The noise perception model proposed by Dooley and Shaw1 includes an experimental function decreasing monotonically with average density. The sample patches they used did not include any periodic structure such as a halftone screen. To establish a similar model for digital images having periodic structures, we first tried to obtain the visual sensitivity function for graininess detection using a noise-free halftone test-chart distributed by the Society of Electrophotography of Japan (SEPJ). The chart consists of halftone tints with 65 to 200 lpi rulings and area coverage ranging from 5% to 95%. Among each patch group of constant area coverage, three observers were asked to choose the threshold patch at which the halftone structure or, in other words, graininess, can be detected. The result shows that human vision has a sensitivity peak at area coverage of about 20%. Because this result must be closely associated with the density dependence of noise detectivity of human vision, we will assume that the threshold patches represent equivalent graininess. Next, similar to the treatment adopted by Dooley and Shaw, the graininess index without the density dependence function was calculated for every patch in the test chart. Our approach is different from theirs in that we use fluctuations of lightness to calculate the Wiener spectrum instead of reflection density. Finally, we calculated our graininess index using a new sensitivity function based on a model describing our observations. To confirm our approach, we made subjective assessments for the patches including selected patches from the test chart, and obtained good relationship between our graininess indexes and subjectively evaluated levels. urthermore, we applied our model to hardcopies of gray scales made by some digital copiers on the market. The hardcopies have their own specific screens depending on the model of copier. Our results reflected the subjective judgments reasonably well.

The Neugebauer equation is generally used to predict full color reproduction for printing. Pollak resolved the Neugebauer equation into factors, assuming the additivity of superimposed solid optical densities. Because of differences between predicted and actual results, various modifications of the formula have been suggested. Yule and Nielsen introduced the parameter n. We have now developed a quadratic equation with a factor corresponding the Yule-Nielsen n. By introducing our correction term to Pollak's equation, it is possible to correct approximately for optical dot gain in the case of halftone dots superimposed on paper.

The inertial effect of a feed stream entering into the center of a coating die with a rectangular channel was studied using the spectral element method. The fluid momentum impinging on the opposite wall causes a rise of pressure approaching one velocity head. The pressure at the slot entrance at the top of the channel, directly above the impingement point, is less than at impingement point. This pressure difference increases with the size of the channel (or distance from the impingement point). Having the feed entrance in the furthest position from the slot entrance, along the bottom of the channel, results in a minimum pressure rise at the slot entrance directly above the impingement point. Because of this higher pressure, there is a velocity spike at the slot entrance above the impingement point. However, this spike was completely damped out over the length of the 50-mm long slot that was examined. The pressure rise in the channel due to the momentum of the flow down the channel is another inertial effect, and it appears to be less than the conservative estimate of two velocity heads. In the one case where applicable data could be obtained it was 1.5 velocity heads.

In contrast with most static studies in nuclear medicine, dynamic studies have an inherently high noise level because of low count statistics. Preprocessing of the raw image data by the application of suitably designed smoothing filters, provides a significant contribution to the dynamic studies. Because dynamic studies are 3-D, consisting of two spatial dimensions and time, preprocessing of the raw image data by a specially tailored 3-D filter, would be expected to fit more precisely and efficiently than the utilization of conventional 2-D filters. In this study, a new 3-D Double Window Adaptive Hybrid Smoothing Algorithm (3-D DWAH filter) is introduced and the results obtained by its application on the pixel basis dynamic renal scintigraphic images are compared with those of the conventional filters and unsmoothed raw data. The 3-D DWAH filter effectively and optimally combines the FIR-Median Hybrid (FMH) and the running mean filters within a variably tuned interval providing a significant improvement in SNR without unacceptable degradation of spatial and temporal resolution.

The photochemical reaction of aqueous dichromated gelatin solution in the intrinsic sensitive region under normal room conditions as investigated employing a water-soluble gelatin. The sample solution, containing dichromate, gelatin, and pH buffer solution, was exposed, and the decrease in absorbance for the photoreduction of Cr(VI) was monitored by UV-vis spectroscopy. Having compared the behavior of gelatin with that of alcohol at photoreduction of dichromate, we found that both systems are consistent with respect to the reaction order, the kinetic order for each reactant solution. Similar results were also obtained from the standpoint of pH dependence,activation energy, and chemical sensitization by EDTA. On the basis of experimental observations and discussion, a mechanism of photoreduction of dichromated gelatin and its rate determining step were suggested.

In this article we present the results obtained on jet break-up using two types of nozzles having the same nozzle aspect ratio but exhibiting different entry and exit holes. To further emphasize the effect of nozzle geometry, we use two different stimulations of the jet, respectively a piezoelectric transducer located upstream the orifice and an ElectroHydroDynamic (EHD) exciter that consists of an electrode situated downstream from the nozzle. The different measurement techniques used are essentially a stroboscopic illumination of the jet and a laser photometry method. These two methods allow us to obtain information on both the break-up lengths and the spatial evolution of the jet shape. Spectral analysis combined with the laser photometric method shows the evolution of Fourier amplitudes of the jet radius and phase shifts between the fundamental and the harmonics for low and high initial perturbations. In particular, this method reveals drastic differences between nozzles that may be ascribed to the drop formation behavior of jets.

Digital halftoning techniques using threshold matrices have clear advantages in their speed of operation together with the possibility of controlling the produced dot patterns. However, due to an inherent restriction discussed in this article, the quality of dispersed dots halftones produced with this technique is not always satisfactory. In this article we describe a technique that overcomes this restriction, thereby allowing for an individual design of each tint value without any loss of speed. We also propose a design strategy for obtaining near optimal tints without losing the necessary correlation between tints. High quality reproduction of both tints and transitions between different intensity levels is thus possible. This technique also allows for new types of dispersed dot halftones with predefined micro structures. Halftones with micro structures are less sensitive to both mechanical and optical dot gain and can advantageously be used in processes with severe dot gain or low printing precision. In this article we present two types of micro structures together with several image examples.