从GIMP的Retinex算法里发现了一种高斯模糊的快速实现方法【开发记录】。

static void
gausssmooth (gfloat *in, gfloat *out, gint size, gint rowstride, gauss3_coefs *c)
{
  /*
   * Papers:  "Recursive Implementation of the gaussian filter.",
   *          Ian T. Young , Lucas J. Van Vliet, Signal Processing 44, Elsevier 1995.
   * formula: 9a        forward filter
   *          9b        backward filter
   *          fig7      algorithm
   */
  gint i,n, bufsize;
  gfloat *w1,*w2;

  /* forward pass */
  bufsize = size+3;
  size -= 1;
  w1 = (gfloat *) g_try_malloc (bufsize * sizeof (gfloat));
  w2 = (gfloat *) g_try_malloc (bufsize * sizeof (gfloat));
  w1[0] = in[0];
  w1[1] = in[0];
  w1[2] = in[0];
  for ( i = 0 , n=3; i <= size ; i++, n++)
    {
      w1[n] = (gfloat)(c->B*in[i*rowstride] +
                       ((c->b[1]*w1[n-1] +
                         c->b[2]*w1[n-2] +
                         c->b[3]*w1[n-3] ) / c->b[0]));
    }

  /* backward pass */
  w2[size+1]= w1[size+3];
  w2[size+2]= w1[size+3];
  w2[size+3]= w1[size+3];
  for (i = size, n = i; i >= 0; i--, n--)
    {
      w2[n]= out[i * rowstride] = (gfloat)(c->B*w1[n] +
                                           ((c->b[1]*w2[n+1] +
                                             c->b[2]*w2[n+2] +
                                             c->b[3]*w2[n+3] ) / c->b[0]));
    }

  g_free (w1);
  g_free (w2);
}