Patent ID: 6014500
Filing Date: 2000-01-11
Classification: H04N

Abstract:
A printing system suitable for forming marks on a substrate at one of c possible levels of colorant, and receiving image signals represented at d possible levels, where d>c, and having a halftone processor to reduce the number of levels at which the image is represented from d levels to c levels in order to replicate gray level printing, including:a memory, storing a set of halftone threshold level signals, each threshold signal corresponding to a unique location in a halftone cell;a comparator, receiving said image signal and one of the halftone threshold signals from the memory, and producing an output signal at one of c possible levels, varying according to the comparison of said halftone threshold signal to said image signal to cause marking at a selected location on a substrate; wherein the comparator comprises:means for associating said set of halftone threshold level signals to a checkerboard pattern;means for dividing halftone threshold level signals into two subsets corresponding to the said checkerboard pattern: one subset includes all halftone threshold level signals spatially located at corresponding ""white cells"" of the checkerboard pattern; while another subset includes all halftone threshold level signals spatially located at corresponding ""black cells"" of the checkerboard pattern;said two subsets individually, as well as the combination of the two subsets of threshold level signals are calculated by an iterative optimization process which moves thresholds through a threshold screen cell matrix order until, for reproduction of an image in which one output level predominates over another level, the screen cell matrix thresholds are ordered to produce predominating output level marks approximately equally spaced throughout the screen cell matrix order.