Calculation of Multiple Halftone Exposure Times for Three Point Control.

This paper introduces a new method for calculating multiple halftone exposure times required to fit a desired halftone characteristic. Contrary to practice, where percent bump is often used to express the required amount of bump exposure, a 2Bump Factor1 is introduced which is useful to control the amount of main exposure as well as the amount of bump exposure. Since the amount of main exposure must be adjusted for each value of bump exposure, use of the Bump Factor simplifies exposure determination where a continuously variable amount of bump exposure is desired. A method for correcting for camera flare is presented and a new method for correction of reciprocity failure is introduced. The complete mathematics required for establishing the constants related to a given set of screening conditions and then for calculating the final exposure times required to fit three density points on the copy are presented.