# © 2017 James R. Barlow: github.com/jbarlow83
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
"""Interface to Tesseract executable"""
import logging
import os
import shutil
from collections import namedtuple
from os import fspath
from pathlib import Path
from subprocess import PIPE, STDOUT, CalledProcessError, TimeoutExpired
from typing import List, Optional
from PIL import Image
from ocrmypdf.exceptions import (
MissingDependencyError,
SubprocessOutputError,
TesseractConfigError,
)
from ocrmypdf.subprocess import get_version, run
log = logging.getLogger(__name__)
OrientationConfidence = namedtuple('OrientationConfidence', ('angle', 'confidence'))
HOCR_TEMPLATE = """
"""
class TesseractLoggerAdapter(logging.LoggerAdapter):
def process(self, msg, kwargs):
kwargs['extra'] = self.extra
return '[tesseract] %s' % (msg), kwargs
def version():
return get_version('tesseract', regex=r'tesseract\s(.+)')
def has_textonly_pdf(langs=None):
"""Does Tesseract have textonly_pdf capability?
Available in v4.00.00alpha since January 2017. Best to
parse the parameter list.
"""
args_tess = tess_base_args(langs, engine_mode=None) + ['--print-parameters', 'pdf']
params = ''
try:
proc = run(args_tess, check=True, stdout=PIPE, stderr=STDOUT)
params = proc.stdout
except CalledProcessError as e:
raise MissingDependencyError(
"Could not --print-parameters from tesseract. This can happen if the "
"TESSDATA_PREFIX environment is not set to a valid tessdata folder. "
) from e
if b'textonly_pdf' in params:
return True
return False
def has_user_words():
"""Does Tesseract have --user-words capability?
Not available in 4.0, but available in 4.1. Also available in 3.x, but
we no longer support 3.x.
"""
return version() >= '4.1'
def get_languages():
def lang_error(output):
msg = (
"Tesseract failed to report available languages.\n"
"Output from Tesseract:\n"
"-----------\n"
)
msg += output
return msg
args_tess = ['tesseract', '--list-langs']
try:
proc = run(
args_tess,
text=True,
stdout=PIPE,
stderr=STDOUT,
logs_errors_to_stdout=True,
check=True,
)
output = proc.stdout
except CalledProcessError as e:
raise MissingDependencyError(lang_error(e.output)) from e
for line in output.splitlines():
if line.startswith('Error'):
raise MissingDependencyError(lang_error(output))
_header, *rest = output.splitlines()
return set(lang.strip() for lang in rest)
def tess_base_args(langs: List[str], engine_mode: Optional[int]) -> List[str]:
args = ['tesseract']
if langs:
args.extend(['-l', '+'.join(langs)])
if engine_mode is not None:
args.extend(['--oem', str(engine_mode)])
return args
def get_orientation(input_file: Path, engine_mode: Optional[int], timeout: float):
args_tesseract = tess_base_args(['osd'], engine_mode) + [
'--psm',
'0',
fspath(input_file),
'stdout',
]
try:
p = run(args_tesseract, stdout=PIPE, stderr=STDOUT, timeout=timeout, check=True)
stdout = p.stdout
except TimeoutExpired:
return OrientationConfidence(angle=0, confidence=0.0)
except CalledProcessError as e:
tesseract_log_output(e.stdout)
tesseract_log_output(e.stderr)
if (
b'Too few characters. Skipping this page' in e.output
or b'Image too large' in e.output
):
return OrientationConfidence(0, 0)
raise SubprocessOutputError() from e
else:
osd = {}
for line in stdout.decode().splitlines():
line = line.strip()
parts = line.split(':', maxsplit=2)
if len(parts) == 2:
osd[parts[0].strip()] = parts[1].strip()
angle = int(osd.get('Orientation in degrees', 0))
oc = OrientationConfidence(
angle=angle, confidence=float(osd.get('Orientation confidence', 0))
)
return oc
def tesseract_log_output(stream):
tlog = TesseractLoggerAdapter(
log, extra=log.extra if hasattr(log, 'extra') else None
)
if not stream:
return
try:
text = stream.decode()
except UnicodeDecodeError:
text = stream.decode('utf-8', 'ignore')
lines = text.splitlines()
for line in lines:
if line.startswith("Tesseract Open Source"):
continue
elif line.startswith("Warning in pixReadMem"):
continue
elif 'diacritics' in line:
tlog.warning("lots of diacritics - possibly poor OCR")
elif line.startswith('OSD: Weak margin'):
tlog.warning("unsure about page orientation")
elif 'Error in pixScanForForeground' in line:
pass # Appears to be spurious/problem with nonwhite borders
elif 'Error in boxClipToRectangle' in line:
pass # Always appears with pixScanForForeground message
elif 'parameter not found: ' in line.lower():
tlog.error(line.strip())
problem = line.split('found: ')[1]
raise TesseractConfigError(problem)
elif 'error' in line.lower() or 'exception' in line.lower():
tlog.error(line.strip())
elif 'warning' in line.lower():
tlog.warning(line.strip())
elif 'read_params_file' in line.lower():
tlog.error(line.strip())
else:
tlog.info(line.strip())
def page_timedout(timeout):
if timeout == 0:
return
log.warning("[tesseract] took too long to OCR - skipping")
def _generate_null_hocr(output_hocr, output_text, image):
"""Produce a .hocr file that reports no text detected on a page that is
the same size as the input image."""
