The background you use with a theme or a full-blown skin makes or breaks the overall effect you are trying to achieve. If you look in the C:\Windows\Web\Wallpaper folder, you will find several image files, such as Stonehenge and Tulips. These files are included with Windows and can be used as backgrounds. Most of these files are in the .jpg or .jpeg file format. The .jpeg format provides good compression of the image file without any obvious image degradation. The default background, Bliss, is a .bmp (bitmap) file. Bitmap files can be large in terms of file size (when compared to the .jpeg format) because they do not use any compression strategy. Bitmaps can also become ragged looking when you enlarge them too much. Windows allows you to apply image files as the desktop background in a number of file formats, such as .gif, .png, .jpg, .bmp, and .dib. Figure 11.1 shows the contents of the C:\Windows\Web\Wallpaper folder.
Figure 11.1. A number of background files are included with Windows.
The Joint Photographic Experts Group (JPEG) file format uses a compression strategy called lossy compression. It can compress the image file to a much smaller size (in terms of bytes), so JPEGs are great for websites and for Windows backgrounds (you will save space on your hard drive). However, lossy compression does mean that some image information is lost, so JPEGs can lose some image detail.
The backgrounds (or wallpapers) are 800 ¥ 600 pixels (the file sizes vary). The 800 ¥ 600 has become the standard (and low end) of the resolution used on the monitors and LCD panels now available. Depending on the size of your monitor, you might be using 1024 ¥ 768 as your resolution (or an even greater resolution such, as 1152 ¥ 864).
Because the background files are 800 ¥ 600 pixels, you don't have to stretch them if you are using the 800 ¥ 600 resolution. When using higher settings such as 1024 ¥ 768, you should select Stretch on the Position list that resides on the Desktop tab of the Display Properties dialog box (see Figure 11.2). Most skinning software, such as StarSkin and Stardock's ThemesManager, also provides you with a choice of positioning settings.
Figure 11.2. You can center, stretch, or tile your background image.
The background files you create and download do not have to be 800 ¥ 600 pixels. For example, some wallpaper websites provide a particular background in different sizes. Thus, you might be able to download a background that is 1024 ¥ 768 pixels, making it a better fit if you are using 1024 ¥ 768 as your screen resolution. Smaller images (in terms of pixels) can also be stretched to cover the desktop, or you can center a small image and then frame it with a particular background color. Stretching a fairly small picture or image, however, can distort the image.
The resolutions (and number of colors) you can achieve on your monitor depend on the graphics adapter installed on your computer.
In terms of themes and skins, you can take two approaches to backgrounds: You can acquire or create backgrounds for specific themes or skins (as you create the theme or skin), or you can build a library of background files and then use them as you see fit (you never know when you might want to use a new background).
One other issue we should discuss before we discuss the storage and maintenance of your background files is the relationship between the use of a background and its effect on system performance. Windows speed purists would advise that you not use a desktop background or even apply themes to Windows (in fact, many Windows speed tweaking websites suggest you turn off the theme service completely). Obviously, high-resolution background images (which are also large in terms of file size) require system resources to be rendered and refreshed by the Windows video subsystems. And it is true that a 256-color background does not require the system resources that a 32-bit color image (containing over 16 million colors) does.
So, theoretically, using lower-resolution (8-bit) wallpaper images would require less system resources. However, these 256-color images don't look very good. And you only see a degradation of system performances when using background images (and other theme elements) if you are running a very marginal system (a computer with less than 128MB of RAM and a processor that runs at less than 600MHz). So, the bottom line is that applying backgrounds, themes, and skins to Windows does require system resources. You won't, however, see any performance degradation, unless you are using an older, slower computer.