Robust phase unwrapping based on non-coprime fringe pattern periods for deflectometry measurements

Phase-measuring deflectometry is a technique for non-contact inspection of reflective surfaces. A camera setup captures the reflection of a sine-modulated fringe pattern shifted across a screen; the location-dependent measured phase effectively encodes the screen coordinates. As the used fringe patterns are much narrower than the screen dimension, the resulting phase maps are wrapped. The number-theoretical solution uses the Chinese remainder theorem to calculate an unwrapped phase map from repeated measurements with coprime fringe widths. The technique is highly susceptible to phase noise, i.e. small deviations of the measured phase values generally lead to unwrapped phase values with large errors. We propose a modification and show how non-coprime period widths make phase unwrapping robust against phase noise. Measurements with two non-coprime fringe period widths introduce the opportunity to discriminate between “legal” measured phase value pairs, that potentially originate from noise-free measurements, and “illegal” phase value pairs, that necessarily result from noise-affected measurements. Arranged as a matrix, the legal measurements lie on distinct diagonals. This insight not only allows to determine the legality of a measurement, but also to provide a correction by looking for the closest legal matrix entry. We present an experimental comparison of the resulting phase maps with reference phase maps. The presented results include descriptive statistics on the average rate of illegal phase measurements as well as on the deviation from the reference. The measured mean absolute deviation decreases from 1.99 pixels before correction to 0.21 pixels after correction, with a remaining maximum absolute deviation of 0.91 pixels

The effects of pattern screen surface deformation on deflectometric measurements - A simulation study

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\u27\u27 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\u27\u27 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

Harpacticoida (Copepoda) in the plankton of Ushuaia and Golondrina Bays, Beagle Channel, Argentina

Harpacticoid copepods form a diverse and abundant group of the meiofauna in marine benthic habitats. Moreover, harpacticoids are frequently found in planktonic samples particularly in shallow and algae-covered coastal waters. Despite their high abundance, little is known about their taxonomy and importance as a component of the food web in the Southern bays of Argentina. Mesozooplankton samples and environmental data were obtained seasonally from Ushuaia and Golondrina Bays (August 2004 to June 2005) and analyzed for the composition and abundance of harpacticoid copepods. Remarkable seasonal changes in the harpacticoid communities were observed. In Ushuaia Bay, nitrogenated nutrients, chlorophyll a, salinity, and temperature were the prevailing environmental parameters that influenced the harpacticoid community, giving rise to different harpacticoid assemblages. The results highlight the importance of the community of Harpacticoida in both bays and provide background data for further studies on zooplankton communities and monitoring programs in marine systems.Fil: Biancalana, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Veit Köhler, G.. German Centre for Integrative Biodiversity Research; AlemaniaFil: Fricke, Anna Lena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Leibniz Centre for Tropical Marine Research; AlemaniaFil: Berasategui, Anabela Anhi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

Reproducibility of two calibration procedures for phase-measuring deflectometry

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

3D confocal laser-scanning microscopy for large-area imaging of the corneal subbasal nerve plexus

The capability of corneal confocal microscopy (CCM) to acquire high-resolution in vivo images of the densely innervated human cornea has gained considerable interest in using this non-invasive technique as an objective diagnostic tool for staging peripheral neuropathies. Morphological alterations of the corneal subbasal nerve plexus (SNP) assessed by CCM have been shown to correlate well with the progression of neuropathic diseases and even predict future-incident neuropathy. Since the field of view of single CCM images is insufficient for reliable characterisation of nerve morphology, several image mosaicking techniques have been developed to facilitate the assessment of the SNP in large-area visualisations. Due to the limited depth of field of confocal microscopy, these approaches are highly sensitive to small deviations of the focus plane from the SNP layer. Our contribution proposes a new automated solution, combining guided eye movements for rapid expansion of the acquired SNP area and axial focus plane oscillations to guarantee complete imaging of the SNP. We present results of a feasibility study using the proposed setup to evaluate different oscillation settings. By comparing different image selection approaches, we show that automatic tissue classification algorithms are essential to create high-quality mosaic images from the acquired 3D dataset

Inequalities in diet and physical activity in Europe

The contribution of food, nutrition and physical activity to inequalities in health across Europe is largely unexplored. This paper summarizes cross sectional survey data on food patterns and nutrient intakes, and briefer data on physical activity, by various indicators of socio-economic status for countries across Europe. Factors are examined which underlie the outcome data seen. These include structural and material conditions and circumstances which contribute to excluding sociodemographic groups from participating in mainstream patterns of living. Trends in social and economic conditions, and their implications for nutritional and physical wellbeing are briefly outlined