opencv/doc/tutorials/imgproc/shapedescriptors/hull/hull.markdown
2014-12-01 16:05:37 +03:00

2.5 KiB

Convex Hull

Goal

In this tutorial you will learn how to:

  • Use the OpenCV function @ref cv::convexHull

Theory

Code

This tutorial code's is shown lines below. You can also download it from here @code{.cpp} #include "opencv2/highgui.hpp" #include "opencv2/imgproc.hpp" #include #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* ); @endcode /* @function main / int main( int argc, char* argv )

{

/// Load source image and convert it to gray src = imread( argv[1], 1 );

    /// Convert image to gray and blur it cvtColor( src, src_gray, COLOR_BGR2GRAY ); blur(
    src_gray, src_gray, Size(3,3) );

    /// Create Window char\* source_window = "Source"; namedWindow( source_window,
    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 src_copy =
src.clone(); 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, RETR_TREE,
CHAIN_APPROX_SIMPLE, Point(0, 0) );

/// Find the convex hull object for each contour vector\<vector\<Point\> \>hull(
contours.size() ); for( int i = 0; i \< contours.size(); i++ ) { convexHull(
Mat(contours[i]), hull[i], false ); }

/// Draw contours + hull results 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, i, color, 1, 8, vector\<Vec4i\>(), 0, Point() ); drawContours( drawing, hull, i,
color, 1, 8, vector\<Vec4i\>(), 0, Point() ); }

/// Show in a window namedWindow( "Hull demo", WINDOW_AUTOSIZE ); imshow( "Hull demo",
drawing );

}

Explanation

Result

  1. Here it is:


    |Hull_0| |Hull_1|