Printing Resolution

Digital pictures like ours consist of pixels or dots (we use the words "pixels" and "dots" interchangeably). Our Model Art Landscapes, for example, are 3600 pixels wide by 2400 pixels high, giving a total number of dots of 3600 x 2400 = 8,640,000 dots, or 8.6 megapixels in digital-camera-speak.

A digital picture can be printed at various sizes by simply varying the spacing between the dots. The number of dots in a unit of length is called the resolution. This is normally expressed as dots per centimeter (dpc) or dots per inch (dpi). To print your picture at the size you want, find the required printing resolution by dividing the number of pixels (width or height) by the width or height you want, and then enter this value where your printing software requests it.


	High Resolution	Low Resolution
	Closely-spaced dots	Widely-spaced dots
	Lots of dots per cm/inch	Not so many dots per cm/inch
	e.g. 120 dpc/300 dpi	e.g. 40 dpc/100 dpi



	Small, sharp picture	Large, fuzzy picture

For example, let's say you first want to make a print of a 3600 x 2400 pixel image that will fit on a postcard, say a picture size of 12 cm x 8 cm. Dividing 3600 pixels by 12 cm (or dividing 2400 pixels by 8 cm) gives a resolution of 300 dots per centimetre. Dividing 3600 pixels by 5 inches gives a resolution of 720 dots per inch.

Most photo and picture software gives you the option of working in either US or metric units. If your software does not, it's useful to remember that to convert dpi to dpc, divide by 2.54, and to convert dpc to dpi, multiply by 2.54.

Now let's say you want to make a big print of your 3600 x 2400 dot picture for your office wall, say 45 cm x 30 cm. Printing resolution will be 3600/45 or 2400/30 = 80 dots per centimeter or 80 x 2.54 = 203 dots per inch.

Don't worry, this arithmetic is as bad as it gets. Master this and you will know all you need to be a digital picture guru!

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