In contrast to the traditional recording from high-altitude aircraft of Earth images directly onto film in their inherently continuous analog form, a Landsat Earth resources satellite samples the ground image brightness and records it on a digital, electronic medium. Although digitization incurs several extra steps in the reproduction of the imagery, it permits manipulation or enhancement of the data for special uses. For instance, image data enhancement techniques can be applied to partially restore contrast lost because of atmospheric luminance and scatter. More significantly, the digital-to-analog transfer function of the film recorder can be modified to simulate certain characteristics of other film types. Manipulation of a film's apparent gamma, relative speed, and linear-response region is easily accomplished by mapping the input data to a new distribution in real time using a hardware-implemented lookup table. To accomplish the desired photographic results, however, full cooperation and communication between photographic, electronic, and computer technologists is essential.
