Quality and file sizes

Digital images are measured by width and height in pixels. The resolution of an image is measured by how many pixels (or dots) there are to an inch. For images being used for the web, since most computer monitors display 72 pixels to an inch, the resolution of these images also needs to be 72 dots per inch (DPI). Litho printing reveals far more detail than a computer monitor and so a resolution of at least 300 DPI is needed for photographic images.

This means that file sizes for images that you intend to use for print will need to be very much larger than those for the web. The larger the end result in terms of width and height the bigger the file will need to be. For example, an image for an A3 poster should be a minimum 60mb in size, for even larger items, such as banners, photographers will take images as large as their camera allows. Similarly, in print, glossy, high quality colour magazines will ask for higher resolution images than newspapers. Picture editors may also ask for a bigger image if they intend to use the picture on their front page than they would if they planned a lower profile picture inside.

The Publications Office can offer more detailed advice depending on the actual end product you are working towards.