OpenCV 4.9基本绘图

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​目标

在本教程中，您将学习如何：

• 使用 OpenCV 函数 line() 画一条线
• 使用 OpenCV 函数 ellipse()绘制椭圆
• 使用 OpenCV 函数 rectangle()绘制矩形
• 使用 OpenCV 函数 circle() 画一个圆
• 使用 OpenCV 函数 fillPoly()绘制填充多边形

OpenCV理论

在本教程中，我们将大量使用两种结构：cv::P oint 和 cv::Scalar ：

点

它表示一个二维点，由其图像坐标 \（x\） 和 \（y\） 指定。我们可以将其定义为：

C++:

Point pt;
pt.x = 10;
pt.y = 8;

 Java:

Point pt = new Point();
pt.x = 10;
pt.y = 8;

or

C++:

Point pt = Point(10, 8);

 Java: 

Point pt = new Point(10, 8);

标量

• 表示一个 4 元素向量。Scalar 类型在 OpenCV 中广泛用于传递像素值。
• 在本教程中，我们将广泛使用它来表示 BGR 颜色值（3 个参数）。如果不打算使用最后一个参数，则无需定义它。
• 让我们看一个例子，如果我们被要求一个颜色参数，我们给出：

• Scalar( a, b, c )

  我们将定义一个 BGR 颜色，例如：蓝色 = a、绿色 = b 和红色 = c

代码
此代码位于 OpenCV 示例文件夹中。否则你可以从这里下载

C++:

#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/highgui.hpp>#define w 400using namespace cv;void MyEllipse( Mat img, double angle );
void MyFilledCircle( Mat img, Point center );
void MyPolygon( Mat img );
void MyLine( Mat img, Point start, Point end );int main( void ){char atom_window[] = "Drawing 1: Atom";char rook_window[] = "Drawing 2: Rook";Mat atom_image = Mat::zeros( w, w, CV_8UC3 );Mat rook_image = Mat::zeros( w, w, CV_8UC3 );MyEllipse( atom_image, 90 );MyEllipse( atom_image, 0 );MyEllipse( atom_image, 45 );MyEllipse( atom_image, -45 );MyFilledCircle( atom_image, Point( w/2, w/2) );MyPolygon( rook_image );rectangle( rook_image,Point( 0, 7*w/8 ),Point( w, w),Scalar( 0, 255, 255 ),FILLED,LINE_8 );MyLine( rook_image, Point( 0, 15*w/16 ), Point( w, 15*w/16 ) );MyLine( rook_image, Point( w/4, 7*w/8 ), Point( w/4, w ) );MyLine( rook_image, Point( w/2, 7*w/8 ), Point( w/2, w ) );MyLine( rook_image, Point( 3*w/4, 7*w/8 ), Point( 3*w/4, w ) );imshow( atom_window, atom_image );moveWindow( atom_window, 0, 200 );imshow( rook_window, rook_image );moveWindow( rook_window, w, 200 );waitKey( 0 );return(0);
}void MyEllipse( Mat img, double angle )
{int thickness = 2;int lineType = 8;ellipse( img,Point( w/2, w/2 ),Size( w/4, w/16 ),angle,0,360,Scalar( 255, 0, 0 ),thickness,lineType );
}void MyFilledCircle( Mat img, Point center )
{circle( img,center,w/32,Scalar( 0, 0, 255 ),FILLED,LINE_8 );
}void MyPolygon( Mat img )
{int lineType = LINE_8;Point rook_points[1][20];rook_points[0][0] = Point( w/4, 7*w/8 );rook_points[0][1] = Point( 3*w/4, 7*w/8 );rook_points[0][2] = Point( 3*w/4, 13*w/16 );rook_points[0][3] = Point( 11*w/16, 13*w/16 );rook_points[0][4] = Point( 19*w/32, 3*w/8 );rook_points[0][5] = Point( 3*w/4, 3*w/8 );rook_points[0][6] = Point( 3*w/4, w/8 );rook_points[0][7] = Point( 26*w/40, w/8 );rook_points[0][8] = Point( 26*w/40, w/4 );rook_points[0][9] = Point( 22*w/40, w/4 );rook_points[0][10] = Point( 22*w/40, w/8 );rook_points[0][11] = Point( 18*w/40, w/8 );rook_points[0][12] = Point( 18*w/40, w/4 );rook_points[0][13] = Point( 14*w/40, w/4 );rook_points[0][14] = Point( 14*w/40, w/8 );rook_points[0][15] = Point( w/4, w/8 );rook_points[0][16] = Point( w/4, 3*w/8 );rook_points[0][17] = Point( 13*w/32, 3*w/8 );rook_points[0][18] = Point( 5*w/16, 13*w/16 );rook_points[0][19] = Point( w/4, 13*w/16 );const Point* ppt[1] = { rook_points[0] };int npt[] = { 20 };fillPoly( img,ppt,npt,1,Scalar( 255, 255, 255 ),lineType );
}void MyLine( Mat img, Point start, Point end )
{int thickness = 2;int lineType = LINE_8;line( img,start,end,Scalar( 0, 0, 0 ),thickness,lineType );
}

