Color Depth - Indexed Color

Indexed Color

With relatively low color depth, the stored value is typically a number representing the index into a color map or palette. The colors available in the palette itself may be fixed by the hardware or modifiable within the limits of the hardware (for instance, both color Macintosh systems and VGA-equipped IBM-PCs typically ran at 8-bit due to limited VRAM, but while the best VGA systems only offered an 18-bit (262,144 color) palette from which colors could be chosen, all color Macintosh video hardware offered a 24-bit (16 million color) palette). Modifiable palettes are sometimes referred to as pseudocolor palettes.

• 1-bit color (21 = 2 colors): monochrome, often black and white, compact Macintoshes, Atari ST.
• 2-bit color (22 = 4 colors): CGA, gray-scale early NeXTstation, color Macintoshes, Atari ST.

• 3-bit color (23 = 8 colors): many early home computers with TV displays, including the ZX Spectrum and BBC Micro

• 4-bit color (24 = 16 colors): as used by EGA and by the least common denominator VGA standard at higher resolution, color Macintoshes, Atari ST, Commodore 64, Amstrad CPC.
• 5-bit color (25 = 32 colors): Original Amiga chipset
• 6-bit color (26 = 64 colors): Original Amiga chipset

• 8-bit color (28 = 256 colors): most early color Unix workstations, VGA at low resolution, Super VGA, color Macintoshes, Atari TT, AGA, Falcon030.
• 12-bit color (212 = 4096 colors): some Silicon Graphics systems, Neo Geo, Color NeXTstation systems, and Amiga systems in HAM mode.

Old graphics chips, particularly those used in home computers and video game consoles, often feature an additional level of palette mapping in order to increase the maximum number of simultaneously displayed colors. For example, in the ZX Spectrum, the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8x8 pixels.