Raster v.
Vector Graphics
Computer graphics can be
created as either raster
or vector images. Raster
graphics are bitmaps. A bitmap
is a grid of individual pixels
that collectively compose
an image. Raster graphics
render images as a collection
of countless tiny squares.
Each square, or pixel, is
coded in a specific hue or
shade. Individually, these
pixels are worthless. Together,
they're worth a thousand
words.
Raster graphics are best
used for non-line art images;
specifically digitized photographs,
scanned artwork or detailed
graphics. Non-line art images
are best represented in raster
form because these typically
include subtle chromatic
gradations, undefined lines
and shapes, and complex composition.
However, because raster images
are pixel-based, they suffer
a malady called image degradation.
Just like photographic images
that get blurry and imprecise
when blown up, a raster image
gets jagged and rough. Why?
Ultimately, when you look
close enough, you can begin
to see the individual pixels
that comprise the image.
Hence, your raster-based
image of Wayne Newton, magnified
to 1000%, becomes bitmapped
before you can isolate that
ravenous glint in his eye.
Although raster images can
be scaled down more easily,
smaller versions often appear
less crisp or "softer" than
the original.
To maximize the quality of
a raster image, you must
keep in mind that the raster
format is resolution-specific
-- meaning that raster images
are defined and displayed
at one specific resolution.
Resolution in raster graphics
is measured in dpi, or dots
per inch. The higher the
dpi, the better the resolution.
Remember also that the resolution
you actually observe on any
output device is not a function
of the file's own internal
specifications, but the output
capacity of the device itself.
Thus, high resolution images
should only be used if your
equipment has the capability
to display them at high resolution.
Better resolution, however,
comes at a price. Just as
raster files are significantly
larger than comparable vector
files, high resolution raster
files are significantly larger
than low resolution raster
files. Overall, as compared
to vector graphics, raster
graphics are less economical,
slower to display and print,
less versatile and more unwieldy
to work with. Remember though
that some images, like photographs,
are still best displayed
in raster format. Common
raster formats include TIFF,
JPEG, GIF, PCX and BMP files.
Despite its shortcomings,
raster format is still the
Web standard -- within a
few years, however, vector
graphics will likely surpass
raster graphics in both prevalence
and popularity.
Unlike pixel-based raster
images, vector graphics are
based on mathematical formulas
that define geometric primitives
such as polygons, lines,
curves, circles and rectangles.
Because vector graphics are
composed of true geometric
primitives, they are best
used to represent more structured
images, like line art graphics
with flat, uniform colors.
Most created images (as opposed
to natural images) meet these
specifications, including
logos, letterhead, and fonts.
Inherently, vector-based
graphics are more malleable
than raster images -- thus,
they are much more versatile,
flexible and easy to use.
The most obvious advantage
of vector images over raster
graphics is that vector images
are quickly and perfectly
scalable. There is no upper
or lower limit for sizing
vector images. Just as the
rules of mathematics apply
identically to computations
involving two-digit numbers
or two-hundred-digit numbers,
the formulas that govern
the rendering of vector images
apply identically to graphics
of any size.
Further, unlike raster graphics,
vector images are not resolution-dependent.
Vector images have no fixed
intrinsic resolution, rather
they display at the resolution
capability of whatever output
device (monitor, printer)
is rendering them. Also,
because vector graphics need
not memorize the contents
of millions of tiny pixels,
these files tend to be considerably
smaller than their raster
counterparts. Overall, vector
graphics are more efficient
and versatile. Common vector
formats include AI, EPS,
CGM, WMF and PICT (Mac).
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