3D Measurement Of Oil Painting Surface Topography Using Structured Light Imaging Technology

With the rapid development of visual imaging technology in modern society,3D imaging technology has also made continuous breakthroughs,and has a wide range of applications in various fields such as industrial production,image recognition and intelligent manufacturing.Among different 3D imaging methods,structured light 3D imaging method obtains object 3D information by projecting the deformed structured light with certain modulating mode on object,and it is widely used because of high spatial resolution,measurement accuracy and better real-time performance.As a major branch of painting and calligraphy,oil painting which has strong three-dimensional effect and scattered brushstrokes which is small and complex on its surface,has many difficulties in digitizing works.In this paper,structured light imaging technology is applied to the threedimensional measurement of oil painting surface topography.Firstly,a threedimensional measurement system is established based on fringe projection profilometry based on structured light,and the performance of the system is verified by geometric model experiments.The applicability of the system to complex threedimensional shapes is verified by the grid model experiment.The measurement accuracy of the system is not less than 0.5mm and the upper limit of the measurement height is 11 mm through the block model and the step model.Then,the threedimensional measurement system is used to obtain the absolute phase distribution of the surface topography of the oil painting.And aiming at the situation that the canvas needs to be disassembled for flattening treatment when detecting oil paintings with serious surface deformation,three different reference lines（surfaces）are proposed to assist the method of calculating the actual phase using structured light imaging technology.Then,the measurement effects of different methods are compared through experiments.Among the three reference line（surface）calculation methods,the method of using a straight line on the background plate as the reference line requires that the maximum thickness of the oil painting cannot exceed 11 mm,otherwise it will exceed the measurement height range of the system in this paper and can be wrong detected;The method of fitting a straight line to the first and last two points of a line of pixels as a reference line requires that the oil painting cannot be too severely deformed,otherwise only the area near the reference line can be detected,and a complete height map cannot be given,so it is only suitable for these paintings with the local measurement or overall deformation is small;the method of fitting the quadratic surface based on the point cloud data of the oil painting surface based on the least square method as the reference surface can achieve better three-dimensional measurement of the oil painting with serious deformation.The experiment of two different oil paintings proves that the last method can obtain ideal measurement results for oil paintings with different degrees of deformation.To sum up,for oil paintings with surface deformation,the method of calculating the actual phase based on the least squares fitting quadratic surface as the reference surface assisted structured light imaging technology has better measurement effect than other methods.The method is a non-contact,non-destructive inspection of the canvas,with low cost,fast running speed,and suitable for oil paintings with different degrees of deformation.This method has the problems of low projection efficiency and insufficient measurement accuracy.