There are two types
of files.
Raster (composed of pixels)
and vector (composed of paths).
Raster images are more commonly called bitmap images.
A bitmap image uses a grid of individual pixels where each
pixel can be a different color or shade. Bitmaps
are composed of pixels.
Vector graphics use mathematical relationships between points
and the paths connecting them to describe an image. Vector
graphics are composed of paths.
The image to the left below is representative of a bitmap
and the image to the right is representative of a vector graphic.
They are shown at four times actual
size to exaggerate the fact that the edges of a bitmap become
jagged as it is scaled up:
Bitmap Image: |
Vector Graphic: |
|
|
With Adobe® Systems' introduction of the PostScript®
page-description language computers could display fonts and
images using point-to-point math rather than by pixels alone.
The advantage to using a page-description language such as
PostScript becomes clear when you scale an image up. The larger
you display a bitmap, the more jagged it appears, while a
vector image remains smooth at any size. That is why PostScript
and TrueType® fonts always appear smooth - they are vector-based.
The jagged appearance of bitmap images can be partially overcome
with the use of "anti-aliasing". Anti-aliasing is
the application of subtle transitions in the pixels along
the edges of images to minimize the jagged effect (below left).
A scalable vector image will always appear smooth (below right):
Anti-Aliased Bitmap Image: |
Smooth Vector Image: |
|
|
Bitmap images require higher resolutions and anti-aliasing
for a smooth appearance. Vector-based graphics on the other
hand are mathematically described and appear smooth at any
size or resolution.
Bitmaps are best used for photographs
and images with subtle shading. Graphics best suited
for the vector format are page layout, type, line art or illustrations.
Wherever possible use the vector format for all your type,
line art and illustrations and only use bitmaps for photos
or images with complex or non-uniform shading. If the graphics
application recognizes native vector files such as those created
by Deneba Canvas™ (a filename with an extension of .CNV-
for versions 6 and 7), Adobe Illustrator® (a filename
with an extension of .AI), CorelDRAW® (a filename with
an extension of .CDR), or Macromedia® FreeHand® (a
filename with an extension of .FH8 - for version 8), then
use them first.
The EPS File Format
If the graphics application you are
using cannot read native vector files the next best thing
would be to save them as EPS (Encapsulated PostScript) files.
These are self-contained PostScript files which contain
the same mathematical descriptions as the vector files they
are made from. Even bitmaps can be saved in the EPS file format.
EPS files are supported by most all graphics applications.
It is the most portable format for this reason. It is best
to use EPS files for all line art and illustrations because
they can be reproduced at any size or resolution and still
display exactly as they were drawn. Use them wherever native
vector files cannot be used.
|
