OpenCV Tutorials —— Creating Bounding rotated boxes and ellipses for contours

外接旋转矩形 ，或外接椭圆

RotatedRect minAreaRect(InputArray points)

返回面积最小的外接矩形

RotatedRect fitEllipse(InputArray points)

The function calculates the ellipse that fits (in a least-squares sense) a set of 2D points best of all. It returns the rotated rectangle in which the ellipse is inscribed.

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) );

	/// 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) );

	/// Find the rotated rectangles and ellipses for each contour
	vector<RotatedRect> minRect( contours.size() );
	vector<RotatedRect> minEllipse( contours.size() );

	for( int i = 0; i < contours.size(); i++ )
	{
		minRect[i] = minAreaRect( Mat(contours[i]) );
		if( contours[i].size() > 5 )
			{ minEllipse[i] = fitEllipse( Mat(contours[i]) ); }
	}

	/// Draw contours + rotated rects + ellipses
	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) );
		// contour
		drawContours( drawing, contours, i, color, 1, 8, vector<Vec4i>(), 0, Point() );
		// ellipse
		ellipse( drawing, minEllipse[i], color, 2, 8 );
		// rotated rectangle
		Point2f rect_points[4]; minRect[i].points( rect_points );
		for( int j = 0; j < 4; j++ )
			line( drawing, rect_points[j], rect_points[(j+1)%4], color, 1, 8 );
	}

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