lum.h

这是三边滤波器算法实现的有关工具

#include <math.h>
#define FTINY        1e-5


typedef double  COLOR[3];       /* red, green, blue (or X,Y,Z) */
double lum (COLOR **rgb_image, int x, int y)
{
  return 0.2125 * rgb_image[y][x][0] + 
         0.7154 * rgb_image[y][x][1] + 
         0.0721 * rgb_image[y][x][2];
}
void compute_luminance (COLOR **rgb_image, double **luminance, int width, int height)
{
  int x, y;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      luminance[y][x] = lum (rgb_image, x, y);
}

void log_space_lum (double **image, int width, int height)
{
  int x, y;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      image[y][x] = log (FTINY + image[y][x]);
}
void compose_luminance (double **detail, double **base, double **luminance,
			int width, int height)
{
  int x, y;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      luminance[y][x] = base[y][x] + detail[y][x];
}
void exponentiate_lum (double **image, int width, int height)
{
  int x, y;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      image[y][x] = exp (image[y][x]) - FTINY;
}
void colour_processing (double **luminance, COLOR **rgb_image, int width, int height, double saturation)
{
  int x, y;
  double L;

  fprintf (stderr, "Colour processing\n");

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
    {
      L = lum (rgb_image, x, y) + FTINY;
      rgb_image[y][x][0] = pow (rgb_image[y][x][0] / L, saturation) * luminance[y][x];
      rgb_image[y][x][1] = pow (rgb_image[y][x][1] / L, saturation) * luminance[y][x];
      rgb_image[y][x][2] = pow (rgb_image[y][x][2] / L, saturation) * luminance[y][x];
    } 
}

void clamp_image (COLOR **rgb_image, int width, int height, double maxval)
{
  int x, y, c;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      for (c = 0; c < 3; c++)
      {
	if (rgb_image[y][x][c] < 0.)
	  rgb_image[y][x][c] = 0.;
	if (rgb_image[y][x][c] > maxval)
	  rgb_image[y][x][c] = maxval;
      }
}

void normalise_image (COLOR **rgb_image, int width, int height, double output_range)
{
  int    x, y, c;
  double minval =  1e20;
  double maxval = -1e20;
  double average = 0.;
  double range;
  double value;

  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
    {
      value = lum (rgb_image, x, y);

      if (value < minval)
	minval = value;
      if (value > maxval)
	maxval = value;
      average += value;
    }
  range    = maxval - minval;
  average /= width * height;

  for (x = 0; x < width; x++)
    for (y = 0; y < height; y++)
      for (c = 0; c < 3; c++)
      {
	rgb_image[y][x][c] = output_range * ((rgb_image[y][x][c] - minval) / range);
	if (rgb_image[y][x][c] < 0.)           rgb_image[y][x][c] = 0.;
	if (rgb_image[y][x][c] > output_range) rgb_image[y][x][c] = output_range;
      }
}