Photography Tech Tip : Megapixels

This is one in a series of 'Tech Tip' articles intended as a guide to digital camera technology and terminology. Its aim is to demystify some of the language used on this site to allow you to make more informed decisions when considering purchasing a new digital camera.

MEGAPIXELS
Megapixels is a reference to the number of picture elements (pixels) on the sensor within the camera, measured (roughly) in millions. E.g. a 2,000 x 1,500 pixel sensor has a total of 3 million pixels or 3 megapixels. Entry-level digital cameras now start around the 5-6 megapixel mark, with top-end resolutions of 12 megapixels available.

In early digital cameras (of less than 1 megapixel), even standard size 6x4-inch (15x10cm) prints appeared pixelated. This means that each individual pixel could be seen on the print. As you increase the number of pixels (keeping print size the same) the pixelation effect reduces, thus improving the apparent quality of the image, until the pixels eventually disappear entirely (in reality, the pixels are still there, they're just too small to be seen).

This was the drive behind the megapixel race that has made resolution synonymous with quality, but the truth is, beyond resolutions of around 3 megapixels, the quality of a standard 6x4 print doesn't improve with increases in resolution.

For larger-scale printing it is necessary to increase the resolution - as the print size increases, so does the reproduction size of each pixel. However, it is also true that larger images are often intended to be viewed from greater distances, so there isn't a linear relationship between print size and required resolution. As a guide:

• standard 6x4 inch (15x10cm) prints require 3 megapixels
• A4 (30x22cm) prints require 5 megapixels
• A3 (45x30cm) prints require 8 megapixels

The emphasis on megapixels during the last few years has confused people into thinking that it's the most important specification of a digital camera. If that were true, there would no longer be a necessity for professional photographers to carry those hefty digital SLRs with huge lenses on the front. Whilst the resolution of the sensor is one important factor, there are many others that determine the quality of the final image.

With entry-level digital cameras starting around the 5-6 megapixel mark today, this should only be a factor in your purchasing decision if you intend to make very large prints.