OpenCv学习笔记（七）：轮廓的检测

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本文介绍了使用OpenCV进行轮廓检测的基本步骤，包括通过Canny算子检测边缘，然后使用findContours函数查找轮廓，并利用drawContours函数将轮廓绘制在图像上。通过示例代码展示了如何在C++中实现这一过程。

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其实要说轮廓的检测，是计算机视觉当中基础的内容，进一步延伸可以用来实现基于轮廓的图像检索。现在是刚看到的一段代码，通知canny算子实现轮廓的检测，特别用到了opencv当中的findContours函数，及drawContours函数实现轮廓的绘制。学习实例源代码如下：

#include "stdafx.h"
/**
* @function findContours_Demo.cpp
* @brief Demo code to find contours in an image
* @author OpenCV team
*/

#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);

/// Function header
void thresh_callback(int, void* );

/**
* @function main
*/
int main( int argc, char** argv )
{
/// Load source image and convert it to gray
src = imread( "d:/2.jpg", 1 );

/// Convert image to gray and blur it
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );

/// Create Window
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);
}

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

/// Detect edges using canny
Canny( src_gray, canny_output, thresh, thresh*2, 3 );
/// Find contours
findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

/// Draw contours
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() );
     }

/// Show in a window
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
}