Modifying a particular pixel value of an Image

In the previous tutorials we learnt how to access a pixel value of a particular co-ordinate,
Refer :
http://opencv-code.blogspot.in/2016/12/how-to-access-extract-pixel-value-particular-location-image.html

This,

OpenCV C++ tutorial

is about accessing and changing the pixel value at a particular co-ordinate of an Image.
Here is the code below:

/*Displaying the Pixel value of the whole Image using Loops*/
 
#include <opencv2/core/core.hpp>  
#include <opencv2/highgui/highgui.hpp>  
#include <iostream> 
 
  using namespace std;  
  using namespace cv;  
 
int main() 
  {  
    Mat image1,image2; 
    //Reading the color image 
    image1 = imread("C:\\Users\\arjun\\Desktop\\image003.png", CV_LOAD_IMAGE_COLOR);  
 
    //If image1 not found 
    if (!image1.data)                                                                          
    {  
     cout << "No image data \n";  
     return -1;  
    } 
 
    //Display the original image
    namedWindow("Original Image");               
    imshow("Original Image", image1);
 
    //Changing the pixel value at just a particular point(100,200)
     Vec3b color = image1.at<Vec3b>(Point(100,200));
      color.val[0] = 100;
      color.val[1] = 0;
      color.val[2] = 0;
    image1.at<Vec3b>(Point(100,200)) = color;
 
    //Save the modified image
    imwrite("C:\\Users\\arjun\\Desktop\\mod_image.png",image1);
    //Reading the modifed image
    image2 = imread("C:\\Users\\arjun\\Desktop\\mod_image.png", CV_LOAD_IMAGE_COLOR);  
 
   //If image2 not found 
     if (!image2.data)                                                                          
       {  
        cout << "No image data \n";  
        return -1;  
       } 
 
    //Display the modified image
    namedWindow("Modified Image");               
    imshow("Modified Image", image2); 
    waitKey(0);
    return 0;
   }

Input:

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Modified Image:

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Accessing Pixel Value at a Location(x,y)

Let us consider a 3 channel image of BGR color ordering
(The BGR color ordering is the default order returned  by imread)
Here the order of the channel is reverse

(We generally use RGB color model while describing about an image.In BGR the color model is same except the order of the channel is reverse)

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We use :
Vec3b imagepixel = image.at(x,y);

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/*Reading the pixel value of an image at a particular location*/
#include <opencv2/core/core.hpp>  
#include <opencv2/highgui/highgui.hpp>  
#include <iostream> 
 
  using namespace std;  
  using namespace cv;  
 
  int main() 
  {  
    Mat image; 
    //Reading the color image 
    image = imread("C:\\Users\\arjun\\Desktop\\image003.png", CV_LOAD_IMAGE_COLOR);  
 
    //If image not found
     if (!image.data)                                                                          
     {  
      cout << "No image data \n";  
      return -1;  
     } 
    
     
     //Reading pixel value at location (i,j)
     Vec3b imagepixel = image.at<Vec3b>(250,500);

     //Displaying the pixel value  
     cout<<"imagepixel(BGR)="<<imagepixel<<"\n" ;  
        
     //Display the original image
     namedWindow("Display Image");               
     imshow("Display Image", image);  
  
     waitKey(0);
     return 0;
   }

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Input:

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Output:

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/*Reading the pixel value of an image at a particular location*/
 
 
#include <opencv2/core/core.hpp>  
#include <opencv2/highgui/highgui.hpp>  
#include <iostream> 
 
  using namespace std;  
  using namespace cv;  
 
int main() 
  {  
    Mat image; 
    //Reading the color image 
    image = imread("C:\\Users\\arjun\\Desktop\\image003.png", CV_LOAD_IMAGE_COLOR);  
 
     //If image not found  
       if (!image.data)                                                             
     {  
      cout << "No image data \n";  
      return -1;  
     } 
 
 
    while(1)
    {
     //Taking inputs from the user for the co-ordinates of the image 
      int i,j;
      cout<<"Enter the co-ordinates of the image where you want to find the pixel value (i,j): \n";
      cout<<"i<"<<image.rows<<"\t"<<"&"<<"\t"<<"j<"<<image.cols<<"\n";
      
     cout<<"i= ";  cin>>i;
     cout<<"j= ";  cin>>j;
     
     if(i < image.rows) 
      { 
        if(j < image.cols)
          {
           //Reading pixel value at location (i,j)
            Vec3b imagepixel = image.at<Vec3b>(i,j); 
           //Displaying the pixel value                                                        
           cout<<"imagepixel(BGR)="<<imagepixel<<"\n" ;
          }  
        }
      else
        { 
           cout<<"Image Co-ordinates value out of range \n"; 
        }
 
     }
        return 0; 
  }

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Input:

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Output:

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