A long time ago, “responsive” didn’t mean “resize your browser window repeatedly while fellow designers orgasm until they resemble a moleskin atop a puddle”. It simply meant “Reacting quickly and positively”, meaning that the page loaded fast and you could interact with it immediately.
One way to do this is to reduce the weight of the page by serving images that have a smaller file-size, thereby consuming less bandwidth and taking less time to download a page. In the last year, web pages download approximately the same number of images, but their total size has increased from about 600K to 812K, making images about 60% of the total page size.
One way to reduce this amount is to encode images in a new(ish) format called webP. It’s developed by Google and is basically a still version of their webM video codec. Google says
WebP is a new image format that provides lossless and lossy compression for images on the web. WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller in size compared to JPEG images at equivalent SSIM index. WebP supports lossless transparency (also known as alpha channel) with just 22% additional bytes. Transparency is also supported with lossy compression and typically provides 3x smaller file sizes compared to PNG when lossy compression is acceptable for the red/green/blue color channels.
Opera uses it precisely for this compression; it’s used in Opera Turbo, which can be enabled in Opera desktop, Opera Mobile and the Chromium-based Yandex browser. This transcodes images on-the-fly to webP before squirting them down the wire and, on slower connections, it’s still faster.
In tests, Yoav Weiss reported that “Using WebP would increase the savings to 61% of image data”.
WebP is currently supported only in Opera (Presto), Google Chrome, Yandex and Android Browser on Ice Cream Sandwich, which makes it difficult to deploy on the Web. new confidence about technologies in the VP8 video codec on which it’s based might make them feel better about it?)
However, there’s some handy new CSS coming to the rescue soon (when browser vendors implement it). We’ve long been able to specify CSS background images using
background-image: url(foo.png);, but now say hello to CSS Image Values and Replaced Content Module Level 4′s Image Fallbacks, which uses this syntax:
background-image: image("wavy.webp", "wavy.png", "wavy.gif");
image rather than
url before the list of images.)
The spec says “Multiple ‘image -srcs’ can be given separated by commas, in which case the function represents the first image that’s not an invalid image.”
Simply: go through the list of images and grab the first you can use. If it 404s, continue going through the list until you find one you can use. Note that this isn’t supported anywhere yet, but I hope to see it soon.
Read more @ Bruce Lawson’s personal site.