There are two different types of images we can use: raster images and vector images. We prefer vector images, and in some cases, require it. Here are some of the qualities and pros and cons of each type of image:
A raster image is made of thousands of little dots, or pixels. Because of all the tiny pieces of the picture, raster images offer rich color; however, each pixel carries information which results in large file sizes. These may be difficult or slow to open or edit. What makes them impossible for some projects is that they do not resize well. These two WaterOUT logos may look the same at this size, but when you try to make the image larger, you'll see the grains, or pixels (top right). Making a small image larger results in the individual pixels just getting larger, making the image appear grainy.
A vector image is made up of a few points rather than pixels. For example, a raster image of a square would have thousands of pixels, but a vector image of a square has just four points - one on each corner. Each vector point has information telling the computer how to connect each point using straight or curved lines, and what color to fill in the closed shape. Vector images are much easier to edit, and when expanded, lines are simply redrawn. No matter how big we make it, the image never becomes grainy or distorted. Images that work well as vector images have solid colors or even gradients with straight lines or sweeping curves.