OpenCV_Tutorials——CORE MODULE.THE CORE FUNCTIONALITY—— Basic Drawing

2.6基础绘画

目标

在这里我们会学习：

1、在图像中使用Point 来定义2D点

2、使用Scalar以及为什么要使用它

3、使用OpenCV函数line来绘制一条直线

4、使用OpenCV函数ellipse来绘制一个椭圆

5、使用OpenCV函数rectangle来绘制一个矩形

6、使用OpenCV函数circle来绘制一个圆

7、使用OpenCV函数fillPoly来填充一个任意图形

OpenCV理论知识

在这个教程中，我们着重使用两种数据结构：Point和Scalar：

Point

它代表2D点，使用x和y指定他的图像中的坐标。我们可以使用如下来定义：

Point 平台；

pt.x=10;

pt.y=8;

或者

Point pt=Point(10,8);

Scalar

1、代表一个4个元素的向量。Scalar类型在OpenCV中被广泛适用于传递像素值。

2、在教程中，我们使用广泛的使用它来表示RGB色彩值（3个参数）。如果最后一个元素不会被使用，那就没有必要去定义它。

3、让我们来看一个例子，如果我们想要一个色彩参数，我们会给：

Scalar(a,b,c)

我们定义一个RGB颜色，例如：Red=c，Green=b，Blue=a

代码

/**

* @file Drawing_1.cpp

* @brief Simple sample code

*/

#include <opencv2/core/core.hpp>

#include <opencv2/highgui/highgui.hpp>

#define w 400

using namespace cv;

/// Function headers

void MyEllipse( Mat img, double angle );

void MyFilledCircle( Mat img, Point center );

void MyPolygon( Mat img );

void MyLine( Mat img, Point start, Point end );

/**

* @function main

* @brief Main function

*/

int main( void ){

/// Windows names

char atom_window[] = "Drawing 1: Atom";

char rook_window[] = "Drawing 2: Rook";

/// Create black empty images

Mat atom_image = Mat::zeros( w, w, CV_8UC3 );

Mat rook_image = Mat::zeros( w, w, CV_8UC3 );

/// 1. Draw a simple atom:

/// -----------------------

/// 1.a. Creating ellipses

MyEllipse( atom_image, 90 );

MyEllipse( atom_image, 0 );

MyEllipse( atom_image, 45 );

MyEllipse( atom_image, -45 );

/// 1.b. Creating circles

MyFilledCircle( atom_image, Point( w/2, w/2) );

/// 2. Draw a rook

/// ------------------

/// 2.a. Create a convex polygon

MyPolygon( rook_image );

/// 2.b. Creating rectangles

rectangle( rook_image,

Point( 0, 7*w/8 ),

Point( w, w),

Scalar( 0, 255, 255 ),

-1,

8 );

/// 2.c. Create a few lines

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 ) );

/// 3. Display your stuff!

imshow( atom_window, atom_image );

moveWindow( atom_window, 0, 200 );

imshow( rook_window, rook_image );

moveWindow( rook_window, w, 200 );

waitKey( 0 );

return(0);

}

/// Function Declaration

/**

* @function MyEllipse

* @brief Draw a fixed-size ellipse with different angles

*/

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 );

}

/**

* @function MyFilledCircle

* @brief Draw a fixed-size filled circle

*/

void MyFilledCircle( Mat img, Point center )

{

int thickness = -1;

int lineType = 8;

circle( img,

center,

w/32,

Scalar( 0, 0, 255 ),

thickness,

lineType );

}

/**

* @function MyPolygon

* @function Draw a simple concave polygon (rook)

*/

void MyPolygon( Mat img )

{

int lineType = 8;

/** Create some points */

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 );

}

/**

* @function MyLine

* @brief Draw a simple line

*/

void MyLine( Mat img, Point start, Point end )

{

int thickness = 2;

int lineType = 8;

line( img,

start,

end,

Scalar( 0, 0, 0 ),

thickness,

lineType );

}

解释

1、因为我们打算画两个例子（一个原子和一个棋子），我们必须创建两个图像和两个窗口来展示他们

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);

2、我们创建函数来画不同的几何形状。例如，画原子我们需要使用MyEllipse和MyFilledCircle：

MyEllipse(atom_image,90);

MyEllipse(atom_image,0);

MyEllipse(atom_image,45);

MyEllipse(atom_image,-45);

MyFilledCircle(atom_image,Point(w/2.0,w/2.0);

3、画棋子，我们需要使用MyLine,rectangle以及MyPolygon函数

MyPolygon(rook_image);

Rectangle(rook_image,Point(0,7*w/8.0),Point(w,w),Scalar(0,255,255),-1,8);

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));

4、让我们看一下上面那些函数中每一个函数里面都有什么：

MyLine

void MyLine(Mat img.Point start,Point end)

{

int thickness=2;

int lineType=8;

Line(img.star.end,Scalar(0,0,0),thickness,lineType);
}

就像我们看到的，MyLine仅仅调用了line函数，line函数会做一下工作：

-从start点到end点做一条直线

-将这条直线显示在img图像中

-线条的颜色在Scalar(0,0,0)中定义出来，这个颜色在RGB色彩系统中对应于黑色

-线条的粗细被设置为thickness(在这种情况下是2)

-这个线条是一个8连接的（lineType=8)

MyEllipse

void MyEllipse(Mat img,double angle)

{

int thickness=2;

int lineType=8;

Ellipse(img,Point(w/2.0,w/2.0),Size(w/4.0,w/16.0),angle,0,360,Scalar（255,0,0），thickness,lineType);

}

}

从上面的代码中我们可以看到ellipse函数画了一个椭圆：

-椭圆显示在img图像中

-椭圆的中心定位在（w/2.0,w/2.0)这个点上，封闭于大小为(w/4.0,w/16.0)的矩形中

-椭圆旋转angle角度

-椭圆弧度从0-360度

-颜色指数是Scalar（255,255,0）在RGB颜色系统中是蓝色

-椭圆线的粗细为thickness，也就是2

MyFillCircle

void MyFilledCircle(Mat img,Point center)

{

int thickness=-1;

int lineType=8;

Circle(img,center,w/32.0,Scalar(0,0,255),thickness,lineType);
}

和ellipse函数相似，我们可以看到circle函数中接受的参数：

-img就是circle将要在哪个图像中显示

-center就是圆心

-w/32.0就是半径

-Scalar(0,0,255)就是颜色；在RGB中就是红色。

-因为thickness=-1,圆将要被填充。

MyPolygon

void MyPolygon(Mat img)

{

int lineType=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);

}
}

为了填充一个任意图形，我们使用fillPoly函数，注意：

-任意图形会被显示在img

-图形的顶点被放置在ppt这个数组中。

- 顶点的数量放置在npt中

-绘画任意图形的数量为1

-任意图形的颜色被定义为Scalar(255,255,255),在RGB色彩系统中就是白色

rectangle

rectangle(rook_image,Point(0,7*w/8.0),Point(w,w),Scalar(0,255,255),-1,8);

最后我们使用rectangle方程（我们没有为这个家伙创建一个特殊的方程）。注意：

-矩形（rectangle）将会被画在rook_image图像上

-两个对角的顶点被定义在**Point(0,7*w/8.0)**和Point(w,w)

-矩形的颜色在Scalar(0,255,255)中给出，在BGR色彩中就是黄色。

-由于thickness这个参数被置-1，所以矩形被填充。

结果

编译并运行程序，你会得到下面的结果