Spectral contrast control in xerography

Claim 1

IN THE METHOD OF CONTRAST CONTROL IN MAKING A REPRODUCTION FROM AN ORIGINAL WHEREIN A PHOTOSENSITIVE MEMBER IS EXPOSED TO A PATTERN OF LIGHT AND SHADOW CONFORMING TO THE ORIGINAL THE COLOR OF WHICH PATTERN IS SELECTED IN ACCORDANCE WITH THE DESIRED CONTRAST AND WHEREIN THE PHOTOSENSITIVE MEMBER COMPRISES AN ELECTROSTATICALLY CHARGED VITREOUS SELENIUM LAYER (A) THE IMPROVED METHOD OF EXTENDING THE TONAL ACCEPTANCE RANGE AT LEAST 50% IN A POSITIVE TO POSITIVE REPRODUCTION SYSTEM WHICH METHOD COMPRISES (B) UTILIZING A PHOTOSENSITIVE LAYER CHARACTERIZED UNIFORMLY ON ITS SURFACE BY A PHOTOCONDUCTIVE RESPONSE IN THE BLUE PORTION OF THE SPECTRUM EXTENDING TO ABOUT 5,600 ANGSTROMS AND A DISTINCT AND SEPARATE RED PHOTOCONDUCTIVE RESPONSE CENTERED AT ABOUT 7,000 ANGSTROMS AND (C) EXPOSING THE PHOTOCONDUCTIVE MEMBER TO A PATTERN OF LIGHT AND SHADOW CONFORMING TO THE ORIGINAL CONTAINING AT LEAST RED LIGHT AT LEAST SOME BLUE LIGHT IN A SUBSTANTIALLY LESSER AMOUNT THAN SAID RED LIGHT, SAID BLUE LIGHT BEING JUST SUFFICIENT RELATIVE TO THE AMOUNT OF RED LIGHT TO PERMIT SUBSTANTIALLY COMPLETE CHARGE DISSIPATION ON THE PHOTOSENSIVE MEMBER.