Java:

import org.opencv.core.*;
import org.opencv.core.Point;
import org.opencv.highgui.HighGui;
import org.opencv.imgproc.Imgproc;import java.util.*;
import java.util.List;class GeometricDrawingRun{private static final int W = 400;public void run(){String atom_window = "Drawing 1: Atom";String rook_window = "Drawing 2: Rook";Mat atom_image = Mat.zeros( W, W, CvType.CV_8UC3 );Mat rook_image = Mat.zeros( W, W, CvType.CV_8UC3 );MyEllipse( atom_image, 90.0 );MyEllipse( atom_image, 0.0 );MyEllipse( atom_image, 45.0 );MyEllipse( atom_image, -45.0 );MyFilledCircle( atom_image, new Point( W/2, W/2) );MyPolygon( rook_image );Imgproc.rectangle( rook_image,new Point( 0, 7*W/8 ),new Point( W, W),new Scalar( 0, 255, 255 ),-1,8,0 );MyLine( rook_image, new Point( 0, 15*W/16 ), new Point( W, 15*W/16 ) );MyLine( rook_image, new Point( W/4, 7*W/8 ), new Point( W/4, W ) );MyLine( rook_image, new Point( W/2, 7*W/8 ), new Point( W/2, W ) );MyLine( rook_image, new Point( 3*W/4, 7*W/8 ), new Point( 3*W/4, W ) );HighGui.imshow( atom_window, atom_image );HighGui.moveWindow( atom_window, 0, 200 );HighGui.imshow( rook_window, rook_image );HighGui.moveWindow( rook_window, W, 200 );HighGui.waitKey( 0 );System.exit(0);}private void MyEllipse( Mat img, double angle ) {int thickness = 2;int lineType = 8;int shift = 0;Imgproc.ellipse( img,new Point( W/2, W/2 ),new Size( W/4, W/16 ),angle,0.0,360.0,new Scalar( 255, 0, 0 ),thickness,lineType,shift );}private void MyFilledCircle( Mat img, Point center ) {int thickness = -1;int lineType = 8;int shift = 0;Imgproc.circle( img,center,W/32,new Scalar( 0, 0, 255 ),thickness,lineType,shift );}private void MyPolygon( Mat img ) {int lineType = 8;int shift = 0;Point[] rook_points = new Point[20];rook_points[0] = new Point( W/4, 7*W/8 );rook_points[1] = new Point( 3*W/4, 7*W/8 );rook_points[2] = new Point( 3*W/4, 13*W/16 );rook_points[3] = new Point( 11*W/16, 13*W/16 );rook_points[4] = new Point( 19*W/32, 3*W/8 );rook_points[5] = new Point( 3*W/4, 3*W/8 );rook_points[6] = new Point( 3*W/4, W/8 );rook_points[7] = new Point( 26*W/40, W/8 );rook_points[8] = new Point( 26*W/40, W/4 );rook_points[9] = new Point( 22*W/40, W/4 );rook_points[10] = new Point( 22*W/40, W/8 );rook_points[11] = new Point( 18*W/40, W/8 );rook_points[12] = new Point( 18*W/40, W/4 );rook_points[13] = new Point( 14*W/40, W/4 );rook_points[14] = new Point( 14*W/40, W/8 );rook_points[15] = new Point( W/4, W/8 );rook_points[16] = new Point( W/4, 3*W/8 );rook_points[17] = new Point( 13*W/32, 3*W/8 );rook_points[18] = new Point( 5*W/16, 13*W/16 );rook_points[19] = new Point( W/4, 13*W/16 );MatOfPoint matPt = new MatOfPoint();matPt.fromArray(rook_points);List<MatOfPoint> ppt = new ArrayList<MatOfPoint>();ppt.add(matPt);Imgproc.fillPoly(img,ppt,new Scalar( 255, 255, 255 ),lineType,shift,new Point(0,0) );}private void MyLine( Mat img, Point start, Point end ) {int thickness = 2;int lineType = 8;int shift = 0;Imgproc.line( img,start,end,new Scalar( 0, 0, 0 ),thickness,lineType,shift );}
}public class BasicGeometricDrawing {public static void main(String[] args) {// Load the native library.System.loadLibrary(Core.NATIVE_LIBRARY_NAME);new GeometricDrawingRun().run();}
}

