While making one of the first digital films at the USC School of Engineering Image Processing Laboratory in 1976, I saw an example of Xeroradiography, commercially known as Mammography. From 1977 to 1983, I used this technology at the Xerox Medical Research Center in Pasadena, producing hundreds of images while investigating the internal structure of the natural and man made world. The color of the images is blue because doctors preferred to look at that color.
First, I placed objects on a charged selenium plate. Then the plate was placed in an X-Ray box and I selected X-Ray intensity relative to the projected density of the object(s) being imaged. The X-Ray changed the charge on the plate. Then the plate was placed in a Xerox machine, dusted with charged toner and in about a minute a print would be produced.