Comparative Study Of Two Kinds Of Sub-pixel Displacement Algorithm Based On The Digital Image Correlation Method

Digital Image Correlation(DIC for short), which is also referred to as the Digital Speckle Correlation Method(DSCM for short), is a method of experimental mechanics to quantify the full-field displacement and strain analysis of an optical measurement. DIC use ordinary white light or natural light illumination and obtain the displacement and stain fields via the analysis of the specimen surface speckle before and after deformation speckle. It has a characteristics that the requirement for experimental environment is low, the light path is simpler and the stability of the algorithm is better.The paperwork is:1.System design and optimization. According to the requirement of the measuring system based on the digital image correlation, forming the speckle by spray paint on the surface, obtaining uniform illumination by the coaxial blue light source, choosing an appropriate industrial camera、telocentric lens and a blue band pass filter to get the speckle images.2.Algorithm comparison. Realizing the precision comparison of two algorithms in the sub-pixel displacement based on the digital image correlation method, which uses the bilinear interpolation and double three interpolation method through the interpolation method based on gray level, during the calculation, we use two different correlation functions and different sub-pixel displacement measurement windows, then we get the following conclusions:1. In the case of calculating the sub-pixel displacement under0.1pixel, if we use the same kind of correlation function, the match degree of the results of two different interpolations is high, when using the same kind of interpolation method, the results accuracy using standardization covariance correlation function is higher than the results accuracy using standardized correlation function;2. In the case of calculating the sub-pixel displacement under O.lpixel, when using the same interpolation method and correlation function, with the full-pixel displacement calculation window enlarger, the accuracy of the calculated value has a tendency to improve, it is closer to the real value, but the computation time is longer;3. The bilinear interpolation and double three interpolation method are not suitable for computing sub-pixel displacement value below O.lpixel, the precision is very low. In conclusion, The bilinear interpolation and double three interpolation methodare suitable for calculating the sub-pixel displacement more than0.1pixel, we can use standardization covariance correlation function and choose a51×51full-pixel calculation window, then the calculation accuracy is higher, errors are smaller, the calculation time is also not too long.