History Lesson: What Is a .webp File? Google’s Web Image Format

What is a .webp file?

A .webp file is an image stored in the WebP format. Spell the idea plainly: it is a compressed raster (bitmap picture) designed for the web, living in a RIFF (Resource Interchange File Format) container with the Internet media type image/webp. On disk the everyday extension is .webp. The search “what is a .webp file” usually means someone just saved a photo from a browser and wonders why the extension is not .jpg or .png.

Lossy WebP compresses with techniques from VP8 video intra-frame coding — the same still-frame idea that underlies a video key frame, applied to one picture. Later modes added a separate lossless coder, an alpha channel for transparency, and multi-frame animation. The container can also carry metadata and a color profile. For neighboring still-format lessons on this site, see History Lesson: What Is a .png File? and History Lesson: What Is a .gif File?.

Why images saved from the web become .webp

Sites chase smaller downloads. After browsers learned to decode WebP, CDNs and page builders started offering it beside or instead of JPEG and PNG so pages transfer fewer bytes. When you right-click Save image as… (or a download keeps the original response), the file on your PC keeps the .webp name the server sent. The browser already had a decoder; your older photo editor may not.

That gap is why these legacy files pile up in Downloads folders in 2026: the picture looked fine on the page, then double-clicking on the desktop fails, shows a generic icon, or opens in a viewer that only understands JPEG/PNG. Upload forms that reject .webp push the same people toward a convert-to-JPG/PNG step before emailing or posting the file.

On2, VP8, and Google’s 2010 announcement

WebP’s compression story starts in video. On2 Technologies built the VP8 video codec. Google announced a deal to acquire On2 in August 2009 and completed the acquisition on 19 February 2010 (On2/SEC merger closing). In May 2010 Google open-sourced VP8 as part of the WebM project for web video. Months later, engineers applied VP8’s intra-frame still coding to photographs.

On 30 September 2010, the Google Developers Blog (cross-posted from the Chromium Blog) announced WebP as a developer preview: a new lossy image format meant to shrink web photos versus typical JPEG while keeping quality and resolution. The post described a compressor based on the VP8 codec Google had open-sourced in May 2010, plus a lightweight RIFF container (they cited about 20 bytes of mandatory overhead for a simple image). Google reported re-encoding roughly one million web images and seeing an average about 39% smaller file size in that internal test — treat that as their published experiment, not a universal law for every photo on your disk.

Lossless, alpha, and animated WebP vs GIF

The 2010 launch was lossy-first — a JPEG-shaped job. Feedback asked for more. On 3 October 2011, Google’s WebP team announced an extended RIFF mux framework (WebP-Mux) covering animation, ICC color profiles, XMP metadata, and tiling drafts. On 18 November 2011, the Google Developers Blog introduced a lossless compression mode and transparency (alpha) support for both lossless and lossy WebP. Google’s own write-up pitched lossy WebP for photos, lossless for icons/graphics versus PNG, lossy-plus-alpha for transparent pictures that need not be fully lossless, and animation as a path for content that had been GIF loops.

So the everyday map is: lossy WebP ≈ photo-style compression (VP8 key-frame roots); lossless WebP ≈ exact pixel recovery after decompress (a different coder); alpha ≈ per-pixel transparency that can ride with either mode; animated WebP ≈ multiple frames with timing and loop control in the container — historically overlapping GIF’s silent-loop niche, but with truecolor and the rest of the WebP toolkit rather than GIF’s classic 256-color palette model. Classic PNG remains the lossless-still specialist with full alpha; see the PNG History Lesson. AVIF is a later open still path in the HEIF family — see History Lesson: What Is an .avif File?.

Turning .webp into JPG or PNG locally

When an editor or form refuses .webp, convert on a machine you control. Decode the WebP, then encode JPG for everyday opaque photos or PNG when you need lossless pixels or an alpha channel. Do that on your own Windows PC so the original never has to leave the house for a random upload site. Renaming the extension alone will not help.

Legacy File Converter lists WebP / .webp among supported images on Supported File Types and converts .webp locally on the user’s own Windows PC to JPG, PNG, and other listed targets — nothing is uploaded. This article stays the history — not a codec cookbook. Formal reading for implementers includes Google’s WebP documentation and RFC 9649 (November 2024), the informational IETF document that describes the format and registers image/webp. For neighboring image-format lessons, see History Lesson: What Is a .png File?, History Lesson: What Is a .gif File?, and History Lesson: What Is an .avif File?.