WebP, Google's answer to JPEG, gets better quality

Google is obsessed with speeding up the Web, and the company hopes sprucing up its image format will help. It's got a lot of convincing to do, though.

Stephen Shankland principal writer
Stephen Shankland has been a reporter at CNET since 1998 and writes about processors, digital photography, AI, quantum computing, computer science, materials science, supercomputers, drones, browsers, 3D printing, USB, and new computing technology in general. He has a soft spot in his heart for standards groups and I/O interfaces. His first big scoop was about radioactive cat poop.
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Stephen Shankland
6 min read
The new version of Google's WebP encoder can concentrate its data on the complicated parts of an image.
The new version of Google's WebP encoder can concentrate its data on the complicated parts of an image. Google

Google has improved the quality of WebP, an image format it promises will speed up the Web--if the company can just convince people to use it instead of JPEG.

WebP, unveiled last year, is a still-image variation of the company's open-source, royalty-free WebM video technology. Google's sales pitch: with its newer compression technology, Web pages will load faster and less network bandwidth is necessary compared to using JPEGs.

Now the company argues that it's improved quality of WebP images through more elaborate encoding software. It can, for example, concentrate its data on the complicated parts of images. And a "fancy upsampler" smooths diagonal edges that otherwise would be prone to artifacts. The improvements don't require new decoding technology, too.

"WebP's compression algorithms have been significantly improved while remaining completely compatible with the previous releases," said Google product manager Richard Rabbat and programmer Pascal Massimino in a blog post last week. Better quality compression means an image can look better at a given file size or match earlier quality without taking up as much storage space and network data.

WebP is one example of the Google obsession to rebuild the Web in faster form. Google is working on many others, ranging from reworking basic communcations protocols with SPDY and preloading some Web pages in the Chrome browser to penalizing slow Web sites in its search-ad business. Another technology, called SSL False Start, cuts the time it takes to set up a Web connection--by 30 percent, the company said at its Google I/O conference.

WebP logo

WebP has major challenges, though. The biggest is convincing backers of the universally supported and very well understood JPEG, but there are others, too: persuading browser makers and Web developers to use WebP, adding features to match JPEG or improve on it, and assure tech companies that they can feel confident in relying on something that's not standardized.

Major new WebP features
Standardization today probably would be premature, though: WebP is being put through the Google wringer of release early, iterate often.

"It's an image format we're looking at to grow in the future. It's still young, and we're adding some more things," Rabbat said in a Google I/O talk. Among the upcoming WebP features:

Alpha channels for transparency--an important feature that JPEG lacks--will come to the next version of WebP. That will let designers designate areas of an image as transparent, which can be useful in contexts such as overlaying graphics on different colored backgrounds.

• Aiding the transparency technology will be a lossless compression option that can be used for when the highest image fidelity is needed. That, along with transparency, could mean Google might position WebP as an alternative to the PNG (Portable Network Graphics) standard, too.

The improved WebP encoder also handles diagonal edges better, with fewer artifacts, Google said.
The improved WebP encoder also handles diagonal edges better, with fewer artifacts, Google said. Google

• WebP will be able to accommodate metadata, the increasingly important mechanism to embed data such as camera exposure information or photo captions within the photo file, but it won't use the EXIF technology that cameras use to record some data. Specifically, Google will use Adobe's XMP (Extensible Metadata Platform) technology.

"We want to support people's need for metadata, and we're adding XMP support," Rabbat said. "We know some people are used to EXIF, but EXIF has been painful for lots of people because there's no real standard around it. It just creates problems for the Web. Because this is a format we want to have for many years in the future, we're focusing on better, cleaner technology."

• 3D "Because we're now in a much newer world, we're adding 3D stereoscopy," Rabbat said. It'll use a multi-image technology that can package several images into one file--in this case right-eye and left-eye images. That approach will help when people want to use a single image file to reach both 2D and 3D displays, he said.

"If you look at 3D images that out there now that are in JPEG, if you display them on a 2D display, they just don't make any sense," Rabbat said. "With our ability to put multiple images in the same image file, we can call the left image vs. the right image separately."

• The multi-image technology also will help Web developers trying to use the Web pages' CSS background image technology.

"Instead of having to figure out what coordinates you're going to pick the image from, you can just refer to to the image within that multi-image format," he said; each image within the file can be referenced with a simple hashtag label. "There won't be any weird CSS to correct."

Massimino also described some plans in a mailing list message yesterday. Among features he announced is experimental support for more detailed color information using 4:4:4 chroma subsampling rather than WebP's coarser 4:2:0 approach.

At its Google I/O conference, the company promised a host of WebP improvements.
At its Google I/O conference, the company promised a host of WebP improvements. screenshot by Stephen Shankland/CNET

He said the WebP encoding software speed has doubled by tapping into an x86 processor feature called SSE2, but that more optimizations can be added. WebP decoding, which is more of a bottleneck when it comes to displaying a Web page, will get faster with similar SSE2 support, but it's still about three times slower than a good JPEG decoder.

The search for WebP allies
Google has found one notable ally. Opera uses WebP for its browsers' Turbo mode, which translates Web pages for mobile or limited-bandwidth Internet connections, and Google's own Chrome supports WebP images too.

But most of the Web's users can't see WebP images, making Google's WebP gallery look pretty lopsided. Google's Android browser also can't view WebP.

Mozilla, maker of the Firefox browser, considered the possibility but decided against WebP support for a number of technical reasons. Mozilla has marked WebP support as a "won't fix" item, at least as WebP currently is defined.

Mozilla's reluctance is notable given that it's perhaps the most prominent Google ally for WebM video.

WebP is missing some useful features that even comparatively ancient JPEG has, said Mozilla graphics programmer Jeff Muizelaar.

"Every image format that becomes 'part of the Web platform' exacts a cost for all time: all clients have to support that format forever, and there's also a cost for authors having to choose which format is best for them," Muizelaar said. "Personally, I'd rather the effort being spent on WebP be spent on an improved JPEG encoder or even an improved JPEG XR encoder."

JPEG XR is a Microsoft-led effort to improve JPEG, and it's resulted in an actual standard; Google hasn't discussed its plans for standardization, but that's an important step for some parts of the computing industry--particularly camera makers considering baking support into their hardware.

The plight of JPEG XR is illustrative. It's made little headway, at least publicly, despite some real advantages such as extended dynamic range and years of Microsoft promotional labor.

WebP has an interesting difference, though: Google. The company has some of the world's most popular Web properties, and it's got a browser used by more than 10 percent of people worldwide today. By controlling what's going on at both ends of the Internet connection, Google can make WebP relevant for a large number of people, even if it's a small fraction of the overall Internet user base.

It's begun expanding WebP use on its own properties. Picasa Web Albums users can upload WebP images and view them with a compatible browser now. Gmail, too, can handle WebP images, and Google's App Engine service for cloud computing will get it. And to try to build software support, Google has released a WebP codec to let Windows software such as file manager thumbnails, Office 2010, and Windows' print engine handle WebP.

It takes a long time to move an entire industry. Google has more patience than most, though, so don't count WebP out yet.