307 lines
11 KiB
Python
307 lines
11 KiB
Python
# SPDX-FileCopyrightText: 2022 James R. Barlow
|
|
# SPDX-License-Identifier: MPL-2.0
|
|
|
|
"""For grafting text-only PDF pages onto freeform PDF pages."""
|
|
|
|
from __future__ import annotations
|
|
|
|
import logging
|
|
from contextlib import suppress
|
|
from pathlib import Path
|
|
|
|
from pikepdf import (
|
|
Dictionary,
|
|
Name,
|
|
Object,
|
|
Operator,
|
|
Pdf,
|
|
PdfError,
|
|
PdfMatrix,
|
|
Stream,
|
|
parse_content_stream,
|
|
unparse_content_stream,
|
|
)
|
|
|
|
log = logging.getLogger(__name__)
|
|
MAX_REPLACE_PAGES = 100
|
|
|
|
|
|
def _ensure_dictionary(obj, name):
|
|
if name not in obj:
|
|
obj[name] = Dictionary({})
|
|
return obj[name]
|
|
|
|
|
|
def _update_resources(*, obj, font, font_key, procset):
|
|
"""Update this obj's fonts with a reference to the Glyphless font.
|
|
|
|
obj can be a page or Form XObject.
|
|
"""
|
|
resources = _ensure_dictionary(obj, Name.Resources)
|
|
fonts = _ensure_dictionary(resources, Name.Font)
|
|
if font_key is not None and font_key not in fonts:
|
|
fonts[font_key] = font
|
|
|
|
# Reassign /ProcSet to one that just lists everything - ProcSet is
|
|
# obsolete and doesn't matter but recommended for old viewer support
|
|
if procset:
|
|
resources['/ProcSet'] = procset
|
|
|
|
|
|
def strip_invisible_text(pdf, page):
|
|
stream = []
|
|
in_text_obj = False
|
|
render_mode = 0
|
|
text_objects = []
|
|
|
|
for operands, operator in parse_content_stream(page, ''):
|
|
if not in_text_obj:
|
|
if operator == Operator('BT'):
|
|
in_text_obj = True
|
|
render_mode = 0
|
|
text_objects.append((operands, operator))
|
|
else:
|
|
stream.append((operands, operator))
|
|
else:
|
|
if operator == Operator('Tr'):
|
|
render_mode = operands[0]
|
|
text_objects.append((operands, operator))
|
|
if operator == Operator('ET'):
|
|
in_text_obj = False
|
|
if render_mode != 3:
|
|
stream.extend(text_objects)
|
|
text_objects.clear()
|
|
|
|
content_stream = unparse_content_stream(stream)
|
|
page.Contents = Stream(pdf, content_stream)
|
|
|
|
|
|
class OcrGrafter:
|
|
"""Manages grafting text-only PDFs onto regular PDFs."""
|
|
|
|
def __init__(self, context):
|
|
self.context = context
|
|
self.path_base = context.origin
|
|
|
|
self.pdf_base = Pdf.open(self.path_base)
|
|
self.font, self.font_key = None, None
|
|
|
|
self.pdfinfo = context.pdfinfo
|
|
self.output_file = context.get_path('graft_layers.pdf')
|
|
|
|
self.procset = self.pdf_base.make_indirect(
|
|
Object.parse(b'[ /PDF /Text /ImageB /ImageC /ImageI ]')
|
|
)
|
|
|
|
self.emplacements = 1
|
|
self.interim_count = 0
|
|
|
|
def graft_page(
|
|
self,
|
|
*,
|
|
pageno: int,
|
|
image: Path | None,
|
|
textpdf: Path | None,
|
|
autorotate_correction: int,
|
|
):
|
|
if textpdf and not self.font:
|
|
self.font, self.font_key = self._find_font(textpdf)
|
|
|
|
emplaced_page = False
|
|
content_rotation = self.pdfinfo[pageno].rotation
|
|
path_image = Path(image).resolve() if image else None
|
|
if path_image is not None and path_image != self.path_base:
|
|
# We are updating the old page with a rasterized PDF of the new
|
|
# page (without changing objgen, to preserve references)
|
|
log.debug("Emplacement update")
|
|
with Pdf.open(path_image) as pdf_image:
|
|
self.emplacements += 1
|
|
foreign_image_page = pdf_image.pages[0]
|
|
self.pdf_base.pages.append(foreign_image_page)
|
|
local_image_page = self.pdf_base.pages[-1]
|
|
self.pdf_base.pages[pageno].emplace(local_image_page)
|
|
del self.pdf_base.pages[-1]
|
|
emplaced_page = True
|
|
|
|
# Calculate if the text is misaligned compared to the content
|
|
if emplaced_page:
|
|
content_rotation = autorotate_correction
|
|
text_rotation = autorotate_correction
|
|
text_misaligned = (text_rotation - content_rotation) % 360
|
|
log.debug(
|
|
f"Text rotation: (text, autorotate, content) -> text misalignment = "
|
|
f"({text_rotation}, {autorotate_correction}, {content_rotation}) -> "
|
|
f"{text_misaligned}"
|
|
)
|
|
|
|
if textpdf and self.font:
