Essentially, a photographic image that is not composed of halftone dots or, in other words, an image that consists of tone values ranging from some minimum density (such as white) to a maximum density (such as black). An example of a continuous tone image is a photograph or a color transparency.
The term continuous tone also refers to a digital image (such as one that has been scanned or generated on the computer) prior to its being screened into halftone dots. Continuous tone also refers to the bit map file of a scanned image.
Continuous tone is often abbreviated CT or referred to as contone.