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The CCD is what a digital camera uses instead of film. It is basically a grid composed of microscopic light-sensitive cells – more than a million in an area no bigger than your thumbnail. When light reaches the CCD, each sensor or “pixel” produces an electrical signal proportional to the intensity of light it receives. From this grid of pixels, an image is built up. It follows that the more pixels that can be crammed onto the CCD chip, the finer the detail will be. A great challenge to manufacturers is trying to produce CCDs with enough pixels to match the quality of film. The average film negative has tens of millions of silver grains, while the most advanced digital camera has but a few million and cost thousands of dollars.

While the quality of digital images is not yet equal to film, there are limits to how much the eye can actually see, especially at the relatively small sizes at which pictures are viewed. This goes back to the “overload theory” – you don’t need a 14 mega-pixel camera for 5x7 print but you might need one for life size prints. The quality difference, therefore, is less marked than it may first appear.

The size of the CCD chips used in digital cameras is reflected in the price. At the bottom end of the spectrum are VGA models (which contain roughly 240,000 pixels) while cameras with CCDs holding more than a million pixels are called mega-pixel cameras. Professional cameras are typically 35 mm SLR cameras with CCDs built into them.