There are two types of digital graphics files – raster and vector. Raster images are composed of pixels. Vector images are made of hundreds of thousands of tiny lines and curves (or paths) to create an image.
Raster images are often called bitmap images because they are made of millions of tiny squares, called pixels. You can identify a raster or bitmap image by looking at it very closely. If you zoom in enough, you will be able to see the square outlines of each pixel (especially around edges where there are dramatic color contrasts).
Raster graphics typically have larger file sizes than their vector counterparts. Higher PPI (pixels per inch) settings also contribute to larger files because software must keep track of and be able to render each pixel. File size can become a concern if storage or server space is limited or if files have to be transmitted electronically.
Vector images, which are made of thin lines and curves known as paths, are rooted in mathematical theory. Vector graphics must be created in computer software that is designed to create this intricate wireframe-type image and each line includes defined node positions, node locations, line lengths and curves. Any of the lines and curves in the image can be assigned a color value. Because of this defined, formulaic approach to drawing, each image can be sized and scaled repeatedly and limitlessly without losing resolution or beginning to look cloudy or pixelated.
You can identify a vector image by looking at its edges — a vector image will always appear smooth no matter how large you make it or how close you zoom in. Text is one of the most common types of vector image. No matter how much you increase a font’s size, for example, its look never changes.
Another advantage to using vector images is file-size efficiency. Because the files are only identified by mathematical descriptions and not individual pixels, files are often much smaller than those of the raster counterparts. Vector images, therefore, are often easy to transmit from one computer to another and over the Internet.
Raster and Vector can be in the same file!
While Adobe Illustrator is primarily a vector-based program, it has some raster-only elements available, such as drop shadows or outer glows. Likewise, Adobe Photoshop now allows you to work with vector-based objects (called smart objects) within the traditionally raster-based program. Don’t be confused…this added flexibility within design programs still doesn’t override the traditional wisdom:
Raster = photographs = can’t enlarge without becoming blurry.
Vector = fonts/created in Illustration program(AI) = ability to enlarge without losing quality