Initial implementation of OCR pluggable backends

mayan/apps/ocr/api.py

@@ -1,4 +1,3 @@
-#Some code from http://wiki.github.com/hoffstaetter/python-tesseract
 from __future__ import absolute_import
 
 import codecs
@@ -14,8 +13,9 @@ from common.conf.settings import TEMPORARY_DIRECTORY
 from converter.api import convert
 from documents.models import DocumentPage
 
-from .conf.settings import (TESSERACT_PATH, TESSERACT_LANGUAGE, UNPAPER_PATH)
-from .exceptions import TesseractError, UnpaperError
+from .backends import ocr_backend
+from .conf.settings import UNPAPER_PATH, LANGUAGE
+from .exceptions import OCRError, UnpaperError
 from .literals import (DEFAULT_OCR_FILE_FORMAT, UNPAPER_FILE_FORMAT,
     DEFAULT_OCR_FILE_EXTENSION)
 from .parsers import parse_document_page
@@ -24,13 +24,13 @@ from .parsers.exceptions import ParserError, ParserUnknownFile
 
 def get_language_backend():
     """
-    Return the OCR cleanup language backend using the selected tesseract
-    language in the configuration settings
+    Return the OCR cleanup language backend using the selected language
+    in the configuration settings
     """
     try:
-        module = import_module(u'.'.join([u'ocr', u'lang', TESSERACT_LANGUAGE]))
+        module = import_module(u'.'.join([u'ocr', u'lang', LANGUAGE]))
     except ImportError:
-        sys.stderr.write(u'\nWarning: No OCR app language backend for language: %s\n\n' % TESSERACT_LANGUAGE)
+        sys.stderr.write(u'\nWarning: No OCR app language backend for language: %s\n\n' % LANGUAGE)
         return None
     return module
 
@@ -47,45 +47,12 @@ def cleanup(filename):
         pass
 
 
-def run_tesseract(input_filename, lang=None):
-    """
-    Execute the command line binary of tesseract
-    """
-    fd, filepath = tempfile.mkstemp()
-    os.close(fd)
-    ocr_output = os.extsep.join([filepath, u'txt'])
-    command = [unicode(TESSERACT_PATH), unicode(input_filename), unicode(filepath)]
-
-    if lang is not None:
-        command.extend([u'-l', lang])
-
-    proc = subprocess.Popen(command, close_fds=True, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
-    return_code = proc.wait()
-    if return_code != 0:
-        error_text = proc.stderr.read()
-        cleanup(filepath)
-        cleanup(ocr_output)
-        if lang:
-            # If tesseract gives an error with a language parameter
-            # re-run it with no parameter again
-            return run_tesseract(input_filename, lang=None)
-        else:
-            raise TesseractError(error_text)
-
-    fd = codecs.open(ocr_output, 'r', 'utf-8')
-    text = fd.read().strip()
-    fd.close()
-
-    os.unlink(filepath)
-
-    return text
-
-
 def do_document_ocr(queue_document):
     """
     Try first to extract text from document pages using the registered
     parser, if the parser fails or if there is no parser registered for
-    the document mimetype do a visual OCR by calling tesseract
+    the document mimetype do a visual OCR by calling the corresponding
+    OCR backend
     """
     for document_page in queue_document.document.pages.all():
         try:
@@ -116,7 +83,7 @@ def do_document_ocr(queue_document):
             pre_ocr_filepath_w_ext = os.extsep.join([pre_ocr_filepath, DEFAULT_OCR_FILE_EXTENSION])
             os.rename(pre_ocr_filepath, pre_ocr_filepath_w_ext)
             try:
-                ocr_text = run_tesseract(pre_ocr_filepath_w_ext, TESSERACT_LANGUAGE)
+                ocr_text = ocr_backend.execute(pre_ocr_filepath_w_ext, LANGUAGE)
 
                 document_page.content = ocr_cleanup(ocr_text)
                 document_page.page_label = _(u'Text from OCR')

