/** Sobel.c **/
#include <stdio.h>
#include <stdlib.h>
#define V_width 320
#define V_height 240
#define amp 1.0
int d[9];
int i, j, dat;
float L;
unsigned char img [V_height][V_width]; /* input image */
unsigned char work[V_height][V_width]={0}; /* work space */
/******* filter coefficients *******/
static int c[9] = {-1, -2, -1,
0, 0, 0,
1, 2, 1};
/*************************************/
int main(int argc, char *argv[])
{
FILE *fpi, *fpo;
unsigned char data;
char str[256];
int width, height;
/* check arg number */
if (argc != 3) {
fprintf(stderr, "Usage: %s [input] [output]\n", argv[0]);
exit(1);
}
/* open input file */
if ((fpi = fopen(argv[1], "rb")) == NULL) {
fprintf(stderr, "input file open error!\n");
exit(1);
}
/* open output file */
if ((fpo = fopen(argv[2], "wb")) == NULL) {
fprintf(stderr, "output file open error!\n");
exit(1);
}
/* read PGM header */
while(1){
fgets(str, 256, fpi);
if(str[0] == '#'){
fprintf( stderr, "%s", str);
}
else if( !strncmp( str, "P5", 2)){
fprintf( stderr, "This file is a PGM file.\n");
}
else if( !strncmp( str, "255", 3)){
fprintf( stderr, "The file is opened.\n");
break;
}
else{
sscanf( str, "%d %d", &width, &height);
fprintf( stderr, "SIZE: %3d x %3d\n", width, height);
}
}
/* read data */
for (i=0; i<height; i++) {
for (j=0; j<width; j++) {
fread( &data, 1, 1, fpi);
img[i][j] = data;
}
}
/* image processing */
for (i=1; i < height-1; i++) {
for (j=1; j < width-1; j++) {
d[0]=img[i-1][j-1]; d[1]=img[i-1][j]; d[2]=img[i-1][j+1];
d[3]=img[i][j-1]; d[4]=img[i][j]; d[5]=img[i][j+1];
d[6]=img[i+1][j-1]; d[7]=img[i+1][j]; d[8]=img[i+1][j+1];
L = (float)(c[0]*d[0] + c[1]*d[1] + c[2]*d[2]
+ c[3]*d[3] + c[4]*d[4] + c[5]*d[5]
+ c[6]*d[6] + c[7]*d[7] + c[8]*d[8]);
L = amp*L;
dat = (int)(L);
if (dat < 0) dat = -dat;
if (dat > 255) dat = 255;
work[i][j] = (unsigned char)dat;
}
}
/* write data */
fprintf(fpo,"P5\n %d %d\n 255\n", width, height);
for (i= 0; i<height; i++) {
for (j= 0; j<width; j++) {
fwrite( &work[i][j], 1, 1, fpo);
}
}
fclose(fpi);
fclose(fpo);
return 0;
}