feat: use OCR pipeline instead of LLM vision for vocab worksheet extraction

process-single-page now runs the full CV pipeline (deskew → dewarp → columns →
rows → cell-first OCR v2 → LLM review) for much better extraction quality.
Falls back to LLM vision if pipeline imports are unavailable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

klausur-service/backend/tests/test_vocab_worksheet.py

@@ -615,6 +615,121 @@ class TestEdgeCases:
         assert len(response.json()) == 5
 
 
+# =============================================
+# OCR PIPELINE INTEGRATION TESTS
+# =============================================
+
+class TestProcessSinglePageOCRPipeline:
+    """Tests for the OCR pipeline integration in process-single-page."""
+
+    @patch("vocab_worksheet_api.OCR_PIPELINE_AVAILABLE", True)
+    @patch("vocab_worksheet_api._run_ocr_pipeline_for_page")
+    def test_process_single_page_uses_ocr_pipeline(self, mock_pipeline, client):
+        """When OCR pipeline is available, process-single-page should use it."""
+        # Create a session with PDF data
+        session_id = str(uuid.uuid4())
+        fake_pdf = b"%PDF-1.4 fake"
+        _sessions[session_id] = {
+            "id": session_id,
+            "name": "Test",
+            "status": "uploaded",
+            "pdf_data": fake_pdf,
+            "pdf_page_count": 2,
+            "vocabulary": [],
+        }
+
+        # Mock the pipeline to return vocab entries
+        mock_pipeline.return_value = [
+            {
+                "id": str(uuid.uuid4()),
+                "english": "to achieve",
+                "german": "erreichen",
+                "example_sentence": "She achieved her goal.",
+                "source_page": 1,
+            },
+            {
+                "id": str(uuid.uuid4()),
+                "english": "goal",
+                "german": "Ziel",
+                "example_sentence": "",
+                "source_page": 1,
+            },
+        ]
+
+        with patch("vocab_worksheet_api.convert_pdf_page_to_image", new_callable=AsyncMock) as mock_convert:
+            mock_convert.return_value = b"fake-png-data"
+            response = client.post(f"/api/v1/vocab/sessions/{session_id}/process-single-page/0")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["success"] is True
+        assert data["vocabulary_count"] == 2
+        assert data["vocabulary"][0]["english"] == "to achieve"
+        assert data["vocabulary"][0]["source_page"] == 1
+
+        # Verify pipeline was called with correct args
+        mock_pipeline.assert_called_once_with(b"fake-png-data", 0, session_id)
+
+    @patch("vocab_worksheet_api.OCR_PIPELINE_AVAILABLE", True)
+    @patch("vocab_worksheet_api._run_ocr_pipeline_for_page")
+    def test_process_single_page_ocr_pipeline_error_returns_failure(self, mock_pipeline, client):
+        """When the OCR pipeline raises an exception, return success=False."""
+        session_id = str(uuid.uuid4())
+        _sessions[session_id] = {
+            "id": session_id,
+            "name": "Test",
+            "status": "uploaded",
+            "pdf_data": b"%PDF-1.4 fake",
+            "pdf_page_count": 1,
+            "vocabulary": [],
+        }
+
+        mock_pipeline.side_effect = ValueError("Column detection failed")
+
+        with patch("vocab_worksheet_api.convert_pdf_page_to_image", new_callable=AsyncMock) as mock_convert:
+            mock_convert.return_value = b"fake-png-data"
+            response = client.post(f"/api/v1/vocab/sessions/{session_id}/process-single-page/0")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["success"] is False
+        assert "OCR pipeline error" in data["error"]
+        assert data["vocabulary"] == []
+
+    @patch("vocab_worksheet_api.OCR_PIPELINE_AVAILABLE", False)
+    @patch("vocab_worksheet_api.extract_vocabulary_from_image", new_callable=AsyncMock)
+    def test_process_single_page_fallback_to_llm(self, mock_llm_extract, client):
+        """When OCR pipeline is not available, fall back to LLM vision."""
+        session_id = str(uuid.uuid4())
+        _sessions[session_id] = {
+            "id": session_id,
+            "name": "Test",
+            "status": "uploaded",
+            "pdf_data": b"%PDF-1.4 fake",
+            "pdf_page_count": 1,
+            "vocabulary": [],
+        }
+
+        mock_entry = MagicMock()
+        mock_entry.dict.return_value = {
+            "id": str(uuid.uuid4()),
+            "english": "house",
+            "german": "Haus",
+            "example_sentence": "",
+        }
+        mock_llm_extract.return_value = ([mock_entry], 0.85, None)
+
+        with patch("vocab_worksheet_api.convert_pdf_page_to_image", new_callable=AsyncMock) as mock_convert:
+            mock_convert.return_value = b"fake-png-data"
+            response = client.post(f"/api/v1/vocab/sessions/{session_id}/process-single-page/0")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert data["success"] is True
+        assert data["vocabulary_count"] == 1
+        assert data["vocabulary"][0]["english"] == "house"
+
+
 # =============================================
 # RUN TESTS
 # =============================================

