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Add rudimentary support for combining OCR layer with existing content

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It appears to be very fragile due to weaknesses in PyPDF. Better
option is probably to use pdftk's watermark feature.
This commit is contained in:
Jim Barlow 2015-03-10 14:28:38 -07:00
parent 9229f7c6cc
commit a99ba3b696
2 changed files with 59 additions and 26 deletions
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9
OCRmyPDF.sh
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@ -50,6 +50,7 @@ Usage: OCRmyPDF.sh [-h] [-v] [-g] [-k] [-d] [-c] [-i] [-o dpi] [-f] [-l languag
(which should not be the case for PDF files built from scanned images)
-s : If pages contain font data, do not perform processing on that page, but include the page in the final output.
-b : Skip big pages
-e : Use exact PDF pages with no changes other than inserting hidden OCR text layer (mutually exclusive with -d/-c/-i/-f)
-l : Set the language of the PDF file in order to improve OCR results (default "eng")
Any language supported by tesseract is supported (Tesseract uses 3-character ISO 639-2 language codes)
Multiple languages may be specified, separated by '+' characters.
@ -93,10 +94,11 @@ PDF_NOIMG="0" # 0=no, 1=yes (generates each PDF page twice, with and without i
FORCE_OCR="0" # 0=do not force, 1=force (force to OCR the whole document, even if some page already contain font data)
SKIP_TEXT="0" # 0=do not skip text pages, 1=skip text pages
SKIP_BIG="0"
EXACT_IMAGE="0"
TESS_CFG_FILES="" # list of additional configuration files to be used by tesseract
# Parse optional command line arguments
while getopts ":hvgkdcio:fsbl:C:" opt; do
while getopts ":hvgkdcio:fsbel:C:" opt; do
case $opt in
h) usage ; exit 0 ;;
v) VERBOSITY=$(($VERBOSITY+1)) ;;
@ -109,6 +111,7 @@ while getopts ":hvgkdcio:fsbl:C:" opt; do
f) FORCE_OCR="1" ;;
s) SKIP_TEXT="1" ;;
b) SKIP_BIG="1" ;;
e) EXACT_IMAGE="1" ;;
l) LAN="$OPTARG" ;;
C) TESS_CFG_FILES="$OPTARG $TESS_CFG_FILES" ;;
\?)
@ -273,10 +276,10 @@ sed '/^$/d' "$FILE_TMP" | awk '{printf "%04d %s\n", NR, $0}' > "$FILE_PAGES_INFO
numpages=`tail -n 1 "$FILE_PAGES_INFO" | cut -f1 -d" "`
# process each page of the input pdf file
parallel --gnu -q -k --halt-on-error 1 python3 -m src.ocrpage \
parallel --gnu -q -k --halt-on-error 1 -j2 python3 -m src.ocrpage \
"$FILE_INPUT_PDF" "{}" "$numpages" "$TMP_FLD" \
"$VERBOSITY" "$LAN" "$KEEP_TMP" "$PREPROCESS_DESKEW" "$PREPROCESS_CLEAN" "$PREPROCESS_CLEANTOPDF" "$OVERSAMPLING_DPI" \
"$PDF_NOIMG" "$FORCE_OCR" "$SKIP_TEXT" "$SKIP_BIG" "$TESS_CFG_FILES" < "$FILE_PAGES_INFO"
"$PDF_NOIMG" "$FORCE_OCR" "$SKIP_TEXT" "$SKIP_BIG" "$EXACT_IMAGE" "$TESS_CFG_FILES" < "$FILE_PAGES_INFO"
ret_code="$?"
[ $ret_code -ne 0 ] && exit $ret_code

