Physical properties have been compared among AgCl, AgBr, and AgI grains. The formation energy of interstitial silver ions through surface kink sites is in the order of AgCl, AgBr, and AgI, while the activation energy of the migration of interstitial silver ions is in the reverse order. This result is ascribed to the difference in ionic character among them, and leads to the fact that the concentration of interstitial silver ions acting as shallow electron traps is in the order of AgI, AgBr, and AgCl. This result is therefore responsible for the fact that the concentration of photoelectrons, as measured by means of a 35 GHz microwave photoconductivity apparatus, is in the order of AgCl, AgBr, and AgI. Since the solubility in water is in the order of AgCl, AgBr, and AgI, it is considered that the concentration of dissolving impurity ions acting as positive hole traps is in the order of AgCl, AgBr, and AgI, and that the silver ion concentration in the vicinity of latent image centers on the grain surface is in the same order. Although these facts make it more difficult to form latent image centers on AgI grains than on AgBr and AgCl grains in conventional photographic materials, in which the concentration of silver ions is kept low for their stability, it is indicated that AgI grains are suitable for photothermographic materials, in which AgI grains are placed in the environment with higher concentration of silver ions than in conventional ones, and are fixed during thermal development, contrary to AgBr and AgCl grains.
It has been observed in the preceding paper that the ionic conductivity of AgI grains with interstitial silver ions as carriers is comparable to that of octahedral AgBr ones. Since the activation energy of the migration of interstitial silver ions in AgI is much smaller than that in AgBr, it is estimated that the concentration of interstitial silver ions acting as shallow electron traps is much larger in AgI grains than in AgBr ones, providing an explanation for the observation by a microwave photoconductivity method that the photoconductivity with photoelectrons as carriers is smaller in AgI grains than in AgBr grains. The observation that latent image centers on AgI grains is oxidized at more negative redox potential than that on AgBr grains has been ascribed to the fact that the concentration of silver ions in the vicinity of the former is smaller than that in the vicinity of the latter owing to the difference in the solubility in water between them. A radiofrequency photoconductivity method has revealed that the activity of positive holes in AgI grains in an emulsion is higher than that in AgBr grains in an emulsion, and is depressed by increasing the concentration of silver ions in the emulsion. Although these results make it more difficult to form latent image centers on AgI grains than on AgBr ones in conventional photographic materials, the latent image formation on AgI grains could be enhanced by increasing the concentration of silver ions in conventional materials, and by using them in photothermographic materials, in which the concentration of silver ions was usually much higher than in conventional ones owing to the presence of silver carboxylate. Recent discovery that AgI grains are fixed during thermal development in photothermographic materials has merged with the above-stated results to reveal that AgI grains are suitable and useful for photothermographic materials.
We have found that nanoparticles of silver iodide have high sensitivity for blue light and are fixed during thermal development in photothermographic materials. Silver iodide particles exhibit high sensitivity and weak LIRF in photothermographic materials, as they do in conventional materials with higher silver ion concentration than usual, and have their sensitivity further improved by reducing agents adsorptive to the particles. The sensitivity of photothermographic materials with nanoparticles of silver iodide for blue laser light could be comparable to that of the materials with silver iodobromide for red laser light. Silver iodide particles are slowly fixed during thermal development in photothermographic materials with existence of either silver carboxylate or phthalazine, and rapidly fixed with coexistence of these two compounds. Fog density of developed layers of photothermographic materials with nanoparticles of silver iodide does not increase under room light illumination.
It has been revealed in this study that the sensitivity of newly developed composite grains with tabular silver iodide grains as hosts and epitaxially formed silver bromide microcrystals as guests is high enough in photothermographic materials to realize a blue medical x-ray film-screen system in combination with BaFBr:Eu fluorescent radiographic intensifying screen. Beside the fact that the quality of the system image is comparable with that of conventional ones, the image stability as well as the haze of the new system is satisfactory, in spite of the fact that the new system uses photothermographic materials, since the grains used as photosensors are fixed during thermal development.
We describe the systematic design and evaluation of new phenolic reducing agents (developers) for dry-processed, silver-based direct thermographic (TG) black-and-white films for medical diagnostic imaging. In TG media, heat exposure as short as 7 ms/pixel is used to induce development, thus highly active developers are needed. Our approach to this problem combined synthesis, coating evaluation, and electronic structure calculations to provide insights into the TG development mechanism. The computed highest occupied molecular orbital (HOMO) energy of the neutral developer did not correlate with maximum image density Dmax. Rather, the best developers (high Dmax, low fog) had relatively low phenol O-H deprotonation energies and high-lying phenolate anion HOMO energies, implying that, in the TG process, silver is reduced primarily by phenolate ion. This information allowed discovery of new categories of potentially useful TG developers, including ortho-aminophenol, para-aminophenol, halophenol, and resorcinol derivatives.
