HE more megapixels the merrier - or so you'd gather from digital camera prices. The higher the number of megapixels, the more expensive the camera will be in comparison with others with similar features. But what are megapixels? How many do you need? Is more always better?

Pixels (known as megapixels when you count them by the million) are picture elements, the tiny spots of data that make up a digital image. All photos are made up of tiny elements: from the ink dots in newspaper photos to the grains of silver or particles of color dye in film photography. A good photo usually has millions of these elements. The more there are, the sharper and more detailed the picture is, and the harder it is to distinguish the elements from one another.

A digital camera's effective pixel count is its horizontal resolution multiplied by its vertical resolution. An image 2,048 pixels across and 1,536 high has just over 3.1 megapixels; a 2,560 x 1,920 image is just over 4.9 megapixels.

Digital cameras made for amateurs usually have between two and five megapixels, though cameras with eight megapixels or more will be available soon.

Those numbers are no match for 35-millimeter film, which has a resolution equivalent to 20 or 30 megapixels, but digital cameras can nonetheless produce excellent images.

How many megapixels you will need depends on how you plan to use your pictures. For e-mail, an image size of 640 by 480 pixels (0.3 megapixel) is usually best: large enough to look sharp on a computer screen but small enough to upload or download quickly. For prints, more resolution is required, and the bigger the print, the greater the difference the pixel count makes.

For prints measuring up to 8 by 10 inches, the difference between shots with two megapixels and five megapixels can be hard to discern. This was not always true, but current digital cameras do a better job of processing the raw data from their image sensors into image files on their memory cards. ("Most people will never, ever need something above three megapixels," said Jon Sienkiewicz, the vice president for marketing at Minolta. "I'll make 8-by-10's all day long from that.")

Cropping and Zooming

In prints larger than 8 by 10 inches, differences in pixel counts become more noticeable. Few amateurs make prints that big, but another reason to go for a higher pixel count is the ability to crop. Pictures that looked good when you shot them may contain distracting elements; cropping allows you to prune those elements away and make the picture stronger. Crop out 40 percent of your picture, though, and you lose 40 percent of its pixels. That might be a worthwhile tradeoff if it reduces a five-megapixel image to three megapixels, but not so if the image goes from two megapixels to a paltry 1.2.

It is also possible to crop within the camera, zeroing in on an important subject area so that it fills as much of the frame as you want. A zoom lens does this by narrowing its view to exclude some subject areas while magnifying whatever is left within the frame. The picture area contains just as many pixels as before, but with more of them now devoted to the subject area you want, its details are clearer. Don't confuse this process, optical zoom, with so-called digital zoom, a purely electronic process that selects a small subject area by throwing away the surrounding pixels: the pixel count of the area you select with digital zoom is the same as before, so you don't gain anything but a tighter composition, and the picture may look fuzzier. It's like cropping your picture in your computer, only with less time to select your composition and no chance to change your cropping if you don't like the result.

"It's not as valuable for cameras that have zoom lenses as it is for entry-level cameras that don't," said Chuck Westfall, director of technical information for camera products at Canon, referring to digital zoom. Entry-level cameras are also, alas, likely to have lower pixel counts to start with. On the other hand, such cameras are mainly used for snapshots, "and for snapshot-sized photos, sometimes digital zoom isn't too bad," said Sally Smith Clemens, a product manager at Olympus.

Get home delivery of The Times from $2.90/week

Continued 1 | 2 | Next>>