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.
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
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
bit mapped 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.
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.
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).