> ## Documentation Index
> Fetch the complete documentation index at: https://docs.upsonic.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Architecture

> Understanding the layered OCR pipeline architecture

## Layered Architecture

The Unified OCR system is built on a layered architecture that separates concerns and enables flexible engine composition.

### Layer 0 — Document Preparation

Handles file validation, PDF-to-image conversion, and image preprocessing before OCR processing begins.

* **File validation**: Checks file existence and supported formats (.png, .jpg, .jpeg, .bmp, .tiff, .tif, .webp, .pdf)
* **PDF conversion**: Converts PDF pages to images at configurable DPI using `convert_document`
* **Image preprocessing**: Optional rotation correction, contrast enhancement, and noise reduction

### Layer 1 — OCR Engines

Each OCR engine runs independently on prepared images and returns structured `OCRResult` objects.

Available engines:

* `EasyOCREngine` — Deep learning-based, 80+ languages
* `RapidOCREngine` — ONNX Runtime-based, lightweight and fast
* `TesseractOCREngine` — Google's open-source engine, 100+ languages
* `DeepSeekOCREngine` — VLLM-based batch processing
* `DeepSeekOllamaOCREngine` — Ollama-based local processing
* `PaddleOCREngine`, `PPStructureV3Engine`, `PPChatOCRv4Engine`, `PaddleOCRVLEngine` — PaddlePaddle family

### Orchestrator — `OCR` Class

The top-level `OCR` class orchestrates the full pipeline:

1. Receives a file path
2. Delegates to Layer 0 for document preparation
3. Passes prepared images to the configured Layer 1 engine
4. Aggregates results, calculates confidence scores, and tracks metrics

## Pipeline Flow

```
File (PDF/Image)
    │
    ▼
Layer 0: convert_document → preprocessed images
    │
    ▼
Layer 1: Engine.process(images) → OCRResult
    │
    ▼
Orchestrator: aggregate results, metrics, confidence
    │
    ▼
Final OCRResult
```