Python :

import cv2 as cv
import numpy as npW = 400def my_ellipse(img, angle):thickness = 2line_type = 8cv.ellipse(img,(W // 2, W // 2),(W // 4, W // 16),angle,0,360,(255, 0, 0),thickness,line_type)def my_filled_circle(img, center):thickness = -1line_type = 8cv.circle(img,center,W // 32,(0, 0, 255),thickness,line_type)def my_polygon(img):line_type = 8# Create some pointsppt = np.array([[W / 4, 7 * W / 8], [3 * W / 4, 7 * W / 8],[3 * W / 4, 13 * W / 16], [11 * W / 16, 13 * W / 16],[19 * W / 32, 3 * W / 8], [3 * W / 4, 3 * W / 8],[3 * W / 4, W / 8], [26 * W / 40, W / 8],[26 * W / 40, W / 4], [22 * W / 40, W / 4],[22 * W / 40, W / 8], [18 * W / 40, W / 8],[18 * W / 40, W / 4], [14 * W / 40, W / 4],[14 * W / 40, W / 8], [W / 4, W / 8],[W / 4, 3 * W / 8], [13 * W / 32, 3 * W / 8],[5 * W / 16, 13 * W / 16], [W / 4, 13 * W / 16]], np.int32)ppt = ppt.reshape((-1, 1, 2))cv.fillPoly(img, [ppt], (255, 255, 255), line_type)# Only drawind the lines would be:# cv.polylines(img, [ppt], True, (255, 0, 255), line_type)def my_line(img, start, end):thickness = 2line_type = 8cv.line(img,start,end,(0, 0, 0),thickness,line_type)atom_window = "Drawing 1: Atom"
rook_window = "Drawing 2: Rook"# Create black empty images
size = W, W, 3
atom_image = np.zeros(size, dtype=np.uint8)
rook_image = np.zeros(size, dtype=np.uint8)# 1.a. Creating ellipses
my_ellipse(atom_image, 90)
my_ellipse(atom_image, 0)
my_ellipse(atom_image, 45)
my_ellipse(atom_image, -45)# 1.b. Creating circles
my_filled_circle(atom_image, (W // 2, W // 2))# 2. Draw a rook
# ------------------
# 2.a. Create a convex polygon
my_polygon(rook_image)cv.rectangle(rook_image,(0, 7 * W // 8),(W, W),(0, 255, 255),-1,8)# 2.c. Create a few lines
my_line(rook_image, (0, 15 * W // 16), (W, 15 * W // 16))
my_line(rook_image, (W // 4, 7 * W // 8), (W // 4, W))
my_line(rook_image, (W // 2, 7 * W // 8), (W // 2, W))
my_line(rook_image, (3 * W // 4, 7 * W // 8), (3 * W // 4, W))cv.imshow(atom_window, atom_image)
cv.moveWindow(atom_window, 0, 200)
cv.imshow(rook_window, rook_image)
cv.moveWindow(rook_window, W, 200)cv.waitKey(0)
cv.destroyAllWindows()

解释

由于我们计划绘制两个示例（一个原子和一个车），我们必须创建两个图像和两个窗口来显示它们。

 C++:

 char atom_window[] = "Drawing 1: Atom";char rook_window[] = "Drawing 2: Rook";Mat atom_image = Mat::zeros( w, w, CV_8UC3 );Mat rook_image = Mat::zeros( w, w, CV_8UC3 );

