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Tutorial Laplace Operator
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‎doc/tutorials/imgproc/imgtrans/laplace_operator/laplace_operator.markdown

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Laplace Operator {#tutorial_laplace_operator}
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================
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@prev_tutorial{tutorial_sobel_derivatives}
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@next_tutorial{tutorial_canny_detector}
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Goal
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----
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In this tutorial you will learn how to:
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- Use the OpenCV function @ref cv::Laplacian to implement a discrete analog of the *Laplacian
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- Use the OpenCV function **Laplacian()** to implement a discrete analog of the *Laplacian
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operator*.
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Theory
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\f[Laplace(f) = \dfrac{\partial^{2} f}{\partial x^{2}} + \dfrac{\partial^{2} f}{\partial y^{2}}\f]
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-# The Laplacian operator is implemented in OpenCV by the function @ref cv::Laplacian . In fact,
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-# The Laplacian operator is implemented in OpenCV by the function **Laplacian()** . In fact,
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since the Laplacian uses the gradient of images, it calls internally the *Sobel* operator to
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perform its computation.
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- Applies a Laplacian operator to the grayscale image and stores the output image
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- Display the result in a window
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@add_toggle_cpp
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-# The tutorial code's is shown lines below. You can also download it from
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[here](https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp)
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp)
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@include samples/cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp
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@end_toggle
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@add_toggle_java
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-# The tutorial code's is shown lines below. You can also download it from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java)
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@include samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java
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@end_toggle
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@add_toggle_python
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-# The tutorial code's is shown lines below. You can also download it from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py)
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@include samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py
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@end_toggle
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Explanation
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-----------
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-# Create some needed variables:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp variables
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-# Loads the source image:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp load
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-# Apply a Gaussian blur to reduce noise:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp reduce_noise
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-# Convert the image to grayscale using @ref cv::cvtColor
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp convert_to_gray
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-# Apply the Laplacian operator to the grayscale image:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp laplacian
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where the arguments are:
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#### Declare variables
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp variables
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java variables
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py variables
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@end_toggle
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#### Load source image
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp load
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java load
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py load
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@end_toggle
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#### Reduce noise
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp reduce_noise
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java reduce_noise
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py reduce_noise
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@end_toggle
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#### Grayscale
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp convert_to_gray
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java convert_to_gray
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py convert_to_gray
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@end_toggle
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#### Laplacian operator
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp laplacian
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java laplacian
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py laplacian
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@end_toggle
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- The arguments are:
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- *src_gray*: The input image.
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- *dst*: Destination (output) image
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- *ddepth*: Depth of the destination image. Since our input is *CV_8U* we define *ddepth* =
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this example.
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- *scale*, *delta* and *BORDER_DEFAULT*: We leave them as default values.
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-# Convert the output from the Laplacian operator to a *CV_8U* image:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp convert
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-# Display the result in a window:
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp display
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#### Convert output to a *CV_8U* image
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp convert
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java convert
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py convert
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@end_toggle
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#### Display the result
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@add_toggle_cpp
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@snippet cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp display
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@end_toggle
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@add_toggle_java
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@snippet samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java display
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@end_toggle
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@add_toggle_python
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@snippet samples/python/tutorial_code/ImgTrans/LaPlace/laplace_demo.py display
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@end_toggle
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Results
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-------

‎doc/tutorials/imgproc/table_of_content_imgproc.markdown

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- @subpage tutorial_laplace_operator
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*Languages:* C++, Java, Python
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*Compatibility:* \> OpenCV 2.0
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*Author:* Ana Huamán

