WebP images are being re-encoded with lossy compression when uploaded, altering image quality

[Neehakethi]

Summary

WebP images are being processed/transformed during upload or when pushed to S3 storage, even when no transformation is requested. This results in visual quality degradation compared to the original uploaded image.

Affected Format

• WebP only - PNG and JPG images work correctly and maintain their original quality
• The same image exported to JPG/PNG before upload preserves quality correctly

Steps to Reproduce

1. Upload a WebP image (especially a lossless WebP) to dotCMS
2. Compare the original image with:
   • The preview displayed inside dotCMS
   • The image when pushed to AWS S3

Expected Behavior

The uploaded WebP image should be stored and served exactly as uploaded, without any re-encoding or transformation unless explicitly requested by the user.

Actual Behavior

The WebP image is being re-encoded, resulting in:

• Noticeable visual differences between the original and the processed image
• Different file sizes (in the reported case: original 64.57KB, AWS version 56.91KB)
• Loss of quality, especially noticeable with images that were originally lossless

Environment

• Reproduced on dotCMS demo environment
• Browser: Chrome 142.0.0.0
• OS: Mac OS 10.15.7

Technical Analysis

Looking at the codebase, the WebPImageFilter (dotCMS/src/main/java/com/dotmarketing/image/filter/WebPImageFilter.java) applies the following logic:

final int qualityParam = parameters.get(getPrefix() +"q") != null
    ? Integer.parseInt(parameters.get(getPrefix() +"q")[0])
    : 85;  // Default to 85% quality

Float quality = Float.valueOf(qualityParam);
quality = quality/100;

if(quality==1) {
    writeParam.setCompressionType("Lossless");
} else {
    writeParam.setCompressionType("Lossy");
    writeParam.setCompressionQuality(quality);
}

Key issue: Unless quality is explicitly set to 100%, the filter defaults to lossy compression at 85% quality. This means:

• Lossless WebP images get converted to lossy
• Already-lossy WebP images get re-compressed, potentially introducing additional artifacts

Suggested Fix

WebP images should be stored as-is during upload without any automatic re-encoding. Processing should only occur when:

1. Explicitly requested through image filter parameters
2. Generating thumbnails or resized versions for display

Related Code Files

• dotCMS/src/main/java/com/dotmarketing/image/filter/WebPImageFilter.java
• dotCMS/src/main/java/com/dotmarketing/image/filter/ImageFilterApiImpl.java
• dotCMS/src/main/java/com/dotmarketing/servlets/BinaryExporterServlet.java (quality_q parameter handling)
• dotCMS/src/main/java/com/dotmarketing/servlets/ShortyServlet.java (image URL processing)

Support Ticket Reference

Reported via support ticket - Customer confirmed issue with WebP images uploaded to their environment.
https://helpdesk.dotcms.com/a/tickets/34265

Additional Context

• Other formats (JPG, PNG) are not affected
• The issue specifically impacts WebP format handling

[dsilvam]

@gortiz-dotcms Please test before trying to make a fix.
Grab the testing image from the freshdesk ticket.

[github-actions]

PRs linked to this issue

• fix: add webp lib and remove broken one (#34082) by @gortiz-dotcms