We present a method to accurately estimate dense motion vectors between two successive color images in a sequence. This study integrates the red, green and blue channels of color images and extends the previous method30 in which the Cai–Wang wavelet representation was employed as a hierarchical motion model to match gray scaled images. The coarse-to-fine wavelet-based motion model is substituted into the objective function where the sum of squared differences (SSD) between two color images is minimized iteratively. Compared with the gray scaled images, our simulated experiments show that color images have better trackability and smaller condition numbers during the optimization process, leading to faster convergence rate and more accurate results. The estimated dense correspondences have been applied effectively to create realistic novel views using trilinear constraints.
Formulae are derived which calculate the bounds of discrete array MTF caused by the non-stationary nature of such devices. It is shown that if the traditional sinc based description of discrete device MTF is used, overestimation occurs. The average of the derived bounds is shown to be a good estimate of the SFR of the device. The formulae are tested against the performance yielded by a commercially available electronic still camera using a Sine wave, Edge and ISO Standard 12233 methods. Confidence limits calculated using the method detailed by Yeadon, Jones and Kelly and sources of errors are discussed. It is suggested that the presented formulae provide a better indication of discrete array performance for inclusion in system design for critical applications.
This article presents a process control strategy for reducing banding artifact in electrophotographic (EP) process. EP banding was shown to be closely related to the angular velocity fluctuation of the photoreceptor. Proper regulation of the photoreceptor rotational velocity under various process uncertainties and variations will improve EP process stability and reduce the occurrence of visual banding. The proposed closed-loop control strategy is to modulate the main drive motor speed based on the velocity measurement of the photoreceptor. The controller featured two levels of angular velocity regulation. The first level utilized the loop-shaping technique to incorporate the human visual system (HVS) model, i.e., an approximation of the human contrast sensitivity function (CSF), into the feedback loop to eliminate low frequency and non-periodic velocity fluctuations. The second level used an internal model based repetitive controller to reduce the effect of periodic velocity fluctuation. The HVS based loop shaping design is intended for addressing the subjective evaluation of the human visual perception. Experimental result from a low cost 600 dpi EP engine showed significant banding reduction from reflectance measurement as well as subjective evaluation of the printed image.
In this paper, we present a technique for measuring the value of charge-to-mass ratio in toners using a newly developed apparatus in which charged toner particles are transported above a periodic array of conductors driven by four-phase rectangular pulses. At the end of the flow path of toner particles in the transport system, parallel electrodes are set up for sensing charge-to-mass ratio. The sensed input signal is amplified by differential amplifier and is converted to digital values. By analyzing the sensed signal, the value of the ratio for the charged toner particles can be calculated. This technique can measure easily the mean value and its distribution under coditions of on-line use. We find that the distribution shows a good correspondence with the result of the E-Spart method near the peak range.
The two-component xerographic developer charging model of Gutman and Hartmann offers two alternative formulations of the interfacial electric field between toner and carrier, based on the assumption of either a continuous charge distribution on the surface of the toner, or a non-uniform patchy charge distribution. They found that m/q:C measurements on some developers were better described by one version of the model, while measurements on other developers were better described by the other version. In this study, we investigate when each version is applicable. We do this by comparing the two versions of the model with measurements of many different developers prepared with toners and carriers having different physical and chemical formulations that alter how charge is distributed throughout the developer. We found that the carrier surface formulation does not influence which version of the model better fits the data, nor does toner polarity. The main influence is the toner formulation, which creates different toner surface structures that presumably have intrinsically different toner surface charge distributions. We find that the patchy charge version fits the measurements if the carbon black is a minor component on the toner surface and an extremum in the triboelectric series. In contrast, the continuous charge version fits the data if the resin is a major component on the toner surface and also an extremum in the triboelectric series. Also, the continuous charge version of the model fits measurements of toners formulated with a charge control additive (CCA), consistent with the assumption that the particular CCA is uniformly distributed over the toner surface. In addition, we compare the two versions of the model to previously published measurements on a variety of toners with structures similar to those mentioned above, and find that the two versions fit the measurements in a similar pattern.
