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Why Mozilla had a change of heart about WebP images

Firefox programmers reconsidered their opposition to Google's image format for two reasons: new data showing graphics files 30 percent smaller for faster page loads -- and that the info came from a close ally.

WebP logo

Sure, technology decisions often are the result of personal predilection, political scheming, and inter-company rivalries. But cold hard data still can win the day -- and that's the main reason why Mozilla is reconsidering its earlier decision not to support Google's WebP image format.

Specifically, new data shows that Google isn't just blowing smoke when it promised that using WebP lets Web site operators save precious bytes when it's sending Web-page data to browsers. Smaller file sizes mean that browsers can show Web pages faster, that Web site operators cut bandwidth usage, and that people with capped data plans get a little more headroom. found that WebP cut data usage with the two major image formats on the Web -- JPEG and PNG -- said Andreas Gal, Mozilla's vice president of mobile engineering.

"A contributor has reported that re-compressing PNG icons with WebP has significant savings when those icons have an alpha mask," Gal said yesterday in an interview over e-mail. "Even recompressing JPG icons seems to yield a 30 percent savings when using WebP."

Alpha masks let people designate part of an image as transparent, something that's very useful for example with icons placed over a background. And is all about that very thing: its app for Firefox OS or Android presents smartphone users with a dynamically generated array of Web apps. is in a good position to bend Mozilla's ear, too: Mozilla just happens to be an investor in it. So although hard data matters in technology decisions, trusting the source of it helps, too.

Mozilla is still evaluating WebP and hasn't yet committed to building it into Firefox. Still, the new situation is a big step forward for a vocal group of WebP fans. Attracting support from multiple browsers makes it much more likely that a technology can be blessed as a Web standard and that Web programmers can use it without fearing that only people with some browsers will be able to make use of it.

Browser makers pay a big price to build a new feature into the Web: if developers use it widely, then browsers must support it for the indefinite future. If they remove that support at some point to streamline the software, for example, then parts of the Web will show up as broken. Adding more image formats makes the Web more complicated to produce and deliver. And new new software to decode images also means a new possible avenue for network attacks.

Thus, Gal was careful to express caution:

These reported benefits and use cases must be weighed against fragmenting the available image formats on the Web, in particular since some browser implementers might not be comfortable implementing WebP. We re-opened the bug to refresh the WebP discussion. We have not committed to a WebP implementation.

We are merely discussing whether we should do so. We are considering a couple alternatives as well, including a CSS property to implement alpha masks, which in combination with JPG could yield similar results as WebP for icons with alpha transparency. We will encourage the contributors working on this evaluation to take the discussion to public mailing lists or the bug.

An image format might seem an odd cause to fight for, but WebP has attracted a passionate following. It's not unlike those who fervently advocate VP8 or H.264 in the present video codec wars.

Indeed, on Mozilla's earlier bug for tracking WebP support, the Firefox developer shut down comments since the discussion was getting out of hand. In the new Firefox bug for WebP support, those passions are showing again.

"Although I am glad this was reopened finally, I hate to sound jaded when I say that you are extraordinarily late to the party," said one commenter who accused Mozilla of trying to control Web standards for its own ends. "You already lost myself and many others users over the bad blood regarding this feature and how it was handled. It is going to take a long time to heal those wounds."

The comment was met with a nearly audible groaning.

"Can we please, please not get into blame, recrimination, accusation or anything beyond implementation progress on this thread?" requested Peter Gasston, a Web developer and author.

Programmer Dave Garrett also tried to settle things down.

"The monumental task of becoming a full-fledged Web image format to eventually be used by the entire world is not going to be instantaneous," he said. "I'm sorry to say, but due to the incomprehensible level of emotion attached to a new file format this bug really should be set to restricted commenting too so as to not let it turn into another unreadable mess."