Note that the color differences in the image are introduced by limitations of the camera system. The above concept is common among othe r techniques in digital image correlation. A method to transfer speckle patterns for digital image correlation article pdf available in measurement science and technology 269 september 2015 with 2,196 reads how we measure reads. Speckle pattern quality assessment for digital image correlation article in optics and lasers in engineering 5112. Speckle pattern quality assessment for digital image. An image with high entropy requires a large number of bits to create an adequate representation of the form in a digital image. Consequently, this method does not require any sample preparation and allows for the measurement of displacement of micro structures in addition to large displacements. In this work, a bspline function is used to represent the object deformation field throughout the entire image area. Digital speckle pattern interferometry and related techniques. Images displacement strain analysis of image surface over time use of cross correlation to determine displacement strain calculated from displacement an optical method to measure deformation on an objects surface 3. In this technique, a coherent 30mw632nm laser beam is expanded with 40x lens and then illuminated on the target surface to. An optical system which is a combination of the two measurement method is proposed in this paper. Three the most widely used formulas of the correlation coefficient are. An effective global parameter for quality assessment of the speckle patterns used in digital image correlation.
It compares the deformed images with the reference image using a specific cross correlation algorithm for retrieving displacement and strain. Digital image correlation setup using one ccd camera for inplane measurement and digital speckle pattern interferometric setup for outplane measurement constitutes this measurement system. The method is based on the correlation of two characteristic images of a speckle pattern on the object, where the grey value distribution is. Pdf the technique of digital image correlation dic, which has been widely used for noncontact deformation measurements in both the scientific and. With the existing dic techniques, the user must rely on experience and intuition to manually define the size of the reference subset, which is found to. Subsequently, each speckle pattern image undergoes a numerically controlled deformation, which is measured with digital image correlation software. It has been shown that the size of the speckles in a given speckle pattern in combination with the size of subset have an influence on the. Testing the method of speckle pattern processing based on the digital image. The aramis digital image correlation system gom mbh, germany was acquired by the defence science and technology organisation for the evaluation of fullfield surface strain in largescale, high strainrate synergistic blast and fragmentation event. This study was concerned with the optimization of the digital speckle pattern dsp for dic in consideration of both the accuracy and efficiency.
Characterization of sem speckle pattern marking and imaging. This software has been developed to produce synthetic specklepattern images, which mimic as realistically as possible real dic speckle patterns, obtained for. Digital holography dh is usually free of misinterpretation, but when an expression like imageplane digital. Characterization of sem speckle pattern marking and imaging distortion 2 1.
Introduction during the last decades, the mechanical behavior of metals at microstructural scales has been increasingly studied with numerical or experimental approaches 1, 2. Then the dynamic deformation modulated speckle images are captured by a highspeed ccd camera and saved in the computer. Oct 31, 2016 the word holography means a drawing that contains all of the information for lightboth amplitude and wavefront. In dic measurements, the speckle pattern serves as a carrier of. Pdf speckle pattern processing by digital image correlation. Laser speckle on a digital camera image from a green laser pointer. A simple and efficient speckle pattern adjusting and optimizing approach presented in this paper is aimed at providing a novel speckle pattern robust. These images are co mposed of several pixels, each one containing a grey level value linked to the random pattern at th e surface of the material, called speckle pattern. In digital image correlation dic, speckle patterns are generated on the surface of a specimen to resolve uniqueness issues. The displacement field is supposed homogeneous inside the pattern.
Hence a pattern with a high shannon entropy value indicates a high level of texture, or broadness in the grey scale distribution of the image, both of which are beneficial for maximising the correlation function. Optimisation and validation of the aramis digital image. Digital image correlation and tracking is an optical method that employs tracking and image registration techniques for accurate 2d and 3d measurements of changes in images. However, measuring these parameters outside of the lab requires a difficult choice between conventional techniques, as accuracy, simplicity and cost must all be balanced. Pdf a method to transfer speckle patterns for digital.
Pdf optimized digital speckle patterns for digital image correlation. Digital image correlation strain and displacement are critical parameters within engineering and construction projects. Microstamping for improved speckle patterns to enable digital image correlation volume 21 supplement andrew h. The correlation calculation are done for a group of pixels called pattern. Experimentally achievable accuracy using a digital image.
Secondly a number of speckle patterns are generated numerically using a given speckle size and image coverage. Microstamping for improved speckle patterns to enable digital image correlation andrew h. It compares the deformed images with the reference image using a specific crosscorrelation algorithm for retrieving displacement and strain. Speckle pattern processing by digital image correlation fedor gubarev1,2,a, lin li1, miron klenovskii1,3 and anatoliy glotov1 1 national research tomsk polytechnic university, 634050 tomsk, russia abstract. Digital image correlation dic is an optical strainmapping technique that measures the deformation directly on the surface of interest. Pdf a method to transfer speckle patterns for digital image. The technique of digital image correlation dic, which has been widely used for noncontact deformation measurements in both the scientific and engineering fields, is greatly affected by the quality of speckle patterns in terms of its performance. These values are then stored into a matrix with the same number of elements as the amount of light sensitive cells. Digital image correlation dic has been established as a flexible and effective technique to measure the displacements on specimen surface by matching the reference subsets in the undeformed image with the target subsets in the deformed image. Using an optimal speckle pattern is one of the most important factors in reducing measurement noise and improving overall results. Digital image correlation is a white light technique based on the comparison of images before, during and after the deformation of a test specimen, typically acquired using a monochromatic ccd camera. Both imposed and measured displacements are compared and it is shown that the size. Realisation of microspeckle patterns for digital image.