with Image.open(image) as im:
w, h = im.size
output_hocr.write_text(HOCR_TEMPLATE.format(w, h), encoding='utf-8')
output_text.write_text('[skipped page]', encoding='utf-8')
def generate_hocr(
input_file: Path,
output_hocr: Path,
output_text: Path,
languages: List[str],
engine_mode: int,
tessconfig: List[str],
timeout: float,
pagesegmode: int,
user_words,
user_patterns,
):
prefix = output_hocr.with_suffix('')
args_tesseract = tess_base_args(languages, engine_mode)
if pagesegmode is not None:
args_tesseract.extend(['--psm', str(pagesegmode)])
if user_words:
args_tesseract.extend(['--user-words', user_words])
if user_patterns:
args_tesseract.extend(['--user-patterns', user_patterns])
# Reminder: test suite tesseract test plugins will break after any changes
# to the number of order parameters here
args_tesseract.extend([input_file, prefix, 'hocr', 'txt'] + tessconfig)
try:
p = run(args_tesseract, stdout=PIPE, stderr=STDOUT, timeout=timeout, check=True)
stdout = p.stdout
except TimeoutExpired:
# Generate a HOCR file with no recognized text if tesseract times out
# Temporary workaround to hocrTransform not being able to function if
# it does not have a valid hOCR file.
page_timedout(timeout)
_generate_null_hocr(output_hocr, output_text, input_file)
except CalledProcessError as e:
tesseract_log_output(e.output)
if b'Image too large' in e.output:
_generate_null_hocr(output_hocr, output_text, input_file)
return
raise SubprocessOutputError() from e
else:
tesseract_log_output(stdout)
# The sidecar text file will get the suffix .txt; rename it to
# whatever caller wants it named
if prefix.with_suffix('.txt').exists():
shutil.move(prefix.with_suffix('.txt'), output_text)
def use_skip_page(output_pdf, output_text):
output_text.write_text('[skipped page]', encoding='utf-8')
# A 0 byte file to the output to indicate a skip
output_pdf.write_bytes(b'')
def generate_pdf(
*,
input_file: Path,
output_pdf: Path,
output_text: Path,
languages: List[str],
engine_mode: int,
tessconfig: List[str],
timeout: float,
pagesegmode: int,
user_words,
user_patterns,
):
"""Use Tesseract to render a PDF.
input_file -- image to analyze
output_pdf -- file to generate
output_text -- OCR text file
languages -- list of languages to consider
engine_mode -- engine mode argument for tess v4
tessconfig -- tesseract configuration
timeout -- timeout (seconds)
"""
args_tesseract = tess_base_args(languages, engine_mode)
if pagesegmode is not None:
args_tesseract.extend(['--psm', str(pagesegmode)])
args_tesseract.extend(['-c', 'textonly_pdf=1'])
if user_words:
args_tesseract.extend(['--user-words', user_words])
if user_patterns:
args_tesseract.extend(['--user-patterns', user_patterns])
prefix = os.path.splitext(output_pdf)[0] # Tesseract appends suffixes
# Reminder: test suite tesseract test plugins might break after any changes
# to the number of order parameters here
args_tesseract.extend([input_file, prefix, 'pdf', 'txt'] + tessconfig)
try:
p = run(args_tesseract, stdout=PIPE, stderr=STDOUT, timeout=timeout, check=True)
stdout = p.stdout
if os.path.exists(prefix + '.txt'):
shutil.move(prefix + '.txt', output_text)
except TimeoutExpired:
page_timedout(timeout)
use_skip_page(output_pdf, output_text)
except CalledProcessError as e:
tesseract_log_output(e.output)
if b'Image too large' in e.output:
use_skip_page(output_pdf, output_text)
return
raise SubprocessOutputError() from e
else:
tesseract_log_output(stdout)