‎samples/cpp/tutorial_code/ImgTrans/Laplace_Demo.cpp

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*/
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int main( int argc, char** argv )
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{
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//![variables]
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Mat src, src_gray, dst;
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int kernel_size = 3;
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int scale = 1;
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int delta = 0;
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int ddepth = CV_16S;
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const char* window_name = "Laplace Demo";
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//![variables]
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//![variables]
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// Declare the variables we are going to use
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Mat src, src_gray, dst;
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int kernel_size = 3;
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int scale = 1;
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int delta = 0;
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int ddepth = CV_16S;
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const char* window_name = "Laplace Demo";
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//![variables]
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//![load]
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String imageName("../data/lena.jpg"); // by default
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if (argc > 1)
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{
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imageName = argv[1];
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}
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src = imread( imageName, IMREAD_COLOR ); // Load an image
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//![load]
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const char* imageName = argc >=2 ? argv[1] : "../data/lena.jpg";
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if( src.empty() )
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{ return -1; }
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//![load]
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src = imread( imageName, IMREAD_COLOR ); // Load an image
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//![reduce_noise]
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/// Reduce noise by blurring with a Gaussian filter
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GaussianBlur( src, src, Size(3,3), 0, 0, BORDER_DEFAULT );
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//![reduce_noise]
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// Check if image is loaded fine
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if(src.empty()){
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printf(" Error opening image\n");
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printf(" Program Arguments: [image_name -- default ../data/lena.jpg] \n");
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return -1;
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}
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//![load]
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//![convert_to_gray]
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cvtColor( src, src_gray, COLOR_BGR2GRAY ); // Convert the image to grayscale
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//![convert_to_gray]
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//![reduce_noise]
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// Reduce noise by blurring with a Gaussian filter ( kernel size = 3 )
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GaussianBlur( src, src, Size(3, 3), 0, 0, BORDER_DEFAULT );
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//![reduce_noise]
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/// Apply Laplace function
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Mat abs_dst;
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//![laplacian]
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Laplacian( src_gray, dst, ddepth, kernel_size, scale, delta, BORDER_DEFAULT );
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//![laplacian]
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//![convert_to_gray]
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cvtColor( src, src_gray, COLOR_BGR2GRAY ); // Convert the image to grayscale
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//![convert_to_gray]
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//![convert]
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convertScaleAbs( dst, abs_dst );
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//![convert]
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/// Apply Laplace function
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Mat abs_dst;
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//![laplacian]
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Laplacian( src_gray, dst, ddepth, kernel_size, scale, delta, BORDER_DEFAULT );
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//![laplacian]
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//![display]
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imshow( window_name, abs_dst );
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waitKey(0);
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//![display]
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//![convert]
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// converting back to CV_8U
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convertScaleAbs( dst, abs_dst );
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//![convert]
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return 0;
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//![display]
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imshow( window_name, abs_dst );
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waitKey(0);
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//![display]
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return 0;
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}

‎samples/java/tutorial_code/ImgTrans/LaPlace/LaplaceDemo.java

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/**
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* @file LaplaceDemo.java
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* @brief Sample code showing how to detect edges using the Laplace operator
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*/
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import org.opencv.core.*;
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import org.opencv.highgui.HighGui;
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import org.opencv.imgcodecs.Imgcodecs;
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import org.opencv.imgproc.Imgproc;
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class LaplaceDemoRun {
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public void run(String[] args) {
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//! [variables]
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// Declare the variables we are going to use
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Mat src, src_gray = new Mat(), dst = new Mat();
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int kernel_size = 3;
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int scale = 1;
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int delta = 0;
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int ddepth = CvType.CV_16S;
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String window_name = "Laplace Demo";
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//! [variables]
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//! [load]
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String imageName = ((args.length > 0) ? args[0] : "../data/lena.jpg");
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src = Imgcodecs.imread(imageName, Imgcodecs.IMREAD_COLOR); // Load an image
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// Check if image is loaded fine
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if( src.empty() ) {
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System.out.println("Error opening image");
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System.out.println("Program Arguments: [image_name -- default ../data/lena.jpg] \n");
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System.exit(-1);
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}
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//! [load]
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//! [reduce_noise]
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// Reduce noise by blurring with a Gaussian filter ( kernel size = 3 )
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Imgproc.GaussianBlur( src, src, new Size(3, 3), 0, 0, Core.BORDER_DEFAULT );
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//! [reduce_noise]
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//! [convert_to_gray]
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// Convert the image to grayscale
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Imgproc.cvtColor( src, src_gray, Imgproc.COLOR_RGB2GRAY );
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//! [convert_to_gray]
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/// Apply Laplace function
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Mat abs_dst = new Mat();
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//! [laplacian]
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Imgproc.Laplacian( src_gray, dst, ddepth, kernel_size, scale, delta, Core.BORDER_DEFAULT );
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//! [laplacian]
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//! [convert]
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// converting back to CV_8U
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Core.convertScaleAbs( dst, abs_dst );
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//! [convert]
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//! [display]
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HighGui.imshow( window_name, abs_dst );
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HighGui.waitKey(0);
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//! [display]
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System.exit(0);
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}
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}
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public class LaplaceDemo {
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public static void main(String[] args) {
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// Load the native library.
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System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
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new LaplaceDemoRun().run(args);
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}
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}

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