轮廓矩

目标

在这节教程中您将学到:

• 使用OpenCV函数 moments 计算图像所有的矩(最高到3阶)
• 使用OpenCV函数 contourArea 来计算轮廓面积
• 使用OpenCV函数 arcLength 来计算轮廓或曲线长度

原理

代码

下面是本节教程源码. 你也可以从 这里 下载.

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace cv;
using namespace std;

Mat src; Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);

/// 函数声明
void thresh_callback(int, void* );

/** @主函数 */
int main( int argc, char** argv )
{
  /// 读入原图像, 返回3通道图像数据
  src = imread( argv[1], 1 );

  /// 把原图像转化成灰度图像并进行平滑
  cvtColor( src, src_gray, CV_BGR2GRAY );
  blur( src_gray, src_gray, Size(3,3) );

  /// 创建新窗口
  char* source_window = "Source";
  namedWindow( source_window, CV_WINDOW_AUTOSIZE );
  imshow( source_window, src );

  createTrackbar( " Canny thresh:", "Source", &thresh, max_thresh, thresh_callback );
  thresh_callback( 0, 0 );

  waitKey(0);
  return(0);
}

/** @thresh_callback 函数 */
void thresh_callback(int, void* )
{
  Mat canny_output;
  vector<vector<Point> > contours;
  vector<Vec4i> hierarchy;

  /// 使用Canndy检测边缘
  Canny( src_gray, canny_output, thresh, thresh*2, 3 );
  /// 找到轮廓
  findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

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

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

  /// 绘制轮廓
  Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
  for( int i = 0; i< contours.size(); i++ )
     {
       Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
       drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
       circle( drawing, mc[i], 4, color, -1, 8, 0 );
     }

  /// 显示到窗口中
  namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
  imshow( "Contours", drawing );

  /// 通过m00计算轮廓面积并且和OpenCV函数比较
  printf("\t Info: Area and Contour Length \n");
  for( int i = 0; i< contours.size(); i++ )
     {
       printf(" * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n", i, mu[i].m00, contourArea(contours[i]), arcLength( contours[i], true ) );
       Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
       drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
       circle( drawing, mc[i], 4, color, -1, 8, 0 );
     }
}

代码说明

结果

1. 如下所示:

翻译者

guoming0000@ OpenCV中文网站 <guoming0000@sina.com>