OpenCV bug 4448: minimal example

opencv-bug-4448.cpp

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>

#include <iostream>
#include <vector>

int main() 
{
	using namespace std;
	using namespace cv;

	// Test data.
	int lineWidth = 1; // Unexpected behavior disappears if >1.
	Scalar color( 255, 255, 255, 255 );
	Mat mask = 255 * Mat::ones(700, 700, CV_8UC1);

	rectangle( mask, Point( 10, 10 ), Point( 200, 200 ), 0, -1 );
	Point br( mask.size().width - 1, mask.size().height - 1 );
	line( mask, Point( 0, 0 ), br, Scalar::all( 0 ), lineWidth );
	line( mask, Point( 0, br.y ), Point( br.x, 0 ), Scalar::all( 0 ), lineWidth );
	circle( mask, Point( 350, 350 ), 100, 0, lineWidth );

	// mask = ( 255 * cv::Mat::ones( mask.size(), mask.type() ) ) - mask; // Invert the mask.

	// Detect contours.
	vector< vector< Point > > contours;
	vector< Vec4i > hierarchy;
	int mode = // Uncomment one of the lines below for testing.
		// RETR_EXTERNAL; 
		// RETR_LIST;
		RETR_CCOMP;
		// RETR_TREE;
		// RETR_FLOODFILL;
	int method = 
		CHAIN_APPROX_NONE;
		// CHAIN_APPROX_SIMPLE;
		// CHAIN_APPROX_TC89_L1;
		// CHAIN_APPROX_TC89_KCOS;
	
	findContours( mask.clone(), contours, hierarchy, mode, method, Point( 0, 0 ) );

	// Draw the contours and display the results.
	Mat contoursImg = Mat::zeros( mask.size(), CV_8UC3 );
	RNG rng;
	for ( size_t i = 0; i < contours.size(); ++i )
	{
		Scalar color = Scalar( rng.uniform( 0, 255 ), rng.uniform( 0, 255 ), rng.uniform( 0, 255 ) );
		drawContours( contoursImg, contours, (int)i, color, 1, 8, hierarchy, 0, Point() );
	}

	cv::Rect magnification( 255, 255, 50, 50 );
	cv::Size dsize( 400, 400 );
	cv::Mat mask_magnified, contours_magnified;
	cv::resize( mask( magnification ), mask_magnified, dsize, 0, 0, INTER_NEAREST );
	cv::resize( contoursImg( magnification ), contours_magnified, dsize, 0, 0, INTER_NEAREST );

	cv::Mat3b maskImg;
	cvtColor( mask, maskImg, COLOR_GRAY2BGR );
	rectangle( maskImg, magnification, cv::Scalar( 0, 0, 255 ), 0 );
	rectangle( contoursImg, magnification, cv::Scalar( 0, 0, 255 ), 0 );

	cv::imwrite( "00_mask.png", maskImg );
	cv::imwrite( "01_mask_magnified.png", mask_magnified );
	cv::imwrite( "02_contours.png", contoursImg );
	cv::imwrite( "03_contours_magnified.png", contours_magnified );

	namedWindow( "mask", WINDOW_AUTOSIZE );
	namedWindow("contours", WINDOW_AUTOSIZE );
	imshow( "mask", maskImg ); 
	imshow( "contours", contoursImg );
	waitKey( 0 );

	return 0;
}