klausur-service/backend/vocab_worksheet_api.py

@@ -59,6 +59,29 @@ except ImportError:
     CV_PIPELINE_AVAILABLE = False
     logger.warning("CV vocab pipeline not available")
 
+# Try to import OCR Pipeline functions (for process-single-page)
+try:
+    import cv2
+    import numpy as np
+    from cv_vocab_pipeline import (
+        deskew_image, deskew_image_by_word_alignment, deskew_image_iterative,
+        dewarp_image, create_ocr_image,
+        detect_column_geometry, analyze_layout_by_words, analyze_layout, create_layout_image,
+        detect_row_geometry, build_cell_grid_v2,
+        _cells_to_vocab_entries, _detect_sub_columns, _detect_header_footer_gaps,
+        expand_narrow_columns, classify_column_types, llm_review_entries,
+        _fix_phonetic_brackets,
+        PageRegion, RowGeometry,
+    )
+    from ocr_pipeline_session_store import (
+        create_session_db as create_pipeline_session_db,
+        update_session_db as update_pipeline_session_db,
+    )
+    OCR_PIPELINE_AVAILABLE = True
+except ImportError as _ocr_pipe_err:
+    OCR_PIPELINE_AVAILABLE = False
+    logger.warning(f"OCR Pipeline functions not available: {_ocr_pipe_err}")
+
 # Try to import Grid Detection Service
 try:
     from services.grid_detection_service import GridDetectionService
@@ -1221,11 +1244,12 @@ async def process_single_page(
     page_number: int,
 ):
     """
-    Process a SINGLE page of an uploaded PDF - completely isolated.
+    Process a SINGLE page of an uploaded PDF using the OCR pipeline.
+
+    Uses the multi-step CV pipeline (deskew → dewarp → columns → rows → words)
+    instead of LLM vision for much better extraction quality.
 
-    This endpoint processes one page at a time to avoid LLM context issues.
     The frontend should call this sequentially for each page.
-
     Returns the vocabulary for just this one page.
     """
     logger.info(f"Processing SINGLE page {page_number + 1} for session {session_id}")
@@ -1244,33 +1268,50 @@ async def process_single_page(
     if page_number < 0 or page_number >= page_count:
         raise HTTPException(status_code=400, detail=f"Invalid page number. PDF has {page_count} pages (0-indexed).")
 
-    # Convert just this ONE page to image
+    # Convert just this ONE page to PNG
     image_data = await convert_pdf_page_to_image(pdf_data, page_number, thumbnail=False)
 
