WebP
| Filename extension | |
|---|---|
| Internet media type | |
| Magic number | WEBP |
| Developed by | |
| Initial release | 30 September 2010[2] |
| Type of format | Image format Lossy compression algorithm |
| Contained by | Resource Interchange File Format (RIFF)[3] |
| Open format? | Yes[4] |
| Website | code.google.com/speed/webp/ |
WebP (pronounced "weppy")[5][6] is an image format that employs lossy compression.[7] It is developed by Google, based on technology acquired with the purchase of On2 Technologies.[8] As a derivative of the video format VP8, it is a sister project to the multimedia container format WebM.[9] WebP related software is released under a BSD license.[10]
The format was first announced in 2010 and is supposed to be a new open standard for lossily-compressed true-color graphics on the web, thereby being presented as a direct competitor to the older JPEG scheme, to which it is meant to compare favorably with the production of smaller files for comparable image quality.[11]
Contents |
[edit] Technology
WebP's compression algorithm is based on the intra-frame coding of the VP8 video format[12] and the classical Resource Interchange File Format (RIFF) as a container format.[2] As such it is a block-based transformation scheme with eight bits of color depth and a luminance-chrominance model with chroma subsampling by a ratio of 1:2 (YCbCr 4:2:0).[13] Without further content the mandatory RIFF container leads to an overhead of only twenty bytes and can hold additional metadata.[2] The side length of WebP images is limited to 16383 pixels (14 bits).[4]
WebP is based on block prediction. Each block is predicted on the values from three blocks above it and from one block left of it (block decoding is done in raster-scan order: left to right and top to bottom). There are four basic modes of block prediction: horizontal, vertical, DC (one color), and TrueMotion. Mispredicted data and non-predicted blocks are compressed in a 4×4 pixel sub-block with Discrete cosine transform and (rare) Walsh–Hadamard transform. Both transforms are done with fixed-point arithmetic to avoid rounding errors. The output is compressed with entropy encoding.[13] WebP also has explicit support for parallel decoding.[13]
The free reference implementation consists of a converter software in the form of a command-line program for Linux (webpconv) and a programming library for the decoding (the same as for WebM). The open source community quickly managed to port the converter to other platforms, such as Windows.[14]
[edit] Support
Amongst web browsers, Google Chrome and Opera natively support WebP.[15][16] (Support for incremental image decoding is scheduled for Google Chrome v12.[17]) All WebM-compatible browsers may also display WebP via a javascript shim.[18][19]
Amongst the graphics software, Pixelmator,[20] ImageMagick,[21] and Konvertor[22] natively support WebP. Telegraphics has released a free plug-in that enables WebP support in Adobe Photoshop CS5 and earlier.[23] Google has also released a plug-in for Microsoft Windows that enables WebP support in Windows Photo Viewer, Microsoft Office 2010, and any other application that uses Windows Imaging Component.[24]
Gmail and Picasa Web Albums (both Google web applications) support WebP. Support for WebP is also planned for Google App Engine. The Instant Previews feature of Google Search currently uses WebP internally to reduce disk space used by previews.[17] Android 4.0 supports encoding and decoding WebP images (via bitmap and Skia).[25]
[edit] Criticism
Jason Garrett-Glaser, a developer of the x264 encoder, gave several points of criticism for WebP.[12] Using a comparison of different encodings (JPEG, x264, Theora, and WebP) of a reference image, he stated that the quality of the WebP-encoded result was the worst of the four, mostly because of blurriness on the image. His main remark was that "libvpx, a much more powerful encoder than ffmpeg's jpeg encoder, loses because it tries too hard to optimize for PSNR" (peak signal-to-noise ratio), arguing instead that "good psy[cho-visual] optimizations are more important than anything else for compression." He also criticized Google's announcement, saying that it shouldn't have publicized the format before its results are better than JPEG's.[12]
[edit] See also
- WebM, a multimedia container format introduced by Google earlier in 2010, on which WebP is based
- JPEG 2000, an improvement intended to replace the older JPEG by the JPEG committee, introduced in 2000
- JPEG XR, a computationally lightweight alternative to JPEG 2000, introduced in 2009
[edit] References
- ^ a b "WEBP file extension". DotWhat.net. http://dotwhat.net/webp/10843/. Retrieved 2010-10-01.
- ^ a b c Rabbat, Richard (2010-09-30). "WebP, a new image format for the Web". Chromium Blog. Google. http://blog.chromium.org/2010/09/webp-new-image-format-for-web.html. Retrieved 2010-10-01.
- ^ "RIFF Container". Google Code. Google. http://code.google.com/speed/webp/docs/riff_container.html. Retrieved 2010-10-01.
