How Digital Photography Works

(^58) PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES
How Digital Zoom Fakes It
A digital zoom begins by concentrating
on just the center portion of the image
frame: the same portion that would have
filled the viewfinder and the entire image
using an optical zoom.
Software built in to a chip inside
the camera expands the pixels
that are in the area being zoomed
so that the pixels fill the frame
evenly. This leaves pixel areas that
are blank surrounding pixels that
contain fragments of the image.
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Most digital cameras give you both optical zoom and digital zoom. Optical zoom, as you saw in the previous illustration, uses the laws
of optics to bend light so that a single lens takes on both the long-distance qualities of a telephoto lens and the expansive vision of a
wide-angle lens. Digital zoom uses the blather of the marketing department to sell folks on the idea that they are getting more if their
new camera has a 10X digital zoom. They aren’t. In fact, a digital zoom only gives you educated guesses about what a picture would
look like if it had been shot with a telephoto lens. Some guesses are pretty good, but they’re never as good as those from a true, optical
zoom. All digital zooms can be created with
more control and finesse after you transfer your
shots to your computer. Here’s how image edit-
ing software, either on-the-fly in your camera or
on your PC, makes something out of nothing.