AVIF to WebP
This is a compatibility step down rather than an optimisation. WebP files are typically 20–30% larger than the equivalent AVIF, but WebP is supported by more design tools, more CMS installations and more image pipelines — and it has been supported for years longer, so the long tail of older clients handles it.
Use it when something in your stack cannot read AVIF and you would rather not fall back all the way to JPG.
What Each Format Is For
AVIF. AVIF, built on the AV1 video codec, compresses harder than WebP — often 20–30% smaller again at the same quality — with alpha, wide colour gamut and HDR. Encoding is slow and browser support, while now broad, is younger than WebP’s.
WebP. WebP does both: lossy mode typically beats JPG by 25–35% at matched quality, and lossless mode beats PNG by around 25%. It supports alpha in both modes and animation, and is supported by every current browser. It is the default choice for web delivery.
| AVIF | WebP | |
|---|---|---|
| Compression | Lossless | Lossless available |
| Transparency | Yes | Yes |
Transparency Survives
Both formats carry an alpha channel, so transparent regions convert without being flattened onto a background. That makes this a safe conversion for logos, icons and cut-out product photography.
The Conversion Runs in Your Browser
The file is decoded and re-encoded locally through a canvas. Nothing is uploaded, nothing is stored, and the conversion works with the network disconnected. For anything containing personal data — identity documents, medical images, private photographs — that is a meaningfully different risk profile from any server-side converter.
The practical limits are your device's memory on very large images, and the browser's own codec support: it can only encode formats it ships an encoder for, and the tool tells you when it cannot.
Quality Settings
WebP can encode losslessly, so a conversion from a lossless source is exact — every pixel is preserved and re-encoding again later costs nothing.
One-Way Doors
Re-encoding never recovers information. If the target is lossy, keep the original: a WebP converted back to AVIF has the same artefacts as the WebP, in a larger file. Treat converted output as a delivery copy and archive the source.
Sizing Before Compressing
Resizing beats compressing. Halving an image's dimensions removes 75% of its pixels, which no quality setting can match, and a 4000px photo displayed at 800px is wasting 96% of what it downloads.
| Displayed at | Serve (1×) | Serve (2× for retina) |
|---|---|---|
| 400px | 400px | 800px |
| 800px | 800px | 1600px |
| 1200px | 1200px | 2400px |
Quality Settings That Hold Up
| Setting | Looks | Use for |
|---|---|---|
| 95–100 | Indistinguishable, large | Masters and print |
| 80–90 | Very good | Hero images, product photography |
| 70–80 | Good | Most web content |
| 50–70 | Visible artefacts on detail | Thumbnails |
| Below 50 | Obvious | Nothing |
Everything Runs Locally
Conversion and compression here use a canvas in your own tab. No file is uploaded, nothing is stored, and the work continues offline once the page has loaded. That is worth knowing for anything containing faces, documents or unreleased work — most online image tools upload by necessity, because they process server-side.
Getting the Rest of the Win
- Serve modern formats with a fallback.
- Always set
widthandheight. Without them the page reflows on load, which
- Lazy-load below the fold — and never the hero, since
loading="lazy"on it delays
- Strip metadata. EXIF can carry GPS coordinates and adds weight to every copy.