Application of two-dimensional wavelet transform to hologram analysis: visualization of glass fibers in a turbulent flame
Samir Belaïd · Optical Engineering · 1997
In different fiberization processes, glass fibers are drawn out in a turbulent flame. High-speed in-line holography is applied to visualize glass fibers. However, the random spatial distribution of temperature in- duces strong local variations of the refraction index. Consequently, the reconstructed images are altered. The direct analysis of the diffraction patterns recorded by the holographic plate can offer an alternative solu- tion. The diffraction process can be interpreted as a convolution with a wavelet family of functions. The scale parameter a is related to the dis- tance between the object and the plane of observation. The 3-D location of a fiber element and its orientationu are estimated by searching for the parameters a and u, which yield a maximum modulus of the wavelet transform. The results are compared with those obtained from a conven- tional optical reconstruction. The application of the wavelet transform improves the SNR in the image and enables the 3-D fiber location to be determined more accurately (650 mm for the axial coordinate estima- tion). © 1997 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(97)02107-7)