Convert PNG to WebP

Two WebPs, and which one you get

WebP is really two formats sharing an extension. Lossless WebP uses a genuinely different algorithm from PNG and usually beats it by twenty to thirty per cent on the same pixels. Lossy WebP throws information away like a JPEG does, including the chroma subsampling that stores colour at half resolution. Both carry full 8-bit transparency, which is the thing WebP has over JPEG and the reason it can replace a PNG at all.

Which one you get follows the quality setting, and that is the single most important thing to know here. Anything below the maximum produces lossy WebP — excellent for photographs, and wrong for the pictures people usually keep as PNG. A screenshot of text, a logo, a chart, a diagram: subsampled colour puts visible fringing on every sharp coloured edge, and red text on white is where it shows worst. Keep the quality at maximum for those and the file stays pixel-perfect while still coming out smaller than the PNG.

The format has a hard ceiling that PNG does not: 16,383 pixels on either side. It is generous for photographs and genuinely restrictive for a stitched panorama, a full-page screenshot of a long web page, or a scanned map — those will not encode at all, whatever the quality. Transparency survives either way.

Support is no longer the reason to hesitate. Every current browser reads WebP, and has for years. What still does not, reliably, is the long tail of everything else — older email clients, some desktop image viewers, a surprising amount of enterprise software, and print workflows. For a web page WebP is simply better; for a file you are sending to a person, PNG or JPG remains the safe choice.

When you want something else

Google's own cwebp exposes what a canvas cannot. cwebp -lossless -z 9 in.png -o out.webp squeezes the lossless mode hardest, -near_lossless 60 gives up a little fidelity for a lot of size on photographic content, and -q 80 is the sane lossy default. It also lets you compress the alpha channel separately, which a browser encoder never exposes.

Before converting at all, consider whether the PNG is the problem. Running oxipng -o 4 or pngquant over it often halves the file with no format change and no compatibility question at all — and if the picture is a photograph rather than a graphic, it probably should have been a JPG from the start.