Median filter source code

//   medianfilter.cpp - impelementation of 
//   1D and 2D median filter routines
//
//   The code is property of LIBROW
//   You can use it on your own
//   When utilizing credit LIBROW site

#include <memory.h>
#include "medianfilter.h"

//   1D MEDIAN FILTER implementation
//     signal - input signal
//     result - output signal
//     N      - length of the signal
void _medianfilter(const element* signal, element* result, int N)
{
   //   Move window through all elements of the signal
   for (int i = 2; i < N - 2; ++i)
   {
      //   Pick up window elements
      element window[5];
      for (int j = 0; j < 5; ++j)
         window[j] = signal[i - 2 + j];
      //   Order elements (only half of them)
      for (int j = 0; j < 3; ++j)
      {
         //   Find position of minimum element
         int min = j;
         for (int k = j + 1; k < 5; ++k)
            if (window[k] < window[min])
               min = k;
         //   Put found minimum element in its place
         const element temp = window[j];
         window[j] = window[min];
         window[min] = temp;
      }
      //   Get result - the middle element
      result[i - 2] = window[2];
   }
}

//   1D MEDIAN FILTER wrapper
//     signal - input signal
//     result - output signal
//     N      - length of the signal
void medianfilter(element* signal, element* result, int N)
{
   //   Check arguments
   if (!signal || N < 1)
      return;
   //   Treat special case N = 1
   if (N == 1)
   {
      if (result)
         result[0] = signal[0];
      return;
   }
   //   Allocate memory for signal extension
   element* extension = new element[N + 4];
   //   Check memory allocation
   if (!extension)
      return;
   //   Create signal extension
   memcpy(extension + 2, signal, N * sizeof(element));
   for (int i = 0; i < 2; ++i)
   {
      extension[i] = signal[1 - i];
      extension[N + 2 + i] = signal[N - 1 - i];
   }
   //   Call median filter implementation
   _medianfilter(extension, result ? result : signal, N + 4);
   //   Free memory
   delete[] extension;
}

//   2D MEDIAN FILTER implementation
//     image  - input image
//     result - output image
//     N      - width of the image
//     M      - height of the image
void _medianfilter(const element* image, element* result, int N, int M)
{
   //   Move window through all elements of the image
   for (int m = 1; m < M - 1; ++m)
      for (int n = 1; n < N - 1; ++n)
      {
         //   Pick up window elements
         int k = 0;
         element window[9];
         for (int j = m - 1; j < m + 2; ++j)
            for (int i = n - 1; i < n + 2; ++i)
               window[k++] = image[j * N + i];
         //   Order elements (only half of them)
         for (int j = 0; j < 5; ++j)
         {
            //   Find position of minimum element
            int min = j;
            for (int l = j + 1; l < 9; ++l)
            if (window[l] < window[min])
               min = l;
            //   Put found minimum element in its place
            const element temp = window[j];
            window[j] = window[min];
            window[min] = temp;
         }
         //   Get result - the middle element
         result[(m - 1) * (N - 2) + n - 1] = window[4];
      }
}

//   2D MEDIAN FILTER wrapper
//     image  - input image
//     result - output image
//     N      - width of the image
//     M      - height of the image
void medianfilter(element* image, element* result, int N, int M)
{
   //   Check arguments
   if (!image || N < 1 || M < 1)
      return;
   //   Allocate memory for signal extension
   element* extension = new element[(N + 2) * (M + 2)];
   //   Check memory allocation
   if (!extension)
      return;
   //   Create image extension
   for (int i = 0; i < M; ++i)
   {
      memcpy(extension + (N + 2) * (i + 1) + 1,
         image + N * i,
         N * sizeof(element));
      extension[(N + 2) * (i + 1)] = image[N * i];
      extension[(N + 2) * (i + 2) - 1] = image[N * (i + 1) - 1];
   }
   //   Fill first line of image extension
   memcpy(extension,
      extension + N + 2,
      (N + 2) * sizeof(element));
   //   Fill last line of image extension
   memcpy(extension + (N + 2) * (M + 1),
      extension + (N + 2) * M,
      (N + 2) * sizeof(element));
   //   Call median filter implementation
   _medianfilter(extension, result ? result : image, N + 2, M + 2);
   //   Free memory
   delete[] extension;
}