This paper describes two techniques to accelerate the Fourier fringe analysis technique. The two ... more This paper describes two techniques to accelerate the Fourier fringe analysis technique. The two 2-D Fourier transforms required for the technique are usually a bottleneck for good-quality images in which unwrapping is straight forward. Automation of the filtering operation is an operation that very often requires user interaction when two peaks at similar frequencies are present in the Fourier transform. The techniques presented in this paper attempt to solve these issues. The first technique proposes a reduction in the number of pixels calculated by the Fourier transform. The second, automates the filtering operation to avoid user interaction.
Proceedings of Spie the International Society For Optical Engineering, 2002
This paper describes the development of an optical method of phase measurement and further three-... more This paper describes the development of an optical method of phase measurement and further three-dimensional surface reconstruction using colored structured light. The paper investigates a new method for improving the measurement of three-dimensional shapes by using color information of the measured scene as an additional parameter. The general problems of the most widely used algorithms (phase shifting profilometry and Fourier fringe analysis) are that phase maps produced by these methods are wrapped, in some cases the acquired fringe pattern does not fill the field of view, there may be spatially isolated areas and there is often invalid and/or noisy data. This paper aims to demonstrate a new method for three- dimensional surface reconstruction using colored fringe patterns. The proposed technique uses colored fringe patterns, which are projected at different angles onto the measured scene. Shortcomings, which arise using standard methods, can be overcome using a color multichannel Fourier fringe technique.
In automotive and glass making industries, there is a need for accurately measuring the 3D shapes... more In automotive and glass making industries, there is a need for accurately measuring the 3D shapes of reflective surfaces to speed up and ensure product development and manufacturing quality by using non-contact techniques. This paper describes a technique for the measurement of non-full-field reflective surfaces of automotive glass by using a fringe reflection technique. Physical properties of the measurement surfaces do not allow us to apply optical geometries used in existing techniques for surface measurement based upon direct fringe pattern illumination. However, this property of surface reflectivity can be used to implement similar ideas from existing techniques in a new improved method. In other words, the reflective surface can be used as a mirror to reflect illuminated fringe patterns onto a screen behind. It has been found that in the case of implementing the reflective fringe technique, the phase-shift distribution depends not only on the height of the object but also on the slope at each measurement point. This requires the solving of differential equations to find the surface slope and height distributions in the x and y directions and development of the additional height reconstruction algorithms. The main focus has been made on developing a mathematical model of the optical sub-system and discussing ways for its practical implementation including calibration procedures. A number of implemented image processing algorithms for system calibration and data analysis are discussed and two experimental results are given for automotive glass surfaces with different shapes and defects. The proposed technique showed the ability to provide accurate non-destructive measurement of 3D shapes of the reflective automotive glass surfaces and can be used as a key element for a glass shape quality control system on-line or in a laboratory environment.
ABSTRACT The rapid, ultra-precision measurement of the shape of engineering components is becomin... more ABSTRACT The rapid, ultra-precision measurement of the shape of engineering components is becominc; a major requirement for today's quality conscious industries. This paper presents a technique for the reconstruction of surfaces underlying optically generated contour maps. The technique views the map as a constant spacing straight fringe pattern phase modulated by the underlying surface shape. The Fourier transform is used as a means of demodulating the pattern producing a 2π wrapped phase distribution. The conversion of this phase information to a range map is performed and so the surface is reconstructed. Methods for the quantitative analysis of the resulting map are discussed, including techniques based on differential geometric analysis, to yield data on items such as the first and second fundamental forms and hence functionally important criteria such as point surface principal curvature etc. The relationship which exists between the accuracy of these measurements and the nature of the demodulation filtering performed in the Fourier domain is briefly discussed.
ABSTRACT Recent work has shown the importance of the fast Fourier transform (FFT) in the automati... more ABSTRACT Recent work has shown the importance of the fast Fourier transform (FFT) in the automatic analysis of fringe patterns. Three problem areas are encountered when the FFT is used as an analysis tool in this fashion, namely, aliasing, the picket fence effect and leakage. The authors consider leakage to be by far the biggest problem in this application. The paper defines what causes leakage and suggests how leakage may be controlled using data weighting functions. Comparative results obtained using a variety of functions are presented.
