Three-Dimensional Shape Measurement Based On Dithering Technique

The world we live in is three-dimensional,and each object is presented in three-dimensional form.With the development of the times,three-dimensional imaging measurement technology has been increasingly used in industrial quality control,three-dimensional modeling of cultural relics,and biomedicine.,Virtual reality,and face recognition have broad application prospects,and have always been hot research directions for scientific researchers.The measurement of three-dimensional topography has increasing social needs.Digital projection technology has the advantages of non-contact,high precision,high stability,etc.,and is widely used in the field of three-dimensional imaging of objects.However,digital projection technology still has many challenges:(1)non-linear problems caused by the gamma effect of commercial projectors;(2)Phase unwrapping problem.In this paper,in-depth research and experimental analysis are made on the non-linear effects caused by the gamma effect of the projector and the transformation relationship between object phase information and depth information in the structured light projection three-dimensional shape measurement technology,and a set of experimental measurement systems are set up.The main research work is as follows:(1)Based on the in-depth description of the defocused binary coding structured light three-dimensional topography measurement coding principle and defocusing characteristics,the paper deeply studies the principle of structured light 3D imaging based on dithering stripes.The dithering algorithm is used to generate high-quality binary structures.The common method of light has the disadvantages of expansion and diffusion.In addition,the higher-order harmonic components caused by the non-linear effect in the defocus binary coding technology will cause errors in the three-dimensional shape measurement.Method for generating binary images.Introducing the parameter a to dynamically adjust the threshold,and considering the influence of different pixel gray values of the image on the dithering algorithm,the sinusoidality of the dithered image stripe after defocusing is improved.Simulation and experiments show that using the threshold optimization dithering algorithm,the fringe after defocusing has better sinusoidality when the parameter a is 50.Compared with the standard sine fringe and the traditional Floyd-Steinberg dithering algorithm,the root mean square error can be reduced by 0.0137rad and 0.0200rad when the fringe period is 40 pixel.The imaging is more clear for the sag of the model,and the image quality of the surface reduction of the object is significantly improved.(2)Based on the analysis of the basic principles of the camera calibration model,this paper proposes a calibration method adapted to the digital fringe defocus projection technology.The projector is used as the inverse "camera".The phase shift method is used to obtain the absolute phase information of the point.Then determine the one-to-one mapping relationship between camera pixels and projector pixels,use the camera calibration method to calibrate the projector,and finally use the phase information of the digital fringe projection system to obtain the actual height information of the object to complete the three-dimensional topography measurement.The experiment proves that with the increase of the defocus amount,using the calibration method proposed in this paper,which is suitable for the digital fringe defocus projection system,can obtain the depth information of the object under close focus.