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()`
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:
