Encode JBIG2 losslessly

COPYING.APACHE2

@@ -0,0 +1,202 @@
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README.md

@@ -1,12 +1,12 @@
 # file-jbig2pdf
 
-GIMP 3.0 plug-in for exporting JBIG2-encoded PDF files
+GIMP 3.0 plug-in for exporting lossless JBIG2-encoded PDF files
 
 ## Usage
 
-file-jbig2pdf has only been tested on Linux. It requires [jbig2enc](https://github.com/agl/jbig2enc) version 0.28 to be installed, and its *jbig2* and *pdf.py* commands to be available on PATH.
+file-jbig2pdf has only been tested on Linux. It requires [jbig2enc](https://github.com/agl/jbig2enc) to be installed, and its *jbig2* command to be available on PATH.
 
-Install *file-jbig2pdf.py* at *$HOME/.config/GIMP/3.0/plug-ins/file-jbig2pdf/file-jbig2pdf.py* and ensure that the file is executable.
+Install *file-jbig2pdf.py* and *jbig2topdf_lossless.py* under *$HOME/.config/GIMP/3.0/plug-ins/file-jbig2pdf/* and ensure that *file-jbig2pdf.py* is executable.
 
 Set up your GIMP image as desired in the standard fashion for PDF export (one layer per page, bottom layer first) and under *File* → *Export As…*, expand *Select File Type (By Extension)* and select *Portable Document Format (JBIG2)*.
 
@@ -14,7 +14,9 @@ Set up your GIMP image as desired in the standard fashion for PDF export (one la
 
 Copyright © 2024  Lee Yingtong Li (RunasSudo)
 
-Loosely adapted from GIMP file-openraster.py – Copyright © 2009 by Jon Nordby \<jononor@gmail.com\>, licensed under the GPLv3\
+*file-jbig2pdf.py* loosely adapted from GIMP file-openraster.py – Copyright © 2009 by Jon Nordby \<jononor@gmail.com\>, licensed under the GPLv3\
 In turn based on MyPaint source code by Martin Renold
 
-Licensed under the GNU General Public License version 3 or later.
+*jbig2topdf_lossless.py* adapted from jbig2enc by Adam Langley <agl@imperialviolet.org> - Copyright (C) 2006 Google Inc., licensed under Apache v2
+
+The file-jbig2pdf project is licensed under the GNU General Public License version 3 or later.

file-jbig2pdf.py

@@ -31,19 +31,16 @@ import subprocess
 import sys
 import tempfile
 
+import jbig2topdf_lossless
+
 def export_jbig2pdf(procedure, run_mode, image, file, options, metadata, config, data):
 	# Check jbig2enc version
 	try:
-		jbig2version = subprocess.run(['jbig2', '-V'], capture_output=True)
+		subprocess.run(['jbig2', '-V'])
 	except FileNotFoundError:
 		Gimp.message('jbig2 command (from jbig2enc) not in PATH')
 		return Gimp.ValueArray.new_from_values([GObject.Value(Gimp.PDBStatusType, Gimp.PDBStatusType.EXECUTION_ERROR)])
 	
-	if jbig2version.stderr != b'jbig2enc 0.28\n':
-		# We only support 0.28 for now, because from 0.29 pdf.py is renamed to jbig2topdf.py
-		Gimp.message('Unsupported version of jbig2enc (expected 0.28, got "{}")'.format(jbig2version.stderr.decode('utf-8').strip()))
-		return Gimp.ValueArray.new_from_values([GObject.Value(Gimp.PDBStatusType, Gimp.PDBStatusType.EXECUTION_ERROR)])
-	
 	# jbig2enc OK!
 	
