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{{Use dmy dates|date=October 2010}}
{{Use dmy dates|date=October 2010}}
{{Infobox file format
{{Infobox file format
| name = WebP
| icon =
| icon =
| logo =
| logo =
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| accessdate = 1 October 2010
| accessdate = 1 October 2010
}}</ref>
}}</ref>
| mime = <tt>image/webp</tt>
| mime = <code>image/webp</code>
| type code =
| type code =
| uniform type =
| uniform type =
| magic =
| magic = WEBP
| owner = [[Google]]
| owner = [[Google]]
| released = {{start date|2010|9|30|df=yes}}<ref name="Announcement-in-chromium">{{Cite web
| released = {{start date|2010|9|30|df=yes}}<ref name="Announcement-in-chromium">{{Cite web
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| accessdate = 1 October 2010
| accessdate = 1 October 2010
}}</ref>
}}</ref>
| url = [http://code.google.com/speed/webp/ WebP Home]
| url = [http://code.google.com/speed/webp/ code.google.com/speed/webp]
}}
}}


'''WebP''' is an [[image format]] which supports a [[lossy compression]] algorithm to reduce image file size. It is developed by [[Google]].<ref>{{Cite web
'''WebP''' (to be pronounced ''“weppy”''<ref>[http://code.google.com/speed/webp/ WebP Home]: “'''Did you know?''' WebP is pronounced "weppy". /(wĕpˈē)/”</ref>) is an [[image file formats|image format]] for [[lossy compression|lossily compressed]] image files. It is developed by [[Google]], based off technology acquired with the purchase of [[On2 Technologies]].<ref>{{Cite web
| url = http://news.cnet.com/8301-30685_3-20018146-264.html
| url = http://news.cnet.com/8301-30685_3-20018146-264.html
| title = Google offers JPEG alternative for faster Web
| title = Google offers JPEG alternative for faster Web
Line 54: Line 53:
| last = Shankland
| last = Shankland
}}</ref>
}}</ref>
As another descendant of the video codec ''[[VP8]]'' it is a sister project of the video format ''[[WebM]]''.


== Technology ==
WebP's compression algorithm is based on [[VP8]]'s intra-frame coding.<ref name="Announcement-in-chromium" /><ref>{{Cite web
WebP′s compression algorithm is based on the [[intra-frame]] coding of the video codec ''[[VP8]]''<ref>{{Cite web
| url = http://x264dev.multimedia.cx/?p=541
| url = http://x264dev.multimedia.cx/?p=541
| title = H.264 and VP8 for still image coding: WebP?
| title = H.264 and VP8 for still image coding: WebP?
Line 63: Line 64:
| first = Jason
| first = Jason
| last = Garrett-Glaser
| last = Garrett-Glaser
}}</ref> and the classical [[Resource Interchange File Format]] (RIFF) as [[container format (digital)|container format]].<ref name="Announcement-in-chromium" /> As such it is a block-based transformation scheme with eight bit of [[colour depth]] and a [[luminance-chrominance model]] with [[chroma subsampling]] by a ratio of 1:2 ([[YCbCr]] 4:2:0).<ref>{{Internetquelle
}}</ref> WebP is meant to produce smaller images than [[JPEG]] format while maintaining image quality.<ref>{{Cite web
|hrsg = WebM Project
|titel = VP8 Video Bitstream Guide
|url = http://www.webmproject.org/media/pdf/vp8-bitstream.pdf
|werk = VP8-Dokumentation des WebM Project
|datum = 2010-09-23
|zugriff = 2010-10-02
|sprache = Englisch
|format = PDF
}}</ref> Without further content the mandatory RIFF container leads to an [[computational overhead|overhead]] of only 20 Bytes and can hold additional [[metadata]]. The side length of WebP images is limited to a maximum of 16383 pixels (14 bits).

