Added module which does OCR for PDF, pdf-ocr in a separate package (#324)

(has a lot of dependencies).  Uses Tesseract.

trustgraph-ocr/trustgraph/decoding/ocr/__init__.py

@@ -0,0 +1,3 @@
+
+from . pdf_decoder import *
+

trustgraph-ocr/trustgraph/decoding/ocr/__main__.py

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+#!/usr/bin/env python3
+
+from . pdf_decoder import run
+
+if __name__ == '__main__':
+    run()
+

trustgraph-ocr/trustgraph/decoding/ocr/pdf_decoder.py

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+
+"""
+Simple decoder, accepts PDF documents on input, outputs pages from the
+PDF document as text as separate output objects.
+"""
+
+import tempfile
+import base64
+import pytesseract
+from pdf2image import convert_from_bytes
+
+from ... schema import Document, TextDocument, Metadata
+from ... schema import document_ingest_queue, text_ingest_queue
+from ... log_level import LogLevel
+from ... base import ConsumerProducer
+
+module = ".".join(__name__.split(".")[1:-1])
+
+default_input_queue = document_ingest_queue
+default_output_queue = text_ingest_queue
+default_subscriber = module
+
+class Processor(ConsumerProducer):
+
+    def __init__(self, **params):
+
+        input_queue = params.get("input_queue", default_input_queue)
+        output_queue = params.get("output_queue", default_output_queue)
+        subscriber = params.get("subscriber", default_subscriber)
+
+        super(Processor, self).__init__(
+            **params | {
+                "input_queue": input_queue,
+                "output_queue": output_queue,
+                "subscriber": subscriber,
+                "input_schema": Document,
+                "output_schema": TextDocument,
+            }
+        )
+
+        print("PDF OCR inited")
+
+    async def handle(self, msg):
+
+        print("PDF message received")
+
+        v = msg.value()
+
+        print(f"Decoding {v.metadata.id}...", flush=True)
+
+        blob = base64.b64decode(v.data)
+
+        pages = convert_from_bytes(blob)
+
+        for ix, page in enumerate(pages):
+
+            try:
+                text = pytesseract.image_to_string(page, lang='eng')
+            except Exception as e:
+                print(f"Page did not OCR: {e}")
+                continue
+
+            r = TextDocument(
+                metadata=v.metadata,
+                text=text.encode("utf-8"),
+            )
+
+            await self.send(r)
+
+        print("Done.", flush=True)
+
+    @staticmethod
+    def add_args(parser):
+
+        ConsumerProducer.add_args(
+            parser, default_input_queue, default_subscriber,
+            default_output_queue,
+        )
+
+def run():
+
+    Processor.launch(module, __doc__)
+