Improving the calibration of phase measuring deflectometry by a polynomial representation of the display shape

Bartsch, Jonas; Kalms, Michael; Bergmann, Ralf B.

doi:10.1186/s41476-019-0116-1

Cited by 17 publications

(9 citation statements)

References 14 publications

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“…The second category of solutions for the presented accuracy limitation is to enhance to measurement processes on the algorithmic side by including the screen surface topography into the reconstruction algorithms as part of the measurement setup model. 24 Of course, this information then also needs to be determined in the calibration process. This is the focus of current research efforts.…”

Section: Discussionmentioning

confidence: 99%

The effects of pattern screen surface deformation on deflectometric measurements: a simulation study

Allgeier

Gengenbach

Köhler

et al. 2021

Automated Visual Inspection and Machine Vision IV

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Phase-measuring deflectometry (PMD) is an optical inspection technique for full-field topography measurements of reflective sample surfaces. The measurement principle relies on the analysis of specific patterns, reflected at the sample surface. Evaluation algorithms often model the respective pattern screen as a planar light source. However, the 32 pattern screen in our inspection setup exhibits a central bulge of its surface of about 2-3 mm. This paper presents a simulation framework for PMD to evaluate the effects of a deformed screen surface. The idea is to simulate image data acquired with screen surface deformations and to examine the effects on the PMD evaluation results. The simulated setup consists of a 32 pattern screen with an adjustable central bulge height of 0-3 mm and two cameras with a field of view (FOV) of approximately 225 mm by 172 mm on the sample surface. A first experiment examines the reconstruction errors for a planar sample surface if the reconstruction algorithm uses perfect calibration data (i.e. the same parameters used for the simulated image acquisition). The reconstructed surfaces exhibit a tilt with a maximum height difference of 174 µm across the FOV. A second experiment repeats the reconstruction process of the same sample surface, using camera parameters determined in a simulated calibration process. The resulting surfaces possess irregular, wave-like errors with amplitudes of up to 9 µm in the FOV. The presented simulation results reveal the accuracy limits if a deformation model of the pattern screen is not explicitly included in the reconstruction process.

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Section: Discussionmentioning

confidence: 99%

The effects of pattern screen surface deformation on deflectometric measurements: a simulation study

Allgeier

Gengenbach

Köhler

et al. 2021

Automated Visual Inspection and Machine Vision IV

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“…Furthermore, the pattern screen is also modeled as a plane, although the monitor surface exhibits a clearly visible convex curvature (caused by its fixation at an angle of approximately 45°with relation to the horizontal plane). 30,31 The monitor curvature is, of course, present for both calibration techniques. However, it may have a stronger influence on the holistic calibration because the measurements performed with varying mirror poses cover a large proportion of the monitor area, whereas the single wafer pose in the stepwise calibration reflects the light from only a smaller, central area of the screen into the cameras.…”

Section: Discussionmentioning

confidence: 99%

Reproducibility of two calibration procedures for phase-measuring deflectometry

et al. 2020

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Phase-measuring deflectometry is an optical inspection technique for reflective surfaces. It enables absolute, quantitative surface measurements, given a calibrated measurement setup. Two general calibration approaches can be found in literature: First, the stepwise approach uses a calibration pattern and determines internal camera parameters and external geometrical parameters in separate, consecutive steps. Second, the holistic approach optimizes all parameters collectively, based on deflectometric measurements of a calibration mirror.Whereas both approaches have been compared regarding the accuracy of subsequent surface measurements, the present contribution focuses on experimental examination of their reproducibility. In experiment E1, we assess the parameter variability by repeating both calibration procedures ten times. In an additional experiment E2, we repeat all calibration measurements related to a mirror/pattern position ten times in a row before rearranging the mirror/pattern, in order to examine the purely noise-related parameter variability. Finally, we calculate the coordinate variability of a set of world points projected onto the image planes of the calibrated cameras.The measured variability is consistently higher in E1 than in E2 (average ratio: 3.2). Unexpectedly, in both experiments, the external parameter variability also turns out to be higher for the holistic approach compared to stepwise calibration (average ratio: 2.3). This is of importance, since the holistic approach is known from literature to be more accurate than the stepwise approach, regarding their respective application to surface measurements. The image coordinate variability is comparable for both calibration approaches with an average of 0.84 and 0.21 camera pixels for E1 and E2, respectively.

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“…In more demanding cases, the details of a real LCD matrix have to be taken into account. In particular, the refraction in the cover glass may be modeled explicitly [75,218,[240][241][242][243] or accounted for by some loworder deformation terms [244][245][246][247]. The latter may also describe the deformation of large screens due to gravity.…”

Section: Coding Screen Modelsmentioning

confidence: 99%

Deflectometry for specular surfaces: an overview

Burke¹,

Pak²,

Höfer³

et al. 2022

Preprint

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Deflectometry as a technical approach to assessing reflective surfaces has now existed for almost 40 years. Different aspects and variations of the method have been studied in multiple theses and research articles, and reviews are also becoming available for certain subtopics. Still a field of active development with many unsolved problems, deflectometry now encompasses a large variety of application domains, hardware setup types, and processing workflows designed for different purposes, and spans a range from qualitative defect inspection of large vehicles to precision measurements of microscopic optics. Over these years, many exciting developments have accumulated in the underlying theory, in the systems design, and in the implementation specifics. This diversity of topics is difficult to grasp for experts and nonexperts alike and may present an obstacle to a wider acceptance of deflectometry as a useful tool in other research fields and in the industry.This paper presents an attempt to summarize the status of deflectometry, and to map relations between its notable "spin-off" branches. The intention of the paper is to provide a common communication basis for practitioners and at the same time to offer a convenient entry point for those interested in learning and using the method. The list of references is extensive but definitely not exhaustive, introducing some prominent trends and established research groups in order to facilitate further selfdirected exploration by the reader.

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Improving the calibration of phase measuring deflectometry by a polynomial representation of the display shape

Cited by 17 publications

References 14 publications

The effects of pattern screen surface deformation on deflectometric measurements: a simulation study

The effects of pattern screen surface deformation on deflectometric measurements: a simulation study

Reproducibility of two calibration procedures for phase-measuring deflectometry

Deflectometry for specular surfaces: an overview

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