Icons are a graphical metaphor presenting a visual image that the user associates with a particular object, state or operation. When a user sees a good icon they are immediately reminded of the item it represents, whether that be an application in the panel menu or the "right aligned" state in a word processor toolbar.
Icons can assist the user in rapidly scanning a large number of objects to select the desired item. Particularly after a user is acustomed to an icon's appearance, they can identify it more rapidly than a text label.
Icons can augment text by providing visual suggestions to accompany the descriptive text. Some things are easier to communicate with a picture, even a very small one.
Icons can compactly represent a large number of objects when there is insufficient space to display textual descriptions (such as in a toolbar).
GNOME uses a soft, three-dimensional look. This style is achieved by using antialiasing, shading and highlighting techniques. The Gnome Icons tutorial details how one of GNOME's leading artists creates some of these effects.
Components of an icon style can be broken down into several categories such as perspective, dimentionality, lighting effects and palette. These components play an important part in giving a group of icons a collectively distinctive look. For instance, the Java Look and Feel is recognizable by its use of a primary eight-color palette, interior highlighting and diagonal gradients. The Macintosh Aqua style is recognizable by its use of a cool palette based on blue, lighting effects mimicking reflectivity and antialiasing. The GNOME style exhibits a subdued thirty-two color palette, soft drop shadows and a mix between cartoonish and photorealistic graphics.
Table perspective. Presents objects as if they were sitting on a table or desk in front of the user.
Shelf perspective. Presents objects as if they were propped up on a shelf at eye level. Make it look like a police line-up.
Upper left. Design as if there is lighting coming from the upper left corner, with a soft drop-shadow cast within the icon's 48x48 (original design size) borders (120 degrees, 4 pixel distance, 4 pixel blur).
Overhead. Design as if there is a light source placed above the "camera", casting a shadow down.
Icons should use colors based on the basic thirty-two color palette, darkening or lightening the colours to achieve the desired look. See the section called “Palette”