为轮廓创建边界框和圆

目录

• 目标
• 理论
• 代码
• 解释
• 结果

上一个教程： 凸包
下一个教程： 为轮廓创建旋转边界框和椭圆

原始作者	Ana Huamán
兼容性	OpenCV >= 3.0

目标

在本教程中，您将学习如何

• 使用OpenCV函数 cv::boundingRect
• 使用OpenCV函数 cv::minEnclosingCircle

理论

代码

C++

本教程代码如下所示。您也可以从此处下载

 
#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!\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 );
 
cv::Mat::empty
    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> > 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], 3, true );
boundRect[i] = boundingRect( contours_poly[i] );
minEnclosingCircle( contours_poly[i], centers[i], radius[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_poly, (int)i, color );
rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2 );
circle( drawing, centers[i], (int)radius[i], color, 2 );
    }
 
    imshow( "Contours", drawing );
}

Java

本教程代码如下所示。您也可以从此处下载

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.MatOfPoint;
import org.opencv.core.MatOfPoint2f;
import org.opencv.core.Point;
import org.opencv.core.Rect;
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 GeneralContours1 {
    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 GeneralContours1(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("Creating Bounding boxes and circles for contours 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 BorderLayout. No need for
        // setLayout(new BorderLayout());
        // Display 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);
 
MatOfPoint2f[] contoursPoly = new MatOfPoint2f[contours.size()];
        Rect[] boundRect = new Rect[contours.size()];
        Point[] centers = new Point[contours.size()];
        float[][] radius = new float[contours.size()][1];
 
        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 Point();
Imgproc.minEnclosingCircle(contoursPoly[i], centers[i], radius[i]);
        }
 
Mat drawing = Mat.zeros(cannyOutput.size(), CvType.CV_8UC3);
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(drawing, centers[i], (int) radius[i][0], color, 2);
        }
 
imgContoursLabel.setIcon(new ImageIcon(HighGui.toBufferedImage(drawing)));
frame.repaint();
    }
}
 
public class GeneralContoursDemo1 {
    public static void main(String[] args) {
        // 加载本地 OpenCV 库
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
 
        // Schedule a job for the event dispatch thread
        // creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
@Override
            public void run() {
                new GeneralContours1(args);
            }
        });
    }
}

Python

本教程代码如下所示。您也可以从此处下载

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
 
    
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)
contours_poly[i] = cv.approxPolyDP(c, 3, True)
boundRect[i] = cv.boundingRect(contours_poly[i])
centers[i], radius[i] = cv.minEnclosingCircle(contours_poly[i])
    
 
    
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_poly, i, color)
        cv.rectangle(drawing, (int(boundRect[i][0]), int(boundRect[i][1])), \
(int(boundRect[i][0]+boundRect[i][2]), int(boundRect[i][1]+boundRect[i][3])), color, 2)
        cv.circle(drawing, (int(centers[i][0]), int(centers[i][1])), int(radius[i]), color, 2)
    
 
    
    cv.imshow('Contours', drawing)
    
 
 
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()
 
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 it
src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
src_gray = cv.blur(src_gray, (3,3))
 
 
 
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()

解释

主函数相当简单，正如注释中所示，我们执行以下操作：

• 打开图像，将其转换为灰度并进行模糊处理以去除噪声。

C++

    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) );

Java

        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));

Python

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()
 
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 it
src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
src_gray = cv.blur(src_gray, (3,3))

• 创建一个标题为“Source”的窗口并在其中显示源文件。

C++

    const char* source_window = "Source";
    namedWindow( source_window );
    imshow( source_window, src );

Java

        // Create and set up the window.
frame = new JFrame("Creating Bounding boxes and circles for contours demo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // Set up the content pane.
Image img = HighGui.toBufferedImage(src);
addComponentsToPane(frame.getContentPane(), img);

Python

source_window = 'Source'
cv.namedWindow(source_window)
cv.imshow(source_window, src)

• 在source_window上创建一个跟踪条，并为其分配一个回调函数。通常，回调函数用于响应某种信号，在本例中是跟踪条状态的变化。有必要显式一次性调用thresh_callback，以便“Contours”窗口与“Source”窗口同时显示。

C++

    const int max_thresh = 255;
    createTrackbar( "Canny thresh:", source_window, &thresh, max_thresh, thresh_callback );
thresh_callback( 0, 0 );

Java

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();
            }
        });

Python

max_thresh = 255
thresh = 100 # initial threshold
cv.createTrackbar('Canny thresh:', source_window, thresh, max_thresh, thresh_callback)
thresh_callback(thresh)

回调函数完成所有有趣的工作。

• 使用cv::Canny检测图像中的边缘。

C++

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

Java

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

Python

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

• 查找轮廓并将其保存到向量contour和hierarchy中。

C++

vector<vector<Point> > contours;
    findContours( canny_output, contours, RETR_TREE, CHAIN_APPROX_SIMPLE );

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)

• 对于每个找到的轮廓，我们现在以±3的精度应用多边形近似，并声明曲线必须是闭合的。之后，我们为每个多边形找到一个边界矩形并将其保存到boundRect。最后，我们为每个多边形找到一个最小外接圆并将其保存到center和radius向量中。

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], 3, true );
boundRect[i] = boundingRect( contours_poly[i] );
        minEnclosingCircle( contours_poly[i], centers[i], radius[i] );
    }

Java

MatOfPoint2f[] contoursPoly = new MatOfPoint2f[contours.size()];
        Rect[] boundRect = new Rect[contours.size()];
        Point[] centers = new Point[contours.size()];
        float[][] radius = new float[contours.size()][1];
 
        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 Point();
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)
contours_poly[i] = cv.approxPolyDP(c, 3, True)
boundRect[i] = cv.boundingRect(contours_poly[i])
centers[i], radius[i] = cv.minEnclosingCircle(contours_poly[i])

我们找到了所有需要的东西，现在只需要绘制。

• 创建新的Mat，由无符号8位字符填充零。它将包含我们所有的绘图（矩形和圆）。

C++

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

Java

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)

• 对于每个轮廓：选择一个随机颜色，绘制轮廓、边界矩形和最小外接圆。

C++

    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 );
        circle( drawing, centers[i], (int)radius[i], color, 2 );
    }

Java

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(drawing, 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.drawContours(drawing, contours_poly, i, color)
        cv.rectangle(drawing, (int(boundRect[i][0]), int(boundRect[i][1])), \
(int(boundRect[i][0]+boundRect[i][2]), int(boundRect[i][1]+boundRect[i][3])), color, 2)
        cv.circle(drawing, (int(centers[i][0]), int(centers[i][1])), int(radius[i]), color, 2)

• 显示结果：创建一个新窗口“Contours”并显示我们添加到绘图中的所有内容。

C++

    imshow( "Contours", drawing );

Java

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

Python

    cv.imshow('Contours', drawing)

结果

就是这样：