feat: add OCR engine abstraction layer (refs #116)
Introduce pluggable OcrEngine ABC with PaddleOCR PP-OCRv4 as primary engine and Tesseract wrapper for backward compatibility. Engine factory reads OCR_PRIMARY_ENGINE config to instantiate the correct engine. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Eric Gullickson
27
ocr/app/engines/__init__.py
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27
ocr/app/engines/__init__.py
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"""OCR engine abstraction layer.
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Provides a pluggable engine interface for OCR processing,
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decoupling extractors from specific OCR libraries.
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"""
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from app.engines.base_engine import (
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EngineError,
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EngineProcessingError,
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EngineUnavailableError,
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OcrConfig,
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OcrEngine,
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OcrEngineResult,
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WordBox,
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)
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from app.engines.engine_factory import create_engine
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__all__ = [
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"OcrEngine",
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"OcrConfig",
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"OcrEngineResult",
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"WordBox",
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"EngineError",
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"EngineUnavailableError",
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"EngineProcessingError",
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"create_engine",
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]
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88
ocr/app/engines/base_engine.py
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88
ocr/app/engines/base_engine.py
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"""OCR engine abstract base class and shared data types."""
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from abc import ABC, abstractmethod
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from dataclasses import dataclass, field
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from typing import Any
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# --- Exception hierarchy ---
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class EngineError(Exception):
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"""Base exception for all OCR engine errors."""
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class EngineUnavailableError(EngineError):
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"""Raised when an engine cannot be initialized (missing binary, bad config)."""
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class EngineProcessingError(EngineError):
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"""Raised when an engine fails to process an image."""
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# --- Data types ---
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@dataclass
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class WordBox:
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"""A single recognized word with position and confidence."""
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text: str
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confidence: float # 0.0-1.0
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x: int = 0
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y: int = 0
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width: int = 0
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height: int = 0
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@dataclass
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class OcrConfig:
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"""Engine-agnostic OCR configuration.
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Common fields cover the most frequent needs. Engine-specific
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parameters go into ``hints`` so the interface stays stable.
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"""
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char_whitelist: str | None = None # e.g. VIN: "ABCDEFGHJKLMNPRSTUVWXYZ0123456789"
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single_line: bool = False # Treat image as a single text line
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single_word: bool = False # Treat image as a single word
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use_angle_cls: bool = True # Enable angle classification (PaddleOCR)
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hints: dict[str, Any] = field(default_factory=dict)
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@dataclass
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class OcrEngineResult:
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"""Normalized result returned by every engine implementation."""
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text: str
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confidence: float # 0.0-1.0
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word_boxes: list[WordBox]
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engine_name: str # "paddleocr", "tesseract", "google_vision"
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# --- Abstract base ---
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class OcrEngine(ABC):
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"""Abstract base class that all OCR engines must implement."""
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@abstractmethod
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def recognize(self, image_bytes: bytes, config: OcrConfig) -> OcrEngineResult:
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"""Run OCR on preprocessed image bytes.
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Args:
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image_bytes: Raw image bytes (PNG/JPEG).
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config: Engine-agnostic configuration.
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Returns:
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Normalized OCR result.
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Raises:
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EngineProcessingError: If recognition fails.
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EngineUnavailableError: If the engine is not ready.
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"""
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@property
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@abstractmethod
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def name(self) -> str:
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"""Short identifier used in OcrEngineResult.engine_name."""
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52
ocr/app/engines/engine_factory.py
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ocr/app/engines/engine_factory.py
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"""Factory function for creating OCR engine instances from configuration."""
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import logging
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from app.config import settings
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from app.engines.base_engine import EngineUnavailableError, OcrEngine
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logger = logging.getLogger(__name__)
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# Valid engine identifiers
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_ENGINE_REGISTRY: dict[str, str] = {
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"paddleocr": "app.engines.paddle_engine.PaddleOcrEngine",
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"tesseract": "app.engines.tesseract_engine.TesseractEngine",
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}
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def create_engine(engine_name: str | None = None) -> OcrEngine:
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"""Instantiate an OCR engine by name (defaults to config value).
