Showing papers on "Digital image correlation published in 1991"

Image analysis to measure strain in wood and paper.

Abstract: A fast and accurate strain measurement method was developed to quantify microscopic deformation in wood and paper using video images. Two or more video images, one of which was undeformed and the others of which were deformed, were digitized and compared using the image correlation technique. This digital computer pattern recognition technique permitted the displacement of any point in the image to be measured. Then, strain between any two points in this observation field could be calculated and, hence, normal, shearing strains and Poisson's ratio could be measured directly. Independent strain measurements showed that the method using video images provided accurate strain measurements and could be applied to complex materials like wood and wood products. The strain measurements using the image analysis produced not only normal strains but strain profiles of the normal strains. From the strain profiles, it was possible to detect local areas of strain concentration which might be beyond the elastic range. As it measures displacements and strains from a set of video images using the image correlation technique, the method is non-contact and the observation field can be adjusted easily by changing magnifying power of the optical devices. Thus, the method can be applied to mechanical testing of wood and wood products from the cellular level to full size lumber and will no longer be limited by the fragile nature of the material being tested, industry standards, or equipment restrictions.

Image correlation calculation apparatus

Abstract: In an image correlation calculation apparatus for optically calculating correlations between reference patterns and an image such as a character or any other figure, the image such as the character or any other figure subjected to correlation calculations is optically multiplied by a multiplier to form simultaneously in parallel a plurality of optical pattern images of a substantially identical shape, and optical correlation calculation between the plurality of optical pattern images and the reference patterns formed on various types of reference masks is performed individually and instantaneously, the various type of reference masks being arranged at a position spaced apart by a predetermined distance from the plurality of optical pattern image, thereby detecting beams emitted through the various types of reference masks. Image multiplication, optical correlation calculation, and transmission of the result of the optical correlation calculation to the photosensors can be simultaneously performed at a light propagation time. The apparatus structure can be simplified at low cost, and image correlation operations can be performed at high speed.

Optical deformation measuring apparatus by double-writing speckle images into a spatial light modulator

Abstract: An object is typically illuminated by laser light, and reflected light carrying a speckle pattern is amplified by an image intensifier. First and second speckle patterns representing the object before and after its deformation, respectively are written by double writing into a ferroelectric liquid crystal spatial light modulator (FLC-SLM). The double-written image is read out from the FLC-SLM, and converted by a Fourier transform optical system into an output optical image, i.e., Young's fringe. The output optical image is detected by a photoelectric converter, and analyzed by an image processing device to determine a deformation of the object.

Coding intensity images as phase-only images for use in an optical correlator

Abstract: A method of performing image correlation in a Fourier transform correlator utilizes phase-encoding of the input image as a phase object with a normalized amplitude component. Phase-only reference image filters are used in conjunction with the phase-encoded input objects to improve the signal to clutter ratio. This technique can employ optical or digital implementation.

Effects of contrast and brightness on subpixel image correlation

Abstract: In the past years a method that uses digital image correlation to determine the deformations of subsets of an object has been developed. In the paper an attempt is made to explore and understand the effects of changing signal amplitude on the errors associated with digital image correlation. This is important because changes in signal amplitude relate to changes in contrast and brightness between the images. The work was prompted by use of substances that change their phosphorescence under UV light as temperature varies. This results in changes in intensity amplitudes (contrast and brightness) between the initial and final images. The system components are simulated, a representative intensity pattern is chosen and then deformed (translated and strained) by known amounts under changing contrast and brightness. Pure translation, with strain set to zero and translation varied was studied first, and repeated using different intensity amplitudes for the deformed object. The absolute normalized error between the actual and calculated displacement was found by a cross-correlation. For the second study, uniform strains of 0.1%, 0.5%, 1.0% and 5.0% were imposed in addition to centerpoint translation and repeated using different intensity amplitudes. >

Industrial vision systems based on a digital image correlation chip

Abstract: A digital image correlation chip was developed as part of an electronic module library for real- time industrial machine vision applications. A core algorithm of the authors' systems is binary edge image correlation. The other electronic modules described in this paper include a monochrome edge detector and color edge detector. These modules were combined in a variety of ways for different applications. High efficiency, in terms of processing speed and hardware size, of the vision systems was confirmed in laboratory prototypes.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.