There are two types of digital images: vector images and raster images.

Vector images are usually logos or line art graphics and can be enlarged or reduced in size without affecting the quality of the printed result. Most commonly used images, including digital photographs (jpeg being the most common file format), are raster images, which means that they are made up of a finite number of dots or pixels. The quality of this type of image when it is printed varies depending on the size it is printed out at.

 

For example, you might have a picture file which is 600 pixels by 300 pixels in size - and this will not change, no matter how much you enlarge or reduce the size of the picture on the page. So if you make the picture 2 inches wide by 1 inch high, its resolution will be 300 dots per inch (dpi). As a rule of thumb, this is the maximum size you can make this particular picture without starting to compromise its quality when it is printed. If you enlarge the picture to 4 inches wide by 2 inches high, its resolution will drop to 150dpi, because you’ve got the same number of pixels spread over a greater area.

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PDF (Portable Document Format)

PDF is now the industry standard method for submitting artwork for printing, because it generates smaller files and, when used correctly, it ensures that all graphics and fonts are properly embedded so that they will print correctly no matter what computer you print them from.