Digital halftoning has, traditionally, been thought of as a bilevel quantization algorithm that converts continuous tone images to images composed exclusively of “on” and “off” pixels. With recent advancements in printing technologies, ink jet and laser printers are now capable of producing dots with more than two intensity levels. These advancements have led to halftoning research on multitoning algorithms or halftoning with more than two levels. An early example of multitoning is the Floyd and Steinberg error diffusion algorithm with an N-level quantizer replacing the conventional binary quantizer. A major problem associated with this approach is the introduction of unwanted texture near the intermediate gray levels in the printed image. A possible solution to this problem is the redistribution of the intermediate gray and black pixels near the printable gray levels. In this article, a novel multitoning algorithm is introduced that can control the amount of printable gray level pixels, represents a particular shade of gray, by using gray level transformation. In this method, the input image is decomposed into the printable gray scale images, by using a set of gray level transformation curves, each channel is halftoned using conventional bilevel error diffusion algorithm, in a correlated way, and the halftoned channels are then recombined to get the final halftoned image. For certain gray level curve specifications, elimination of the undesirable banding artifacts has been achieved, near the intermediate gray levels, in the output. The suggested method is mean preserving and has a very little computational overhead involved as compared to the conventional error diffusion.

Drop-on-demand devices are the heart of most modern ink jet printers. The fluid dynamic process during drop ejection is complex with time-dependent fluid interface disruptions. Based on computations with a generic problem configuration, the present work attempts to provide an insight into the drop ejection behavior for establishing general design rules in device development. The computational results show that the volume of ejected drop is very close to the volume of fluid pushed through the nozzle by an actuation pulse. The speed of the ejected drop is typically between one third and two thirds of the average velocity of the fluid pushed through the nozzle during actuation. The conditions for obtaining various (desirable or undesirable) drop shapes immediately after ejection are examined. The cases when drops may not be successfully ejected are also discussed.

This article addresses acoustic wave propagation in a piezoelectric ink jet printer. Acoustic resonances limit the operating frequency of ink jet devices and influence the timings of the electrical drive signals. In this study, the resonant frequencies in a multichannel printhead are determined through feedback from the fluid to the piezoelectric structure using an electrical impedance analyzer. We also analyze the influence of channel length on resonant frequency. In addition, the effect of different boundary conditions on the acoustic resonance of the channels was observed. Because the channels walls are compliant, the propagation of acoustic pressure waves in them is slower than the speed of sound in the fluid, which is a fluid property. The electrical impedance measurements allow the determination of the effective speed of sound in the channel and the optimal timing for the driving electrical signal. During printhead operation, the drop velocity can be modified by changing the duration of the electrical pulse sent to the piezoelectric actuator. The timing that produces the maximum drop velocity can be also related to the effective speed of sound in the channel. Comparison of the two data sets show that a printhead channel has an acoustical behavior closer to an open-open pipe.

Applications for drop ejectors range from ink jet printing to drug delivery systems. MEMS (Micro-Electro-Mechanical Systems) fabrication techniques, particularly surface micromachining, allow production of small monolithic structures that can be adapted to many applications. We report on the design, fabrication, and testing of a surface micromachined MEMS liquid ejection system for printing applications. The ejectors were fabricated using the SUMMiT™ process,¹ a surface micromachining technique. The only assembly required is electrical connection and attachment of a fluid reservoir. The process features three, four or five layers of structural polysilicon, separated by layers of sacrificial silicon dioxide. The final step of the fabrication process is the removal of the oxide to release the “machined” structure. The ejector produces small volume (2 – 4 picoliters), satellite-free drops traveling at 5 – 10 m/s. To eject a drop a piston is drawn rapidly towards a plate containing a nozzle through which the drop is ejected. The piston is electrostatically actuated. Since the electric field acts across the liquid bath, device operation is sensitive to the dielectric strength, breakdown voltage and conductivity of the fluid.

Experimental, numerical, and theoretical investigations have been carried out on statics of a magnetic bead chain in the magnetic field. Chains formed on a solenoid coil were observed and chain lengths and slant angles were measured by a digital microscope. It was deduced that (1) the chain length depends on both the surface loading of magnetic particles and the magnetic flux density, and is almost independent of the particle diameter if the sufficient amount of particles are provided; (2) chains incline in the inclined magnetic field and the inclination of the chain is enlarged by the gravitational force. These configurations of chains are approximately determined to minimize the total potential energy that consisted of the gravitational and magnetic potential energy. These characteristics were qualitatively confirmed by the numerical calculation with the two-dimensional Distinct Element Method. The investigation is expected to be utilized for the improvement of the two-component magnetic brush development system in electrophotography.

This article presents an experimental study on the application of a piezoelectric laser beam deflection device to reduce banding in electrophotographic processes. Using an offline print-and-scan measurement method, the static characteristic of the deflection device is obtained. Using online measurements of the laser beam position with an optical sensor, the dynamic behavior of the device is identified. Using the identified model, a scan line spacing compensation strategy is proposed and implemented. Experimental results showed significant visual and measured improvements in test patterns and halftoned images.

A triage metric is proposed to determine the extent of blocking and contouring artifacts in an image due to JPEG compression. It is found that this metric has a linear correlation with subjective judgements of print quality. This triage metric can be used to determine the amount of needed image enhancement or achieve a good trade-off between image quality and system throughput.

This article describes the basic concept of fractal analysis with relation to printed structures and introduces “intensity fractal function” as a tool of practical factor analysis of printed images. The properties of the “intensity fractal function” are demonstrated on samples of printed images.

This article presents a new approach in the selection of auspicious sites to be watermarked. The selection takes into account human visual system properties including luminance adaptation, contrast sensitivity and spatio-frequential selectivity. This article exploits also the local band limited contrast to determine the maximum watermark strength to be applied without inducing visible degradations. Compared to the well-known approaches, a contrast masking model is used here to adjust, site by site, the watermark strength. To test the approach efficiency, obtained results are considered in the context of an adaptive watermarking algorithm. The performance of this latter is evaluated in terms of watermark invisibility and robustness. Watermark invisibility is judged through subjective tests conducted with three observers according to the CCIR recommendations. Original watermark detection results are also presented to analyze the robustness of the scheme to most common attacks such as JPEG compression, cropping (with zero padding) and blur.

The synthesis and properties of well defined carbazolyl-containing molecular glasses is reported. They were prepared by the nucleophilic opening of the oxirane ring of 1,3-di(carbazol-9-yl)-2-propanol, 1-(carbazol-9-yl)-3-diphenylamino-2-propanol or 1-(3,6-dibromocarbazol-9-yl)-3-(carbazol-9-yl)-2-propanol glycidyl ethers with 1,3-benzenediol in the presence of triethylamine. The electrophotographic parameters of undoped films of the molecular glasses and of those doped with difluoroboron-1,3- bis(4-methoxyphenyl)-1,3-propanedionate have been studied. The hole drift moblities measured by the time of flight technique in the molecular glasses containing carbazole and diphenylamino groups reach 10⁻⁴ cm²V⁻¹s⁻¹ at an electric field of 10⁶ V cm⁻¹. The ionization potentials measured by electron photoemission method in air are close to those reported for the other organic photoconductors containing electronically isolated carbazole moieties.