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doc/devdocs/modules/imageresizer.md

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+# Image Resizer
+
+[Public overview - Microsoft Learn](https://learn.microsoft.com/en-us/windows/powertoys/image-resizer)
+
+## Quick Links
+
+[All Issues](https://github.com/microsoft/PowerToys/issues?q=is%3Aopen%20label%3A%22Product-Image%20Resizer%22)<br>
+[Bugs](https://github.com/microsoft/PowerToys/issues?q=is%3Aopen%20label%3AIssue-Bug%20label%3A%22Product-Image%20Resizer%22)<br>
+[Pull Requests](https://github.com/microsoft/PowerToys/pulls?q=is%3Apr+is%3Aopen+label%3A%22Product-Image+Resizer%22)
+
+Image Resizer is a Windows shell extension that enables batch resizing of images directly from File Explorer.
+
+## Overview
+
+Image Resizer provides a convenient way to resize images without opening a dedicated image editing application. It is accessible through the Windows context menu and allows users to:
+- Resize single or multiple images at once
+- Choose from predefined sizing presets or enter custom dimensions
+- Maintain or modify aspect ratios
+- Create copies or overwrite original files
+- Apply custom filename formats to resized images
+- Select different encoding quality settings
+
+## Architecture
+
+Image Resizer consists of multiple components:
+- Shell Extension DLL (context menu integration)
+- WinUI 3 UI application
+- Core image processing library
+
+### Technology Stack
+- C++/WinRT
+- WPF (UI components)
+- Windows Imaging Component (WIC) for image processing
+- COM for shell integration
+
+## Context Menu Integration
+
+Image Resizer integrates with the Windows context menu following the [PowerToys Context Menu Handlers](../common/context-menus.md) pattern. It uses a dual registration approach to ensure compatibility with both Windows 10 and Windows 11.
+
+### Registration Process
+
+The context menu integration follows the same pattern as PowerRename, using:
+- A traditional shell extension for Windows 10
+- A sparse MSIX package for Windows 11 context menus
+
+For more details on the implementation approach, see the [Dual Registration section](../common/context-menus.md#1-dual-registration-eg-imageresizer-powerrename) in the context menu documentation.
+
+### Context Menu Appearance Logic
+
+Image Resizer dynamically determines when to show the context menu option:
+- `AppxManifest.xml` registers the extension for all file types (`Type="*"`)
+- The shell extension checks if the selected files are images using `AssocGetPerceivedType()`
+- The menu appears only for image files (returns `ECS_ENABLED`); otherwise, it remains hidden (returns `ECS_HIDDEN`)
+
+This approach provides flexibility to support additional file types by modifying only the detection logic without changing the system-level registration.
+
+## UI Implementation
+
+Image Resizer uses WPF for its user interface, as evidenced by the App.xaml.cs file. The UI allows users to:
+- Select from predefined size presets or enter custom dimensions
+- Configure filename format for the resized images
+- Set encoding quality and format options
+- Choose whether to replace or create copies of the original files
+
+From the App.xaml.cs file, we can see that the application:
+- Supports localization through `LanguageHelper.LoadLanguage()`
+- Processes command line arguments via `ResizeBatch.FromCommandLine()`
+- Uses a view model pattern with `MainViewModel`
+- Respects Group Policy settings via `GPOWrapper.GetConfiguredImageResizerEnabledValue()`
+
+## Debugging
+
+### Debugging the Context Menu
+
+See the [Debugging Context Menu Handlers](../common/context-menus.md#debugging-context-menu-handlers) section for general guidance on debugging PowerToys context menu extensions.
+
+For Image Resizer specifically, there are several approaches:
+
+#### Option 1: Manual Registration via Registry
+
+1. Create a registry file (e.g., `register.reg`) with the following content:
+```
+Windows Registry Editor Version 5.00
+
+[HKEY_CLASSES_ROOT\CLSID\{51B4D7E5-7568-4234-B4BB-47FB3C016A69}]
+@="PowerToys Image Resizer Extension"
+
+[HKEY_CLASSES_ROOT\CLSID\{51B4D7E5-7568-4234-B4BB-47FB3C016A69}\InprocServer32]
+@="D:\\PowerToys\\x64\\Debug\\PowerToys.ImageResizerExt.dll"
+"ThreadingModel"="Apartment"
+
+[HKEY_CURRENT_USER\Software\Classes\SystemFileAssociations\.png\ShellEx\ContextMenuHandlers\ImageResizer]
+@="{51B4D7E5-7568-4234-B4BB-47FB3C016A69}"
+```
+
+2. Import the registry file:
+```
+reg import register.reg
+```
+
+3. Restart Explorer to apply changes:
+```
+taskkill /f /im explorer.exe && start explorer.exe
+```
+
+4. Attach the debugger to `explorer.exe`
+
+5. Add breakpoints to relevant code in the Image Resizer shell extension
+
+#### Option 2: Using regsvr32
+
+1. Register the shell extension DLL:
+```
+regsvr32 "D:\PowerToys\x64\Debug\PowerToys.ImageResizerExt.dll"
+```
+
+2. Restart Explorer and attach the debugger as in Option 1
+
+### Common Issues
+
+- Context menu not appearing: 
+  - Ensure the extension is properly registered
+  - Verify you're right-clicking on supported image files
+  - Restart Explorer to clear context menu cache
+  
+- For Windows 11, check AppX package registration:
+  - Use `get-appxpackage -Name *imageresizer*` to verify installation
+  - Use `Remove-AppxPackage` to remove problematic registrations
+
+- Missing UI or processing failures:
+  - Check Event Viewer for application errors
+  - Verify file permissions for both source and destination folders