The WebP experiment

You might have noticed over the last few days that my blog underwent some surgery, and in particular that some even now, on some browsers, the home page does not really look all that well. In particular, I’ve removed all but one of the background images and replaced them with CSS3 linear gradients. Users browsing the site with the latest version of Chrome, or with Firefox, will have no problem and will see a “shinier” and faster website, others will see something “flatter”, I’m debating whether I want to provide them with a better-looking fallback or not; for now, not.

But this was also a plan B — the original plan I had in mind was to leverage HTTP content negotiation to provide WebP variants of the images of the website. This was a win-win situation because, ludicrous as it was when WebP was announced, it turns out that with its dual-mode, lossy and lossless, it can in one case or the other outperform both PNG and JPEG without a substantial loss of quality. In particular, lossless behaves like a charm with “art” images, such as the CC logos, or my diagrams, while lossy works great for logos, like the Autotools Mythbuster one you see on the sidebar, or the (previous) gradient images you’d see on backgrounds.

So my obvious instinct was to set up content negotiation — I’ve used it before for multiple-language websites, I expected it to work for multiple times as well, as it’s designed to… but after setting all up, it turns out that most modern web browsers still do not support WebP *at all*… and they don’t handle content negotiation as intended. For this to work we need either of two options.

The first, best option, would be for browsers only Accept the image formats they support, or at least prefer them — this is what Opera for Android does: Accept: text/html, application/xml;q=0.9, application/xhtml+xml, multipart/mixed, image/png, image/webp, image/jpeg, image/gif, image/x-xbitmap, */*;q=0.1 but that seems to be the only browser doing it properly. In particular, in this listing you’ll see that it supports PNG, WebP, JPEG, GIF and bimap — and then it accepts whatever else with a lower reference. If WebP was not in the list, even if it had an higher preference for the server, it would not be sent to the client. Unfortunately, this is not going to work, as most browsers send Accept: */* without explicitly providing the list of supported image formats. This includes Safari, Chrome, and MSIE.

Point of interest: Firefox does explicit one image format before others: PNG.

The other alternative is for the server to default to the “classic” image formats (PNG, JPEG, GIF) and then expect the browsers supporting WebP prioritizing it over the other image formats. Again this is not the case; as shown above, Opera lists it but does not prioritize, and again, Firefox prioritizes PNG over anything else, and makes no special exception for WebP.

Issues are open at Chrome and Mozilla to improve the support but they haven’t reached mainstream yet. Google’s own suggested solution is to use mod_pagespeed instead — but this module – which I already named in passing in my post about unfriendly projects – is doing something else. It’s on-the-fly changing the content that is provided, based on the reported User-Agent.

Given that I’ve spent some time on user agents, I would say I have the experiences to say that this is a huge pandora’s vase. If I have trouble with some low-development browsers reporting themselves as Chrome to fake their way in with sites that check the user agent field in JavaScript, you can guess how many of those are going to actually support the features that PageSpeed thinks they support.

I’m going to go back to PageSpeed in another post, for now I’ll stop to say that WebP has the numbers to become the next generation format out there, but unless browser developers, as well as web app developers start to get their act straight, we’re going to have hacks over hacks over hacks for the years to come… Currently, my blog is using a CSS3 feature with the standardized syntax — not all browsers understand it, and they’ll see a flat website without gradients; I don’t care and I won’t start adding workarounds for that just because (although I might use SCSS which will fix it for Safari)… new browsers will fix the problem, so just upgrade, or use a sane browser.