Chapter 7 Digital Prepress 137
by changing the size and horizontal alignment of
dots to make curves smoother. Other printers reduce
the size of those dots that make up a curved line to
create a smoother appearance.
Some graphics programs incorporate an
autotracing feature. Autotracing is a process for
converting a bitmapped image into a vector image.
Most autotracing packages read fi les in a variety of
bitmapped formats (GIF and TIFF are very common)
and produce a vector format fi le, such as an EPS.
The conversion techniques used and the accuracy
of the conversion process differs from one software
package to another.
Vector Images
Vector images are represented as mathematical
formulas that defi ne all the shapes in the image, as
well as their placement in a document. In computer
graphics, a vector is a line that is defi ned by its start
point and endpoint. A piece of line art generated by a
drawing program is a vector graphic, Figure 7-18. A
drawing program gives the designer control over shape,
placement, line width, and object pattern, Figure 7-19.
A Bezier curve is a vector graphic named after
French mathematician Pierre Bezier. It is defi ned
mathematically by two endpoints and two or more
other points that control its shape, Figure 7-20.
Nearly all drawing programs support Bezier curves.
The two endpoints of the curve are called anchor
Marquee……
Lasso……
Airbrush……
Eraser……
Rubber stamp……
Blur……
Pen……
Line……
Paint bucket……
Hand……
Foreground color……
Default colors……
Standard mode……
Standard screen……
mode
……Move
……Magic wand
……Paintbrush
……Pencil
……Smudge
……Dodge
……Type
……Gradient
……Eyedropper
……Zoom
……Switch colors
……Background color
……Quick mask mode
……Full screen mode
……
Full screen mode with menu bar
Figure 7-16. Most paint programs are limited to the
basic tools indicated above.
Aliased Image
Antialiased Image
Figure 7-17. The antialiasing technique helps smooth
jaggies by fi lling in squares along the edge with color
that varies slightly from that on the image.
Figure 7-18. A drawing program generates vector
images that can be easily scaled and modifi ed because
the object is defi ned geometrically.
bitmapped images: Graphics fi les that contain a map of
pixels, each of which is assigned characteristics such as
color and brightness, to make up the image.
aliasing: The process in which smooth curves and other
lines become jagged because an image is enlarged or the
resolution of the graphics device or fi le is reduced.
antialiasing: Software technique for diminishing the jagged
edges of an image that should be smooth.
smoothing: A technique used by some printers to reduce
jaggies.
autotracing: A feature of some graphics programs; allows
bitmapped images to be converted into vector format.
vector images: Images that are defi ned in terms of
mathematical parameters, which gives the artist or designer
control over shape, placement, line width, and pattern.
Bezier curve: A vector graphic defi ned mathematically by
two endpoints and two or more other points that control its
shape.