Image Format Converter

Overview

Image Format Converter is a highly optimized, production-grade WordPress plugin designed to reduce page size and solve image delivery warnings in Google Lighthouse (Core Web Vitals). It translates uploaded raster images into next-generation formats (WebP and AVIF) and rewrites DOM paths dynamically—or serves them natively at the server level via Apache/Nginx—without relying on heavy third-party CDNs or cloud-based compression SaaS. Deploying from a staging environment? EZ Page Sync pairs well for pushing content to production before this plugin optimizes the incoming media.

Key Features

How It Works

Image Format Converter operates on a dual-phase pipeline system. The Conversion Pipeline processes the files, while the HTML Rewrite Pipeline takes care of presenting the optimized images to visitors.

Technical Architecture

The plugin is organized into six core modular classes, strictly decoupled to separate settings, conversion, and output presentation:

Configuration Settings

Server-Level Serving (Zero-PHP Overhead)

For high-traffic production environments, relying on PHP's output buffering to parse and rewrite HTML is inefficient. Instead, we can bypass PHP completely for image serving. When a user requests a file like image.png, the web server (Apache or Nginx) intercepts the request, detects if the browser accepts AVIF/WebP, checks if the optimized file exists on disk, and serves it directly.

# BEGIN Image Format Converter
<IfModule mod_rewrite.c>
  RewriteEngine On

  # 1. Try AVIF first
  RewriteCond %{HTTP_ACCEPT} image/avif
  RewriteCond %{REQUEST_FILENAME} ^(.+)\.(jpe?g|png|gif|bmp)$
  RewriteCond %1.avif -f
  RewriteRule ^(.+)\.(jpe?g|png|gif|bmp)$ $1.avif [T=image/avif,E=WPWO_AVIF:1,L]

  # 2. Fall back to WebP
  RewriteCond %{HTTP_ACCEPT} image/webp
  RewriteCond %{REQUEST_FILENAME} ^(.+)\.(jpe?g|png|gif|bmp)$
  RewriteCond %1.webp -f
  RewriteRule ^(.+)\.(jpe?g|png|gif|bmp)$ $1.webp [T=image/webp,E=WPWO_WEBP:1,L]
</IfModule>

<IfModule mod_headers.c>
  # Vary Accept ensures proxies/CDNs cache separately for AVIF, WebP, and original
  Header merge Vary Accept env=WPWO_AVIF
  Header merge Vary Accept env=WPWO_WEBP
</IfModule>

<IfModule mod_mime.c>
  AddType image/webp .webp
  AddType image/avif .avif
</IfModule>
# END Image Format Converter

# Define modern image suffix map based on Accept headers
map $http_accept $modern_suffix {
    default        "";
    "~*image/avif" ".avif";
    "~*image/webp" ".webp";
}

# Match static upload images and serve next-gen duplicates
location ~* ^/wp-content/uploads/(.+)\.(jpe?g|png|gif|bmp)$ {
    add_header Vary Accept;
    
    # Try serving $1 (path) + modern suffix first, falling back to original
    try_files /wp-content/uploads/$1$modern_suffix $uri =404;
    expires 365d;
}

Frequently Asked Questions

Changelog