 	Gimp.progress_init('Exporting PDF JBIG2 image')
@@ -57,7 +54,7 @@ def export_jbig2pdf(procedure, run_mode, image, file, options, metadata, config,
 				for sublayer in unroll_layers(layer.get_children()):
 					yield sublayer
 	
-	pngs_out = []
+	jb2s_out = []
 	
 	# Export image layer by layer (bottom layer first)
 	for i, layer in enumerate(reversed(list(unroll_layers(image.get_layers())))):
@@ -91,33 +88,35 @@ def export_jbig2pdf(procedure, run_mode, image, file, options, metadata, config,
 		
 		tmp_img.delete()  # Clean up buffer
 		
-		if os.path.exists(png_out):
+		# Execute jbig2enc
-			pngs_out.append(png_out)
+		jb2_out = os.path.join(tempdir, '{:03d}.jb2'.format(i))
-		else:
+		
-			Gimp.message('Unknown error exporting layer {}'.format(i))
+		try:
+			with open(jb2_out, 'wb') as jb2_file:
+				# Passing "-s" uses lossly JBIG2 encoding, so we do not pass this option
+				subprocess.run(['jbig2', '-p', '-v', png_out], cwd=tempdir, check=True, stdout=jb2_file)
+		except subprocess.CalledProcessError:
+			Gimp.message('Unknown error in jbig2enc')
 			os.rmdir(tempdir)
 			Gimp.progress_end()
 			return Gimp.ValueArray.new_from_values([GObject.Value(Gimp.PDBStatusType, Gimp.PDBStatusType.EXECUTION_ERROR)])
 		
-	# Execute jbig2enc
+		os.unlink(png_out)
-	try:
+		jb2s_out.append(jb2_out)
-		subprocess.run(['jbig2', '-s', '-p', '-v'] + pngs_out, cwd=tempdir, check=True)
-	except subprocess.CalledProcessError:
-		Gimp.message('Unknown error in jbig2enc')
-		os.rmdir(tempdir)
-		Gimp.progress_end()
-		return Gimp.ValueArray.new_from_values([GObject.Value(Gimp.PDBStatusType, Gimp.PDBStatusType.EXECUTION_ERROR)])
 	
-	# Execute pdf.py
+	# Convert to PDF
 	# Use .tmpsave extension, so we don't overwrite a valid file if there is an exception
 	pdf_tmpout = file.peek_path() + '.tmpsave'
+	
 	try:
 		with open(pdf_tmpout, 'wb') as pdf_file:
-			subprocess.run(['pdf.py', 'output'], cwd=tempdir, check=True, stdout=pdf_file)
+			# The Python script supplied with jbig2enc only supports lossy JBIG2 encoding (https://github.com/agl/jbig2enc/pull/77)
+			# So therefore we bundle a modified script which works on lossless JBIG2 images
+			jbig2topdf_lossless.create_pdf(None, jb2s_out, pdf_file)
 			success = True
-	except subprocess.CalledProcessError:
+	except Exception:
 		success = False
-		Gimp.message('Unknown error in jbig2enc pdf.py')
+		Gimp.message('Unknown error converting JBIG2 images to PDF')
 		os.rmdir(tempdir)
 		Gimp.progress_end()
 		return Gimp.ValueArray.new_from_values([GObject.Value(Gimp.PDBStatusType, Gimp.PDBStatusType.EXECUTION_ERROR)])
@@ -127,16 +126,11 @@ def export_jbig2pdf(procedure, run_mode, image, file, options, metadata, config,
 	
 	# Success! - Finalise and clean up
 	
-	# Remove intermediate PNG files
-	for png_out in pngs_out:
-		os.unlink(png_out)
-	
 	# Remove intermediate JBIG2 files
-	for i in range(len(pngs_out)):
+	for i in range(len(jb2s_out)):
-		os.unlink(os.path.join(tempdir, 'output.{:04d}'.format(i)))
+		os.unlink(os.path.join(tempdir, '{:03d}.jb2'.format(i)))
 	
-	# Remove intermediate JBIG2 symbol file and temp directory
+	# Remove temp directory
-	os.unlink(os.path.join(tempdir, 'output.sym'))
 	os.rmdir(tempdir)
 	
