Journal:Informatica
Volume 14, Issue 4 (2003), pp. 431–444
Abstract
In this paper, we shall propose a new method for the copyright protection of digital images. To embed the watermark, our new method partitions the original image into blocks and uses the PCA function to project these blocks onto a linear subspace. There is a watermark table, which is computed from projection points, kept in our new method. When extracting a watermark, our method projects the blocks of the modified image by using the PCA function. Both the newly projected points and the watermark table are used to reconstruct the watermark. In our experiments, we have tested our scheme to see how it works on original images modified by JPEG lossy compression, blurring, cropping, rotating and sharpening, and the experimental results show that our method is very robust and indeed workable.
Journal:Informatica
Volume 14, Issue 4 (2003), pp. 421–430
Abstract
The discrete Fourier transform (DFT) is used for determining the coefficients of a transfer function for n‐order singular linear systems, Ex(n)=Σi=1nAix(n−1)+Bu, where E may be singular. The algorithm is straight forward and easily can be implemented. Three step‐by‐step examples illustrating the application of the algorithm are presented.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 403–416
Abstract
The results of experimental testing of balanced random interval arithmetic with typical mathematical test functions and practical problem are presented and discussed. The possibility of evaluation ranges of functions using balanced random interval arithmetic is investigated. The influence of the predefined probabilities of standard and inner interval operations to the ranges of functions is experimentally investigated.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 393–402
Abstract
In 2001, Hsu et al. proposed a non‐repudiable threshold proxy signature with known signers. In their scheme, the proxy group cannot deny having signed the proxy signature if they did. However, Hsu et al.'s scheme is vulnerable to some attacks. A malicious original signer or malicious proxy signer can impersonate some other proxy signers to generate proxy signatures. In this article, we shall present our cryptanalysis of the Hsu et al.'s scheme. After that, we shall propose a new threshold proxy signature that can overcome the weaknesses.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 375–392
Abstract
The study of 3‐D indoor accurate scenery modeling is an active research area. The produced model can be used in a number of virtual reality applications, in digital documentation of monuments and sites, and so on. Digital photogrammetry and CAD technology have to play a vital role in this field. Photogrammetry's contribution is mainly on data acquisition from imagery, whilst the necessary image knowledge is derived from geometry and topology of image contents. While the first is traditionally used, the second one only lately is been tackled.
In this paper, a technique is presented for modeling of indoor scenery based on digital images, photo‐derived intra‐component, geometric and topologic constraints, object‐oriented graphic databases containing 3‐D parametric models and a rough (generic) CAD model. Optionally, an absolute reference system could be applied, but for VR applications a relative reference system is adequate.
The original contribution with respect to related works in this field is mainly the introduction of Display File, Segment Table, Scene Parts Table and Constraint Table structures which deal with the constraints and “drive” a modeling control program called the Constraint Modeler. The use of these structures leads in a direct, global, portable, and semi‐automated technique for 3‐D indoor modeling. Experimental results from simulated images are presented, and the robustness of the technique is discussed.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 357–374
Abstract
This paper deals with the absolute stability of single‐input single‐output time‐delay systems with, in general, a finite number of non commensurate constant internal point delays for any nonlinearity satisfying a time positivity inequality related to the first and third quadrants. The results are obtained based on Lyapunov's stability analysis via appropriate Lyapunov's functions and the related stability study is performed to obtain both delay independent and delay dependent results.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 349–356
Abstract
Recently iterative procedure for the restoration of speech signals when prosodic elements: stress and accent, of comparatively long duration are missing was developed. Alternatively, it could be cast in a signal generation framework. Basing on that view the paper presents the efficient implementation scheme for the restoration of voiced speech signals. It enjoys parallel order of multirate processing utilizing interpolation and decimation filters parameterized by specific to problem coefficients. Presented simulation results confirm the feasibility of developed implementation.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 337–348
Abstract
In the paper the sequential nonlinear mapping has been investigated in order to reveal its features. The method was investigated by a plenty of experiments using various sorts of data. For illustrations there are presented results using “marginal” data: the first data gives the smallest mapping error, and the other data gives the largest one. The sequential nonlinear mapping has been investigated according ability to differ the data groups (clustering) when at the beginning the number of groups is taken to be less than really exists. It was showed that the sequential nonlinear mapping differs the groups of data well even though the number of them is taken to be less by one than really exists. The experiments show that the factor for correction co‐ordinates on the plane for the sequential nonlinear mapping can be taken in the range from 0.25 to 0.75. Mapping errors depend on both the sort of initial conditions and the nature of data.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 323–336
Abstract
This paper analyses coupled control of a nonlinear, time‐varying plant. Uncoupled and coupled direct adaptive controllers, based on fuzzy logics, are synthesized to control the water level and the air pressure in a closed tank. The satisfactory efficiency of the controllers is experimentally demonstrated running the plant under the different working conditions. Coupled fuzzy controllers are compared with the uncoupled fuzzy controllers.
Journal:Informatica
Volume 14, Issue 3 (2003), pp. 295–322
Abstract
This paper considers an information aspect of the problem of the joint filtering and generalized extrapolation, when the output of observation channels (data transmission) is the realizations set of the processes with continuous and discrete time, which depend on both the current and the past values of unobservable process (useful signal). The relations defining time evolution of Shannon information are obtained. The particular problems of the memory channels information efficiency and optimal transmission of stochastic processes, with applying the general results are considered.