Digital Image Processing for Optical Metrology
The basic principle of modern optical methods in experimental solid mechanics such as holographic interferometry, speckle metrology, fringe projection, and moiré techniques consists either of a specific structuring of the illumination of the object by inc
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Digital Image
19. Digital Image Processing for Optical Metrology
The basic principle of modern optical methods in experimental solid mechanics such as holographic interferometry, speckle metrology, fringe projection, and moiré techniques consists either of a specific structuring of the illumination of the object by incoherent projection of fringe patterns onto the surface under test or by coherent superposition (interference) of light fields representing different states of the object. A common property of the applied methods is that they produce fringe patterns as output. In these intensity fluctuations the quantities of interest such as coordinates, displacements, refractive index, and others are coded in the scale of the fringe period. Consequently one main task to be solved in processing can be defined as the conversion of the fringe pattern into a continuous phase map taking into account the quasisinusoidal character of the intensity distribution. The chapter starts with a discussion of some image processing basics. After that the main techniques for the quantitative evaluation of optical metrology data are presented. Here we start with the physical modeling of the image content and complete the chapter with a short introduction to the basics of digital holography, which is becoming increasingly important for optical imaging and metrology. Section 19.2 deals with the postprocessing of fringe patterns and phase distributions. Here the unwrapping and absolute phase problems as well as the transformation of phase
Look but don’t touch is an important rule for modern measurement and testing systems in industrial quality control. What is required are measurement and inspection techniques that are very fast, robust, and relatively low cost compared to the products being investigated. Modern full-field optical methods such as holographic interferometry, speckle metrology, moiré, and fringe
19.1 Basics of Digital Image Processing.......... 483 19.1.1 Components and Processing Steps .. 483 19.1.2 Basic Methods of Digital Image Processing............ 484 19.2 Techniques for the Quantitative Evaluation of Image Data in Optical Metrology 19.2.1 Intensity Models in Optical Metrology ..................... 19.2.2 Modeling of the Image Formation Process in Holographic Interferometry ....... 19.2.3 Computer Simulation of Holographic Fringe Patterns....... 19.2.4 Techniques for the Digital Reconstruction of Phase Distributions from Fringe Patterns .. 19.3 Techniques for the Qualitative Evaluation of Image Data in Optical Metrology ........ 19.3.1 The Technology of Optical Nondestructive Testing (ONDT) ........ 19.3.2 Direct and Indirect Problems ......... 19.3.3 Fault Detection in HNDT Using an Active Recognition Strategy .......
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References .................................................. 557 data into displacement values are addressed. Because image processing plays an important role in optical nondestructive testing, finally in Sect. 19.3 some modern approaches for automatic fault
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