Picture color tone controlling method and apparatus

Abstract

In a picture color tone control method and apparatus for a printing press, in order to make it possible to use an IRGB densitometer to perform color tone control even when printing is performed with a density which exceeds an estimated maximum color space, a target color mixture halftone density for each ink supplying unit width when a printing picture is divided with an ink supplying unit width of ink supplying apparatusis set, and an actual color mixture halftone density for each ink supplying unit width of an actually printed sheet obtained by printing is measured using an IRGB densitometer. The color mixture halftone densities are individually converted into tone values. Thereupon, for the conversion into actual tone values, the publicly known Neugebauer expression wherein the Yule-Nielsen coefficient n is set to such a value that the tone values and the color mixture halftone density value have a substantially linear relationship to each other is used. Further, the tone values are converted into a monochromatic halftone density, and a solid density difference corresponding to the difference between the target monochromatic halftone density and an actual monochromatic halftone density is determined using the Yule-Nielsen expression or the like. Then, the ink supplying amount is adjusted for each ink supplying unit width in response to the solid density difference.