The Use of Frequency Properties of Image in the Classification of Transparent Polymeric Foils

The contribution treats the topic of processing the experimentally gained information on the properties of optically transparent polymeric foils. Schlieren optical system was used to examine and visualize refractive index distribution. Frequency approach enables an useful classification of different types of foils into classes. Experimental results are presented as well. Optical visualization methods are sensitive to the changes in the absorption of photons during their transmission through mechanically loaded regions of transparent materials such as optically transparent polymers and, especially, polymeric foils. The methods use the fact that the material density is a function of the refractive index of tested foil. The intensity of photon absorption changes especially in the area of deformation, which results in a change of the refraction index. The change of the refraction index can be visualized (1). And therefore the main advantage of all visualized methods is that they provide useful information for further processing after photographic or digital recording. Considering the available instrumental facilities and required sensitivity of measurement, we have chosen the schlieren method. An optical apparatus using a traditional photographic apparatus constructed after J.Bolf was modified and completed with a camera (2). The schlieren system enables to measure the amount of light deflection generated by a transparent optical phase object. When there is a disturbance in the optical path the light is deviated from its nominal course in the absence of refractive index variations. Optical disturbance in the test object will produce variations of recorded light intensity that are a measure of the deflection experienced by the light in the test object. Obtained results can be processed using methods of image processing. Results of paper (3) refer to possibilities of schlieren visualization method in the field of the diagnostics of optically transparent polymeric foils using statistical methods.