The terms wallpaper, desktop picture and desktop background refer to an image used as a background on a computer screen, usually for the desktop of a graphical user interface. "Wallpaper" is the term used in Microsoft Windows before Windows 7 (where it is called the Desktop "Background"), while Mac OS X calls it a "desktop picture" (previously, 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 usually raster graphics with the same size as the display resolution (for example 1024×768 pixels, or 1280×1024 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 connected to common desktop resolutions: 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. 2560×1024) 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.

Technical aspects

The main problem when enlarging an image to match the desktop resolution is the quality loss that appears during the resize process and the distorted image that appear when aspect ratio of the wallpaper is different than the aspect ratio of the desktop. However, there are applications that can automatically decide if an image is better to be displayed using its original resolution, resized (enlarge or shrink) or tiled. For example, BioniX Wallpaper Changer can automatically detect when the wallpaper image is smaller than the desktop or it has a different aspect ratio and apply a special image processing to make the discrepancy less visible. The process is backed up by a high-resolution resampling (using special resampling algorithms like B-Spline) in order to decrease the quality loss during image resizing. Even if the resulted wallpaper may not always match the desktop resolution and aspect ratio perfectly, the uncovered areas are generally reduced.

These problems can be eliminated by using vector images. However, these images are not very popular and are hard to find.