Full characterization of the surface strain requires the measurement of six displacement gradient components of the surface strain tensor. The out-of-plane displacement gradient component may be directly measured using the full-field speckle interferometry technique of shearography, but to fully characterize the surface strain using shearography, a minimum of three illumination, or viewing, directions are required. The image processing technique of digital speckle photography (DSP) is sensitive to in-plane displacement for normal collinear illumination and viewing, with the displacement gradient components obtained by differentiation. A combination of shearography and digital speckle photography is used to perform full characterization of the surface strain using a single illumination and viewing direction. The increase in complexity compared with a standard single-channel shearography system lies predominantly in the additional image processing requirements. Digital speckle photography image processing is performed using the optical flow field technique and the advantages of this technique compared with correlation are discussed. The design of the instrument is described and full surface strain measurements made with the system are presented.
Shearography is a full-field interferometric optical technique that is usually used for the qualitative investigation of defects in non-destructive testing applications. The optical configuration is sensitive directly to displacement gradient, a parameter closely related to the surface strain. The component of the displacement gradient that is measured is determined by the illumination and viewing directions and by the direction of the applied shear. The sensitivity is governed by the magnitude of applied shear and by the optical wavelength. Full characterisation of the surface strain requires a measurement of six-components of displacement gradient; this is achieved in shearography by forming a number of distinct measurement channels using multiple illumination, or viewing, directions. In this paper the authors discuss the quantitative measurement of the strain field around a fatigue crack, using a time-division-multiplexed diode laser shearography instrument. To investigate moving objects, a pulsed laser provides a method of freezing the object position at two points in the loading cycle. A shearography instrument incorporating two frequency doubled pulsed Nd:YAG lasers, with a common injection seeder is described. The measurement channels are spatially-multiplexed by viewing from four directions using an optical fibre imaging bundle, with optical processing at a remotely located interferometer head. Preliminary experimental measurements are presented.
In common with many other application areas, visual signals are becoming an increasingly important information source for many automotive applications. For several years CCD cameras have been used as research tools for a range of automotive applications. Infrared cameras, RADAR and LIDAR are other types of imaging sensors that have also been widely investigated for use in cars. This paper will describe work in this field performed in C2VIP over the last decade - starting with Night Vision Systems and looking at various other Advanced Driver Assistance Systems. Emerging from this experience, we make the following observations which are crucial for "intelligent’ imaging systems:
1. Careful arrangement of sensor array.
2. Dynamic-Self-Calibration.
3. Networking and processing.
4. Fusion with other imaging sensors, both at the image level and the feature level, provides much more flexibility and reliability in complex situations.
We will discuss how these problems can be addressed and what are the outstanding issues.
Full surface strain measurement requires the determination of two out-of-plane and four in-plane displacement gradient components of the surface strain tensor. Shearography is a full-field speckle interferometry technique with a sensitivity predominately to the out-of-plane displacenet gradient. Speckle pattern photography has the sensitivity to the in-plane displacement, and taking the derivative yields the in-plane dipslacment gradient. In this paper the two techniques are combined to yield a single-access multi-component surface strain measurement using shearography to measure the out-of-plane components and speckle pattern photography to measure the in-plane components. Results are presented of a multi-component surface strain measurement.
Multiphase pipeline flow is very important to oil, gas and process industry. This is a class of problems where comprehensive simulations, although desirable on physical grounds, are not practical due to the large aspect ratio between the pipe length and diameter. In order to enhance the understanding of the pipeline flow, as well as to validate and identify the critical aspects of these models, intensive experimental data are needed. This will define how these models can be improved.
The measurement of in-plane surface strain is very important in structural material research. The traditional strain measurement techniques, however, have their clear constaint and inconveniency in terms of both sensor system arrangement and data analysis. This paper presents the development of a novel technique for estimating the local surface strain over a region. The key element of the technique is a high accurate image displacement detection algorithm. This algorithm is based on the Optical Flow concept and implemented in a multi-scale analysis scheme. This technique is aiming at covering large viewing area and detecting small deformation components on the top of large translation with high accuracy. A numerical differentiation procedure is also discussed to derive strain field from the displacement field. The test procedure of this technique is also presented in this paper. The test procedure consists of absolute translation calibration and strain calibration against strain-gauge measurement. The experimental results show a very good agreement between the proposed technique and the well-established traditional measurement.
Text, voice and video images are the most common forms of media content for instant communication on the Internet. Studies have shown that facial expressions convey much richer information than text and voice during a face-to-face conversation. The currently available real time means of communication (instant text messages, chat programs and videoconferencing), however, have major drawbacks in terms of exchanging facial expression. The first two means do not involve the image transmission, whilst video conferencing requires a large bandwidth that is not always available, and the transmitted image sequence is neither smooth nor without delay. The objective of the work presented here is to develop a technique that overcomes these limitations, by extracting the facial expression of speakers and to realise real-time communication. In order to get the facial expressions, the main characteristics of the image are emphasized. Interpolation is performed on edge points previously detected to create geometric shapes such as arcs, lines, etc. The regional dominant colours of the pictures are also extracted and the combined results are subsequently converted into Scalable Vector Graphics (SVG) format. The application based on the proposed technique aims at being used simultaneously with chat programs and being able to run on any platform.
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