Fourier transform profilometry based on defocusing

Sinusoidal fringe patterns are popularly used in conventional Fourier transform profilometry. There are numerous harmonics in the Fourier spectrum, so as to avoid spectrum overlapping; the maximum range of measurement is limited. The present paper studies FTP based on properly defocusing a binary square wave. There are only odd harmonics in the Fourier spectrum of a binary square wave, and the maximum range of measurement is expanded 1.5 times. Defocusing has a low-pass filtering effect and higher-order odd harmonics are suppressed. Therefore, the fundamental spectrum is easy to extract. The proposed method overcomes the filtering problem of conventional FTP. Measurement experiments show that the proposed method has a good measurement result and the measurement accuracy is improved.

► We proposed the Fourier transform profilometry based on defocusing. ► Ideal sinusoidal fringe pattern was generated by properly defocusing a binary square wave. ► The proposed method overcomes the filtering problem of the traditional FTP. ► The maximum range of measurement is expanded 1.5 times. ► Measurement experiments show that the method has good measurement results and the measurement accuracy is improved.