init - 初始化项目
This commit is contained in:
Lee Nony
@@ -0,0 +1,243 @@
|
||||
Adding borders to your images {#tutorial_copyMakeBorder}
|
||||
=============================
|
||||
|
||||
@tableofcontents
|
||||
|
||||
@prev_tutorial{tutorial_filter_2d}
|
||||
@next_tutorial{tutorial_sobel_derivatives}
|
||||
|
||||
| | |
|
||||
| -: | :- |
|
||||
| Original author | Ana Huamán |
|
||||
| Compatibility | OpenCV >= 3.0 |
|
||||
|
||||
Goal
|
||||
----
|
||||
|
||||
In this tutorial you will learn how to:
|
||||
|
||||
- Use the OpenCV function **copyMakeBorder()** to set the borders (extra padding to your
|
||||
image).
|
||||
|
||||
Theory
|
||||
------
|
||||
|
||||
@note The explanation below belongs to the book **Learning OpenCV** by Bradski and Kaehler.
|
||||
|
||||
-# In our previous tutorial we learned to use convolution to operate on images. One problem that
|
||||
naturally arises is how to handle the boundaries. How can we convolve them if the evaluated
|
||||
points are at the edge of the image?
|
||||
-# What most of OpenCV functions do is to copy a given image onto another slightly larger image and
|
||||
then automatically pads the boundary (by any of the methods explained in the sample code just
|
||||
below). This way, the convolution can be performed over the needed pixels without problems (the
|
||||
extra padding is cut after the operation is done).
|
||||
-# In this tutorial, we will briefly explore two ways of defining the extra padding (border) for an
|
||||
image:
|
||||
|
||||
-# **BORDER_CONSTANT**: Pad the image with a constant value (i.e. black or \f$0\f$
|
||||
-# **BORDER_REPLICATE**: The row or column at the very edge of the original is replicated to
|
||||
the extra border.
|
||||
|
||||
This will be seen more clearly in the Code section.
|
||||
|
||||
- **What does this program do?**
|
||||
- Load an image
|
||||
- Let the user choose what kind of padding use in the input image. There are two options:
|
||||
|
||||
-# *Constant value border*: Applies a padding of a constant value for the whole border.
|
||||
This value will be updated randomly each 0.5 seconds.
|
||||
-# *Replicated border*: The border will be replicated from the pixel values at the edges of
|
||||
the original image.
|
||||
|
||||
The user chooses either option by pressing 'c' (constant) or 'r' (replicate)
|
||||
- The program finishes when the user presses 'ESC'
|
||||
|
||||
Code
|
||||
----
|
||||
|
||||
The tutorial code's is shown lines below.
|
||||
|
||||
@add_toggle_cpp
|
||||
You can also download it from
|
||||
[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp)
|
||||
@include samples/cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
You can also download it from
|
||||
[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java)
|
||||
@include samples/java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
You can also download it from
|
||||
[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py)
|
||||
@include samples/python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py
|
||||
@end_toggle
|
||||
|
||||
Explanation
|
||||
-----------
|
||||
|
||||
#### Declare the variables
|
||||
|
||||
First we declare the variables we are going to use:
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp variables
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java variables
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py variables
|
||||
@end_toggle
|
||||
|
||||
Especial attention deserves the variable *rng* which is a random number generator. We use it to
|
||||
generate the random border color, as we will see soon.
|
||||
|
||||
#### Load an image
|
||||
|
||||
As usual we load our source image *src*:
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp load
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java load
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py load
|
||||
@end_toggle
|
||||
|
||||
#### Create a window
|
||||
|
||||
After giving a short intro of how to use the program, we create a window:
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp create_window
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java create_window
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py create_window
|
||||
@end_toggle
|
||||
|
||||
#### Initialize arguments
|
||||
|
||||
Now we initialize the argument that defines the size of the borders (*top*, *bottom*, *left* and
|
||||
*right*). We give them a value of 5% the size of *src*.
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp init_arguments
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java init_arguments
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py init_arguments
|
||||
@end_toggle
|
||||
|
||||
#### Loop
|
||||
|
||||
The program runs in an infinite loop while the key **ESC** isn't pressed.
|
||||
If the user presses '**c**' or '**r**', the *borderType* variable
|
||||
takes the value of *BORDER_CONSTANT* or *BORDER_REPLICATE* respectively:
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp check_keypress
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java check_keypress
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py check_keypress
|
||||
@end_toggle
|
||||
|
||||
#### Random color
|
||||
|
||||
In each iteration (after 0.5 seconds), the random border color (*value*) is updated...
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp update_value
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java update_value
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py update_value
|
||||
@end_toggle
|
||||
|
||||
This value is a set of three numbers picked randomly in the range \f$[0,255]\f$.
|
||||
|
||||
#### Form a border around the image
|
||||
|
||||
Finally, we call the function **copyMakeBorder()** to apply the respective padding:
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp copymakeborder
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java copymakeborder
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py copymakeborder
|
||||
@end_toggle
|
||||
|
||||
- The arguments are:
|
||||
|
||||
-# *src*: Source image
|
||||
-# *dst*: Destination image
|
||||
-# *top*, *bottom*, *left*, *right*: Length in pixels of the borders at each side of the image.
|
||||
We define them as being 5% of the original size of the image.
|
||||
-# *borderType*: Define what type of border is applied. It can be constant or replicate for
|
||||
this example.
|
||||
-# *value*: If *borderType* is *BORDER_CONSTANT*, this is the value used to fill the border
|
||||
pixels.
|
||||
|
||||
#### Display the results
|
||||
|
||||
We display our output image in the image created previously
|
||||
|
||||
@add_toggle_cpp
|
||||
@snippet cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp display
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_java
|
||||
@snippet java/tutorial_code/ImgTrans/MakeBorder/CopyMakeBorder.java display
|
||||
@end_toggle
|
||||
|
||||
@add_toggle_python
|
||||
@snippet python/tutorial_code/ImgTrans/MakeBorder/copy_make_border.py display
|
||||
@end_toggle
|
||||
|
||||
Results
|
||||
-------
|
||||
|
||||
-# After compiling the code above, you can execute it giving as argument the path of an image. The
|
||||
result should be:
|
||||
|
||||
- By default, it begins with the border set to BORDER_CONSTANT. Hence, a succession of random
|
||||
colored borders will be shown.
|
||||
- If you press 'r', the border will become a replica of the edge pixels.
|
||||
- If you press 'c', the random colored borders will appear again
|
||||
- If you press 'ESC' the program will exit.
|
||||
|
||||
Below some screenshot showing how the border changes color and how the *BORDER_REPLICATE*
|
||||
option looks:
|
||||
|
||||
|
||||
Binary file not shown.
|
After Width: | Height: | Size: 20 KiB |
Reference in New Issue
Block a user