Comparing WebP's lossless mode specifically to PNG
This comparison matters most in WebP's lossless mode, since that's the direct apples-to-apples equivalent to PNG — both fully lossless, both supporting alpha transparency. WebP lossless typically achieves 25–35% smaller files than PNG for the same visual content, primarily from more advanced prediction and entropy-coding techniques in its compression pipeline compared to PNG's deflate-based approach — newer compression research applied to essentially the same lossless goal.
Where the size savings actually come from
WebP's lossless encoder uses more sophisticated pixel prediction (guessing a pixel's value from its neighbors before encoding the difference, rather than PNG's simpler prediction filters) and a more efficient entropy coder for the resulting residual data. The net effect: the same exact pixels, encoded more efficiently — not a different tradeoff, just better compression technology applied to the identical lossless goal PNG already targets.
The compatibility check that still matters
WebP support is now near-universal across modern browsers, but "near-universal" isn't "universal" — certain older browser versions, some email clients, and specific third-party integrations (certain CMS plugins, older image processing pipelines) may not handle WebP correctly. Before switching a critical asset (like a logo used across email templates) entirely to WebP, verify support across every actual context the image needs to work in — not just modern browsers.
| PNG | WebP (lossless) | |
|---|---|---|
| Compression | Lossless (deflate) | Lossless (modern prediction + entropy coding) |
| Alpha transparency | Yes | Yes |
| Typical size vs. equivalent PNG | Baseline | ~25–35% smaller |
| Compatibility | Universal, decades of support | Near-universal, some legacy gaps |
Common mistakes
- Assuming WebP always wins on size regardless of content. The savings are real and consistent on average, but individual images can vary — worth spot-checking actual output size rather than assuming a fixed percentage every time.
- Switching a critical, widely-embedded asset to WebP without checking every actual delivery context. Modern browsers are fine; older tooling, some email clients, and certain legacy integrations may not be.
- Not providing a fallback for the rare unsupported context. A
<picture>element with a WebP source and a PNG fallback covers the compatibility gap without sacrificing the size benefit where it's supported.
FAQ
Is WebP always smaller than PNG for the exact same image?
Typically yes, often by 25–35% in lossless mode, though the exact savings vary by image content — some images compress better than others under either format.
Does WebP support full alpha transparency like PNG?
Yes — WebP's lossless mode supports a full alpha channel, matching PNG's capability with a smaller resulting file size.
Is it safe to fully replace PNG with WebP everywhere on a site?
For most modern web delivery, yes — but verify support across any legacy tooling, email clients, or third-party integrations the image also needs to work in before removing PNG entirely.
Convert PNG to WebP (and compare resulting file sizes) directly with the Image Converter — processed entirely in your browser.