CSS Image Sprites
Image Sprites
An image sprite is a collection of images put into a single image.
A web page with many images can take a long time to load and generates multiple server requests.
Using image sprites will reduce the number of server requests and save bandwidth.
CSS sprites technique is a way to reduce the number of HTTP requests made for image resources, by combining images in a single file.
What is a Sprite
Sprites are two-dimensional images which are made up of combining small images into one larger image at defined X and Y coordinates.
To display a single image from the combined image, you could use the CSS background-position property, defining the exact position of the image to be displayed.
Advantage of Using CSS Image Sprite
A web page with many images, particularly many small images, such as icons, buttons, etc. can take a long time to load and generates multiple server requests.
Using the image sprites instead of separate images will significantly reduce the number of HTTP requests a browser makes to the server, which can be very effective for improving the loading time of web pages and overall site performance.
Checkout the following examples and you will see one visible difference; when you place the mouse pointer over the browser icons in non-sprite version for the first time the hover image will appear after some time, it happens because the hover image is loaded from the server on mouse hover, since the normal and hover images are two different images.
Whereas in sprite version, since all images are combined in a single image the hover image is displayed immediately on mouse hover that results in smooth hover effect.
Image Sprites - Simple Example
Instead of using three separate images, we use this single image ("img_navsprites.gif"):
With CSS, we can show just the part of the image we need.
In the following example the CSS specifies which part of the "img_navsprites.gif" image to show:
Example -
Image Sprites - Create a Navigation List
We want to use the sprite image ("img_navsprites.gif") to create a navigation list.We will use an HTML list, because it can be a link and also supports a background image:
Example -
Example explained : -
- #navlist {position:relative;} - position is set to relative to allow absolute positioning inside it
- #navlist li {margin:0;padding:0;list-style:none;position:absolute;top:0;} - margin and padding is set to 0, list-style is removed, and all list items are absolute positioned
- #navlist li, #navlist a {height:44px;display:block;} - the height of all the images are 44px
Now start to position and style for each specific part : -
- #home {left:0px;width:46px;} - Positioned all the way to the left, and the width of the image is 46px
- #home {background:url(img_navsprites.gif) 0 0;} - Defines the background image and its position (left 0px, top 0px)
- #prev {left:63px;width:43px;} - Positioned 63px to the right (#home width 46px + some extra space between items), and the width is 43px.
- #prev {background:url('img_navsprites.gif') -47px 0;} - Defines the background image 47px to the right (#home width 46px + 1px line divider)
- #next {left:129px;width:43px;}- Positioned 129px to the right (start of #prev is 63px + #prev width 43px + extra space), and the width is 43px.
- #next {background:url('img_navsprites.gif') -91px 0;} - Defines the background image 91px to the right (#home width 46px + 1px line divider + #prev width 43px + 1px line divider )
Image Sprites - Hover Effect
Our new image ("img_navsprites_hover.gif") contains three navigation images and three images to use for hover effects:
Because this is one single image, and not six separate files, there will be no loading delay when a user hovers over the image.We only add three lines of code to add the hover effect : -