DocScanner - High-Performance Document Scanning & Contrast Enhancement

DocScanner is a modern Windows desktop application built with .NET 8 WPF and OpenCvSharp4. It provides professional document scanning capabilities—including perspective unwarping, illumination normalization (shadow elimination), high-contrast optical enhancement filters, and multi-page PDF compilation.

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Architectural Overview

The application is structured around a modular MVVM architecture coupled with high-performance C++ OpenCV computer vision bindings:

[ Input: Image / Drag-Drop / Clipboard ]
                   │
                   ▼
┌─────────────────────────────────────────────────────────────┐
│                 Document Processing Pipeline                │
├─────────────────────────────────────────────────────────────┤
│ 1. Boundary & Quad Detection (Canny + Convex Hull + Approx) │
│ 2. Perspective Homography Warping (4-Corner Unwarping)      │
│ 3. Illumination Normalization (Morphological BG Division)   │
│ 4. Adaptive Contrast & Sharpening Filters (LAB CLAHE)       │
│ 5. Multi-Page Session Queue & PDF Compilation (PdfSharp)    │
└─────────────────────────────────────────────────────────────┘
                   │
                   ▼
[ Output: Multi-Page PDF / High-Res PNG / JPEG / TIFF / WebP ]

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Key Features

1. Optical Illumination Normalization & Shadow Removal

• Employs morphological dilation and Gaussian background division model (Image / Dilated_Background * 255).
• Eliminates phone shadows, finger shadows, gradient lighting, and yellowed paper tones.

2. Enhancement Presets

• Enhanced Color: High-performance illumination normalization. Flattens backgrounds to pure paper white, enhances character edge contrast via high-pass unsharp masking, and preserves vivid color on stamps, signatures, and markers in LAB color space.
• B&W Clean Document: Adaptive Gaussian binarization (Cv2.AdaptiveThreshold) with morphological noise reduction, generating pure #000000 text on #FFFFFF paper suitable for high-speed printing and OCR.
• Grayscale High-Contrast: Contrast-Limited Adaptive Histogram Equalization (CLAHE) for monochrome legal and academic records.
• Detail Sharpening: High-frequency edge boosting for soft-focus or motion-blurred captures.
• Custom Mode: Real-time slider controls for Shadow Suppression, Contrast, Brightness, Sharpening, and Binarization Threshold.

3. Lightweight OCR Text-Aware & Perspective Crop

• Lightweight OCR Text Saliency: High-speed morphological character stroke detection (Sobel + Otsu + horizontal kernel bridging) that accurately identifies the bounding envelope of text lines, signatures, and printed paragraphs.
• Hybrid Boundary Fusion: Validates paper candidate contours against text containment (>80%) to avoid cropping into text or capturing extraneous desk background.
• Interactive 4-Point Quadrilateral Manipulation: Vector-based WPF overlay (InteractiveCropCanvas) with draggable corner handles, midpoint edge sliders, and dimmed boundary masks.

4. Multi-Page Document Management & PDF Export

• Thumbnail sidebar for page reordering (Move Up, Move Down, Delete).
• Asynchronous non-blocking background rendering.
• Direct multi-page PDF document compilation with A4 page fitting and DPI scaling.
• Batch export to local directory.

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System Requirements & Prerequisites

• Operating System: Windows 10 / Windows 11 (x64)
• Runtime: .NET 8.0 Windows Desktop Runtime (Microsoft.WindowsDesktop.App 8.0+)
• Dependencies: OpenCvSharp4 (4.13+), OpenCvSharp4.runtime.win, PdfSharpCore, CommunityToolkit.Mvvm

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Build & Execution Instructions

Building the Application

To build the solution in Release mode:

cd DocScanner
dotnet build -c Release

Running the Application

To launch the desktop application:

cd DocScanner
dotnet run -c Release

Publishing Standalone Self-Contained Binary (Zero Dependencies)

To bundle the full .NET 8 runtime, CoreCLR, and all native C++ libraries (OpenCvSharpExtern.dll) with zero external prerequisites:

dotnet publish DocScanner/DocScanner.csproj -c Release -r win-x64 --self-contained true -o ./publish /p:PublishSingleFile=false /p:IncludeNativeLibrariesForSelfExtract=true

Compiling Native Setup Installer (.exe)

To compile the standalone Windows installer wizard using Inno Setup:

"C:\Program Files (x86)\Inno Setup 6\ISCC.exe" installer/DocScanner_Setup.iss

The compiled installer is generated in installer/output/DocScanner_Setup_v0.4.0_x64.exe.

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File Structure

DocScanner/
├── Controls/
│   └── InteractiveCropCanvas.cs    # Custom WPF vector overlay for 4-point quadrilateral dragging
├── Converters/
│   └── ValueConverters.cs          # WPF XAML UI bindings converters
├── Models/
│   ├── DocumentCorners.cs          # Quad coordinate data model (TopLeft, TopRight, BR, BL)
│   ├── EnhancementFilterType.cs    # Filter presets enum (EnhancedColor, B&W, Grayscale, etc.)
│   ├── FilterParameters.cs         # Numerical tuning parameters (Contrast, Sharpness, etc.)
│   └── ScannedPage.cs              # Multi-page document model and thumbnail cache
├── Services/
│   ├── IImageProcessingService.cs  # Computer vision processing contract
│   ├── ImageProcessingService.cs   # OpenCV processing algorithms & filter implementations
│   ├── IPdfExportService.cs        # PDF export service contract
│   └── PdfExportService.cs         # PdfSharp multi-page document compiler
├── Themes/
│   └── DarkTheme.xaml              # Dark Modern (#1f1f1f) theme dictionary
├── ViewModels/
│   └── MainViewModel.cs            # MVVM ViewModel with reactive debounced processing
├── App.xaml / App.xaml.cs          # Application entry point
├── MainWindow.xaml / .cs           # 3-panel UI layout (Sidebar, Canvas, Controls)
└── DocScanner.csproj               # .NET 8 WPF project file