This check identifies raster images that may transfer fewer bytes in a modern format such as AVIF or WebP.
Why this matters
Modern codecs can reduce image weight at comparable visual quality, improving load time and data usage. Format conversion alone is not enough: dimensions, quality, responsive candidates, and caching still matter.
How to fix it
- Compare AVIF, WebP, JPEG, and PNG output visually and choose the smallest format that preserves the required detail and transparency.
- Use
<picture>when format fallbacks are needed, with a standard<img>as the final fallback. - Generate multiple dimensions and provide accurate
srcsetandsizesvalues. - Avoid converting tiny icons better served by SVG or enlarging an already well-optimized source.
When the finding appears across many URLs, fix the shared component or layout that produces it instead of patching generated HTML page by page. Recheck representative templates and responsive states after deployment so the correction does not create a regression elsewhere.
How to verify the fix
Inspect the selected network response in supported browsers at several viewport widths. Compare transferred bytes and visual quality, and confirm fallback behavior in environments without the preferred format.
Keep before-and-after evidence for the affected URL, original output, correction, and verification method. If markup changes after load, test consent states, localization, responsive variants, and client-side navigation because the initial HTML and rendered DOM can differ.