Frame your choice with megapixels

The Fuji FinePix S3 Pro, priced at $2,096, boasts a whopping 12.3- megapixel rating.

Megapixels are like the clock speed on a computer. They are the first and easiest point of comparison and, generally speaking, you can never have too much clock speed or too many pixels.

The price-per-pixel for digital cameras has dropped dramatically. You can now get a 4-megapixel, pocket-size camera such as the Olympus D-580 or the Fuji FinePix A340 for around $300. Eight-megapixel cameras, including the Nikon CoolPix 8700 or the Sony DSC F828, cost $1,000.

More pixels means higher resolution, though it may be debatable whether you really need it all. If you are taking pictures for a Web site or for viewing on a computer at the usual 72 pixels per inch, a 2.1-megapixel image'1,600 by 1,200 resolution'is large enough to fill a 27-inch diagonal monitor, far larger than you'll find sitting around the office.

For printed images at 300 dpi, however, it's a different matter. You need 2.3 megapixels to make a 4- by 6-inch inch print, 4 megapixels for a 5-by-8, and 8 megapixels for an 8-by-10 at full resolution. While you can blow up a low-resolution digital image to a larger size, picture quality suffers. Using a higher-resolution image also allows you to zoom in on only a part of the picture and use that section at full resolution.

While shooting at the camera's highest resolution provides the best quality, it does have two drawbacks. Large files take longer to store, slowing down your picture-taking. And they eat up a lot of storage.

For example, the 6.1-megapixel Canon EOS Digital Rebel needs about 7M of storage for a single, full-sized picture in its native (RAW) format. If you are using a 64M Compact Flash card, that only lets you take nine photos before you run out of storage. Buying a 4G CF card would let you store over 500 photos, but it also costs as much as the camera itself.

To solve the storage problem, most cameras let users select both the resolution and the data compression level. The Konica Minolta Dimage XT, for example, has four resolution settings and four compression settings. Storing a full 3.2-megapixel image at the super fine level would take up an entire 16M Secure Digital memory card, but using one of the compression modes allows for storage of 9, 17 or 32 pictures on the same card.

While using compression lets you store more photos, it also lowers the quality of the color and could produce unwanted artifacts in the image. A better solution is to buy more storage, but you need to include this cost in the camera budget.

It isn't cheap, but it does no good to spend more for a high-resolution camera if you don't have enough storage. SD cards now go up to 1G, CF Cards up to 4G, xD Picture Disks to 512M, Multimedia cards to 512M and Memory Sticks to 3G.

'If you just want to snap a photo now and then, you don't need a high-resolution camera,' said Ted Schadler, vice president and principal analyst for Forrester Inc. of Cambridge, Mass. 'But if you take a lot of pictures and want to print them out in 8-by-10 format, you need a 5-megapixel camera.'


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