Programs like MS Paint
and PhotoShop are both bitmap applications, treating the images you work
with as a fixed-size resource made up of a fixed number of dots, or pixels.
Once a line or curve or piece of text has been 'committed' to the canvas you
can not go back and change it without undoing and starting over again.
Also, since the
information in a picture is represented by dots, you cannot enlarge the
image without exaggerating the effect of these dots and making the picture
look jagged. One advantage of using this scheme is that scanned photographs
are always represented as bitmaps (the detail in the average photograph is
way too complex to be represented as vectors), so if you want to work with
these items you'll need a bitmap based program. Another advantage is the
mathematical functions that can be performed on a bitmap, such as averaging
the pixels to create a blur, or edge detection routines that emboss.
Vector based
applications such as Corel Draw and Adobe Illustrator treat images as
collections of vectors and shapes. A line would have a starting point,
direction and length, a rectangle would have a starting point, width and
height, circles would have a center and radius, and so on. After drawing a
rectangle you can go back and change its width and height, bring it to the
foreground or send it to the background, even after other shapes had been
drawn on top of it later. When saved to file, vector images also take up
less disk space, since, for example in the case of a rectangle, the program
is only storing four numbers no matter what its size: the x and y starting
point, plus the width and height. In comparison, a bitmap application would
have to store color information for the 10,000 pixels that make up a 100x100
pixel rectangle.
Another advantage of
Vector based applications is that you can re-size the final image to be as
large or as small as you like and never obscure the detail with jagged
edges.
