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Color depth

Color depth

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In computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

, color depth or bit depth is the number of bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s used to represent the color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

 of a single pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

 in a bitmap
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

ped image or video frame buffer. This concept is also known as bits per pixel (bpp), particularly when specified along with the number of bits used. Higher color depth gives a broader range of distinct colors.

Color depth is only one aspect of color representation, expressing how finely levels of color can be expressed; the other aspect is how broad a range of colors can be expressed (the gamut
Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...

).

Indexed color



With relatively low color depth, the stored value is typically a number representing the index into a color map or palette
Palette (computing)
In computer graphics, a palette is either a given, finite set of colors for the management of digital images , or a small on-screen graphical element for choosing from a limited set of choices, not necessarily colors .Depending on the context In computer graphics, a palette is either a given,...

. 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
Macintosh
The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

 systems and VGA
Video Graphics Array
Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...

-equipped IBM-PCs typically ran at 8-bit due to limited VRAM
VRAM
Video RAM, or VRAM, is a dual-ported variant of dynamic RAM , which was once commonly used to store the framebuffer in some graphics adapters....

, 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
    Monochrome
    Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Images using only shades of grey are called grayscale or black-and-white...

    , often black and white, compact Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    es, Atari ST
    Atari ST
    The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...

    .
  • 2-bit color (22 = 4 colors) CGA
    Color Graphics Adapter
    The Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC....

    , gray-scale early NeXTstation
    NeXTstation
    NeXTstation was a high-end workstation computer developed, manufactured and sold by NeXT from 1990 until 1993. It ran the NeXTSTEP operating system. The NeXTstation was released as a more affordable alternative to the NeXTcube at about US $4,995 or about half the price...

    , color Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    es, Atari ST
    Atari ST
    The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...

    .

  • 3-bit color (23 = 8 colors) many early home computers with TV displays

  • 4-bit color (24 = 16 colors) as used by EGA
    Enhanced Graphics Adapter
    The Enhanced Graphics Adapter is the IBM PC computer display standard specification which is between CGA and VGA in terms of color and space resolution. Introduced in October 1984 by IBM shortly after its new PC/AT, EGA produces a display of 16 simultaneous colors from a palette of 64 at a...

     and by the least common denominator VGA standard at higher resolution, color Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    es, Atari ST
    Atari ST
    The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...

    .
  • 5-bit color (25 = 32 colors) Original Amiga chipset
    Original Amiga chipset
    The Original Chip Set was a chipset used in the earliest Commodore Amiga computers and defined the Amiga's graphics and sound capabilities...

  • 6-bit color (26 = 64 colors) Original Amiga chipset
    Original Amiga chipset
    The Original Chip Set was a chipset used in the earliest Commodore Amiga computers and defined the Amiga's graphics and sound capabilities...


  • 8-bit color
    8-bit color
    8-bit color graphics is a method of storing image information in a computer's memory or in an image file, such that each pixel is represented by one 8-bit byte. The maximum number of colors that can be displayed at any one time is 256....

     (28 = 256 colors) most early color Unix workstations, VGA at low resolution, Super VGA, color Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    es, Atari TT, AGA
    Advanced Graphics Architecture
    Advanced Graphics Architecture is the third generation Amiga graphic chip set, first used in the Amiga 4000 in 1992. AGA was codenamed the Pandora chipset by Commodore International internally....

    , Falcon030.
  • 12-bit color (212 = 4096 colors) some Silicon Graphics
    Silicon Graphics
    Silicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...

     systems, Neo Geo
    Neo Geo (console)
    The is a cartridge-based arcade and home video game system released on July 1, 1991 by Japanese game company SNK. Being in the Fourth generation of Gaming, it was the first console in the former Neo Geo family, which only lived through the 1990s...

    , Color NeXTstation
    NeXTstation
    NeXTstation was a high-end workstation computer developed, manufactured and sold by NeXT from 1990 until 1993. It ran the NeXTSTEP operating system. The NeXTstation was released as a more affordable alternative to the NeXTcube at about US $4,995 or about half the price...

     systems, and Amiga
    Amiga
    The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...

     systems in HAM mode.
  • 16-bit color (216 = 65536 colors) some color Macintosh
    Macintosh
    The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

    es.


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
ZX Spectrum
The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...

, the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8x8 pixels.

Direct color


As the number of bits increases, the number of possible colors becomes impractically large for a color map. So in higher color depths, the color value typically directly encodes relative brightnesses of red, green, and blue to specify a color in the RGB color model
RGB color model
The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...

.

A typical computer monitor and video card may offer 8 bits of resolution (256 output levels) per R/G/B color channel, for an overall 24-bit color space (or 32-bit space, with alpha transparency bits, which have no bearing on the output resolution), though earlier standards offered 6 bits per channel (64 levels) or less; the DVD standard defines up to 10 bits of resolution (1024 levels) for each of the Y/U/V video encoding channels (luminance plus two chrominance channels).

