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Tutorial Adding Images
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‎doc/tutorials/core/adding_images/adding_images.markdown

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Adding (blending) two images using OpenCV {#tutorial_adding_images}
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=========================================
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@prev_tutorial{tutorial_mat_operations}
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@next_tutorial{tutorial_basic_linear_transform}
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Goal
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----
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In this tutorial you will learn:
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- what is *linear blending* and why it is useful;
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- how to add two images using @ref cv::addWeighted
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- how to add two images using **addWeighted()**
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Theory
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------
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Source Code
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-----------
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@add_toggle_cpp
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Download the source code from
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[here](https://github.com/opencv/opencv/tree/master/samples/cpp/tutorial_code/core/AddingImages/AddingImages.cpp).
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/cpp/tutorial_code/core/AddingImages/AddingImages.cpp).
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@include cpp/tutorial_code/core/AddingImages/AddingImages.cpp
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@end_toggle
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@add_toggle_java
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Download the source code from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/java/tutorial_code/core/AddingImages/AddingImages.java).
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@include java/tutorial_code/core/AddingImages/AddingImages.java
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@end_toggle
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@add_toggle_python
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Download the source code from
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[here](https://raw.githubusercontent.com/opencv/opencv/master/samples/python/tutorial_code/core/AddingImages/adding_images.py).
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@include python/tutorial_code/core/AddingImages/adding_images.py
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@end_toggle
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Explanation
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-----------
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-# Since we are going to perform:
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Since we are going to perform:
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\f[g(x) = (1 - \alpha)f_{0}(x) + \alpha f_{1}(x)\f]
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We need two source images (\f$f_{0}(x)\f$ and \f$f_{1}(x)\f$). So, we load them in the usual way:
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@add_toggle_cpp
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp load
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@end_toggle
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@add_toggle_java
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@snippet java/tutorial_code/core/AddingImages/AddingImages.java load
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@end_toggle
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@add_toggle_python
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@snippet python/tutorial_code/core/AddingImages/adding_images.py load
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@end_toggle
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We used the following images: [LinuxLogo.jpg](https://raw.githubusercontent.com/opencv/opencv/master/samples/data/LinuxLogo.jpg) and [WindowsLogo.jpg](https://raw.githubusercontent.com/opencv/opencv/master/samples/data/WindowsLogo.jpg)
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@warning Since we are *adding* *src1* and *src2*, they both have to be of the same size
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(width and height) and type.
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Now we need to generate the `g(x)` image. For this, the function **addWeighted()** comes quite handy:
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@add_toggle_cpp
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp blend_images
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@end_toggle
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\f[g(x) = (1 - \alpha)f_{0}(x) + \alpha f_{1}(x)\f]
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@add_toggle_java
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@snippet java/tutorial_code/core/AddingImages/AddingImages.java blend_images
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@end_toggle
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We need two source images (\f$f_{0}(x)\f$ and \f$f_{1}(x)\f$). So, we load them in the usual way:
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp load
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@add_toggle_python
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@snippet python/tutorial_code/core/AddingImages/adding_images.py blend_images
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Numpy version of above line (but cv2 function is around 2x faster):
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\code{.py}
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dst = np.uint8(alpha*(img1)+beta*(img2))
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\endcode
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@end_toggle
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**warning**
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since **addWeighted()** produces:
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\f[dst = \alpha \cdot src1 + \beta \cdot src2 + \gamma\f]
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In this case, `gamma` is the argument \f$0.0\f$ in the code above.
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Since we are *adding* *src1* and *src2*, they both have to be of the same size (width and
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height) and type.
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Create windows, show the images and wait for the user to end the program.
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@add_toggle_cpp
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp display
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@end_toggle
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-# Now we need to generate the `g(x)` image. For this, the function @ref cv::addWeighted comes quite handy:
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp blend_images
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since @ref cv::addWeighted produces:
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\f[dst = \alpha \cdot src1 + \beta \cdot src2 + \gamma\f]
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In this case, `gamma` is the argument \f$0.0\f$ in the code above.
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@add_toggle_java
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@snippet java/tutorial_code/core/AddingImages/AddingImages.java display
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@end_toggle
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-# Create windows, show the images and wait for the user to end the program.
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@snippet cpp/tutorial_code/core/AddingImages/AddingImages.cpp display
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@add_toggle_python
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@snippet python/tutorial_code/core/AddingImages/adding_images.py display
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@end_toggle
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Result
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------

‎doc/tutorials/core/table_of_content_core.markdown

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- @subpage tutorial_adding_images
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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/core/AddingImages/AddingImages.cpp

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* @brief Simple linear blender ( dst = alpha*src1 + beta*src2 )
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* @author OpenCV team
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*/
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#include "opencv2/imgcodecs.hpp"
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#include "opencv2/highgui.hpp"
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#include <iostream>
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/// Ask the user enter alpha
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cout << " Simple Linear Blender " << endl;
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cout << "-----------------------" << endl;
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cout << "* Enter alpha [0-1]: ";
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cout << "* Enter alpha [0.0-1.0]: ";
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cin >> input;
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// We use the alpha provided by the user if it is between 0 and 1

‎samples/java/tutorial_code/core/AddingImages/AddingImages.java

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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 java.util.Locale;
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import java.util.Scanner;
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class AddingImagesRun{
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public void run() {
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double alpha = 0.5; double beta; double input;
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Mat src1, src2, dst = new Mat();
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System.out.println(" Simple Linear Blender ");
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System.out.println("-----------------------");
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System.out.println("* Enter alpha [0.0-1.0]: ");
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Scanner scan = new Scanner( System.in ).useLocale(Locale.US);
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input = scan.nextDouble();
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if( input >= 0.0 && input <= 1.0 )
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alpha = input;
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//! [load]
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src1 = Imgcodecs.imread("../../images/LinuxLogo.jpg");
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src2 = Imgcodecs.imread("../../images/WindowsLogo.jpg");
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//! [load]
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if( src1.empty() == true ){ System.out.println("Error loading src1"); return;}
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if( src2.empty() == true ){ System.out.println("Error loading src2"); return;}
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//! [blend_images]
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beta = ( 1.0 - alpha );
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Core.addWeighted( src1, alpha, src2, beta, 0.0, dst);
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//! [blend_images]
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//![display]
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HighGui.imshow("Linear Blend", 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 AddingImages {
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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 AddingImagesRun().run();
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}
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}

‎samples/python/tutorial_code/core/AddingImages/adding_images.py

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from __future__ import print_function
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import sys
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import cv2
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alpha = 0.5
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print(''' Simple Linear Blender
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-----------------------
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* Enter alpha [0.0-1.0]: ''')
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if sys.version_info >= (3, 0): # If Python 3.x
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input_alpha = float(input())
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else:
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input_alpha = float(raw_input())
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if 0 <= alpha <= 1:
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alpha = input_alpha
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## [load]
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src1 = cv2.imread('../../../../data/LinuxLogo.jpg')
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src2 = cv2.imread('../../../../data/WindowsLogo.jpg')
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## [load]
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if src1 is None:
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print ("Error loading src1")
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exit(-1)
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elif src2 is None:
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print ("Error loading src2")
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exit(-1)
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## [blend_images]
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beta = (1.0 - alpha)
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dst = cv2.addWeighted(src1, alpha, src2, beta, 0.0)
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## [blend_images]
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## [display]
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cv2.imshow('dst', dst)
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cv2.waitKey(0)
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## [display]
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cv2.destroyAllWindows()

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