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How tightly can you crop your digital photos and still get great results when you enlarge them?

We spoke with staff photographer John B. Carnett to get to the bottom of this not-so-simple question. Carnett says that it really depends on what you plan to do with the image. Great results for one person might be a grainy image, but one blown up large enough to cover a gaping hole in a bedroom wall. Others demand images that look just like the real thing.

As a general rule, he says, digital photos taken for the Web, or to be viewed on a computer monitor, can be lower in resolution (measured in dots per inch, or dpi). Going higher than 72 dpi is unnecessary, since the typical screen can’t display anything much crisper.

It also depends on your camera. When you enlarge a digital photo taken by a higher-end camera, you seek out that extra information that typically gets compressed; the extra pixels that don’t show up on the computer screen; the close-up details. If your image is low resolution, sometimes that information simply doesn’t exist, and your computer and/or printer has to synthesize it–this is what leads to grainy or pixelated images.

Another factor is the storage file type. Higher-end cameras offer the option of saving your images as RAW files, which retain lots of information and, consequently, eat up more space on your camera or memory card. RAW files are good for print-quality images, since you want to retain as much pixel information as possible; Carnett says that the minimum in this case is about 150 dpi. Other file types save less information but also take up less memory. Settling for 72 dpi, for example, allows you to hold on to more pictures.

If you have professional tastes but lack the budget for a higher-end camera, you may want to consider software such as Genuine Fractal, which claims to enable enlargements of up to 600% without a loss of image quality. While the program won’t enhance the quality of your image, it may allow you to enlarge it and still maintain the same resolution by using fractal technology to generate pixels. You can download a free trial version of the software at www.lizardtech.com.

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