8-bit direct color


A very limited but true direct color system, there are 3 bits (8 possible levels) for each of the R and G components, and the two remaining bits in the byte pixel to the B component (four levels), enabling 256 (8 × 8 × 4) different colors. The normal human eye is less sensitive to the blue component than to the red or green, so it is assigned one bit less than the others. Used, amongst others, in the MSX2
MSX2
MSX2 may refer to:* Msh homeobox 2, a human gene* The second generation of the MSX home computers...

 system series of computers in the early to mid 1990s.

Do not confuse with an indexed color depth of 8bpp (although it can be simulated in such systems by selecting the adequate table).

16-bit direct color


In 16-bit direct color, there can be 4 bits (16 possible levels) for each of the R, G, and B components, plus optionally 4 bits for alpha (transparency), enabling 4,096 (16 × 16 × 16) different colors with 16 levels of transparency. Or in some systems there can be 5 bits per color component and 1 bit of alpha (32768 colors, just fully transparent or not); or there can be 5 bits for red, 6 bits for green, and 5 bits for blue, for 65536 colors with no transparency.
These color depths are sometimes used in small devices with a color display, such as mobile telephones.

Variants with 5 or more bits per color component are sometimes called high color,
which is sometimes considered sufficient to display photographic images.

LCD displays


Almost all cheap LCD displays (such as typical twisted nematic types) use dithered 18-bit color (64 × 64 × 64 = 262,144 combinations) to achieve faster transition times, but they must use either dither
Dither
Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images...

ing or Frame Rate Control
Frame Rate Control
Frame Rate Control is a method for achieving higher color quality in low color resolution display panels such as TN+film LCD.Most TN panels represent colors using only 6 bits per RGB color, or 18 bit in total, and are unable to display the 16.7 million color shades that are available from...

 to fake 24-bit-per-pixel truecolor, or throw away 6 bits of color information away entirely. The best LCD displays can display 24-bit or greater color depth.

Truecolor


Truecolor is a method of representing and storing graphical image information (especially in computer processing) in an RGB color space
RGB color space
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...

 such that a very large number of colors, shades, and hues can be displayed in an image, such as in high quality photographic images or complex graphics. Usually, truecolor is defined to mean at least 256 shades of red, green, and blue, for a total of at least 16,777,216 color variations. The human eye is popularly believed to be capable of discriminating among as many as ten million colors.
Truecolor can also refer to an RGB display mode that does not need a color look-up table (CLUT
CLUT
A colour look-up table is a mechanism used to transform a range of input colours into another range of colours. It can be a hardware device built into an imaging system or a software function built into an image processing application...

).

For each pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

, generally one byte is used for each channel while the fourth byte (if present) is being used either as an alpha channel data or simply ignored. Byte order is usually either RGB or BGR. Some systems exist with more than 8 bits per channel, and these are often also referred to as truecolor (for example a 48-bit truecolor scanner).

Even with truecolor, monochromatic images, which are restricted to 256 levels, owing to their single channel, can sometimes still reveal visible banding
Posterization
Posterization of an image entails conversion of a continuous gradation of tone to several regions of fewer tones, with abrupt changes from one tone to another. This was originally done with photographic processes to create posters...

 artifacts.

Truecolor, like other RGB color models, cannot express colors outside of the gamut
Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...

 of its RGB color space
RGB color space
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...

 (generally sRGB).

On Macintosh systems, 24-bit color is referred to as "millions of colors."

Beyond truecolor


Video cards with 10 bits per color, or 30-bit color, started coming into the market in the late 1990s. An early example was the Radius
Radius (computer)
Radius was an American computer hardware firm founded in May 1986 by Burrell Smith, Andy Hertzfeld, Mike Boich, Matt Carter, Alain Rossmann and other members of the original Mac team specializing in Macintosh equipment....

 ThunderPower card for the Macintosh, which included extensions for QuickDraw
QuickDraw
QuickDraw is the 2D graphics library and associated Application Programming Interface which is a core part of the classic Apple Macintosh operating system. It was initially written by Bill Atkinson and Andy Hertzfeld. QuickDraw still exists as part of the libraries of Mac OS X, but has been...

 and Adobe Photoshop
Adobe Photoshop
Adobe Photoshop is a graphics editing program developed and published by Adobe Systems Incorporated.Adobe's 2003 "Creative Suite" rebranding led to Adobe Photoshop 8's renaming to Adobe Photoshop CS. Thus, Adobe Photoshop CS5 is the 12th major release of Adobe Photoshop...

 plugins to support editing 30-bit images.

Deep color is a term used to describe a gamut
Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...

 comprising a billion or more colors.
The xvYCC
XvYCC
xvYCC or Extended-gamut YCC is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space...

, sRGB, and YCbCr
YCbCr
YCbCr or Y′CbCr, sometimes written or , is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components...

 color space
Color space
A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components...

s can be used with deep color systems.

Systems using more than 24 bits in a 32-bit pixel for actual color data exist, but most of them opt for a 30-bit implementation with two bits of padding so that they can have an even 10 bits of color for each channel, similar to many HiColor systems.

While some high-end graphics workstation systems and the accessories marketed toward use with such systems, as from SGI
Silicon Graphics
Silicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...

