A speckle pattern subtraction technique applied to automatic displacement and deformation measurement

The common digital speckle pattern correlation is a non-contact optical technique which allows the measurement of the surface deformation of a test object after it has been exposed to external factors (high temperatures, mechanical stress, humidity, etc.). This technique uses a charge-coupled device (CCD) camera connected to a computer to obtain images of the object in order to compare them. We propose the use of a subtraction algorithm which speeds up the processing of the images. This optical technique has been successfully applied to measuring controlled displacements of 10 μm on an object. We also suggest a way of combining this technique of speckle subtraction with electronic speckle pattern interferometry (ESPI), to obtain the benefits of both numerical and fringe analysis.