-    # Extract vocabulary from this single page
-    vocabulary, confidence, error = await extract_vocabulary_from_image(
-        image_data,
-        f"page_{page_number + 1}.png",
-        page_number=page_number
-    )
-
-    if error:
-        logger.warning(f"Page {page_number + 1} failed: {error}")
-        return {
-            "session_id": session_id,
-            "page_number": page_number + 1,
-            "success": False,
-            "error": error,
-            "vocabulary": [],
-            "vocabulary_count": 0,
-        }
-
-    # Convert vocabulary entries to dicts with page info
-    page_vocabulary = []
-    for entry in vocabulary:
-        entry_dict = entry.dict() if hasattr(entry, 'dict') else (entry.__dict__.copy() if hasattr(entry, '__dict__') else dict(entry))
-        entry_dict['source_page'] = page_number + 1
-        page_vocabulary.append(entry_dict)
+    # --- OCR Pipeline path ---
+    if OCR_PIPELINE_AVAILABLE:
+        try:
+            page_vocabulary = await _run_ocr_pipeline_for_page(
+                image_data, page_number, session_id,
+            )
+        except Exception as e:
+            logger.error(f"OCR pipeline failed for page {page_number + 1}: {e}", exc_info=True)
+            return {
+                "session_id": session_id,
+                "page_number": page_number + 1,
+                "success": False,
+                "error": f"OCR pipeline error: {e}",
+                "vocabulary": [],
+                "vocabulary_count": 0,
+            }
+    else:
+        # Fallback to LLM vision extraction
+        logger.warning("OCR pipeline not available, falling back to LLM vision")
+        vocabulary, confidence, error = await extract_vocabulary_from_image(
+            image_data,
+            f"page_{page_number + 1}.png",
+            page_number=page_number
+        )
+        if error:
+            logger.warning(f"Page {page_number + 1} failed: {error}")
+            return {
+                "session_id": session_id,
+                "page_number": page_number + 1,
+                "success": False,
+                "error": error,
+                "vocabulary": [],
+                "vocabulary_count": 0,
+            }
+        page_vocabulary = []
+        for entry in vocabulary:
+            entry_dict = entry.dict() if hasattr(entry, 'dict') else (entry.__dict__.copy() if hasattr(entry, '__dict__') else dict(entry))
+            entry_dict['source_page'] = page_number + 1
+            if 'id' not in entry_dict or not entry_dict['id']:
+                entry_dict['id'] = str(uuid.uuid4())
+            page_vocabulary.append(entry_dict)
 
     logger.info(f"Page {page_number + 1}: {len(page_vocabulary)} Vokabeln extrahiert")
 
@@ -1290,10 +1331,225 @@ async def process_single_page(
         "vocabulary": page_vocabulary,
         "vocabulary_count": len(page_vocabulary),
         "total_vocabulary_count": len(existing_vocab),
-        "extraction_confidence": confidence,
+        "extraction_confidence": 0.9,
     }
 
