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518 lines
18 KiB
518 lines
18 KiB
#!/usr/bin/env python3
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#
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# Copyright (c) 2010, Jonathan Brinley
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# Original version from: https://github.com/jbrinley/HocrConverter
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#
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# Copyright (c) 2013-14, Julien Pfefferkorn
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# Modifications
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#
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# Copyright (c) 2015-16, James R. Barlow
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# Set text to transparent
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# Copyright (c) 2022, WordMord & Alex Roidl
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# Set text back to visible and change bounding boxes
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#
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# Permission is hereby granted, free of charge, to any person obtaining a
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# copy of this software and associated documentation files (the
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# "Software"), to deal in the Software without restriction, including
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# without limitation the rights to use, copy, modify, merge, publish,
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# distribute, sublicense, and/or sell copies of the Software, and to
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# permit persons to whom the Software is furnished to do so, subject to
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# the following conditions:
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#
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# The above copyright notice and this permission notice shall be included
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# in all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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# OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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import argparse
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import os
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import re
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from itertools import chain
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from math import atan, cos, sin
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from pathlib import Path
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from typing import Any, NamedTuple, Optional, Tuple, Union
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from xml.etree import ElementTree
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from reportlab.lib.colors import black, cyan, magenta, red
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from reportlab.lib.units import inch
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from reportlab.pdfgen.canvas import Canvas
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from reportlab.pdfbase import pdfmetrics
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from reportlab.pdfbase.ttfonts import TTFont
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from reportlab.pdfbase.pdfmetrics import registerFontFamily
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# According to Wikipedia these languages are supported in the ISO-8859-1 character
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# set, meaning reportlab can generate them and they are compatible with hocr,
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# assuming Tesseract has the necessary languages installed. Note that there may
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# not be language packs for them.
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HOCR_OK_LANGS = frozenset(
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[
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# Languages fully covered by Latin-1:
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'afr', # Afrikaans
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'alb', # Albanian
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'ast', # Leonese
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'baq', # Basque
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'bre', # Breton
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'cos', # Corsican
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'eng', # English
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'eus', # Basque
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'fao', # Faoese
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'gla', # Scottish Gaelic
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'glg', # Galician
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'glv', # Manx
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'ice', # Icelandic
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'ind', # Indonesian
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'isl', # Icelandic
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'ita', # Italian
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'ltz', # Luxembourgish
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'mal', # Malay Rumi
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'mga', # Irish
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'nor', # Norwegian
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'oci', # Occitan
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'por', # Portugeuse
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'roh', # Romansh
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'sco', # Scots
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'sma', # Sami
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'spa', # Spanish
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'sqi', # Albanian
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'swa', # Swahili
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'swe', # Swedish
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'tgl', # Tagalog
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'wln', # Walloon
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# Languages supported by Latin-1 except for a few rare characters that OCR
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# is probably not trained to recognize anyway:
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'cat', # Catalan
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'cym', # Welsh
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'dan', # Danish
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'deu', # German
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'dut', # Dutch
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'est', # Estonian
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'fin', # Finnish
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'fra', # French
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'hun', # Hungarian
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'kur', # Kurdish
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'nld', # Dutch
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'wel', # Welsh
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]
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)
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Element = ElementTree.Element
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class Rect(NamedTuple): # pylint: disable=inherit-non-class
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"""A rectangle for managing PDF coordinates."""
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x1: Any
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y1: Any
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x2: Any
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y2: Any
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class HocrTransformError(Exception):
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pass
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class HocrTransform:
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"""
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A class for converting documents from the hOCR format.
