Twitter offers a number of basic backgrounds, but let's face it: they're mostly generic and boring. In order to get noticed for both your tweets and your style, you'll want to create your own custom background.
In this first of a two-part series, we'll show you how to create a simple, single-image background. In the second part, we'll discuss how to create a tiled (or patterned) background.
Designing for Twitter
Creating a compelling background design can be a challenge. Your followers will come to associate you with this image and color scheme, so you'll want to craft a background that has character, that says something about you. If you're a long-time gamer, you might want to brand your page with an image of an old-school gamepad; if you're an avid toy-collector, maybe you'd like to decorate your page with your most prized collectible, for example.
Once you've come up with an idea, you'll need to adapt it to the page layout. Twitter has two visible areas you can design for--the top margin and the left margin. The top margin is smaller and more restrictive due to the masthead and navigation menu, and if you start to scroll down, the image disappears. The left margin is a better choice for most designs. It varies in size depending on the width of the browser window, but there is significantly more viewable area than the top margin.
A top-left background image should blend seamlessly into the page's background colour. In my example, I've taken a photo of a toy and then knocked out (or masked) the background. All areas around the toy are transparent, and as a result, the toy image can now be placed on a background of any colour. This is a somewhat cumbersome step that is beyond the scope of this article, but have a look at Masking 101 to get you started with Photoshop masking techniques.
Launch Photoshop CS4 (or any recent version of Photoshop) and the file that contains your masked image. In the layers palette (Window>Layers) you should see two icons on one layer: one will show a thumbnail of the image itself, and the other will show a black and white thumbnail of the mask. Right-click on the mask icon and choose Apply Layer Mask, and then copy the contents of the layer (Cmd/Ctrl-A and then Cmd/Ctrl-C).