Mean filter, or average filter source code

Category. Digital signal and image processing (DSP and DIP) software development.
Description. Mean, or average filter C++ source code — implementation file.
meanfilter.cpp
//   meanfilter.cpp - implementation of 
//   1D and 2D mean filter routines
//
//   The code is property of LIBROW
//   You can use it on your own
//   When utilizing credit LIBROW site

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

//   1D MEAN FILTER implementation
//     signal - input signal
//     result - output signal
//     N      - length of the signal
void _meanfilter(const element* signal, element* result, int N)
{
   //   Move window through all elements of the signal
   for (int i = 2; i < N - 2; ++i)
      //   Take the average
      result[i - 2] = (
         signal[i - 2] +
         signal[i - 1] +
         signal[i] +
         signal[i + 1] +
         signal[i + 2]) / 5;
}

//   1D MEAN FILTER wrapper
//     signal - input signal
//     result - output signal
//     N      - length of the signal
void meanfilter(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 mean filter implementation
   _meanfilter(extension, result ? result : signal, N + 4);
   //   Free memory
   delete[] extension;
}

//   2D MEAN FILTER implementation
//     image  - input image
//     result - output image
//     N      - width of the image
//     M      - height of the image
void _meanfilter(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)
         //   Take the average
         result[(m - 1) * (N - 2) + n - 1] = (
            image[(m - 1) * N + n - 1] + 
            image[(m - 1) * N + n] + 
            image[(m - 1) * N + n + 1] +
            image[m * N + n - 1] + 
            image[m * N + n] + 
            image[m * N + n + 1] +
            image[(m + 1) * N + n - 1] + 
            image[(m + 1) * N + n] + 
            image[(m + 1) * N + n + 1]) / 9;
}

//   2D MEAN FILTER wrapper
//     image  - input image
//     result - output image
//     N      - width of the image
//     M      - height of the image
void meanfilter(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 mean filter implementation
   _meanfilter(extension, result ? result : image, N + 2, M + 2);
   //   Free memory
   delete[] extension;
}
Article 5 — Appendix A.2

meanfilter.cpp
