OpenCV Tutorials —— Creating Bounding boxes and circles for contours

同样是提取出轮廓之后的处理 ~~

void approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed)

Parameters:

• curve –
  
  Input vector of a 2D point stored in:
  • std::vector or Mat (C++ interface)
  • Nx2 numpy array (Python interface)
  • CvSeq or CvMat (C interface)
• approxCurve – Result of the approximation. The type should match the type of the input curve. In case of C interface the approximated curve is stored in the memory storage and pointer to it is returned.
• epsilon – Parameter specifying the approximation accuracy. This is the maximum distance between the original curve and its approximation.
• closed – If true, the approximated curve is closed (its first and last vertices are connected). Otherwise, it is not closed.
• header_size – Header size of the approximated curve. Normally, sizeof(CvContour) is used.
• storage – Memory storage where the approximated curve is stored.
• method – Contour approximation algorithm. Only CV_POLY_APPROX_DP is supported.
• recursive – Recursion flag. If it is non-zero and curve is CvSeq*, the function cvApproxPolyapproximates all the contours accessible from curve by h_next and v_next links.

Rect boundingRect(InputArray points)

Calculates the up-right bounding rectangle of a point set.

void minEnclosingCircle(InputArray points, Point2f& center, float& radius)

Parameters:

• points –
  
  Input vector of 2D points, stored in:
  • std::vector<> or Mat (C++ interface)
  • CvSeq* or CvMat* (C interface)
  • Nx2 numpy array (Python interface)
• center – Output center of the circle.
• radius – Output radius of the circle.

 

Code

#include "stdafx.h"

#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( "img2.jpg", 1 );

	/// Convert image to gray and blur it
	cvtColor( src, src_gray, CV_BGR2GRAY );
	blur( src_gray, src_gray, Size(3,3) );	// 均值滤波 —— 去除小的噪声

	/// Create Window
	char* source_window = "Source";
	namedWindow( source_window, CV_WINDOW_AUTOSIZE );
	imshow( source_window, src );

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

	waitKey(0);
	return(0);
}

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

	/// Detect edges using Threshold
	threshold( src_gray, threshold_output, thresh, 255, THRESH_BINARY );
	/// Find contours
	findContours( threshold_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

	/// Approximate contours to polygons + get bounding rects and circles
	vector<vector<Point> > contours_poly( contours.size() );
	vector<Rect> boundRect( contours.size() );
	vector<Point2f>center( contours.size() );
	vector<float>radius( contours.size() );

	for( int i = 0; i < contours.size(); i++ )
	{
		approxPolyDP( Mat(contours[i]), contours_poly[i], 3, true );	// 原始曲线和近似曲线的精度为3， 近似曲线封闭
		boundRect[i] = boundingRect( Mat(contours_poly[i]) );
		minEnclosingCircle( (Mat)contours_poly[i], center[i], radius[i] );
	}

	/// Draw polygonal contour + bonding rects + circles
	Mat drawing = Mat::zeros( threshold_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_poly, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
		rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2, 8, 0 );
		circle( drawing, center[i], (int)radius[i], color, 2, 8, 0 );
	}

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