, have always used more than 8 bits per channel, such as 12 or 16 (36-bit or 48-bit color), such color depths have only worked their way into the general market more recently.

As bit depths climb above 8 bits per channel, some systems use the extra bits to store more intensity range than can be displayed all at once, as in high dynamic range imaging
High dynamic range imaging
In image processing, computer graphics, and photography, high dynamic range imaging is a set of techniques that allows a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging techniques or photographic methods...

 (HDRI). Floating point
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...

 numbers are used to describe numbers in excess of 'full' white and black. This allows an image to describe accurately the intensity of the sun and deep shadows in the same color space for less distortion after intensive editing. Various models describe these ranges, many employing 32-bit accuracy per channel. A new format is the ILM "half"
Half precision floating-point format
In computing, half precision is a binary floating-point computer number format that occupies 16 bits in computer memory.In IEEE 754-2008 the 16-bit base 2 format is officially referred to as binary16...

 using 16-bit floating point numbers, it appears this is a much better use of 16 bits than using 16-bit integers and is likely to replace it entirely as hardware becomes fast enough to support it.

Many modern desktop systems (Mac OS X, GNOME, KDE, Windows XP/Vista/7, etc.) offer a 32-bit color option (given a suitably modern video card), but in that context, 32-bit color refers to 24-bit TrueColor with 8 bits for an alpha channel. When switching to an 8/16/24-bit color option in those systems, generally transparency/translucency effects are disabled, and the only reduction in color depth is seen when going to 8/16-bit color.

Industry support


The HDMI
HDMI
HDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...

 1.3 specification defines bit depths of 30 bits (1.073 billion colors), 36 bits (68.71 billion colors), and 48 bits (281.5 trillion colors).
In that regard, the NVIDIA Quadro
NVIDIA Quadro
The Nvidia Quadro series of AGP, PCI, and PCI Express graphics cards comes from the NVIDIA Corporation. Their designers aimed to accelerate CAD and DCC , and the cards are usually featured in workstations....

 graphics cards support 30-bit deep color as do some models of the Radeon
Radeon
Radeon is a brand of graphics processing units and random access memory produced by Advanced Micro Devices , first launched in 2000 by ATI Technologies, which was acquired by AMD in 2006. Radeon is the successor to the Rage line. There are four different groups, which can be differentiated by...

 5800 series such as the HD 5970. The ATI FireGL
ATI FireGL
The ATI FireGL range of video cards, renamed to FirePro 3D in late 2008, is the series specifically for CAD and DCC software, usually found in workstations.-History:...

 V7350 graphics card supports 40-bit and 64-bit color.

The DisplayPort
DisplayPort
DisplayPort is a digital display interface standard produced by the Video Electronics Standards Association . The specification defines a royalty-free digital interconnect for audio and video. The interface is primarily used to connect a video source to a display device such as a computer monitor...

 specification also supports color depths greater than 24 bpp.

At WinHEC
Windows Hardware Engineering Conference
The Windows Hardware Engineering Conference is the annual software and hardware developer-oriented trade show and business conference where Microsoft elaborates on its hardware plans for Microsoft Windows-compatible PCs...

 2008, Microsoft announced that color depths of 30 bits and 48 bits would be supported in Windows 7, along with the wide color gamut scRGB (which can be converted to xvYCC output).

Television color


Virtually all television displays and computer displays form images by varying the strength (technically, tristimulus values) of just three primary colors: red, green, and blue. Bright yellow, for example, is formed by roughly equal red and green contributions, with little or no blue contribution. Recent technologies such as Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...

's BrilliantColor augment the typical red, green, and blue channels with up to three other primaries: cyan, magenta and yellow.
Mitsubishi
Mitsubishi
The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...

 and Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

, among others, use this technology in some TV sets. However, the associated signal processing typically fails to mimic additive mixing; hence, the displayed colors are distorted (for example, compared to sRGB source values). The Sharp Aquos
Sharp Aquos
The Sharp Aquos is a range of LCD televisions and component screens made by Sharp Corporation of Japan. It encompasses small, portable models up to large home-theater screens , as well as component screens for portable devices including mobile phones...

 line of televisions has introduced Quattron
Quattron
Quattron is the brand name of an LCD color display technology produced by Sharp Electronics. The technology utilizes a fourth color subpixel, yellow, in addition to the standard RGB color subpixels, which Sharp claims increases the range of displayable colors, and which may mimic more closely the...

 technology, which augments the usual RGB pixel components with a yellow subpixel. Again, signal processing fails in general to follow the laws of additive mixing, and colors are distorted.

Analog TVs use continuous signals which have no fixed number of different colors, although subject to noise introduced in transmission.

See also

  • Bit plane
    BIT plane
    This article is about Natalie Jeremijenko and the Bureau of Inverse Technology's project. For the company, see Bitplane. For the digital information term, see bit plane....

  • RGB color model
    RGB color model
    The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...

  • List of colors
  • List of colors (compact)
  • List of color palettes
  • Mach banding

External links