 	# Save over destination file

jbig2topdf_lossless.py

@@ -0,0 +1,234 @@
+#!/usr/bin/env python3
+
+#   GIMP plug-in for JBIG2-encoded PDF files
+#   Copyright (C) 2024  Lee Yingtong Li (RunasSudo)
+#
+#   Adapted from jbig2enc by Adam Langley <agl@imperialviolet.org> - Copyright (C) 2006 Google Inc., licensed under Apache v2
+#   Loosely adapted from file-openraster.py - Copyright (C) 2009 by Jon Nordby <jononor@gmail.com>, licensed under the GPLv3
+#   In turn based on MyPaint source code by Martin Renold
+#
+#   This program 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.
+#
+#   This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import glob
+import struct
+import sys
+from pathlib import Path
+
+dpi = 72  # Default DPI value
+
+class Ref:
+	def __init__(self, x: int):
+		self.x = x
+	
+	def __str__(self) -> str:
+		return f"{self.x} 0 R"
+
+class Dict:
+	def __init__(self, values: dict = None):
+		if values is None:
+			values = {}
+		self.d = values.copy()
+	
+	def __str__(self) -> str:
+		entries = [f"/{key} {value}" for key, value in self.d.items()]
+		return f"<< {' '.join(entries)} >>\n"
+
+class Obj:
+	next_id = 1
+	
+	def __init__(self, d: dict = None, stream: str = None):
+		if d is None:
+			d = {}
+		if stream is not None:
+			d["Length"] = str(len(stream))
+		self.d = Dict(d)
+		self.stream = stream
+		self.id = Obj.next_id
+		Obj.next_id += 1
+	
+	def __str__(self) -> str:
+		result = [str(self.d)]
+		if self.stream is not None:
+			result.append(f"stream\n{self.stream}\nendstream\n")
+		result.append("endobj\n")
+		return "".join(result)
+
+class Doc:
+	def __init__(self):
+		self.objs = []
+		self.pages = []
+	
+	def add_object(self, obj: Obj) -> Obj:
+		"""Adds an object to the document."""
+		self.objs.append(obj)
+		return obj
+	
+	def add_page(self, page: Obj) -> Obj:
+		"""Adds a page to the document and the list of objects."""
+		self.pages.append(page)
+		return self.add_object(page)
+	
+	def __str__(self) -> str:
+		output = []
+		offsets = []
+		current_offset = 0
+		
+		def add_line(line: str):
+			nonlocal current_offset
+			output.append(line)
+			current_offset += len(line) + 1  # Adding 1 for the newline character
+		
+		# PDF header
+		add_line("%PDF-1.4")
+		
+		# Add each object and track its byte offset
+		for obj in self.objs:
+			offsets.append(current_offset)
+			add_line(f"{obj.id} 0 obj")
+			add_line(str(obj))
+		
+		# Cross-reference table
+		xref_start = current_offset
+		add_line("xref")
+		add_line(f"0 {len(offsets) + 1}")
+		add_line("0000000000 65535 f ")
+		for offset in offsets:
+			add_line(f"{offset:010} 00000 n ")
+		
+		# Trailer and EOF
+		add_line("trailer")
+		add_line(f"<< /Size {len(offsets) + 1}\n/Root 1 0 R >>")
+		add_line("startxref")
+		add_line(str(xref_start))
+		add_line("%%EOF")
+		
+		return "\n".join(output)
+
+def ref(x: int) -> str:
+	"""Creates a PDF reference string."""
+	return f"{x} 0 R"
+
+def create_pdf(symboltable: str = "symboltable", pagefiles: list = None, outf = sys.stdout.buffer):
+	"""Creates a PDF document from a symbol table and a list of page files."""
