C++ Image Draw Bounding Box

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Goal

In this tutorial you will learn how to:

• Apply the OpenCV function cv::boundingRect
• Utilise the OpenCV function cv::minEnclosingCircle

Theory

Code

C++

This tutorial lawmaking'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}" );

{

cout << "Could not open or find the image!\due north" << endl;

cout << "usage: " << argv[0] << " <Input paradigm>" << endl;

return -1;

}

blur( src_gray, src_gray, Size(3,3) );

const char* source_window = "Source";

imshow( source_window, src );

const int max_thresh = 255;

createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );

thresh_callback( 0, 0 );

return 0;

}

void thresh_callback(int, void* )

{

Mat canny_output;

Canny( src_gray, canny_output, thresh, thresh*ii );

vector<vector<Signal> > contours;

vector<vector<Bespeak> > contours_poly( contours.size() );

vector<Rect> boundRect( contours.size() );

vector<Point2f>centers( contours.size() );

vector<float>radius( contours.size() );

for( size_t i = 0; i < contours.size(); i++ )

{

approxPolyDP( contours[i], contours_poly[i], iii, true );

}

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_poly, (int)i, color );

rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2 );

circumvolve( drawing, centers[i], (int)radius[i], colour, 2 );

}

imshow( "Contours", drawing );

}

Coffee

This tutorial code'due south is shown lines beneath. You can besides download it from here

import coffee.awt.BorderLayout;

import java.awt.Container;

import java.awt.Epitome;

import coffee.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.consequence.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.MatOfPoint;

import org.opencv.core.MatOfPoint2f;

import org.opencv.core.Indicate;

import org.opencv.core.Rect;

import org.opencv.cadre.Scalar;

import org.opencv.core.Size;

import org.opencv.highgui.HighGui;

import org.opencv.imgcodecs.Imgcodecs;

import org.opencv.imgproc.Imgproc;

class GeneralContours1 {

private Mat srcGray = new Mat();

private JFrame frame;

individual JLabel imgSrcLabel;

private JLabel imgContoursLabel;

private static final int MAX_THRESHOLD = 255;

private int threshold = 100;

private Random rng = new Random(12345);

public GeneralContours1(Cord[] 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.mistiness(srcGray, srcGray, new Size(3, 3));

frame = new JFrame("Creating Bounding boxes and circles for contours demo");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Image img = HighGui.toBufferedImage(src);

addComponentsToPane(frame.getContentPane(), img);

frame.pack();

frame.setVisible(true);

update();

}

individual void addComponentsToPane(Container pane, Image img) {

if (!(pane.getLayout() instanceof BorderLayout)) {

pane.add(new JLabel("Container doesn't utilise BorderLayout!"));

return;

}

JPanel sliderPanel = new JPanel();

sliderPanel.setLayout(new BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));

sliderPanel.add together(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 eastward) {

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.Middle);

}

private void update() {

Mat cannyOutput = new Mat();

Imgproc.Canny(srcGray, cannyOutput, threshold, threshold * 2);

List<MatOfPoint> contours = new ArrayList<>();

Mat bureaucracy = new Mat();

Imgproc.findContours(cannyOutput, contours, bureaucracy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);

MatOfPoint2f[] contoursPoly = new MatOfPoint2f[contours.size()];

Rect[] boundRect = new Rect[contours.size()];

Point[] centers = new Signal[contours.size()];

float[][] radius = new bladder[contours.size()][1];

for (int i = 0; i < contours.size(); i++) {

contoursPoly[i] = new MatOfPoint2f();

Imgproc.approxPolyDP(new MatOfPoint2f(contours.become(i).toArray()), contoursPoly[i], three, true);

boundRect[i] = Imgproc.boundingRect(new MatOfPoint(contoursPoly[i].toArray()));

centers[i] = new Point();

Imgproc.minEnclosingCircle(contoursPoly[i], centers[i], radius[i]);

}

Mat drawing = Mat.zeros(cannyOutput.size(), CvType.CV_8UC3);

Listing<MatOfPoint> contoursPolyList = new ArrayList<>(contoursPoly.length);

for (MatOfPoint2f poly : contoursPoly) {

contoursPolyList.add(new MatOfPoint(poly.toArray()));

}

for (int i = 0; i < contours.size(); i++) {

Scalar color = new Scalar(rng.nextInt(256), rng.nextInt(256), rng.nextInt(256));

Imgproc.drawContours(cartoon, contoursPolyList, i, color);

Imgproc.rectangle(drawing, boundRect[i].tl(), boundRect[i].br(), color, 2);

