The developed film was backlighted and the image was picked up by a television camera. A scanner then digitized the image by assigning to each point a number which corresponded to the intensity of the light passing through the film. Once the image is stored in the form of numbers the resolution can be improved by several possible enhancement processes. For example the light intensity can be re-scaled so that an intensity above or below a certain value is reduced to zero, which will emphasize specific features, like concealed materials of different densities. Another useful manipulation is the so called edge contrast operation. Here the numbers are processed so that only sudden changes are emphasized.