Measuring the 'heart' of a digital camera

With digital cameras, the most expensive feature is the image sensor. This is the heart of the machine. It records light, like film in regular cameras. Image sensors come in two types: low-cost CMOS (complementary metal-oxide silicon) and more popular and expensive CCD (charge-coupled device).

But what matters most: the image sensor's capacity, which determines a picture's sharpness.

The minimum is 640 (dots wide) by 480 (dots tall), or 307,200 pixels. That's enough for posting photos on the Web and printing 3x5 snapshots. Anything bigger will look grainy.

By comparison, professional digital cameras have 3,040 x 2,016, or 6,128,640 pixels (6.1 megapixels). They also cost several thousand dollars. The higher the resolution, the sharper the pictures, and the higher the price.

Most popular consumer digital cameras range from 1.2 megapixels to 3 megapixels. The lower end of that range will produce excellent 5x7 prints and good 8x10s. The upper range will print high-quality 8x10s -about what most consumers expect.

Even some of the cheapest $100 cameras on the market today advertise 1.2 megapixel resolution, but use software, not actual pixels to reach that. So their images aren't quite as sharp.

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