Decompression: Process of returning a compressed file to its full bitmap.

Depth Of Field: Means of describing the area of a photograph that is in focus. A photograph that shows the area close to the camera and things far away all in good focus is said to have a large depth of field. A narrow depth of field is when only a thin section of the scene, say from ten to twelve feet away from the lens, is in focus. 

With a film camera, setting a large aperture (wide open iris) gives narrow depth of field, and a small aperture (closed down iris) gives a wide depth of field. Few cameras in the price range below $1500 can control depth of field from user input. A change in aperture means that the camera should also change the shutter speed to maintain correct exposure

Digital Zoom: Uses digital technology to enlarge an image. Digital zoom does not have moving parts. It is the electronic enlarging of the middle of an image. The pixels at the center portion of the CCD are digitally doubled to make the image appear larger on the display.

Existing data is interpolated to create new data. Resolution is reduced as the center pixels are enlarged to fill the display. Image files are HALF size (smaller) and require less space. 

In some digital cameras the manufacturer makes the choice to not include an optical zoom lens. This makes the camera quite a bit smaller as can be seen with some of the pocket-sized digitals on the market. Some of those pocket cameras offer digital zoom. The camera takes a portion of the image and magnifies it digitally. Unfortunately, these images get fuzzy in a hurry because a smaller amount of information is being used to create a larger image because the camera has to create the missing information.

DPI: Printing term that describes the number of dots per inch that are used to create an image. (The image can be a font or graphic).