In order to measure the full-field thermal deformation of materials in high temperature environment, a full-field thermal deformation measurement method based on high temperature digital image correlation is proposed in this paper.In this method, monochromatic polarized light is used as the lighting source, and the polarizing camera combined with narrowband filter is used as the image acquisition system to collect images under high temperature environment. Through optical imaging and optical filtering system, visible radiation can be initially filtered to minimize the thermal radiation on the specimen surface. And the image gray average method is also used in this paper to eliminate the thermal disturbance error and vibration error in the measurement process to improve the measurement accuracy.Finally, a set of high temperature digital image correlation measurement system was built, and the thermal deformation test was carried out on the ceramic materials. The experimental results show that the system can realize the clear image with high-contrast acquisition under high temperature conditions, and can effectively eliminate the interference of vibration and thermal disturbance noise in the measurement under high temperature .
In the practical application of speckle pattern interference, it is often necessary to measure the deformation or defects of some specimens placed in the box. Transparent glass observation windows are usually used on one side of these boxes. In the measurement of laser speckle pattern interference, glass windows often cause overexposure in a certain area of the field of view, which has a great influence on the measurement. In this paper, a method of recognizing and eliminating high reflective region based on polaroid is proposed. By adjusting the polaroid to filter the stray and chaotic obtrusive light, the overexposed area in the field of view is greatly reduced, and then the exposure area caused by glass windows in the field of view is identified and extracted by feature extraction technology. Finally, the overexposed area is interpolated and filled according to the surrounding region information to obtain the measurement map without overexposure. Experimental results show that the proposed method can effectively extract and eliminate the overexposed area, and good measurement results are obtained.
KEYWORDS: Image fusion, Phase shifts, Cameras, High dynamic range imaging, 3D metrology, Polarization, Polarizers, Fringe analysis, Reflectivity, 3D modeling
It is challenging to measure objects with a high dynamic range surface. We propose a three-dimensional measurement method of high dynamic surfaces based on multi-polarization fringe projection. The saturated pixels can be recognized to get the optimal exposure time by projecting a series of designed auxiliary patterns onto the surface of the object. It does not need to project multiple N-step phase-shifting fringe patterns for recognition, and it greatly improves the detection speed and efficiency. A multi-polarization camera captures full-resolution phase-shifting images with four polarization directions simultaneously. An appropriate polarization direction is selected by analyzing the per-pixel of auxiliary images captured by camera, and then optimal phase-shifting fringe images with high quality are obtained. The effectiveness and rapidness of this method are verified by the measurement experiments of different objects, and the method provides a new idea for rapid measurement.
KEYWORDS: Cameras, Digital image correlation, Optical engineering, Digital imaging, Optical spheres, 3D image processing, Speckle, 3D displays, 3D metrology, Stereoscopic cameras
In the measurement of the 3-D shape of a large curved object using traditional 3-D-digital image correlation (DIC), the left and right camera images are relatively rotated or deformed too much, which will cause the matching to fail. We propose a 3D-DIC matching method. Compared with traditional methods having fixed-size templates, this method is robust to relative rotation and deformation between dual cameras and is suitable for 3D-DIC measurement of nonplanar objects. In the proposed method, we use polar coordinates to define the matching template as a variable circle, which is convenient for interpolation calculation and changing the template size. The zero-mean normalized cross-correlation method is used to determine the position of an entire pixel on the distorted image. This step can provide an initial value close to the true value for subsequent iterations of the inverse compositional Gauss–Newton algorithm. The performance of the proposed method is verified by experiments. Compared with the traditional matching method, the proposed method is suitable for matching large curved surfaces between 3D-DIC dual cameras and extends the application of DIC technology.
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