Algebraic masks for color halftoning

Abstract

Linear Pixel Shuffling (LPS) dithering produces blue-noise-like patterns, but the placement of thresholds in a dither matrix is a result of an exact algebra, rather than iterative procedure -- as is usually the case. In this paper, we investigate the potential use of LPS for construction of color (CMYK) dithering masks. In case of LPS dithering, the addition of the same value to each mask threshold, using modular arithmetic, is equivalent to the spatial mask shift. We propose a set of three shifted color masks for C, M, and Y that we construct from the original LPS mask using modular arithmetic. The main advantage of this approach is its simplicity. These shifts can be "tailored" to the statistical properties of the image and the set of new screens can be calculated on the fly. The proposed method enables creation of screens of arbitrary size, since the dithering masks are tiled automatically (actually, the masks are of unlimited size). The number of gray levels in each screen is limited by the choice of a modulus number used for mask thresholds calculation. This enables us to use a virtually unlimited number of thresholds that are not necessarily linearly related to the LPS calculated matrix values. Thus, it is relatively easy to construct a non-linear dither screen that will compensate for any printer non-linearity.