Color bitmap merging of black objects using partially correlated

Abstract

A bitmap-based digital color printing method and system is described which automatically detects when a black object is to be printed and changes the Bit Block Transfer (BitBlt) method so that the black color becomes a mixture of black plus the background colorants, limited both by a clipping of one colorant against another and by an allowed maximum value for each remaining non-black separation. More specifically, the process reads the existing background color bits, does a first clip of one separation against another assuming that for correcting certain printing defects some separations are more important than others, and then does a second clip of remaining non-black separations to a pre-set maximum allowable amount. The result is an efficient way to control total colorant while allowing some separations precedence over others; with the result that the amount of colorant in one separation is dependent on or partially correlated with the amount of colorant in another. This preferentially limits colorants in a black object. As an example, reducing the amount of a high luminance separation (eg, yellow) relieves toner pile height problems without creating significant trapping problems. Therefore, in order to preferentially reduce yellow, the cyan or magenta components may be used to clip the yellow component in a first clipping step. By doing so, the maximum allowed colorant in both the cyan and magenta separations can be increased, which for some printing systems creates fewer visual defects in color prints.