feat: add "auto" language for TesseractOcr (#759)

* Add "auto" language for TesseractOcr

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

* Add tesseract-ocr-script-latn installation for the "auto" language

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

* Modify "auto" language in TesseractOcr to initialize the script readers lazily

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

* Finalize script readers

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

* Fix script models prefix for Linux

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

---------

Signed-off-by: Pavel Denisov <pavel.denisov@iais.fraunhofer.de>

.github/workflows/checks.yml

@@ -10,7 +10,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install tesseract
-        run: sudo apt-get update && sudo apt-get install -y tesseract-ocr tesseract-ocr-eng tesseract-ocr-fra tesseract-ocr-deu tesseract-ocr-spa libleptonica-dev libtesseract-dev pkg-config
+        run: sudo apt-get update && sudo apt-get install -y tesseract-ocr tesseract-ocr-eng tesseract-ocr-fra tesseract-ocr-deu tesseract-ocr-spa tesseract-ocr-script-latn libleptonica-dev libtesseract-dev pkg-config
       - name: Set TESSDATA_PREFIX
         run: |
           echo "TESSDATA_PREFIX=$(dpkg -L tesseract-ocr-eng | grep tessdata$)" >> "$GITHUB_ENV"

docling/models/tesseract_ocr_model.py

@@ -54,43 +54,56 @@ class TesseractOcrModel(BaseOcrModel):
             # Initialize the tesseractAPI
             _log.debug("Initializing TesserOCR: %s", tesseract_version)
             lang = "+".join(self.options.lang)
+
+            self.script_readers: dict[str, tesserocr.PyTessBaseAPI] = {}
+
+            if any([l.startswith("script/") for l in tesserocr_languages]):
+                self.script_prefix = "script/"
+            else:
+                self.script_prefix = ""
+
+            tesserocr_kwargs = {
+                "psm": tesserocr.PSM.AUTO,
+                "init": True,
+                "oem": tesserocr.OEM.DEFAULT,
+            }
+
             if self.options.path is not None:
+                tesserocr_kwargs["path"] = self.options.path
+
+            if lang == "auto":
                 self.reader = tesserocr.PyTessBaseAPI(
-                    path=self.options.path,
+                    **{"lang": "osd", "psm": tesserocr.PSM.OSD_ONLY} | tesserocr_kwargs
-                    lang=lang,
-                    psm=tesserocr.PSM.AUTO,
-                    init=True,
-                    oem=tesserocr.OEM.DEFAULT,
                 )
             else:
                 self.reader = tesserocr.PyTessBaseAPI(
-                    lang=lang,
+                    **{"lang": lang} | tesserocr_kwargs,
-                    psm=tesserocr.PSM.AUTO,
-                    init=True,
-                    oem=tesserocr.OEM.DEFAULT,
                 )
+
             self.reader_RIL = tesserocr.RIL
 
     def __del__(self):
         if self.reader is not None:
             # Finalize the tesseractAPI
             self.reader.End()
+        for script in self.script_readers:
+            self.script_readers[script].End()
 
     def __call__(
         self, conv_res: ConversionResult, page_batch: Iterable[Page]
     ) -> Iterable[Page]:
-
         if not self.enabled:
             yield from page_batch
             return
 
+        import tesserocr
+
         for page in page_batch:
             assert page._backend is not None
             if not page._backend.is_valid():
                 yield page
             else:
                 with TimeRecorder(conv_res, "ocr"):
-
                     assert self.reader is not None
 
                     ocr_rects = self.get_ocr_rects(page)
@@ -106,20 +119,55 @@ class TesseractOcrModel(BaseOcrModel):
 
                         # Retrieve text snippets with their bounding boxes
                         self.reader.SetImage(high_res_image)
-                        boxes = self.reader.GetComponentImages(
+
+                        if self.options.lang == ["auto"]:
+                            osd = self.reader.DetectOrientationScript()
+
+                            # No text, probably
+                            if osd is None:
+                                continue
+
+                            script = osd["script_name"]
+
+                            if script == "Katakana" or script == "Hiragana":
+                                script = "Japanese"
+                            elif script == "Han":
+                                script = "HanS"
+                            elif script == "Korean":
+                                script = "Hangul"
+
+                            _log.debug(
+                                f'Using model for the detected script "{script}"'
+                            )
+
+                            if script not in self.script_readers:
+                                self.script_readers[script] = tesserocr.PyTessBaseAPI(
+                                    path=self.reader.GetDatapath(),
+                                    lang=f"{self.script_prefix}{script}",
+                                    psm=tesserocr.PSM.AUTO,
+                                    init=True,
+                                    oem=tesserocr.OEM.DEFAULT,
+                                )
+
+                            local_reader = self.script_readers[script]
+                            local_reader.SetImage(high_res_image)
+                        else:
+                            local_reader = self.reader
+
+                        boxes = local_reader.GetComponentImages(
                             self.reader_RIL.TEXTLINE, True
                         )
 
                         cells = []
                         for ix, (im, box, _, _) in enumerate(boxes):
                             # Set the area of interest. Tesseract uses Bottom-Left for the origin
-                            self.reader.SetRectangle(
+                            local_reader.SetRectangle(
                                 box["x"], box["y"], box["w"], box["h"]
                             )
 
                             # Extract text within the bounding box
-                            text = self.reader.GetUTF8Text().strip()
+                            text = local_reader.GetUTF8Text().strip()
-                            confidence = self.reader.MeanTextConf()
+                            confidence = local_reader.MeanTextConf()
                             left = box["x"] / self.scale
                             bottom = box["y"] / self.scale
                             right = (box["x"] + box["w"]) / self.scale

tests/test_e2e_ocr_conversion.py

@@ -60,6 +60,7 @@ def test_e2e_conversions():
         RapidOcrOptions(),
         EasyOcrOptions(force_full_page_ocr=True),
         TesseractOcrOptions(force_full_page_ocr=True),
+        TesseractOcrOptions(force_full_page_ocr=True, lang=["auto"]),
         TesseractCliOcrOptions(force_full_page_ocr=True),
         RapidOcrOptions(force_full_page_ocr=True),
     ]
@@ -70,7 +71,9 @@ def test_e2e_conversions():
         engines.append(OcrMacOptions(force_full_page_ocr=True))
 
     for ocr_options in engines:
-        print(f"Converting with ocr_engine: {ocr_options.kind}")
+        print(
+            f"Converting with ocr_engine: {ocr_options.kind}, language: {ocr_options.lang}"
+        )
         converter = get_converter(ocr_options=ocr_options)
         for pdf_path in pdf_paths:
             print(f"converting {pdf_path}")