1Basic Drawing {#tutorial_basic_geometric_drawing} 2============= 3 4@tableofcontents 5 6@next_tutorial{tutorial_random_generator_and_text} 7 8| | | 9| -: | :- | 10| Original author | Ana Huamán | 11| Compatibility | OpenCV >= 3.0 | 12 13Goals 14----- 15 16In this tutorial you will learn how to: 17 18- Draw a **line** by using the OpenCV function **line()** 19- Draw an **ellipse** by using the OpenCV function **ellipse()** 20- Draw a **rectangle** by using the OpenCV function **rectangle()** 21- Draw a **circle** by using the OpenCV function **circle()** 22- Draw a **filled polygon** by using the OpenCV function **fillPoly()** 23 24@add_toggle_cpp 25OpenCV Theory 26------------- 27 28For this tutorial, we will heavily use two structures: @ref cv::Point and @ref cv::Scalar : 29 30### Point 31 32It represents a 2D point, specified by its image coordinates \f$x\f$ and \f$y\f$. We can define it as: 33@code{.cpp} 34Point pt; 35pt.x = 10; 36pt.y = 8; 37@endcode 38or 39@code{.cpp} 40Point pt = Point(10, 8); 41@endcode 42### Scalar 43 44- Represents a 4-element vector. The type Scalar is widely used in OpenCV for passing pixel 45 values. 46- In this tutorial, we will use it extensively to represent BGR color values (3 parameters). It is 47 not necessary to define the last argument if it is not going to be used. 48- Let's see an example, if we are asked for a color argument and we give: 49 @code{.cpp} 50 Scalar( a, b, c ) 51 @endcode 52 We would be defining a BGR color such as: *Blue = a*, *Green = b* and *Red = c* 53@end_toggle 54 55@add_toggle_java 56OpenCV Theory 57------------- 58 59For this tutorial, we will heavily use two structures: @ref cv::Point and @ref cv::Scalar : 60 61### Point 62 63It represents a 2D point, specified by its image coordinates \f$x\f$ and \f$y\f$. We can define it as: 64@code{.java} 65Point pt = new Point(); 66pt.x = 10; 67pt.y = 8; 68@endcode 69or 70@code{.java} 71Point pt = new Point(10, 8); 72@endcode 73### Scalar 74 75- Represents a 4-element vector. The type Scalar is widely used in OpenCV for passing pixel 76 values. 77- In this tutorial, we will use it extensively to represent BGR color values (3 parameters). It is 78 not necessary to define the last argument if it is not going to be used. 79- Let's see an example, if we are asked for a color argument and we give: 80 @code{.java} 81 Scalar( a, b, c ) 82 @endcode 83 We would be defining a BGR color such as: *Blue = a*, *Green = b* and *Red = c* 84@end_toggle 85 86Code 87---- 88 89@add_toggle_cpp 90- This code is in your OpenCV sample folder. Otherwise you can grab it from 91 [here](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp) 92 @include samples/cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp 93@end_toggle 94 95@add_toggle_java 96- This code is in your OpenCV sample folder. Otherwise you can grab it from 97 [here](https://raw.githubusercontent.com/opencv/opencv/master/samples/java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java) 98 @include samples/java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java 99@end_toggle 100 101@add_toggle_python 102- This code is in your OpenCV sample folder. Otherwise you can grab it from 103 [here](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py) 104 @include samples/python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py 105@end_toggle 106 107Explanation 108----------- 109 110Since we plan to draw two examples (an atom and a rook), we have to create two images and two 111windows to display them. 112@add_toggle_cpp 113@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp create_images 114@end_toggle 115 116@add_toggle_java 117@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java create_images 118@end_toggle 119 120@add_toggle_python 121@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py create_images 122@end_toggle 123 124We created functions to draw different geometric shapes. For instance, to draw the atom we used 125**MyEllipse** and **MyFilledCircle**: 126@add_toggle_cpp 127@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp draw_atom 128@end_toggle 129 130@add_toggle_java 131@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java draw_atom 132@end_toggle 133 134@add_toggle_python 135@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py draw_atom 136@end_toggle 137 138And to draw the rook we employed **MyLine**, **rectangle** and a **MyPolygon**: 