8-bit color
Encyclopedia
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.
There are two forms of 8-bit color graphics. The most common uses a separate palette of 256 colors, where each of the 256 entries in the palette map to given red, green, and blue values. In most color maps, each color is usually chosen from a palette of 16,777,216 colors (24 bits: 8 red, 8 green, 8 blue). But in the original VGA card's 320x200 mode, 256 on-screen colors could be chosen from a palette of 262144 colors (18 bits: 6 red, 6 green, 6 blue). Some older cards prior to the VGA (like the Professional Graphics Controller
) can only choose the 256 color palette from 4096 colors (12 bits: 4 red, 4 green, 4 blue).
The other form is where the 8 bits directly describe red, green, and blue values, typically with 3 bits for red, 3 bits for green and 2 bits for blue. This second form is often called 8-bit truecolor, as it does not use a palette at all, and is thus more similar to the 15, 16 and 24 bit truecolor modes.
Most 8-bit image formats store a local image palette
of 256 colors in addition to the raw image data. If such an image is to be displayed on 8-bit graphics hardware, the graphics hardware's global palette will be overwritten with the local image palette. This can result in other images on the screen having wildly distorted colors due to differences in their palettes.
For this reason, on 8-bit graphics hardware, programs such as web browsers must address this issue when simultaneously displaying multiple images from different sources. Each image may have its own palette, but the colors in each image will be remapped to a single palette, probably using some form of dithering.
Nowadays, most graphics hardware runs in 24-bit or 32-bit truecolor, and this problem is largely a thing of the past. However, some remote desktop software (Virtual Network Computing
, Remote Desktop Protocol
) can switch to 8-bit color to conserve bandwidth
.
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....
is represented by one 8-bit byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
. The maximum number of colors that can be displayed at any one time is 256.
There are two forms of 8-bit color graphics. The most common uses a separate palette of 256 colors, where each of the 256 entries in the palette map to given red, green, and blue values. In most color maps, each color is usually chosen from a palette of 16,777,216 colors (24 bits: 8 red, 8 green, 8 blue). But in the original VGA card's 320x200 mode, 256 on-screen colors could be chosen from a palette of 262144 colors (18 bits: 6 red, 6 green, 6 blue). Some older cards prior to the VGA (like the Professional Graphics Controller
Professional Graphics Controller
Professional Graphics Controller was a graphics card manufactured by IBM for the PC. It consisted of three interconnected PCBs, and contained its own processor and memory....
) can only choose the 256 color palette from 4096 colors (12 bits: 4 red, 4 green, 4 blue).
The other form is where the 8 bits directly describe red, green, and blue values, typically with 3 bits for red, 3 bits for green and 2 bits for blue. This second form is often called 8-bit truecolor, as it does not use a palette at all, and is thus more similar to the 15, 16 and 24 bit truecolor modes.
Bit 7 6 5 4 3 2 1 0
Data R R R G G G B B
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,...
of 256 colors in addition to the raw image data. If such an image is to be displayed on 8-bit graphics hardware, the graphics hardware's global palette will be overwritten with the local image palette. This can result in other images on the screen having wildly distorted colors due to differences in their palettes.
For this reason, on 8-bit graphics hardware, programs such as web browsers must address this issue when simultaneously displaying multiple images from different sources. Each image may have its own palette, but the colors in each image will be remapped to a single palette, probably using some form of dithering.
Nowadays, most graphics hardware runs in 24-bit or 32-bit truecolor, and this problem is largely a thing of the past. However, some remote desktop software (Virtual Network Computing
Virtual Network Computing
In computing, Virtual Network Computing is a graphical desktop sharing system that uses the RFB protocol to remotely control another computer...
, Remote Desktop Protocol
Remote Desktop Protocol
Remote Desktop Protocol is a proprietary protocol developed by Microsoft, which provides a user with a graphical interface to another computer. The protocol is an extension of the ITU-T T.128 application sharing protocol. Clients exist for most versions of Microsoft Windows , Linux, Unix, Mac OS...
) can switch to 8-bit color to conserve bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
.
See also
- Planar
- Packed pixel
- HighcolorHighcolourHigh color graphics is a method of storing image information in a computer's memory such that each pixel is represented by two bytes...
- Truecolor
- Color depthColor depthIn computer graphics, color depth or bit depth is the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel , particularly when specified along with the number of bits used...
- List of palettes