Digital images can be acquired from various devices. Image scanners on personal computers can generate digital images of hard copy material. New digital cameras operate without film, recording a digital image of the scene in local solid state memory. Remote sensing instruments routinely return digital imagery to receiving stations for processing and display. Digital processing of remotely sensed imagery is a technology that is now over thirty years old. Earth orbitting and deep space exploration spacecraft have been returning digital imagery for many years. Earth-based systems, including biomedical imaging devices and other commercially available types of equipment, have also been producing digital imagery for many years. Each of these devices produce a digital version of an image as a two dimensional array of numbers. The values in the matrix represent the brightness of the scene at each individual sampled position in the image.</p