76
src/ocrpage.py
View File

@ -6,6 +6,8 @@ import os.path
import fileinput
import re
from parse import parse
import PyPDF2 as pypdf
import shutil
from subprocess import Popen, check_call, PIPE, CalledProcessError, \
TimeoutExpired
@ -73,6 +75,9 @@ parser.add_argument(
parser.add_argument(
'skip_big', type=int,
help="Skip OCR for pages that are very large")
parser.add_argument(
'exact_image', type=int,
help="Use original page from PDF without re-rendering")
parser.add_argument(
'tess_cfg_files', default='', nargs='*', # Implemented
help="Tesseract configuration")
@ -225,11 +230,11 @@ def setup_working_directory(input_file, soft_link_name):
pass
@active_if(not ocr_required)
@active_if(not ocr_required or (ocr_required and options.exact_image))
@transform(setup_working_directory,
formatter(),
os.path.join(options.tmp_fld, '%04i.skip.pdf' % pageno))
def skip_ocr(
os.path.join(options.tmp_fld, '%04i.page.pdf' % pageno))
def extract_single_page(
input_file,
output_file):
args_pdfseparate = [
@ -526,27 +531,25 @@ def ocr_tesseract(
raise CalledProcessError(p.returncode, args_tesseract)
if os.path.exists(output_file + '.html'):
# Tesseract 3.02 appends suffix ".html" on its own
re_symlink(output_file + ".html", output_file,
logger, logger_mutex)
# Tesseract 3.02 appends suffix ".html" on its own (.hocr.html)
shutil.move(output_file + '.html', output_file)
elif os.path.exists(output_file + '.hocr'):
# Tesseract 3.03 appends suffix ".hocr" on its own
re_symlink(output_file + ".hocr", output_file,
logger, logger_mutex)
# Tesseract 3.03 appends suffix ".hocr" on its own (.hocr.hocr)
shutil.move(output_file + '.hocr', output_file)
# The filename gets inserted to hocr
# but Tesseract does not verify that it is escaped XML
# it's not necessary so strip it out
regex_nested_single_quotes = re.compile(
r"""title='image "([^"]*)";""")
with fileinput.input(files=(output_file,), inplace=True) as f:
for line in f:
line = regex_nested_single_quotes.sub(
r"""title='image " ";""", line)
print(line, end='') # stdout is redirected here
# Tesseract inserts source filename into hocr file without escaping
# it. This could break the XML parser. Rewrite the hocr file,
# replacing the filename with a space.
regex_nested_single_quotes = re.compile(
r"""title='image "([^"]*)";""")
with fileinput.input(files=(output_file,), inplace=True) as f:
for line in f:
line = regex_nested_single_quotes.sub(
r"""title='image " ";""", line)
print(line, end='') # fileinput.input redirects stdout
@active_if(ocr_required)
@active_if(ocr_required and not options.exact_image)
@merge([unpack_with_ghostscript, convert_to_png,
deskew_imagemagick, deskew_leptonica, cleaned_to_png],
os.path.join(options.tmp_fld, "%04i.image_for_pdf" % pageno))
@ -567,7 +570,7 @@ def select_image_for_pdf(infiles, output_file):
re_symlink(input_file, output_file, logger, logger_mutex)
@active_if(ocr_required)
@active_if(ocr_required and not options.exact_image)
@merge([ocr_tesseract, select_image_for_pdf],
os.path.join(options.tmp_fld, '%04i.rendered.pdf' % pageno))
def render_page(infiles, output_file):
@ -590,7 +593,34 @@ def render_text_output_page(input_file, output_file):
showBoundingboxes=True, invisibleText=False)
@merge([render_page, skip_ocr],
@active_if(ocr_required and options.exact_image)
@transform(ocr_tesseract, suffix(".hocr"), ".hocr.pdf")
def render_hocr_blank_page(input_file, output_file):
dpi = round(max(pageinfo['xres'], pageinfo['yres']))
hocrtransform = HocrTransform(input_file, dpi)
hocrtransform.to_pdf(output_file, imageFileName=None,
showBoundingboxes=False, invisibleText=True)
@active_if(ocr_required and options.exact_image)
@merge([render_hocr_blank_page, extract_single_page],
os.path.join(options.tmp_fld, "%04i.merged.pdf") % pageno)
def merge_hocr_with_original_page(infiles, output_file):
with open(infiles[0], 'rb') as hocr_input, \
open(infiles[1], 'rb') as page_input, \
open(output_file, 'wb') as output:
hocr_reader = pypdf.PdfFileReader(hocr_input)
page_reader = pypdf.PdfFileReader(page_input)
writer = pypdf.PdfFileWriter()
the_page = hocr_reader.getPage(0)
the_page.mergePage(page_reader.getPage(0))
writer.addPage(the_page)
writer.write(output)
@merge([render_page, merge_hocr_with_original_page, extract_single_page],
os.path.join(options.tmp_fld, '%04i.ocred.pdf' % pageno))
def select_final_page(infiles, output_file):
re_symlink(infiles[-1], output_file, logger, logger_mutex)
@ -600,7 +630,7 @@ cmdline.run(options)
# parser.add_argument(
# 'tess_cfg_files',
# help="Specific configuration files to be used by Tesseract during OCRing")
# help="Specific configuration files to be used by Tesseract during OCRing")
def main():