On computer displays, a computer icon (or simply an icon) is a small pictogram. Icons have been used to supplement the normal alphanumerics of the computer. Modern computers now can handle bitmapped graphics on the display terminal, so the icons are widely used to assist users.
Icons were first developed as a tool for making computer interfaces easier for novices to grasp in the 1970s, at the Xerox Palo Alto Research Center facility. Icon-driven interfaces were later popularized by the Apple Macintosh and the Microsoft Windows operating environments.
A computer icon usually ranges from 16 by 16 pixels up to 128 by 128 pixels. Some operating systems feature icons up to 512 by 512 pixels. When the graphical output device has a smaller size, the icon size is small. Vision-impaired users (due to such conditions as poor lighting, tired eyes, medical impairments, bright backgrounds, or color blindness) may need to utilize the self-selected icon size options.
Icons may represent a file, folder, application or device on a computer operating system. In modern usage today, the icon can represent anything that the users want it to: any macro command or process, mood-signaling, or any other indicator. User friendliness also demands error-free operation, where the icons are distinct from each other, self-explanatory, and easily visible under all possible user setups.
Icons may also be found on the desktop, toolbars and in the menus of computer application software such as Microsoft Office Word. Icons are made more user-friendly by being very distinct from every other icon. Each icon set may also have unifying features that show that similar icons are related to each other. Icons show this by:
Virtually every major modern computer operating system has the ability to use an icon-based graphical user interface (GUI) to display information to end users; this is evident in the usage of the term "icon" in the WIMP computing paradigm (for Windows, Icons, Menu, Pointers).
Most computer functions in a GUI are represented by a function icon. Placing the cursor on the icon, and clicking (or double-clicking) a mouse, trackball or other button starts the function or program.
The icon must be original, distinctive and tiny. It must be useful on a wide variety of monitors set at different resolutions. This work is further complicated by the need to create several sets of function icons for several types of views in several types of operating systems, for any given program. For instance, the GUI guidelines in one operating system might specify the need to create sets of 16, 32, and 48 pixel icons for any program while the GUI guidelines in another system might specify sets of 16, 24, 48 and 96 pixel icons.
Icon software (such as an icon editor) is software for creating and editing computer icons.
Icon software is generally only found on Microsoft Windows and Apple Macintosh operating systems as Unix-like operating systems generally use the PNG and XPM image formats and instead use software such as GIMP or Inkscape to create icons.
Icon editors usually contain a rudimentary raster image editor capable of modifying images of an icon pixel by pixel, by using simple drawing tools, or by applying simple image filters. Professional icon designers seldom modify icons inside an icon editor and use a more advanced drawing or 3D modeling application instead.
The main function performed by an icon editor is generation of icons from images. An icon editor resamples a source image to the resolution and color depth required for an icon. Some icon editors can apply preconfigured effects on the generated images during the conversion. Effects include softening, sharpening, edge enhancement, or drop shadow effect.
Other functions usually included into icon editors are icon extraction from executable files (exe, dll), creation of icon libraries, or saving individual images of an icon.
All icon editors can make icons for system files (folders, text files, etc.), and for web pages. These have a file extension of .ICO for Windows and web pages or .ICNS for the Macintosh. If the editor can also make a cursor, the image can be saved with a file extension of .CUR or .ANI for both Windows and the Macintosh. Using a new icon is simply a matter of moving the image into the correct file folder and using the system tools to select the icon. (In Windows you could go to My Computer, open Tools on the explorer window, choose Folder Options, then File Types, select a file type, click on Advanced and select an icon to be associated with that file type.)
It is rare for an icon editor to make icons for specific program files (a program you wrote as opposed to any file ending in .EXE). To assign an icon to a newly created program is usually done within the Integrated Development Environment. Many icon editors can copy a unique icon from a program file for editing. Only a few can assign an icon to a program file.
Simple icon editors and image to icon converters are also available as online services.