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| Original author | Ana Huamán |
|---|---|
| Compatibility | OpenCV >= 3.0 |
Goals
In this tutorial you will learn how to
- Use the OpenCV function cv::convexHull
Code
C++
The tutorial code is shown below. You can also download it from here
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#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!\
" << 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, & amp;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 );
vector<vector<Point> >hull( contours.size() );
for( size_t i = 0; i < contours.size(); i + + )
{<!-- -->
convexHull( contours[i], hull[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) );
drawContours( drawing, contours, (int)i, color );
drawContours( drawing, hull, (int)i, color );
}
imshow( "Hull demo", drawing );
}
Java
The tutorial code is shown below. You can also download it from here
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Image;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.MatOfInt;
import org.opencv.core.MatOfPoint;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.core.Size;
import org.opencv.highgui.HighGui;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
class Hull {<!-- -->
private Mat srcGray = new Mat();
private JFrame frame;
private JLabel imgSrcLabel;
private JLabel imgContoursLabel;
private static final int MAX_THRESHOLD = 255;
private int threshold = 100;
private Random rng = new Random(12345);
public Hull(String[] args) {<!-- -->
String filename = args.length > 0 ? args[0] : "../data/stuff.jpg";
Mat src = Imgcodecs.imread(filename);
if (src.empty()) {<!-- -->
System.err.println("Cannot read image: " + filename);
System.exit(0);
}
Imgproc.cvtColor(src, srcGray, Imgproc.COLOR_BGR2GRAY);
Imgproc.blur(srcGray, srcGray, new Size(3, 3));
// Create and set up the window.
frame = new JFrame("Convex Hull demo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Set up the content pane.
Image img = HighGui.toBufferedImage(src);
addComponentsToPane(frame.getContentPane(), img);
// Use the content pane's default border layout. No need
// setLayout(new BorderLayout());
//Show the window.
frame.pack();
frame.setVisible(true);
update();
}
private void addComponentsToPane(Container pane, Image img) {<!-- -->
if (!(pane.getLayout() instanceof BorderLayout)) {<!-- -->
pane.add(new JLabel("Container doesn't use BorderLayout!"));
return;
}
JPanel sliderPanel = new JPanel();
sliderPanel.setLayout(new BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));
sliderPanel.add(new JLabel("Canny threshold: "));
JSlider slider = new JSlider(0, MAX_THRESHOLD, threshold);
slider.setMajorTickSpacing(20);
slider.setMinorTickSpacing(10);
slider.setPaintTicks(true);
slider.setPaintLabels(true);
slider.addChangeListener(new ChangeListener() {<!-- -->
@Override
public void stateChanged(ChangeEvent e) {<!-- -->
JSlider source = (JSlider) e.getSource();
threshold = source.getValue();
update();
}
});
sliderPanel.add(slider);
pane.add(sliderPanel, BorderLayout.PAGE_START);
JPanel imgPanel = new JPanel();
imgSrcLabel = new JLabel(new ImageIcon(img));
imgPanel.add(imgSrcLabel);
Mat blackImg = Mat.zeros(srcGray.size(), CvType.CV_8U);
imgContoursLabel = new JLabel(new ImageIcon(HighGui.toBufferedImage(blackImg)));
imgPanel.add(imgContoursLabel);
pane.add(imgPanel, BorderLayout.CENTER);
}
private void update() {<!-- -->
Mat cannyOutput = new Mat();
Imgproc.Canny(srcGray, cannyOutput, threshold, threshold * 2);
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(cannyOutput, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);
List<MatOfPoint> hullList = new ArrayList<>();
for (MatOfPoint contour : contours) {<!-- -->
MatOfInt hull = new MatOfInt();
Imgproc.convexHull(contour, hull);
Point[] contourArray = contour.toArray();
Point[] hullPoints = new Point[hull.rows()];
List<Integer> hullContourIdxList = hull.toList();
for (int i = 0; i < hullContourIdxList.size(); i + + ) {<!-- -->
hullPoints[i] = contourArray[hullContourIdxList.get(i)];
}
hullList.add(new MatOfPoint(hullPoints));
}
Mat drawing = Mat.zeros(cannyOutput.size(), CvType.CV_8UC3);
for (int i = 0; i < contours.size(); i + + ) {<!-- -->
Scalar color = new Scalar(rng.nextInt(256), rng.nextInt(256), rng.nextInt(256));
Imgproc.drawContours(drawing, contours, i, color);
Imgproc.drawContours(drawing, hullList, i, color);
}
imgContoursLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(drawing)));
frame.repaint();
}
}
public class HullDemo {<!-- -->
public static void main(String[] args) {<!-- -->
//Load the local OpenCV library
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
// Arrange tasks for the event dispatch thread:
// Create and display the graphical user interface for this application.
javax.swing.SwingUtilities.invokeLater(new Runnable() {<!-- -->
@Override
public void run() {<!-- -->
new Hull(args);
}
});
}
}
Python
The tutorial code is shown below. You can also download it from here
from __future__ import print_function
import cv2 as cv
import numpy as np
import argparse
import random as rng
rng.seed(12345)
def thresh_callback(val):
threshold = val
# Use Canny to detect edges
canny_output = cv.Canny(src_gray, threshold, threshold * 2)
# Find contours
contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
# Find convex hull objects for each contour
hull_list = []
for i in range(len(contours))：
hull = cv.convexHull(contours[i])
hull_list.append(hull)
# Draw contours + hull results
drawing = np.zeros((canny_output.shape[0], canny_output.shape[1], 3), dtype=np.uint8)
for i in range(len(contours))：
color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))
cv.drawContours(drawing, contours, i, color)
cv.drawContours(drawing, hull_list, i, color)
# Display in window
cv.imshow('Contours', drawing)
#Load source image
parser = argparse.ArgumentParser(description='Code for Convex Hull tutorial.')
parser.add_argument('--input', help='Path to input image.', default='stuff.jpg')
args = parser.parse_args()
src = cv.imread(cv.samples.findFile(args.input))
if src is None:
print('Could not open or find the image:', args.input)
exit(0)
# Convert image to gray and blur
src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
src_gray = cv.blur(src_gray, (3,3))
#Create window
source_window = 'Source'
cv.namedWindow(source_window)
cv.imshow(source_window, src)
max_thresh = 255
thresh = 100 # initial threshold
cv.createTrackbar('Canny thresh:', source_window, thresh, max_thresh, thresh_callback)
thresh_callback(thresh)
cv.waitKey()
Results
The following is the result
Original image
Results