detects edges in an image using the homogeneity operator

/***************************************************************************
* Func: homog_op *
* *
* Desc: detects edges in an image using the homogeneity operator *
* *
* Params: source - pointer to image in memory *
* cols - number of columns in image *
* rows - number of rows in image *
* filename - name of output file *
***************************************************************************/ http://wangzaiqiqi.taobao.com
void homog_op(image_ptr source, int cols, int rows, char *filename)
{
int x, y, i; /* image loop variables */
int index; /* image index */
int winx, winy; /* indices for filling sample window */
int xextra, yextra; /* size of boundary */
int conv_line; /* size of output line */
unsigned long destadd; /* destination image address */
unsigned long sourceadd, sourcebase; /* source addressing */
char dest[1024]; /* destination image line */
FILE *fp; /* output file pointer */
unsigned char window[9]; /* storage for window samples */
unsigned char left[25]; /* storage for left edge pixel duplication */
unsigned char right[25]; /* storage for right edge pixel duplication */
int xpad, ypad; /* number of pixels to duplicate */
int last_line; /* last line number to process */
int new_pixel; /* newly computed pixel value */

yextra = 2;
ypad = 1;
xextra = 2;
xpad = 1;
conv_line = cols - xextra;

if((fp=fopen(filename, "wb")) == NULL)
{
printf("Unable to open %s for output\n",filename);
exit(1);
}
fprintf(fp, "P5\n%d %d\n255\n", cols, rows); /* print out header */
last_line = rows - yextra;
for(y=0; y<last_line; y++)
{
sourcebase=(unsigned long) cols * y;
destadd=0;
for(x=xpad; x<(cols - xpad); x++)
{
index=0;
for(winy=0; winy<3; winy++)
for(winx=0; winx<3; winx++)
{
sourceadd=sourcebase+winx+winy*cols;
window[index++] = source[sourceadd];
}
new_pixel = homogeneity(window) + 64;
CLIP(new_pixel,0.0,255.0);

dest[destadd++]=(unsigned char) new_pixel;
sourcebase++;
} /* for x */
for(i=0; i<xpad; i++)
left[i]=dest[0];
for(i=0; i<xpad; i++)
right[i]=dest[conv_line-1];
if(y==0)
for(i=0; i<ypad; i++)
{
fwrite(left, 1, xpad, fp);
fwrite(dest, 1, conv_line, fp);
fwrite(right, 1, xpad, fp);
}
fwrite(left, 1, xpad, fp);
fwrite(dest, 1, conv_line, fp);
fwrite(right, 1, xpad, fp);
if(y==(last_line-1))
for(i=0; i<ypad; i++)
{
fwrite(left, 1, xpad, fp);
fwrite(dest, 1, conv_line, fp);
fwrite(right, 1, xpad, fp);
}
} /* for y */

}

/****************************************************************************
* Func: homogeneity *
* *
* Desc: finds edges in an image window *
* *
* Param: window - 3x3 window of source image |0 1 2| *
* |3 4 5| *
* |6 7 8| *
* *
* Returns: the maximum value of the difference between the center pixel and*
* all adjacent pixels *
****************************************************************************/

int homogeneity(unsigned char *window)
{
int max; /* current maximum difference */
int diff; /* current difference */

diff = abs(window[4] - window[0]); /* upper left pixel */
max = diff;

diff = abs(window[4] - window[1]); /* upper pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[2]); /* upper right pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[5]); /* right pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[8]); /* lower left pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[7]); /* lower pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[6]); /* bottom left pixel */
if(diff > max)
max = diff;

diff = abs(window[4] - window[3]); /* left pixel */
if(diff > max)
max = diff;

return max;
}