Periodic clustered-dot screens are widely used for electrophotographic printers due to their print stability. However,
moir´e is a ubiquitous problem that arises in color printing due to the beating together of the clustered-dot,
periodic halftone patterns that are used to represent different colorants. This beating or interference phenomenon
introduces spurious low frequency (large period) patterns in the printed output that are very objectionable to
the viewer. The traditional solution in the graphic arts and printing industry is to rotate identical square screens
to angles that are maximally separated from each other. For example, the classic three-color screen set rotates
three identical square screens to the angles 15°, 45°, and 75°, respectively. However, the effectiveness of this
approach is limited when printing with more than four colorants, i.e. N-color printing, where N >4. Moreover,
accurately achieving the angles that have maximum angular separation requires a very high resolution plate
writer, as is used in commercial offset printing.
In this paper, we propose a systematic way to design color screen sets for periodic, clustered-dot screens
that offers more explicit control of the moir´e properties of the resulting screens when used in color printing. We
find a general concept for moir´e-free screen design that is called lattice-based screen design. The basic concept
behind our approach is the creation of the screen set on a 2-dimensional lattice in the frequency domain and
then picking each fundamental frequency vector of the individual colorant planes in the created spectral lattice
according to the desired properties. The halftone geometry of a screen set is the set of angles and frequencies
in units of lines per inch (LPI) of each screen plane. The lattice-based screen design offers more flexibility in
designing N-color screen sets with different halftone geometries, and all of them are guaranteed to be all-orders
moir´e-free. For example, by creating a square lattice in the frequency domain, square N-color moir´e-free screen
sets that consist of N rotated square screens can be achieved. The proposed approach maintains the advantage
of square clustered-dot screen design and is based on low addressability of digital printing. We also propose
several symmetry measures, and use them to compare the proposed 4-color square screen set and the screen
sets based on a previous moir´e-free N-color non-orthogonal approach. The proposed screen set is shown to have
better symmetry properties.

The lattice-based screen set: a square N-color all-orders Moiré-free screen set

Periodic clustered-dot screens are widely used for electrophotographic printers due to their print stability. However, moire is a ubiquitous problem that arises in color printing due to the beating together of the clustered-dot, periodic halftone patterns that are used to represent different colorants. The traditional solution in the graphic arts and printing industry is to rotate identical square screens to angles that are maximally separated from each other. However, the effectiveness of this approach is limited when printing with more than four colorants, i.e., $N$ -color printing, where $N>4$ . Moreover, accurately achieving the angles that have maximum angular separation requires a very high-resolution plate writer, as is used in commercial offset printing. Commercially available high-end digital printers cannot achieve this resolution. In this paper, we propose a systematic way to design color screen sets for periodic, clustered-dot screens that offer more explicit control of the moire properties of the resulting screens when used in color printing. We develop a principled approach for the moire-free screen design that is called lattice-based screen design. The basic concept behind our approach is the creation of the screen set on a 2D lattice in the frequency domain, and then picking each fundamental frequency vector of the individual colorant planes in the created spectral lattice according to the desired properties. The lattice-based screen design offers more flexibility in designing ${N}$ -color screen sets with different halftone geometries, and all of them are guaranteed to be all-orders moire-free. We demonstrate the efficacy of our proposed method by introducing several new screen designs, and a comparison with published screen designs.

The Lattice-Based Screen Set: A Square $N$ -Color All-Orders Moiré-Free Screen Set

A display device includes an array of display pixels having display pixel apertures that are periodic along two orthogonal directions, x and y, at spatial frequencies f x and f y , respectively. An array of electrodes is overlaid on the array of display pixel apertures. The array of electrodes is comprised of a metal mesh having openings that are periodic along a first direction u at an angle θ u relative to x, and along a second direction v at an angle θ v relative to y, and at spatial frequencies f u and f v . The array of electrodes is overlaid on the array of display pixels such that the parameter set {θ u , f x , f u , θ v , f y , f v } satisfies specific geometric criteria in order to minimize perceptible moire patterns.

