Hello @ivanpr
Thank you for reaching out with this valuable feedback and for your detailed observations. We appreciate you taking the time to compare our output with ShortPixel. Your findings highlight a key trade-off in image optimization, and we’d be happy to share some insights from a technical and experienced perspective:
1. Lightly pre-compressing an original JPG/PNG (for example, from 100% to 85% quality) can offer a modest file size reduction of 5-15% when converting to WebP or AVIF. However, for images already compressed, for example, by WordPress’s default 82% compression setting, the additional benefit of a second compression is minimal, typically offering only a 3-8% size reduction, in our view, the risk of degrading the image quality far outweighs this small gain.
2. If the original image is strongly compressed, this can reduce the size (5-15%) but can significantly lose detail and cause color banding or blocky artifacts. These flaws will be permanently “baked into” the WebP/AVIF, and the quality degradation can be very obvious.
The conclusion from points 1 and 2 is that light pre-compression has almost no effect on quality but offers little extra benefit, while strong pre-compression can reduce file size but severely damages image quality.
3. For SEO, light compression provides almost no effect on final rankings and indexing as far as we know, while strong compression may have a negative impact.
Based on the above, we believe the best approach is to always retain a high-quality original and then optimize loading on the front end with WebP/AVIF. This ensures both quality for search engine recognition and fast access for users.
We hope this helps. Please don’t hesitate to let us know if you have any more questions. We’re always here to help you get the most out of your images.
All the best,
CompressX Support Team
