PNG's one mode vs. WebP's two
PNG only does lossless compression — there's no alternative mode. WebP supports both lossy and lossless compression within the same format, which is actually the more meaningful comparison point: WebP isn't just "a better PNG," it's a format flexible enough to replace PNG in the lossless case and JPEG in the lossy case, depending on which mode you choose per image.
Lossy WebP with alpha: something PNG's rivals couldn't do
This is a genuinely distinguishing feature: WebP's lossy mode still supports an alpha channel — something JPEG has never been able to do at all. Before WebP, if you needed transparency, PNG (lossless-only) was essentially your only mainstream option, even for an image that didn't need per-pixel-exact color accuracy — you paid PNG's larger file size just to get transparency. WebP lossy-with-alpha lets you get both a much smaller file size and transparency, for content where lossy compression is acceptable.
| PNG | WebP lossy | WebP lossless | |
|---|---|---|---|
| Compression | Lossless only | Lossy | Lossless |
| Alpha transparency | Yes | Yes | Yes |
| Typical size vs. equivalent-quality PNG | Baseline | Much smaller | ~25–35% smaller |
| Best for | Content needing pixel-exact preservation | Photographic content needing transparency | Direct PNG replacement, same guarantees |
Choosing lossy vs. lossless WebP
- Lossy WebP: photographic or gradient-heavy content where transparency is also needed (e.g., a product photo with a transparent background) — gets both size reduction and alpha support that JPEG structurally can't offer.
- Lossless WebP: anything that would otherwise be PNG for pixel-exact reasons — screenshots, logos, UI graphics, or any image where even minor lossy artifacts aren't acceptable.
Common mistakes
- Treating WebP as a single, uniform alternative to PNG. It's actually two different modes with different tradeoffs — picking the wrong one (lossy for something needing pixel accuracy, or lossless for a large photo where lossy would suffice) leaves savings or quality on the table.
- Not realizing lossy WebP with alpha is genuinely novel. Before WebP, transparency essentially meant accepting PNG's lossless-only file size, even for content that didn't need that guarantee.
- Assuming all WebP images are equally compressed. Encoder settings (quality level for lossy, effort level for lossless) meaningfully affect output size and quality — export settings still matter, the same way they do for JPEG.
FAQ
Can WebP's lossy mode support transparency, unlike JPEG?
Yes — this is one of WebP's genuinely distinguishing features; JPEG has no alpha channel in any mode, while WebP supports transparency in both its lossy and lossless modes.
When should I use lossy WebP instead of lossless?
For photographic or gradient-heavy content, especially when transparency is also needed — lossy WebP achieves much smaller files than lossless while still supporting alpha, unlike PNG or JPEG individually.
Is lossless WebP a safe drop-in replacement for existing PNG files?
Generally yes — it preserves the same pixel-exact guarantee at a smaller file size, with the main caveat being compatibility in a few legacy tools or contexts (see PNG vs WebP).
Convert to WebP and choose between lossy and lossless modes with the Image Converter — entirely in your browser.