{{unreferenced, date=June 2009, bot=yes There are three different addressing schemes for display devices: ''direct'', ''matrix'', and ''raster''. The purpose of each scheme is to set (or maintain) the state of a

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...

to either black/white or, more commonly, a

grayscale In digital photography, computer-generated imagery, and colorimetry, a grayscale image is one in which the value of each pixel is a single sample representing only an ''amount'' of light; that is, it carries only intensity information. Graysc ...

level.

Direct addressing

A direct addressed display runs individual control signals to each pixel. This allows the state, whether on/off or grayscale, to be set and maintained on each pixel. For a screen size of ''m''×''n'' pixels, this scheme would require ''m''×''n'' control signals. This is generally considered to be an inefficient use of I/O and physical space. Direct addressing mode means that the value for a given instruction in assembly programming is pointed to by a given value. This means the value is variable, based on what is stored in memory at a given address

Matrix addressing

A matrix addressed display runs control signals only to the rows and columns of the display. (See also:

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

) For a screen size of ''m''×''n'' pixels, this scheme would require ''m''+''n'' control signals. In

active matrix addressing Active may refer to: Music * ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * ''Active'' (ship), several commercial ships by that name * HMS ''Active'', the name of various ships of the British Royal ...

, some sort of capacitor (external to the cell proper) is used to maintain the state of the cell.

Passive matrix addressing Passive matrix addressing is an addressing scheme used in early LCDs. This is a matrix addressing scheme meaning that only ''m'' + ''n'' control signals are required to address an ''m'' × ''n'' display. A pixel in a pass ...

is used when cell itself has a bistability, so no external capacitor is needed. In some situations passive matrix addressing is used with the help of persistence of vision of the (usually human) eye so the cell need not be bistable. Persistence of vision is used in simpler, slower changing displays such as clocks.

Raster addressing

A raster addressed display (e.g., a CRT) works by scanning across the entire display in sequence while modulating control signal to activate each pixel as it is scanned. This display uses persistence of the pixel element (e.g., phosphor) to maintain the pixel state until the scan can visit that pixel again. There are only three control signals required for this to work: a horizontal scan control signal, a vertical scan control signal, and an intensity control signal. Timing between these signals is very important, else the image on the screen will show artifacts. Display technology