Optical measurement techniques for structures and systems pages:95-102
4th International Conference on Optical Measurement Techniques for Structures and Systems (OPTIMESS2009) Antwerp, BELGIUM, MAY 25-26, 2009
The use of liquid crystal grid projection for profilometry gains in popularity because of its flexibility and ease-of-use. Liquid crystal projection devices facilitate easy adoption of the grid pitch (and thus sensitivity) and translation of the relative grid position. However, all current methods combine this type of structured light projection either with one-shot Fourier analysis, or with digital demodulation to achieve moire fringes in the computer. The advantage is that a fast measurement speed is achieved as only one image needs to be recorded. The major disadvantage is that the resolution is compromised. Fourier transform profilometry is based on frequency domain band filtering, thus the image content is changed. In case of digital demodulation, the projected grid lines have to be resolved thus high spatial resolution is required of the recording device. Furthermore, if no phase-stepping algorithm is used in moire techniques, grid noise needs to be removed by low-pass filtering.