ABSTRACT This paper describes the development of an optical method of phase measurement and furth... more ABSTRACT This paper describes the development of an optical method of phase measurement and further three-dimensional surface reconstruction using colored structured light. The paper investigates a new method for improving the measurement of three-dimensional shapes by using color information of the measured scene as an additional parameter. The general problems of the most widely used algorithms (phase shifting profilometry and Fourier fringe analysis) are that phase maps produced by these methods are wrapped, in some cases the acquired fringe pattern does not fill the field of view, there may be spatially isolated areas and there is often invalid and/or noisy data. This paper aims to demonstrate a new method for three- dimensional surface reconstruction using colored fringe patterns. The proposed technique uses colored fringe patterns, which are projected at different angles onto the measured scene. Shortcomings, which arise using standard methods, can be overcome using a color multichannel Fourier fringe technique.
Microsystems Engineering: Metrology and Inspection III, 2003
ABSTRACT In high speed grinding research it is required to measure temperature within the workpie... more ABSTRACT In high speed grinding research it is required to measure temperature within the workpiece. Present techniques are thermocouple based, and often suffer from excessive electrical noise on the signal. This paper presents a number of novel fiber optic sensing devices that overcome this limitation and also offer greater performance. Optical fiber devices are simpler to place in situ prior to the machining tests and they offer faster response and greater sensitivity than was previously possible. Results are presented from machining tests and the new devices are compared with each other and previous techniques.
Three-Dimensional Imaging and Laser-based Systems for Metrology and Inspection III, 1997
ABSTRACT This paper describes a method for the treatment of non- fullfield images by means of the... more ABSTRACT This paper describes a method for the treatment of non- fullfield images by means of the Fourier fringe analysis technique. With this type of images, the borders of the data appear as high frequencies in the Fourier domain while the areas with the same intensity (background) appear as low frequency components. This information interferes with the signal peak and leads to large errors in the phase result throughout the image. This paper proposes a two dimensional mapping operation to overcome the problem. By a mapping of the original image into a square, the image can be processed by conventional FFA. The final result is obtained by the application of the inverse of the mapping function.
This paper proposes the use of a modified Morlet wavelet in order to demodulate fringe patterns i... more This paper proposes the use of a modified Morlet wavelet in order to demodulate fringe patterns in conjunction with the one-dimensional continuous wavelet transform (1D-CWT). Our investigations demonstrate that the modified Morlet wavelet produces better results compared to the conventional Morlet wavelet when used in fringe pattern analysis. This novel technique offers superior performance in analysing fringe patterns from objects that exhibit large height variations. This new technique has been used in conjunction with the direct maximum ridge extraction algorithm and an improvement in performance is observed. The algorithm has been tested using both computer-generated and real fringe patterns; and was found to be suitable for fringe pattern demodulation and robust in operation.
A prospective new optical non-contact method for the assessment of surface texture is presented. ... more A prospective new optical non-contact method for the assessment of surface texture is presented. A dual-beam laser Doppler anemometer is employed and the parameter "fringe visibility" is used as an indication of surface asperity size and geometry. The method was tested on specimens resulting from three different manufacturing processes, i.e. grinding, milling and turning, which possessed a range of R, values from 0.025 to 50 pm. Both static and dynamic measurement configurations were examined.
Over the years two-dimensional Fourier Fringe Analysis (2D-FFA) has demonstrated both its capabil... more Over the years two-dimensional Fourier Fringe Analysis (2D-FFA) has demonstrated both its capability and its relative robustness in analysing fringe patterns within a short time-frame from static objects. Nowadays, there is an increasing demand to measure dynamic objects. Today 2D-FFA is seen as a fast and flexible method of processing fringe patterns for dynamic objects. But it is still inherently a 2D approach, i.e. it deals with three-dimensional data (video sequences) on an individual 2D frame-by-frame basis. In this paper, a novel three-dimensional Fourier Fringe Analysis (3D-FFA) algorithm is proposed to demodulate fringe pattern sequences taken from dynamic objects. This technique processes the stack of fringe patterns as a single 3D volume, not as a set of individual 2D frames that are each processed in isolation. The proposed algorithm has been evaluated on both computer simulated and real dynamic objects. Results show that the proposed technique is able to demodulate fringe pattern volumes successfully. r
ABSTRACT A new phase-unwrapping algorithm for the phase map containing discontinuities by the use... more ABSTRACT A new phase-unwrapping algorithm for the phase map containing discontinuities by the use of a system with crossed grating is described in this paper. A crossed grating is projected onto the object in the usual way, the deformed grating image acquired is Fourier transformed and the frequency spectra for the individual gratings are separated. Using both phase distributions which have different sensitivities, the correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of a three-dimensional object with height steps are presented.
