The Theory of Screenless Lithography in Relation to Plate Grain Structure

MS received initially 6 August 1977 and in revised form 8 March 1978.

Abstract

The function of the grain structure of a lithographic plate is examined in relation to the production of an image by a continuous-tone film. A theory is presented describing the mechanism of the partial distribution of light-hardened coating material on a grain surface, and is developed to provide a graphical method of constructing an ideal grain profile for facsimile reproduction. Negative and positive processes are considered, and theory shows that the ideal grain structure for facsimile reproduction is composed of a uniform distribution of precisely defined geometric units. Attention is drawn to two important conclusions of commercial significance, viz. whilst a uniform grain structure serves with advantage to increase the tonal range available for reproduction, this same factor introduces a possible disadvantage if moiré effects must be considered.

Notes

MS received initially 6 August 1977 and in revised form 8 March 1978.