In this paper, we present a new algorithm for aperiodic clustered-dot halftoning based on direct binary search (DBS). The DBS optimization framework has been modified for designing clustered-dot texture, by using filters with different sizes in the initialization and update steps of the algorithm. Following an intuitive explanation of how the clustered-dot texture results from this modified framework, we derive a closed-form cost metric which, when minimized, equivalently generates stochastic clustered-dot texture. An analysis of the cost metric and its influence on the texture quality is presented, which is followed by a modification to the cost metric to reduce computational cost and to make it more suitable for screen design.

Most electrophotographic printers use periodic, clustered-dot screening for rendering smooth and stable prints. However, when used for color printing, this approach suffers from the problem of periodic moire resulting from interference between the periodic halftones of individual color planes. There has been proposed an approach, called CLU-DBS for stochastic, clustered-dot halftoning and screen design based on direct binary search. We propose a methodology to embed a printer model within this halftoning algorithm to account for dot-gain and dot-loss effects. Without accounting for these effects, the printed image will not have the appearance predicted by the halftoning algorithm. We incorporate a measurement-based stochastic model for dot interactions of an electro-photographic printer within the iterative CLU-DBS binary halftoning algorithm. The stochastic model developed is based on microscopic absorptance and variance measurements. The experimental results show that electrophotography-model based stochastic clustered dot halftoning improves the homogeneity and reduces the graininess of printed halftone images.

Periodic clustered-dot screens are widely used for electrophotographic printers due to their homogeneous halftone texture and their robustness to dot gain. However, when applied to color printing, there are two important phenomena that limit the quality of printed color halftones generated using a screening technology: (1) moire´ due to the superposition halftone patterns corresponding to different periodicity matrices, and (2) appearance changes due to misregistration between different colorant planes. This paper focuses on analyzing the registration sensitivity of periodic, clustered-dot screens. To quantitatively measure the effect of registration errors, we introduce two new functions: (1) cost, and (2) risk of registration errors. We propose the notion of “visual equivalence”, and derive three propositions under which visual equivalence can be achieved, even when registration errors occur.