Choosing PNG over JPG as the target
Both PNG and JPG open everywhere, so the question is which one suits the image. PNG is the right target when:
- The image has transparency. Stickers, logos, icons and cut-out product shots saved from websites are often WebP with an alpha channel. PNG keeps it; JPG would fill it with a solid colour.
- It contains text, lines or flat colour. Screenshots, diagrams, charts and UI graphics stay crisp in PNG. JPG adds faint noise around every sharp edge.
- You are going to edit it. PNG is lossless, so opening, changing and saving it any number of times never adds new compression damage. That makes it a sensible working copy for design tools and presentations.
For an ordinary photo you only want to view or send, WebP to JPG gives a much smaller file with no visible difference.
What lossless means for an already compressed image
The browser decodes the WebP, and the decoded pixels are written to the PNG without any further compression loss. That is why there is no quality slider. For opaque areas the result is exact; semi-transparent pixels can shift by a tiny rounding step because the canvas stores colour premultiplied by alpha, which is not visible in practice.
It is worth being clear about what that does not do. Most WebP images on websites are lossy, compressed once when the site produced them. PNG preserves that state precisely, including any softness or faint blocking the WebP already had, but it cannot bring back detail that was removed. If the WebP was lossless to begin with, the PNG is a perfect copy of the original.
Why the PNG is so much larger
Expect a big jump in size. A 90 KB lossy WebP photo at 1200×800 px can become 1 to 1.5 MB as PNG, ten times or more. Lossy WebP keeps size down by discarding detail and storing colour at reduced resolution; PNG has to describe each of the 960,000 pixels exactly, using compression that works well only when colours repeat.
For flat graphics the difference is much smaller, often under two times, because large single-colour areas compress well in PNG too.
If the size becomes a problem:
- Run the result through Compress PNG, which reduces the colour palette and often cuts the file by 50 to 70 percent with little visible change for graphics.
- For photos, reconsider the format: if transparency is not needed, JPG is the better fit.
- Scale it down first if the image is larger than where it will be shown.
Details of the conversion
The image is decoded and re-encoded by your browser using the Canvas API, in a background worker where supported, and never uploaded. Pixel dimensions stay the same, and partial transparency, such as soft shadows and anti-aliased edges, is carried over. Any EXIF or XMP metadata a WebP may contain is not copied.
Animated WebP files give a PNG of the first frame only. Files up to 50 MB each are accepted, and a batch can be downloaded as a single ZIP, with each file keeping its original name and a .png extension.