mayan/apps/ocr/backends/__init__.py

@@ -0,0 +1,26 @@
+from __future__ import absolute_import
+
+from django.utils.importlib import import_module
+
+from ..conf.settings import BACKEND
+
+
+class BackendBase(object):
+    def execute(input_filename, language=None):
+        raise NotImplemented
+
+
+def get_ocr_backend():
+    """
+    Return the OCR backend using the path specified in the configuration
+    settings
+    """
+    try:
+        module = import_module(BACKEND)
+    except ImportError:
+        sys.stderr.write(u'\nWarning: No OCR backend named: %s\n\n' % BACKEND)
+        raise
+    else:
+        return module
+
+ocr_backend = get_ocr_backend()

mayan/apps/ocr/backends/tesseract.py

@@ -0,0 +1,45 @@
+from __future__ import absolute_import
+
+import codecs
+import os
+import subprocess
+import tempfile
+import sys
+
+from . import BackendBase
+from ..conf.settings import TESSERACT_PATH
+
+
+def Tesseract(BackendBase):
+    def execute(input_filename, language=None):
+        """
+        Execute the command line binary of tesseract
+        """
+        fd, filepath = tempfile.mkstemp()
+        os.close(fd)
+        ocr_output = os.extsep.join([filepath, u'txt'])
+        command = [unicode(TESSERACT_PATH), unicode(input_filename), unicode(filepath)]
+
+        if lang is not None:
+            command.extend([u'-l', language])
+
+        proc = subprocess.Popen(command, close_fds=True, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        return_code = proc.wait()
+        if return_code != 0:
+            error_text = proc.stderr.read()
+            cleanup(filepath)
+            cleanup(ocr_output)
+            if lang:
+                # If tesseract gives an error with a language parameter
+                # re-run it with no parameter again
+                return run_tesseract(input_filename, language=None)
+            else:
+                raise TesseractError(error_text)
+
+        fd = codecs.open(ocr_output, 'r', 'utf-8')
+        text = fd.read().strip()
+        fd.close()
+
+        os.unlink(filepath)
+
+        return text

mayan/apps/ocr/conf/settings.py

@@ -9,12 +9,13 @@ register_settings(
     module=u'ocr.conf.settings',
     settings=[
         {'name': u'TESSERACT_PATH', 'global_name': u'OCR_TESSERACT_PATH', 'default': u'/usr/bin/tesseract', 'exists': True},
-        {'name': u'TESSERACT_LANGUAGE', 'global_name': u'OCR_TESSERACT_LANGUAGE', 'default': u'eng'},
+        {'name': u'LANGUAGE', 'global_name': u'OCR_LANGUAGE', 'default': u'eng'},
         {'name': u'REPLICATION_DELAY', 'global_name': u'OCR_REPLICATION_DELAY', 'default': 0, 'description': _(u'Amount of seconds to delay OCR of documents to allow for the node\'s storage replication overhead.')},
         {'name': u'NODE_CONCURRENT_EXECUTION', 'global_name': u'OCR_NODE_CONCURRENT_EXECUTION', 'default': 1, 'description': _(u'Maximum amount of concurrent document OCRs a node can perform.')},
         {'name': u'AUTOMATIC_OCR', 'global_name': u'OCR_AUTOMATIC_OCR', 'default': True, 'description': _(u'Automatically queue newly created documents for OCR.')},
         {'name': u'QUEUE_PROCESSING_INTERVAL', 'global_name': u'OCR_QUEUE_PROCESSING_INTERVAL', 'default': 10},
         {'name': u'UNPAPER_PATH', 'global_name': u'OCR_UNPAPER_PATH', 'default': u'/usr/bin/unpaper', 'description': _(u'File path to unpaper program.'), 'exists': True},
         {'name': u'PDFTOTEXT_PATH', 'global_name': u'OCR_PDFTOTEXT_PATH', 'default': u'/usr/bin/pdftotext', 'description': _(u'File path to poppler\'s pdftotext program used to extract text from PDF files.'), 'exists': True},
+        {'name': u'BACKEND', 'global_name': u'OCR_BACKEND', 'default': u'ocr.backends.tesseract', 'description': _(u'Full path to the backend to be used to do OCR.')},
     ]
 )

mayan/apps/ocr/exceptions.py

@@ -5,9 +5,9 @@ class AlreadyQueued(Exception):
     pass
 
 
-class TesseractError(Exception):
+class OCRError(Exception):
     """
-    Raised by tesseract
+    Raised by the OCR backend
     """
     pass