CSS sprites is a technique to combine unlimited number of images into one to improve the performance of your web page.Have you ever seen the CSS technique where the “on” and “off” states of a button are contained within the same image and are activated by shifting the background-position? Think of CSS Sprites as an extension of that technique.With millions of users Google,Yahoo!,MySpace,YouTube and AOL do everything they can to improve the user experience. As all of them use CSS sprites to save numerous HTTP requests for their intricate interfaces.

What does css sprites does…

Group multiple images together (usually icons or decorative images) into one sprite
Evenly space these images, aligned into one or more lines
Set this sprite to the background image of an element (usually a list)
Position the sprite to display the appropriate image by shifting the X or Y position by a multiple of the spacing
Enjoy the increased speed and reduced HTTP requests

Create your own CSS Sprite…
Step1-Create an image (or collect it from anywhere)using photshop,fireworks,gimp etc.. depends on your choice.

#nav li a.item1 {background-image:url('../img/image1.jpg')}
#nav li a:hover.item1 {background-image:url('../img/image1_over.jpg')}
#nav li a.item2 {background-image:url('../img/image2.jpg')}
#nav li a:hover.item2 {background-image:url('../img/image2_over.jpg')}
#nav li a.item3 {background-image:url('../img/image3.jpg')}
#nav li a:hover.item3 {background-image:url('../img/image3_over.jpg')}
#nav li a.item4 {background-image:url('../img/image4.jpg')}
#nav li a:hover.item4 {background-image:url('../img/image4_over.jpg')}
#nav li a.item5 {background-image:url('../img/image5.jpg')}
#nav li a:hover.item5 {background-image:url('../img/image5_over.jpg')}
As above image displays that img1,img1_over,img2,img2_over
it means that when background position changes image display changes
By using CSS Sprites we are able to lighten up this interface.We may use one single image instead of 6 images.We can combine them into one big image.Create a new image that is as wide as your widest image and and as tall as the combined height of all your images plus X pixels, where X is the number of images you have. Now place you images into this new image, left aligned, one on top of the other with one pixel of white space in between.
Now look at css after combining the images into one
#nav li a.item1 {background-position:0px 0px;}
#nav li a:hover.item1 {background-position:0px -72px;}
#nav li a.item2 {background-position:0px -143px;}
#nav li a:hover.item2 {background-position:0px -215px;}
#nav li a.item3 {background-position:0px -287px;}
#nav li a:hover.item3 {background-position:0px -359px;}
#nav li a.item4 {background-position:0px -431px;}
#nav li a:hover.item4 {background-position:0px -503px;}
#nav li a.item5 {background-position:0px -575px;}
#nav li a:hover.item5 {background-position:0px -647px;}

There is a single background-image applied to the anchor element itself, and the unique classes merely shift the background position with negative Y coordinates.

During this the HTTP Request time reduces and size of images reduces.This is done for only 6 images ,and if you are usimg it in your website then you will be able to find some dynamic changes.

CSS  Sprite Generator

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Tagged as: css techniques, css.css sprites, web performance