A combination of normal Raman spectroscopy, surface-enhanced Raman scattering spectroscopy, and transmission electron microscopy has been used to demonstrate that phthalazine is the predominant species on the surface of metallic silver nanoparticles in the image at the final stage of development in photothermographic films. Evidence for a small amount of a cotoner, 4-methylphthalic acid, as Ag2(4-MPA), has also been found. In addition, the organic components around the developed Ag0 nanoparticles have been directly observed by transmission electron microscopy using RuO4 staining techniques. A model system, based on interaction between the toner chemicals with nanoparticulate Ag dispersions, has shown that PHZ can directly cause Ag nanoparticles to aggregate but not coalesce. Based on these results, phthalazine adsorption is proposed to play a major role, and the phthalic acid component a lesser role, in controlling metallic silver formation of the preferred metallic silver dendritic morphology.
In order to study the effect of the silver particle morphologies in photothermographic images, we calculate exactly the scattering and absorption cross sections for a few distinct morphologies representing simplified limits of the morphologies actually seen in photothermographic images. In particular, we consider isolated spheres, isolated prolate spheroids, and isolated 3×3×3 clusters of spheres. These results are then extended to compute approximately the covering power and tone in a slab containing a collection of such scattering and absorbing particles by using the solution to the telegrapher's equation that models the propagation of the light in a medium under the assumption that the light is scattered isotropically by the particles. The anisotropy of the scattering is treated using a widely-used approximate correction that is shown to give reasonably good agreement with a Monte Carlo simulation of the light propagation for the case when the particles are spheres. Our results show that, for solid silver spheres, there is an optimum diameter of approximately 100 nm that yields the highest covering power and the most neutral tone. Higher covering power can be obtained using prolate spheroids having a diameter of 40 nm and a length of about twice that. However, as the aspect ratio of the spheroid increases beyond this, the covering power decreases fairly rapidly, thus suggesting that isolated filaments are not optimal. Finally, the results using clusters of spheres suggest that when the spheres are packed close together the covering power can be greater than that of an isolated sphere containing the same volume of silver as the cluster.
It is inevitable that there are some colors that cannot be reproduced with three primaries even in the case of a laser display. The purpose of this study is to define a new set of RGB primaries for display that can reproduce all real world object colors. At the first step, the region of real world object colors was estimated from the comparison between the measurement data of 453 object colors and the 1294 standard data of Munsell colors. Through the second step, the region boundary of real world object colors was optimized as a triangle according to two rules. Accordingly the wavelengths of RGB primaries were defined as 630, 532, and 468 nm, respectively. At the third step, with the help of 53,361 SOCS data, the tolerance limit of B primary was also defined as the range of 463–468 nm. Finally, the color reproducibility of commercial laser display systems was evaluated using the optimum gamut as a criterion.
The original JPEG compression standard is efficient at low to medium levels of compression with relatively low levels of loss in visual image quality and has found widespread use in the imaging industry. Excessive compression using JPEG however, results in well-known artifacts such as "blocking" and "ringing," and the variation in image quality as a result of differing scene content is well documented. JPEG 2000 has been developed to improve on JPEG in terms of functionality and image quality at lower bit rates. One of the more fundamental changes is the use of a discrete wavelet transform instead of a discrete cosine transform, which provides several advantages both in terms of the way in which the image is encoded and overall image quality. This study involves a comparison of subjective image quality between JPEG and JPEG 2000 to establish whether JPEG 2000 does indeed demonstrate significant improvements in visual quality. A particular focus of this work is the inherent scene dependency of the two algorithms and their influence on subjective image quality results. Further work on the characterization of scene content is carried out in a connected study [S. Triantaphillidou, E. Allen, and R. E. Jacobson, “Image quality comparison between JPEG and JPEG2000. II. Scene dependency, scene analysis, and classification”, J. Imaging Sci. Technol. 51, 259 (2007)]. © 2007 Society for Imaging Science and Technology.
Image quality assessments have shown that both JPEG and JPEG2000 compression schemes are dependent on scene content. This paper addresses the problem of scene dependency and scene susceptibility in image quality assessments and proposes image analysis as a means to group test scenes, according to basic inherent scene properties that human observers refer to when they judge the quality of images. Experimental work is carried out to investigate the relationship between scene content and the subjective results obtained from experimental work carried out in [S. Triantaphillidou, E. Allen, and R. E. Jacobson, “Image quality comparison between JPEG and JPEG2000. II. Scene dependency, scene analysis, and classification”, J. Imaging Sci. Technol. 51, 259 (2007)]. © 2007 Society for Imaging Science and Technology. The content of the test images used in this work is analyzed using simple image analysis measures that quantify various image features, such as original scene contrast and global brightness, amount of dominant lines, scene busyness (defined here as a scene/image property indicating the presence or absence of detail), and flat areas within the scene. Preliminary results and conclusions are obtained and suggestions are made to form a basis for further studies on scene dependency and scene classification with respect to image quality measurements.