 
+async def _run_ocr_pipeline_for_page(
+    png_data: bytes,
+    page_number: int,
+    vocab_session_id: str,
+) -> list:
+    """Run the full OCR pipeline on a single page image and return vocab entries.
+
+    Steps: deskew → dewarp → columns → rows → words → (LLM review)
+    Returns list of dicts with keys: id, english, german, example_sentence, source_page
+    """
+    import time as _time
+
+    t_total = _time.time()
+
+    # 1. Decode PNG → BGR numpy array
+    arr = np.frombuffer(png_data, dtype=np.uint8)
+    img_bgr = cv2.imdecode(arr, cv2.IMREAD_COLOR)
+    if img_bgr is None:
+        raise ValueError("Failed to decode page image")
+
+    img_h, img_w = img_bgr.shape[:2]
+    logger.info(f"OCR Pipeline page {page_number + 1}: image {img_w}x{img_h}")
+
+    # 2. Create pipeline session in DB (for debugging in admin UI)
+    pipeline_session_id = str(uuid.uuid4())
+    try:
+        await create_pipeline_session_db(
+            pipeline_session_id,
+            name=f"vocab-ws-{vocab_session_id[:8]}-p{page_number + 1}",
+            filename=f"page_{page_number + 1}.png",
+            original_png=png_data,
+        )
+    except Exception as e:
+        logger.warning(f"Could not create pipeline session in DB: {e}")
+
+    # 3. Deskew (3 methods, pick best)
+    t0 = _time.time()
+    try:
+        deskewed_hough, angle_hough = deskew_image(img_bgr.copy())
+    except Exception:
+        deskewed_hough, angle_hough = img_bgr, 0.0
+
+    success_enc, png_orig = cv2.imencode(".png", img_bgr)
+    orig_bytes = png_orig.tobytes() if success_enc else b""
+    try:
+        deskewed_wa_bytes, angle_wa = deskew_image_by_word_alignment(orig_bytes)
+    except Exception:
+        deskewed_wa_bytes, angle_wa = orig_bytes, 0.0
+
+    try:
+        deskewed_iter, angle_iterative, _ = deskew_image_iterative(img_bgr.copy())
+    except Exception:
+        deskewed_iter, angle_iterative = img_bgr, 0.0
+
+    # Pick best
+    if abs(angle_iterative) >= 0.05:
+        deskewed_bgr = deskewed_iter
+        angle_applied = angle_iterative
+    elif abs(angle_wa) >= abs(angle_hough) or abs(angle_hough) < 0.1:
+        angle_applied = angle_wa
+        wa_array = np.frombuffer(deskewed_wa_bytes, dtype=np.uint8)
+        deskewed_bgr = cv2.imdecode(wa_array, cv2.IMREAD_COLOR)
+        if deskewed_bgr is None:
+            deskewed_bgr = deskewed_hough
+            angle_applied = angle_hough
+    else:
+        deskewed_bgr = deskewed_hough
+        angle_applied = angle_hough
+
+    logger.info(f"  deskew: hough={angle_hough:.2f} wa={angle_wa:.2f} "
+                f"iter={angle_iterative:.2f} → applied={angle_applied:.2f} "
+                f"({_time.time() - t0:.1f}s)")
+
+    # 4. Dewarp
+    t0 = _time.time()
+    dewarped_bgr, dewarp_info = dewarp_image(deskewed_bgr)
+    logger.info(f"  dewarp: shear={dewarp_info['shear_degrees']:.3f} ({_time.time() - t0:.1f}s)")
+
+    # 5. Column detection
+    t0 = _time.time()
+    ocr_img = create_ocr_image(dewarped_bgr)
+    h, w = ocr_img.shape[:2]
+
+    geo_result = detect_column_geometry(ocr_img, dewarped_bgr)
+    if geo_result is None:
+        layout_img = create_layout_image(dewarped_bgr)
+        regions = analyze_layout(layout_img, ocr_img)
+        word_dicts = None
+        inv = None
+        content_bounds = None
+    else:
+        geometries, left_x, right_x, top_y, bottom_y, word_dicts, inv = geo_result
+        content_w = right_x - left_x
+        header_y, footer_y = _detect_header_footer_gaps(inv, w, h) if inv is not None else (None, None)
+        geometries = _detect_sub_columns(geometries, content_w, left_x=left_x,
+                                          top_y=top_y, header_y=header_y, footer_y=footer_y)
+        geometries = expand_narrow_columns(geometries, content_w, left_x, word_dicts)
+        regions = classify_column_types(geometries, content_w, top_y, w, h, bottom_y,
+                                        left_x=left_x, right_x=right_x, inv=inv)
+        content_bounds = (left_x, right_x, top_y, bottom_y)
+
+    logger.info(f"  columns: {len(regions)} detected ({_time.time() - t0:.1f}s)")
+
+    # 6. Row detection
+    t0 = _time.time()
+    if word_dicts is None or inv is None or content_bounds is None:
+        # Re-run geometry detection to get intermediates
+        geo_result2 = detect_column_geometry(ocr_img, dewarped_bgr)
+        if geo_result2 is None:
+            raise ValueError("Column geometry detection failed — cannot detect rows")
