Source file imageJPG.ml

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(*
 * This file is part of Imagelib.
 *
 * Imagelib is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Imabelib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Imabelib.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Copyright (C) 2014 Rodolphe Lepigre.
 *)
open Stdlib
open ImageUtil
open Image

module ReadJPG : ReadImage = struct
  let extensions = ["jpg"; "jpeg"; "jpe"; "jif"; "jfif"; "jfi"]

  let read_marker ich =
    let ff = chunk_byte ich in
    if ff <> 0xff then
      raise (Corrupted_image "Expected marker...");
    let rec read_first_not_ff ich =
      let c = chunk_byte ich in
      if c = 0xff then read_first_not_ff ich else c
    in
    let c = read_first_not_ff ich in
    if c = 0 then
      raise (Corrupted_image "0xFF00 is not a valid marker...");
    c

  let read_header_data ich =
    (* Read magic number (i.e. marker 0xffd8) *)
    let magic = read_marker ich in
    if magic <> 0xd8 then
      raise (Corrupted_image "First marker should be SOI...");

    (* Read other header sections *)
    let rec read_header_sections ich acc =
      let mrk = read_marker ich in
      let sz = get_bytes ich 2 in
      let size = ((int_of_char sz.[0]) lsl 8) lor (int_of_char sz.[1]) in
      let data = get_bytes ich (size - 2) in
      if mrk = 0xda then (* SOS reached *)
        List.rev ((mrk, data) :: acc)
      else
        read_header_sections ich ((mrk, data) :: acc)
    in
    read_header_sections ich []

  (* Read the size of a XCF image.
   * Arguments:
   *   - fn : filename.
   * Returns a couble (width, height).
   * Note: the image is not checked for inconsistency, only the signature and
   * header are checked.
   *)
  let size ich =
    let headers = read_header_data ich in
    close_chunk_reader ich;

    let rec find_SOF ls =
      match ls with
      | []        -> raise (Corrupted_image "No SOFn marker...");
      | (m,d)::bs -> if m >= 0xc0 && m <= 0xcf && m <> 0xc4 && m <> 0xcc
                     then (m - 0xc0, d)
                     else find_SOF bs
    in
    let (_, sof) = find_SOF headers in
    (*
    Printf.fprintf stderr "SOF%i: " n;
    show_string_hex sof;
    *)
    let height = ((int_of_char sof.[1]) lsl 8) lor (int_of_char sof.[2]) in
    let width = ((int_of_char sof.[3]) lsl 8) lor (int_of_char sof.[4]) in
    width, height

  let parsefile _ =
    raise (Not_yet_implemented "ImageJPG.openfile") (* TODO  *)
end
include ReadJPG