Profiling of objects with height steps by wavelet analysis of shadow moiré fringes
A temporal wavelet analysis algorithm is proposed for shadow-moiré-based three-dimensional surface profiling on objects having discontinuous height steps. A grating is positioned close to an object, and its shadow is observed through the grating. The moiré fringe patter...
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| Main Authors: | , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | English |
| Published: |
2010
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| Subjects: | |
| Online Access: | https://hdl.handle.net/10356/91921 http://hdl.handle.net/10220/6464 |
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| Institution: | Nanyang Technological University |
| Language: | English |
| Summary: | A temporal wavelet analysis algorithm is proposed for shadow-moiré-based three-dimensional surface
profiling on objects having discontinuous height steps. A grating is positioned close to an object, and its
shadow is observed through the grating. The moiré fringe patterns vary when the grating is in-plane
rotating. A series of fringe patterns are captured by a CCD camera at different rotating angles. Phase
values are evaluated point by point with the continuous wavelet transform. From the phase values of each
point on the object, the distance between the object and the grating can be retrieved. The surface profile
is obtained without temporal or spatial phase unwrapping. This technique is applicable to objects with
discontinuous height steps, which are impossible to measure with conventional shadow moiré topography.
Two specimens are tested to demonstrate the validity of the method: One is an object with a height
step of 1.6 mm, and another is a small coin with unevenness of less than 0.2 mm. The experimental
results are compared with test results by use of the mechanical stylus method. |
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