Electrostatic gray-scale facsimile recording

Gray-scale facsimile recording is achieved by using a special electrode arrangement together with the common electrostatic printing technique. The original optical density of a document is reconstructed on an electrostatic recording medium by varying size and charge density of small charged dots. Thus, the developed charged dots allow a continuous gray scale with optical densities in the limits of 0.05 and 1.6 according to the developing procedure. The resolution of this recording technique may be increased up to 10 dots/mm depending on the geometry of the printing device and the scan mode. A recording speed of several pictures per second of size A4 is possible.