Imgproc.circumvolve(drawing, centers[i], (int) radius[i][0], colour, 2);

}

imgContoursLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(drawing)));

frame.repaint();

}

}

public form GeneralContoursDemo1 {

public static void main(Cord[] args) {

Organisation.loadLibrary(Core.NATIVE_LIBRARY_NAME);

javax.swing.SwingUtilities.invokeLater(new Runnable() {

@Override

public void run() {

new GeneralContours1(args);

}

});

}

}

Python

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

from __future__ import print_function

import cv2 equally cv

import numpy as np

import argparse

import random as rng

rng.seed(12345)

def thresh_callback(val):

threshold = val

canny_output = cv.Canny(src_gray, threshold, threshold * 2)

_, contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

contours_poly = [None]*len(contours)

boundRect = [None]*len(contours)

centers = [None]*len(contours)

radius = [None]*len(contours)

for i, c in enumerate(contours):

drawing = np.zeros((canny_output.shape[0], canny_output.shape[ane], 3), dtype=np.uint8)

for i in range(len(contours)):

color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))

cv.rectangle(drawing, (int(boundRect[i][0]), int(boundRect[i][ane])), \

(int(boundRect[i][0]+boundRect[i][2]), int(boundRect[i][1]+boundRect[i][3])), colour, 2)

cv.circle(drawing, (int(centers[i][0]), int(centers[i][1])), int(radius[i]), color, 2)

parser = argparse.ArgumentParser(description='Code for Creating Bounding boxes and circles for contours tutorial.')

parser.add_argument('--input', help='Path to input image.', default='stuff.jpg')

args = parser.parse_args()

if src is None:

print('Could not open or find the image:', args.input)

exit(0)

src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)

src_gray = cv.blur(src_gray, (iii,three))

source_window = 'Source'

max_thresh = 255

thresh = 100

cv.createTrackbar('Canny thresh:', source_window, thresh, max_thresh, thresh_callback)

thresh_callback(thresh)

Explanation

The master office is rather elementary, every bit follows from the comments we exercise the post-obit:

• Open the prototype, convert it into grayscale and blur information technology to become rid of the noise.

C++

CommandLineParser parser( argc, argv, "{@input | stuff.jpg | input image}" );

if( src.empty() )

{

cout << "Could not open or find the image!\n" << endl;

cout << "usage: " << argv[0] << " <Input prototype>" << endl;

return -1;

}

blur( src_gray, src_gray, Size(3,3) );

Java

String filename = args.length > 0 ? args[0] : "../data/stuff.jpg";

Mat src = Imgcodecs.imread(filename);

if (src.empty()) {

Organization.err.println("Cannot read prototype: " + filename);

System.exit(0);

}

Imgproc.cvtColor(src, srcGray, Imgproc.COLOR_BGR2GRAY);

Imgproc.blur(srcGray, srcGray, new Size(3, 3));

Python

parser = argparse.ArgumentParser(description='Code for Creating Bounding boxes and circles for contours tutorial.')

parser.add_argument('--input', assist='Path to input epitome.', default='stuff.jpg')

args = parser.parse_args()

if src is None:

print('Could non open or discover the image:', args.input)

get out(0)

src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)

src_gray = cv.blur(src_gray, (3,3))

• Create a window with header "Source" and display the source file in it.

C++

const char* source_window = "Source";

imshow( source_window, src );

Java

frame = new JFrame("Creating Bounding boxes and circles for contours demo");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Image img = HighGui.toBufferedImage(src);

addComponentsToPane(frame.getContentPane(), img);

Python

• Create a trackbar on the source_window and assign a callback part to it. In general callback functions are used to react to some kind of signal, in our case it'south trackbar's state change. Explicit one-time call of thresh_callback is necessary to display the "Contours" window simultaniously with the "Source" window.

C++

const int max_thresh = 255;

createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );

thresh_callback( 0, 0 );

Java

sliderPanel.add together(new JLabel("Canny threshold: "));

JSlider slider = new JSlider(0, MAX_THRESHOLD, threshold);

slider.setMajorTickSpacing(twenty);

slider.setMinorTickSpacing(x);

slider.setPaintTicks(true);

slider.setPaintLabels(true);

slider.addChangeListener(new ChangeListener() {

@Override

public void stateChanged(ChangeEvent due east) {

JSlider source = (JSlider) due east.getSource();

threshold = source.getValue();

update();

}

});

Python

max_thresh = 255

thresh = 100

cv.createTrackbar('Canny thresh:', source_window, thresh, max_thresh, thresh_callback)

thresh_callback(thresh)

The callback office does all the interesting job.

