Non - standard methods of data processing in thermographic non - destructive testing of light ballistic protections

IR thermography is a technique used to detection, registration, processing and visualization of invisible infrared radiation emitted by a tested object. Image (thermogram) is a result of this technique and it maps the distribution of temperature on surface of tested object. The image after entering in digital form into the computer needs to get certain treatments on it to separate information of interest through its processing. A characteristic feature of image processing is that the image exists at either the input or output of information processing. The output images should be free from disturbances and they should have distinctly separated features of interest. After the initial processing of the image, the next steps of its analysis follow. In the result of the analysis quantitative data is received that describes some determined features of the image and the complete image comprising hundreds details is substituted by a limited population of separated features. This population can be used effectively by different recognition methods and algorithms. In thermographic investigations, situations occur when treatment of images applied in standard software is not fully efficient to obtain information, which is "camouflaged" in taken thermogram. Such event takes place particularly in the case of looking for thermal "disturbances" onto the surface, which are caused by the undersurface defects. Such situation needs the application of special transformations carried out on thermograms. These transformations lead to selecting from all information included in the thermogram only such part of it that is essential from the point of view of conducted tests. In such case it is required the usage of advanced data processing techniques like thermal tomography, one-dimensional Fourier analysis, principle component analysis (PCA), an approximation by means of polynominals, wavelet analysis, neural network and reconstruction of thermographic signal. In this paper, these methods are described and examples of their use in tests of light ballistic protections are presented.