Chromium Blog
News and developments from the open source browser project
Data Compression in Chrome Beta for Android
Tuesday, March 5, 2013
Today’s Chrome Beta for Android
update
brings your saved passwords and autofill entries from your desktop to your phone and tablet. This release also introduces an experimental data compression feature that will yield substantial bandwidth savings. This feature is powered by a connection to a
SPDY
proxy running on Google’s servers, paired with content optimization performed by our
open-source PageSpeed libraries
, specifically tuned for Chrome Beta on Android.
By using SPDY, the proxy is able to multiplex multiple request and response streams in parallel over a single TCP connection to your phone or tablet. When this new feature is enabled (enable the “Experimental Data Compression Proxy” under
chrome://flags
) the browser-to-proxy connection is over SSL, for a more secure browsing experience. In addition, only HTTP traffic is routed through and optimized by the proxy, so secure (HTTPS) requests will bypass the proxy and continue to connect directly to the destination. Furthermore, DNS lookups are performed by the proxy, instead of on the mobile device. Turning on this experimental feature also enables
Safe Browsing
.
For an average web page, over 60% of the transferred bytes are images. The proxy optimizes and transcodes all images to the
WebP format
, which requires fewer bytes than other popular formats, such as JPEG and PNG. The proxy also performs intelligent compression and minification of HTML, JavaScript and CSS resources, which removes unnecessary whitespace, comments, and other metadata which are not essential to render the page. These optimizations, combined with mandatory gzip compression for all resources, can result in substantial bandwidth savings.
For a deeper dive into the technical details, check out our
whitepaper
in Chrome for Android’s developer documentation. The latest version of Chrome Beta for Android is available on
Google Play
(use the link, you won't find it in search)! We look forward to your early
feedback
.
Posted by Matt Welsh, Software Engineer & Mobile Web Performance Gearhead
Update April 10, 2013:
To enable this experimental data compression feature, go to “Bandwidth Management” in Settings and enable “Reduce Data Usage.” From the most recent Chrome Beta for Android
release
onwards, no need to look under
chrome://flags
.
Using WebP to Improve Speed
Thursday, February 7, 2013
Since speed is critical for a good experience when using the web, at Google we’re always exploring ways to make the web faster. As it turns out, one of the biggest bang-for-the-buck ways to do that is by replacing JPEG and PNG images with
WebP
. WebP offers significantly better compression than these legacy formats (around
35% better
in most cases), and when you consider that
over 60%
of typical page sizes are images, the benefits can be substantial. WebP translates directly into less bandwidth consumption, decreased latency, faster page loads, better battery consumption on mobile, and overall happier users.
Case in point: the
Chrome Web Store
uses many large promotional images and tiles on its home page, making it a very heavyweight page. The team was eager to find ways to improve its speed, without sacrificing the user experience or giving up image quality. WebP to the rescue!
By converting PNGs and JPEGs to WebP, the Chrome Web Store was able to reduce image sizes by about 30% on average (here’s one sample image in
WebP
at 8.3kB and
JPEG
at 32kB). Given the number of requests Chrome Web Store serves, this adds up to
several terabytes
of savings every day.
For users, the rubber meets the road when it comes to how fast the page loads though. On this score, with WebP we were able to reduce average home page load time by nearly one-third — a huge benefit for our users.
To implement WebP, the team first added transcoding support to the image request pipeline; then at runtime the site checks whether the client browser supports WebP and requests the WebP version for each image when it does. The effort to implement it turned out to be not much work for a lot of benefit.
To find out more about how you can make your site faster, visit our
Make the Web Faster
site and dive into
WebP
.
Posted by Stephen Konig, Product Manager
Lossless and Transparency Modes in WebP
Thursday, August 30, 2012
Cross-posted on the
Google Developers Blog
At Google, we are constantly looking at ways to make web pages load faster. One way to do this is by making web images smaller. This is especially important for mobile devices where smaller images save both bandwidth and battery life. Earlier this month, we released
version 0.2 of the WebP library
that adds support for lossless and transparency modes to compress images. This version provides CPU and memory performance comparable to or better than PNG, yet results in
26% smaller files
.
WebP’s improved compression comes from advanced techniques such as dedicated
entropy codes
for different color channels, exploiting 2D locality of
backward reference distances
and a color cache of recently used colors. This complements basic techniques such as
dictionary coding
,
Huffman coding
and
color indexing transform
. We think that we've only scratched the surface in improving compression. Our newly added support for
alpha transparency
with lossy images promises additional gains in this space, helping make WebP an efficient replacement for PNG.
The new WebP modes are supported natively in the latest Beta version of Chrome. The
bit stream specification
for these new WebP modes has been finalized and the
container specification
has been updated. We thank the community for their valuable feedback and for helping us evolve WebP as a new image compression format for the web. We encourage you to try these new compression methods on your favorite set of images, check out the code, and continue to provide
feedback
.
Posted by Jyrki Alakuijala - Software Engineer
Lossless and Transparency Encoding in WebP
Thursday, November 17, 2011
In September 2010 we announced the
WebP
image format with lossy compression. WebP was proposed as an alternative to JPEG, with
25–34%
better compression compared to JPEG images at equivalent SSIM index. We received lots of feedback, and have been busy improving the format.
Last month
we announced WebP support for animation, ICC profile, XMP metadata and tiling. Today, we introduce a new mode in WebP to compress images losslessly, and support for transparency – also known as alpha channel – in both the lossless and lossy modes.
