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A colour look-up table (CLUT) is a mechanism used to transform a range of input colors into another range of colors. It can be a hardware device built into an imaging system or a software function built into an image processing
Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
 application. The hardware color look-up table will convert the logical colour numbers stored in each pixel
Pixel

In digital imaging, a pixel is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles....
 of video memory
Video memory

Video memory is a term generally used in computers to describe some form of writable memory, usually random access memory, dedicated to the purpose of holding the information necessary for a graphics card to drive a display device....
 into physical colours, normally represented as RGB
RGB color model

The RGB color model is an additive color in which red, green, and blue light are added together in various ways to reproduce a broad array of colors....
 triplets, that can be displayed on a computer monitor.






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A colour look-up table (CLUT) is a mechanism used to transform a range of input colors into another range of colors. It can be a hardware device built into an imaging system or a software function built into an image processing
Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
 application. The hardware color look-up table will convert the logical colour numbers stored in each pixel
Pixel

In digital imaging, a pixel is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles....
 of video memory
Video memory

Video memory is a term generally used in computers to describe some form of writable memory, usually random access memory, dedicated to the purpose of holding the information necessary for a graphics card to drive a display device....
 into physical colours, normally represented as RGB
RGB color model

The RGB color model is an additive color in which red, green, and blue light are added together in various ways to reproduce a broad array of colors....
 triplets, that can be displayed on a computer monitor. The palette is simply a block of fast RAM which is addressed by the logical colour and whose output is split into the red, green, and blue levels which drive the actual display (e.g., a CRT
Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen....
 or cathode ray tube).

The number of entries ("logical colours") in the palette is the total number of colours which can appear on screen simultaneously. The width of each entry determines the number of colours which the palette can be set to produce.

A common example would be a palette of 256 colours (that is, addressed by 8-bit
8-bit

Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their address space is limited to 64 KBs. This is not a "natural law", however, so there are exceptions....
 pixel values) where each colour can be chosen from a total of 16.7 million colours (combinations of 256 for each of red, green, and blue).

Changes to the palette affect the whole screen at once and can be used to produce special effects which would be much slower to produce by updating pixels.

See also

  • Palette (computing)
    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 ....
  • Lookup table
    Lookup table

    In computer science, a lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation....
  • Truecolor
    Truecolor

    Truecolor is a method of representing and storing graphical image information in an RGB color space 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....