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Creating Bounding rotated boxes and ellipses for contours

Table of Contents

Prev Tutorial: Creating Bounding boxes and circles for contours
Next Tutorial: Image Moments

Original author Ana Huamán
Compatibility OpenCV >= 3.0

Goal

In this tutorial you will learn how to:

Theory

Code

This tutorial code's is shown lines below. You can also download it from here

#include <iostream>
using namespace cv;
using namespace std;
Mat src_gray;
int thresh = 100;
RNG rng(12345);
void thresh_callback(int, void* );
int main( int argc, char** argv )
{
CommandLineParser parser( argc, argv, "{@input | stuff.jpg | input image}" );
Mat src = imread( samples::findFile( parser.get<String>( "@input" ) ) );
if( src.empty() )
{
cout << "Could not open or find the image!\n" << endl;
cout << "Usage: " << argv[0] << " <Input image>" << endl;
return -1;
}
cvtColor( src, src_gray, COLOR_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
const char* source_window = "Source";
namedWindow( source_window );
imshow( source_window, src );
const int max_thresh = 255;
createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );
thresh_callback( 0, 0 );
waitKey();
return 0;
}
void thresh_callback(int, void* )
{
Mat canny_output;
Canny( src_gray, canny_output, thresh, thresh*2 );
vector<vector<Point> > contours;
findContours( canny_output, contours, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0) );
vector<RotatedRect> minRect( contours.size() );
vector<RotatedRect> minEllipse( contours.size() );
for( size_t i = 0; i < contours.size(); i++ )
{
minRect[i] = minAreaRect( contours[i] );
if( contours[i].size() > 5 )
{
minEllipse[i] = fitEllipse( contours[i] );
}
}
Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
for( size_t i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );
// contour
drawContours( drawing, contours, (int)i, color );
// ellipse
ellipse( drawing, minEllipse[i], color, 2 );
// 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 );
}
}
imshow( "Contours", drawing );
}
Designed for command line parsing.
Definition utility.hpp:820
n-dimensional dense array class
Definition mat.hpp:812
MatSize size
Definition mat.hpp:2160
bool empty() const
Returns true if the array has no elements.
Random Number Generator.
Definition core.hpp:2889
Template class for specifying the size of an image or rectangle.
Definition types.hpp:335
std::string String
Definition cvstd.hpp:151
#define CV_8UC3
Definition interface.h:90
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
void ellipse(InputOutputArray img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a simple or thick elliptic arc or fills an ellipse sector.
void line(InputOutputArray img, Point pt1, Point pt2, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a line segment connecting two points.
void drawContours(InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar &color, int thickness=1, int lineType=LINE_8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point())
Draws contours outlines or filled contours.
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
"black box" representation of the file storage associated with a file on disk.
Definition core.hpp:102
STL namespace.

Explanation

Result

Here it is: