Abstract: An electrostatic charge pattern is developed into a visual image with the aid of a current-sensitive recording element that is disposed against one face of an array of a plurality of field-effect devices. The charge pattern, on an electrically insulating film, is disposed against an opposite face of the array. An electrical circuit, connected to source and drain regions of the field-effect devices, causes current to flow in each of the devices in accordance with the intensity of each elemental portion of the charge pattern adjacent a respective channel region in each of the devices. The electrical current causes a color change in the recording element in accordance with the intensity of the current flowing therethrough.

Abstract: An original electrostatic charge pattern on an electrically insulating image-bearing surface is reproduced, on an electrically insulating film, in an intensified form by the steps of:A. placing one surface of the film in contact with the original charge pattern on the image-bearing surface,B. wiping, with a grounded wetted sponge, the other surface of the film to induce thereon a monopolar charge pattern of opposite polarity to that of the original charge pattern,C. separating the film from the image-bearing surface and wiping, with a grounded wetted sponge, said one surface, whereby to induce a bipolar charge pattern on the film,D. disposing said one surface of the film in contact with the image-bearing surface so that the electrostatic charge patterns of the same polarities contact each other and are in register with each other,E. wiping, with a grounded wetted sponge, said other surface of the film to induce thereon a monopolar electrostatic charge pattern superimposed on the bipolar charge pattern, andF.