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.

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

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

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

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Posted by Richard Rabbat, Product Manager and Pascal Massimino, Software Engineer