Understanding vector and raster graphics

There are two types of computer graphics: vector and raster. They’re very

different from one another, and each is best suited for a different purpose.

Clip art is a type of vector graphic. A vector graphic is created behind the

scenes by using math formulas; if you’ve taken a geometry class where you

plotted a function on graph paper, you get the idea. Computerized clip art

builds images by layering and combining individual lines and shapes, each

one constructed via a math formula. As a result, the clips can be resized with-

out losing any quality because resizing simply changes the math formula. Clip

art files are also very small compared with raster graphics. The main draw-

back of clip art is that the images don’t look real — they look like drawings.

Photos from digital cameras are examples of raster graphics. A raster graphic

is a densely packed collection of colored dots that together form an image. If

you zoom in on a photo on a computer, you can see these dots individually.

In a raster graphic, each dot is called a pixel, and its color is represented by

a numeric code (usually 24 or 32 binary digits in length per pixel). Raster

graphics can be photorealistic, but because so much data is required to

define each pixel, the file sizes tend to be large.

Microsoft Office uses the terms image, picture, and graphic interchangeably

in its documentation and help system, and so does this book. All three refer

generically to any picture, regardless of its type or source. The term photo-

graph refers specifically to raster images, and the terms clip art and illustra-

tion refer specifically to vector images.