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For details of the hOCR format, see:
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http://kba.cloud/hocr-spec/
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"""
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box_pattern = re.compile(r'bbox((\s+\d+){4})')
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baseline_pattern = re.compile(
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r'''
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baseline \s+
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([\-\+]?\d*\.?\d*) \s+ # +/- decimal float
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([\-\+]?\d+) # +/- int''',
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re.VERBOSE,
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)
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ligatures = str.maketrans(
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{'ff': 'ff', 'ffi': 'ffi', 'ffl': 'ffl', 'fi': 'fi', 'fl': 'fl'}
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)
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def __init__(self, *, hocr_filename: Union[str, Path], dpi: float):
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self.dpi = dpi
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self.hocr = ElementTree.parse(os.fspath(hocr_filename))
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# if the hOCR file has a namespace, ElementTree requires its use to
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# find elements
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matches = re.match(r'({.*})html', self.hocr.getroot().tag)
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self.xmlns = ''
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if matches:
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self.xmlns = matches.group(1)
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# get dimension in pt (not pixel!!!!) of the OCRed image
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self.width, self.height = None, None
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for div in self.hocr.findall(self._child_xpath('div', 'ocr_page')):
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coords = self.element_coordinates(div)
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pt_coords = self.pt_from_pixel(coords)
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self.width = pt_coords.x2 - pt_coords.x1
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self.height = pt_coords.y2 - pt_coords.y1
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# there shouldn't be more than one, and if there is, we don't want
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# it
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break
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if self.width is None or self.height is None:
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raise HocrTransformError("hocr file is missing page dimensions")
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def __str__(self): # pragma: no cover
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"""
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Return the textual content of the HTML body
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"""
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if self.hocr is None:
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return ''
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body = self.hocr.find(self._child_xpath('body'))
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if body:
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return self._get_element_text(body)
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else:
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return ''
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def _get_element_text(self, element: Element):
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"""
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Return the textual content of the element and its children
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"""
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text = ''
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if element.text is not None:
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text += element.text
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for child in element:
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text += self._get_element_text(child)
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if element.tail is not None:
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text += element.tail
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return text
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@classmethod
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def element_coordinates(cls, element: Element) -> Rect:
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"""
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Returns a tuple containing the coordinates of the bounding box around
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an element
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"""
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out = Rect._make(0 for _ in range(4))
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if 'title' in element.attrib:
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matches = cls.box_pattern.search(element.attrib['title'])
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if matches:
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coords = matches.group(1).split()
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out = Rect._make(int(coords[n]) for n in range(4))
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return out
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@classmethod
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def baseline(cls, element: Element) -> Tuple[float, float]:
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"""
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Returns a tuple containing the baseline slope and intercept.
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"""
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if 'title' in element.attrib:
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matches = cls.baseline_pattern.search(element.attrib['title'])
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if matches:
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return float(matches.group(1)), int(matches.group(2))
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return (0.0, 0.0)
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def pt_from_pixel(self, pxl) -> Rect:
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"""
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Returns the quantity in PDF units (pt) given quantity in pixels
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"""
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return Rect._make((c / self.dpi * inch) for c in pxl)
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def _child_xpath(self, html_tag: str, html_class: Optional[str] = None) -> str:
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xpath = f".//{self.xmlns}{html_tag}"
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if html_class:
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xpath += f"[@class='{html_class}']"
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return xpath
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@classmethod
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def replace_unsupported_chars(cls, s: str) -> str:
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"""
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Given an input string, returns the corresponding string that:
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* is available in the Helvetica facetype
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* does not contain any ligature (to allow easy search in the PDF file)
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"""
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return s.translate(cls.ligatures)
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def topdown_position(self, element):
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pxl_line_coords = self.element_coordinates(element)
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line_box = self.pt_from_pixel(pxl_line_coords)
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# Coordinates here are still in the hocr coordinate system, so 0 on the y axis
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# is the top of the page and increasing values of y will move towards the
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# bottom of the page.
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return line_box.y2
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def to_pdf(
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self,
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*,
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out_filename: Path,
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image_filename: Optional[Path] = None,
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show_bounding_boxes: bool = False,
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fontname: str = "Helvetica",
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invisible_text: bool = False,
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interword_spaces: bool = False,
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) -> None:
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"""
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Creates a PDF file with an image superimposed on top of the text.
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Text is positioned according to the bounding box of the lines in
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the hOCR file.
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The image need not be identical to the image used to create the hOCR
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file.
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It can have a lower resolution, different color mode, etc.
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Arguments:
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out_filename: Path of PDF to write.
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image_filename: Image to use for this file. If omitted, the OCR text
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is shown.
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show_bounding_boxes: Show bounding boxes around various text regions,
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for debugging.
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fontname: Name of font to use.