+        _, left_x, right_x, top_y, bottom_y, word_dicts, inv = geo_result2
+        content_bounds = (left_x, right_x, top_y, bottom_y)
+
+    left_x, right_x, top_y, bottom_y = content_bounds
+    rows = detect_row_geometry(inv, word_dicts, left_x, right_x, top_y, bottom_y)
+    logger.info(f"  rows: {len(rows)} detected ({_time.time() - t0:.1f}s)")
+
+    # 7. Word recognition (cell-first OCR v2)
+    t0 = _time.time()
+    col_regions = regions  # already PageRegion objects
+
+    # Populate row.words for word_count filtering
+    for row in rows:
+        row_y_rel = row.y - top_y
+        row_bottom_rel = row_y_rel + row.height
+        row.words = [
+            wd for wd in word_dicts
+            if row_y_rel <= wd['top'] + wd['height'] / 2 < row_bottom_rel
+        ]
+        row.word_count = len(row.words)
+
+    cells, columns_meta = build_cell_grid_v2(
+        ocr_img, col_regions, rows, img_w, img_h,
+        ocr_engine="auto", img_bgr=dewarped_bgr,
+    )
+
+    col_types = {c['type'] for c in columns_meta}
+    is_vocab = bool(col_types & {'column_en', 'column_de'})
+    logger.info(f"  words: {len(cells)} cells, vocab={is_vocab} ({_time.time() - t0:.1f}s)")
+
+    if not is_vocab:
+        logger.warning(f"  Page {page_number + 1}: layout is not vocab table "
+                       f"(types: {col_types}), returning empty")
+        return []
+
+    # 8. Map cells → vocab entries
+    entries = _cells_to_vocab_entries(cells, columns_meta)
+    entries = _fix_phonetic_brackets(entries, pronunciation="british")
+
+    # 9. Optional LLM review
+    try:
+        review_result = await llm_review_entries(entries)
+        if review_result and review_result.get("changes"):
+            # Apply corrections
+            changes_map = {}
+            for ch in review_result["changes"]:
+                idx = ch.get("index")
+                if idx is not None:
+                    changes_map[idx] = ch
+            for idx, ch in changes_map.items():
+                if 0 <= idx < len(entries):
+                    for field in ("english", "german", "example"):
+                        if ch.get(field) and ch[field] != entries[idx].get(field):
+                            entries[idx][field] = ch[field]
+            logger.info(f"  llm review: {len(review_result['changes'])} corrections applied")
+    except Exception as e:
+        logger.warning(f"  llm review skipped: {e}")
+
+    # 10. Map to frontend format
+    page_vocabulary = []
+    for entry in entries:
+        if not entry.get("english") and not entry.get("german"):
+            continue  # skip empty rows
+        page_vocabulary.append({
+            "id": str(uuid.uuid4()),
+            "english": entry.get("english", ""),
+            "german": entry.get("german", ""),
+            "example_sentence": entry.get("example", ""),
+            "source_page": page_number + 1,
+        })
+
+    # 11. Update pipeline session in DB (for admin debugging)
+    try:
+        success_dsk, dsk_buf = cv2.imencode(".png", deskewed_bgr)
+        deskewed_png = dsk_buf.tobytes() if success_dsk else None
+        success_dwp, dwp_buf = cv2.imencode(".png", dewarped_bgr)
+        dewarped_png = dwp_buf.tobytes() if success_dwp else None
+
+        await update_pipeline_session_db(
+            pipeline_session_id,
+            deskewed_png=deskewed_png,
+            dewarped_png=dewarped_png,
+            deskew_result={"angle_applied": round(angle_applied, 3)},
+            dewarp_result={"shear_degrees": dewarp_info.get("shear_degrees", 0)},
+            column_result={"columns": [{"type": r.type, "x": r.x, "y": r.y,
+                                         "width": r.width, "height": r.height}
+                                        for r in col_regions]},
+            row_result={"total_rows": len(rows)},
+            word_result={
+                "entry_count": len(page_vocabulary),
+                "layout": "vocab",
+                "vocab_entries": entries,
+            },
+            current_step=6,
+        )
+    except Exception as e:
+        logger.warning(f"Could not update pipeline session: {e}")
+
+    total_duration = _time.time() - t_total
+    logger.info(f"OCR Pipeline page {page_number + 1}: "
+                f"{len(page_vocabulary)} vocab entries in {total_duration:.1f}s")
+
+    return page_vocabulary
+
+
 @router.post("/sessions/{session_id}/process-pages")
 async def process_pdf_pages(
     session_id: str,