The Research Of Structured Light Measurement Based On Fourier Transform

Three-dimensional structure of light measurement is a kind of new technologies which is an active and non-contact measurement.This technology plays an important role in the study of the National Heritage,industry product processing and other technologies.Its principle is using a projector instead of a camera in Binocular vision to project gratings onto the surface of the object,with the camera capturing the deformed gratings which are modulated by the surface of the object.Then we can calculate the phase and obtain the three-dimensional reconstruction according to the triangulation principle.Finally we can obtain morphology of the object.Because the human visual system is less sensitive to the darker color gamut,projectors now available in the market in order to compensate for the human visual characteristics,have carried out Gamma encoding.But this phenomenon has brought trouble for experiments,which leads to the non-linear input and output intensity light.In the subsequent phase of the calculation,the light of absolute phase would appear wavy instead of straight.And finally the point cloud showing three-dimensional profile would appear the phenomenon of vertical fluctuations.In this paper,put the principle of structure of the optical measurement as the background,based on knowledge of the structure of the optical measurement technique,we focus on the relevant methods of Gamma correction from the frequency domain.The main contents of this paper is as follow:Firstly,an overview of the various methods used to measure the three-dimensional profile are introduced,which focuses on the optical measurement based on the structured light measurement of sinusoidal gratings.This paper also analysis the principles of Gamma nonlinear that is one of the main reason causing the error.Defocusing models and the principle of the Fourier transform for the spatial domain are analyzed in detail to laid the theoretical foundation for a variety of methods of Gamma correction.Secondly,this paper investigates the correction method based on Gamma values measured.Gamma value is measured through projecting particular gratings on a white flat board and capturing the scene by the camera.Then pre-compilation process will be conducted in accordance with the corresponding value on all those involved three-step phase shifting gratings to be projected in order to eliminate the purpose of Gamma values.Again,the methods of defocusing square wave used to avoid Gamma nonlinear are investigated.The most important reason of Gamma nonlinear is because of the light intensity on the addition of a power index,while only two values of the square wave is able to circumvent this problem.Combining the defocusing model,the characteristics of the various types of square wave are studied in from the principle,and use its properties to generate the gratings.Gaussian filter in Matlab is used to simulate defocusing and spatial domain and frequency domain representation of each method are compared and analyzed to get the performance through the phase error.Finally,the principles and methods of three-dimensional reconstruction are studied.Also through point clouds and three-dimensional reconstruction obtained from varieties of methods,the validity of methods can be verified.