WebP を GIF に変換

Reading the individual frames of an animated WebP needs the WebCodecs ImageDecoder API. It is available in Chrome, Edge and Opera from version 94 and in Firefox from version 133. In those browsers the converter decodes each frame fully composited, reads its duration, and writes the same sequence into the GIF.

Safari does not ship ImageDecoder yet (it is only in Safari Technology Preview). There, and in older browsers, the converter can only see the image the way an <img> tag shows it, so an animated WebP becomes a GIF of its first frame. If you need the full animation from an iPhone or Mac, open this page in Chrome, Edge or Firefox.

A still WebP converts the same way in every browser: one frame, no loop.

GIF has two hard limits that WebP does not. Each frame can use at most 256 colours, and a pixel is either fully transparent or fully opaque. The converter builds a separate 256-colour palette for every frame, so flat artwork, logos and screen recordings usually look unchanged, while photographic animations and soft gradients can show visible banding. Semi-transparent edges, such as a soft shadow under a sticker, are rounded to on or off at 50% opacity.

Timing is copied frame by frame. GIF counts delays in hundredths of a second, so durations are rounded to the nearest 10 ms; a frame of 10 ms or less is written as 100 ms, which is how browsers play such frames anyway. The loop setting is kept: an animation that repeats forever still repeats forever, and one that plays a fixed number of times keeps that count.

WebP compresses far better than GIF, so the GIF is almost always larger. Our 320×200 animated test WebP (lossless, 30 frames of 40 ms) is 61,840 bytes; the GIF made from it in Chrome was 147,397 bytes, 2.4 times larger, with all 30 frames and the 1.2-second loop intact. A 300×200 still image saved as lossy WebP went from 6,670 bytes to a 25,569-byte GIF. To keep the size down, the converter stores only the pixels that change between frames, with unchanged areas left transparent so the earlier frame shows through.

If the GIF is too heavy for where it is going, run it through the GIF compressor afterwards to cut colours, drop frames or scale it down; GitHub, for example, accepts GIFs up to 10 MB in issues and pull requests.

The WebP is decoded by your own browser and the GIF is assembled in JavaScript in the same tab. Nothing is sent to a server, so stickers from a private chat or unreleased product animations stay on your device. You can convert several files in one go and download them together.