When using the interferometric techniques, the optical path changes induce the wavefront deformations that in turn cause
the appearance of fringes. One general characteristic of such an approach is the measurement sensitivity. The actual
sensitivity of a holographic interferometer is a function of, on one hand, the parameters of the measuring system (such as
the wavelength of the light used) and, on the other hand, the environmental conditions in which the measurements are
being made. The later depend predominately on statistical fluctuations inherent to the particular laboratory conditions. In
many applications the sensitivity is near the limits of the deformation detectability. In such cases, it is of vital interest to
increase the number of interferometric fringes thus improving the quality of the acquired data. In this paper, we give an
overview of the sensitivity increase through various experimental and numerical approaches. We also present a new
numerical iterative method in which every cycle doubles the number of interferometric fringes. The method has shown to
be especially useful in applications with sub-wavelength wavefront deformations.
Image moments analysis is a very useful tool which allows image description invariant to translation and rotation, scale
change and some types of image distortions. The aim of this work was development of simple method for fast and
reliable classification of characters by using Hu's and affine moment invariants. Measure of Eucleidean distance was
used as a discrimination feature with statistical parameters estimated. The method was tested in classification of Times
New Roman font letters as well as sets of the handwritten characters. It is shown that using all Hu's and three affine
invariants as discrimination set improves recognition rate by 30%.
In digital holography, primary holographic fringes are recorded using a matricial CCD sensor. Because of the low spatial
resolution of currently available CCD arrays, the angle between the reference and object beams must be limited to a few
degrees. Namely, due to the digitization involved, the Shannon's criterion imposes that the Nyquist sampling frequency
be at least twice the highest signal frequency. This means that, in the case of the recording of an interference fringe
pattern by a CCD sensor, the inter-fringe distance must be larger than twice the pixel period. This in turn limits the angle
between the object and the reference beams. If this angle, in a practical holographic interferometry measuring setup,
cannot be limited to the required value, aliasing will occur in the reconstructed image. In this work, we demonstrate that
the low spatial frequency metrology data could nevertheless be efficiently extracted by careful choice of twofold, and
even threefold, undersampling of the object field. By combining the time-averaged recording with subtraction digital
holography method, we present results for a loudspeaker membrane interferometric study obtained under strong aliasing
conditions. High-contrast fringes, as a consequence of the vibration modes of the membrane, are obtained.
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