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Perhaps this is a naive question, but are there any benchmarks comparing client-side load times for actual images vs. images rendered in CSS?

Server-side bandwidth savings is easier to calculate, and while I realize this kind of savings for sites like Twitter can create noticeable margins, I'm curious as to what the cost-benefit threshold is.

Can't give you any hard numbers but I'm quite sure that "CSS images" this size load faster in most cases. But, once you load an actual raster image you're done with it: you can cache it, reuse it as many times as you want, manipulate it's placement, etc. - all without significant performance issues. With "CSS images" that's not the case. Placing a few on one page and/or allowing user any interaction with them will create performance bottlenecks more often than not. For the 'real world usage' it's safer to stay with the raster images.

Matt Seeley, UI Engineer at Netflix, made a presentation in which he touches these issues. It's available here: http://dl.dropbox.com/u/5618867/mseeley-2011-09-27-html5devc...

I have an Atom-Netbook and didn't notice any delay. The decoding of an image file is also a little work, i assume both are very low.

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