Chapter 9 - Goodheart-Willcox

epresents one character according to the ASCII
code. The ASCII code represents English characters
as numbers, with each assigned a number from zero
to 127.
Although formatting is lost when a file is saved
as an ASCII file, the text can still be repurposed.
Repurposing is reusing content intended for one
medium by reformatting it for another. Most computers
use ASCII codes to represent text so it is possible
to transfer data from one computer to another.
It is important to maintain your original text
and image files. You should make copies and work
from the copies. If data is lost or destroyed during
prepress production and you need to recreate your
work, or if you need to drastically resize or modify
graphics, you will be able to do so.
Creating computer images
Graphic images can be created and saved in a
variety of ways. Digital images can be created
through paint programs, draw programs, digital
photography, and electronic scanning, Figure 9-3.
The electronic images created are saved as one of
many formats. File formats of the graphics are very
important because they determine how much
manipulation can be done to the image and how
well it will be reproduced. (Paint and draw
programs are discussed in the following sections.
Digital camera and electronic scanner operation are
covered in detail in Chapter 10.)
Figure 9-3. Flatbed scanners can be used to capture
images from many different types of originals. Scanners
vary in size, capabilities, and method of operation.
(FUJI Photo Film U.S.A., Inc.)
Chapter 9 Electronic Prepress and Digital Printing 175
Paint programs
Paint programs allow the user to create freehand
drawings. The images are stored as bitmaps,
or raster graphics, and can be edited easily. Bitmap
images use a grid of small squares (pixels) to
represent graphics. The bitmap image is represented
as rows and columns of dots on this grid.
The value of each dot is stored in one or more bits
of data. Each pixel is encoded as a single binary
digit. For simple black and white images, one bit is
sufficient to represent each dot. However, for colors
and shades of gray, each dot may require anywhere
from 8 to 32 bits of information. The more bits that
are used to represent a dot, the more colors and
shades of gray can be represented.
When using a paint program, the user can see
the rows and columns of dots that compose the
image by zooming in on any given area, Figure 9-4.
The user is able to add or delete color by filling in or
“emptying” each square on the grid. In other words,
when you work with bitmap images, you edit
pixels rather than objects or shapes. Through
these actions, the user is able to modify the image
size, shape, or colors. When bitmaps are enlarged
or reduced, the edges become ragged because they
are composed of “squares” that do not create a
smooth line. This process is referred to as aliasing,
Figure 9-5.
Aliasing is the process by which smooth curves
and other lines become jagged (jaggies) because
the resolution of the graphics device or file is
reduced. Antialiasing is a software technique for
diminishing jaggies. Jaggies are stairstep-like lines
that occur because the output device doesn’t have
high enough resolution to represent a smooth line.
Antialiasing reduces the prominence of jaggies
by surrounding them with intermediate shades of
gray or color. The gray, of course, would be for
gray-scaling devices and the color for color devices.
Although this reduces the jagged appearance of the
lines, it also makes them fuzzier. Many programs
provide an antialiasing option that is extremely
useful when placing text in an image.
Another method for reducing jaggies is called
smoothing. Refer to Figure 9-5. Some printers
change the size and horizontal alignment of dots to
make curves smoother. Other printers reduce dot
size of those dots that make up a curved line.
Simple paint programs are usually included on
most personal computers and are adequate for
home use or simple office functions. More advanced
176 Graphic Communications
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 9-4. Most paint programs are limited to the basic tools indicated above.
Aliased image
Antialiased image
Figure 9-5. The antialiasing technique helps smooth
jaggies by filling in squares along the edge with color that
varies slightly from that on the image.
paint programs are used professionally for creating
print, electronic, and video images, Figure 9-6.
Many graphic designers also use draw or
illustration/design programs.
Draw programs
Like paint programs, draw programs enable the
user to create, store, and merge images into
documents. Unlike paint programs, draw programs
use vector graphics instead of raster graphics,
Figure 9-7. In computer graphics, a vector is a line
that is defined by its start and end point. With
Figure 9-6. Digitizing tablets, paint pens, and a computer
mouse can be used with most professional paint
programs. (Graphic Paintbox 2 by Quantel)
vector graphics, images are represented as mathematical
formulas that define all the shapes in the
image as well as their placement on a document.
Vector graphics are more flexible than raster graphics
because they look the same even when they are
scaled to different sizes and they can be represented
at any resolution. This makes them ideal for highresolution
output. Vector graphics are also referred
to as object-oriented graphics.