Cyanine dye J-aggregates, a principal material which absorbs visible light in photographic films, are expected to adsorb on every AgBr microcrystal in equal quantity to achieve uniform sensitivity to exposing light throughout the photographic material. However the population densities of the J-aggregates on AgBr particles grown in gelatin differed significantly as identified by the cathodoluminescence from the aggregates; some particles adsorb little dye while others adsorb more, i.e. a few particles adsorb most of the dye and the rest adsorb little. The reason for the wide spread of J-aggregate distribution is unknown. The shapes of AgBr microcrystals look alike in microscopic observations and do not explain why such a significant difference of adsorbed dye quantities occurs. The wide variations of adsorbed dye, quantities on AgBr particles must be a major factor with respect to the sensitization/desensitization effects or latent image formation of silver halides with photosensitizing dyes.

The spectral-sensitization of an AgCl emulsion was investigated in the presence of some fog inhibitors. It was found that the sensitivity of spectral-sensitized emulsions could be increased or decreased by these inhibitors according to the order of addition of the compounds. On the basis of spectral measurements, one reason could be the influence of these compounds on the aggregation behavior of the cyanine dyes. When it was beneficial to the formation of dye J-aggregates, sensitization took place; and when it was beneficial to the formation of dye H-aggregates, desensitization appeared. ESR experiments show that the addition of inhibitors can decrease the number and accelerate the decay of dye positive holes. The desensitization, caused by the recombination of dye positive holes with photoelectrons and/or latent image centers, was reduced in the presence of these fog inhibitors, leading to an increase in sensitivity of the emulsion.

Recent experimental characterization of the reconstructed AgBr(111) surface (a half-layer covering of Ag ions segregated into rows 7.07 Å apart) has been used to construct a theoretical model (within the framework of an approximate molecular orbital method) of that surface. Our calculations indicate that these surface Ag rows give rise to states at the bottom of the conduction band, which could serve as shallow trapping sites for photoelectrons. The theoretical model provides a mechanism for the formation of a latent image cluster through trapping of photoelectrons in the low lying state and subsequent pairwise distortion of the surface Ag within the rows to form Ag–Ag bonds. The calculations also indicate that substantial electron transfer from the ionic extreme occurs in both the bulk and surface models.

Models and mechanisms which have been proposed for silver sulfide and silver-gold sulfide sensitization are reviewed. These sulfides are not involved in the primary photochemical processes of the direct photolysis theories of Sheppard, Gurney and Mott, Hamilton, Kanzaki and Tadakuma, and Tani. In these theories, photoelectrons and positive holes are created in pairs and the role of sulfide sensitization in trapping photoelectrons is emphasized. With a chemically sensitized silver halide emulsion grain, there are, however, a large number of equivalent sites at which electron trapping can occur and the theories provide no process for the efficient formation of a development center by the separation of a small number of silver and gold atoms at one particular site. According to the photoaggregation theory, chemical sensitization results in the formation of small monolayer islands of Ag₂S and (Ag,Au)S molecules at surface sites with Ag₂ molecules adsorbed around their edges. These sensitizing molecules are dissociated by the annihilation of energy quanta with creation of photoelectrons and release of Ag_o⁺ or Au_o⁺ interstitial ions. A development center is formed at an Ag₂ latent image growth nucleus precursor by two effective events. In the first event, a photoelectron and interstitial ion combine with an Ag₂ molecule to form a Ag₃ or AuAg₂ molecule that adsorbs a Ag⁺ ion to give an Ag₄⁺ or AuAg₃⁺ latent image growth nucleus. In the second event, this positively charged nucleus attracts and traps a photoelectron and the positive charge is restored by the effective adsorption of an Ag_o⁺ ion giving an Ag₅⁺ or AuAg₄⁺ development center of minimum size, adsorbed to a sulfide monolayer island. This center grows by the repetition of these electronic and ionic events and this provides an efficient concentration process.

Photographic properties of 1-benzyl-1,4-dihydronicotinamide (BNAH) are studied for better understanding of the mechanism of the production of high contrast by the infectious development induced by the combination of a pyridinium salt and Metol-ascorbate developer. Treatment of silver bromide emulsion or silver chlorobromo emulsion by BNAH and redox buffer followed by development gave high fog density. It has been suggested that the oxidation product of BNAH by redox buffer nucleates silver halide grains and makes them developable. Results support the hypothesis that dihydropyridine works as an intermediate in the production of high contrast by the infectious development in the presence of a pyridinium salt.

A new method of recording for tone reproduction was developed by application of the state of ink flight peculiar to the electrostatically extracted ink-jet method. In the state of ink flight in this new method, the ink forms a liquid thread from the nozzle tip, turns into ink corpuscles from the leading edge of the liquid thread, and then scatters like mist. The state of flight from a liquid thread to corpuscles is consecutive and continuous. For expressing tonal differences, the state around the leading edge of the liquid thread was used for recording the high-density area of the image and the state of scattering corpuscles for the low-density area. This differentiation in usage was confirmed workable and favorable results obtained.

Neuron count in various brain structures is an important factor in many neurobiological studies. Alzheimer's disease researchers, for example, have recently suggested staging models that link clinical phenomena of the disease to characteristic neural transformations at a cellular level. An automated system for quantifying cell populations in tissue samples would improve the reliability and reduce the cost associated with obtaining cellular data. We describe a machine vision system that uses color images for the automated classification and counting of neurons in 3-D tissue samples. Samples are sliced into registered sections with thicknesses on the order of the diameter of a neuronal nucleus. Sections are stained so that the spectral transmission of neuronal nuclei differs from the surrounding tissue in preparation for imaging using a light microscope. A Bayesian classifier and geometric analysis system are employed to segment neuron regions in each section. The 3-D tissue sample is reconstructed using registered neuron regions from section to section. This allows an unbiased neuron count estimate for the sample. Preliminary experimental results are presented and compare favorably with results obtained independently by a histologist.

In this paper, a least-square model-based halftoning technique using a genetic algorithm is proposed to produce a halftone image by minimizing the perceived reflectance difference between the halftone image and its original image. We use a least-square criterion incorporating with the property of the human visual system to measure the difference between the two images. The genetic algorithm is used for investigating the complicated search problem. The standard halftoning techniques, such as error diffusion and least-square halftoning, produce gray-level distortion because of dot-gain problem. In this study, we use a modified dot-overlap printer model to compensate the gray-level distortion. The printer model combines with a measurement-based algorithm to estimate the print-dot radius and makes the proposed halftoning approach adapted to a wide variety of printers and papers. Experiments show that the proposed approach produces more accurate gray levels than several common-used halftoning methods produce.

This article deals with estimating the quality of natural color images from the digital image itself, for the purpose of determining whether the quality is sufficient for printing or displaying at some specified quality level. The problem of measuring simply defined parameters that correlate reasonably with human perception is discussed. Then an algorithm is described that measures sharpness, stochastic noise, and the blocking artifact of JPEG compression. The sharpness measure is the maximum of local sharpness, defined as the maximum gradient at an edge divided by the edge contrast. The algorithm behaves fairly consistently with respect to the amount of simulated blur and the measure correlates with the subjective sharpness of different images. The output of the stochastic noise algorithm is an unspecified number of noise levels, each of which is associated with the corresponding mean luminance. The algorithm computes a gradient image using the Sobel filters and uses the bivariate histogram of gradient and luminance to find the noise levels. The gradient filters are suitable for estimating the effect of power spectrum on noise visibility, but the discrimination between image details and noise is only partially solved by this method. The blocking artifact measure describes a characteristic spikiness in the histogram of the Sobel gradient.