- ^ a b "WebP FAQs". Google Code. Google. http://code.google.com/speed/webp/faq.html. Retrieved 2010-10-06.
- ^ WebP Home: "Did you know? WebP is pronounced 'weppy'. /(wĕpˈē)/"
- ^ Chapman, Stephen (2010-10-04). "Google's New WebP Image Standard Is All About SEO". ZDNet. http://www.zdnet.com/blog/seo/google-8217s-new-webp-image-standard-is-all-about-seo/669. Retrieved 2010-10-06.
- ^ Calore, Michael (2010-10-01). "Meet WebP, Google's New Image Format". Wired. http://www.wired.com/epicenter/2010/10/meet-webp-googles-new-image-format/. Retrieved 2010-10-05.
- ^ Shankland, Stephen (2010-09-30). "Google offers JPEG alternative for faster Web". CNET News. CBS Interactive. http://news.cnet.com/8301-30685_3-20018146-264.html. Retrieved 2010-10-01.
- ^ Paul, Ryan (2010-10-02). "Google's new VP8-based image format could replace JPEG". Ars Technica. http://arstechnica.com/open-source/news/2010/10/googles-new-vp8-based-image-format-could-replace-jpeg.ars. Retrieved 2010-10-05.
- ^ Rabbat, Richard (2010-10-03). "License/Patent clarification". http://groups.google.com/a/webmproject.org/group/webp-discuss/browse_thread/thread/5b8fe3ed39687eff. Retrieved 2011-03-11.
- ^ "Comparative Study of WebP, JPEG and JPEG 2000". Google Code. Google. http://code.google.com/intl/no/speed/webp/docs/c_study.html. Retrieved 2010-10-01.
- ^ a b c Garrett-Glaser, Jason (2010-09-30). "H.264 and VP8 for still image coding: WebP?". Diary Of An x264 Developer. http://x264dev.multimedia.cx/?p=541. Retrieved 2010-10-01.
- ^ a b c "VP8 Data Format and Decoding Guide" (PDF). Google. 2010-09-23. http://www.webmproject.org/media/pdf/vp8-bitstream.pdf. Retrieved 2010-10-02.
- ^ "WebP for .NET". Codeplex. Microsoft. 2010-10-01. http://webp.codeplex.com/.
- ^ Metz, Cade (2010-09-30). "Google open sources JPEG assassin". The Register (San Francisco). http://www.theregister.co.uk/2010/09/30/google_webp/. Retrieved 2010-10-03.
- ^ Ødegaard, Ruarí (2011-03-15). "CSS gradients, WebP, and Declarative UI". Opera Desktop Team. My Opera (Opera Software ASA). http://my.opera.com/desktopteam/blog/2011/03/15/css-gradients-webp-declarativeui. Retrieved 2011-03-15.
- ^ a b "The Chromium Blog: WebP in Chrome, Picasa, Gmail With a Slew of New Features and Improvements". Google. 2011-05-21. http://blog.chromium.org/2011/05/webp-in-chrome-picasa-gmail-with-slew.html. Retrieved 2011-05-20.
- ^ "Weppy Demo: WebP in modern browsers today". GitHub. http://antimatter15.github.com/weppy/demo.html. Retrieved 2010-10-11.
- ^ "Weppy: Javascript Shim for WebP on Chrome 6 and Firefox 4.0". Blog: this title probably isn't very original. antimatter15.com. 2010-10-03. http://antimatter15.com/wp/2010/10/weppy-javascript-shim-for-webp-on-chrome-6-and-firefox-4-0/. Retrieved 2011-05-24.
- ^ David, Chartier (2010-10-04). "Pixelmator to Add Support for Google's WebP Image Format". PC World. IDG. http://www.pcworld.com/businesscenter/article/206899/pixelmator_to_add_support_for_googles_webp_image_format.html. Retrieved 2010-10-05.
- ^ "ImageMagick Image Formats". ImageMagick.org. ImageMagick Studio LLC. http://www.imagemagick.org/script/formats.php. Retrieved 2011-05-24.
- ^ "Konvertor: Images Formats (v 4.06 Build 11)". Logipole. http://www.konvertor.net/formats-g_en.htm. Retrieved 2011-05-23.
- ^ "WebP Format". Free plugins for Photoshop & Illustrator. Telegraphics. http://telegraphics.com.au/sw/product/WebPFormat. Retrieved 2011-05-23.
- ^ "WebP Codec for Windows". WebP website. Google Code. http://code.google.com/intl/en/speed/webp/docs/webp_codec.html. Retrieved 2011-05-24.
- ^ Android 4.0 Platform Highlights
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