|
|
# Graft the text layer onto this page, whether new or old, possibly
|
|
# rotating the text layer by the amount is misaligned.
|
|
strip_old = self.context.options.redo_ocr
|
|
self._graft_text_layer(
|
|
page_num=pageno + 1,
|
|
textpdf=textpdf,
|
|
font=self.font,
|
|
font_key=self.font_key,
|
|
text_rotation=text_misaligned,
|
|
procset=self.procset,
|
|
strip_old_text=strip_old,
|
|
)
|
|
|
|
# Correct the overall page rotation if needed, now that the text and content
|
|
# are aligned
|
|
page_rotation = (content_rotation - autorotate_correction) % 360
|
|
self.pdf_base.pages[pageno].Rotate = page_rotation
|
|
log.debug(
|
|
f"Page rotation: (content, auto) -> page = "
|
|
f"({content_rotation}, {autorotate_correction}) -> {page_rotation}"
|
|
)
|
|
if self.emplacements % MAX_REPLACE_PAGES == 0:
|
|
self.save_and_reload()
|
|
|
|
def save_and_reload(self):
|
|
"""Save and reload the Pdf.
|
|
|
|
This will keep a lid on our memory usage for very large files. Attach
|
|
the font to page 1 even if page 1 doesn't use it, so we have a way to get it
|
|
back.
|
|
"""
|
|
page0 = self.pdf_base.pages[0]
|
|
_update_resources(
|
|
obj=page0, font=self.font, font_key=self.font_key, procset=self.procset
|
|
)
|
|
|
|
# We cannot read and write the same file, that will corrupt it
|
|
# but we don't to keep more copies than we need to. Delete intermediates.
|
|
# {interim_count} is the opened file we were updating
|
|
# {interim_count - 1} can be deleted
|
|
# {interim_count + 1} is the new file will produce and open
|
|
old_file = self.output_file.with_suffix(f'.working{self.interim_count - 1}.pdf')
|
|
if not self.context.options.keep_temporary_files:
|
|
with suppress(FileNotFoundError):
|
|
old_file.unlink()
|
|
|
|
next_file = self.output_file.with_suffix(
|
|
f'.working{self.interim_count + 1}.pdf'
|
|
)
|
|
self.pdf_base.save(next_file)
|
|
self.pdf_base.close()
|
|
|
|
self.pdf_base = Pdf.open(next_file)
|
|
self.procset = self.pdf_base.pages[0].Resources.ProcSet
|
|
self.font, self.font_key = None, None # Ensure we reacquire this information
|
|
self.interim_count += 1
|
|
|
|
def finalize(self):
|
|
self.pdf_base.save(self.output_file)
|
|
self.pdf_base.close()
|
|
return self.output_file
|
|
|
|
def _find_font(self, text):
|
|
"""Copy a font from the filename text into pdf_base."""
|
|
font, font_key = None, None
|
|
possible_font_names = ('/f-0-0', '/F1')
|
|
try:
|
|
with Pdf.open(text) as pdf_text:
|
|
try:
|
|
pdf_text_fonts = pdf_text.pages[0].Resources.get('/Font', {})
|
|
except (AttributeError, IndexError, KeyError):
|
|
return None, None
|
|
pdf_text_font = None
|
|
for f in possible_font_names:
|
|
pdf_text_font = pdf_text_fonts.get(f, None)
|
|
if pdf_text_font is not None:
|
|
font_key = f
|
|
break
|
|
if pdf_text_font:
|
|
font = self.pdf_base.copy_foreign(pdf_text_font)
|
|
return font, font_key
|
|
except (FileNotFoundError, PdfError):
|
|
# PdfError occurs if a 0-length file is written e.g. due to OCR timeout
|
|
return None, None
|
|
|
|
def _graft_text_layer(
|
|
self,
|
|
*,
|
|
page_num: int,
|
|
textpdf: Path,
|
|
font: Object,
|
|
font_key: Object,
|
|
procset: Object,
|
|
text_rotation: int,
|
|
strip_old_text: bool,
|
|
):
|
|
"""Insert the text layer from text page 0 on to pdf_base at page_num."""
