Next-Gen Image Formats (WebP, AVIF)

Definition

Next-gen image formats are modern compression formats that achieve significantly smaller file sizes than the legacy JPEG and PNG formats at equivalent visual quality. The two primary next-gen formats used in web production are: **WebP** — Developed by Google and released in 2010; open-source, royalty-free. Delivers 25–35% smaller files than JPEG for photographic images and 26% smaller than PNG for images with transparency, at equivalent perceptual quality. Supports both lossy and lossless compression, transparency (like PNG), and animation (like GIF). Browser support: universal across all modern browsers (Chrome, Firefox, Safari, Edge) since 2020. WebP is the standard next-gen format for web production — the practical recommendation for all new image workflows. **AVIF** — Based on the AV1 video codec; AV1 Image File Format. Delivers 50% smaller file sizes than JPEG at equivalent quality, outperforming WebP by a further 20–35%. Supports HDR content, wide colour gamut, and both lossy and lossless compression. Browser support: Chrome (from 85), Firefox (from 93), Safari (from Safari 16/iOS 16, released 2022). Encoding speed limitation: AVIF compression is significantly more CPU-intensive than WebP — real-time AVIF encoding on the server requires more compute resources than WebP encoding. For static image assets, the encoding cost is paid once (at build or upload time); for dynamic image CDNs (Cloudinary, Imgix, Bunny CDN), AVIF generation requires CDN infrastructure support. **Responsive format delivery via `<picture>`**: use the `<picture>` element to serve AVIF for browsers that support it, WebP as the primary fallback, and JPEG as the universal legacy fallback: `<picture><source type="image/avif" srcset="img.avif"><source type="image/webp" srcset="img.webp"><img src="img.jpg" alt="..."></picture>`. Modern frameworks handle this automatically: Next.js `<Image>` serves AVIF and WebP from JPEG/PNG sources; Nuxt `<NuxtImg>` via @nuxt/image; SvelteKit via vite-imagetools.

Why it matters for SEO

Image file size is the largest contributor to total page weight on most sites, and total page weight directly affects LCP (time to download the LCP image element) and Time to Interactive. Google PageSpeed Insights (via Lighthouse) reports "Serve images in next-gen formats" as one of its most frequent recommendations and estimates the potential savings in KB and seconds for each page. For Core Web Vitals: switching the LCP image from JPEG to WebP typically reduces LCP by 200–600ms for users on median connections — a meaningful improvement toward the ≤2.5s LCP Good threshold. AVIF can reduce LCP by a further 100–300ms. For CrUX field data: the improvement in LCP from next-gen formats is visible in real Chrome user data within 28 days of deployment (the CrUX rolling window), directly improving the page experience signals Google uses for ranking.

How DeepSEOAnalysis checks this

The audit checks image elements on all crawled pages for format detection via HTTP response `Content-Type` header: JPEG images flagged if a WebP or AVIF alternative is not present in `srcset` sources; PNG images flagged if no next-gen format alternative exists; GIF images flagged (animated WebP is typically 40–60% smaller than GIF). The audit also checks whether the Next.js `<Image>` component (or equivalent framework image optimiser) is in use — a strong signal that next-gen format delivery is handled automatically. For each flagged image, the estimated file size reduction is calculated based on typical WebP/AVIF compression ratios for the detected format and image dimensions, providing a concrete estimated LCP improvement.

Useful tools and resources

• Free image format audit