Double-tone printer and method of making density correction curve for double-tone printing

摘要

A double-tone printer includes an image scanner which inputs an image signal representing an original. The image signal is converted into a density signal according to a density correction curve for a light color and a stencil master making signal for the light color is made by binary-coding the density signal. Further the image signal is converted into a density signal according to a density correction curve for a dark color and a stencil master making signal for the dark color is made by binary-coding the density signal components. Images of the respective stencil masters made on the basis of the stencil master making signals for the light color and the dark color are printed on a printing paper in light color ink and dark color ink so that the printed images in the respective color inks overlap each other. The density correction curve for the light color gives a print density which increases with increase in the value of the image signal in a first range where the value of the image signal is lower than a threshold value and is a fixed maximum print density in a second range where the value of the image signal is not lower than the threshold value, and the density correction curve for the dark color gives a print density which is a fixed minimum print density in the first range and increases with increase in the value of the image signal in the second range.