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Vector-Based
Graphics Programs
The major software players
by Douglas Grigar, Master
Screen Printer
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(A version of this article originally appeared
in the February 2005 issue of PRINTWEAR.)
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In most shops, a vector drawing program
is used to create and separate the majority of production art, often
representing over 80% of all the art created to be printed on garments,
signs, bumper stickers, and just about everything else that can be screened
(see Figure 1). Vector graphics are easily modified, colors changed,
and elements moved or enlarged or reduced to any dimensions without
loss of the original line or edge quality.
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[Figure 1: The same vector graphic
file can be used for any product, changed to any size, and used for
countless derivative designs to fit the customer’s needs.]
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One of the most asked questions in a new
shop is what art programs are needed to produce T-shirts. As with many
basic-seeming questions, this one is more complicated than it first
looks.
Many programs are used to produce graphics
but the two most used professional-level programs are of the vector-drawing
type (such as Adobe Illustrator, Macromedia Freehand, and CorelDraw)
and the photographic-editing type (such as Adobe Photoshop).
If forced to choose one type of graphic
program over the other, a new shop would likely want to purchase one
of the vector-drawing programs as the primary working platform. The
majority of screen printing needs can be met by a vector program. Eventually,
the demands of art production will require both types of programs on
a regular basis along with several support items such as vector tracing
aids and a large typeface collection. If possible, both types of programs
should be part of any short-term start-up plan, as the needs for both
vector and pixel editing will present themselves in short order.
Highlighting the Differences
Many years ago I theorized that Adobe Illustrator
and Photoshop would eventually merge into one behemoth multi-use program.
To this date, many features have crossed over but the basic programs
are fundamentally different and designed for specific tasks.
The basic operations of vector programs
such as Adobe Illustrator use mathematically defined outlines, often
called wire frames, to represent objects and lines forming a graphic
image. Vector drawings are similar to paper and string stacked upon
each other in an artist’s collage (see Figure 2).
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[Figure 2: Vector programs used basic
framework lines, or wire frames, to construct an image in a way similar
to a collage.]
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Pixel-editing programs such as Adobe Photoshop build grids
of small individual pixel blocks similar to large complex formations of
children’s building blocks, with each block having an individual
set of information such as color and tint (see Figure 3).
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[Figure 3: Pixel-editing programs such
as Photoshop create designs formed of thousands of individual blocks
with specific information for each block.]
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Pixels simulate smooth curves
by following the grid limits closely and creating blends of colors to
fool the eye into visualizing a smooth curve (see Figure 4). Pixel programs
must build blocks into formations to simulate curves and lines; the smaller
the grid blocks, the more accurate the curves and lines will be.
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[Figure 4: Curves in pixel programs
are simulated by blending colors; note, the enlargement shows how increasing
size can lower perceived quality.]
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The vector forms change proportionally under command from the user and
are always at maximum resolution. Changes in pixel-building programs force
the program to make new calculations to fit redrawn pixels into the set
pixel grid (see Figure 5). The basic differences in the way graphic files
are built and saved explain why vector drawings are often much smaller
in file size than pixel-based drawings.
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[Figure 5: Vector-based programs produce
smooth, sharp lines and curves regardless of size, with mathematical
formulae, while pixel-editor programs must conform to pixel grids.]
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| The Component Parts
Vector drawings contain joined or overlapping objects
that are made of lines defined by paths which are connected and controlled
by points along the path segments. Closed paths or paths that form a complete
shape are considered objects. Objects and line paths can be assigned any
color, or can even be without a color and be “see-through.”
Any path can form a line and be used as an independent element in a design.
The control of a path is managed by a point at the end of each segment.
Curved line segments have extension controls that define the curve shape.
The extension controls help define what is called a Bezier curve (a French
word pronounced bez’-e-ay). Curve extension controls are visible
only to the user of the program while drawing (see Figure 6).
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[Figure 6: Objects such as the square,
the curved mouth shape, the eyes, and the circular outlines are made
of straight lines or curves. “A” and “B” are
line segments, while the blue squares represent the connected points.
Curved lines are modified by extension controls such as “C”
that define the curve.]
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| The line segments can be used
to define a visible line and can be assigned a color, be either solid or
dashed, or have a special effect. Line segments assigned a color will have
half of the chosen line thickness on each side of the centered line. The
ends of paths and object corners can be rounded or formed into sharp corners.
Controls for specific corner results are a part of every vector program.
Compound paths are linked objects where one part of
the path forms a cut or removed section from the host object; an example
being the center of the letter “O.” Compound paths are pre-formed
in text when converted to paths. Compound paths can be defined by the
user for any object as needed. Graphics such as a logo can have compound
paths that allow background objects to show through (see Figure 7).
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[Figure 7: Compound paths make the
center of the smiling face “clear” to allow the red ‘sun’
to show from the back position.]
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| Text can be used for bold headlines
or to list hundreds of names in a list from a school graduation class. Any
text can be integrated into a design in a vector program from just about
any compatible source. Typeface designs called fonts can be assigned to
text in a design and even edited later by simply highlighting the error
and typing the correction. Text can also be converted into objects that
can be used to form parts of a design. Figure 7 is an example type converted
to an object for manipulation into a finished design.
Quick Shapes, Effects, and Modifications
Vector programs also have tools to form simple
shapes such as stars, circles, rectangles, ovals, polygons, and other
useful shapes to help create elements in a design. All objects in a vector
program can be duplicated as needed. For example, if a designed wanted
to draw the stars and stripes in the U. S. flag, only one stripe and one
star would be needed, then duplicated and moved into position to form
each part of the design.
Vector programs can modify an object or group
of objects into a new angle or direction, and can squeeze, shrink, distort,
flip, and rotate in almost endless ways (see Figure 8). Modifications
that would have taken several hours of drawing time with pen and ink 25
years ago can be made with vector programs in seconds.
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[Figure 8: Object distortions and text
effects are simple procedures for vector programs.]
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| Color: Quick and Easy
Vector programs have almost infinite control
of color choice and placement. Color modifications and changes are quite
easy. Vector programs can also break designs into custom colors that can
be separated into component areas for screen printing or even printed
into four-color process, or combinations of the two. Vector drawings can
have the objects and colors form chokes, traps, and overlays with simple
command changes in the color control palettes.
Using Clip Art
Thousands of vector drawings are available
as “clip art” - everything from design elements, complete
drawings, and design templates, to sports, seasonal, and other themed
designs. Clip art can help designers create attractive drawings for printing
and help keep art charges lower for the client (see Figure 9).
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[Figure 9: Interesting designs can
be created from clip art; modifications and additions taking little
time to complete can produce satisfying art with much lower art charges.]
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| Printing the Image for
Exposing Screens
Vector programs such as Adobe Illustrator
have color-separation software built into the functionality of the program
and can print a design’s color elements onto film for screen exposure.
Postscript-compatible printers or independent RIP (raster image processor)
software is often needed for the vector program to complete the printing
process or form correct-sized dots for efficient printing.
Understanding the Choice
A general and basic understanding about the
features and use of vector-based software will help a new shop justify
the purchase of such a program. Creative design work for screen printing
often demands a specific type of graphic and often, that need points to
a vector drawing program. While this article is not a lesson on how to
use a vector program, it is intended to provide the prospective purchaser
or new owner with an idea of the basic workings and uses.
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