Graphics Programs Reference
In-Depth Information
use a scanned photo of your house in Photoshop to paint the side of the house red to see
what it might look like before you run down to the local paint store.
A raster or bitmap image is a mosaic of pixels, so the
resolution
of an image is defined
by the number of pixels in the horizontal and vertical directions. Because they're based on
a grid of a fixed size, raster images don't scale up well. The closer you get to a raster image,
the bigger the pixels become, making the image look blocky, or
pixelated
. To make large
raster images, you need to begin with a higher resolution. The higher the resolution, the
larger the file size will be. Figure 1.1 shows what happens when you blow up a raster image.
Figure 1.1
A raster image at its
original size (left)
and blown up sev-
eral times (right)
Most common raster displays are television or computer screens. In fact, the term
ras-
ter
originally referred to the display area of a television or computer monitor. To form an
image, the electronics in these devices essentially paint it as a grid of red, green, and blue
pixels on a glowing screen. Every image generated by a computer, therefore, must either
begin as a raster image or be rasterized as part of rendering for display.
Vector Images
Vector images are created in a completely different way. They're formed using mathemat-
ical algorithms and geometric functions. Instead of defining the color of each and every
pixel in a grid of a raster image, a vector image uses coordinates and geometric formulas
to plot points that define
areas
,
volumes
, and
shapes
.
Popular vector-based image applications include Adobe Illustrator and Flash, as
well as practically all computer-aided design (CAD) programs, such as AutoCAD and
SolidWorks. These programs let you define shapes and volumes and add color and tex-
ture to them through their toolsets. They store the results in scene files containing coor-
dinates and equations of points in space and the color values that have been assigned to
them. This vector information is then converted into raster images (called
rasterization
)
through rendering so you can view the final image or animation.
When scaled, vector graphics don't suffer from the same limitations as raster images.
As you can see in Figure 1.2, vectors can be scaled with no loss of quality; they will never
pixelate.