JPG is the compatibility workhorse for photos, PNG is the lossless/transparency workhorse, WebP is a flexible modern web format, and AVIF can deliver very efficient compression with modern codec features. The best format is the one that preserves the features you need at an acceptable size and compatibility level.
The four formats in one table
| Format | Compression | Transparency | Typical strength |
|---|---|---|---|
| JPG | Lossy | No | Photos + broad compatibility |
| PNG | Lossless | Yes | Graphics, UI, alpha |
| WebP | Lossy or lossless | Yes | Flexible modern web delivery |
| AVIF | Lossy/lossless capabilities | Yes | High compression efficiency |
Why we test real files instead of declaring a winner
Our Chromium test used ten JPEG sources. Nine already efficient JPEGs became an average of 27.4% larger when re-encoded as high-quality WebP. One bloated source shrank by 93.3%.
That is why a practical optimizer compares output bytes and visual quality rather than assuming “WebP is always smaller.”
When JPG is still the right answer
JPG remains a safe choice for photographs that must work across virtually any image workflow. It is simple, widely supported and efficient when encoded well. Its biggest limitations are lossy generation loss and the lack of transparency.
When PNG is worth the extra bytes
PNG is ideal when transparency or exact lossless pixels matter. It is not automatically efficient for photographs. If a photo-like PNG has no transparency, converting it to a high-quality lossy format can produce dramatic savings.
WebP vs AVIF for modern websites
MDN describes both WebP and AVIF as strong modern choices. WebP has broad modern browser support and supports transparency and animation. AVIF can offer even stronger compression efficiency and higher color capabilities, but workflow compatibility and encoder behavior still matter.
Use a <picture> fallback strategy when your audience or stack requires it, and verify what your CMS actually serves.
A practical decision checklist
- Start from the highest-quality source you have.
- Preserve transparency when the design needs it.
- Compare actual file bytes after conversion.
- Check the result at normal viewing size and at 100% around text, hair and hard edges.
- Keep the source file so you can export a different format later without another generation of loss.
A format comparison is useful only when it changes a decision. If two outputs look the same and one is clearly smaller in your real workflow, choose the smaller one. If compatibility or transparency changes, those requirements take priority over a few extra kilobytes.
Frequently asked questions
Which image format is best for SEO?
Search engines do not reward a file extension by itself. Fast, crawlable, appropriately sized images with good page context and alt text matter more than chasing one format.
Is AVIF always smaller than WebP?
Not always. Efficiency depends on the source and encoder settings. Test representative files.
Can WebP replace PNG?
Often for web delivery, especially when transparency is needed, but PNG can still be useful for editing and exact lossless workflows.
Should I convert every JPG to WebP?
No. Compare the actual result. Already optimized JPEGs can become larger after re-encoding.
Bottom line
Treat image format as an engineering choice, not a ranking. For each important image class—photos, graphics, transparent assets—test a few representative files and standardize on the smallest visually acceptable output your delivery stack supports.
Technical references: MDN image format guide
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