void PGMtoPPM(struct Image *Img)
{
int i;
if (Img->iscolor) return;

Img->iscolor = 1;
if (Img->red == NULL) Img->red = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->red == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
if (Img->green == NULL) Img->green = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->green == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
if (Img->blue == NULL) Img->blue = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->blue == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}

for (i=0; i<Img->NofR*Img->NofC; i++)
{
   Img->red[i] = Img->gray[i];
   Img->green[i] = Img->gray[i];
   Img->blue[i] = Img->gray[i];
}
free(Img->gray);
}

// Read PPM & PGM files (P2, P3, P5, P6)
void ReadImage(char *name, struct Image *Img)
{
int i,j,pixel,k;
FILE *fp;
char s[256];
int filetype, nlevels;
byte *in;

printf("\nReading input file '%s'\n",name);
if ((fp = fopen(name, "rb")) == NULL) {
fprintf(stderr,"Can't open input file %s\n",name);
exit(1);
}
label1 :
if (fgets(s, 80, fp)==NULL)
   {
fprintf(stderr,"<EOF> character found in input file %s\n", name);
exit(1);
   }

if (strcmp("P2\n",s)==0) filetype = 2;
else if (strcmp("P3\n",s)==0) filetype = 3;
else if (strcmp("P5\n",s)==0) filetype = 5;
else if (strcmp("P6\n",s)==0) filetype = 6;
else {
if (s[0] == '#') goto label1;
fprintf(stderr,"Input file %s is of wrong type %s\n",name,s);
exit(1);
}

label2:
if (fgets(s, 80, fp)==NULL) {
fprintf(stderr,"Size line does not exist in input file %s\n", name);
exit(1);
}
if (s[0] == '#') goto label2;
sscanf(s,"%d %d",&(Img->NofC),&(Img->NofR));

label3:
if (fgets(s, 80, fp)==NULL) {
fprintf(stderr,"<EOF> character found in input file %s\n", name);
exit(1);
}
if (s[0] == '#') goto label3;
sscanf(s,"%d",&nlevels);

switch (filetype) { // read pixels
case 2: // P2 - ascii file, gray level image
Img->iscolor = 0;
if (Img->gray == NULL) Img->gray = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->gray == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
k = 0;
for (i=0; i<Img->NofR; i++) for (j=0; j<Img->NofC; j++) {
   fscanf(fp,"%d",&pixel);
   Img->gray[k++] = pixel;
}
break;
case 3: // P3 - ascii file, color image
Img->iscolor = 1;
if (Img->red == NULL) Img->red = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->red == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
if (Img->green == NULL) Img->green = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->green == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
if (Img->blue == NULL) Img->blue = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->blue == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
k = 0;
for (i=0; i<Img->NofR; i++) for (j=0; j<Img->NofC; j++) {
   fscanf(fp,"%d",&pixel);    Img->red[k] = pixel;
   fscanf(fp,"%d",&pixel);    Img->green[k] = pixel;
   fscanf(fp,"%d",&pixel);    Img->blue[k++] = pixel;
}
break;
case 5: // P5 - raw file, gray level image
Img->iscolor = 0;
if (Img->gray == NULL) Img->gray = (byte *)malloc(sizeof(byte)*Img->NofC*Img->NofR);
if (Img->gray == NULL)
{
   fprintf(stderr,"Not enough memory, malloc failed!");
   exit(1);
}
k = 0;
in = (byte *)malloc(sizeof(byte)*Img->NofC);
if (in == NULL

1 Background In the exciting world of information security, there...