Request pdf assessment of speckle pattern quality in digital image correlation based on gray intensity and speckle morphology in digital image correlation dic, speckle patterns are generated. Analysis of speckle patterns for deformation measurements. Microstamping for improved speckle patterns to enable. However, it has been during the last 15 years that espi, boosted by the availability of affordable and increasingly powerful digital image processing systems, has grown into one of the leading optical measurement techniques, receiving new names such as tv holography or digital speckle pattern interferometry. The image of the body could be represented by a discrete function. A comparative study of random patterns for digital image correlation 57 patterns with in advance known characteristics, a necessity for numerical generation and printing of random patterns on a surface arises. Osa neighborhood binary speckle pattern for deformation. This paper explores the possibilities for vibration analysis using digital speckle projection together with dicm. Quality assessment of speckle patterns for digital image. The final step in the measurement process is the digital image correlation routine, in which two parameters are predominantthe nature of the speckle pattern and the size of the subset. Speckle pattern processing by digital image correlation core. However, because of the insufficient bandwidth of current electronics, the.
Study on subset size selection in digital image correlation. Figure 1 setup for displacement measurement using digital image correlation figure 2 matching the subset before and after deformation. During the manufacturing process, wafer undergoes many microfabrication process steps, which would make wafer experience thermal cycles. We would like to note that the actuality of this matter is discussed in 9, while the present work aims at the initiation of such. Assessment of specklepattern quality in digital image.
Digital image correlation dic also referred to as white light speckle. A digital speckle pattern, generated by computer, is projected on an object surface using an lcd projector. Experimental investigation of speckle pattern by laser. With the development of digital image correlation dic, kinematic measurements via sem. Impact of speckle pattern parameters on dic strain resolution calculated from insitu sem experiments jennifer l. Sign in view cart help conference proceedings papers presentations journals. Assessment of digital image correlation measurement. It is now well recognized that the accuracy and precision in dic measurements not only rely on correlation algorithms, but. Digital image correlation dic is an opticalnumerical fullfield displacement measuring technique, which is. Fabrication and optimization of microscale speckle patterns.
Osa optimized digital speckle patterns for digital image. Subpixel displacement and deformation gradient measurement. Digital speckle projection for vibration measurement by. Fullfield speckle pattern image correlation with bspline. Using an optimal speckle pattern is one of the most important factors in reducing measurement noise and improvin. Testing the method of speckle pattern processing based on the digital image correlation is carried out in the current work. Presented at the sustainable construction and design scad 2012, ghent, belgium. Analysis of speckle patterns for deformation measurements by.
Speckle pattern fundamentals in digital image correlation, the quality of the data is often dependent on the quality of the speckle pattern. Realisation of microspeckle patterns for digital image correlation on dental implants. A fullfield speckle pattern image correlation method is presented that will determine directly the complete, twodimensional deformation field during the image correlation process on digital images obtained using computer vision systems. Quality assessment of speckle patterns for digital image correlation d. Combination of digital speckle pattern interferometry and. This method is often used to measure fullfield displacement and strain s, and it is widely applied in many areas of science and engineering, with new applications being. A speckle pattern is an intensity pattern produced by the. Speckle pattern based characteristics of digital image correlation dic restrict its application in engineering fields and nonlaboratory environments, since serious decorrelation effect occurs due to localized sudden illumination variation. The advent of smallscale testing procedures coupled with scanning electron microscopy sem imaging allow for highresolution digital image correlation dic. Quality assessment of speckle patterns for digital image correlation. In the present paper, the accuracy of the digital image correlation technique is studied in function of the nature of the speckle pattern i. A speckletexture image generator archive ouverte hal.
Impact of speckle pattern parameters on dic strain resolution. Speckle pattern processing by digital image correlation. In digital image correlation, the quality of the data is often dependent on the quality of the speckle pattern. Speckle pattern quality assessment for digital image correlation. Mills 1 the ohio state university 477 watts hall, 2041 college rd. Digital image processing is becoming more important for optical metrology, because the introduction of electronic imaging devices, such as chargecoupled devices ccd. Assessment of specklepattern quality in digital image correlation.
323 1156 185 1482 1331 1174 1259 1396 364 604 1156 390 283 380 1631 570 838 227 592 559 1450 286 1106 660 218 660 738 141 1295 1521 1020 303 1507 1176 1517 1119 335 521 632 1116 491 927 1275 248 1187 5 268 654 737