Digital color halftoning with generalized error diffusion vector green-noise masks

Summary

Color printing works by overlaying tiny dots of cyan, magenta, yellow, and black ink. Look closely at a magazine cover and you can see the rosette pattern those four screens make. The catch is that each color is running its own halftone independently — and when the screens collide on the page they can interfere in messy, unpredictable ways, including the wavy “moiré” patterns sometimes seen in reproductions.

The simplest fix is to make each color a random scatter, which avoids moiré but ends up muddy because dots have lots of perimeter and ink spreads at every edge. The classic alternative — fixed-grid screens rotated to different angles — controls ink spread but still lets the screens collide in patterned ways. Neither approach gives the operator any control over the variable that matters most in color printing: where one color’s dots overlap with another’s.

This patent extends green-noise halftoning from one color to four, treating the print as a vector across all channels instead of a set of independent screens. A new construction algorithm directly controls not only where each color’s dots cluster, but how those clusters overlap or avoid each other across the inks. The operator can dial up overlap for richer secondaries, dial it down for cleaner separations, or decorrelate the channels entirely. The result is finer control over color reproduction across the wide range of printer hardware in the field — from dye-sublimation and inkjet to commercial offset.