int>(pca.mean.at<double>(, )));
    circle(image,cnt,,Scalar(,,),,,);

    vector<Point2d>vecs();
    vector<double>vals();
    for (int i = ; i < ; i++)
    {
        vals[i] = pca.eigenvalues.at<double>(i, );//特征值
        cout << "第" << i << "个特征值：" << vals[i]<<endl;
        vecs[i] = Point2d(pca.eigenvectors.at<double>(i, ),    //特征向量
                         (pca.eigenvectors.at<double>(i, )));
    }
    Point p1 = cnt + 0.02*Point(static_cast<int>(vecs[].x*vals[]), static_cast<int>(vecs[].y*vals[]));
    Point p2  = cnt - 0.05*Point(static_cast<int>(vecs[].x*vals[]), static_cast<int>(vecs[].y*vals[]));

    line(image, cnt, p1, Scalar(, , ), , , );
    line(image, cnt, p2, Scalar(, , ), , , );

    double angle = atan2(vecs[].y,vecs[].x);
    cout << "angle:" <<  * (angle / CV_PI)<<endl;
}

void main()
{
    Mat src = imread("E://2.jpg");
    imshow("src", src);
    Mat gray, binary;
    cvtColor(src, gray,CV_BGR2GRAY);
    threshold(gray, binary,,, THRESH_BINARY|THRESH_OTSU);//自动阈值：OTSU找到一个它认为最好的阈值
    //imshow("binary", binary);

    //轮廓提取
    vector<Vec4i>hierarchy;
    vector<vector<Point>>contours;
    findContours(binary, contours, hierarchy, RETR_LIST, CHAIN_APPROX_NONE);//查找所有轮廓，存储所有轮廓点
    Mat result = src.clone();//复制，不随原图改变
    for (int i = ; i < contours.size(); i++)
    {
        double area = contourArea(contours[i]);
        if (area>1e5 || area < 1e2)    continue;//面积大于10^5或者小于10^2的轮廓，不要
        drawContours(result, contours, i, Scalar(, , ), , );

        calcPCAOrientation(contours[i], result);//调用PCA
    }
    imshow("contours result", result);

    waitKey();
}