Java:

String atom_window = "Drawing 1: Atom";String rook_window = "Drawing 2: Rook"; Mat atom_image = Mat.zeros( W, W, CvType.CV_8UC3 );Mat rook_image = Mat.zeros( W, W, CvType.CV_8UC3 );

Python:  

# Windows names
atom_window = "Drawing 1: Atom"
rook_window = "Drawing 2: Rook"# Create black empty images
size = W, W, 3
atom_image = np.zeros(size, dtype=np.uint8)
rook_image = np.zeros(size, dtype=np.uint8)

我们创建了函数来绘制不同的几何形状。例如，为了绘制原子，我们使用了 MyEllipse 和 MyFilledCircle：

 MyEllipse( atom_image, 90 );MyEllipse( atom_image, 0 );MyEllipse( atom_image, 45 );MyEllipse( atom_image, -45 );MyFilledCircle( atom_image, Point( w/2, w/2) );

Java:

 MyEllipse( atom_image, 90.0 );MyEllipse( atom_image, 0.0 );MyEllipse( atom_image, 45.0 );MyEllipse( atom_image, -45.0 );MyFilledCircle( atom_image, new Point( W/2, W/2) );

Python: 

# 1. Draw a simple atom:
# -----------------------# 1.a. Creating ellipses
my_ellipse(atom_image, 90)
my_ellipse(atom_image, 0)
my_ellipse(atom_image, 45)
my_ellipse(atom_image, -45)# 1.b. Creating circles
my_filled_circle(atom_image, (W // 2, W // 2))

为了绘制车，我们使用了 MyLine、矩形和 MyPolygon：

 MyPolygon( rook_image );rectangle( rook_image,Point( 0, 7*w/8 ),Point( w, w),Scalar( 0, 255, 255 ),FILLED,LINE_8 );MyLine( rook_image, Point( 0, 15*w/16 ), Point( w, 15*w/16 ) );MyLine( rook_image, Point( w/4, 7*w/8 ), Point( w/4, w ) );MyLine( rook_image, Point( w/2, 7*w/8 ), Point( w/2, w ) );MyLine( rook_image, Point( 3*w/4, 7*w/8 ), Point( 3*w/4, w ) );

Java:

 MyPolygon( rook_image );Imgproc.rectangle( rook_image,new Point( 0, 7*W/8 ),new Point( W, W),new Scalar( 0, 255, 255 ),-1,8,0 );MyLine( rook_image, new Point( 0, 15*W/16 ), new Point( W, 15*W/16 ) );MyLine( rook_image, new Point( W/4, 7*W/8 ), new Point( W/4, W ) );MyLine( rook_image, new Point( W/2, 7*W/8 ), new Point( W/2, W ) );MyLine( rook_image, new Point( 3*W/4, 7*W/8 ), new Point( 3*W/4, W ) );

Python: 

# 2. Draw a rook
# ------------------
# 2.a. Create a convex polygon
my_polygon(rook_image)cv.rectangle(rook_image,(0, 7 * W // 8),(W, W),(0, 255, 255),-1,8) # 2.c. Create a few lines
my_line(rook_image, (0, 15 * W // 16), (W, 15 * W // 16))
my_line(rook_image, (W // 4, 7 * W // 8), (W // 4, W))
my_line(rook_image, (W // 2, 7 * W // 8), (W // 2, W))
my_line(rook_image, (3 * W // 4, 7 * W // 8), (3 * W // 4, W))

让我们检查一下这些函数中的每一个都包含什么：

我的线条：

void MyLine( Mat img, Point start, Point end )
{int thickness = 2;int lineType = LINE_8;line( img,start,end,Scalar( 0, 0, 0 ),thickness,lineType );
}

Java:

 private void MyLine( Mat img, Point start, Point end ) {int thickness = 2;int lineType = 8;int shift = 0;Imgproc.line( img,start,end,new Scalar( 0, 0, 0 ),thickness,lineType,shift );}

Python: 

def my_line(img, start, end):thickness = 2line_type = 8cv.line(img,start,end,(0, 0, 0),thickness,line_type)

