Separation of isoclinics and isochromatics from photoelastic data with a regularized phase-tracking technique

Quiroga, Juan Antonio; González-Cano, Agustı́n

doi:10.1364/ao.39.002931

Cited by 37 publications

(19 citation statements)

References 17 publications

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“…In the case of Yoneyama et al 5 a special tricolour source is especially designed for this purpose. On the other hand, Quiroga and Gonzalez-Cano 9 show that a commercially available discrete-spectrum fluorescent lamp can also be used. Thus we have used the commercial type of illumination.…”

Section: Improved Rgb Calibration Algorithmmentioning

confidence: 99%

“…1 For the analysis of photoelastic fringe patterns, various techniques have been applied, such as phase shifting, 2 Fourier transforms, 3 spectral content analysis, 4 tricolor image analysis, 5 red-blue-green ͑RGB͒ calibration, 6,7 load stepping, 8 and regularization techniques. 9,10 One of the objectives in these techniques is the use of the smallest possible number of images.…”

Section: Introductionmentioning

confidence: 99%

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Improved method for isochromatic demodulation by RGB calibration

2002

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The red-blue-green ͑RGB͒ calibration technique consists in constructing an a priori calibration table of the isochromatic retardation versus the triplet of RGB values obtained with a RGB CCD camera. In this way a lookup table ͑LUT͒ is built in which the entry is the corresponding RGB triplet and the output is the given retardation. This calibration ͑a radiometric quantity͒ depends on the geometric and chromatic parameters of the setup. Once the calibration is performed, the isochromatic retardation at a given point of the sample is computed as the one that minimizes the Euclidean distance between the measured RGB triplet and the triplets stored in the LUT. We present an enhanced RGB calibration algorithm for isochromatic fringe pattern demodulation. We have improved the standard demodulation algorithm used in RGB calibration by changing the Euclidean cost function to a regularized one in which the fidelity term corresponds to the Euclidean distance between RGB triplets; the regularizing term forces piecewise continuity for the isochromatic retardation. Additionally we have implemented a selective search in the RGB calibration LUT. We have tested the algorithm with simulated as well as real photoelastic data with good results.

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Section: Improved Rgb Calibration Algorithmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improved method for isochromatic demodulation by RGB calibration

2002

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“…Ströbel [11] rst proposed this in the context of phase unwrapping. The objective of the quality map is to guide the RPT in such a way that it should process locally, in the rst place, the highest quality areas (high signal-to-noise ratio), leaving aside the low quality regions so that they are processed last [8,9]. In this way the possible errors that occur in the areas of low quality will be con ned to these areas.…”

Section: Sequential Demodulation Strategy For Isochromatics Demodulationmentioning

confidence: 99%

“…Recently, Villa et al [8] and Quiroga and Gonzalez-Cano [9] used the modulation (fringe contrast) information to guide the phase estimation strategy using a regularized phase tracking (RPT) to demodulate moire de ectograms and photoelastic fringe patterns. In this case the best fringes are demodulated rst and then proceeds towards the regions of poorer contrast.…”

Section: Introductionmentioning

confidence: 99%

Isochromatics demodulation from a single image using the regularized phase tracking technique

Servı́n¹,

Quiroga²

2001

Journal of Modern Optics

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In this work we propose a robust fringe demodulation technique applied to the analysis of a single isochromatics fringe pattern produced in photoelasticity. The method used is a regularized phase tracking algorithm with a new sequential scanning technique speci cally adapted for the characteristics of the isochromatic fringe patterns: possible apparition of closed fringes, large dynamic range in its spatial frequency content and low noise. The performance of the method is discussed and experimental results are presented. IntroductionDuring the last few years much eå ort has gone into developing methods for the automatic analysis of photoelastic fringe patterns. For this purpose diå erent techniques, such as phase shifting [1], Fourier transform [2], spectral content analysis [3], tricolour image analysis [4] and load stepping [5], have been applied. One of the objectives for all these techniques is the analysis of photoelastic fringe patterns by using the smallest number of images. In the case of isochromatic fringe patterns, the tricolour, spectral contents and Fourier transform techniques need only one image.The spectral content analysis technique [3] determines the isochromatic fringe order by using a white light source and measuring the output spectrum emerging from a polariscope. This technique is very accurate but the measurement is pointwise, and a spectrometer is needed to perform the spectrum analysis. Related to the spectral content analysis technique, the tricolour isochromatic method [4] is based on the construction of a given red, green and blue (RGB) look-up table which gives the relation between a RGB triplet and the fractional isochromatic fringe order. In this case the experimental set-up is simple: a polariscope and a colour charge-coupled device (CCD) camera. The main problem is that using 8 bit digitization for each RGB channel this technique can discriminate only up to 4-5 orders owing to the lack of contrast in the colour signal as the fringe order increases.A totally diå erent approach is used by the Fourier transform technique for isochromatic fringe analysis [2]; here monochromatic illumination is used and a carrier is introduced by means of a quartz wedge, with further Fourier transform

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“…Extending the idea of phase unwrapping in other fields of interferometry, Asundi & Wenson (1998) proposed a fast phase unwrapping algorithm for processing isochromatic phase maps in digital photoelasticity based on gray scale masking and flood-fill approach so that it unwraps phase from an area with higher reliability to the one with lower reliability. Quiroga & Gonzalez (2000) presented a regularization algorithm for processing photoelastic fringe pattern using a modified cost functional approach. Servin & Quiroga (2001) used the contrast of the isochromatic fringes as a measure of quality to unwrap ischromatic fringe order from a single dark field image recorded.…”

Section: Introductionmentioning

confidence: 99%

Assessment of autonomous phase unwrapping of isochromatic phase maps in digital photoelasticity

Ramji

Nithila

Devvrath

et al. 2008

Sadhana

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Photoelasticity is the only whole-field experimental technique which can analyse both 2-D and 3-D elasticity problems. In digital photoelasticity one gets two phase maps, one corresponding to principal stress direction (isoclinic) and the other corresponding to principal stress difference (isochromatic). The phase maps for both isoclinics and isochromatics are to be unwrapped differently for obtaining continuous phase values. Autonomous phase unwrapping is one of the challenging issues and this paper focuses on recent advances on isochromatic phase map unwrapping. A comparative study of different autonomous phase unwrapping algorithm is done by solving a bench mark problem and a stress frozen slice with cut-outs. The need for domain delimiting in addition to domain masking is brought out while using autonomous phase unwrapping algorithms.

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Separation of isoclinics and isochromatics from photoelastic data with a regularized phase-tracking technique

Cited by 37 publications

References 17 publications

Improved method for isochromatic demodulation by RGB calibration

Improved method for isochromatic demodulation by RGB calibration

Isochromatics demodulation from a single image using the regularized phase tracking technique

Assessment of autonomous phase unwrapping of isochromatic phase maps in digital photoelasticity

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