Troubleshooting 'Unsupported Color Conversion' Errors in WebP Express

Users of the WebP Express plugin for WordPress may occasionally encounter an error message stating Unsupported color conversion request or icc_import: no input profile. This error typically prevents a specific image from being converted to the WebP format, while other images convert without issue. This guide explains the cause of this error and provides practical solutions to resolve it.

Why This Error Occurs

This is not a bug specific to the WebP Express plugin itself. The error originates deeper in the image processing stack. The issue is related to how the underlying conversion libraries, namely cwebp (the official WebP conversion tool from Google) and libvips, handle JPEG files that contain certain color profiles or metadata that they do not support.

As confirmed by the WebP Express team's own testing, the same error can be reproduced by running the cwebp command directly on the problematic image. This confirms the issue is with the conversion library, not the WordPress plugin that acts as a bridge to it.

How to Resolve the 'Unsupported Color Conversion' Error

Solution 1: Switch to an ImageMagick-Based Converter (Recommended)

The most effective solution is to configure WebP Express to use a conversion method that relies on ImageMagick or GraphicsMagick, as these tools are more robust at handling a wider variety of color profiles.

1. In your WordPress admin dashboard, navigate to Settings > WebP Express.
2. Click on the "Converters" tab.
3. Locate the conversion methods that use Imagick, Gmagick, or ImageMagick.
4. Move your preferred ImageMagick-based converter to the top of the stack. This instructs WebP Express to prioritize this method.
5. Save your changes and attempt to convert the problematic image again.

Testing shows that while cwebp and vips fail on these specific images, ImageMagick and its derivatives typically succeed.

Solution 2: Re-save the Problematic Image

If switching converters is not an option, you can address the image itself. The issue is often caused by an embedded color profile that the libjpeg library (used by cwebp) cannot parse.

1. Open the problematic JPEG image in an image editor like Photoshop, GIMP, or even a free online tool.
2. Re-save or export the image as a new JPEG file. This process often strips out or normalizes the problematic metadata.
3. Replace the original image on your WordPress site with the newly saved version.
4. Run the WebP Express conversion again.

Conclusion

The Unsupported color conversion request error is a known limitation of certain image conversion libraries when processing JPEGs with uncommon color profiles. The WebP Express plugin provides the flexibility to work around this by allowing users to switch to a more compatible conversion method like ImageMagick. For a single troublesome image, re-saving it is also a reliable fix.