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Color Depth

The number of bits used that a given device or system can use to represent the color of a pixel. Common color depths include 8-bit, 16-bit and 32-bit.

Color depth or colour depth (see spelling differences), also known as bit depth, is either the number of bits used to indicate the color of a single pixel, in a bitmapped image or video framebuffer, or the number of bits used for each color component of a single pixel. For consumer video standards, such as High Efficiency Video Coding (H.265), the bit depth specifies the number of bits used for each color component. When referring to a pixel, the concept can be defined as bits per pixel (bpp), which specifies the number of bits used. When referring to a color component, the concept can be defined as bits per component, bits per channel, bits per color (all three abbreviated bpc), and also bits per pixel component, bits per color channel or bits per sample (bps). Color depth is only one aspect of color representation, expressing the precision with which colors can be expressed; the other aspect is how broad a range of colors can be expressed (the gamut). The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a digital code value to a location in a color space.

With the relatively low color depth, the stored value is typically a number representing the index into a color map or palette (a form of vector quantization). The colors available in the palette itself may be fixed by the hardware or modifiable by software. 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, Amiga AGA chipset, Falcon030, Acorn Archimedes.
  • 12-bit color (212 = 4096 colors): some Silicon Graphics systems, Color NeXTstation systems, and Amiga systems in HAM mode.

Old graphics chips, particularly those used in home computers and video game consoles, often have the ability to use a different palette per sprites and tiles in order to increase the maximum number of simultaneously displayed colors, while minimizing use of then-expensive memory (& bandwidth). 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.

The palette itself has a color depth (number of bits per entry). 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. 24-bit palettes are pretty much universal on any recent hardware or file format using them.

Key Terms

color
color component
color depth
color macintoshes
colors
concept
gamut
number bits
palette
single pixel

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Color Depth
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Last modified on May 10 2019
Content adapted from Wikipedia
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