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Add skeleton for CCITT G3 compression

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John Whitington 2025-01-10 15:00:17 +08:00
parent cf2999d7e8
commit 0bb5f154cb
1 changed files with 47 additions and 1 deletions
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48
cpdfimage.ml
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@ -823,6 +823,41 @@ let jpeg_to_jpeg_wrapper objnum pdf ~target_dpi_info ~pixel_threshold ~length_th
with
Not_found -> if !debug_image_processing then Printf.printf "Warning: orphaned image, skipping\n" (* Could not find DPI data - an orphan image. *)
let recompress_1bpp_ccitt_lossless ~pixel_threshold ~length_threshold pdf s dict reference =
let old = !reference in
let restore () = reference := old 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
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 data = match s with Pdf.Stream {contents = _, Pdf.Got d} -> d | _ -> assert false in
let compressed = data in
let newsize = bytes_size compressed in
if newsize < size then
begin
if !debug_image_processing then Printf.printf "1bpp to CCITT %i -> %i (%i%%)\n%!" size newsize (int_of_float (float newsize /. float size *. 100.));
reference :=
(Pdf.remove_dict_entry
(Pdf.add_dict_entry
(Pdf.add_dict_entry dict "/Length" (Pdf.Integer newsize))
"/Filter"
(Pdf.Name "/CCITTFaxDecode")) "/DecodeParms"),
Pdf.Got (compressed)
end
else
if !debug_image_processing then Printf.printf "no size reduction\n%!"
end
let recompress_1bpp_ccittg4_lossless ~pixel_threshold ~length_threshold pdf s dict reference = ()
let recompress_1bpp_jbig2_lossless ~pixel_threshold ~length_threshold ~path_to_jbig2enc pdf s dict reference =
complain_jbig2enc path_to_jbig2enc;
let old = !reference in
@ -1018,7 +1053,18 @@ let process
if !debug_image_processing then Printf.printf "(%i/%i) Object %i (1bpp)... %!" !ndone nobjects objnum;
recompress_1bpp_jbig2_lossless ~pixel_threshold ~length_threshold ~path_to_jbig2enc pdf s dict reference
end
| _ -> ()
| "CCITT" ->
begin
if !debug_image_processing then Printf.printf "(%i/%i) Object %i (1bpp)... %!" !ndone nobjects objnum;
recompress_1bpp_ccitt_lossless ~pixel_threshold ~length_threshold pdf s dict reference
end
| "CCITTG4" ->
begin
if !debug_image_processing then Printf.printf "(%i/%i) Object %i (1bpp)... %!" !ndone nobjects objnum;
recompress_1bpp_ccittg4_lossless ~pixel_threshold ~length_threshold pdf s dict reference
end
| "JBIG2Lossy" -> ()
| _ -> error "unknown 1bpp method"
end
| Some (Pdf.Name "/Image"), _, _, _ ->
if qlossless < 101. then