+	if pagefiles is None:
+		pagefiles = glob.glob("page-*")
+	
+	doc = Doc()
+	
+	# Add catalog and outlines objects
+	catalog_obj = Obj({"Type": "/Catalog", "Outlines": ref(2), "Pages": ref(3)})
+	outlines_obj = Obj({"Type": "/Outlines", "Count": "0"})
+	pages_obj = Obj({"Type": "/Pages"})
+	
+	doc.add_object(catalog_obj)
+	doc.add_object(outlines_obj)
+	doc.add_object(pages_obj)
+	
+	# Read the symbol table
+	# RUNASSUDO: Remove this as unnecessary with lossless encoding
+	#try:
+	#	with open(symboltable, "rb") as sym_file:
+	#		symd = doc.add_object(Obj({}, sym_file.read().decode("latin1")))
+	#except IOError:
+	#	sys.stderr.write(f"Error reading symbol table: {symboltable}\n")
+	#	return
+	
+	page_objs = []
+	pagefiles.sort()
+	
+	for p in pagefiles:
+		try:
+			with open(p, mode="rb") as page_file:
+				contents = page_file.read()
+		except IOError:
+			sys.stderr.write(f"Error reading page file: {p}\n")
+			continue
+		
+		try:
+			width, height, xres, yres = struct.unpack(">IIII", contents[11:27])
+		except struct.error:
+			sys.stderr.write(f"Error unpacking page file: {p}\n")
+			continue
+		
+		# Set default resolution if missing
+		xres = xres or dpi
+		yres = yres or dpi
+		
+		# Create XObject (image) for the page
+		xobj = Obj(
+			{
+				"Type": "/XObject",
+				"Subtype": "/Image",
+				"Width": str(width),
+				"Height": str(height),
+				"ColorSpace": "/DeviceGray",
+				"BitsPerComponent": "1",
+				"Filter": "/JBIG2Decode",
+				#"DecodeParms": f"<< /JBIG2Globals {symd.id} 0 R >>",  # RUNASSUDO: Remove this as unnecessary with lossless encoding
+			},
+			contents.decode("latin1"),
+		)
+		
+		# Create content stream for the page
+		contents_obj = Obj(
+			{},
+			f"q {float(width * 72) / xres} 0 0 {float(height * 72) / yres} 0 0 cm /Im1 Do Q",
+		)
+		
+		# Create resource dictionary for the page
+		resources_obj = Obj(
+			{"ProcSet": "[/PDF /ImageB]", "XObject": f"<< /Im1 {xobj.id} 0 R >>"}
+		)
+		
+		# Create the page object
+		page_obj = Obj(
+			{
+				"Type": "/Page",
+				"Parent": "3 0 R",
+				"MediaBox": f"[ 0 0 {float(width * 72) / xres} {float(height * 72) / yres} ]",
+				"Contents": ref(contents_obj.id),
+				"Resources": ref(resources_obj.id),
+			}
+		)
+		
+		# Add objects to the document
+		for obj in (xobj, contents_obj, resources_obj, page_obj):
+			doc.add_object(obj)
+		
+		page_objs.append(page_obj)
+		
+		# Update pages object
+		pages_obj.d.d["Count"] = str(len(page_objs))
+		pages_obj.d.d["Kids"] = "[" + " ".join([ref(x.id) for x in page_objs]) + "]"
+	
+	# Output the final PDF document to stdout
+	outf.write(str(doc).encode("latin1"))
+
+def usage(script, msg):
+	"""Display usage information and an optional error message."""
+	if msg:
+		sys.stderr.write("%s: %s\n" % (script, msg))
+	sys.stderr.write("Usage: %s [file_basename] > out.pdf\n" % script)
+	sys.exit(1)
+
+if __name__ == "__main__":
+	# RUNASSUDO: Overhauled to use lossless encoding
+	
+	pages = sys.argv[1:]
+	
+	# Validate that pages were found
+	if not pages:
+		usage(sys.argv[0], "no pages found!")
+	
+	create_pdf(None, pages)