High Performance Images

Chapter 5. Browser-Specific Formats

Nick Doyle

While the traditional image formats used on the Web—GIF, JPEG, and PNG—have served us well and will continue to be useful long into the future, there are a number of new formats that can be particularly useful on the Web today. The most notable and useful of these formats are Google’s WebP, Microsoft’s JPEG XR, and JPEG 2000. All three of these formats improve on the features of GIF, JPEG, and PNG while often also improving compression and fidelity.

The biggest improvement these formats all provide to the Web is that they all support lossy compression with alpha transparency. Traditionally, to have an image on the Web with alpha transparency, the only option was to use PNG. While this enabled alpha transparency, it came at the cost of dramatically heavier images because PNG’s compression is lossless. Now, with these new formats, it’s possible to get the best of both worlds: alpha transparency at a fraction of the byte size.

The second improvement WebP, JPEG XR, and JPEG 2000 provide is smarter and more robust image compression. We’ve learned a lot about image compression since JPEG was first introduced in 1992, and these three formats have capitalized on that. While these formats each use a different approach to compression, they often outperform JPEG at comparable fidelity levels for byte savings.

There’s one drawback to these formats, though, at least on today’s Web: not all browsers support them. Actually, for the most part, any ...