Interpolation and Sampling

The tools for resizing pictures that you'll find in various photo-editing programs are remarkably easy to use. But don't let their simplicity fool you. These are powerful commands that alter the very fabric of your pictures.

■ Sampling changes the number of pixels that define your photos.

■ Subsampling reduces the number of pixels. Therefore, if you have a photo that is 3MB in size, for example, and you want to email it, you might subsample it down (throwing away data) to about 350K.

■ Interpolation will enlarge an image file by analyzing the data that already exists and inventing new data. It's nothing more than guesswork on the part of the program and usually involves simply duplicating data. Although, you'll end up with a larger file, image quality is not only not improved, but can actually be diminished.

In other words, reducing the size of a photo file can be a worthwhile process, making sure a picture isn'ttoo big for applications such as emailing or Web site design. Increasing the size of a photo is generally not recommended. But when done correctly by a good interpolation program, it might take an expert to discern the difference that a small amount of interpolation makes.

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