With these new modes, you can now use WebP to better compress all types of images on the web. Photographic images typically encoded as JPEG can be encoded in WebP lossy mode to achieve smaller file size. Icons and graphics can be encoded better in WebP lossless mode than in PNG. WebP lossy with alpha can be used to create transparent images that have minimal visual degradation, yet are much smaller in file size. Animations compressed as GIFs can use animation support in WebP.
New lossless mode
Our main focus for lossless mode has been in compression density and simplicity in decoding. On average, we get a 45% reduction in size when starting with PNGs found on the web, and a
28% reduction
in size compared to PNGs that are re-compressed with pngcrush and pngout. Smaller images on the page mean faster page loads.
New transparency mode
Today, webmasters who need transparency must encode images losslessly in PNG, leading to a significant size bloat. WebP alpha encodes images with low bits-per-pixel and provides an effective way to reduce the size of such images. Lossless compression of the alpha channel adds just
22% bytes
over lossy (quality 90) WebP encoding. Smaller alpha overhead means richer images on webpages.
You can find a more detailed compression study for these modes
here
and sample images in the
WebP-Gallery
. The bit stream specification has not been finalized, and the encoding and decoding implementations have not yet been optimized for processing speed. We encourage you to
try it out
on your favorite set of images, check out the
code
, and
provide feedback
. We hope WebP will now handle all your needs for web images, and we're working to get WebP supported in more browsers.
Posted by Jyrki Alakuijala, Vikas Arora, and Urvang Joshi, Software Engineers
WebP in Chrome, Picasa, Gmail With a Slew of New Features and Improvements
Friday, May 20, 2011
Since we
announced
WebP
, a new image format based on WebM technology and the VP8 codec, we’ve been working hard with the open web community to improve and enhance it. Today we are happy to share news about a few new features and expanded support for WebP.
New Features
WebP's compression algorithms have been significantly improved while remaining completely
compatible with the previous releases. We hope the quality of a few sample images in the new gallery will
delight you
.
On the decoding side, we have integrated a fancy upsampler. Fancy upsampling reduces the pixelation of strong edges. You can see this feature when you zoom in, for example on a
WebP image with red edges
converted from this PNG original:
Original image in PNG format
Without fancy upsampling: strong stair-like pattern
With fancy upsampling: smoother edge
We also introduced the ability to incrementally decode the data as your computer downloads it from the web, a feature that allows the browser to display images without having to wait for the whole file to download. This feature is already enabled in Chrome 12.
On the encoding side, to further improve quality, we focused on segmenting the picture into areas with similar compressibility. For each of these segments, we tune the amount of compression and filtering differently, and bits are redistributed where they are most useful. Take for instance the image reproduced below [1]:
The easy segment contains lot of disparate signals and can be compressed more than the difficult one, which will be assigned more bits. In this example, the encoder only used two segments. By using even more segments (up to four), WebP is now able to retain many of the original
details
of the image [2]. This is in contrast to the frequent
ringing artifacts
one can clearly
see in JPEG
images.
The uneven distribution of bits between difficult and easy area is controlled in the new encoder using the
-sns
parameter, short for Spatial Noise Shaping. Its value can be set from 0 to 100 (0 meaning OFF) and with a default of 80. Note that when you enable SNS,
PSNR
may be degraded, but the overall visual quality is much improved.
We’ve added simple encoding and decoding example binaries to the
libwebp library
. In addition, we’ve added JNI support that allows Java programs to decode WebP images. Next up is transparency, also known as Alpha channel; we’re experimenting with it
now
and planning to add it to the next stable version of the codec. In parallel, we continue to improve the codec’s speed and will release a complete specification for the metadata format.
Increased adoption
WebP is now natively supported in Chrome and
Opera
. Google products including Gmail and Picasa Web Albums, have also added support to WebP so you can share, send and receive WebP images. WebP support is coming to AppEngine. In addition,
Google Instant Previews
now store images in WebP to reduce their storage needs.
Users that want to manipulate WebP images can now do so using software developed by the community including
Pixelmator
,
ImageMagick
, the
WebP format plugin
for Photoshop and the
Java VP8 decoder
. The open-source community has also contributed support for Mac OS X with
MacPorts packages
, Linux
Debian
,
OpenSUSE
and
Gentoo
packages and the
Apache HTTP Server
. On Windows, users who want to view WebP images natively, can download the
WebP codec
. This codec brings WebP support to such software as Microsoft Office 2010, Windows Media Center and Photo Edit.
The new features,
quality improvements
and increased adoption of WebP get us excited about its future. As always, we’re looking for more feedback as well as code contributions from the community. Let us know on the
mailing list
how your experiments are panning out and what new features you’d like to see in the future.
Image credits:
[1]: "Kayaker at Ekstremsportveko 2010, Voss". Image Author: Kjetil Birkeland Moe. Reproduced with permission of the author.
PNG source
, and
Blog post
by author with comparison of JPEG and WebP.
[2]: A storm at Pors-Loubous,
Plogoff
,
Finistère
, France. Image Author: Henri Camus. Permission: CC-BY; CC-BY-1.0. Source:
http://commons.wikimedia.org/wiki/File:A_storm_at_Pors-Loubous.jpg
Posted by Richard Rabbat, Product Manager and Pascal Massimino, Software Engineer
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