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Args:
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engine_name: Engine identifier ("paddleocr", "tesseract").
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Falls back to ``settings.ocr_primary_engine``.
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Returns:
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Initialized OcrEngine instance.
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Raises:
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EngineUnavailableError: If the engine cannot be loaded or initialized.
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"""
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name = (engine_name or settings.ocr_primary_engine).lower().strip()
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if name not in _ENGINE_REGISTRY:
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raise EngineUnavailableError(
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f"Unknown engine '{name}'. Available: {list(_ENGINE_REGISTRY.keys())}"
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)
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module_path, class_name = _ENGINE_REGISTRY[name].rsplit(".", 1)
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try:
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import importlib
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module = importlib.import_module(module_path)
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engine_cls = getattr(module, class_name)
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engine: OcrEngine = engine_cls()
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logger.info("Created OCR engine: %s", name)
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return engine
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except EngineUnavailableError:
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raise
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except Exception as exc:
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raise EngineUnavailableError(
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f"Failed to create engine '{name}': {exc}"
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) from exc
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133
ocr/app/engines/paddle_engine.py
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133
ocr/app/engines/paddle_engine.py
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"""PaddleOCR engine wrapper using PP-OCRv4 models."""
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import io
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import logging
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from typing import Any
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from app.engines.base_engine import (
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EngineProcessingError,
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EngineUnavailableError,
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OcrConfig,
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OcrEngine,
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OcrEngineResult,
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WordBox,
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)
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logger = logging.getLogger(__name__)
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class PaddleOcrEngine(OcrEngine):
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"""PaddleOCR PP-OCRv4 engine with angle classification, CPU-only."""
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def __init__(self) -> None:
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self._ocr: Any | None = None
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@property
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def name(self) -> str:
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return "paddleocr"
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def _get_ocr(self) -> Any:
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"""Lazy-initialize PaddleOCR instance on first use."""
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if self._ocr is not None:
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return self._ocr
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try:
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from paddleocr import PaddleOCR # type: ignore[import-untyped]
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self._ocr = PaddleOCR(
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use_angle_cls=True,
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lang="en",
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use_gpu=False,
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show_log=False,
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)
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logger.info("PaddleOCR PP-OCRv4 initialized (CPU, angle_cls=True)")
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return self._ocr
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except ImportError as exc:
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raise EngineUnavailableError(
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"paddleocr is not installed. "
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"Install with: pip install paddlepaddle paddleocr"
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) from exc
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except Exception as exc:
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raise EngineUnavailableError(
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f"Failed to initialize PaddleOCR: {exc}"
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) from exc
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def recognize(self, image_bytes: bytes, config: OcrConfig) -> OcrEngineResult:
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"""Run PaddleOCR on image bytes.
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PaddleOCR returns: list of pages, each page is a list of
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``[[box_coords], (text, confidence)]`` entries.
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"""
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ocr = self._get_ocr()
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try:
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import numpy as np # type: ignore[import-untyped]
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from PIL import Image
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image = Image.open(io.BytesIO(image_bytes)).convert("RGB")
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img_array = np.array(image)
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# PaddleOCR accepts numpy arrays
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results = ocr.ocr(img_array, cls=config.use_angle_cls)
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if not results or not results[0]:
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return OcrEngineResult(
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text="",
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confidence=0.0,
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word_boxes=[],
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engine_name=self.name,
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)
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word_boxes: list[WordBox] = []
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texts: list[str] = []
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confidences: list[float] = []
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for line in results[0]:
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box_coords = line[0] # [[x1,y1],[x2,y2],[x3,y3],[x4,y4]]
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text = line[1][0]
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conf = float(line[1][1])
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# Apply character whitelist filter if configured
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if config.char_whitelist:
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allowed = set(config.char_whitelist)
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text = "".join(ch for ch in text if ch in allowed)
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if not text.strip():
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continue
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# Convert quadrilateral to bounding box
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xs = [pt[0] for pt in box_coords]
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ys = [pt[1] for pt in box_coords]
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x_min, y_min = int(min(xs)), int(min(ys))
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x_max, y_max = int(max(xs)), int(max(ys))
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word_boxes.append(
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WordBox(
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text=text.strip(),
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confidence=conf,
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x=x_min,
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y=y_min,
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width=x_max - x_min,
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height=y_max - y_min,
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)
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)
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texts.append(text.strip())
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confidences.append(conf)
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combined_text = " ".join(texts)
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avg_confidence = (
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sum(confidences) / len(confidences) if confidences else 0.0
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)
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return OcrEngineResult(
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text=combined_text,
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confidence=avg_confidence,
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word_boxes=word_boxes,
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engine_name=self.name,
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)
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except (EngineUnavailableError, EngineProcessingError):
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raise
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except Exception as exc:
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raise EngineProcessingError(
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f"PaddleOCR recognition failed: {exc}"
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) from exc
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114
ocr/app/engines/tesseract_engine.py
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ocr/app/engines/tesseract_engine.py
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"""Tesseract engine wrapper for backward compatibility."""
