This article provides a review of the state of the art in watermarking techniques specifically designed for color images. It presents an overview of the color image watermarking methods and an analysis of the advantages and disadvantages of several recent schemes. It also presents solutions and arguments supporting the idea that methods based on human visual sensitivity provide more robust watermarks than do other ones. Furthermore, this article treats the question of the evaluation of watermarking quality according to fidelity. Finally, based on this analysis, research directions in color image watermarking are suggested.
The aim of the study was to create an improved colorimetric and broadband spectral characterization for scanners and cameras. In such characterization, selecting an adequate number of color samples of known reflection spectra is necessary. And though countless sample data sets are available, the properties required of a data set for such optimal characterization remain elusive. Therefore a new methodology was required to address the characterization task. Such a characterization method is introduced in this article and is based on statistical classification of the colorimetric and broadband spectral properties of color sample sets. It introduces and effectively utilizes both the reflectance spectrum of the color sample and the spectral power distribution of the source. However it is shown that characterization methods based on a regression model can be used only if the conditions of the regression model are satisfied and that most statistical estimation errors are caused by conditions of the regression model not being satisfied (for instance heteroscedasticity, autocorrelation, multicollinearity). Nevertheless, the method introduced selects optimal representative color samples, so that with these samples the spectral responsivity of the detector can be estimated more precisely. The selection method is self-adaptive. If the reflectance spectra of the color samples and the spectral power distribution of the source are known, the optimal number of color samples, the number of principal eigenvectors, etc., are automatically set up according to the given a priori information, and the responsivity curves are determined where, the given z target function [see Eq. (5)] is minimal. The study has shown that the estimation error of broadband characterization can be decreased significantly if an optimal set of color samples is selected using these statistical methods. If there is more a priori information (for instance the spectral power distribution of the source of the scanner) the estimation error can be further decreased.
In this article, a corresponding metadata-based stereo object tracking system using disparity-motion estimation (DME) is proposed. In the proposed method, object tracking is performed based on robust characteristics of an object, such as its motion, shape, and color. Elements of metadata and the optimal tracking method are selected at each frame. Because the characteristics of an object are affected by the camera position and by environmental conditions, a tracking method between individual cameras is selected by means of the optimal metadata. Additionally, the time-sequential disparity motion vector (DMV) can be estimated from the feature-based DME, which is extracted from the sequence of the stereo images, and metadata sequences. Using the DMV, the area where the target object is located and its location coordinate are then detected from the stereo images. In an experiment, the proposed system is shown to be robust for nonrigid objects and demonstrates its ability to track a target object adaptively with an average low error ratio of approximately 2.37% between the detected and actual location coordinates of the target object.
The title compound (quaternary ammonium salt: P-51 from Orient Chemical Industries, Ltd.) is a well-known charge-control agent (CCA) used widely in electrophotography. Structure analysis and electrical measurements have been carried out in the present investigation in order to study its high thermal stability as well as to give more experimental evidence for our charge-control mechanism that assumes an appreciable temperature increase at the "toner/carrier" interface. P-51 is found to crystallize in a space group of P21/n. Observed unexpectedly were chains of OH··O intermolecular hydrogen bonds between the OH group of one anion and the O atom of the other, leading to a polymerlike stabilization of P-51, as characterized by a high melting point. On the other hand, the electrical conductivity is shown to increase exponentially with temperature by 2 to 3 orders of magnitude in the temperature range between room temperature and 100° C. This supports out our charge-control mechanism.
The authors have recently proposed a novel charge-control mechanism that assumes an appreciable temperature increase at the "toner/carrier" interface due to the triboelectrification. In this model, the temperature dependence of the electrical conductivity of charge-control agents (CCAs) plays the crucial role. Therefore, electrical and thermal properties of azo-metal complexes used as CCAs have been investigated in order to provide additional evidence for our model as well as to study their high thermal stability. The electrical conductivity of a typical azo-Fe complex (i.e., T-77 from Hodogaya Chemical) is found to increase exponentially with temperature, and the value around 100° C is about two to three orders of magnitude higher than that at room temperature. This supports our charge-control mechanism. On the other hand, the structure analyses of T-77, sodium salt of T-77, and sodium salt of a Cr-complex revealed that there are intermolecular hydrogen-bond networks or coordination networks, in which each cation bridges neighboring anions. This type of network is found to be responsible for high thermal stability above 250° C.
The objective of this paper is to investigate the effect of toner charge on the developed toner mass in a two-component development process using the discrete element method. The behavior of toner particles having homogeneous charge (-40 to +140 μC/g) or distributed charges (which were measured in experimental work) were simulated. When toner particles had extremely large charge, they failed to adhere properly on the latent images, because only a few toners bridge the electric potential difference between the photoreceptor and the latent image. On the other hand, the adhesion force between toner and carrier was much larger than the electrostatic force under the conditions of smaller toner charge. Then, the toner particles could not fly to the latent image from the surface of carrier particles under the applied electric field. The adhered toner mass becomes large when the average charge is around 25-45 μC/g. In particular, homogeneous toner charge is better for printing with high efficiency.
Recent measurements of toner adhesion have been reported [Dejesus et al., J. Imag. Sci. Technol. 52, 010503 (2008)] in which the ground plane was separated from the charged toner particles by a thin dielectric coating of varying thickness (0.8, 4.5, 9, and 22 μm thick), which is less than and approximately equal to the diameter of the toner particles used in the experiment, 7.1 μm. It is claimed that such data can be understood only in terms of an adhesion theory based on van der Waals adhesion. It is demonstrated in this article that the data are, in fact, consistent with the Proximity Theory of toner adhesion, which is an electrostatic theory of toner adhesion that assumes that there is electrostatic adhesion at every contact point due to the discreteness of charge. Combining this result with a comparison of theories of toner adhesion with data showing the effects on toner adhesion of changing the toner charge-to-mass ratio and the extraparticulate concentration leads to the conclusion that the Proximity Force dominates toner adhesion.
The sensitivity of ultra-fine-grain (UFG) emulsions (minimum size 35 nm) was studied and was found to be proportional to the fourth and fifth powers of the grain size. The sensitivity decreased more than expected from the decrease in the absorption of light. A desensitizing factor peculiar to UFG emulsions was suggested. A large increase in the sensitivity was observed for low-intensity light exposure when a coated film was immersed in a sodium nitrite solution before exposure. Under these conditions, sensitivity became proportional to the third power of the grain size. Rehalogenation is the desensitizing factor in the UFG emulsion and the sodium nitrite solution functions as a halogen acceptor. Rehalogenation proceeds markedly in UFG emulsions because silver atoms and halogen atoms/molecules are formed nearby and could therefore react easily with each other. The sensitivity increase of the UFG emulsion due to sulfur-gold sensitization was smaller than that due to immersion in the sodium nitrite solution; both increases were additive for low-intensity exposure. In contrast, the sensitivity increases were inversely related (and not additive) for high-intensity exposure.