Mean filter, or average filter source code

// 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;
}