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(* GIF header parser.
* $Id: gif.ml 142 2008-07-17 15:45:56Z richard.wm.jones $
*)
open Printf
let () =
if Array.length Sys.argv <= 1 then
failwith "usage: gif input.gif";
let filename = Sys.argv.(1) in
let bits = Bitstring.bitstring_of_file filename in
bitmatch bits with
| { ("GIF87a"|"GIF89a") : 6*8 : string; (* GIF magic. *)
width : 16 : littleendian;
height : 16 : littleendian;
colormap : 1; (* Has colormap? *)
colorbits : 3; (* Color res = colorbits+1 *)
sortflag : 1;
bps : 3; (* Bits/pixel = bps+1 *)
bg : 8; (* Background colour. *)
aspectratio : 8 } ->
printf "%s: GIF image:\n" filename;
printf " size %d %d\n" width height;
printf " has global colormap? %b\n" colormap;
printf " colorbits %d\n" (colorbits+1);
printf " global colormap is sorted? %b\n" sortflag;
printf " bits/pixel %d\n" (bps+1);
printf " background color index %d\n" bg;
printf " aspect ratio %d\n" aspectratio
| { _ } ->
eprintf "%s: Not a GIF image\n" filename
|
