What Are Icons?

Computer icons are incorporated into any graphical user interface. Icons are small pictures of standard resolutions that depict objects, actions, and other concepts. In window-based systems, icons are used as a faster, more intuitive way to communicate with the user. Icons depicting typical elements of a user interface are better visible than text, can be recognized faster, and are easier for new computer users.


There are several graphic formats for storing icons. Microsoft Windows systems store Windows icons in the platform-specific ICO format. Apple Macintosh systems store Mac icons in their specific formats, while Unix-based systems employ PNG icons for most applications. As such, icon software is generally available for the Windows and Apple systems, while Unix users can create PNG icons with any graphic editor.

Generally speaking, icons are square pictures that come in a variety of standard sizes and color resolutions. Most platforms support icons of 16×16 to 128×128 pixels, while some systems readily accept icons as large as 512×512 pixels. The high-resolution 512×512 pixel icons were first used in Mac OS Leopard.

Pixel resolutions of all icons are operating system dependent. For example, Windows icons are specified as images in 16 and 256-color gammas as well as True Color pictures with alpha channel. Windows icons come in standard sizes of 16×16, 32×32, and 48×48 pixels. Windows Vista defines new standards for Windows icons, including icons in sizes of up to 256×256 pixels in True Color only. Optionally, icons of 128×128 and 512×512 pixels are supported. Interestingly, the higher resolution versions of Windows Vista icons are stored in compressed PNG format instead of Windows ICO used in older versions of Windows and for lower resolution icons. Other systems such as Windows Mobile can use standard icons of other resolutions, e.g. 24×24 pixels.


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