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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,
and then enter this value where your printing software requests it.
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 centimetre or 80 x 2.54 = 203 dots per inch.
The minimum resolution for a clear (non-fuzzy) print is around 60 dpc/150 dpi. However, printers these days are so
good you may be able to go even lower for an even larger printed picture. The only way to find out is to do some trial prints.
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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