OpenCV4入门教程096：查找和绘制图像轮廓矩

索引地址：系列索引

图像矩：图像距(几何矩、中心矩、hu矩)

根据矩的定义，我们从图像中找到并画出来。

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
using namespace cv;
using namespace std;

//-----------------------------------【宏定义部分】--------------------------------------------
//      描述：定义一些辅助宏
//------------------------------------------------------------------------------------------------
#define WINDOW_NAME1 "Original" //为窗口标题定义的宏
#define WINDOW_NAME2 "Result"   //为窗口标题定义的宏

//-----------------------------------【全局变量声明部分】--------------------------------------
//      描述：全局变量的声明
//-----------------------------------------------------------------------------------------------
Mat                   g_srcImage;
Mat                   g_grayImage;
int                   g_nThresh    = 100;
int                   g_nMaxThresh = 255;
RNG                   g_rng(12345);
Mat                   g_cannyMat_output;
vector<vector<Point>> g_vContours;
vector<Vec4i>         g_vHierarchy;

//-----------------------------------【全局变量声明部分】--------------------------------------
//      描述：全局变量的声明
//-----------------------------------------------------------------------------------------------
void on_ThreshChange(int, void *);

//-----------------------------------【main( )函数】--------------------------------------------
//      描述：控制台应用程序的入口函数，我们的程序从这里开始执行
//-----------------------------------------------------------------------------------------------
int main(int argc, char **argv) {
    // 读入原图像, 返回3通道图像数据
    g_srcImage = imread("1.jpg", 1);

    // 把原图像转化成灰度图像并进行平滑
    cvtColor(g_srcImage, g_grayImage, COLOR_BGR2GRAY);
    blur(g_grayImage, g_grayImage, Size(3, 3));

    // 创建新窗口
    namedWindow(WINDOW_NAME1, WINDOW_AUTOSIZE);
    imshow(WINDOW_NAME1, g_srcImage);

    //创建滚动条并进行初始化
    createTrackbar(" 阈值", WINDOW_NAME1, &g_nThresh, g_nMaxThresh, on_ThreshChange);
    on_ThreshChange(0, 0);

    waitKey(0);
    return (0);
}

//-----------------------------------【on_ThreshChange( )函数】-------------------------------
//      描述：回调函数
//-----------------------------------------------------------------------------------------------
void on_ThreshChange(int, void *) {
    // 使用Canndy检测边缘
    Canny(g_grayImage, g_cannyMat_output, g_nThresh, g_nThresh * 2, 3);

    // 找到轮廓
    findContours(g_cannyMat_output, g_vContours, g_vHierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE,
                 Point(0, 0));

    // 计算矩
    vector<Moments> mu(g_vContours.size());
    for (unsigned int i = 0; i < g_vContours.size(); i++) {
        mu[ i ] = moments(g_vContours[ i ], false);
    }

    //  计算中心矩
    vector<Point2f> mc(g_vContours.size());
    for (unsigned int i = 0; i < g_vContours.size(); i++) {
        mc[ i ] = Point2f(static_cast<float>(mu[ i ].m10 / mu[ i ].m00),
                          static_cast<float>(mu[ i ].m01 / mu[ i ].m00));
    }

    // 绘制轮廓
    Mat drawing = Mat::zeros(g_cannyMat_output.size(), CV_8UC3);
    for (unsigned int i = 0; i < g_vContours.size(); i++) {
        Scalar color = Scalar(g_rng.uniform(0, 255), g_rng.uniform(0, 255),
                              g_rng.uniform(0, 255)); //随机生成颜色值
        drawContours(drawing, g_vContours, i, color, 2, 8, g_vHierarchy, 0,
                     Point()); //绘制外层和内层轮廓
        circle(drawing, mc[ i ], 4, color, -1, 8, 0);
        ; //绘制圆
    }

    // 显示到窗口中
    namedWindow(WINDOW_NAME2, WINDOW_AUTOSIZE);
    imshow(WINDOW_NAME2, drawing);

    // 通过m00计算轮廓面积并且和OpenCV函数比较
    printf("\t 输出内容: 面积和轮廓长度\n");
    for (unsigned int i = 0; i < g_vContours.size(); i++) {
        printf(" >通过m00计算出轮廓[%d]的面积: (M_00) = %.2f \n OpenCV函数计算出的面积=%.2f , "
               "长度: %.2f \n\n",
               i, mu[ i ].m00, contourArea(g_vContours[ i ]), arcLength(g_vContours[ i ], true));
        Scalar color = Scalar(g_rng.uniform(0, 255), g_rng.uniform(0, 255), g_rng.uniform(0, 255));
        drawContours(drawing, g_vContours, i, color, 2, 8, g_vHierarchy, 0, Point());
        circle(drawing, mc[ i ], 4, color, -1, 8, 0);
    }
}

效果为

中心的点就是图像的矩。