• Use cv::Canny to detect edges in the images.

C++

Mat canny_output;

Canny( src_gray, canny_output, thresh, thresh*2 );

Coffee

Mat cannyOutput = new Mat();

Imgproc.Canny(srcGray, cannyOutput, threshold, threshold * 2);

Python

canny_output = cv.Canny(src_gray, threshold, threshold * two)

• Finds contours and saves them to the vectors profile and hierarchy.

C++

vector<vector<Bespeak> > contours;

Java

List<MatOfPoint> contours = new ArrayList<>();

Mat hierarchy = new Mat();

Imgproc.findContours(cannyOutput, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);

Python

_, contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

• For every found contour we at present apply approximation to polygons with accuracy +-three and stating that the curve must be closed. Subsequently that we find a bounding rect for every polygon and save information technology to boundRect. At terminal we notice a minimum enclosing circle for every polygon and save it to centre and radius vectors.

C++

vector<vector<Point> > contours_poly( contours.size() );

vector<Rect> boundRect( contours.size() );

vector<Point2f>centers( contours.size() );

vector<float>radius( contours.size() );

for( size_t i = 0; i < contours.size(); i++ )

{

approxPolyDP( contours[i], contours_poly[i], iii, true );

}

Java

MatOfPoint2f[] contoursPoly = new MatOfPoint2f[contours.size()];

Rect[] boundRect = new Rect[contours.size()];

Signal[] centers = new Point[contours.size()];

float[][] radius = new float[contours.size()][one];

for (int i = 0; i < contours.size(); i++) {

contoursPoly[i] = new MatOfPoint2f();

Imgproc.approxPolyDP(new MatOfPoint2f(contours.get(i).toArray()), contoursPoly[i], 3, true);

boundRect[i] = Imgproc.boundingRect(new MatOfPoint(contoursPoly[i].toArray()));

centers[i] = new Signal();

Imgproc.minEnclosingCircle(contoursPoly[i], centers[i], radius[i]);

}

Python

contours_poly = [None]*len(contours)

boundRect = [None]*len(contours)

centers = [None]*len(contours)

radius = [None]*len(contours)

for i, c in enumerate(contours):

We found everything we need, all nosotros have to do is to draw.

• Create new Mat of unsigned 8-fleck chars, filled with zeros. It will comprise all the drawings nosotros are going to make (rects and circles).

C++

Mat cartoon = Mat::zeros( canny_output.size(), CV_8UC3 );

Coffee

Mat drawing = Mat.zeros(cannyOutput.size(), CvType.CV_8UC3);

Python

drawing = np.zeros((canny_output.shape[0], canny_output.shape[1], 3), dtype=np.uint8)

• For every profile: selection a random color, draw the contour, the bounding rectangle and the minimal enclosing circle with it.

C++

for( size_t i = 0; i< contours.size(); i++ )

{

Scalar color = Scalar( rng.uniform(0, 256), rng.compatible(0,256), rng.uniform(0,256) );

drawContours( cartoon, contours_poly, (int)i, color );

rectangle( cartoon, boundRect[i].tl(), boundRect[i].br(), colour, 2 );

circumvolve( drawing, centers[i], (int)radius[i], color, two );

}

Coffee

List<MatOfPoint> contoursPolyList = new ArrayList<>(contoursPoly.length);

for (MatOfPoint2f poly : contoursPoly) {

contoursPolyList.add(new MatOfPoint(poly.toArray()));

}

for (int i = 0; i < contours.size(); i++) {

Scalar color = new Scalar(rng.nextInt(256), rng.nextInt(256), rng.nextInt(256));

Imgproc.drawContours(drawing, contoursPolyList, i, color);

Imgproc.rectangle(drawing, boundRect[i].tl(), boundRect[i].br(), color, 2);

Imgproc.circle(cartoon, centers[i], (int) radius[i][0], color, 2);

}

Python

for i in range(len(contours)):

color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))

cv.rectangle(drawing, (int(boundRect[i][0]), int(boundRect[i][1])), \

(int(boundRect[i][0]+boundRect[i][2]), int(boundRect[i][one]+boundRect[i][3])), colour, 2)

cv.circle(cartoon, (int(centers[i][0]), int(centers[i][i])), int(radius[i]), colour, two)

• Display the results: create a new window "Contours" and testify everything we added to drawings on it.

C++

imshow( "Contours", cartoon );

Java

imgContoursLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(drawing)));

frame.repaint();

Python

Outcome

Here it is:

strangewittappona.blogspot.com

Source: https://docs.opencv.org/3.4/da/d0c/tutorial_bounding_rects_circles.html

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