1,前言

自己學的方向需要學習opencv,但一直沒有找到合適的方法,一直在博客,github等上找到一些碎片的東西來學習,感覺根本不夠.

在最近的摸索中發現,結合OpenCV官方tutorial,OpenCV官網下載的source包,可以很好地進行系統學習實踐.

OpenCV官方tutorial:https://docs.opencv.org/master/d7/da8/tutorial_table_of_content_imgproc.html

OpenCV官網下載的source包:https://opencv.org/releases/

2,代碼實踐源代碼

自己目前在ubuntu系統上進行實踐,推薦source包可以下載兩個:最新版和自己當前使用的版本,這里并不需要執行安裝步驟,只是需要source檔案中的tutorial檔案夾內的內容,下圖以OpenCV-4.5.3為例,其他版本也可以.

進入到下面的檔案夾中即可查看到OpenCV代碼實踐的源代碼,其中cpp檔案夾內的代碼都可以作為c++學習opencv的參考源代碼,之后構建作業空間(下篇博客會詳細說)即可.

opencv-4.5.3/samples/cpp/tutorial_code/ImgProc/basic_drawing/

3,代碼實踐的參考

首先在源代碼中就有參考,下面源代碼的路徑:

/home/meng/下載/opencv-4.5.3/samples/cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp

其代碼如下,代碼中會有些英文注釋,可以讀得慢些,就比較容易理解:

/**
 * @file Drawing_1.cpp
 * @brief Simple geometric drawing
 * @author OpenCV team
 */
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/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 ){

  //![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

/**
 * @function MyEllipse
 * @brief Draw a fixed-size ellipse with different angles
 */
//![my_ellipse]
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 );
}
//![my_ellipse]

/**
 * @function MyFilledCircle
 * @brief Draw a fixed-size filled circle
 */
//![my_filled_circle]
void MyFilledCircle( Mat img, Point center )
{
  circle( img,
      center,
      w/32,
      Scalar( 0, 0, 255 ),
      FILLED,
      LINE_8 );
}
//![my_filled_circle]

/**
 * @function MyPolygon
 * @brief Draw a simple concave polygon (rook)
 */
//![my_polygon]
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 );
}
//![my_polygon]

/**
 * @function MyLine
 * @brief Draw a simple line
 */
//![my_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 );
}
//![my_line]

其次在OpenCV官方tutorial中也有代碼解讀,如下圖所示: