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More jbig2lossy work

This commit is contained in:
John Whitington 2024-01-11 16:48:34 +00:00
parent cfe33f2002
commit c924865349
1 changed files with 47 additions and 5 deletions
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46
cpdfimage.ml
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@ -710,8 +710,50 @@ let recompress_1bpp_jbig2_lossless ~pixel_threshold ~length_threshold ~path_to_j
remove out2
end
let preprocess_jbig2_lossy ~path_to_jbig2enc inrange highdpi pdf = ()
(* Recompress 1bpp images, compressed any way (none, flate, ccitt, jbig2 lossless) to lossy jbig2 *)
(* For now, just example 6406.pdf, which is CCITT, so simple decompression will do. For lossless
to lossy JBIG2, we will need to write out and convert to PNM with jbig2dec *)
(* FIXME: Need interface for jbig2 lossy parameters *)
let preprocess_jbig2_lossy ~path_to_jbig2enc ~length_threshold ~pixel_threshold ~dpi_threshold inrange highdpi pdf =
let objnum_name_pairs = ref [] in
let process_obj objnum s =
(* Write out each stream as a *.pnm, if we choose to process it, restoring if not. *)
match s with
| Pdf.Stream ({contents = dict, _} as reference) ->
let old = !reference in
let restore () = reference := old in
if Hashtbl.mem inrange objnum && (dpi_threshold = 0 || Hashtbl.mem highdpi objnum) then begin match
Pdf.lookup_direct pdf "/Subtype" dict,
Pdf.lookup_direct pdf "/BitsPerComponent" dict,
Pdf.lookup_direct pdf "/ImageMask" dict
with
| Some (Pdf.Name "/Image"), Some (Pdf.Integer 1), _
| Some (Pdf.Name "/Image"), _, Some (Pdf.Boolean true) ->
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
if w * h < pixel_threshold then (if !debug_image_processing then Printf.printf "pixel threshold not met\n%!") else (* (but also, jbig2enc fails on tiny images) *)
let size = match Pdf.lookup_direct pdf "/Length" dict with Some (Pdf.Integer i) -> i | _ -> 0 in
if size < length_threshold then (if !debug_image_processing then Printf.printf "length threshold not met\n%!") else
begin
Pdfcodec.decode_pdfstream_until_unknown pdf s;
match Pdf.lookup_direct pdf "/Filter" (fst !reference) with
| Some x ->
if !debug_image_processing then Printf.printf "could not decode - skipping %s length %i\n%!" (Pdfwrite.string_of_pdf x) size;
restore ()
| None ->
let out = Filename.temp_file "cpdf" "convertin" ^ ".pnm" in
let fh = open_out_bin out in
let data = match s with Pdf.Stream {contents = _, Pdf.Got d} -> d | _ -> assert false in
pnm_to_channel_1_inverted fh w h data;
close_out fh;
Printf.printf "obj %i = %s\n%!" objnum out;
objnum_name_pairs := (objnum, out)::!objnum_name_pairs
end
| _ -> () (* not a 1bpp image *)
end
| _ -> () (* not a stream *)
in
Pdf.objiter process_obj pdf
(* Call jbig2 to generate one *.jbig2 for each, and a *.jbig2globals *)
(* Build the JBIG2Globals stream for the file *)
(* For each file, read in the new JBIG2 data, and build each new image stream to replace the old one *)
@ -740,7 +782,7 @@ let process
in
hashset_of_list objnums
in
begin match onebppmethod with Some "JBIG2Lossy" -> preprocess_jbig2_lossy ~path_to_jbig2enc inrange highdpi pdf | _ -> () end;
begin match onebppmethod with Some "JBIG2Lossy" -> preprocess_jbig2_lossy ~path_to_jbig2enc ~dpi_threshold ~length_threshold ~pixel_threshold inrange highdpi pdf | _ -> () end;
let nobjects = Pdf.objcard pdf in
let ndone = ref 0 in
let process_obj objnum s =