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First implementation of -lossless-to-jpeg

This commit is contained in:
John Whitington 2023-12-18 15:13:40 +00:00
parent ec91b49bfe
commit 16278b03f6
1 changed files with 49 additions and 8 deletions
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57
cpdfimage.ml
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@ -1,5 +1,6 @@
open Pdfutil
open Pdfio
open Cpdferror
(* Extract Images. *)
let pnm_to_channel_24 channel w h s =
@ -22,7 +23,6 @@ let pnm_to_channel_24 channel w h s =
done
done
let jbig2_serial = ref 0
let jbig2_globals = null_hash ()
@ -464,6 +464,8 @@ let image_of_input fobj i =
(* FIXME Need the "is it smaller" check from Pdfcodec.encode here too? *)
(* FIXME (this appears to make the file larger than ./cpdf ~/repos/pdfs/PDFTests/main128fail.pdf -recrypt -o out.pdf. Why? Seems to not create new object streams. Make it do so, since this a compression mechanism? An empty Pdf.objiter should not blow up a file like this!) *)
(* For each image xobject, process it through convert to reduce size. *)
(* FIXME What about predictors? Audit to see if files get smaller. *)
(* FIXME if lossy only 5% smaller, ignore? Set this parameter... *)
let process pdf ~q ~qlossless ~path_to_convert =
let process_obj _ s =
match s with
@ -500,18 +502,57 @@ let process pdf ~q ~qlossless ~path_to_convert =
(* 0. Test if this is one we can do - for now just Colourspace=RGB, BPC=8 *)
begin match Pdf.lookup_direct pdf "/ColorSpace" dict, Pdf.lookup_direct pdf "/BitsPerComponent" dict with
| Some (Pdf.Name "/DeviceRGB"), Some (Pdf.Integer 8) ->
Printf.printf "Found a lossless(rgb, 8) image to JPEGify\n"
(* 1. Decompress it - check we succeeded, bail if not *)
(* 1. Output to pnm *)
(* 2. Convert to JPEG with convert *)
(* 3. Check smaller, Read file, and build new dictionary - removing ColorSpace, BitsPerComponent replacing Filter *)
let size = match Pdf.lookup_direct pdf "/Length" dict with Some (Pdf.Integer i) -> i | _ -> 0 in
(* 1. Decompress it - check we succeeded, bail if not *)
Pdfcodec.decode_pdfstream_until_unknown pdf s;
begin match Pdf.lookup_direct pdf "/Filter" (fst !reference) with Some _ -> () | None ->
(* 1. Output to pnm *)
let out = Filename.temp_file "cpdf" "convertin" ^ ".pnm" in
let out2 = Filename.temp_file "cpdf" "convertout" ^ ".jpg" in
let fh = open_out_bin out in
let w = match Pdf.lookup_direct pdf "/Width" dict with Some (Pdf.Integer i) -> i | _ -> error "bad width" in
let h = match Pdf.lookup_direct pdf "/Height" dict with Some (Pdf.Integer i) -> i | _ -> error "bad height" in
let data = match s with Pdf.Stream {contents = _, Pdf.Got d} -> d | _ -> assert false in
pnm_to_channel_24 fh w h data;
close_out fh;
(* 2. Convert to JPEG with convert *)
let retcode =
let command =
(Filename.quote_command path_to_convert
[out; "-quality"; string_of_int qlossless ^ "%"; out2])
in
(*Printf.printf "%S\n" command;*)
Sys.command command
in
(* 3. Check smaller, Read file, and build new dictionary - removing ColorSpace, BitsPerComponent replacing Filter *)
if retcode = 0 then
begin
let result = open_in_bin out2 in
let newsize = in_channel_length result in
Printf.printf "Lossless to JPEG %i -> %i\n" size newsize;
if newsize < size then
reference :=
(Pdf.remove_dict_entry
(Pdf.remove_dict_entry
(Pdf.add_dict_entry
(Pdf.add_dict_entry dict "/Length" (Pdf.Integer newsize))
"/Filter"
(Pdf.Name "/DCTDecode"))
"/ColorSpace")
"/BitsPerComponent"),
Pdf.Got (Pdfio.bytes_of_input_channel result)
end;
(* 4. Clean up. *)
Sys.remove out;
Sys.remove out2
end
| colspace, bpc ->
let colspace, bpc, filter =
(*let colspace, bpc, filter =
(match colspace with None -> "none" | Some x -> Pdfwrite.string_of_pdf x),
(match bpc with None -> "none" | Some x -> Pdfwrite.string_of_pdf x),
(match Pdf.lookup_direct pdf "/Filter" dict with None -> "none" | Some x -> Pdfwrite.string_of_pdf x)
in
print_string (Printf.sprintf "%s (%s) [%s]\n" colspace bpc filter);
print_string (Printf.sprintf "%s (%s) [%s]\n" colspace bpc filter);*)
() (* an image we cannot or do not handle *)
end
| _ -> () (* not an image *)