This paper describes two techniques to accelerate the Fourier fringe analysis technique. The two ... more This paper describes two techniques to accelerate the Fourier fringe analysis technique. The two 2-D Fourier transforms required for the technique are usually a bottleneck for good-quality images in which unwrapping is straight forward. Automation of the filtering operation is an operation that very often requires user interaction when two peaks at similar frequencies are present in the Fourier transform. The techniques presented in this paper attempt to solve these issues. The first technique proposes a reduction in the number of pixels calculated by the Fourier transform. The second, automates the filtering operation to avoid user interaction.
Proceedings of Spie the International Society For Optical Engineering, 2002
This paper describes the development of an optical method of phase measurement and further three-... more This paper describes the development of an optical method of phase measurement and further three-dimensional surface reconstruction using colored structured light. The paper investigates a new method for improving the measurement of three-dimensional shapes by using color information of the measured scene as an additional parameter. The general problems of the most widely used algorithms (phase shifting profilometry and Fourier fringe analysis) are that phase maps produced by these methods are wrapped, in some cases the acquired fringe pattern does not fill the field of view, there may be spatially isolated areas and there is often invalid and/or noisy data. This paper aims to demonstrate a new method for three- dimensional surface reconstruction using colored fringe patterns. The proposed technique uses colored fringe patterns, which are projected at different angles onto the measured scene. Shortcomings, which arise using standard methods, can be overcome using a color multichannel Fourier fringe technique.
In automotive and glass making industries, there is a need for accurately measuring the 3D shapes... more In automotive and glass making industries, there is a need for accurately measuring the 3D shapes of reflective surfaces to speed up and ensure product development and manufacturing quality by using non-contact techniques. This paper describes a technique for the measurement of non-full-field reflective surfaces of automotive glass by using a fringe reflection technique. Physical properties of the measurement surfaces do not allow us to apply optical geometries used in existing techniques for surface measurement based upon direct fringe pattern illumination. However, this property of surface reflectivity can be used to implement similar ideas from existing techniques in a new improved method. In other words, the reflective surface can be used as a mirror to reflect illuminated fringe patterns onto a screen behind. It has been found that in the case of implementing the reflective fringe technique, the phase-shift distribution depends not only on the height of the object but also on the slope at each measurement point. This requires the solving of differential equations to find the surface slope and height distributions in the x and y directions and development of the additional height reconstruction algorithms. The main focus has been made on developing a mathematical model of the optical sub-system and discussing ways for its practical implementation including calibration procedures. A number of implemented image processing algorithms for system calibration and data analysis are discussed and two experimental results are given for automotive glass surfaces with different shapes and defects. The proposed technique showed the ability to provide accurate non-destructive measurement of 3D shapes of the reflective automotive glass surfaces and can be used as a key element for a glass shape quality control system on-line or in a laboratory environment.
ABSTRACT The rapid, ultra-precision measurement of the shape of engineering components is becomin... more ABSTRACT The rapid, ultra-precision measurement of the shape of engineering components is becominc; a major requirement for today's quality conscious industries. This paper presents a technique for the reconstruction of surfaces underlying optically generated contour maps. The technique views the map as a constant spacing straight fringe pattern phase modulated by the underlying surface shape. The Fourier transform is used as a means of demodulating the pattern producing a 2π wrapped phase distribution. The conversion of this phase information to a range map is performed and so the surface is reconstructed. Methods for the quantitative analysis of the resulting map are discussed, including techniques based on differential geometric analysis, to yield data on items such as the first and second fundamental forms and hence functionally important criteria such as point surface principal curvature etc. The relationship which exists between the accuracy of these measurements and the nature of the demodulation filtering performed in the Fourier domain is briefly discussed.
ABSTRACT Recent work has shown the importance of the fast Fourier transform (FFT) in the automati... more ABSTRACT Recent work has shown the importance of the fast Fourier transform (FFT) in the automatic analysis of fringe patterns. Three problem areas are encountered when the FFT is used as an analysis tool in this fashion, namely, aliasing, the picket fence effect and leakage. The authors consider leakage to be by far the biggest problem in this application. The paper defines what causes leakage and suggests how leakage may be controlled using data weighting functions. Comparative results obtained using a variety of functions are presented.
