Computer Graphics: They're Not All the
Same
By Mandar
Graphic images on your computer come in two different forms,
raster images and vector images. Raster images are made by
programs such as Photoshop and Corel Photopaint. Vector images
are produced by Adobe Illustrator, Freehand, and CorelDraw.
While the results from these different programs can look
similar, the ways in which they are made are very different.
Raster images are made up of millions of individual squares, or
pixels, of various colors. The more pixels you have, the better
the image will look. The number of pixels, or resolution, is
usually expressed in dots per inch (dpi). Images on the Web are
shown at 72 dpi. A high-resolution image would run 300 dpi or
higher. Some types of printing can get into the 1600 dpi range.
Much like a mosaic, a raster image can look smooth from a
distance but as you zoom in closer you can see the individual
pixels.
A vector image is drawn from mathematical formulas for lines
and curves and is redrawn each time you zoom in for a closer
look. The quality of the image stays the same regardless of the
level of magnification. Vector files, since they are formulas
instead of information on millions of individual pixels, tend
to use less memory than raster files.
The edge of a circle, rendered as a raster image, may look
smooth initially, but eventually as you zoom in you will see a
jagged stair-step edge of the individual square pixels that make
up the image. A lower resolution image will look jagged or
pixellated much sooner than a high resolution image. A circle's
edge in vector form will always be smooth no matter how close
you zoom in since it is recalculated each time you change the
view.
Raster based programs are best at working with photo-realistic
images and make subtle (or bold) changes in color, shadow and
texture. Vector based programs excel at easy control of edges
and tend to produce a more graphic style of art. Regardless of
the type of image, higher resolution is always better for
producing a good result. While your image may be vector or
raster, or even a combination of the two, the Art Staff at
ExpertShirt.com will work hard to translate it into the best
textile printing possible. •
About the Author
Mandar is a graphic artist and man-about-town
with Expertshirt.com. Design your own custom t-shirt online at www.expertshirt.com.
08/19/05
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