If you’re a beginning graphic designer, or a new desktop publisher looking for clip art to use in a newsletter, it’s important to understand the differences between raster images, which are created with painting programs, and vector images, created with drawing programs. Knowing why these two major formats exist and how they are used can mean the difference between a graphic that works the way you want it to and one that doesn’t.

Raster graphics

Also frequently referred to as bitmap graphics, raster images are the most common. They are formed by a series of tiny individual squares that together create a larger picture, kind of like a mosaic is made of a series of smaller tiles. If you were to look closely at any number of every day images you would see how these images work. Documents that come from a fax machine or printer are made up of a series of tiny dots. The text and graphics on your computer screen are made up of a number of small image elements called pixels. When you take a photo with a digital camera, the picture is saved in memory as a long series of bits of information representing tiny squares of colors in a grid. These are all raster-based graphics.

The main problem with using raster graphics is that they are size-dependent. Normally the dots or pixels involved are so small that they blend together and look like one continuous image. If you try to print them out at a size larger than what the file was intended for, at some point you’ll start seeing the individual pieces as blocks. Making the image smaller than it was created for can also have bad consequences. For example, a line that is printed two dots thick can disappear entirely if the graphic is printed at less than half its original size, because the printer can’t draw anything smaller than one dot.

Raster graphics are typically used for complex images formed from lots of different colors and shapes, most notably photos. These graphics can be saved in a variety of formats with file extensions like .TIF, .JPG, .GIF and .BMP.

Vector graphics

Vector-based images follow a very different method in generating an image. These kinds of graphics don’t break an image down into individual parts of the same shape. Instead, they keep track of the instructions on how to draw that image. An image of a triangle would be formed by drawing three lines of a certain thickness and length that join at their end points and then filling it with a specific color. A vector image doesn’t know how many dots a printer will need to print that triangle, it just knows the size, shape, angles, colors and so forth of the parts that make up the image.

Vector graphics usually resize much more gracefully than raster-based images, because the file can just tell the computer or printer to draw the image larger or smaller than normal. The lines in such images are always smooth and do not become blocky when magnified. Because it typically has less overall information to keep track of, a vector file usually takes up less memory than a raster one. The more complex an image is, however, the more difficult it is for it to be stored in a vector format; this is why all photos except for the most basic or stylized should be in raster format instead of vector.

Diagrams, logos, fonts and other graphics that have basic shapes and curves are the main uses of vector images. The font files that generate type are stored as vector-based information, and many logos are as well. The main file extensions used with vector-based graphics are .EPS and .SVG.

Raster versus vector

A desktop publisher choosing clip art to use in a project or ordering a custom image from a graphic designer should pick a format that will best suit the intended use. If it’s a photo, or an image for use on a website, you’ll definitely want one of the raster-based file formats. If the image will be used in a print-based product like a newsletter or book and it consists of line art, such as in logos or diagrams, you’ll probably want a vector image. Raster images can also work just fine in print projects as long as the graphic is the right size, but if you try to cut corners and print one bigger than the file can support you’ll end up with a blurry mess.
u8232 If you are a graphic designer creating work for other people or saving your own projects, you’ll want to create each image with its format in mind from the beginning. Paint and photo editing applications, such as Adobe Photoshop and Microsoft Paint, create graphics as raster images even if you incorporate vector-based elements, such as fonts. If you save a graphic from one of these applications in .EPS format it won’t be automatically converted to a vector image. There are some software applications that can do that with varying degrees of success, but if you want a vector image you should create it from scratch in a drawing program like Adobe Illustrator, Corel Draw or Inkscape. Vector images are relatively easy to convert to raster-based ones once you know what size you want them to be; the option to convert it is available in every major graphic design application, whether it’s a painting or drawing program.
u8232 Once you have experience with the two major types of graphics under your belt you’ll be able to choose the ones that work best for your purposes without a second thought.

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