Raw Image Manipulation in C

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

FILE **init_in(int ac, char **av) {
  FILE **in = (FILE **) malloc(sizeof(FILE *) * (ac - 1 - 1));
  for (int i = 0; i < ac - 1; i++) in[i] = fopen(av[i], "rb");
  return in;
}

unsigned char **init_reader(int ac) {
  unsigned char **reader =
    (unsigned char **) malloc(sizeof(unsigned char *) * (ac - 1 - 1));
  for (int i = 0; i < ac - 1; i++)
    reader[i] = (unsigned char *) malloc(sizeof(unsigned char));
  return reader;
}

int reader_read(int ac, FILE **in, unsigned char **reader) {
  int read_count;
  for (int i = 0; i < ac - 1; i++)
    read_count = fread(reader[i], sizeof(unsigned char), 1, in[i]);
  return read_count;
}

void close_in(int ac, FILE **in) {
  for (int i = 0; i < ac - 1; i++) fclose(in[i]);
}

int main(int ac, char **av) {
  if (ac < 5) return EXIT_FAILURE;
  FILE **in = init_in(ac, av);
  FILE *out = fopen(av[ac - 1], "wb");
  unsigned char **r = init_reader(ac);
  while (true) {
    int status = reader_read(ac, in, r);
    if (status < 1) break;
    unsigned char *w = 0;
    unsigned char sum = 0;
    for (int i = 0; i < ac - 1; i++) sum += *r[i];
    if (sum == 0) *w = 0;
    else *w = (unsigned char) ((1UL << 8) - 1) * *r[0] / sum;
    fwrite(w, sizeof(unsigned char), 1, out);
  }
  fclose(out);
  close_in(ac, in);
  return EXIT_SUCCESS;
}