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What is WebP?
WebP is a modern image format that supports lossy compression, lossless compression, alpha transparency, and animation inside a single container. Google introduced it in 2010, and every current major browser now supports it.
What this guide explains
WebP is a modern image format that supports lossy compression, lossless compression, alpha transparency, and animation inside a single container. Google introduced it in 2010, and every current major browser now supports it.
Technical scope
This guide describes browser-based file workflows, format tradeoffs, and ConvertUnlimited processing boundaries for supported tools.
The Origin of WebP
Google announced the WebP format in 2010, building its lossy compression mode on the intra-frame (keyframe) coding tools from the VP8 video codec, which Google had acquired along with On2 Technologies not long before. Instead of compressing each block of pixels as if it had no relationship to its neighbors, VP8's predictive coding guesses a block from the pixels already decoded around it and stores only the difference, which is part of why WebP files are often smaller than formats that compress each block independently.
Container structure: RIFF chunks
A WebP file is a RIFF container: a 'WEBP' four-character code followed by a sequence of chunks. The image data itself lives in a VP8 chunk for lossy images or a VP8L chunk for lossless images. An optional VP8X chunk marks 'extended' features — alpha transparency, animation, an embedded ICC color profile, or EXIF/XMP metadata — so a decoder knows what to expect before it reads any pixel data. Animated files add an ANIM chunk plus one ANMF chunk per frame, each carrying its own duration and disposal method.
Lossy VP8 vs lossless VP8L
| Mode | How it compresses | Alpha support | Typical use |
|---|---|---|---|
| Lossy (VP8) | Predicts each block from neighboring pixels, then discards fine detail a viewer is less likely to notice, broadly similar in spirit to JPEG's transform-based approach but with stronger prediction | Yes, via a separate compressed alpha chunk | Photographs and general web images where some quality loss is an acceptable trade for a smaller file |
| Lossless (VP8L) | Built specifically for images rather than adapted from a video codec: uses spatial prediction, a color-indexing transform for graphics with few distinct colors, and a color cache instead of general-purpose DEFLATE | Yes, alpha is stored natively alongside color data | Graphics, screenshots, and any image that must reproduce the source pixels exactly |
Alpha transparency
Both WebP modes support full alpha-channel transparency, something JPEG cannot do at all. Lossy WebP keeps the alpha channel in its own compressed chunk, separate from the color data, so a lossy photo can still have a transparent background. Lossless WebP stores alpha as part of the same ARGB pixel data used for color, the same approach PNG uses.
Animation
WebP can hold an animated sequence as an alternative to animated GIF, storing each frame in its own ANMF chunk with an independent duration and letting each frame use either the lossy or lossless mode. Encoder and browser support for animated WebP matured later than support for still WebP images, so it is worth confirming support in your specific target browsers before relying on it as a full GIF replacement.
Dimension limits
The WebP bitstream stores width and height as 14-bit values, which caps supported image dimensions at 16383 by 16383 pixels. That ceiling sits far above what a camera photo, a screenshot, or a typical web image needs, so it rarely comes up in practice; it mainly matters when a script is generating very large stitched panoramas or print-resolution canvases programmatically.
Browser support history
Chrome has supported WebP since the format's original 2010 launch. Firefox added support in Firefox 65, released in January 2019. Safari added support in Safari 14, released in 2020 alongside macOS Big Sur and iOS 14. Any browser or operating-system version older than that will not display WebP images, which is why sites that still need to support older devices typically serve WebP inside a picture element with a JPEG or PNG fallback rather than replacing the fallback outright.
Related guides
WebP vs JPG: photo format tradeoffs · WebP vs PNG: format differences and use cases
FAQ
Which browsers support WebP?
Current versions of Chrome, Firefox, Edge, and Safari support WebP. Older versions released before each vendor added support — this came later for Firefox and Safari than for Chrome — cannot display it.
Is WebP lossless?
It can be either, depending on which chunk the encoder writes. A VP8 chunk means lossy compression; a VP8L chunk means the pixels are reproduced exactly, with no visual data discarded.
Does WebP support animation like GIF?
Yes. WebP can store a sequence of frames with per-frame timing as an alternative to animated GIF, though animated WebP support was added to encoders and browsers later than support for still WebP images, so check your target browsers if this matters for your project.
Is there a maximum WebP image size?
Yes. The format's bitstream limits width and height to 16383 pixels each, since both dimensions are stored as 14-bit values. That is well above the resolution of ordinary photos and screenshots.
Why did Google build a new format instead of extending JPEG or PNG?
JPEG and PNG were both standardized decades earlier around the constraints and encoding tools available at the time, and neither format's underlying bitstream was designed to add a fundamentally different compression method later. Building WebP as a new format on top of VP8's existing prediction tools let Google combine lossy and lossless modes, alpha, and animation in one container without being limited by either older format's original design.
Action
Convert images to WebP in the browser: Image Converter.