• 正如我们所看到的，MyLine 只需调用函数 line（） ，它执行以下操作：
  • 从点起点到点终点画一条线
  • 该线显示在图像 img 中
  • 线条颜色由 （ 0， 0， 0 ） 定义，它是与黑色相对应的 RGB 值
  • 线条粗细设置为粗细（在本例中为 2）
  • 该线是 8 连接的线 （lineType = 8）

MyEllipse（椭圆）

void MyEllipse( Mat img, double angle )
{int thickness = 2;int lineType = 8;ellipse( img,Point( w/2, w/2 ),Size( w/4, w/16 ),angle,0,360,Scalar( 255, 0, 0 ),thickness,lineType );
}

Java:

 private void MyEllipse( Mat img, double angle ) {int thickness = 2;int lineType = 8;int shift = 0;Imgproc.ellipse( img,new Point( W/2, W/2 ),new Size( W/4, W/16 ),angle,0.0,360.0,new Scalar( 255, 0, 0 ),thickness,lineType,shift );}

Python: 

def my_ellipse(img, angle):thickness = 2line_type = 8cv.ellipse(img,(W // 2, W // 2),(W // 4, W // 16),angle,0,360,(255, 0, 0),thickness,line_type)

• 从上面的代码中，我们可以观察到函数 ellipse（） 绘制一个椭圆，使得：
  • 椭圆显示在图像 img 中
  • 椭圆中心位于点 （w/2， w/2） 中，并封闭在大小为 （w/4， w/16） 的盒子中
  • 椭圆是旋转角度度数
  • 椭圆在 0 到 360 度之间延伸一条弧线
  • 图形的颜色将是 （ 255， 0， 0 ），表示 BGR 值中的蓝色。
  • 椭圆的厚度为 2。

MyFilledCircle（圆）

void MyFilledCircle( Mat img, Point center )
{circle( img,center,w/32,Scalar( 0, 0, 255 ),FILLED,LINE_8 );
}

Java:

 private void MyFilledCircle( Mat img, Point center ) {int thickness = -1;int lineType = 8;int shift = 0;Imgproc.circle( img,center,W/32,new Scalar( 0, 0, 255 ),thickness,lineType,shift );}

Python: 

def my_filled_circle(img, center):thickness = -1line_type = 8cv.circle(img,center,W // 32,(0, 0, 255),thickness,line_type)

• 与椭圆函数类似，我们可以观察到 circle 接收为参数：
  • 将显示圆圈的图像（img)
  • 圆的中心表示为点中心
  • 圆的半径：w/32
  • 圆圈的颜色：（ 0， 0， 255 ） 在 BGR 中表示红色
  • 由于厚度 = -1，因此圆将被绘制填充。

MyPolygon

void MyPolygon( Mat img )
{int lineType = LINE_8;Point rook_points[1][20];rook_points[0][0] = Point( w/4, 7*w/8 );rook_points[0][1] = Point( 3*w/4, 7*w/8 );rook_points[0][2] = Point( 3*w/4, 13*w/16 );rook_points[0][3] = Point( 11*w/16, 13*w/16 );rook_points[0][4] = Point( 19*w/32, 3*w/8 );rook_points[0][5] = Point( 3*w/4, 3*w/8 );rook_points[0][6] = Point( 3*w/4, w/8 );rook_points[0][7] = Point( 26*w/40, w/8 );rook_points[0][8] = Point( 26*w/40, w/4 );rook_points[0][9] = Point( 22*w/40, w/4 );rook_points[0][10] = Point( 22*w/40, w/8 );rook_points[0][11] = Point( 18*w/40, w/8 );rook_points[0][12] = Point( 18*w/40, w/4 );rook_points[0][13] = Point( 14*w/40, w/4 );rook_points[0][14] = Point( 14*w/40, w/8 );rook_points[0][15] = Point( w/4, w/8 );rook_points[0][16] = Point( w/4, 3*w/8 );rook_points[0][17] = Point( 13*w/32, 3*w/8 );rook_points[0][18] = Point( 5*w/16, 13*w/16 );rook_points[0][19] = Point( w/4, 13*w/16 );const Point* ppt[1] = { rook_points[0] };int npt[] = { 20 };fillPoly( img,ppt,npt,1,Scalar( 255, 255, 255 ),lineType );
}

