Most electrophotographic printers use periodic, clustered-dot screening for rendering smooth and stable prints.
However, periodic, clustered-dot screening suffers from the problem of periodic moir´e resulting from interference
between the component periodic screens superposed for color printing. There has been proposed an approach,
called CLU-DBS for stochastic, clustered-dot halftoning and screen design based on direct binary search. This
method deviates from conventional DBS in its use of different filters in different phases of the algorithm. In this
paper, we derive a closed-form expression for the cost metric which is minimized in CLU-DBS. The closed-form
expression provides us with a clearer insight on the relationship between input parameters and processes, and
the output texture, thus enabling us generate better quality texture. One of the limitations of the CLU-DBS
algorithm proposed earlier is the inversion in the distribution of clusters and voids in the final halftone with
respect to the initial halftone. In this paper, we also present a technique for avoiding the inversion by negating
the sign of one of the error terms in the newly derived cost metric, which is responsible for clustering. This
not only simplifies the CLU-DBS screen design process, but also significantly reduces the number of iterations
required for optimization.
Printers employing electrophotographic technology typically use clustered-dot screening to avoid potential artifacts
caused by unstable dot rendering. Periodic clustered-dot screens are quite smooth, but also suffer from
periodic moir´e artifacts due to interference with other color channels. Stochastic, clustered-dot screens provide
an alternative solution. In this paper, we introduce a new approach for stochastic, clustered-dot screen design
based on Direct Binary Search (DBS). The method differs from the conventional DBS in its use of a modified cost
metric which was derived in an earlier work from using different filters in the initialization and update phases
of DBS. The objective of the chosen approach is to design screen for improved print smoothness by generating
a homogeneous distribution of compact, uniformly-sized clusters. The results include halftone of a screened
folded-ramp, compared against a screen designed with a previous method.
Most halftoning algorithms assume there is no interaction between neighboring dots or if there is, it is additive.
Without accounting for dot-gain effect, the printed image will not have the appearance predicted by the halftoning
algorithm. Thus, there is need to embed a printer model in the halftoning algorithm which can predict such
deviations and develop a halftone accordingly.
The direct binary search (DBS) algorithm employs a search heuristic to minimize the mean squared perceptually
filtered error between the halftone and continuous-tone original images. We incorporate a measurementbased
stochastic model for dot interactions of an electro-photographic printer within the iterative DBS binary
halftoning algorithm. The stochastic model developed is based on microscopic absorptance and variance measurements.
We present an efficient strategy to estimate the impact of 5×5 neighborhood pixels on the central
pixel absorptance. By including the impact of 5×5 neighborhood pixels, the average relative error between the
predicted tone and tone observed is reduced from around 21% to 4%. Also, the experimental results show that
electrophotography-model based halftoning reduces the mottle and banding artifacts.
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