125 lines
4.5 KiB
Python
125 lines
4.5 KiB
Python
# © 2015 James R. Barlow: github.com/jbarlow83
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#
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# This file is part of OCRmyPDF.
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#
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# OCRmyPDF is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# OCRmyPDF is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with OCRmyPDF. If not, see <http://www.gnu.org/licenses/>.
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"""
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Utilities for PDF/A production and confirmation with Ghostspcript.
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"""
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import base64
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from pathlib import Path
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from string import Template
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from typing import Dict, Union
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import pikepdf
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import pkg_resources
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ICC_PROFILE_RELPATH = 'data/sRGB.icc'
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SRGB_ICC_PROFILE = pkg_resources.resource_filename('ocrmypdf', ICC_PROFILE_RELPATH)
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# This is a template written in PostScript which is needed to create PDF/A
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# files, from the Ghostscript documentation. Lines beginning with % are
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# comments. Python substitution variables have a '$' prefix.
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pdfa_def_template = u"""%!
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% Define an ICC profile :
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/ICCProfile $icc_profile
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def
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[/_objdef {icc_PDFA} /type /stream /OBJ pdfmark
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[{icc_PDFA} << /N 3 >> /PUT pdfmark
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[{icc_PDFA} ICCProfile /PUT pdfmark
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% Define the output intent dictionary :
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[/_objdef {OutputIntent_PDFA} /type /dict /OBJ pdfmark
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[{OutputIntent_PDFA} <<
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/Type /OutputIntent % Must be so (the standard requires).
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/S /GTS_PDFA1 % Must be so (the standard requires).
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/DestOutputProfile {icc_PDFA} % Must be so (see above).
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/OutputConditionIdentifier ($icc_identifier)
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>> /PUT pdfmark
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[{Catalog} <</OutputIntents [ {OutputIntent_PDFA} ]>> /PUT pdfmark
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"""
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def generate_pdfa_ps(target_filename: Path, icc: str = 'sRGB'):
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"""Create a Postscript PDFMARK file for Ghostscript PDF/A conversion
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pdfmark is an extension to the Postscript language that describes some PDF
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features like bookmarks and annotations. It was originally specified Adobe
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Distiller, for Postscript to PDF conversion.
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Ghostscript uses pdfmark for PDF to PDF/A conversion as well. To use Ghostscript
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to create a PDF/A, we need to create a pdfmark file with the necessary metadata.
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This function takes care of the many version-specific bugs and pecularities in
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Ghostscript's handling of pdfmark.
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The only information we put in specifies that we want the file to be a
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PDF/A, and we want to Ghostscript to convert objects to the sRGB colorspace
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if it runs into any object that it decides must be converted.
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Arguments:
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target_filename: filename to save
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icc: ICC identifier such as 'sRGB'
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References:
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Adobe PDFMARK Reference: https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/pdfmark_reference.pdf
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"""
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if icc == 'sRGB':
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icc_profile = SRGB_ICC_PROFILE
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else:
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raise NotImplementedError("Only supporting sRGB")
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# Read the ICC profile, encode as ASCII85 and convert to a string which we
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# will insert in the .ps file
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bytes_icc_profile = Path(icc_profile).read_bytes()
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icc_profile = base64.a85encode(bytes_icc_profile, adobe=True).decode('ascii')
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t = Template(pdfa_def_template)
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ps = t.substitute(icc_profile=icc_profile, icc_identifier=icc)
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# We should have encoded everything to pure ASCII by this point, and
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# to be safe, only allow ASCII in PostScript
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Path(target_filename).write_text(ps, encoding='ascii')
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return target_filename
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def file_claims_pdfa(filename: Path):
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"""Determines if the file claims to be PDF/A compliant
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This only checks if the XMP metadata contains a PDF/A marker. It does not
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do full PDF/A validation.
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"""
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with pikepdf.open(filename) as pdf:
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pdfmeta = pdf.open_metadata()
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if not pdfmeta.pdfa_status:
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return {
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'pass': False,
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'output': 'pdf',
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'conformance': 'No PDF/A metadata in XMP',
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}
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valid_part_conforms = {'1A', '1B', '2A', '2B', '2U', '3A', '3B', '3U'}
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conformance = f'PDF/A-{pdfmeta.pdfa_status}'
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pdfa_dict: Dict[str, Union[str, bool]] = {}
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if pdfmeta.pdfa_status in valid_part_conforms:
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pdfa_dict['pass'] = True
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pdfa_dict['output'] = 'pdfa'
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pdfa_dict['conformance'] = conformance
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return pdfa_dict
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