CSS Sprites is a technique by which we can combine multiple images in a single big image and position the various parts of this big image with our elements u

sing pure CSS attributes. The primary objective behind using CSS Sprites is to decrease the number of HTTP requests and thus decreasing the request stress on server. The idea behind CSS Sprites is to consolidate multiple images into one sprite and then selectively display portions of this sprite with positioning. It starts by creating a larger CSS Sprite by grouping more than one images (usually icons) together and aligning them in proper grid style to aid the positioning. Then it is aligning used a proper positioning values on the webpages to show their respective images. This way it decreases the number of HTTP requests and thus increases the overall speed of webpages.

Sometimes back, we used the favourite slicing technique to break down a larger image into smaller slices (parts) so as to make pages load faster, but all this technique was only fooling our eyes as the page looked like loading faster, while in reality it was not. Each of those images was fed up as a separate request to the server and would increase the time of loading actually.

According to Yahoo UI blog, the resultant sprite created by joining smaller images is always smaller in size than the combined contributed parts. It is because we have to use a single color table for the sprite instead of individual color tables for the contributed ones. Another advantage of using sprites is that this way we save the overhead required by the images.

How do CSS Sprites work?

As it turns out, the basic tools to do this are built into CSS, given a bit of creative thinking.

Let’s start with the master image itself. Dividing a rectangle into four items, you’ll observe in this master image that our intended “before” link images are on the top row, with “after”:hover states immediately below. There’s no clear division between the four links at the moment, so imagine that each piece of text is a link for now. (For the sake of simplicity, we’ll continue to refer to link images as “before” images and the :hover state as “after” for the rest of this article. It’s possible to extend this method to :active, :focus, and :visitedlinks states as well, but we won’t go into that here.)

Those familiar with Petr Stanicek’s (Pixy) Fast Rollovers may already see where we’re going with this. This article owes a debt of gratitude to Pixy’s example for the basic function we’ll be relying on. But let’s not get ahead of ourselves.

On to the HTML. Every good CSS trick strives to add a layer of visuals on top of a clean block of code, and this technique is no exception:

  <ul id="skyline">
    <li id="panel1b"><a href="#1"></a></li>
    <li id="panel2b"><a href="#2"></a></li>
    <li id="panel3b"><a href="#3"></a></li>
    <li id="panel4b"><a href="#4"></a></li>
  </ul>

This code will serve as a base for our example. Light-weight, simple markup that degrades well in older and CSS-disabled browsers is all the rage, and it’s a trend that’s good for the industry. It’s a great ideal to shoot for. (We’ll ignore any text inside the links for the time being. Apply your favorite image replacement technique later to hide the text you’ll end up adding.) Read more…

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