Method for forming color images, using a hue-plus-gray color model and error diffusion

摘要

The invention is for use with a visible medium capable of light reflection etc., and for use with a color-image source that defines a desired color. Here a device for causing the medium to appear colored includes a gray-scale subsystem to achromatically suppress a stated fraction of the reflection; and at least two device-primary subsystems to cause selective reflection of light of two associated device-primary colors. Even if the device, as originally made, in effect uses the gray- scale subsystem to help construct colors, or the device-primary subsystems to help form gray-scale "values", such cross-dependency is essentially removed. A programmed processor resolves the desired- rendition information into Fraction-Black, Fraction-Colorant, and hue. Fraction-Black information is applied exclusively to control only the gray-scale subsystem; Fraction-Colorant to control only the device- primary subsystem; and hue to select a dominant and a subordinate primary subsystem and as between them apportion the Fraction-Colorant. These parameters are used not only in color selection but also in halftoning, where they enable colorant choice at each pixel in terms of input color rather than after resolution into pigment terms; this capability is used to prevent color artifacts such as pixels of pigment irrelevant to the desired color.