Convert bitmap ( bmp ) files to raw 16 bit data using C program in Linux

bmptoraw is utility to convert bitmap files to raw 16 bit data. This program assumes a 24 bit bitmap file with a 54 byte header, which is the most common form of bitmap. One can convert other image files to that format using GIMP or MS Paint.

 $ vim bmptoraw.c

#include<unistd.h>
#include<sys/types.h>
#include<sys/mman.h>
#include<sys/time.h>
#include<stdio.h>
#include<fcntl.h>
#include<string.h>
#include<stdlib.h>
#include<assert.h>
 
int main(int argc, char **argv) {
 
  volatile unsigned char *bmp;
  int fd;
  int i, j, offset;
  int length, page;
  char red, blue, green, char1, char2;
   
  assert(argc = 2);
   
  page = getpagesize();
  length = (((480*800*3 + 56)/page) + 1) * page;
   
  fd = open(argv[1], O_RDONLY);
  bmp = (unsigned char *)mmap(0, length,
    PROT_READ, MAP_SHARED, fd, 0);
   
  assert(bmp[0] == 'B');
  assert(bmp[1] == 'M');
   
  assert(bmp[0xa] == 54);
   
  for(i=0;i<480;i++) {
    for(j=0;j<800;j++) {
      offset = 2400 * (479 - i) + 54 + j * 3;
      blue = bmp[offset];
      green = bmp[offset + 1];
      red = bmp[offset + 2];
      char2 = red & 0xf8;
      char2 |= green >> 5;
      char1 = blue >> 3;
      char1 |= (green & 0xf8) << 3;
      putchar(char1);
      putchar(char2);
    }
  }
   
  munmap((unsigned int *)bmp, length);
  close(fd);
  return 0;
}

 $  gcc -Wall bmptoraw.c -o bmptoraw 

 $ ./bmptoraw pic.bmp > pic.raw 

pic.raw can then be used for a splashscreen.

 $ cat pic.raw > /dev/fb0