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import io
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import logging
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from app.config import settings
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from app.engines.base_engine import (
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EngineProcessingError,
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EngineUnavailableError,
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OcrConfig,
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OcrEngine,
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OcrEngineResult,
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WordBox,
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)
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logger = logging.getLogger(__name__)
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class TesseractEngine(OcrEngine):
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"""pytesseract wrapper conforming to the OcrEngine interface."""
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def __init__(self) -> None:
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try:
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import pytesseract # type: ignore[import-untyped]
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pytesseract.pytesseract.tesseract_cmd = settings.tesseract_cmd
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self._pytesseract = pytesseract
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logger.info("TesseractEngine initialized (cmd=%s)", settings.tesseract_cmd)
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except ImportError as exc:
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raise EngineUnavailableError(
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"pytesseract is not installed. "
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"Install with: pip install pytesseract"
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) from exc
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@property
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def name(self) -> str:
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return "tesseract"
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def recognize(self, image_bytes: bytes, config: OcrConfig) -> OcrEngineResult:
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"""Run Tesseract OCR on image bytes."""
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try:
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from PIL import Image
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image = Image.open(io.BytesIO(image_bytes))
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# Build Tesseract config string from OcrConfig
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tess_config = self._build_config(config)
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# Get word-level data
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ocr_data = self._pytesseract.image_to_data(
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image,
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config=tess_config,
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output_type=self._pytesseract.Output.DICT,
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)
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word_boxes: list[WordBox] = []
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texts: list[str] = []
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confidences: list[float] = []
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for i, text in enumerate(ocr_data["text"]):
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conf = int(ocr_data["conf"][i])
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if text.strip() and conf > 0:
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normalized_conf = conf / 100.0
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word_boxes.append(
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WordBox(
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text=text.strip(),
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confidence=normalized_conf,
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x=int(ocr_data["left"][i]),
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y=int(ocr_data["top"][i]),
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width=int(ocr_data["width"][i]),
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height=int(ocr_data["height"][i]),
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)
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)
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texts.append(text.strip())
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confidences.append(normalized_conf)
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combined_text = " ".join(texts)
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avg_confidence = (
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sum(confidences) / len(confidences) if confidences else 0.0
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)
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return OcrEngineResult(
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text=combined_text,
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confidence=avg_confidence,
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word_boxes=word_boxes,
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engine_name=self.name,
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)
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except (EngineUnavailableError, EngineProcessingError):
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raise
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except Exception as exc:
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raise EngineProcessingError(
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f"Tesseract recognition failed: {exc}"
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) from exc
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def _build_config(self, config: OcrConfig) -> str:
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"""Translate OcrConfig into a Tesseract CLI config string."""
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parts: list[str] = []
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# Page segmentation mode
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if config.single_word:
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parts.append("--psm 8")
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elif config.single_line:
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parts.append("--psm 7")
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else:
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# Default: assume uniform block of text
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psm = config.hints.get("psm", 6)
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parts.append(f"--psm {psm}")
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# Character whitelist
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if config.char_whitelist:
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parts.append(f"-c tessedit_char_whitelist={config.char_whitelist}")
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return " ".join(parts)
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