What are megapixels?

What does it mean when you buy an 8 megapixels camera? The lens of a digital camera focuses the image onto electronic sensors. The sensor points are called pixels, and the more that you have, the better the quality of the picture. Have you noticed when poor quality pictures are enlarged the picture becomes 'pixelated'? You can see the individual blocks of the image formed by each pixel.

Mega means million, so if you buy an 8 megapixels camera it has 8 million electronic sensors. It sounds fantastic until you do some maths. To print a good quality image you need 300 pixels per inch. If you take a 10"x 8" photo it needs 300 x 8 pixels for the width, and 300 x 10 pixels for the length. The total number of pixels in this photo is (300 x 8) x (300 x 10) = 7,200,000 i.e. 7.2 megapixels. That marvellous 8 megapixel camera that you bought will only give you 10" x 8" prints!

This is not quite true. I have an 8 megapixels camera that give me very nice A1 sized photos. Why is there such a difference? Partly it is because you will get away with less than 300ppi, partly it depends on the quality of the camera, in particular the quality of the lens, and it also depends on the quality of your printing equipment.

The next time that you see one of those really large photos on a wall then have a look for the pixelation or if it is a film photo have a look for the grain.

Happy snapping