8-bit color graphics are a method of storing image information in a computer's memory or in an image file, so that each
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 smal ...
is represented by 8 bits (1
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
). The maximum number of colors that can be displayed at any one time is 256 or 2
8.
Color quantization
![256colour](https://upload.wikimedia.org/wikipedia/commons/9/93/256colour.png)
In order to turn a
true color 24-bit image into an 8-bit image, the image must go through a process called color quantization. Color quantization is the process of creating a color map for a less color dense image from a more dense image.
The simplest form of quantization is to simply assign 3 bits to red, 3 bits to green and 2 bits to blue, as the human eye is less sensitive to blue light. This creates a so called 3-3-2 8-bit color image, arranged like on the following table:
Bit 7 6 5 4 3 2 1 0
Data R R R G G G B B
This process is sub optimal. There could be different groupings of colors that make evenly spreading the colors out inefficient and likely to misrepresent the actual image.
An alternative approach is to use a
palette, with each of the 256 possible
indexes
Index (or its plural form indices) may refer to:
Arts, entertainment, and media Fictional entities
* Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index''
* The Index, an item on a Halo megastru ...
pointing towards a larger color space (ex: 256 colors chosen from 4096).
Because the color map doesn't need to have every color in it and just needs to accurately represent the more color dense image, an arbitrary color can be assigned to each of the 256 available color indexes on the map.
Popular approaches for creating these maps (also known as palettes) include the ''
popularity algorithm'' which chooses the 256 most common colors and creates a map from them. The more accurate ''
median cut Median cut is an algorithm to sort data of an arbitrary number of dimensions into series of sets by recursively cutting each set of data at the median point along the longest dimension. Median cut is typically used for color quantization. For exam ...
'' algorithm resorts and divides colors to find the median of different color groups resulting in a more accurate final color map.
Usage
Because of the low amount of memory and resultant higher speeds of 8-bit color images, 8-bit color was a common ground among computer graphics development until more memory and higher CPU speeds became readily available to consumers. 8-bit color was used in many different applications including:
*The
MSX2
MSX is a standardized home computer architecture, announced by Microsoft and ASCII Corporation on June 16, 1983. It was initially conceived by Microsoft as a product for the Eastern sector, and jointly marketed by Kazuhiko Nishi, then vice- ...
series of personal computer
*The
Uzebox
The open-design movement involves the development of physical products, machines and systems through use of publicly shared design information. This includes the making of both free and open-source software (FOSS) as well as open-source hardwar ...
gaming console
*The
Atari Falcon
The Atari Falcon030 (usually shortened to Atari Falcon), released in 1992, was the final personal computer product from Atari Corporation. A high-end model of the Atari ST line, the machine is based on a Motorola 68030 CPU and a Motorola 56001 d ...
*The NTSC version of the Atari
GTIA
Color Television Interface Adaptor (CTIA) and its successor Graphic Television Interface Adaptor (GTIA) are custom chips used in the Atari 8-bit family of computers and in the Atari 5200 home video game console. In these systems, a CTIA or GTIA ch ...
*The
Tiki 100
Tiki-100 was a desktop home/personal computer manufactured by Tiki Data of Oslo, Norway. The computer was launched in the spring of 1984 under the original name Kontiki-100, and was first and foremost intended for the emerging educational sector ...
personal computer (limited to 16 simultaneous color display)
*The
Research Machines 380Z
The Research Machines 380Z (often called the RML 380Z or RM 380Z) was an early 8-bit microcomputer produced by Research Machines in Oxford, England, from 1977 to 1985.
Description
The 380Z used a Z80 microprocessor (hence the name) with up to 56 ...
computer equipped with a High Resolution Graphics board.
*Wearable OS smartwatches with ambient displays
*Many scanners use an 8-bit grey scale as their standard
Most notably, the
VGA
Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can no ...
standard for graphical interface uses an 8-bit color. Developed in 1987 by IBM, the VGA interface supported a maximum resolution of 640x480 pixels. Many different image types such as GIF and TIFF use an 8-bit color system to store data.
Even though it is now outdated for most consumer applications, 8-bit color encoding can still be useful in imaging systems with limited data bandwidth or memory capacity. For example, both
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...
s used an 8-bit grayscale format for navigation imaging.
Issues
Due to the nature of the 8-bit system, most images have different color maps. Since an 8-bit color display can't display two images with different color maps at the same time, it is usually impossible to display two different 8-bit images on the same such display at the same time. In practice, in order to avoid this problem, most images don't use the full range of 256 colors. Another problem comes when doing image processing: whenever two images with different color maps are added to each other, the resulting image has to have a new color map created, meaning another quantization operation has to occur, making the resulting image an imperfect version of the expected result.
8-bit color today
Currently, most graphics hardware runs in 24-bit truecolor or 32-bit truecolor (24-bit truecolor and an 8-bit
alpha channel
In computer graphics, alpha compositing or alpha blending is the process of combining one image with a background to create the appearance of partial or full transparency. It is often useful to render picture elements (pixels) in separate pas ...
). However, some remote desktop software (
Virtual Network Computing
Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer. It transmits the keyboard and mouse input from one computer to another, relaying the g ...
,
Remote Desktop Protocol) can switch to 8-bit color to conserve
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
. With the comparative low cost and high speeds of modern computers, some image editing is even done in a
raw
Raw is an adjective usually describing:
* Raw materials, basic materials from which products are manufactured or made
* Raw food, uncooked food
Raw or RAW may also refer to:
Computing and electronics
* .RAW, a proprietary mass spectrometry dat ...
format with anywhere from 12 to 14 bits from each of the camera's
image sensor
An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of c ...
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 smal ...
s in order to avoid image quality reduction while editing.
See also
*
Planar
Planar is an adjective meaning "relating to a plane (geometry)".
Planar may also refer to:
Science and technology
* Planar (computer graphics), computer graphics pixel information from several bitplanes
* Planar (transmission line technologies), ...
*
Packed pixel In packed pixel or chunky framebuffer organization, the bits defining each pixel are clustered and stored consecutively. For example, if there are 16 bits per pixel, each pixel is represented in two consecutive (contiguous) 8-bit bytes in the frameb ...
*
15/16-bit color (High color)
*
24-bit color (True color)
*
Raw images
*
Color depth
*
List of palettes
This article is a list of the color palettes for notable computer graphics, terminals and video game console hardware.
Only a sample and the palette's name are given here. More specific articles are linked from the name of each palette, for the ...
*
Indexed color
In computing, indexed color is a technique to manage digital images' colors in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers. It is a form of vector quantization comp ...
References
{{DEFAULTSORT:8-Bit Color
Color depths