|
|
# pylint: disable=invalid-name
|
|
|
|
log.debug("Grafting")
|
|
if Path(textpdf).stat().st_size == 0:
|
|
return
|
|
|
|
# This is a pointer indicating a specific page in the base file
|
|
with Pdf.open(textpdf) as pdf_text:
|
|
pdf_text_contents = pdf_text.pages[0].Contents.read_bytes()
|
|
|
|
base_page = self.pdf_base.pages.p(page_num)
|
|
|
|
# The text page always will be oriented up by this stage but the original
|
|
# content may have a rotation applied. Wrap the text stream with a rotation
|
|
# so it will be oriented the same way as the rest of the page content.
|
|
# (Previous versions OCRmyPDF rotated the content layer to match the text.)
|
|
mediabox = [float(pdf_text.pages[0].MediaBox[v]) for v in range(4)]
|
|
wt, ht = mediabox[2] - mediabox[0], mediabox[3] - mediabox[1]
|
|
|
|
mediabox = [float(base_page.MediaBox[v]) for v in range(4)]
|
|
wp, hp = mediabox[2] - mediabox[0], mediabox[3] - mediabox[1]
|
|
|
|
translate = PdfMatrix().translated(-wt / 2, -ht / 2)
|
|
untranslate = PdfMatrix().translated(wp / 2, hp / 2)
|
|
corner = PdfMatrix().translated(mediabox[0], mediabox[1])
|
|
# -rotation because the input is a clockwise angle and this formula
|
|
# uses CCW
|
|
text_rotation = -text_rotation % 360
|
|
rotate = PdfMatrix().rotated(text_rotation)
|
|
|
|
# Because of rounding of DPI, we might get a text layer that is not
|
|
# identically sized to the target page. Scale to adjust. Normally this
|
|
# is within 0.998.
|
|
if text_rotation in (90, 270):
|
|
wt, ht = ht, wt
|
|
scale_x = wp / wt
|
|
scale_y = hp / ht
|
|
|
|
# log.debug('%r', scale_x, scale_y)
|
|
scale = PdfMatrix().scaled(scale_x, scale_y)
|
|
|
|
# Translate the text so it is centered at (0, 0), rotate it there, adjust
|
|
# for a size different between initial and text PDF, then untranslate, and
|
|
# finally move the lower left corner to match the mediabox
|
|
ctm = translate @ rotate @ scale @ untranslate @ corner
|
|
|
|
base_resources = _ensure_dictionary(base_page, Name.Resources)
|
|
base_xobjs = _ensure_dictionary(base_resources, Name.XObject)
|
|
text_xobj_name = Name.random(prefix="OCR-")
|
|
xobj = self.pdf_base.make_stream(pdf_text_contents)
|
|
base_xobjs[text_xobj_name] = xobj
|
|
xobj.Type = Name.XObject
|
|
xobj.Subtype = Name.Form
|
|
xobj.FormType = 1
|
|
xobj.BBox = mediabox
|
|
_update_resources(
|
|
obj=xobj, font=font, font_key=font_key, procset=[Name.PDF]
|
|
)
|
|
|
|
pdf_draw_xobj = (
|
|
(b'q %s cm\n' % ctm.encode()) + (b'%s Do\n' % text_xobj_name) + b'\nQ\n'
|
|
)
|
|
new_text_layer = Stream(self.pdf_base, pdf_draw_xobj)
|
|
|
|
if strip_old_text:
|
|
strip_invisible_text(self.pdf_base, base_page)
|
|
|
|
base_page.contents_add(new_text_layer, prepend=True)
|
|
|
|
_update_resources(
|
|
obj=base_page, font=font, font_key=font_key, procset=procset
|
|
)
|