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invisible_text: If True, text is rendered invisible so that is
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selectable but never drawn. If False, text is visible and may
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be seen if the image is skipped or deleted in Acrobat.
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interword_spaces: If True, insert spaces between words rather than
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drawing each word without spaces. Generally this improves text
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extraction.
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"""
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# create the PDF file
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# page size in points (1/72 in.)
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pdfmetrics.registerFont(TTFont('Greek', '../styles/fonts/greek.ttf'))
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pdfmetrics.registerFont(TTFont('GreekB', '../styles/fonts/greek-bold.ttf'))
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registerFontFamily('Greek', normal='Greek', bold='GreekB')
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pdf = Canvas(
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os.fspath(out_filename),
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pagesize=(self.width, self.height),
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pageCompression=1,
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)
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if image_filename is not None:
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pdf.drawImage(
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os.fspath(image_filename), 0, 0, width=self.width, height=self.height
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)
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# draw bounding box for each paragraph
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# light blue for bounding box of paragraph
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pdf.setStrokeColor(black)
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# light blue for bounding box of paragraph
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pdf.setFillColor(black)
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pdf.setLineWidth(1) # no line for bounding box
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for elem in self.hocr.iterfind(self._child_xpath('p', 'ocr_par')):
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elemtxt = self._get_element_text(elem).rstrip()
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if len(elemtxt) == 0:
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continue
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pxl_coords = self.element_coordinates(elem)
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pt = self.pt_from_pixel(pxl_coords)
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# draw the bbox border
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if show_bounding_boxes: # pragma: no cover
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pdf.rect(
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pt.x1, self.height - pt.y2, pt.x2 - pt.x1, pt.y2 - pt.y1, fill=1
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)
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found_lines = False
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for line in sorted(
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chain(
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self.hocr.iterfind(self._child_xpath('span', 'ocr_header')),
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self.hocr.iterfind(self._child_xpath('span', 'ocr_line')),
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self.hocr.iterfind(self._child_xpath('span', 'ocr_textfloat')),
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),
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key=self.topdown_position,
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):
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found_lines = True
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self._do_line(
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pdf,
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line,
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"ocrx_word",
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fontname,
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invisible_text,
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interword_spaces,
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show_bounding_boxes,
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)
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if not found_lines:
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# Tesseract did not report any lines (just words)
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root = self.hocr.find(self._child_xpath('div', 'ocr_page'))
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self._do_line(
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pdf,
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root,
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"ocrx_word",
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fontname,
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invisible_text,
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interword_spaces,
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show_bounding_boxes,
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)
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# put the image on the page, scaled to fill the page
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# finish up the page and save it
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pdf.showPage()
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pdf.save()
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@classmethod
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def polyval(cls, poly, x): # pragma: no cover
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return x * poly[0] + poly[1]
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def _do_line(
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self,
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pdf: Canvas,
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line: Optional[Element],
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elemclass: str,
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fontname: str,
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invisible_text: bool,
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interword_spaces: bool,
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show_bounding_boxes: bool,
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):
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if not line:
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return
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pxl_line_coords = self.element_coordinates(line)
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line_box = self.pt_from_pixel(pxl_line_coords)
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line_height = line_box.y2 - line_box.y1
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slope, pxl_intercept = self.baseline(line)
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if abs(slope) < 0.005:
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slope = 0.0
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angle = atan(slope)
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cos_a, sin_a = cos(angle), sin(angle)
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text = pdf.beginText()
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intercept = pxl_intercept / self.dpi * inch
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# Don't allow the font to break out of the bounding box. Division by
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# cos_a accounts for extra clearance between the glyph's vertical axis
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# on a sloped baseline and the edge of the bounding box.
