Lesson One - Types of Programs
There are different kinds of graphic programs, and you need to use the right program for the job you need to do. Some graphic programs are intended to manipulate photographs, some create line art, and others let you paint with electronic oils, charcoals and waterpaints. While it's true that most can do more than just one thing, (a paint program can create a vector path, for example) every art program is intended to fall more into one of these categories.
Today I'm going to tell you about vectors and bitmaps.
Vector programs (CorelDRAW, Adobe Illustrator) create OBJECTS - shapes and fills. If you draw an egg, and then put a blue square on top of it, you can move the square around, delete it, place it behind the egg, resize and reshape. The program remembers each object, with its dimensions, outline and fill.
Bitmap programs (Corel Photopaint, Adobe Photoshop) manipulate the colors of pixels. The pixel has no inherent size - it could be 1/72 of an inch, or 1/300, or any other size you specify. It is a dot of color - the smallest picture element (hence the word "pixel.") If you draw an egg in a bitmap, or raster, program, and then draw a square on top of it, you have an oval with a square on it. If you erase the square, you have a hole in your egg. If you resize one, you resize both. The program doesn't care where the pixels turn blue; it only knows that there are blue pixels and egg colored ones.
With a Vector program, the shape and fill of the object are remembered, and can be manipulated.
Bitmap programs don't know a square from a donut, but they can change your chocolate cake into green fungus.
Vector programs, like Coreldraw and Illustrator, are used to create crisp illustrations, with distinct outlines and fills. They aren't used to manipulate photos — to put your dog's head onto your boy friend's body, for example. Coreldraw can make a logo for the Goodyear Blimp, but to change the blimp from silver to gold, you really should import it into a bitmap program. A vector program can draw an oval, and it will remember that the object is an oval, but you can't use it to draw a realistic leak and a puff of air escaping from it (except as a line drawing with a fill.) For this type of artwork use Photopaint or PhotoShop.
If you still have any doubts about bitmaps vs. vectors, go to the Puddle Project, on this web site. The table and spill are created in Coreldraw, the spill on the carpet is a Photoshop composition.