Format is based on block prediction. Each block is predicted on the values from 3 blocks upper to it and from 1 block left to it (block decoding is done in raster-scan order: Left-to-Right and Top-to-Bottom).
There are 4 basic modes of block prediction: Horisontal, Vertical, DC (one color), TrueMotion. Mispredicted data and not predicted blocks are compressed in 4x4 pixel subblock with [[Discrete cosine transform]] and (rare) [[Walsh–Hadamard transform]]. Both transforms are done with fixed point to avoid rounding errors. <ref name=bitspec>http://www.webmproject.org/media/pdf/vp8-bitstream.pdf</ref> Output of DCT & WHT is compressed with enthropy coder.

Format has explicit support of parallel decoding. <ref name=bitspec/>

The [[free software|free]] [[reference implementation]] consists of a converter software in form of a [[command-line interface|command-line]] program for Linux (webpconv) and a [[library (computing)|programming library]] for the decoding (the same as for WebM).

== Usage ==
The format is supposed to be a new [[open standard]] for lossly 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 favourably with the production of smaller files for comparable image quality.<ref>{{Cite web
| url = http://code.google.com/intl/no/speed/webp/docs/c_study.html
| url = http://code.google.com/intl/no/speed/webp/docs/c_study.html
| title = Comparative Study of WebP, JPEG and JPEG 2000
| title = Comparative Study of WebP, JPEG and JPEG 2000
Line 69: Line 89:
| publisher = Google
| publisher = Google
| accessdate = 1 October 2010
| accessdate = 1 October 2010
}}</ref>
}}</ref> WebP uses a [[Resource Interchange File Format]] (RIFF)-based [[container format (digital)|container format]]. <ref name="Announcement-in-chromium" />
[[Google Chrome|Chrome]] will be the first browser to support WebP;<ref>{{Internetquelle | url=http://blog.chromium.org/2010/09/webp-new-image-format-for-web.html | titel=Chromium Blog: WebP, a new image format for the Web | zugriff=2010-10-1 | datum=2010-9-30 | autor=Richard Rabbat}}</ref> support in upcoming versions of [[Mozilla Firefox|Firefox]] and [[Opera (web browser)|Opera]] is certain.<ref>[http://www.theregister.co.uk/2010/09/30/google_webp/ Google open sources JPEG assassin], theregister.co.uk</ref> Furthermore, there are plans to add support to [[WebKit]], thereby adding support for the format in the whole series of WebKit-based browsers.


== See also ==
== Criticism ==
The format and its (reference) implementation presented with the first publication is known to still be notably unusable.
'''Video formats'''
Jason Garrett-Glaser, a developer of the [[x264]] encoder, gave several points of criticism for WebP.<ref>{{Internetquelle | url=http://x264dev.multimedia.cx/?p=541 | titel=Diary Of An x264 Developer » H.264 and VP8 for still image coding: WebP? | zugriff=2010-10-1 | datum=2010-9-30 | autor=Jason Garrett-Glaser}}</ref> WebP would support only 4:2:0 color subsampling. The 4:2:2 and 4:4:4 schemes also present in JPEG are missing. The quality of reference files in WebP format would be worse and more blurry at comparable filesize compared to JPEG-encoded counterparts.
* [[WebM]], a video format introduced by Google earlier in 2010
'''Still image formats'''
* [[JPEG 2000]], an improvement intended to replace the older JPEG by the JPEG committee, introduced in 2000
* [[JPEG XR]], an improvement to JPEG, introduced by Microsoft in 2009

⚫
== References ==
⚫
{{Reflist|2}}


== External links ==
== External links ==
* {{Official|http://code.google.com/speed/webp/}}
* {{Official|http://code.google.com/speed/webp/}}

⚫
== References ==
⚫
{{Reflist|2}}


{{Graphics file formats}}
{{Graphics file formats}}
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Revision as of 14:10, 3 October 2010

WebP
Filename extension
.webp[1]
Internet media type
image/webp
Magic numberWEBP
Developed byGoogle
Initial release30 September 2010 (2010-09-30)[2]
Type of formatImage format
Lossy compression algorithm
Contained byResource Interchange File Format (RIFF)[3]
Free format?Yes[4]
Websitecode.google.com/speed/webp

WebP (to be pronounced “weppy”[5]) is an image format for lossily compressed image files. It is developed by Google, based off technology acquired with the purchase of On2 Technologies.[6] As another descendant of the video codec VP8 it is a sister project of the video format WebM.

