Bitmap
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.
| Format | Description |
| BMP | The bit-mapped file format used by Microsoft Windows. |
| GIF | The bit-mapped file format used by CompuServe and many other BBSs. |
| PCX | Originally 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. |
Vector
Same as object-oriented graphics, refers to
software and hardware that use geometrical
formulas to represent images. The other
method for representing graphical images is
through bit maps, in which the image is
composed of a pattern of dots. This is
sometimes called raster graphics. Programs
that enable you to create and manipulate
vector graphics are called draw programs,
whereas programs that manipulated
bit-mapped images are called paint
programs.
Vector-oriented images are more flexible
than bit maps because they can be resized
and stretched. In addition, images stored as
vectors look better on devices (monitors and
printers) with higher resolution, whereas
bit-mapped images always appear the same
regardless of a device's resolution. Another
advantage of vector graphics is that
representations of images often require less
memory than bit-mapped images do.
Almost all sophisticated graphics systems, including CADD systems
and animation software, use vector graphics. In addition, many
printers (PostScript printers, for example) use vector graphics.
Fonts represented as vectors are called vector fonts, scalable
fonts, object-oriented fonts, and outline fonts.
Note that most output devices, including dot-matrix printers,
laser printers, and display monitors, are raster devices (plotters
are the notable exception). This means that all objects, even
vector objects, must be translated into bit maps before being
output. The difference between vector graphics and raster
graphics, therefore, is that vector graphics are not translated
into bit maps until the last possible moment, after all sizes and
resolutions have been specified. PostScript printers, for
example, have a raster image processor (RIP) that performs the
translation within the printer. In their vector form, therefore,
graphics representations can potentially be output on any
device, with any resolution, and at any size.
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Format
Description CGM (Computer Graphics Metafile)
A format developed by several standards organizations, CGM is supported by many PC software products.
DXF (Data Exchange File)
A format created by AutoDesk. Almost all PC-based CAD systems support DXF.
EPS (Encapsulated PostScript)
The file format for the PostScript language. EPS uses a combination of PostScript commands and TIFF or PICT formats.
GEM The graphics file format used by GEM-based applications. GEM is a graphical user interface (GUI) developed by Digital Research.
HPGL (Hewlett-Packard Graphics Language)
One of the oldest file formats. Although it is not very sophisticated, it is supported by many PC-based graphics products.
IGES (Initial Graphics Exchange Specification)
An ANSI standard for three-dimensional wire frame models. IGES is supported by most PC-based CAD systems.
PIC (Lotus Picture File)
A relatively simple file format developed by Lotus for representing graphs generated by Lotus 1-2-3. PIC is supported by a wide variety of PC applications.
PICT Developed by Apple Computer in 1984 as the standard format for storing and exchanging graphics files. It is supported by all graphics programs that run on a Macintosh.
WMF (Windows Metafile Format)
A file format for exchanging graphics between Microsoft Windows applications. WMF files can also hold bit-mapped images.