The terms wallpaper and desktop picture refer to an image used as a background on a computer screen, typically for the desktop of a graphical user interface. 'Wallpaper' is the term used in Microsoft Windows, while the Mac OS calls it a 'desktop picture' (prior to Mac OS X, the term desktop pattern was used to refer to a small pattern that was repeated to fill the screen).

Formats

Images used as computer wallpaper are typically raster graphics with the same size as the display resolution (for example 1024x768 pixels, or 1280x1024 pixels) in order to fill the whole background.

Dimensions

Many screen resolutions are proportional in a 4:3 ratio, so an image scaled to fit in a different-sized screen will still be the correct shape, although that scaling may impact quality. Common wallpaper resolutions are 800x600, 1024x768, 1280x1024 and 1600x1200.

Users with widescreen (16:9 or 16:10) monitors have different aspect ratio requirements for wallpaper, although images designed for standard (4:3) monitors can often be scaled or cropped to the correct shape without undue loss of quality.

Wallpapers are sometimes available in double-width versions (e.g. 2560x1024) for displaying on multi-monitor computers, where the image appears to fill two monitors.

Some display systems allow unconventionally-proportioned images (1:1, 2:1, or even 1:3) to be scaled without change of proportion, to fit the screen, whether it be 16:9 or 4:3. The image would be sized just large enough that one pair of edges touch the edges of the screen, but not all four, as this would unduly distort the image. In these cases, the system's "default" background color is visible around the other two sides of the image.

A further common option, particularly for images much smaller than the resolution of the display, is having the image displayed multiple times like a series of tiles. This avoids the distortion of scaling.

Image types

PNG and JPEG format are common. Some desktop systems, such as Mac OS (version 8.6 or later), KDE (version 3.4 or later), and GNOME, support vector wallpapers (PICT in Mac and SVG in KDE and GNOME). This has the advantage that a single file may be used for screens of any size, or stretched across several screens, without loss of quality.

Most display systems are capable of specifying a single colour to use as the background in place of a wallpaper, and some (such as KDE or GNOME) allow colour-gradients to be specified. Early versions of Mac OS and Microsoft Windows allowed for small repeating patterns to tile the desktop.

History

Original computer wallpaper pattern, as used in Xerox's Officetalk and Star; actual size.

The first use of a distinguishable background in conjunction with overlapping windows was in an experimental office system, Officetalk, developed in 1975 at Xerox PARC on the Alto. Prior to that, the white backgrounds to overlapping windows (for example, in Smalltalk) could be difficult to distinguish from window interiors. The pattern used in Officetalk produced a 25% gray, using dots two pixels high to avoid flicker on the Alto's interlaced screen. The same pattern was adopted for the Xerox Star.

Apple used a similar gray background for their Lisa and Macintosh. However, since these machines had non-interlaced screens it was possible to use a less noticeable background pattern, formed from a simple 2x2 repeating pattern that gave a 50 percent gray. The introduction of color monitors for personal computers led to non-patterned, single-color backgrounds and then to arbitrary 'wallpapers'.

Styles

Wallpaper styles are as varied as people themselves, using photographs, drawings, 3D renders or abstract pattern with complex gradients. It can be useful to have plain areas so that icons can be clearly seen atop the wallpaper.

Typical categories can include cars, models and celebrities, scenery, abstract art, movies, pets, family, symmetry, and personal photos.

In business use, corporate logos or plain backgrounds are often specified by the companies' guidelines.

When using rack mounted computers through a KVM switch, it can often be useful to create a wallpaper with the computer's name on it, to easily identify which computer the user is connected to.

System themes are often distributed with a background image that fits the style of the theme.

Dynamic backgrounds

Some operating environments (e.g. KDE and Mac OS X) allow a number of different wallpapers to be used, and "rotated" to display a different wallpaper at different times, to display a random image from a directory. If the facility is not available in the OS's wallpaper settings, it may be possible to get an external program that can change the wallpaper at certain times. Microsoft Windows 98 and higher allow webpages to be set as frames on the desktop which may be dynamic pages.

Microsoft Windows Vista Ultimate also has the ability to use a a video (technically a Silverlight file), as a wallpaper. Users can choose to use their own home videos which loop continuously, or use one already installed.

Certain media players (mplayer) provide the option to output video to the background of X11, making them suitable as engine for animated backgrounds from a wide range of video formats.

Programs such as Xplanet and EarthDesk use Internet connections and graphics calculations to change the wallpaper with real data, such as a shadowed view of the earth, the latest cloud or weather map, or various events. Some media players can redirect video playback to desktop, allowing any video to be used as a wallpaper.

Macromedia/Adobe Flash animated movies and games can be set as a dynamic interactive background as well. Point your desktop background settings to an html file with embedded flash movie instead of an image.