What are megapixels?

If you are about to buy a digital camera, (or a mobile phone with a camera, for that matter) one of the many details you will find in the camera specifications is ''mega pixels''. As with many such things, you may well conclude that the higher the number of mega pixels the better the camera is. And, largely, you would be right.

However, there are two questions we need to ask before we can decide which camera is most suited to your needs. The first question is: how many mega pixels do you really need? OK, there is another side question we need to ask before we can ask that one. What are mega pixels, anyway?

Let's start with a pixel. A pixel (short for 'picture element') is a single point in a graphic image. The more pixels used to represent an image, the better will the image look. In a broad sense, you may say that an image with more pixels per square inch has better 'resolution'. A mega pixel is a million pixels.

How does that translate into the resolution a digital camera gives? Mega pixels are not just so many million pixels; they also indicate the number of image sensor elements in digital cameras or the number of display elements of digital displays. A camera with an array of 2,048×1,536 sensor elements is said to have "3.1 mega pixels" (2048 × 1536 = 3,145,728).

So how many mega pixels should your camera really have? It depends entirely on what you want to do with the photographs. If you want a camera merely to share a rough likeness of something you have seen, a 1 mega pixel camera should be adequate. If you plan to use the camera to take photographs you can use on a website, you may need, say, 2 mega pixels. But if you aim to use the photographs for a well-printed brochure or magazine, you will need at least 5 mega pixels. For most ordinary purposes this is more than adequate. Remember that the more the megapixels, the more the camera is likely to cost.

Now we come to the second question. If one camera has 7 megapixels and another has 8, will the second one necessarily give a better quality of picture? The simple answer to this is: no, not necessarily.

The truth is that resolution also depends on the size of the camera's sensor. A camera with less megapixels than another may produce better quality pictures if the other camera has a smaller sensor. This is because a larger sensor, with larger pixels, is able to record more information about the scene being captured, resulting in more realistic and detailed pictures.

Also there are other factors that affect the quality of the picture, such as the quality of the lens used. So while the number of megapixels in the camera does make a big difference to the quality of the images it produces, you do look at other factors to ensure great quality pictures.