Technology

WebP′s compression algorithm is based on the intra-frame coding of the video codec VP8[7] and the classical Resource Interchange File Format (RIFF) as container format.[2] As such it is a block-based transformation scheme with eight bit of colour depth and a luminance-chrominance model with chroma subsampling by a ratio of 1:2 (YCbCr 4:2:0).[8] Without further content the mandatory RIFF container leads to an overhead of only 20 Bytes and can hold additional metadata. The side length of WebP images is limited to a maximum of 16383 pixels (14 bits).

Format is based on block prediction. Each block is predicted on the values from 3 blocks upper to it and from 1 block left to it (block decoding is done in raster-scan order: Left-to-Right and Top-to-Bottom). There are 4 basic modes of block prediction: Horisontal, Vertical, DC (one color), TrueMotion. Mispredicted data and not predicted blocks are compressed in 4x4 pixel subblock with Discrete cosine transform and (rare) Walsh–Hadamard transform. Both transforms are done with fixed point to avoid rounding errors. [9] Output of DCT & WHT is compressed with enthropy coder.

Format has explicit support of parallel decoding. [9]

The free reference implementation consists of a converter software in form of a command-line program for Linux (webpconv) and a programming library for the decoding (the same as for WebM).

Usage

The format is supposed to be a new open standard for lossly 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 favourably with the production of smaller files for comparable image quality.[10] Chrome will be the first browser to support WebP;[11] support in upcoming versions of Firefox and Opera is certain.[12] Furthermore, there are plans to add support to WebKit, thereby adding support for the format in the whole series of WebKit-based browsers.

Criticism

The format and its (reference) implementation presented with the first publication is known to still be notably unusable. Jason Garrett-Glaser, a developer of the x264 encoder, gave several points of criticism for WebP.[13] WebP would support only 4:2:0 color subsampling. The 4:2:2 and 4:4:4 schemes also present in JPEG are missing. The quality of reference files in WebP format would be worse and more blurry at comparable filesize compared to JPEG-encoded counterparts.

External links

References

  1. ^ "WEBP file extension". DotWhat.net. Retrieved 1 October 2010.
  2. ^ a b Rabbat, Richard (20 September 2010). "WebP, a new image format for the Web". Chromium Blog. Google. Retrieved 1 October 2010.
  3. ^ "RIFF Container". Google Code. Google. Retrieved 1 October 2010.
  4. ^ "WebP FAQs". Google Code. Google. Retrieved 1 October 2010.
  5. ^ WebP Home: “Did you know? WebP is pronounced "weppy". /(wĕpˈē)/”
  6. ^ Shankland, Stephen (30 September 2010). "Google offers JPEG alternative for faster Web". CNET News. CBS Interactive. Retrieved 1 October 2010.
  7. ^ Garrett-Glaser, Jason (30 September 2010). "H.264 and VP8 for still image coding: WebP?". Diary Of An x264 Developer. Retrieved 1 October 2010.
  8. ^ "VP8 Video Bitstream Guide" (PDF). VP8-Dokumentation des WebM Project. WebM Project. 23 September 2010. Retrieved 2 October 2010.
  9. ^ a b http://www.webmproject.org/media/pdf/vp8-bitstream.pdf
  10. ^ "Comparative Study of WebP, JPEG and JPEG 2000". Google Code. Google. Retrieved 1 October 2010.
  11. ^ Richard Rabbat (2010-9-30). "Chromium Blog: WebP, a new image format for the Web". Retrieved 2010-10-1. {{cite web}}: Check date values in: |access-date= and |date= (help)
  12. ^ Google open sources JPEG assassin, theregister.co.uk
  13. ^ Jason Garrett-Glaser (2010-9-30). "Diary Of An x264 Developer » H.264 and VP8 for still image coding: WebP?". Retrieved 2010-10-1. {{cite web}}: Check date values in: |access-date= and |date= (help)
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