Tone-dependent noise model for high-quality halftones

A digital halftone of blue noise characteristics is preferred as dots in the halftone of a constant input should be isotropically and homogeneously distributed. In practice, the placement of dots is constrained by a sampling grid and hence aliasing happens when the input gray level is in the middle range. To solve this problem, Lau et al. suggested replacing isolated dots by dot clusters to maintain the principal frequency of the output to be 1/2 when this happens. However, this model does not take into account that, due to the stochastic nature of the dot distribution, there is a considerable amount of energy distributed around the principal frequency and it causes aliasing problems even when the principal frequency of the output is 1/2. This paper presents a new noise model which takes this factor into account. A halftoning algorithm is then proposed to generate halftones that satisfy the new noise model. By comparing its performance with that of some other algorithms which are proposed based on the traditional blue noise model and Lau et al.’s noise model, one can see that the proposed noise model can be a better model to describe the noise characteristics of a high-quality halftone. † Corresponding author (Email: [email protected])