The Complex Wavelet Transform is applied to analyse thermographic data (in a similar way as the ‘classical’ Fourier transform but with the advantage of preserving time information of the signal). This information can be correlated e.g. to defect depth, allowing a quantitative evaluation of defects. Based on these results we determine the ‘phase velocity’ of thermal diffusion waves by application of Complex Wavelets (dispersion relation).

Blue line: theoretical dispersion curve; red markers: results derived from Complex Wavelet Analysis
Time-Frequency analysis: phase contrast images which indicate different “frequency”-content at various subsurface defect depths

Image Processing and Computer Vision in Thermography

The acquisition system represents a combination of a thermal imaging system and a 3D surface measurement. It will link the depth information and the color image of a low-cost sensor with the information of a thermography camera to support and extend the non-destrutive testing method.

Figure: Measurement setup
Figure : Back-transformation of the IR image
Results of the projective image rectification