Algiment Aleksa

Image hiding in time-averaged deformable moiré gratings

A new image hiding technique based on time-averaged moire fringes is proposed in this paper. The secret image is embedded into a single cover image which is constructed as a deformable stochastic moire grating. The secret image is leaked in the form of a time-averaged fringe when the cover image is deformed according to a predetermined periodic law of motion. The proposed image hiding approach opens new possibilities for the optical control of vibrating deformable structures.

Near-Optimal Moire Grating for Chaotic Dynamic Visual Cryptography

Image hiding based on chaotic oscillations and near-optimal moire gratings is presented in this paper. The secret image is embedded into a single cover image. The encrypted secret image appears in a form of time-averaged moire fringes when the cover image is oscillated in a predefined direction, according to a chaotic law of motion. The criterion of the optimality of a moire grating is based on the absolute difference between the standard deviation of time-averaged images of near-optimal moire gratings in the background and in the zones associated to the secret image. Genetic algorithms are used for the identification of a nearoptimal set of moire gratings for image hiding applications. Numerical experiments are used to illustrate the functionality of the method.

Visual Cryptography Based on Optical Image Projection

A visual cryptography scheme based on optical image projection is proposed in this paper. Initially the secret image is split into two shares. Then, such digital images are constructed in share’s planes that their projections in the projection screen would correspond to each of the appropriate shares. Geometrical parameters describing the location of shares’ planes and focus points of projectors are additional security parameters of the encoded image. Direct overlapping of the reconstructed shares does not leak any information on the encrypted image. The original image can be interpreted by a naked eye when appropriate projectors are placed at predefined locations of the geometrical setup.

Adaptive conjugate smoothing of digital images using photo-elastic coatings

The methods for investigation of the element under vibration of smart structures is proposed. The first eigenmodes of bending vibrations of a circular pezoceramic plate with fixed internal radius are determined and it is assumed that vibrations take place according to the eigenmode. The stresses in the coating are calculated by using the procedure of conjugate approximation. Then the relative error norms for the finite elements are determined. They are used in the proposed procedure of adaptive conjugate approximation with smoothing. From the presented results it is shown that the adaptively smoothed image is advantageous when compared with the conventionally smoothed images. Thus the proposed procedure of adaptive conjugate smoothing builds the ground for realistic reconstruction of experimentally produced photo-elastic fringes and effective application of digitally reconstructed images in hybrid numerical - experimental procedures. Analysis is performed using a plate bending element assuming that a coating has no effect to the motion of a plate. Relative error norms for the finite elements are determined. They are used in the procedure of adaptive conjugate approximation with smoothing.

Hybrid Numerical-Experimental Technique of Transverse Vibration of Fluid in Tube

The object of our paper is the formation of optical fringes in a time average hologram produced by vibrating fluid in axi-symmetric tube. Fluid vibrations in axi-symmetric geometry according to the first harmonics are analyzed. This problem has a practical application in the analysis of transverse vibrations of fluid in an axi-symmetric pipe. The numerical model is developed using finite element techniques in axi-symmetric geometry. Irrotational motions of ideal compressible fluid are analyzed. Finite element model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the harmonic variation of the volumetric strain is calculated exploiting conjugate approximation techniques. Obtained volumetric strains are used for the numerical construction of interference pattern of the vibrating fluid. For this purpose the Abel transform which is usually exploited in axi-symmetric problems is generalized for the problems with the periodic variation of displacements. The obtained interference patterns are used in hybrid experimental – numerical procedures and help to interpret experimental results.Copyright