When you have finished reading this article, you will know the difference between vector file formats and bitmap file formats, and how to determine the difference between the two.

The following uses content by CHUCK GREEN from IdeaBook. Thanks for the great info Chuck!

What are vector graphics? Vector graphics, also referred to as “object-oriented” or “draw” graphics, are created using geometric objects—lines, ovals, rectangles, and curves.

The key to this format is this—it is the primary advantage of a vector over a bitmap image—once you establish the points (the edges of the image), the program draws a line between the points at the highest resolution the screen can show and your printer can print. That means you can reduce a vector graphic to half an inch or blow it up to three feet and the program simply recalculates the position of the points and draws the highest quality line between them—hence, large or small, your image is crystal clear [2]. In other words, vectors are “resolution-independent.”

Computer fonts are another form of vector graphics—that’s why you can make them large or small without any loss of quality. Computer-Assisted Design (CAD) drawings, the line drawings created by engineers and architects, are vector graphics too—created entirely from points, lines, and shapes.

Just because they are drawn using a simple method does not mean the resulting images are simple. A shape can have hundreds of points and a single illustration can have hundreds, even thousands, of shapes.

Another big advantage of vectors over bitmaps is file size. No matter what size you make the final image, that file size remains the same. In contrast, changing the size of a bitmap to a larger physical size will increase its file size.

The primary disadvantage of vectors is they are time-consuming to create. They take experience and patience to create but images in vector form are among the easiest to use, edit, and store. How are they used? A drawing program such as Adobe Illustrator is excellent for everything from creating simple graphics such as logos to composing short documents such as advertisements and brochures. They are also the ideal venue for editing vector clip art.

Below are a few of the most common vector file formats.

Generally speaking, using a universal format such as an EPS vector or TIFF bitmap allows more users access to the file.

What are bitmap graphics? Bitmap graphics are sometimes referred to as “digital,” “raster,” or “paint” graphics.

The advantage of a bitmap over a vector is that it can represent a much more complex range of colours and shades—photographic detail. Bitmaps, of course, are found everywhere. The images digital cameras and scanners produce are bitmaps, as are most of the graphics you see on the World Wide Web.

A bitmap image is very different from a vector. Instead of connect-the-dots think paint-by-numbers. A typical bitmap is divided into a grid of thousands of tiny rectangles (A) called “pixels” and each pixel can be assigned a different colour or shade of gray.

Generally speaking, bitmaps are far easier to create than vectors but they present a complication: they are “resolution-dependent.” Resolution refers to the number of pixels there are in every linear inch of the image. The more pixels per inch (ppi) the higher the resolution. The idea is to keep the pixels small enough that the human eye blends them into continuous tones.

The problem is the number of pixels per inch necessary for the eye to do the blending varies among different media. For Web graphics on a computer screen it’s only 72 pixels per inch. But images that will be reproduced on a printing press require 250 or more pixels per inch. Hence, if you copy an image from the Web and reproduce it in print your eye sees the pixels—there are not enough pixels per inch.

The rule of thumb, therefore, is to anticipate in what medium and at what size you will use the image before you create it. And when in doubt, to create originals with as high a resolution as is practical.

The point here is you can’t start with a small bitmap image and blow it up. Start with the small file and blow it up and you get “the jaggies” (A)—a malady exposed as your eye picks up the saw-tooth edges of the pixels. Low resolution is the reason you can’t use Web graphics in a brochure and why you can’t blow up a 2 x 2 inch 300 ppi image to 4 x 4. It is worth noting, too, that you should not use high-resolution images (more than 72 ppi) on your Web. The image won’t look any better but it will take far longer to open.

Here are some common bitmap file formats.

How to Determine Picture File Formats?
Once you know the basics the image file formats are easy to spot. Vectors generally have flat colors and hard edges—bitmaps have continuous tones and a photographic quality.

If you can’t spot them outright, check the file name. In Windows you can tell the file format by the three letters that follow the period in the file name. For example, the “eps” in the file name “trumpet.eps” means the file is an Encapsulated PostScript file (filename abbreviations or extensions are listed in the tables above). On the Macintosh, you can read the file icon or single click on the file and choose Command-I to see the file information.

We hope this explanation provided by Ideabook and edited and reduced for reading here provides a clear overview of graphic file formats and why a design agency may ask for an EPS file.