Research On Digital Speckle Correlation And Contrast Imaging Method

Speckle is an interesting and useful physical phenomenon that has important applications in many fields such as industrial measurement,biomedicine,and life sciences.Digital speckle correlation method(DSCM),as a non-contact optical measurement method using speckle effect,is widely used in the deformation and displacement measurement of objects.By collecting the digital speckle image of the moving object,DSCM analyzes the gray value feature of the image by using image processing technology,and determines the deformation and displacement of the object according to the correlation of the gray feature.Laser speckle contrast imaging(LSCI)is an important research tool in the biomedical field.It uses laser speckle with the characteristics of scattering particle motion information to image the microcirculation of tissues such as the retina and skin.LSCI imaging image can effectively reflect information such as blood flow velocity and perfusion rate in the region.Both methods take advantage of the correlation between speckle images.The difference is that DSCM uses the gray distribution feature of the digital speckle image to match the correlation coefficients between the images;while LSCI uses the statistical property of the grayscale(intensity)of the speckle image,the contrast ratio,to show the spatial and temporal correlation of the speckle image.The research work of this thesis mainly focuses on the theoretical analysis and application practice of these two methods.The main research contents are divided into the following two parts.First,the paper discusses the basic principles of DSCM and LSCI in detail.For DSCM,this paper elaborates the mathematical model and algorithm implementation of various integer pixel and subpixel search algorithms,and analyzes and compares the performance of several search algorithms in actual test;in order to apply DSCM to real-time vibration measurement,In this paper,the computational efficiency of the point-by-point search method is optimized and specific measures are given.For LSCI,based on the original method of estimating the contrast value,this paper improves the method of estimating the contrast value of spatial and temporal.Secondly,this paper implements a method of imaging speckle simulation based on the copula,and applies the improved contrast value estimation method to simulated speckle.Then,this paper applies the optimized DSCM to real-time vibration measurement,successfully measures the vibration frequency of the horn,and uses the FPGA module to realize the process of collecting and processing the speckle image.Finally,the experiment of DSCM applied to human pulse detection was carried out,and the waveform of the pulse wave was successfully measured.