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hocr-pdf
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hocr-pdf
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#!/usr/bin/env python
#
# Copyright 2013 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# Create a searchable PDF from a pile of HOCR + JPEG. Tested with
# Tesseract.
from __future__ import print_function
import argparse
import base64
import glob
import io
import os.path
import re
import sys
import zlib
from bidi.algorithm import get_display
from reportlab.pdfbase import pdfmetrics
from reportlab.pdfbase.ttfonts import TTFont
from reportlab.pdfgen.canvas import Canvas
from lxml import etree, html
from PIL import Image
class StdoutWrapper:
"""
Wrapper around stdout that ensures 'bytes' data is decoded
to 'latin1' (0x00 - 0xff) before writing out. This is necessary for
the invisible font to be injected as bytes but written out as a string.
"""
def write(self, data, *args, **kwargs):
if bytes != str and isinstance(data, bytes):
data = data.decode('latin1')
sys.stdout.write(data)
def export_pdf(playground, default_dpi, savefile=False):
"""Create a searchable PDF from a pile of HOCR + JPEG"""
images = sorted(glob.glob(os.path.join(playground, '*.jpg')))
if len(images) == 0:
print(f"WARNING: No JPG images found in the folder {playground}"
"\nScript cannot proceed without them and will terminate now.\n")
sys.exit(0)
load_invisible_font()
pdf = Canvas(savefile if savefile else StdoutWrapper(), pageCompression=1)
pdf.setCreator('hocr-tools')
pdf.setTitle(os.path.basename(playground))
dpi = default_dpi
for image in images:
im = Image.open(image)
w, h = im.size
try:
dpi = im.info['dpi'][0]
except KeyError:
pass
width = w * 72 / dpi
height = h * 72 / dpi
pdf.setPageSize((width, height))
pdf.drawImage(image, 0, 0, width=width, height=height)
add_text_layer(pdf, image, height, dpi)
pdf.showPage()
pdf.save()
def add_text_layer(pdf, image, height, dpi):
"""Draw an invisible text layer for OCR data"""
p1 = re.compile(r'bbox((\s+\d+){4})')
p2 = re.compile(r'baseline((\s+[\d\.\-]+){2})')
hocrfile = os.path.splitext(image)[0] + ".hocr"
hocr = etree.parse(hocrfile, html.XHTMLParser())
for line in hocr.xpath('//*[@class="ocr_line"]'):
linebox = p1.search(line.attrib['title']).group(1).split()
try:
baseline = p2.search(line.attrib['title']).group(1).split()
except AttributeError:
baseline = [0, 0]
linebox = [float(i) for i in linebox]
baseline = [float(i) for i in baseline]
xpath_elements = './/*[@class="ocrx_word"]'
if (not (line.xpath('boolean(' + xpath_elements + ')'))):
# if there are no words elements present,
# we switch to lines as elements
xpath_elements = '.'
for word in line.xpath(xpath_elements):
rawtext = word.text_content().strip()
if rawtext == '':
continue
font_width = pdf.stringWidth(rawtext, 'invisible', 8)
if font_width <= 0:
continue
box = p1.search(word.attrib['title']).group(1).split()
box = [float(i) for i in box]
b = polyval(baseline,
(box[0] + box[2]) / 2 - linebox[0]) + linebox[3]
text = pdf.beginText()
text.setTextRenderMode(3) # double invisible
text.setFont('invisible', 8)
text.setTextOrigin(box[0] * 72 / dpi, height - b * 72 / dpi)
box_width = (box[2] - box[0]) * 72 / dpi
text.setHorizScale(100.0 * box_width / font_width)
rawtext = get_display(rawtext)
text.textLine(rawtext)
pdf.drawText(text)
def polyval(poly, x):
return x * poly[0] + poly[1]
# Glyphless variation of vedaal's invisible font retrieved from
# http://www.angelfire.com/pr/pgpf/if.html, which says:
# 'Invisible font' is unrestricted freeware. Enjoy, Improve, Distribute freely
def load_invisible_font():
font = """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""".encode('latin1')
uncompressed = bytearray(zlib.decompress(base64.b64decode(font)))
ttf = io.BytesIO(uncompressed)
setattr(ttf, "name", "(invisible.ttf)")
pdfmetrics.registerFont(TTFont('invisible', ttf))
if __name__ == "__main__":
parser = argparse.ArgumentParser(
description="Create a searchable PDF from a pile of hOCR and JPEG")
parser.add_argument(
"imgdir",
help=("directory with the hOCR and JPEG files (corresponding "
"JPEG and hOCR files have to have the same name with "
"their respective file ending)")
)
parser.add_argument(
"--savefile",
help="Save to this file instead of outputting to stdout"
)
args = parser.parse_args()
if not os.path.isdir(args.imgdir):
sys.exit(f"ERROR: Given path '{args.imgdir}' is not a directory")
export_pdf(args.imgdir, 300, args.savefile)