OpenCV实践（5）- 基本绘图

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1 目标

（1）用Point绘制图像中的二维点；
（2）使用Scalar，有什么用？
（3）用OpenCV提供的line画线；
（4）用OpenCV提供的ellipse画椭圆；
（5）用OpenCV提供的rectangle画矩形；
（6）用OpenCV提供的circle画圆；
（7）用OpenCV提供的fillPoly画实心多边形；

2 说明

（1）Point
描述了一个2D点，指定了该像素点在图像中的坐标，（x,y）。我们可以如下定义：

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

或

Point pt =  Point(10, 8);

（2）Scalar
表示具有4个元素的矢量vector。Scalar在OpenCV中被用来传递像素值。
在本文中我们用Scalar表述RGB色彩值。如果第四个元素不使用，可以不定义。
语法如下：

Scalar( a, b, c )

在这里，Red = c；Green = b；Blue = a。

3 代码实现

本文的代码可以在OpenCV源代码目录下的samples目录下找到。或者可以在这儿下载。

4 代码解释

（1）因为我们打算绘制两个图像-atom和rook，所以，我们需要绘制两个窗口进行显示：

/// Windows nameschar atom_window[] = "Drawing 1: Atom";char rook_window[] = "Drawing 2: Rook";/// Create black empty imagesMat atom_image = Mat::zeros( w, w, CV_8UC3 );Mat rook_image = Mat::zeros( w, w, CV_8UC3 );

（2）我们创建几个不同的几何图形。对于该例，我们使用MyEllipse 和 MyFilledCircle绘制atom图像。

/// 1. Draw a simple atom:/// 1.a. Creating ellipsesMyEllipse( atom_image, 90 );MyEllipse( atom_image, 0 );MyEllipse( atom_image, 45 );MyEllipse( atom_image, -45 );/// 1.b. Creating circlesMyFilledCircle( atom_image, Point( w/2.0, w/2.0) );

（3）绘制rook对象

/// 2. Draw a rook/// 2.a. Create a convex polygonMyPolygon( rook_image );/// 2.b. Creating rectanglesrectangle( rook_image,           Point( 0, 7*w/8.0 ),           Point( w, w),           Scalar( 0, 255, 255 ),           -1,           8 );/// 2.c. Create a few linesMyLine( 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）让我们看一下使用的函数的内部实现。
a）MyLine

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

如代码所示，就是调用了OpenCV的line函数。代码的意思不能理解，就不做解释了。
b）MyEllipse

void MyEllipse( Mat img, double angle ){  int thickness = 2;  int lineType = 8;  ellipse( img, /* 几何图形显示的位置 */           Point( w/2.0, w/2.0 ), /* 中心点 */           Size( w/4.0, w/16.0 ), /* a和b */           angle, /* 图形旋转角度 */           0,           360, /* 0-360度延伸 */           Scalar( 255, 0, 0 ), /* 蓝色 */           thickness, /* 线粗 = 2 */           lineType );}

c）MyFilledCircle

void MyFilledCircle( Mat img, Point center ){ int thickness = -1; int lineType = 8; circle( img,         center,         w/32.0, /* 半径 */         Scalar( 0, 0, 255 ), /* 红色 */         thickness, /* = -1，将会被填充 */         lineType );}

d）MyPolygon

void MyPolygon( Mat img ){  int lineType = 8;  /* 创建像素点 */  Point rook_points[1][20];  rook_points[0][0] = Point( w/4.0, 7*w/8.0 );  rook_points[0][1] = Point( 3*w/4.0, 7*w/8.0 );  rook_points[0][2] = Point( 3*w/4.0, 13*w/16.0 );  rook_points[0][3] = Point( 11*w/16.0, 13*w/16.0 );  rook_points[0][4] = Point( 19*w/32.0, 3*w/8.0 );  rook_points[0][5] = Point( 3*w/4.0, 3*w/8.0 );  rook_points[0][6] = Point( 3*w/4.0, w/8.0 );  rook_points[0][7] = Point( 26*w/40.0, w/8.0 );  rook_points[0][8] = Point( 26*w/40.0, w/4.0 );  rook_points[0][9] = Point( 22*w/40.0, w/4.0 );  rook_points[0][10] = Point( 22*w/40.0, w/8.0 );  rook_points[0][11] = Point( 18*w/40.0, w/8.0 );  rook_points[0][12] = Point( 18*w/40.0, w/4.0 );  rook_points[0][13] = Point( 14*w/40.0, w/4.0 );  rook_points[0][14] = Point( 14*w/40.0, w/8.0 );  rook_points[0][15] = Point( w/4.0, w/8.0 );  rook_points[0][16] = Point( w/4.0, 3*w/8.0 );  rook_points[0][17] = Point( 13*w/32.0, 3*w/8.0 );  rook_points[0][18] = Point( 5*w/16.0, 13*w/16.0 );  rook_points[0][19] = Point( w/4.0, 13*w/16.0) ;  const Point* ppt[1] = { rook_points[0] };  int npt[] = { 20 };  fillPoly( img,            ppt, /* 首个顶点 */            npt, /* 顶点个数 */            1, /* 多边形的个数 */            Scalar( 255, 255, 255 ), /* 白色 */            lineType ); }

e）rectangle

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

5 运行结果

这里写图片描述

附代码

/** * @file Drawing_1.cpp * @brief Simple sample code */#include <opencv2/core/core.hpp>#include <opencv2/imgproc/imgproc.hpp>#include <opencv2/highgui/highgui.hpp>#define w 400#define FILLED      -1  #define LINE_8      8using namespace cv;/// Function headersvoid 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 ){    //![create_images]    /// 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 );    //![create_images]    /// 1. Draw a simple atom:    /// -----------------------    //![draw_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) );    //![draw_atom]    /// 2. Draw a rook    /// ------------------    //![draw_rook]    /// 2.a. Create a convex polygon    MyPolygon( rook_image );    //![rectangle]    /// 2.b. Creating rectangles    rectangle( rook_image,                 Point( 0, 7*w/8 ),                 Point( w, w),                 Scalar( 0, 255, 255 ),                 FILLED,                 LINE_8 );    //![rectangle]    /// 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 ) );    //![draw_rook]    /// 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//![myellipse]/** * @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 );}//![myellipse]//![myfilledcircle]/** * @function MyFilledCircle * @brief Draw a fixed-size filled circle */void MyFilledCircle( Mat img, Point center ){    circle( img,            center,            w/32,            Scalar( 0, 0, 255 ),            FILLED,            LINE_8 );}//![myfilledcircle]//![mypolygon]/** * @function MyPolygon * @brief Draw a simple concave polygon (rook) */void MyPolygon( Mat img ){    int lineType = LINE_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 );}//![mypolygon]//![myline]/** * @function MyLine * @brief Draw a simple line */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 );}//![myline]

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