ABSTRACT This paper describes the development of an optical method of phase measurement and furth... more ABSTRACT This paper describes the development of an optical method of phase measurement and further three-dimensional surface reconstruction using colored structured light. The paper investigates a new method for improving the measurement of three-dimensional shapes by using color information of the measured scene as an additional parameter. The general problems of the most widely used algorithms (phase shifting profilometry and Fourier fringe analysis) are that phase maps produced by these methods are wrapped, in some cases the acquired fringe pattern does not fill the field of view, there may be spatially isolated areas and there is often invalid and/or noisy data. This paper aims to demonstrate a new method for three- dimensional surface reconstruction using colored fringe patterns. The proposed technique uses colored fringe patterns, which are projected at different angles onto the measured scene. Shortcomings, which arise using standard methods, can be overcome using a color multichannel Fourier fringe technique.
Microsystems Engineering: Metrology and Inspection III, 2003
ABSTRACT In high speed grinding research it is required to measure temperature within the workpie... more ABSTRACT In high speed grinding research it is required to measure temperature within the workpiece. Present techniques are thermocouple based, and often suffer from excessive electrical noise on the signal. This paper presents a number of novel fiber optic sensing devices that overcome this limitation and also offer greater performance. Optical fiber devices are simpler to place in situ prior to the machining tests and they offer faster response and greater sensitivity than was previously possible. Results are presented from machining tests and the new devices are compared with each other and previous techniques.
Three-Dimensional Imaging and Laser-based Systems for Metrology and Inspection III, 1997
ABSTRACT This paper describes a method for the treatment of non- fullfield images by means of the... more ABSTRACT This paper describes a method for the treatment of non- fullfield images by means of the Fourier fringe analysis technique. With this type of images, the borders of the data appear as high frequencies in the Fourier domain while the areas with the same intensity (background) appear as low frequency components. This information interferes with the signal peak and leads to large errors in the phase result throughout the image. This paper proposes a two dimensional mapping operation to overcome the problem. By a mapping of the original image into a square, the image can be processed by conventional FFA. The final result is obtained by the application of the inverse of the mapping function.
This paper proposes the use of a modified Morlet wavelet in order to demodulate fringe patterns i... more This paper proposes the use of a modified Morlet wavelet in order to demodulate fringe patterns in conjunction with the one-dimensional continuous wavelet transform (1D-CWT). Our investigations demonstrate that the modified Morlet wavelet produces better results compared to the conventional Morlet wavelet when used in fringe pattern analysis. This novel technique offers superior performance in analysing fringe patterns from objects that exhibit large height variations. This new technique has been used in conjunction with the direct maximum ridge extraction algorithm and an improvement in performance is observed. The algorithm has been tested using both computer-generated and real fringe patterns; and was found to be suitable for fringe pattern demodulation and robust in operation.
A prospective new optical non-contact method for the assessment of surface texture is presented. ... more A prospective new optical non-contact method for the assessment of surface texture is presented. A dual-beam laser Doppler anemometer is employed and the parameter "fringe visibility" is used as an indication of surface asperity size and geometry. The method was tested on specimens resulting from three different manufacturing processes, i.e. grinding, milling and turning, which possessed a range of R, values from 0.025 to 50 pm. Both static and dynamic measurement configurations were examined.
Over the years two-dimensional Fourier Fringe Analysis (2D-FFA) has demonstrated both its capabil... more Over the years two-dimensional Fourier Fringe Analysis (2D-FFA) has demonstrated both its capability and its relative robustness in analysing fringe patterns within a short time-frame from static objects. Nowadays, there is an increasing demand to measure dynamic objects. Today 2D-FFA is seen as a fast and flexible method of processing fringe patterns for dynamic objects. But it is still inherently a 2D approach, i.e. it deals with three-dimensional data (video sequences) on an individual 2D frame-by-frame basis. In this paper, a novel three-dimensional Fourier Fringe Analysis (3D-FFA) algorithm is proposed to demodulate fringe pattern sequences taken from dynamic objects. This technique processes the stack of fringe patterns as a single 3D volume, not as a set of individual 2D frames that are each processed in isolation. The proposed algorithm has been evaluated on both computer simulated and real dynamic objects. Results show that the proposed technique is able to demodulate fringe pattern volumes successfully. r
ABSTRACT A new phase-unwrapping algorithm for the phase map containing discontinuities by the use... more ABSTRACT A new phase-unwrapping algorithm for the phase map containing discontinuities by the use of a system with crossed grating is described in this paper. A crossed grating is projected onto the object in the usual way, the deformed grating image acquired is Fourier transformed and the frequency spectra for the individual gratings are separated. Using both phase distributions which have different sensitivities, the correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of a three-dimensional object with height steps are presented.
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Papers by Michael Lalor