Fixing Black Backgrounds and Transparency Issues in PNG Images with Converter for Media

Many users of the 'Converter for Media – Optimize images | Convert WebP & AVIF' plugin report a common issue: their PNG images with transparent backgrounds are being converted with an unwanted black background. This problem is frustrating, especially for logos, icons, and other graphics that rely on transparency. This guide explains why this happens and provides the most effective solutions.

Why Does This Happen?

Based on community reports and developer responses, the black background issue is not a flaw in the plugin's core design but rather a limitation of the underlying image processing libraries on your server.

The plugin uses one of two common PHP extensions to convert images: GD or Imagick. The 'Converter for Media – Optimize images | Convert WebP & AVIF' team has identified that the GD library, in particular, can sometimes mishandle the alpha channel (transparency) in certain PNG files during the conversion process to WebP, resulting in a solid black fill where transparency should be.

How to Fix the Black Background Issue

Solution 1: Switch Your Conversion Method

The most recommended fix is to switch from the GD library to the Imagick library, if it is available on your server.

1. Go to your WordPress dashboard.
2. Navigate to Settings > Converter for Media.
3. Find the option for Conversion method.
4. If available, select Imagick instead of GD.
5. Save your changes and restart the conversion process.

Many users have confirmed that using Imagick resolves the transparency problem, as it generally has better support for handling PNG alpha channels.

Solution 2: Exclude Specific Problematic Images

If switching libraries doesn't work or isn't an option, you can prevent specific images from being converted. This is ideal for a favicon or a logo that consistently causes problems. You can add a custom code snippet to your theme's functions.php file.

Warning: Always use a child theme when editing theme files and consider creating a backup first.

add_filter( 'webpc_files_paths', function( $paths ) {
  $excludes_files = [
    'my-logo.png',
    'favicon.png',
  ];
  foreach ( $paths as $path_index => $path ) {
    if ( in_array( basename( $path ), $excludes_files ) ) {
      unset( $paths[ $path_index ] );
    }
  }
  return $paths;
} );

Replace the filenames in the $excludes_files array (e.g., 'my-logo.png') with the actual names of the images you want to exclude. After adding this code, remember to delete the already converted versions of these images from the /uploads-webpc/ directory on your server to ensure the original files are served.

Solution 3: A Note on Animated PNGs (APNG)

It's important to note that this plugin converts APNG (Animated PNG) files into static images, which breaks their animation. Currently, the best solution for APNG files is to exclude them using the method shown in Solution 2. The 'Converter for Media – Optimize images | Convert WebP & AVIF' team has acknowledged this behavior and may address it in a future update.

What About SVG Files?

Some users have reported issues with SVG files disappearing. It is important to clarify that the 'Converter for Media – Optimize images | Convert WebP & AVIF' plugin does not process or convert SVG files. If SVGs are affected, the issue is almost certainly a conflict with another plugin or theme. A standard troubleshooting step is to deactivate other plugins one by one to identify the conflict.

Conclusion

The black background issue is a known challenge primarily linked to the GD library. The two main solutions are switching to the Imagick library or excluding specific images from conversion. Remember, the original images are never modified by the plugin; they remain safe in your uploads folder. All conversions are stored separately, so deactivating the plugin will immediately stop serving the converted images and revert your site to display the original, unmodified files.