In computer graphics, a palette is a finite set of colors in no particular order. Palettes can be optimized to improve image accuracy in the presence of software or hardware constraints.
Depending on the context, the term palette and related terms such as Web palette and RGB palette can have somewhat different meanings. The following are some of the widely used meanings for palette in computer graphics:
- The total number of colors that a given system is able to generate or manage (though, due to video memory limitations, it may not be able to display them all simultaneously):
- full palette: For example, Highcolor displays are said to have a 16-bit RGB palette.
- The limited selection of colors that can be displayed simultaneously:
- On the whole screen:
- fixed palette selection: A given display adapter can offer a fixed color selection when its hardware registers are appropriately set. For example, the Color Graphics Adapter (CGA), in one of the standard graphics modes, can be set to show the so-called palette #1 or the palette #2: two combinations of 3 fixed colors and one user-defined background color each.
- selected colors or picked colors: In this case, the color selection, generally from a wider explicitly available full palette, is always chosen by software, both by the user or by a program. For example, the standard VGA display adapter is said to provide a palette of 256 simultaneous colors from a total of 262,144 different colors.
- default palette or system palette: The given selected colors have been officially standardized by somebody or corporation. For example, the well known Web-safe colors for use with Internet browsers, or the Microsoft Windows default palette.
- On an individual image:
- color map or color table: The limited color selection is stored inside the given indexed color image file. For example, GIF.
- image palette or image colors: The limited color selection is assumed to be the full list of the colors the given digital image has, even when the image file does not employ indexed-color pixel encoding.
- The underlying hardware that may be used to hold those simultaneous colors:
- hardware palette or Color Look-Up Table (CLUT): In order to show them, the selected colors' values must be loaded in the color hardware registers of the display subsystem. For example, the hardware registers of the Commodore Amiga are known both as their color palette and their CLUT, depending on sources.
- GUI palettes
- An arrangement of a limited set of user or system colors that can be chosen. In such cases, the expression color palette or user color palette are common equivalents. This usage resembles a true artist's palette.
- A tool palette, a rectangular area, called a palette window, of the application screen with buttons, icons or another GUI controls available for quick command or symbol access; if the user is able to place it anywhere by moving it through a mouse or similar pointing device, it is known as a floating palette. A palette for choosing colors can be also a floating palette.