Measurement of Dot Area and Sharpness.

A measurement of percent dot area of a halftone negative is important in the study of tone reproduction in the printing process. Previous methods have been laborious or inaccurate. The measured area of a dot depends upon what part of the dot is selected as the dot boundary. When a printing plate is made from a halftone negative, the dot boundary is a fixed density such that all parts of the dot above this density do not print and all parts of the dot below this density do print. This density is equal to that of the first step of the sensitivity guide which prints on the press sheet. An instrument has been constructed which scans many dots and measures the average percent dot area at a given density. Measurement of dot area at several densities may be used as an indication of dot sharpness. The area of a dot examined visually may be different from its printing density. A boundary definition corresponding to the visual boundary of a dot may be established and visual dot area measured directly.