Sometimes the smallest part of a digital camera becomes a buyer's greatest concern. Camera shoppers always talk of pixels, but the number of pixels -- measured, in 2011, in the millions -- doesn't make much of a difference in image quality. Similarly, the size of the pixels doesn't matter a huge amount, except in a very basic sense.
What is a Pixel?
Pixel is short for "picture element." All computer (or digital-based) displays are made up of pixels, which are square bits of image information. Each pixel contains color information that, when put together, creates a shade. When placed beside another pixel of a slightly different shade, and then placed besides other pixels with different shades, these pixels form an image. Usually, you only see images zoomed out, but if you were to use a computer program and zoom in as far as you could on any digital image, you would see squares of different colors.
Different Sizes of Pixels
Not every pixel is the same size. Think of the LCD screen on the back of your camera, which might have a resolution of 320-by-240 pixels but measure 3 inches across. Each of these pixels takes up quite a bit more space than the pixels on the camera sensor, which contains millions of pixels spread over a much smaller area. Similarly, different camera sensors are different sizes and therefore have different sizes of pixels. A digital single-lens reflex (DSLR) camera has a sensor about four times the size of a typical compact point-and-shoot, so if both cameras have the same number of pixels it follows that each pixel is physically larger on the DSLR.
Megapixels
A digital camera sensor holds so many pixels that manufacturers measure them by the millions. You can commonly find entry-level, compact point-and-shoot cameras with 10 megapixels, and some high-end DSLRs max out above 25 megapixels. The number of pixels only matters when comparing cameras with a similarly sized sensor -- two point-and-shoot cameras, for example.
Why Pixels Matter
The number of pixels compressed onto a tiny digital camera sensor is important when shooting in low-light or when blowing up prints. Unlike film cameras, which allow light to expose the film for a set amount of time (the ISO speed), digital cameras use electronic signals to create this same effect by magnifying light signals. If you set your digital camera to a high ISO and shoot in low light, the electronic pulse is magnified to create light where none exists, which creates digital noise. On smaller sensors with only a few million pixels (a 4 MP point-and-shoot, for example), this noise will be physically larger and evident to the naked eye. On a large sensor with several million pixels (a DSLR with 14 MP, for example) you may not notice the noise even in very low light.
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