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bit map
bit-mapped graphics
optical scanner

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 text or 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 scale them 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 device and a specific size and resolution.

Bit-Mapped Graphics File Formats

BMPThe bit-mapped file format used by Microsoft Windows.
GIFThe bit-mapped file format used by CompuServe and many other BBSs.
PCXOriginally developed by ZSOFT for its PC Paintbrush program, PCX is a common graphics file format supported by many graphics programs, as well as most optical scanners and fax modems.
TIFF (Tagged Image File Format) A standard file format for storing images as bit maps. It is used especially for scanned images because it can support any size, resolution, and color depth.

For pages about bit map, . Also, check out the following links!

More Information

  Bit maps in QuickDraw
This Apple technical support page explains how bit maps work in QuickDraw.

  Ilustrated explanation of bit map
Contains a short description of bit map along with some examples and links to related information.


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