Bit Map

)A representation, consisting of rows and columns of dots, of a graphics image in computer memory. The value of each dot (whether it is filled in or not) is stored in one or more bits of data. For simple monochrome images, one bit is sufficient to represent each dot, but for colors and shades of gray, each dot requires more than one bit of data. The more bits used to represent a dot, the more colors and shades of gray that can be represented.

The density of the dots, known as the resolution, determines how sharply the image is represented. This is often expressed in dots per inch (dpi )or simply by the number of rows and columns, such as 640 by 480.

To display a bit-mapped image on a monitor or to print it on a printer, the computer translates the bit map into pixels (for display screens) or ink dots (for printers). Optical scanners and fax machines work by transforming textor pictures on paper into bit maps.

Bit-mapped graphics are often referred to as raster graphics. The other method for representing images is known as vector graphics or object-oriented graphics. With vector graphics, images are represented as mathematical formulas that define all the shapes in the image. Vector graphics are more flexible than bit-mapped graphics because they look the same even when you scalethem to different sizes. In contrast, bit-mapped graphics become ragged when you shrink or enlarge them.

Fonts represented with vector graphics are called scalable fonts , outline fonts , or vector fonts. The best-known example of a vector font system is PostScript. Bit-mapped fonts, also called raster fonts, must be designed for a specific deviceand a specific size and resolution.

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  • bit-mapped graphics

    )Refers to hardware and software that represent graphics images as bit maps. The other method for representing images is known as vector graphics.

  • bit rate

    The ratio of the number of bits that are transferred between devices in a specified amount of time, typically one second. Bit rate is the same as data rate, data transfer rate and bit time.

  • bit-slice

    Refers to a type of microprocessor in which the MPU is split apart into CU (control unit) and ALU (arithmetic logic unit) chips.

  • bit stuffing

    The practice of adding bits to a stream of data. Bit stuffing is required by many network and communications protocols for the following reasons: To prevent data being interpreted as control information. For example, many frame-based protocols, such as X.25, signal the beginning and end of a frame with six consecutive 1 bits. Therefore, if […]

  • bit block transfer

    A transformation of a rectangular block of pixels. Typical transformations include changing the color or shade of all pixels or rotating the entire rectangle. Many modern video adapters include hardwired bit block transformations, which execute much faster than they do when executed by software routines.

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