It has recently been proposed to use ultrasonic energy to dry ink jet printed materials. This work presents the results of a feasibility study of such technology. Both calculations and experiments show that direct heat transfer may be of significant influence only for MHz range ultrasonic frequencies. Thus, any attempt to use ultrasonic energy to speed drying on non-absorbing substrates should involve moving to MHz frequencies, and this move may prove useful.
A new thin film heater for thermal print heads was developed. The thin film heater includes a resistor portion and a conductor portion that supplies voltage to the resistor. The resistor portion has a thin insulating self-oxidizing coat, which prevents oxidation and electrolytic corrosion by ink, so the thin film heater does not require a thick overcoat. The anode side of the conductor is covered with an ink barrier layer, so electrolytic corrosion is prevented. Furthermore, a print head structure that does not generate cavitation was developed, and it was shown that the thin film heater could be used in this print head. The heater requires remarkably little energy to eject ink droplets. Also, the heater rapidly heats up the ink, which translates into more uniform velocity of ejected ink droplets.
The dispersed mist phenomenon occurs when small ink droplets are blown up and contaminate the inside of the printer. In this paper, we numerically predict the motion of ink droplets in a confined space through Computational Fluid Dynamics to better understand this phenomenon. Our numerical calculations correlate well with our experimental results. A vortex is generated by the interaction of ink droplets and the flow field through momentum exchange. Consequently, ink droplet behavior can primarily be defined by the velocity relative to the surrounding flow field. Experiments reveal that the optical density of the dispersed mist has a minimum peak for jetting frequency. We investigate the effects of jetting frequency on misting and find that air current generated by main drops tends to transport small mist particles to the paper at higher frequencies. This explains why misting is high at low frequencies. It is shown that the nonlinear coupling between the flow field and ink droplets defines the property of the dispersed mist phenomenon in detail.
The ink jet printing properties of papers coated with two different types of aggregated silica were compared. The structure of the nanoporous aggregates has been investigated with different techniques such as BET and CTAB surface area, Hg porometry and light scattering. The aggregates were thereafter mixed with polyvinylalcohol (PVA). The affinity of the PVA for the silica surface has been studied through adsorption isotherms at pH 5 and 9. It appears that the affinity is much more important at pH 5. PVA– silica slurries were prepared at pH 5 and coated on a non-coated common copier paper and finally printed. Swelling experiments and transmission electron microscopy have been performed on the coatings in order to have additional information on its structure. Black and white image analysis of typographic characters printed on the coatings show that smoothness of contours, gray level, contrast, definition, surface area of the typographic characters depend mostly on the structural properties of the silica, but also on its compatibility with the binder. The combination of both effects determines how important the remaining free porous volume accessible to ink fluids will be, and ultimately how the printing properties, such as shade and pixel resolution, will be. When pores are too large, they become filled with polymer and the silica aggregates lose their absorbency capacity.
A unique feature of photothermographic (PTG) imaging systems, compared to conventional AgX materials, is that all of the components needed to form high quality images are present in the film prior to imaging, and are not removed from the film during or after processing. The residual photoactive silver halide may continue to catalyze formation of metallic silver during room light handling. A continuing challenge for PTG imaging systems is to prevent pre- and post-process image (fog) formation caused by the inherent coexistence of these imaging chemistries within the film. The addition of separate post-processing image stabilizers or stabilizer precursors provides post-processing stability. Stabilizer precursors have blocking or modifying groups that are usually cleaved with heat during processing, or light after processing. This provides the primary active stabilizer that can prevent undesirable printout from the remaining photoactive silver halide in the unexposed and undeveloped areas of the film. The current review deals with antifoggants, their mechanism, and various blocking techniques used in preventing print stabilizers from premature activity in PTG materials. In describing these techniques, the chemistry, advantages, and disadvantages of individual approaches are also examined.