A review of the human visual system, the CIE L*, a*, b* color space and its use in evaluating color image quality, and digital image capture is presented, the goal of which is to provide background information for imaging professionals involved in creating digital image databases for museums, galleries, archives, and libraries. Following this review, an analysis was performed to determine the effects of bit depth, dynamic range, gamma correction, and color correction on the ability to estimate colorimetric data from R, G, B digital images with a minimum of error. The proper use of gray scale and color targets was also considered. Recommendations are presented for the direct digital image capture of paintings. Finally, a brief look into the future using spectral imaging techniques is presented.
An appreciation of the potential of silver halide as an image capture material for digital applications can benefit from an understanding of the characteristics and potential of silicon-based imagers. Here, we compare the imaging characteristics of contemporaneous silicon and AgX imagers on a common basis. Sensitometric and image structure comparisons of first generation Kodak Advantix 400 AgX color film and contemporary (1997–1998) Kodak Professional digital camera system (DCS) color imagers at 393 K, 1.6 M, and 6.3 M pixel sensor resolution are presented. The imagers compared have similar useful color imaging exposure thresholds. In speed-grain terms, the 6.3 M sensor DCS provides similar speed-grain in the lower scale and superior speed-grain in the upper scale when compared to the AgX film. The smaller sensors appear less capable in this regard. The sensors all provide shorter exposure latitude than the film. Further, within the context of pictorial imaging, it appears that the silicon array as employed in the DCS is close to its fundamental imaging efficiency limits.
Thin AgCl layers photocatalytically oxidize water to O2 under appropriate conditions. The photoactivity of AgCl extends from the UV into the visible light region in a process known as self-sensitization, which is due to the formation of silver during the photoreaction. This silver can be almost quantitatively reoxidized electrochemically, making it feasible that a thin AgCl layer deposited on a conducting substrate can be used as a photoanode for water splitting if coupled with an appropriate photocathode. The silver chloride/silver cluster phase boundary plays a decisive role in the photocatalytic silver chloride electrode system. We have therefore studied this interphase by means of quantum chemical calculations from which we report first results, specifically for the (Ag)115(AgCl)192 composite. Clusters of semiconducting materials are interesting considering their application as a photocathode in such a device. In this context, we also report the synthesis and properties of luminescent quantum-sized silver sulfide clusters in the cavities of zeolite A. The color of the silver sulfide zeolite A composites ranges from colorless (low loading) to yellow–green (medium loading) to brown (high loading). A low silver sulfide content is characterized by a blue–green luminescence and distinct absorption bands, while samples with medium or high silver sulfide content show an orange or red colored emission and a continuous absorption.
Effects of iridium doping on the differences in photographic behavior between cubic and octahedral AgBr grains have been investigated. The experimental AgBr grains were prepared without spectral or chemical sensitization. The iridium ions were incorporated into the major shell region of each grain (shell/core = 36/1) with different concentrations of iridium (0 ∼ 10−5 mol Ir/mol Ag). Regardless of the iridium doping amount, it was observed that latent images of cubic grains are almost all located at the surface, while in octahedral grains some latent images are also located inside the grains. These features are explained by relat-ing the latent image position to the potential difference across the space charge layer in octahedral and cubic grains. Undoped octahedral grains exhibited reduced effectiveness in latent image formation than undoped cubic grains. Introduction of iridium doping (with a concentration of 10−6 mol Ir/mol Ag) remarkably eliminates this reduced effectiveness observed for octahedral grains. In addition, iridium doping gives the octahedral grains a higher sensitivity increase during delayed latent image formation, compared to cubic grains. Such behavior is discussed in terms of a greater number of electrons being temporarily trapped by iridium centers.
An overview is given of non-tabular crystals with {111} surfaces occurring in emulsions of silver bromide and silver chloride tabular grains. The crystal defects are characterized by transmission electron microscopy (TEM) and their influence on the growth process is discussed. It is proven that in all cases of non-tabular growth twins on two non-parallel {111} type planes are present. Different morphologies have been observed in AgBr and AgCl emulsions. The most frequently occurring morphologies are needle and tetrahedron shaped crystals in AgBr and thick tabular crystals with an incomplete microtwin as well as crystals consisting of a tetrahedral shaped part and a flat triangular to trapezoidal part in AgCl. A comparison will be made between the silver bromide and the silver chloride crystals.
Photothermographic materials that contain silver halide grain and organic silver salts are widely used in dry processing imaging systems. Because its characteristic curves are very sensitive to development condition, precise calculations of the characteristic curves under various development conditions are essential for practical development system designing. Though some previous models for the characteristic curves had been proposed, those uses are limited because they based on some ideal assumptions. In this study, change of experimental characteristic curves under various development conditions was analyzed, and a new model using semiempirical simulation method was found. This method gives both the fraction of silver halide grains receiving a latent image exposure and the radius of sphere of influence from the experimental characteristic curves of several development conditions. The fraction is an intrinsic value of the film, and it represents the photosensitive character including fog. The radius of sphere of influence represents the degree of development, and its rate of increase is constant under fixed development temperature. These parameters are useful for analysis of development rate. Once these parameters were defined, exact characteristic curves of any development conditions are calculable. The found simulation method is useful for analysis and design of practical photothermographic system.
The chemistry of a thermally developed photographic system based on silver carboxylate is investigated both in the model system and in the film sample. The reaction path is found to consist of the disintegration of the silver carboxylate crystal structure under thermal development (step 1), the formation of silver ion carriers which can diffuse in the molten media (step 2), and the reduction reactions of silver ion to metallic silver by the reducing agent (step 3). In the first reaction step, XRD patterns and FT–IR spectra show that phthalic acid receives silver ion from crystalline silver behenate and becomes di-silver-phthalate. In the second reaction step, the complexes of phthalazine and silver ion are identified as the silver ion carriers in molten media by 13C–NMR, density functional calculations of 13C–NMR chemical shift, and TOF–SIMS. The diffusion coefficients of silver ion carriers are measured by pulsed field gradient 1H–NMR at the development temperature. In the final step, the reduction of silver ion by the bisphenol-type reducing agent is analyzed by the identification of the reaction products. It is found that this reducing agent has eight equivalent reducing power. An overall reaction mechanism for thermally developed photographic systems based on silver carboxylate is proposed.
The spectral sensitivities of image capture devices should be carefully designed to guarantee colorimetric color reproduction. As a standard color test chart, ISO/DIS 12641 is conveniently used for calibrating the scanners or printers. However, its color gamut is not wide enough to evaluate the devices such as digital camera and display systems and the color distributions are not uniform because the chart is a photographic print. This article proposes a virtual color target to estimate the spectral goodness of color devices. A virtual spectrum with given L*a*b* value is generated from the fundamental metamer uniquely obtained by inverse projection of XYZ tristimulus value and an addition of arbitrary metameric black spectrum. The goodness of typical color input sensors is estimated and compared with actual color chips using this virtual spectral target.
The mechanisms underlying the generation of magnetic background in magnetography are analyzed from the standpoint of random collisions between toner particles during development. Particles are supposed to be either already captive in non-image area, or still free in the developer bed. The outcome of collisions is determined by comparing the magnetostatic energy of the former type of particles, with the kinetic energy of the latter type. The critical process speed, at which background is minimum, depends on the imaging media permeability and the toner magnetic characteristics. The rate at which background decreases for sub-critical speeds is related to the particle size distribution and the number of collisions expected at each development position. Quantitative results from the model are shown to be in fair agreement with experimental data.