A phase φ of specklegram is a function both of an optical path difference L and wavelength λ . From this function, the optical path difference L, which is directly used to calculate a shape of an object, can be given as a function of d φ/d λ. In the proposed technique, a widely used laser diode is adopted as a wavelength-changeable light source, and its wavelength λ is scanned slowly within 0.25 nm by using current injection control of the diode. From specklegrams captured during wavelength scanning, changing amounts of φ are extracted on individual pixels with a modified phase shifting technique. Since a scanning range is very short, it is difficult to measure a changing amount of λ along each specklegram capturing. Then a reference height step is also inserted in a vision of CCD camera and changing amounts of φ are measured both on the reference step and the object. From the ratio of the total changing amounts of φ, the shape of the object is calculated. Experiments are carried out to confirm the validity of the method.
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