Optical surface flatness recognized by discrete wavelet transform and grey level co-occurrence matrix

Optical surface flatness evaluated by the discrete wavelet transform and grey level co-occurrence matrix (GLCM) is presented. A PC-based measurement system can be used to detect the interference fringe of an optical reflective surface captured from a Twyman - Green interferometer. Wavelet analysis and GLCM process associated with the entropy criterion appears to be a good method for recognizing automatically the flatness of the optical surfaces. Three-dimensional plots of the GLCM and surface deformation contour for various captured interference patterns of glass substrates have been compared and discussed. The parameter of entropy has been calculated from the GLCM and then can be used as an indicator for optical surface characteristics.