A brief but in-depth description of Vector and Raster imagery follows below. You may find this useful if unsure of the differences or the technical details.

Vector
Vector drawings are done by drawing lines between two points. They are similar to CAD and engineering drawings but have more artistic flexibility. Shapes created can be filled with colours and gradients.
Their main advantage is that the file sizes are relatively small but the image can be scaled up easily with no loss of quality.

These files are often called EPS files as they are usually saved in a EPS format which stands for Encapsulated Post Script.
Post Script is a computer language used by most decent printers (the type found in an office) and it enables the files to be pretty much universal, read by PCs or Macs.

Raster
Raster images are pixel-based images such as photographs. The suitability of these is very much dependant on the resolution.
Resolution is very important. It is measured in Dots Per Inch (DPI). Images used primarily on-screen will be 72dpi whereas the recommended resolution for printed images is 300dpi. So if we were to take an image from a web site and print it the image would need to be 25% the size of the original to look okay. If it is printed at the same physical dimension each pixel will become a dot four times its original size making it appear to be made out of Lego.

A decent modern digital SLR camera has a sensor resolution of about 10 megapixels (10 million pixels). This means it can produce an image of approximately 3888x2592 pixels (3888 x 2592 = 100776966). For printing purposes this would make an image 13 inches by 8.6 inches, enough for an A4 page.

Many clients do not realise / understand this and I am often given a logo, for example, from a web site as an image to use on printed material.


Vector images can be converted to raster but raster can not be converted to vector (at least not without a large amount of time and money).