init - 初始化项目
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Lee Nony
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Basic Drawing {#tutorial_basic_geometric_drawing}
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=============
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@tableofcontents
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@next_tutorial{tutorial_random_generator_and_text}
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| | |
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| -: | :- |
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| Original author | Ana Huamán |
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| Compatibility | OpenCV >= 3.0 |
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Goals
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-----
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In this tutorial you will learn how to:
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- Draw a **line** by using the OpenCV function **line()**
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- Draw an **ellipse** by using the OpenCV function **ellipse()**
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- Draw a **rectangle** by using the OpenCV function **rectangle()**
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- Draw a **circle** by using the OpenCV function **circle()**
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- Draw a **filled polygon** by using the OpenCV function **fillPoly()**
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@add_toggle_cpp
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OpenCV Theory
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-------------
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For this tutorial, we will heavily use two structures: @ref cv::Point and @ref cv::Scalar :
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### Point
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It represents a 2D point, specified by its image coordinates \f$x\f$ and \f$y\f$. We can define it as:
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@code{.cpp}
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Point pt;
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pt.x = 10;
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pt.y = 8;
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@endcode
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or
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@code{.cpp}
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Point pt = Point(10, 8);
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@endcode
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### Scalar
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- Represents a 4-element vector. The type Scalar is widely used in OpenCV for passing pixel
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values.
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- In this tutorial, we will use it extensively to represent BGR color values (3 parameters). It is
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not necessary to define the last argument if it is not going to be used.
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- Let's see an example, if we are asked for a color argument and we give:
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@code{.cpp}
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Scalar( a, b, c )
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@endcode
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We would be defining a BGR color such as: *Blue = a*, *Green = b* and *Red = c*
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@end_toggle
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@add_toggle_java
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OpenCV Theory
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-------------
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For this tutorial, we will heavily use two structures: @ref cv::Point and @ref cv::Scalar :
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### Point
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It represents a 2D point, specified by its image coordinates \f$x\f$ and \f$y\f$. We can define it as:
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@code{.java}
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Point pt = new Point();
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pt.x = 10;
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pt.y = 8;
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@endcode
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or
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@code{.java}
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Point pt = new Point(10, 8);
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@endcode
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### Scalar
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- Represents a 4-element vector. The type Scalar is widely used in OpenCV for passing pixel
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values.
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- In this tutorial, we will use it extensively to represent BGR color values (3 parameters). It is
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not necessary to define the last argument if it is not going to be used.
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- Let's see an example, if we are asked for a color argument and we give:
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@code{.java}
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Scalar( a, b, c )
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@endcode
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We would be defining a BGR color such as: *Blue = a*, *Green = b* and *Red = c*
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@end_toggle
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Code
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----
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@add_toggle_cpp
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- This code is in your OpenCV sample folder. Otherwise you can grab it from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp)
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@include samples/cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp
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@end_toggle
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@add_toggle_java
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- This code is in your OpenCV sample folder. Otherwise you can grab it from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java)
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@include samples/java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java
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@end_toggle
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@add_toggle_python
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- This code is in your OpenCV sample folder. Otherwise you can grab it from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py)
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@include samples/python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py
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@end_toggle
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Explanation
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-----------
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Since we plan to draw two examples (an atom and a rook), we have to create two images and two
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windows to display them.
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp create_images
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java create_images
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py create_images
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@end_toggle
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We created functions to draw different geometric shapes. For instance, to draw the atom we used
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**MyEllipse** and **MyFilledCircle**:
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp draw_atom
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java draw_atom
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py draw_atom
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@end_toggle
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And to draw the rook we employed **MyLine**, **rectangle** and a **MyPolygon**:
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp draw_rook
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java draw_rook
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py draw_rook
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@end_toggle
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Let's check what is inside each of these functions:
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@add_toggle_cpp
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@end_toggle
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<H4>MyLine</H4>
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_line
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_line
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_line
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@end_toggle
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- As we can see, **MyLine** just call the function **line()** , which does the following:
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- Draw a line from Point **start** to Point **end**
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- The line is displayed in the image **img**
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- The line color is defined by <B>( 0, 0, 0 )</B> which is the RGB value correspondent
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to **Black**
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- The line thickness is set to **thickness** (in this case 2)
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- The line is a 8-connected one (**lineType** = 8)
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<H4>MyEllipse</H4>
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_ellipse
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_ellipse
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_ellipse
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@end_toggle
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- From the code above, we can observe that the function **ellipse()** draws an ellipse such
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that:
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- The ellipse is displayed in the image **img**
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- The ellipse center is located in the point <B>(w/2, w/2)</B> and is enclosed in a box
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of size <B>(w/4, w/16)</B>
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- The ellipse is rotated **angle** degrees
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- The ellipse extends an arc between **0** and **360** degrees
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- The color of the figure will be <B>( 255, 0, 0 )</B> which means blue in BGR value.
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- The ellipse's **thickness** is 2.
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<H4>MyFilledCircle</H4>
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_filled_circle
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_filled_circle
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_filled_circle
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@end_toggle
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- Similar to the ellipse function, we can observe that *circle* receives as arguments:
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- The image where the circle will be displayed (**img**)
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- The center of the circle denoted as the point **center**
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- The radius of the circle: **w/32**
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- The color of the circle: <B>( 0, 0, 255 )</B> which means *Red* in BGR
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- Since **thickness** = -1, the circle will be drawn filled.
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<H4>MyPolygon</H4>
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp my_polygon
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java my_polygon
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py my_polygon
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@end_toggle
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- To draw a filled polygon we use the function **fillPoly()** . We note that:
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- The polygon will be drawn on **img**
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- The vertices of the polygon are the set of points in **ppt**
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- The color of the polygon is defined by <B>( 255, 255, 255 )</B>, which is the BGR
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value for *white*
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<H4>rectangle</H4>
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgProc/basic_drawing/Drawing_1.cpp rectangle
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/ImgProc/BasicGeometricDrawing/BasicGeometricDrawing.java rectangle
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/imgProc/BasicGeometricDrawing/basic_geometric_drawing.py rectangle
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@end_toggle
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- Finally we have the @ref cv::rectangle function (we did not create a special function for
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this guy). We note that:
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- The rectangle will be drawn on **rook_image**
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- Two opposite vertices of the rectangle are defined by <B>( 0, 7*w/8 )</B>
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and <B>( w, w )</B>
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- The color of the rectangle is given by <B>( 0, 255, 255 )</B> which is the BGR value
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for *yellow*
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- Since the thickness value is given by **FILLED (-1)**, the rectangle will be filled.
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Result
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------
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Compiling and running your program should give you a result like this:
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Binary file not shown.
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