What's the name of the technique where the images on a web page fade in as they scroll into view?

Here's a webpage that does what I'm describin开发者_运维百科g: http://mashable.com/2010/05/13/mobile-tech-journalists/

What's going on with the images? It seems that they get loaded and fade in as you scroll them into view.

Is there a name for this technique? Is it a new optimization technique? Where can I read more about it?

The images are downloaded using Ajax, and once loaded on the client-side they are displayed using the fade-in effect (probably using jQuery). It's an optimization technique, because it means you're only loading images that a user actually looks at. If a user only reads the top of the page, there is no point to send him all the page's images. This way it cuts down some of the web traffic generated by the web server.

It's called lazy loading and there's a jQuery plugin for that.