Contributed by: C@tz
For many
members considering the purchase of a digital camera for
the first time, one question that keeps cropping up is
"
how many megapixels should my camera have?"
One way to answer the question is to work on the
basis of the finished print size. The number of pixels
required to print an image so that the print becomes
almost indistinguishable from a print made from film,
varies according to the size of the print. Indeed, past
a certain number of pixels (around 1.3 megapixels), the
quality of the image is not directly linked to the
number of pixels on the sensor; the image contains a
sufficient amount of information to create a clear and
sharp photo. Digital images can be printed in different
sizes, but to get the best quality image, printers need
a sufficient number of pixels every square inch, or
square centimetres, to produce a print that appears
smooth. In short, the number of dots placed on the paper
must be sufficiently high that the eye will not detect
jaggies, or other artefacts.
The vast majority
of digital images, in particular JPEG format images,
start life with a pixel per inch (PPI) count of 72. The
reason for this is that the image is destined for a
monitor and that 72 pixels per inch is the standard
definition of the latter. When this count of the image's
Pixel Per Inch is converted to the Dot Per Inch count of
a printer, the image's size changes accordingly as the
printer requires many more dots per square inch than the
monitor's 72 pixels per inch. Probably the easiest way
to visualize this is by looking through the chart below.
The chart assumes a printer DPI (Dot Per Inch) of 300,
which will usually yield a sharp image without any
obvious artefacts:
