In the context of this book, image is the optical counterpart (pictorial representation) of an object produced by an optical device or an electronic device. An example of an image is a photograph, which is the likeliness of an object or scene recorded on photographic material. Another example is the picture produced on a computer screen or a television set.
The term “remote sensing image” is frequently used to either distinguish arbitrary images on an electronic display from those originating from a sensor or to denote raw data produced by an electronic sensor, which are in fact not pictorial but arrays of digital numbers; the digital numbers are related to a property of an object or scene, such as the amount of reflected light. Similarly also the term digital image is commonly used for an array of digital numbers, which can readily be converted to an image on a computer screen or by a printer. It is convenient to call the result of scanning a photograph or the data produced by a digital camera ‘digital images’.