Computer_Processing_and_Analysis_of_Holographic_Interferograms
3.6.2 Computer Processing and Analysis of Holographic Interferograms
The interpretation of interferograms obtained from interferometric measurements is a slow, laborious and time-consuming process, therefore, it is advantageous to use computing technology and replace the whole process by automatic computing. This process also increases the precision of computing and partially eliminates subjective influences in the process of analysis.
During the analysis it is necessary to identify the objects in the image which comes under the field of computer vision and artificial intelligence (Šipoš, Csongrády, 2006). The final outputs of interferometric measurements are sometimes different, which then puts high demands on the analysing software. To interprete the interferograms, a lot of special-purpose programs to our disposal. They are developed in research departments for their own actual applications (for example the software for analysis of the holographic interferograms of temperature fields ARDEL (authors: Elena Pivarčiová, Peter Olšiak), the software for analysis of holographic interferograms VIBRA (authors: Jozef Černecký, Jozef Siláči) both developed at the Technical University in Zvolen, or the software for analysis of interferograms INTERFER (Pavelek et al, 2001) developed at Technical University in Brno. Besides this we can also find commercial products that enable to execute the process of analysis of interferograms more or less effectively.
From the commercial software for holographic interferogram analysis the software Corel Draw by Corel Company is suitable that serves not only for modification of image quality, but also for example, for determination of interference fringe course. Such analysis is, however, inaccurate and non-effective.
One of the most complicated steps in the process of computer interferogram analysis is detection of the interference fringe positions and determination of the interference order. These procedures are followed by refractive index determination itself and calculation of studied parameters.
The programs for analysis and interpretation of holographic interferograms help obtain the necessary input data for mathematical formulae and thus calculate the particular parameters. By drawing of the obtained values to the graphs we get the time or other dependencies.
From the viewpoint of analysis of holographic interferograms the software mostly contains the following important functions:
- setting input parameters,
- adjustment of brightness and contrasts,
- corrections of dark and bright parts,
- measurement and calibration,
- sections of the maximum and minimum intensities of interference fringe blackening,
- calculation of studied parameters (for example temperature, concentration, amplitude of mechanical oscillations),
- display of graphical relations.
Functions in the programs for holographic interferogram analysis can be divided into two basic fields (Pavelek et al, 2001):
- The first field is aimed at image modifications of holographic interferograms obtained by CCD camera or by scanning from photographs, improvement of recording quality of individual holograms, i.e. increase of brightness, contrast, elimination of noise, etc.
- The second field is aimed at obtaining of quantitative data from interference images and their utilisation for calculations and graphical display (determination of interference order, determination of interference fringe minimum positions, calculation of studied parameters for individual areas on dark fringes, drawing of graphs representing the whole studied profile).
