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|
open Pdfutil
open Pdfio
open Cpdferror
let read_word i =
let a = i32ofi (i.input_byte ()) in
let b = i32ofi (i.input_byte ()) in
let c = i32ofi (i.input_byte ()) in
let d = i32ofi (i.input_byte ()) in
lor32 (lor32 (lor32 (lsl32 a 24) (lsl32 b 16)) (lsl32 c 8)) d
exception Answer of int * int
let id_IMAGE_HEADER_BOX = 0x69686472l (* ihdr *)
(* Return the width and height of a JPEG2000 (.jp2 or .jpx) image. *)
let jpeg2000_dimensions_inner bs =
let i = Pdfio.input_of_bytes bs in
let a = read_word i in
let b = read_word i in
let c = read_word i in
if a <> 0x0000000cl || b <> 0x6a502020l || c <> 0x0d0a870al then
Cpdferror.error "bad JPEG2000 header"
else
while true do
let box = read_word i in
if box = id_IMAGE_HEADER_BOX then
begin
let h = read_word i in
let w = read_word i in
raise (Answer (i32toi w, i32toi h))
end;
(* Read words starting at each byte until we find ihdr. *)
i.seek_in (i.pos_in () - 3)
done
let jpeg2000_dimensions bs =
try ignore (jpeg2000_dimensions_inner bs); (0, 0) with
| Answer (w, h) -> (w, h)
| Exit -> error "could not determine JPEG2000 dimensions"
|
