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OpenCV Tutorials —— Basic Drawing

2024-08-02 11:38:49   221人阅读

Point

It represents a 2D point, specified by its image coordinates x and y. We can define it as:

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

or

Point pt = Point(10, 8);

 

Scalar

  • Represents a 4-element vector. The type Scalar is widely used in OpenCV for passing pixel values.

  • represent RGB color values (3 parameters). It is not necessary to define the last argument if it is not going to be used.

  • Scalar( a, b, c )

    We would be defining a RGB color such as: Red = c, Green = b and Blue = a

 

/// Create black empty imagesMat 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 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) );

line( img,start,end,Scalar( 0, 0, 0 ),thickness,lineType );
  • Draw a line from Point start to Point end
  • The line is displayed in the image img
  • The line color is defined by Scalar( 0, 0, 0) which is the RGB value correspondent to Black
  • The line thickness is set to thickness (in this case 2)
  • The line is a 8-connected one (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 );
  • The ellipse is displayed in the image img
  • The ellipse center is located in the point (w/2.0, w/2.0) and is enclosed in a box of size (w/4.0, w/16.0)
  • The ellipse is rotated angle degrees
  • The ellipse extends an arc between 0 and 360 degrees
  • The color of the figure will be Scalar( 255, 255, 0) which means blue in RGB value.
  • The ellipse’s thickness is 2.

 

circle( img,center,w/32.0,Scalar( 0, 0, 255 ),thickness,lineType );
  • The image where the circle will be displayed (img)
  • The center of the circle denoted as the Point center
  • The radius of the circle: w/32.0
  • The color of the circle: Scalar(0, 0, 255) which means Red in BGR
  • Since thickness = -1, the circle will be drawn filled.

 

fillPoly( img,ppt,npt,1,Scalar( 255, 255, 255 ),lineType );
  • The polygon will be drawn on img
  • The vertices of the polygon are the set of points in ppt
  • The total number of vertices to be drawn are npt
  • The number of polygons to be drawn is only 1
  • The color of the polygon is defined by Scalar( 255, 255, 255), which is the BGR value for white

 

rectangle( rook_image,Point( 0, 7*w/8.0 ),Point( w, w),Scalar( 0, 255, 255 ),-1,8 );
  • The rectangle will be drawn on rook_image
  • Two opposite vertices of the rectangle are defined by ** Point( 0, 7*w/8.0 )** and Point( w, w)
  • The color of the rectangle is given by Scalar(0, 255, 255) which is the BGR value for yellow
  • Since the thickness value is given by -1, the rectangle will be filled.

 

都是一些基本函数的调用，注意创建新图像 —— zeros

还有将窗口尺度定义出来也非常明智~

 

#include "stdafx.h"#include <opencv2/core/core.hpp>#include <opencv2/imgproc/imgproc.hpp>#include <opencv2/highgui/highgui.hpp>#define w 400using 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 ){  /// 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 );}

 

 

OpenCV Tutorials —— Basic Drawing


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