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gaussian_smooth.c
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Tue, May 7, 10:17

gaussian_smooth.c
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#include <math.h>
#include <stdlib.h>
#include <string.h>
#include "mex.h"
#include "gaussian_smooth.h"
/*******************************************************************************
* Adapted from MathWorks :
*
* File ID: #20899
* Canny Edge Detection
* by Anthony Gabrielson
*
* 29 Jul 2008 (Updated 30 Jul 2008)
*
* Code covered by the BSD License
* http://www.mathworks.com/matlabcentral/fileexchange/20899-canny-edge-detection
*
*******************************************************************************/
/*******************************************************************************
* PROCEDURE: gaussian_smooth
* PURPOSE: Blur an image with a gaussian filter.
* NAME: Mike Heath
* DATE: 2/15/96
*******************************************************************************/
void gaussian_smooth(double *image, int rows, int cols, double sigma)
{
int r, c, rr, cc, /* Counter variables. */
windowsize, /* Dimension of the gaussian kernel. */
center; /* Half of the windowsize. */
double *tempim, /* Buffer for separable filter gaussian smoothing. */
*kernel, /* A one dimensional gaussian kernel. */
dot, /* Dot product summing variable. */
sum; /* Sum of the kernel weights variable. */
/****************************************************************************
* Create a 1-dimensional gaussian smoothing kernel.
****************************************************************************/
make_gaussian_kernel(sigma, &kernel, &windowsize);
center = windowsize / 2;
/****************************************************************************
* Allocate a temporary buffer image and the smoothed image.
****************************************************************************/
if((tempim = mxCalloc(rows*cols, sizeof(double))) == NULL){
mexErrMsgTxt("Memory allocation failed for the buffer image !");
}
/****************************************************************************
* Blur in the x - direction.
****************************************************************************/
for(r=0;r<rows;r++){
for(c=0;c<cols;c++){
dot = 0.0;
sum = 0.0;
for(cc=(-center);cc<=center;cc++){
if(((c+cc) >= 0) && ((c+cc) < cols)){
dot += image[r*cols+(c+cc)] * kernel[center+cc];
sum += kernel[center+cc];
}
}
tempim[r*cols+c] = dot/sum;
}
}
/****************************************************************************
* Blur in the y - direction.
****************************************************************************/
for(c=0;c<cols;c++){
for(r=0;r<rows;r++){
sum = 0.0;
dot = 0.0;
for(rr=(-center);rr<=center;rr++){
if(((r+rr) >= 0) && ((r+rr) < rows)){
dot += tempim[(r+rr)*cols+c] * kernel[center+rr];
sum += kernel[center+rr];
}
}
image[r*cols+c] = dot/sum;
}
}
mxFree(tempim);
mxFree(kernel);
}
/*******************************************************************************
* PROCEDURE: make_gaussian_kernel
* PURPOSE: Create a one dimensional gaussian kernel.
* NAME: Mike Heath
* DATE: 2/15/96
*******************************************************************************/
void make_gaussian_kernel(double sigma, double **kernel, int *windowsize)
{
int i, center;
double x, fx, sum=0.0, sqrttwopi;
sqrttwopi = sqrt(M_PI * 2);
*windowsize = 1 + 2 * ceil(2.5 * sigma);
center = (*windowsize) / 2;
if((*kernel = mxCalloc((*windowsize), sizeof(double))) == NULL){
mexErrMsgTxt("Memory allocation failed for kernel !");
}
for(i=0;i<(*windowsize);i++){
x = (double)(i - center);
fx = exp(-0.5*x*x/(sigma*sigma)) / (sigma * sqrttwopi);
(*kernel)[i] = fx;
sum += fx;
}
for(i=0;i<(*windowsize);i++) (*kernel)[i] /= sum;
}

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