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Computer graphics fall into two main categories--bitmap and
vector. You can work with both types of graphics in Photoshop and
ImageReady; moreover, a Photoshop file can contain both bitmap and vector data.
Understanding the difference between the two categories helps as you create,
edit, and import artwork.
Bitmap images
Bitmap images--technically
called raster images--use a grid of colors known as pixels to represent images.
Each pixel is assigned a specific location and color value. For example,
a bicycle tire in a bitmap image is made up of a mosaic of pixels in that
location. When working with bitmap images, you edit pixels rather than objects
or shapes.
Bitmap images are the most
common electronic medium for continuous-tone images, such as photographs or
digital paintings, because they can represent subtle gradations of shades and
color. Bitmap images are resolution-dependent--that is, they contain a fixed
number of pixels. As a result, they can lose detail and appear jagged if they
are scaled on-screen or if they are printed at a lower resolution than they
were created for.
Example of a bitmap image at
different levels of magnification
Vector graphics
Vector graphics are made up
of lines and curves defined by mathematical objects called vectors.
Vectors describe an image according to its geometric characteristics. For
example, a bicycle tire in a vector graphic is made up of a mathematical
definition of a circle drawn with a certain radius, set at a specific location,
and filled with a specific color. You can move, resize, or change the color of
the tire without losing the quality of the graphic.
Vector graphics are
resolution-independent--that is, they can be scaled to any size and
printed at any resolution without losing detail or clarity. As a result,
vector graphics are the best choice for representing bold graphics that must
retain crisp lines when scaled to various sizes--for example, logos.
Example of a vector graphic
at different levels of magnification
Because computer monitors
represent images by displaying them on a grid, both vector and bitmap data is
displayed as pixels on-screen.
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