A Probabilistic Approach for Spatio-Temporal Phase Unwrapping in Multi-Frequency Phase-Shift Coding

Multi-frequency techniques with temporally encoded pattern sequences are used in phase-measuring methods of 3D optical metrology to suppress phase noise but lead to ambiguities that can only be resolved by phase unwrapping. However, classical phase unwrapping methods do not use all the information to unwrap all measurements simultaneously and do not consider the periodicity of the phase, which can lead to errors. We present an approach that optimally reconstructs the phase on a pixel-by-pixel basis using a probabilistic modeling approach. The individual phase measurements are modeled using circular probability densities. Maximizing the compound density of all measurements yields the optimal decoding. Since the entire information of all phase measurements is simultaneously used and the wrapping of the phases is implicitly compensated, the reliability can be greatly increased. In addition, a spatio-temporal phase unwrapping is introduced by a probabilistic modeling of the local pixel neighborhoods. This leads to even higher robustness against noise than the conventional methods and thus to better measurement results

Vision Sensors and Edge Detection

Vision Sensors and Edge Detection book reflects a selection of recent developments within the area of vision sensors and edge detection. There are two sections in this book. The first section presents vision sensors with applications to panoramic vision sensors, wireless vision sensors, and automated vision sensor inspection, and the second one shows image processing techniques, such as, image measurements, image transformations, filtering, and parallel computing

A Multiple Height Transfer Interferometric Technique and Its Applications

Absolute distance interferometric metrology is one of the most useful techniques for dimensional measurements. Without movement, measurements can be made without ambiguity, by using either one or several synthetic wavelengths. Synthetic wavelengths result from the beating of two or more wavelengths in multiple-wavelength interferometry (MWI), or a wavelength scan in wavelength-scanning interferometry (WSI). However, conventional MWI requires accurate wavelength information for a large measurement range, while WSI is limited by a mode-hop-free laser tuning range. A multiple height-transfer interferometric technique (MHTIT) is proposed based on concepts from both MWI and WSI. Using multiple accurately calibrated reference heights, this technique preserves the capabilities to determine the optical path difference (OPD) unambiguously without accurate wavelength information, and yet does not require the laser to be continuously tuned. A multiple reference height calibration artifact is proposed and installed in a holographic measuring system. Applying the MHTIT with the calibration artifact, the metrology system measurement range is increased from 5 mm to over 100 mm without accurate wavelength information. Three-dimensional images of discontinuous surface heights obtained from a variety of automotive parts demonstrate the applicability of the MHTIT in workshop environments. We present an uncertainty analysis, analyzing the primary sources of uncertainties that limit the performance of the MHTIT and discuss how errors can be minimized. The measurement uncertainty is experimentally demonstrated to be about 0.3 µm for 50.8 mm at a confidence level of 95% for two discontinuous surfaces under lab environments. Another application of the MHTIT for measuring the thickness of a transparent plate is investigated. WSI can measure the thickness of transparent plates by differentiating OPDs from multiple surface interferences in the Fourier domain. However, nonlinear laser tuning deviates the measurement result from the correct value. We propose a wavelength-stepping method for application to thickness measurements of transparent plates. Systematic errors caused by nonlinearity in laser source stepping are reduced with accurate synthetic wavelengths measured by the MHTIT. A 10-µm step height standard etched on a 25 mm × 25 mm × 3 mm quartz block is measured to demonstrate the proposed method with sub-micron accuracy.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91426/1/haoyu_1.pd

Three-dimensional geometry characterization using structured light fields

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200