Sometimes people ask me why Adobe made Photoshop and Illustrator and when they should use either program and for what... First I'd like to define the groups Raster and Vector: Adobe Photoshop, Jasc PaintShop Pro, & Macromedia Fireworks are all Raster programs, while Illustrator and Freehand are Vector based.

Raster images are those based on pixels like the image of the squares to the right. As I have shown I started with a representation of a two by two pixel image, which was then resized to a five by six image. Since five is not divisible by two, the computer chooses to make the middle column a cross between the two neighboring columns so it is 50% of the color instead of 100%.

If I were to save the first 2/2 as a file, it would record the following data: 1/1=Yellow, 1/2=White, 2/1=White, 2/2=Red. Of course it would do it in a far more numerical manner, but the principal is the same. Vector files are different, and do not think of, or record visual information in that way. Inside the image of the yellow circle I have written the information that a vector file would record: The shape is given a name: "Circle1", the center of the circle has a set location and from there the computer has the rest of the instructions for the size and color to apply to the circle. There are many benefits of recording information by using vector instructions and math rather than recording the color of each pixel. You can multiply the scale of the circle 1001 times and it would still be as sharp, and even if it becomes an image billboard sized it would still be the same file size as if it were tiny. Illustrator can import raster images, but you cannot change the content of the photo as you can in Photoshop, so for any type of photo manipulation Photoshop will always be best. Illustrator is what you would want to use if you were drawing a logo or other such artwork that you want to be very scalable and always crisp.