Philip Siegmann

A robust approach to demodulating and unwrapping phase-stepped photoelastic data

New algorithms are proposed for processing wrapped isochromatic and isoclinic fringe data generated by the digital photoelastic technique of phase-stepping. The new algorithms are based on processing areas rather than individual pixels to demodulate the data and employing quality assessments of the data to guide the unwrapping procedure. Comparisons with an existing algorithm, manual analysis, and finite element modeling have been used to demonstrate that the new approach is more robust without any reduction in speed or accuracy. This represents a significant advance for processing complex fringe patterns, which are often encountered in the aerospace industry from which the exemplars are drawn.

Traffic sign recognition system for inventory purposes

This paper describes the evaluation of the characteristics of a real automatic traffic sign detection system. The objective of this review is to provide the basis of quality of a whole system, which is capable of identifying the different signs that can be found in route. At the moment, our work is concerned with the developing of an inventory system capable to get a complete catalog of all the traffic signs and their corresponding state information. The paper analyzes exhaustively the different problems that can appear in real environments and shows how the system implemented overcomes all these difficulties with a high success. The flexibility of the system allows it to run new algorithms even though several of them can be run in parallel and, on the other hand, it is relatively easy to change the training traffic sign according to the circumstances: urban or non-urban environments and traffic signs from different countries.

Traffic sign shape classification based on Support Vector Machines and the FFT of the signature of blobs

In many traffic sign recognition systems, one of the main tasks is the classification of the shape of the blob, which is intended to simplify the recognition process. In this paper, we have developed a new shape classification algorithm based on Support Vector Machines classifiers and the FFT of the signature of the blob. The FFT of the signature yields invariance to object scalings and rotations. Furthermore, the FFT is the vector input to the classifier. This classifier is trained to cope with projection deformations and occlusions. The algorithm has been tested under adverse conditions, such as geometric distortions, i.e. scaling, rotations and projection deformations, and occlusions. The experimental results show good robustness when the system is working with real, outdoor road images.

A simultaneous in- and out-of-plane displacement measurement method

A method is presented that allows real-time three-dimensional displacement maps to be obtained for deformable objects using a single color camera and a color fringe projector. The acquired images have speckle and fringe information embedded in them, which are separated using the R, G, and B color signals from a color CCD camera to permit the independent use of a two-dimensional digital image correlation to obtain the x- and y-direction displacements and fringe projection to obtain the displacement in the z direction.

Automatic Control of Video Surveillance Camera Sabotage

One of the main characteristics of a video surveillance system is its reliability. To this end, it is needed that the images captured by the videocameras are an accurate representation of the scene. Unfortunately, some activities can make the proper operation of the cameras fail, distorting in some way the images which are going to be processed. When these activities are voluntary, they are usually called sabotage, which include partial o total occlusion of the lens, image defocus or change of the field of view. In this paper, we will analyze the different kinds of sabotage that could be done to a video surveillance system, and some algorithms to detect these inconveniences will be developed. The experimental results show good performance in the detection of sabotage situations, while keeping a very low false alarm probability.

Fast Communication: Computational load reduction in decision functions using support vector machines

A new method of reducing the computational load in decision functions provided by a support vector classification machine is studied. The method exploits the geometrical relations when the kernels used are based on distances to obtain bounds of the remaining decision function and avoids to continue calculating kernel operations when there is no chance to change the decision. The method proposed achieves savings in operations of 25-90% whilst keeping the same accuracy. Although the method is explained for support vector machines, it can be applied to any kernel binary classifier that provides a similar evaluation function.

Fundaments in Luminance and Retroreflectivity Measurements of Vertical Traffic Signs Using a Color Digital Camera

This paper is a study of the influences of the different parameters which affect the photometric evaluation of light-emitting surfaces (due to reflection or self-emission) when a conventional color digital camera is used. The overall purpose of this paper is to evaluate the luminance and the reflectivity of the vertical traffic sign with the camera in order to provide an automatic recognition of deteriorated reflective sheeting material of which the traffic signs were made. This paper describes how the A/D converter output signal given by a pixel of the digital camera can be related to the luminance and the reflectivity of the corresponding surface element whose image is formed on a pixel. Thus, each surface element of the traffic signs surface can be separately evaluated. By photometrically calibrating the camera, we have been able to prove this relationship in our experiments.

Optical technique for the automatic detection and measurement of surface defects on thin metallic wires

In industrial applications of thin metallic wires it is important to characterize the surface defects of the wires. We present an optical technique for the automatic detection of surface defects on thin metallic wires (diameters, 50-2000 microm) that can be used in on-line systems for surface quality control. This technique is based on the intensity variations on the scattered cone generated when the wire is illuminated with a beam at oblique incidence. Our results are compared with those obtained by atomic-force microscopy and scanning-electron microscopy.

Integrating fringe projection and digital image correlation for high-quality measurements of shape changes

Abstract. An approach for the measurement of surface displacement fields in three dimensions is presented based on the combination of two-dimensional digital image correlation with fringe projection. Only a single RGB image is required at each deformation state, thereby allowing real-time data acquisition, which is achieved using red speckle and projected blue fringes that are captured in the single image and separated using a Bayer filter. The approach allows both a perpendicular alignment relative to a flat reference surface and self-calibration, i.e., no calibration object is employed. The minimum measurement uncertainty of such a system is found to be 0.0083±0.00239 and 0.0238±0.0068  mm, respectively, for the in-plane and out-of-plane displacements. The potential of the approach is demonstrated for an elastic membrane undergoing large (5 to 20 mm) applied out-of-plane displacements, and the results show no significant difference (<1%) in the measured in-plane displacement fields compared with a commercially available system for stereoscopic digital image correlation.

Robust approach to regularize an isochromatic fringe map

The computation of a continuous map of isochromatic fringe order from an isochromatic phase map or relative retardation based on a photoelastic fringe pattern is a difficult task, particularly when the direction of the principal stress is ambiguous. This happens in most experiments and introduces abrupt changes in the slope of the computed relative retardation map. We present a novel regularized phase-tracking method that at each pixel chooses the unambiguous relative retardation value. This unambiguous relative retardation map is wrapped, however the unwrapping is straightforward and fast using the already known techniques. With the presented method we have been able to process successfully complex experimental data with several isotropic points, high fringe density and low resolution, as is shown in a number of examples.