WP WebP Intervention Converter

A complete WordPress plugin that converts JPG/PNG images to WebP format using Intervention Image v3, with automatic file size optimization.

Features

• ✅ Auto Convert on Upload: Automatically converts images to WebP when uploaded to Media Library
• ✅ File Size Optimization: Intelligent algorithm reduces quality and/or resizes images to meet file size limits
• ✅ Batch Conversion: Convert all existing images with progress tracking
• ✅ Frontend URL Replacement: Automatically serves WebP versions on frontend while preserving originals
• ✅ Configurable Settings: Control quality, file size limits, and enable/disable auto-conversion
• ✅ PHP 8.1+ Compatible: Modern, object-oriented code

Installation

1. Upload the plugin to /wp-content/plugins/wp-webp-intervention-converter/

2. Install Intervention Image v3 via Composer:

   cd wp-content/plugins/wp-webp-intervention-converter
   composer require intervention/image

3. Activate the plugin through the 'Plugins' menu in WordPress

4. Configure settings at 'WebP Converter' menu in WordPress admin

Requirements

• PHP 8.1 or higher
• WordPress 5.0 or higher
• GD or Imagick PHP extension
• Composer (for installing dependencies)

Usage

Settings

Navigate to WebP Converter in WordPress admin to configure:

• Enable Auto Convert: Toggle automatic conversion on image upload
• Default Quality: Set WebP quality (40-100, default: 80)
• Max File Size Limit (KB): Maximum allowed WebP file size (default: 200KB)

Auto Conversion

When auto-convert is enabled, newly uploaded JPG/PNG images are automatically converted to WebP format. The plugin will:

1. Convert the image to WebP at the configured quality
2. Check if file size is under the limit
3. If over limit, automatically reduce quality or resize until it fits

Batch Conversion

To convert all existing images:

1. Go to WebP Converter settings page
2. Scroll to "Batch Convert Existing Images"
3. Click Start Batch Conversion
4. Watch the progress bar as images are processed sequentially

Frontend Display

The plugin automatically replaces image URLs on the frontend:

• Original JPG/PNG files are NOT deleted
• WebP versions are served when available
• Browsers that don't support WebP will fall back to originals
• Works with the_content, wp_get_attachment_url, and wp_get_attachment_image_src filters

File Size Optimization Algorithm

The plugin uses an intelligent optimization algorithm to ensure WebP files stay under the configured size limit:

1. Start with default quality (e.g., 80)
2. Convert and save as WebP
3. Check file size:
   • ✅ If under limit → Done!
   • ❌ If over limit → Continue
4. Reduce quality by 5 (80 → 75 → 70...)
5. If quality reaches minimum (40) and still too large:
   • Resize dimensions by 10% (width × 0.9, height × 0.9)
   • Reset quality to default
   • Repeat optimization
6. Continue until file size is under limit or dimensions are too small

File Structure

wp-webp-intervention-converter/
├── wp-webp-intervention-converter.php  # Main plugin file
├── composer.json                        # Intervention Image dependency
├── includes/
│   ├── class-webp-converter.php        # Conversion logic
│   └── class-webp-settings.php         # Settings page
├── assets/
│   ├── js/
│   │   └── batch-convert.js            # AJAX batch processing
│   └── css/
│       └── admin-style.css             # Admin styling
└── README.md                            # This file

Technical Details

Intervention Image v3

This plugin uses Intervention Image v3 for all image manipulations. It's a modern, powerful PHP image handling library.

WordPress Hooks Used

• wp_generate_attachment_metadata: Auto-convert on upload
• the_content: Replace URLs in post content
• wp_get_attachment_url: Replace attachment URLs
• wp_get_attachment_image_src: Replace image source arrays
• AJAX actions: get_images_for_batch, batch_convert_image

Security

• Nonce verification for all AJAX requests
• Capability checks (manage_options)
• Sanitized input/output
• Escaped HTML output

Support

For issues or feature requests, please contact the plugin author.

License

GPL v2 or later

Changelog

1.0.0

• Initial release
• Auto convert on upload
• Batch conversion with progress bar
• File size optimization
• Frontend URL replacement