122 lines
3.5 KiB
Python
122 lines
3.5 KiB
Python
# pdf-segmented: Generate PDFs using separate compression for foreground and background
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# Copyright (C) 2025 Lee Yingtong Li
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero 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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# This program 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 Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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from ..compression import CompressedLayer, CompressedPage
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from ..compression.jbig2 import JBIG2Layer
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from ..compression.jpeg import JPEGLayer
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from ..input import InputPages
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from pikepdf import ContentStreamInstruction, Name, Operator, Page, Pdf, Stream, unparse_content_stream
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from typing import Generator
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def pdf_write_pages(
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input_pages: InputPages,
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compressed_pages: Generator[CompressedPage],
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output_file: str
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) -> None:
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# Get size of image in PostScript points
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width_pt = input_pages.width / input_pages.dpi * 72
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height_pt = input_pages.height / input_pages.dpi * 72
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# Build PDF
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pdf = Pdf.new()
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# Write each page
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for compressed_page in compressed_pages:
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page = pdf.add_blank_page(page_size=(width_pt, height_pt))
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# Write each layer to the page
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content_instructions = []
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pdf_write_layer(input_pages=input_pages, pdf=pdf, page=page, layer=compressed_page.bg, content_instructions=content_instructions)
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pdf_write_layer(input_pages=input_pages, pdf=pdf, page=page, layer=compressed_page.fg, content_instructions=content_instructions)
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# Generate content stream
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wrapped_instructions = [
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ContentStreamInstruction([], Operator('q')),
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ContentStreamInstruction([width_pt, 0, 0, height_pt, 0, 0], Operator('cm'))
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] + content_instructions + [
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ContentStreamInstruction([], Operator('Q')),
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]
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content_stream = unparse_content_stream(wrapped_instructions)
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page.Contents.write(content_stream)
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# Save PDF
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pdf.save(output_file)
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def pdf_write_layer(
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input_pages: InputPages,
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pdf: Pdf,
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page: Page,
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layer: CompressedLayer,
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content_instructions,
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) -> None:
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# Write the layer to PDF
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if isinstance(layer, JBIG2Layer):
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pdf_write_image(
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input_pages=input_pages,
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pdf=pdf,
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page=page,
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value=layer.data,
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content_instructions=content_instructions,
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ColorSpace=Name.DeviceGray,
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Filter=Name.JBIG2Decode,
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BitsPerComponent=1,
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Mask=[1, 1] # Layer mask
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)
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elif isinstance(layer, JPEGLayer):
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pdf_write_image(
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input_pages=input_pages,
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pdf=pdf,
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page=page,
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value=layer.data,
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content_instructions=content_instructions,
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ColorSpace=Name.DeviceRGB,
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Filter=Name.DCTDecode,
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BitsPerComponent=8
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)
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else:
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raise NotImplementedError()
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def pdf_write_image(
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input_pages: InputPages,
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pdf: Pdf,
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page: Page,
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value: bytes,
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content_instructions,
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**kwargs
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) -> None:
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# Write the layer as an Image
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# Insert the Image as an XObject resource
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xobj = Stream(
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pdf,
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value,
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Type=Name.XObject,
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Subtype=Name.Image,
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Width=input_pages.width,
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Height=input_pages.height,
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**kwargs
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)
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xobj_name = page.add_resource(xobj, '/XObject')
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# Add render instruction to the content stream
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content_instructions.append(
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ContentStreamInstruction([xobj_name], Operator('Do'))
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)
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