Dielectric receptor sheets which are transported seriatim from a tray into the gas-filled interelectrode gap of an ionography imaging chamber are arrested ahead of the chamber, and a corona generating device is moved along each arrested sheet to apply a uniform electrostatic charge to or to neutralize the electrostatic charge of the arrested sheet. Each arrested sheet whose charge is influenced by the corona generating device is attracted by suction to the concave side of an arcuate guide. The corona generating device is mounted on a carrier which is pivotable about an axis including the center of curvature of the concave side of the guide. The carrier further supports a pivotable retainer which moves the central portions of the leaders of successive sheets against the concave side of the guide if the leaders exhibit the tendency to bend or bulge away from the concave side. The marginal portions of sheets which are advanced along the guide extend into arcuate channels which flank the concave side. The treatment by the corona generating device can serve to destroy non-uniform positive or negative charges or to apply uniform background potential.