Moiré topography, sampling theory, and charged-coupled devices.

Area of Science:

• Optics and Photonics
• Metrology
• Image Processing

Background:

• Classical moiré contouring methods suffer from unwanted sum, shadow, and grid terms.
• Spurious moiré fringes often arise from higher harmonics in traditional techniques.
• A reference grid is typically required for conventional projection-type moiré contouring.

Purpose of the Study:

• To develop a reference-grid-free projection-type moiré contouring technique.
• To eliminate unwanted terms and spurious fringes in moiré contouring.
• To enhance the visibility and sensitivity of moiré contour fringes.

Main Methods:

• Undersampling projected cosine fringes using a charged-coupled-device (CCD) detector array.
• Eliminating sum, shadow, and grid terms by exploiting aliasing effects.
• Applying higher-order aliasing for increased measurement sensitivity.

Main Results:

• A high-visibility sampled version of moiré difference contour fringes is produced.
• Elimination of unwanted classical moiré terms and spurious higher-harmonic fringes.
• Demonstration of increased sensitivity through higher-order aliasing.

Conclusions:

• The proposed technique offers a simplified and more robust approach to moiré contouring.
• The method effectively overcomes limitations of classical moiré techniques.
• The findings extend the Whittaker-Shannon sampling theorem to moiré applications.