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fontsize = (line_height - abs(intercept)) / cos_a * 1.2
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#fontsize = 10.5
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text.setFont('Greek', fontsize)
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#if invisible_text:
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# text.setTextRenderMode(3) # Invisible (indicates OCR text)
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# Intercept is normally negative, so this places it above the bottom
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# of the line box
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baseline_y2 = self.height - (line_box.y2 + intercept)
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if False: # pragma: no cover
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# draw the baseline in magenta, dashed
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pdf.setDash()
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pdf.setStrokeColor(magenta)
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pdf.setLineWidth(0.5)
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# negate slope because it is defined as a rise/run in pixel
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# coordinates and page coordinates have the y axis flipped
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pdf.line(
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line_box.x1,
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baseline_y2,
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line_box.x2,
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self.polyval((-slope, baseline_y2), line_box.x2 - line_box.x1),
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)
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# light green for bounding box of word/line
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pdf.setDash(6, 3)
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pdf.setStrokeColor(red)
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#text.setTextTransform(cos_a, -sin_a, sin_a, cos_a, line_box.x1, baseline_y2)
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text.setTextOrigin(line_box.x1, baseline_y2)
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##pdf.translate(line_box.x1, baseline_y2)
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pdf.setFillColor(black) # text in black
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elements = line.findall(self._child_xpath('span', elemclass))
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for elem in elements:
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elemtxt = self._get_element_text(elem).strip()
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elemtxt = self.replace_unsupported_chars(elemtxt)
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if elemtxt == '':
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continue
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pxl_coords = self.element_coordinates(elem)
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box = self.pt_from_pixel(pxl_coords)
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if False:
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# if `--interword-spaces` is true, append a space
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# to the end of each text element to allow simpler PDF viewers
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# such as PDF.js to better recognize words in search and copy
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# and paste. Do not remove space from last word in line, even
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# though it would look better, because it will interfere with
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# naive text extraction. \n does not work either.
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elemtxt += ' '
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box = Rect._make(
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(
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box.x1,
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line_box.y1,
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box.x2 + pdf.stringWidth(' ', fontname, line_height),
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line_box.y2,
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)
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)
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box_width = box.x2 - box.x1
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font_width = pdf.stringWidth(elemtxt, fontname, fontsize)
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# draw the bbox border
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if False: # pragma: no cover
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pdf.rect(
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box.x1, self.height - line_box.y2, box_width, line_height, fill=0
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)
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# Adjust relative position of cursor
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# This is equivalent to:
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# text.setTextOrigin(pt.x1, self.height - line_box.y2)
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# but the former generates a full text reposition matrix (Tm) in the
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# content stream while this issues a "offset" (Td) command.
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# .moveCursor() is relative to start of the text line, where the
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# "text line" means whatever reportlab defines it as. Do not use
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# use .getCursor(), since moveCursor() rather unintuitively plans
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# its moves relative to .getStartOfLine().
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# For skewed lines, in the text transform we set up a rotated
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# coordinate system, so we don't have to account for the
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# incremental offset. Surprisingly most PDF viewers can handle this.
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cursor = text.getStartOfLine()
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dx = box.x1 - cursor[0]
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dy = baseline_y2 - cursor[1]
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text.moveCursor(dx, dy)
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# If reportlab tells us this word is 0 units wide, our best seems
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# to be to suppress this text
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if font_width > 0:
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#text.setHorizScale(100 * box_width / font_width)
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text.textOut(elemtxt)
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pdf.drawText(text)
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if __name__ == "__main__":
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parser = argparse.ArgumentParser(description='Convert hocr file to PDF')
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parser.add_argument(
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'-b',
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'--boundingboxes',
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action="store_true",
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default=False,
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help='Show bounding boxes borders',
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)
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parser.add_argument(
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'-r',
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'--resolution',
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type=int,
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default=300,
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help='Resolution of the image that was OCRed',
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)
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parser.add_argument(
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'-i',
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'--image',
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default=None,
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help='Path to the image to be placed above the text',
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)
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parser.add_argument(
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'--interword-spaces',
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action='store_true',
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default=False,
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help='Add spaces between words',
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)
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parser.add_argument('hocrfile', help='Path to the hocr file to be parsed')
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parser.add_argument('outputfile', help='Path to the PDF file to be generated')
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args = parser.parse_args()
|
|
|
|
hocr = HocrTransform(hocr_filename=args.hocrfile, dpi=args.resolution)
|
|
hocr.to_pdf(
|
|
out_filename=args.outputfile,
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|
image_filename=args.image,
|
|
show_bounding_boxes=args.boundingboxes,
|
|
interword_spaces=args.interword_spaces,
|
|
)
|
|
|
|
|