Touch display system with reduced moiré patterns

A large network of cameras is necessary for covering large areas in surveillance applications. In such systems, gaps between the fields of view of different cameras are often unavoidable. In this paper we address the problem of path recovery of a single target in such a system, where objects can be out of sight for a long period of time. We assume that the spatio-temporal topology of the network is known, and that an available tracker produces an object identity that might be unreliable (e.g., unreliable object appearance). The task difficulty depends on the spatio-temporal topology, as well as the possibility to confuse other objects that moves around. We propose a function for measuring this confusion. Our tracking method consists of two phases. The first phase produces possible solutions for the location of the target. It is an efficient new approach that is based on a modified particle filtering framework. The tracking is performed in a state space that consists of object locations and identities. Invisible locations are explicitly modeled by the states. Hence, the detection of targets disappearing and re-appearing is inherent in the algorithm. The second phase computes the object path by applying a shortest path algorithm to the results of the first phase. We tested our tracking approach on a system with hundreds of cameras and thousands of moving objects, and obtained good results. This is perhaps the first solution for this problem that is effective, robust and scalable to large networks of cameras. The results, as expected, vary for different network topologies and the possible confusion between objects.

The Interdisciplinary Center, Herzlia

A barcode is an optical machine-readable representation of data that is commonly used in the automation industry. Barcode systems have wide applications involving automatic identification and data capture (AIDC), which includes source tracking, labeling, packaging, pointing the reader to on-line content by means of a uniform resource locator (URL), and so on. Although barcodes are frequently used for encoding information for printed matter, they add unsightly overt content. This paper proposes a novel barcode system, in which a data message is hidden in the printed image, thus requiring no barcode area. In addition, hiding data in images other than barcode areas, e.g. commercial logos, can greatly increase the added values of using barcode systems. In this paper, we first applied the regular screening process to divide the input continuous-tone image into discrete parameter halftone cells. The hidden data message was encoded by the proposed encoding toggles in the halftone cells. To ensure the optimal image quality, a modified direct binary search (DBS) optimization framework was integrated in the proposed system. It ensures that the output data-embedded halftones achieve the best image quality from the viewpoint of human visual system (HVS). The simulation results indicated that the proposed method outperformed state-of-the-art approach in terms of data capacity and image quality.

A novel barcode system for intelligent automation industry

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

Design of color screen sets for robustness to color plane misregistration

For electrophotographic printers, periodic clustered screens are preferable due to their homogeneous halftone
texture and their robustness to dot gain. In traditional periodic clustered-dot color halftoning, each color plane
is independently rendered with a different screen at a different angle. However, depending on the screen angle
and screen frequency, the final halftone may have strong visible moire due to the interaction of the periodic
structures, associated with the different color planes.
This paper addresses issues on finding optimal color screen sets which produce the minimal visible moire and
homogeneous halftone texture. To achieve these goals, we propose new features including halftone microtexture
spectrum analysis, common periodicity, and twist factor. The halftone microtexture spectrum is shown to predict
the visible moire more accurately than the conventional moire-free conditions. Common periodicity and twist
factor are used to determine whether the halftone texture is homogeneous. Our results demonstrate significant
improvements to clustered-dot screens in minimizing visible moire and having smooth halftone texture.

Design of color screen tile vector sets

A method for designing a screen set for color halftoning includes selecting a screen set that includes at least two screens. The screens are applied to a uniform color image so as to form a set of corresponding colorant halftones. The colorant halftones are superposed to form a color halftone. A spatial frequency spectrum of the color halftone is calculated. Maxima of the spatial frequency spectrum that occur at two effective frequencies are identified, the two effective frequencies being located in two adjacent quadrants of a complex spatial frequency space. A magnitude of each effective frequency is compared with a predetermined frequency magnitude. The screen set is accepted for future application for color halftoning only if both effective frequency magnitudes are greater than the predetermined frequency magnitude. Relating computer program product and data processing system are also disclosed.

Jin-Young Kim

Papers

Design of color screen sets for robustness to color plane misregistration

Design of color screen tile vector sets

Color screen sets