Salt and Pepper Noise removal using C++

Salt-and-pepper noise is a form of noise sometimes seen on images. It is also known as impulse noise. This noise can be caused by sharp and sudden disturbances in the image signal. It presents itself as sparsely occurring white and black pixels. An effective noise reduction method for this type of noise is a median filter or a morphological filter.
In this article, we will learn how to remove Salt-Pepper Noise from the image simply using C++ (without using any external image processing library like OpenCV). 
Approach:

1. Store the pixel values of input image in an array.
2. For each pixel value if it contains 0(black) or 255(white) then compute the average value of its neighbor pixel values, else that pixel value is stored in another array.
3. Pixel values of the new array are used for output file.

Below is the simple C++ implementation of Salt-Pepper Noise removal : 

CPP

#include <fstream>
#include <iostream>
#include <sstream>

using namespace std;

int array[2000][2000]; // used for input image
int arr[2000][2000]; // used for output image
int hist[255];

int main()
{
    int i, row = 0, j = 0, col = 0, numrows = 0, numcols = 0, MAX = 0;

    // input image
    ifstream infile("saltpepper.pgm");
    stringstream ss;
    string inputLine = "";

    // First line : version
    getline(infile, inputLine);
    if (inputLine.compare("P2") != 0)
        cerr << "Version error" << endl;
    else
        cout << "Version : " << inputLine << endl;

    // Continue with a stringstream
    ss << infile.rdbuf();

    // Secondline : size
    ss >> numcols >> numrows >> MAX;

    // print total number of columns,
    // rows and maximum intensity of the image
    cout << numcols << " columns and " << numrows << " rows" << endl
         << " Maximum Intensity " << MAX << endl;

    // Initialize a new array of
    // same size of the image with 0
    for (row = 0; row <= numrows; ++row)
        array[row][0] = 0;

    for (col = 0; col <= numcols; ++col)
        array[0][col] = 0;

    printf("****\n");

    // Following lines : data
    for (row = 1; row <= numrows; ++row) {
        for (col = 1; col <= numcols; ++col) {
            // original data store in new array
            ss >> array[row][col];
        }
    }

    for (row = 1; row <= numrows; ++row) {
        for (col = 1; col <= numcols; ++col) {

            // check if intensity is black or white
            if (array[row][col] == 0 || array[row][col] == 255)
            {
                // compute average of neighbours pixels
                // and store the pixel value in another
                // array for output image
                arr[row][col] = (array[row - 1][col] +
                                 array[row - 1][col - 1] +
                                 array[row - 1][col + 1] +
                                 array[row][col - 1] +
                                 array[row][col + 1] +
                                 array[row + 1][col + 1] +
                                 array[row + 1][col] +
                                 array[row + 1][col - 1]) / 8;
            }
            else {
                // store pixel value in another
                // array for output image
                arr[row][col] = array[row][col];
            }
        }
    }

    ofstream outfile;

    // new file open to store the output image
    outfile.open("salt and pepper.pgm");
    outfile << "P2" << endl;
    outfile << numcols << " " << numrows << endl;
    outfile << "255" << endl;

    for (row = 1; row <= numrows; ++row) {
        for (col = 1; col <= numcols; ++col) {

            // store resultant pixel intensity to the output file
            outfile << arr[row][col] << " ";
        }
    }

    outfile.close();
    infile.close();
    return 0;
}

Input Image:

Output Image: