How to convert PNG to WebP on iPhone
This is the conversion WebP was built for. PNG's transparency survives intact, the file usually gets dramatically smaller, and if you keep the quality slider at 100% you do not lose a single pixel of accuracy.
Why PNG to WebP is the best case for WebP
PNG is lossless and alpha-capable, and that combination makes it enormous. A photographic PNG is often 5–10x the size of the equivalent JPG. But you cannot just switch to JPG, because JPG has no alpha channel — the moment your image has a transparent background, JPG is off the table entirely.
WebP resolves that dilemma. It supports a full 8-bit alpha channel in both its lossy and lossless modes. So you can keep the transparency and get a modern codec's compression. For a photographic image with a cut-out background, lossy WebP can be a fraction of the PNG's size with no visible difference.
Lossy or lossless — the slider decides
Convexy maps its quality slider onto libwebp's two modes, and the distinction genuinely matters here:
- 100%: lossless WebP. Not “quality factor 100” — the actual lossless encoder. Every pixel is preserved exactly, like PNG, but WebP's lossless algorithm is usually 20–30% more compact than PNG. This is the setting to use for logos, icons, UI assets and line art, where a lossy codec would ruin the sharp edges.
- Below 100%: lossy VP8. The colour planes are compressed lossily at that quality factor, while the alpha channel is still stored losslessly. So the transparent cut-out stays crisp even when the picture inside it is lossily compressed. This is the setting for photographic content.
Match the mode to the content: graphics → 100% (lossless), photos → lossy. That single choice matters more than anything else on this page.
iOS cannot normally write WebP at all. Apple's ImageIO framework decodes WebP but ships no WebP encoder — there is no CGImageDestination for it. That is why most iPhone converters accept WebP as an input and refuse to produce it. Convexy bundles Google's libwebp and encodes through that instead. Stated once, as fact, because it explains why this page exists at all.
When to stay on PNG
- The destination might not accept WebP. Browsers all support it; a lot of desktop software, print services and upload forms still do not. PNG is accepted literally everywhere.
- It is an app icon or a platform asset. These pipelines usually specify PNG explicitly.
- It is your archival master. PNG is boring, universal and will still open in thirty years.
For anything destined for a web page, though, WebP is the better answer, and the size difference is not subtle.
Don't use lossy WebP on flat graphics. Lossy codecs put ringing and colour noise around hard edges — exactly what a logo, screenshot or chart is made of. It will look worse and may not even be smaller than the lossless mode, since lossless WebP compresses flat colour brilliantly. Use 100%.
On-device
The encoding runs on your iPhone or iPad through the bundled libwebp. No upload, no server, no account — which matters, because PNGs are so frequently screenshots of things you would not want on someone else's machine. Metadata is stripped by default; you can keep it from Options.
How to do it
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Pick the PNG
Tap Browse files, choose from Photos, or share the image in. Select several at once to convert a whole set of web assets in one batch.
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Choose WebP
WebP is offered as an output because Convexy ships Google's libwebp encoder — Apple's own frameworks cannot write the format.
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Set the quality deliberately
100% gives you lossless WebP: pixel-exact, and typically smaller than the PNG was. Below 100% gives lossy VP8 for the colour, with the alpha channel still stored losslessly. Graphics want 100%; photographs do not need it.
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Resize if this is for a web page
Set a maximum dimension in Options. Serving a 3000px image into a 600px slot wastes far more bytes than any codec choice can recover.
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Convert, then save or share
The result screen shows the size before and after. Save to Files, rename the output, or share it straight into your editor or publishing tool.
Common questions
Does WebP keep PNG transparency?
Yes, completely. WebP has a full 8-bit alpha channel, so semi-transparent pixels and anti-aliased edges survive exactly. In Convexy the alpha is stored losslessly even when you choose a lossy quality setting for the colour — so a cut-out stays clean regardless.
Is PNG to WebP lossless?
It can be. Set the quality slider to 100% and Convexy uses libwebp's lossless encoder — the output is pixel-identical to the PNG, and usually 20–30% smaller. Any setting below 100% uses lossy VP8 compression on the colour data, which is the right choice for photographic content and the wrong one for logos and text.
How much smaller will the WebP be?
For a photographic PNG converted to lossy WebP, the drop is often enormous — PNG is a poor fit for photographs to begin with. For a flat graphic converted to lossless WebP, expect something more like 20–30% off the PNG. The starting point matters far more than the destination.
Why don't other iPhone apps offer PNG to WebP?
Because iOS provides no WebP encoder. ImageIO can read the format but not write it, so any app built purely on Apple's frameworks can only convert from WebP. Producing WebP on iOS requires bundling a third-party encoder like Google's libwebp, which is what Convexy does.
Should I use WebP or PNG for my website?
WebP, for almost all image content — every current browser supports it and the bandwidth saving is real. Keep PNG where a build tool, an icon spec or a third-party service demands it. A common approach is to author in PNG and export WebP for delivery, which is exactly what this conversion is for.