Java:

 private void MyPolygon( Mat img ) {int lineType = 8;int shift = 0;Point[] rook_points = new Point[20];rook_points[0] = new Point( W/4, 7*W/8 );rook_points[1] = new Point( 3*W/4, 7*W/8 );rook_points[2] = new Point( 3*W/4, 13*W/16 );rook_points[3] = new Point( 11*W/16, 13*W/16 );rook_points[4] = new Point( 19*W/32, 3*W/8 );rook_points[5] = new Point( 3*W/4, 3*W/8 );rook_points[6] = new Point( 3*W/4, W/8 );rook_points[7] = new Point( 26*W/40, W/8 );rook_points[8] = new Point( 26*W/40, W/4 );rook_points[9] = new Point( 22*W/40, W/4 );rook_points[10] = new Point( 22*W/40, W/8 );rook_points[11] = new Point( 18*W/40, W/8 );rook_points[12] = new Point( 18*W/40, W/4 );rook_points[13] = new Point( 14*W/40, W/4 );rook_points[14] = new Point( 14*W/40, W/8 );rook_points[15] = new Point( W/4, W/8 );rook_points[16] = new Point( W/4, 3*W/8 );rook_points[17] = new Point( 13*W/32, 3*W/8 );rook_points[18] = new Point( 5*W/16, 13*W/16 );rook_points[19] = new Point( W/4, 13*W/16 );MatOfPoint matPt = new MatOfPoint();matPt.fromArray(rook_points);List<MatOfPoint> ppt = new ArrayList<MatOfPoint>();ppt.add(matPt);Imgproc.fillPoly(img,ppt,new Scalar( 255, 255, 255 ),lineType,shift,new Point(0,0) );}

Python: 

def my_polygon(img):line_type = 8# Create some pointsppt = np.array([[W / 4, 7 * W / 8], [3 * W / 4, 7 * W / 8],[3 * W / 4, 13 * W / 16], [11 * W / 16, 13 * W / 16],[19 * W / 32, 3 * W / 8], [3 * W / 4, 3 * W / 8],[3 * W / 4, W / 8], [26 * W / 40, W / 8],[26 * W / 40, W / 4], [22 * W / 40, W / 4],[22 * W / 40, W / 8], [18 * W / 40, W / 8],[18 * W / 40, W / 4], [14 * W / 40, W / 4],[14 * W / 40, W / 8], [W / 4, W / 8],[W / 4, 3 * W / 8], [13 * W / 32, 3 * W / 8],[5 * W / 16, 13 * W / 16], [W / 4, 13 * W / 16]], np.int32)ppt = ppt.reshape((-1, 1, 2))cv.fillPoly(img, [ppt], (255, 255, 255), line_type)# Only drawind the lines would be:# cv.polylines(img, [ppt], True, (255, 0, 255), line_type)

• 为了绘制一个填充的多边形，我们使用函数 fillPoly（） 。我们注意到：
  • 多边形将在 img 上绘制
  • 多边形的顶点是 ppt 中的点集
  • 多边形的颜色由 （ 255， 255， 255 ） 定义，这是白色的 BGR 值

矩形

 rectangle( rook_image,Point( 0, 7*w/8 ),Point( w, w),Scalar( 0, 255, 255 ),FILLED,LINE_8 );

Java:

 Imgproc.rectangle( rook_image,new Point( 0, 7*W/8 ),new Point( W, W),new Scalar( 0, 255, 255 ),-1,8,0 );

Python:

# 2.b. Creating rectangles
cv.rectangle(rook_image,(0, 7 * W // 8),(W, W),(0, 255, 255),-1,8)

• 最后，我们有了cv::rectangle函数（我们没有为这个家伙创建一个特殊函数）。我们注意到：
  • 矩形将绘制在rook_image
  • 矩形的两个相对顶点由 （ 0， 7*w/8 ） 和 （ w， w ） 定义
  • 矩形的颜色由 （ 0， 255， 255 ） 给出，它是黄色的 BGR 值
  • 由于厚度值由 FILLED （-1） 给出，因此矩形将被填充。

结果

编译和运行程序应该会得到这样的结果：