3: Principles 4: Materials and Process Images Printing To Do

Image Resolution

Pixels and vector graphics
There are two distinct ways in which your computer stores visual information digitally: you can
have either pixel images or vector graphics. If you take a magnifying glass to any computer
screen you will see that it is made up of tiny squares or dots. These are the smallest single
components of a digital image and are called pixels.
Pixels are arranged in a two-dimensional grid with each square containing a solid colour. Pixels
are good at describing colours, tones and complex visual information such as photographs.
If you scanned a conventional 35mm colour photograph into the computer it would convert
the continuous tones of the photograph into a staggered series of whole colours within the
pixel grid to give the impression of a continuous tone. Photo manipulation software generally
concerns itself with pixel-based information. Pixels are not as good at describing lines or
geometric shapes and can give typography a poor quality appearance.
Vector graphics works in a completely different way and is not generally suitable for dealing
with photographs; it tends to be used to deal with typography, logos and graphics that use
geometric shapes and lines. Vector graphics uses mathematical equations to plot a shape. This
means that these graphics can be scaled up to any size without losing quality, something that
pixel images cannot do. Vectors can be manipulated by using small points on the line that can
be moved or, in the case of a curved line, have their angles changed.
Software such as Illustrator or Freehand mainly uses vector graphics, though it is possible to
work with both pixel and vector formats in Illustrator and Photoshop.
Book Design 1 55
Resolution refers to the amount of visual information contained in a file. Resolution is important
because you need to have good quality images if your work is to be printed.
Resolution is measured in dots per inch (dpi) or lines per inch (lpi). If you are scanning images
into your computer to use in paper-based design work then they need to be 300dpi.
If you’re downloading from a camera, keep your files as big as possible until you re-size for print.
Always keep the original version.
If you’re working on the internet then images are scanned at 72dpi. It is worth remembering
that once you get rid of resolution, for example downscaling an image from 300 to 72dpi, you
can’t then go back and replace it. This is why it’s important to save the original version.
If you’re having serious problems working with any of your software, contact your tutor. He or
she should be able to suggest a way forward. You might also find it helpful to talk to fellow
students via the OCA website. If you’re having problems, the likelihood is that someone else is