OpenCV Tutorials--basic Drawing

Point

It represents a 2D point, specified by its image coordinates and. 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's not necessary to define the last argument if it's not going to being 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 was displayed in the Image img
• The line color are defined by Scalar (0, 0, 0) which are the RGB value correspondent to Black
• The line thickness are 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 are 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 degrees
• The color of the figure would be a 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 would 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 would be drawn filled.

Fillpoly (Img,ppt,npt,1,scalar (255, 255, 255), linetype);

• The polygon is drawn on img
• The vertices of the polygon is the set of points in ppt
• The total number of vertices to be drawn is NPT
• The number of polygons to be drawn are only 1
• The color of the polygon is defined by Scalar (255, 255, 255), which are 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 is drawn on rook_image
• Opposite vertices of the rectangle is 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 are the BGR value for yellow
• Since the thickness value is given by -1, the rectangle would be filled.

Are all calls to basic functions, note the creation of new images--zeros

It's also very sensible to define the window scale.

#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, 2  55, 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 myellips  E (Mat img, double angle) {int thickness = 2;  int linetype = 8; Ellipse (IMG, point (W/2, W/2), Size (W/4, W/16), angle, 0,, Scalar (255, 0, 0) , ThicknESS, Linetype);} /** * @function myfilledcircle * @brief Draw a fixed-size filled circle */void myfilledcircle (Mat img, point center) {I  NT 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