139@add_toggle_cpp 140@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp draw_rook 141@end_toggle 142 143@add_toggle_java 144@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java draw_rook 145@end_toggle 146 147@add_toggle_python 148@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py draw_rook 149@end_toggle 150 151 152Let's check what is inside each of these functions: 153@add_toggle_cpp 154@end_toggle 155 156<H4>MyLine</H4> 157@add_toggle_cpp 158@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_line 159@end_toggle 160 161@add_toggle_java 162@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_line 163@end_toggle 164 165@add_toggle_python 166@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_line 167@end_toggle 168 169- As we can see, **MyLine** just call the function **line()** , which does the following: 170 - Draw a line from Point **start** to Point **end** 171 - The line is displayed in the image **img** 172 - The line color is defined by <B>( 0, 0, 0 )</B> which is the RGB value correspondent 173 to **Black** 174 - The line thickness is set to **thickness** (in this case 2) 175 - The line is a 8-connected one (**lineType** = 8) 176 177<H4>MyEllipse</H4> 178@add_toggle_cpp 179@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_ellipse 180@end_toggle 181 182@add_toggle_java 183@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_ellipse 184@end_toggle 185 186@add_toggle_python 187@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_ellipse 188@end_toggle 189 190- From the code above, we can observe that the function **ellipse()** draws an ellipse such 191 that: 192 193 - The ellipse is displayed in the image **img** 194 - The ellipse center is located in the point <B>(w/2, w/2)</B> and is enclosed in a box 195 of size <B>(w/4, w/16)</B> 196 - The ellipse is rotated **angle** degrees 197 - The ellipse extends an arc between **0** and **360** degrees 198 - The color of the figure will be <B>( 255, 0, 0 )</B> which means blue in BGR value. 199 - The ellipse's **thickness** is 2. 200 201<H4>MyFilledCircle</H4> 202@add_toggle_cpp 203@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_filled_circle 204@end_toggle 205 206@add_toggle_java 207@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_filled_circle 208@end_toggle 209 210@add_toggle_python 211@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_filled_circle 212@end_toggle 213 214- Similar to the ellipse function, we can observe that *circle* receives as arguments: 215 216 - The image where the circle will be displayed (**img**) 217 - The center of the circle denoted as the point **center** 218 - The radius of the circle: **w/32** 219 - The color of the circle: <B>( 0, 0, 255 )</B> which means *Red* in BGR 220 - Since **thickness** = -1, the circle will be drawn filled. 221 222<H4>MyPolygon</H4> 223@add_toggle_cpp 224@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_polygon 225@end_toggle 226 227@add_toggle_java 228@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_polygon 229@end_toggle 230 231@add_toggle_python 232@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_polygon 233@end_toggle 234 235- To draw a filled polygon we use the function **fillPoly()** . We note that: 236 237 - The polygon will be drawn on **img** 238 - The vertices of the polygon are the set of points in **ppt** 239 - The color of the polygon is defined by <B>( 255, 255, 255 )</B>, which is the BGR 240 value for *white* 241 242<H4>rectangle</H4> 243@add_toggle_cpp 244@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp rectangle 245@end_toggle 246 247@add_toggle_java 248@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java rectangle 249@end_toggle 250 251@add_toggle_python 252@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py rectangle 253@end_toggle 254 255- Finally we have the @ref cv::rectangle function (we did not create a special function for 256 this guy). We note that: 257 258 - The rectangle will be drawn on **rook_image** 259 - Two opposite vertices of the rectangle are defined by <B>( 0, 7*w/8 )</B> 260 and <B>( w, w )</B> 261 - The color of the rectangle is given by <B>( 0, 255, 255 )</B> which is the BGR value 262 for *yellow* 263 - Since the thickness value is given by **FILLED (-1)**, the rectangle will be filled. 264 265Result 266------ 267 268Compiling and running your program should give you a result like this: 269 270 271
